Objective: We sought to quantify the anti-inflammatory effects of two cannabinoid drugs, cannabidiol (CBD) and palmitoylethanolamide (PEA), in cultured cell lines and compared this effect with experimentally inflamed explant human colonic tissue. These effects were explored in acutely and chronically inflamed colon, using inflammatory bowel disease and appendicitis explants. Design: Caco-2 cells and human colonic explants collected from elective bowel cancer, inflammatory bowel disease (IBD) or acute appendicitis resections, and were treated with the following drug treatments: vehicle, an inflammatory protocol of interferon γ (IFNγ) and tumour necrosis factor α (TNFα; 10 ng/ml), inflammation and PEA (10 µM), inflammation and CBD (10 µM), and PEA or CBD alone, CBD or vehicle were added simultaneously with IFNγ. Nine intracellular signalling phosphoproteins were determined by multiplex. Inflammatory cytokine secretion was determined using ELISA. Receptor mechanisms were investigated using antagonists for CB 1 , CB 2 , PPARα, PPARγ, TRPV1 and GPR55. Results: IFNγ and TNFα treatment increased phosphoprotein and cytokine levels in Caco-2 cultures and colonic explants. Phosphoprotein levels were significantly reduced by PEA or CBD in Caco-2 cultures and colonic explants. CBD and PEA prevented increases in cytokine production in explant colon, but not in Caco-2 cells. CBD effects were blocked by the CB 2 antagonist AM630 and TRPV1 antagonist SB366791. PEA effects were blocked by the PPARα antagonist GW6471. PEA and CBD were anti-inflammatory in IBD and appendicitis explants. Conclusion: PEA and CBD are anti-inflammatory in the human colon. This effect is not seen in cultured epithelial cells. Appropriately sized clinical trials should assess their efficacy.

Many studies demonstrate that activation of aldehyde dehydrogenase 2 (ALDH2) protects against oxidative stress via detoxification of cytotoxic aldehydes, and could attenuate cardiac, cerebral, lung and renal ischaemia–reperfusion (I/R) injuries. However, the effect of ALDH2 in intestinal I/R is unknown. The present study was set up to determine whether an ALDH2 agonist, Alda-1, could alleviate intestinal injury after gut I/R. In a mouse model of intestinal I/R injury, histological grading, proinflammatory cytokines, oxidative stress, cellular apoptosis, chemokine contents, ALDH2 activity, 4-hydroxy- trans -2-nonenal (4-HNE) and malondialdehyde (MDA) were evaluated. The results indicated that I/R treatment conferred elevation in pathological scores, proinflammatory cytokines, oxidative stress, cellular apoptosis and chemokine levels, accompanied by accumulated 4-HNE and MDA. No significant changes in ALDH2 activity were observed after I/R. However, Alda-1 pretreatment significantly decreased these injurious indicators, concomitant with up-regulated ALDH2 activity, and lessened 4-HNE and MDA accumulation. Taken together, our results implicate activation of ALDH2 by Alda-1 in the significant abatement intestinal I/R injury.

In the intestine, a single layer of epithelial cells sealed together at their apical surfaces by tight junctions helps to prevent the luminal commensal and pathogenic micro-organisms and their toxins from entering host tissues. The intestinal epithelium also helps to maintain homoeostasis in the mucosal immune system by expressing anti-inflammatory cytokines in the steady state and inflammatory cytokines in response to pathogens. Although the function of the mucosal immune system is impaired in elderly humans, the molecular mechanisms which cause this dramatic functional decline are poorly understood. Our current understanding of the effects of aging on the physical and immunological properties of the intestinal epithelial barrier is also very limited. In this issue of Clinical Science , Man et al. provide further insight into the effects of aging on small intestinal barrier function in humans and the influence that gut luminal micro-organisms may have on it. Using human terminal ileal biopsy tissues they show that intestinal permeability to solutes, but not macromolecules, was significantly increased in the intestines of elderly humans. This was accompanied by elevated expression of the pro-inflammatory cytokine interleukin (IL)-6 which appeared to modulate claudin-2 expression and solute permeability in the epithelium. Conversely, IL-8 synthesis in response to flagellin stimulation was reduced in intestines of the elderly subjects, but was not associated with effects on Toll-like receptor 5 (TLR5) expression. These data provide an important advance in our understanding on the effects of aging on intestinal permeability and innate mucosal immune responsiveness in elderly humans.

The physical and immunological properties of the human intestinal epithelial barrier in aging are largely unknown. Ileal biopsies from young (7–12 years), adult (20–40 years) and aging (67–77 years) individuals not showing symptoms of gastrointestinal (GI) pathologies were used to assess levels of inflammatory cytokines, barrier integrity and cytokine production in response to microbial challenges. Increased expression of interleukin (IL)-6, but not interferon (IFN)γ, tumour necrosis factor (TNF)-α and IL-1β was observed during aging; further analysis showed that cluster of differentiation (CD)11c + dendritic cells (DCs) are one of the major sources of IL-6 in the aging gut and expressed higher levels of CD40. Up-regulated production of IL-6 was accompanied by increased expression of claudin-2 leading to reduced transepithelial electric resistance (TEER); TEER could be restored in in vitro and ex vivo cultures by neutralizing anti-IL-6 antibody. In contrast, expression of zonula occludens-1 (ZO-1), occludin and junctional-adhesion molecule-A1 did not vary with age and overall permeability to macromolecules was not affected. Finally, cytokine production in response to different microbial stimuli was assessed in a polarized in vitro organ culture (IVOC). IL-8 production in response to flagellin declined progressively with age although the expression and distribution of toll-like receptor (TLR)-5 on intestinal epithelial cells (IECs) remained unchanged. Also, flagellin-induced production of IL-6 was less pronounced in aging individuals. In contrast, TNF-α production in response to probiotics (VSL#3) did not decline with age; however, in our experimental model probiotics did not down-regulate the production of IL-6 and expression of claudin-2. These data suggested that aging affects properties of the intestinal barrier likely to impact on age-associated disturbances, both locally and systemically.

IBD (inflammatory bowel disease), where CD (Crohn's disease) and UC (ulcerative colitis) represent the two main forms, are chronic inflammatory conditions of the intestine. Macrophages play a central role in IBD pathogenesis and are regulated by major differentiation factors such as CSF-1 (colony-stimulating factor 1) in homoeostasis and inflammation. IL (interleukin)-34 has recently been discovered as a second ligand for CSF-1R (CSF-1 receptor). However, expression and involvement of IL-34 in IBD remain unknown. In the present paper, we investigated the expression of IL34 , CSF1 and their shared receptor CSF1R in normal human ileum and colon, in inflamed and non-inflamed tissues of CD and UC patients, and in a mouse model of experimental colitis. We found distinct expression patterns of IL34 and CSF1 in ileum and colon, with higher IL34 in ileum and, in contrast, higher CSF1 in colon. Furthermore, IL34 and CSF1 expression was increased with inflammation in IBD patients and in experimental colitis. In humans, infiltrating cells of the lamina propria and intestinal epithelial cells expressed IL-34, and TNF-α (tumour necrosis factor α) regulated IL-34 expression in intestinal epithelial cells through the NF-κB (nuclear factor κB) pathway. These data demonstrate the expression pattern of IL-34 in ileum and colon and suggest IL-34 as a new modulator of inflammation in IBD.

IBD (inflammatory bowel disease)-related tissue damage occurs in areas which are massively infiltrated with monocytes/macrophages. These cells respond to inflammatory stimuli with enhanced production of cytokines/chemokines. In the present study, we analysed the expression and role of IL (interleukin)-34, a regulator of monocyte/macrophage differentiation, survival and function, in IBD. A significant increase in IL-34 mRNA and protein expression was seen in inflamed mucosa of patients with CD (Crohn's disease) and patients with UC (ulcerative colitis) compared with the uninvolved areas of the same patients and normal controls. IL-34 was up-regulated in LPMCs (lamina propria mononuclear cells) isolated from normal colon by TNF-α (tumour necrosis factor α) and TLR (Toll-like receptor) ligands and was down-regulated in intestinal biopsies and LPMCs of IBD patients upon treatment with infliximab. Treatment of normal LPMCs with IL-34 increased TNF-α expression in an ERK1/2 (extracellular-signal-regulated kinase 1/2)-dependent fashion and neutralization of IL-34 in IBD mucosal explants reduced TNF-α and IL-6 synthesis. In conclusion, our results indicate that IL-34 is up-regulated in IBD and suggest a role for this cytokine in sustaining the inflammatory responses in this disease.

IR (ischaemia/reperfusion) injury of the intestine occurs commonly during abdominal surgery. We have previously shown that PDTC (pyrrolidine dithiocarbamate), an HO-1 (haem oxygenase-1) donor, improves intestinal microvascular perfusion. In the present study, we have investigated the effects of PDTC on the intestinal microcirculation following IR (ischaemia/reperfusion) injury of the intestine. Male Sprague–Dawley rats ( n =72) were randomly assigned to four groups ( n =18/group): (i) sham-operated group, who underwent laparotomy without induction of IR of the intestine; (ii) IR group, who were subjected to 30 min of superior mesenteric artery occlusion and 2 h of reperfusion; (iii) PDTC+IR group, who received PDTC prior to IR; and (iv) ZnPP group, who received the HO-1 inhibitor ZnPP (zinc protoporphyrin) followed by procedures as in group (iii). The ileum was evaluated for changes in tissue cytochrome c oxidase redox status, RBC (red blood cell) dynamics and leucocyte–endothelial interactions. The expression of HO-1 in the ileal tissue was examined at the end of the reperfusion. PDTC significantly improved the intestinal tissue oxygenation, mucosal perfusion index and RBC velocity compared with the IR and ZnPP groups. PDTC also decreased the leucocyte–endothelial interactions ( P <0.05 compared with the IR and ZnPP groups). PDTC induced the expression of HO-1, whereas ZnPP abolished this effect.

Although glucose and protein metabolism have been investigated extensively in experimental models of hypodynamic sepsis, relatively little information is available regarding the compensated stage of sepsis. We investigated interorgan amino acid and glucose metabolism in a porcine model of compensated hyperdynamic sepsis. Fasting catheterized pigs received endotoxin ( Escherichia coli lipopolysaccharide; 3 µ g·h -1 ·kg -1 ; intravenous) or saline (controls) and volume resuscitation over 24h to reproduce hyperdynamic sepsis. Primed-constant infusions of p -aminohippurate and 3 H-labelled isotopes were used to measure glucose, amino acid and protein metabolism across the portal-drained viscera, liver and hindquarters (to represent muscle) at 0 and 24h of endotoxaemia. Whole-body protein and glucose flux were increased during hyperdynamic compensated sepsis. In endotoxaemic pigs, visceral protein was conserved, and hindquarter protein breakdown exceeded the increase in liver protein synthesis, resulting in net whole-body protein loss. Endotoxaemia increased hindquarter and visceral glycolysis and branched-chain amino acid transamination. The rate of efflux of glutamine and alanine from the hindquarters was higher than anticipated from protein breakdown, indicating de novo synthesis of these amino acids during endotoxaemia. In addition to the hindquarters, the portal-drained viscera provided substantial gluconeogenic amino acids and lactate to the liver. Although increased liver glutamate release constitutes an important nitrogen-sparing mechanism and carbon skeletons are effectively being cycled in glucose, net body protein is lost through increased ureagenesis during the hyperdynamic stage of sepsis. Specific amino acid requirements may develop in compensated hyperdynamic sepsis that is characterized by maintained organ perfusion and increased substrate utilization at the expense of body protein.

Previous studies have suggested that the production of interleukin-6 (IL-6) is increased in the intestinal mucosa during inflammation, and that nuclear factor-κB (NF-κB) is an important regulator of the IL-6 gene in the enterocyte. We tested the hypothesis that sodium arsenite inhibits IL-6 production in stimulated enterocytes and that this effect of arsenite is caused by down-regulation of NF-κB activity. Cultured Caco-2 cells were treated with sodium arsenite and were then stimulated with IL-1β. IL-6 production and gene expression were determined by ELISA and reverse transcriptase–PCR respectively. NF-κB DNA binding activity was determined by electrophoretic mobility shift assay. IL-1β increased NF-κB DNA binding activity, IL-6 mRNA levels and IL-6 production. These effects of IL-1β were inhibited by treatment of the cells with sodium arsenite in a dose- and time-dependent fashion. When cells were transfected with a plasmid expressing the p65 subunit of NF-κB, the inhibitory effect of sodium arsenite on NF-κB activity and IL-6 production was blunted. These results suggest that sodium arsenite inhibits IL-6 production in enterocytes subjected to an inflammatory stimulus, and that this effect, at least in part, reflects down-regulated NF-κB activity.

Vasoactive intestinal contractor (VIC)/endothelin-2 (ET2) is a vasoactive peptide hormone comprising 21 amino acids. The complete nucleotide sequence of the full-length gene encoding preproVIC (PPVIC) was determined. The PPVIC gene contains five exons that span 6kb and shows a duplication on exons 2 and 3, coding for the VIC and VIC-like peptides respectively. Similarities between the genomic organization of the PPVIC/preproET2 and preproendothelin-1 genes suggest that the two are distantly related. PPVIC gene expression was observed in foetal and adult mouse intestine. The expression level in adults was approx. 10-fold higher than in the foetus, suggesting an involvement of VIC in intestinal development.

1. In a previous study we found that the protein synthesis rate was increased by 50–60% in the mucosa of the jejunum and ileum during sepsis in rats. It is not known if sepsis affects protein turnover in other parts of the gastrointestinal tract as well. 2. In the present study, the influence of sepsis on mucosal protein synthesis in different parts of the gastrointestinal tract, from the stomach to the rectum, was determined in rats. 3. Sepsis was induced by caecal ligation and puncture; control rats underwent sham-operation. Protein synthesis rate was measured in vivo after administration of a flooding dose of [ 14 C]leucine. 4. Basal mucosal protein synthesis rates were lower in the colon than in the rest of the gastrointestinal tract. Sixteen hours after caecal ligation and puncture, the protein synthesis rates were increased by 40–85% in the mucosa of the small and large intestine and the rectum, whereas in the gastric mucosa, the protein synthesis rate was reduced by approximately 40%. 5. The results suggest that mucosal protein synthesis rates differ in the various regions of the gastrointestinal tract, and that the metabolic response to sepsis is different in the stomach than in the rest of the gastrointestinal tract. The finding of a reduced protein synthesis rate in the gastric mucosa may partly explain the tendency to gastric stress ulcers and bleeding seen clinically in sepsis.

1. It has recently been suggested that glutamine may be a conditionally essential nutrient rather than a non-essential amino acid. Therefore, administration of methionine sulphoximine was used to create a model of decreased arterial glutamine concentrations for 4 days. Glutamine consumption in portal-drained viscera and liver was measured after an overnight fast by determining fluxes and intracellular concentrations in normal rats, methionine sulphoximine-treated rats and pair-fed controls. Moreover, fluxes and intracellular concentrations of several other amino acids and ammonia and production of urea by the liver were determined concomitantly. 2. Methionine sulphoximine treatment for 4 days resulted in a 50% decrease in arterial glutamine concentration. Although the glutamine consumption and the intracellular glutamine concentration of the intestine were reduced by 50% at day 4, no changes in intestinal amino acid and ammonia metabolism were observed. 3. In the liver, glutamine consumption was reduced and ammonia uptake was increased, but urea synthesis was not changed. The decreased intracellular glutamine, glutamate, aspartate and ammonia concentrations coincided with a substantial reduction in liver branched-chain amino acid production. 4. These results suggest that reduced intestinal glutamine uptake does not induce marked changes in intestinal amino acid metabolism. The decreased liver branched-chain amino acid production suggests a reduction in the net liver protein degradation rate during methionine sulphoximine treatment.

1. After operation, changes in nitrogen metabolism occur. Although increased flux of amino acids from peripheral to splanchnic organs after operation has been described, substrate utilization by the individual organs in the splanchnic area is less well characterized. We were specifically interested in substrate flux across the spleen as it is an organ with important immunological functions. 2. Therefore, hindquarter, gut, spleen and liver fluxes of amino acids, ammonia, glucose, lactate and blood gases were measured for 4 days after a standard operation in pigs. In a separate control group, fluxes were measured 2–3 weeks after this operation and these values were assumed to represent the normal situation. 3. One day after operation, the hindquarter effluxes of glutamine, alanine and several essential amino acids were increased ( P <0.001), but these normalized at the end of the observation period. In the same period, liver glutamine uptake increased ( P <0.01), concomitantly with increased HCO - 3 , glucose and urea production, which also normalized. Portal drained viscera ammonia production decreased, concomitant with decreased glutamine uptake ( P <0.001). After operation, the splenic release of ammonia increased sevenfold ( P <0.05) and that of lactate increased from −158 ± 544 to 3294 ± 642 nmol min −1 kg −1 body weight ( P <0.001). Glucose uptake increased from −964 ± 632 to −3933 ± 1524 nmol min −1 kg −1 body weight and glutamine efflux (391 ± 143) reversed to uptake (−752 ± 169 nmol min −1 kg −1 body weight) ( P <0.001). 4. The experiments show that after operation in the pig, amino acid flow is from peripheral tissue to liver, probably for gluconeogenesis. The increased postoperative splenic metabolism possibly represents an indication of increased substrate utilization by the immune system.

1. The transport of 6-thioguanine and 6-mercaptopurine has been studied with isolated jejunal loops of mouse small intestine. H.p.l.c. was used to identify and quantify the thiopurines and their metabolites in the serosal secretions. 2. When the lumen of the intestinal loops contained either 6-thioguanine or 6-mercaptopurine at a concentration of 1 mmol/l, the concentration of unmetabolized drug in the serosal secretions reached a maximum of 0.13 ± 0.02 mmol/l (mean ± sem ). 3. Analysis of the serosal secretions from the perfusions with either of the drugs revealed the appearance of an unknown compound which had the characteristics of a thiopurine and the same time course of appearance as the unmetabolized drug. Thus 6-thioguanine and 6-mercaptopurine are significantly metabolized during absorption in mouse intestine. 4. The unknown compound was identified as 6-thiouric acid, and with 1 mmol/l 6-thioguanine or 6-mercaptopurine in the lumen the concentration of this metabolite in the serosal secretions rose to a maximum of 0.13 ± 0.01 and 0.18 ± 0.03 mmol/l, respectively. At luminal drug concentrations of 0.1 mmol/l, the metabolite accounted for approximately 90% of the serosal thiopurine. 5. After an initial lag period of 20 min, linear rates of appearance in the serosal secretions were obtained for both the unmetabolized drugs and 6-thiouric acid. 6. Addition of the xanthine oxidase inhibitor oxypurinol at a luminal concentration of 0.3 mmol/l prevented the formation of 6-thiouric acid from 6-thioguanine. However, the inhibitor reduced the rate of 6-thioguanine appearance in the serosal secretions by 50%. 7. The conversion of 6-mercaptopurine to 6-thiouric acid was prevented when allopurinol or oxypurinol were added to the lumen. At a luminal drug concentration of 1 mmol/l, allopurinol increased the rate at which 6-mercaptopurine appeared in the serosal secretions by 90% compared with an increase of only 50% with oxypurinol. 8. The transport of water and glucose by the mouse intestinal loops was unaffected by 6-thioguanine or the xanthine oxidase inhibitors. However, 6-mercaptopurine caused significant reductions in the rate of water transport (30%) and glucose transport (39%). These effects were observed at a luminal drug concentration of 0.1 mmol/l and there was no further increase at a drug concentration of 1 mmol/l.

1. Intestinal epithelial cell production and intestinal absorption were measured in fed, starved and refed rats. 2. Four days' starvation significantly decreased the crypt cell production rate (CCPR), absorption, small intestinal length and crypt cell population. 3. There was an immediate increase in absorption 1 day after refeeding, which preceded a slower increase in CCPR. The absorption rate then decreased progressively after refeeding, and was significantly lower than control levels 1 week after refeeding. The CCPR, however, increased more gradually, reaching control levels after 2 days and then ‘overshooting’ control values. 4. There was no significant change in the crypt cell population immediately after refeeding; thus we propose that the initial increase in absorption on refeeding is either due to an accelerated maturation rate of the enterocytes or to the migration of enterocytes from the base of the villus to the functional zone. 5. The rapid recruitment of absorptive function appeared to be a ‘one-off’ event, the villus compartment then having to wait for increased cell production in the crypts to repopulate the villi.

1. The structural integrities of various preparations of rat small intestine for the study of absorption in vitro have been compared after incubation or perfusion. 2. Perfused intestines removed from anaesthetized rats, and thus never deprived of a supply of oxygen, maintain their structural integrity even after perfusion for 1 h provided that a Krebs–Henseleit bicarbonate perfusate is used. However, intestines removed from freshly killed rats show severe villus disruption and oedema after perfusion for only 20 min. 3. Extensive damage to both crypts and villi is observed in everted sacs of small intestine incubated for 20 min, regardless of the buffer system used. Intestinal rings show damage at the tips of the villi after incubation for 2 min, but otherwise remain morphologically intact; this damage is progressive with time. 4. It is concluded that the exact mode of preparation of intestinal tissue is critical for preservation of structural and functional integrity and that this is especially important in quantitative studies on transport processes. Further, it is recommended that routine monitoring of the integrity of intestinal preparations in vitro is desirable and that histological assessment is an appropriate technique.

1. We report observations on transport of the hydrolysis-resistant dipeptide glycylsarcosine by rings of everted hamster jejunum in vitro in the presence and absence of Na + , using several substituents for Na + : Li + , K + , Cs + , Tris, choline and mannitol. 2. At most concentrations, mediated influx of glycylsarcosine was depressed by Li + , K + , Cs + and Tris, though not abolished. At high concentrations, it was moderately increased by choline and mannitol. Under conditions in which the tissue could concentrate the peptide in the presence of Na + , uptake was greatly depressed by all the substituents and the ability to concentrate was abolished. 3. The K t of mediated influx was affected in different ways according to the substituent used. K t was reduced by Li + replacement of Na + and increased by choline replacement. V max. was greatly reduced by all metallic substituents but not by non-metallic substituents. 4. Though the results cannot yet be satisfactorily interpreted, they suggest possible reasons for previous conflicting results and show that it is impossible to make the unqualified statement that transport of glycylsarcosine is ‘Na + -dependent’. It is now doubtful whether transport of this peptide into the intestinal cells is by co-transport with Na + , and the whole matter of Na + -dependence of intestinal peptide transport is in question.

1. The transport of 5-fluorouracil, uracil and thymine has been studied with isolated jejunal loops of rat small intestine. High performance liquid chromatography was used to identify the pyrimidines and measure their concentrations. 2. When the lumen of the intestine was perfused with 5-fluorouracil or uracil at 0.1 mmol/l or 0.2 mmol/l, the concentration in the serosal secretions was significantly higher than that in the lumen. For thymine the serosal concentration exceeded that in the lumen only at 0.1 mmol/l. 3. Analysis of the mucosal tissue water at the end of the perfusion demonstrated that when the intestinal lumen was perfused with any one of the three pyrimidines at 0.1 mmol/l or 0.2 mmol/l the concentration within the tissue was significantly above that in the lumen. 4. After an initial lag period linear rates of transport from the lumen to the serosal secretions were obtained for all three pyrimidines over a 10-fold concentration range from 0.1 mmol/l to 1 mmol/l. 5. Uracil and thymine inhibited the transmural transport of 5-fluorouracil. 6. The transport of 5-fluorouracil was also studied with a vascularly perfused preparation of rat small intestine. At 0.1 mmol/l the rate of transmural transport of the drug in this preparation was substantially higher than in the jejunal loops. This difference was eliminated by adding 5-fluorouracil to the vascular perfusate, suggesting that the higher transport rate in the vascularly perfused preparation was due to the lower serosal drug concentrations in the mesenteric circulation of the perfused intestine. 7. At a concentration of 5 mmol/l 5-fluorouracil inhibited water transport in the isolated loops and transmural D-galactose transport in the vascular perfusions.

1. In studies on intestinal adaptation it is often important to obtain contemporaneous data on the rate of cell production and the functional status of the intestine. 2. The measure of the rate of accumulation of vincristine arrested metaphases in microdissected intestinal crypts to determine the crypt cell production rate (CCPR), is one of the most effective methods of estimating intestinal epithelial cell proliferation which is robust enough to withstand scrutiny. However, studies in the field of intestinal adaptation could be much more informative if a valid measure of intestinal function could also be included. One such method is the water absorption capacity in vitro . 3. The intraperitoneal injection of vincristine sulphate (1 mg/kg) had no significant effect on the water absorption capacity of the small intestine, as measured by the segmented flow single pass perfusion method; thus the CCPR of the jejunum and intestinal water absorption were both measured in 19 groups of hypo- and hyper-proliferative rats which should have been in a relatively ‘steady state’ of cell production and turnover. 4. The minimum values were obtained after hypophysectomy and the maximum values were observed in lactation. CCPR and absorption were significantly correlated ( P < 0.001) with each other. There was a significant ( P < 0.001) correlation between both CCPR and absorption and dry weight of the intestinal segment studies with food intake. Body weight was a poor predictor of either CCPR or absorption. 5. The combined study of CCPR and water absorption is a practical and convenient approach to the study of intestinal cell proliferation and intestinal adaptation, and shows that in ‘steady state’ models of hypoplasia and hyperplasia, cell production is closely linked to functional capacity and both of these are also related to the food intake.

1. Alkaline phosphatase, sucrase, Na + , K + -ATPase and Mg 2+ -ATPase specific activities of crude membrane fractions, prepared from duodenal, jejunal, ileal and colonic mucosa, have been estimated in three types of hypertensive rats: the spontaneously hypertensive rat (SHR), the DOCA-saline-treated rat and the renovascular rat (Goldblatt one-kidney, one-clip rat; 1K-1C). Alkaline phosphatase and sucrase specific activities have also been measured in purified jejunal brush-border membranes. 2. When compared with its normotensive age-matched control (WKY rat), the SHR has a lower activity of alkaline phosphatase in duodenal and jejunal crude membrane fractions, whereas a higher activity in colonic Na + , K + -ATPase is recorded. In purified jejunal brush-border membranes, lower alkaline phosphatase activity and higher sucrase activity were found. These differences occur in the young prehypertensive SHR as well as in the adult animal. 3. In the DOCA-treated rat, the only significant alteration in crude membrane fractions is a decreased Mg 2+ -ATPase activity at all regions of intestinal mucosa. In purified jejunal brush-border membranes both alkaline phosphatase and sucrase activities are increased at 4 or 7 weeks but especially at 13 weeks of hypertension. 4. In the 1K-1C rat, no significant modification appears in crude membrane fractions or in purified jejunal brush-border membranes, but a decrease in alkaline phosphatase and in sucrase activities is probable afer 13 weeks of hypertension. 5. Since alterations of the intestinal enzymes are different in the three types of hypertensive rats it is concluded that the changes are not secondary to the hypertension condition. In the SHR, these alterations are present in the young prehypertensive animal. Abnormalities of intestinal function may be implicated in the origin of genetic hypertension. 6. All recorded alterations represent 25-50% variations from control values. They indicate disturbances of intestinal ion transport in the three types of hypertensive animals.

1. This paper is the last of a set reporting an investigation of the kinetics of jejunal uptake and inhibitory ability of a series of neutral dipeptides, glycylglycine, l-ananyl-l-alanine, l-valyl-l-valine and l-leucyl-l-leucine, with progressively longer and more lipophilic side chains. 2. The results suggested that at pH 5, uptake of l-alanyl-l-alanine, like that of l-valyl-l-valine and l-leucyl-l-leucine, was the result of two processes, uptake of intact peptide and uptake of free amino acid released extracellularly. On the other hand, uptake of glycylglycine was entirely in the form of intact peptide. In contrast to uptake of l-valyl-l-valine and l-leucyl-l-leucine, the proportion of intact l-alanyl-l-alanine taken up by mediated transport was greatest at the lowest concentration studied and smallest at the highest concentration. 3. Taking the series of results as a whole, whereas the corresponding series of amino acids, glycine, l-alanine, l-valine and l-leucine, showed a progressive increase in apparent affinity for uptake and a decrease in V max. , we could find no such regular progression with the peptides. 4. The results of work on inhibition of uptake of one dipeptide by another were unexpectedly complex. Examples were the very powerful inhibitory effect of l-valyl-l-valine on uptake of glycylsarcosine, not suggested by the K t of the former peptide, and the failure of glycylsarcosine to cause complete inhibition of uptake of l-alanyl-l-alanine and l-leucyl-l-leucine, though it could completely inhibit uptake of l-valyl-l-valine. There may be more than one uptake system for intact peptides, but we cannot yet suggest an explanation for all the results on inhibitions of uptake.

1. Preliminary observations concerned with the effect of the lipophilic properties of the amino acid side-chains of peptides on their apparent affinity for uptake by rings of everted hamster jejunum showed that of the series glycylglycine, l-alanyl-l-alanine, l-valyl-l-valine and l-leucyl-l-leucine, with increasingly lipophilic side-chains, l-valyl-l-valine, not l-leucyl-l-leucine, was the most powerful inhibitor of uptake of the hydrolysis-resistant dipeptide glycylsarcosine. This apparently anomalous observation indicated a need for further investigation, and this paper reports investigations of the kinetics of uptake of l-valyl-l-valine and of competition for uptake between l-valyl-l-valine and glycylsarcosine. 2. l-Valyl-l-valine was capable of complete competitive inhibition of mediated uptake of glycylsarcosine. Free l-valine did not inhibit mediated uptake of glycylsarcosine. Glycylsarcosine could inhibit mediated uptake of l-valyl-l-valine only partially, but a mixture of glycylsarcosine and l-valine was capable of producing complete inhibition of mediated uptake of l-valyl-l-valine. 3. Investigation of the kinetics of uptake of l-valyl-l-valine indicated two mediated components. Component (a), which disappeared in the presence of free l-leucine, probably represented uptake of free l-valine after hydrolysis of the peptide. Component (b) probably represented peptide uptake. 4. The estimates of K t obtained for uptake of intact l-valyl-l-valine were many times greater than K i for inhibition of uptake of glycylsarcosine by l-valyl-l-valine. A possible explanation of the discrepancy is the existence of two pathways for uptake of l-valyl-l-valine and glycylsarcosine, for one of which l-valyl-l-valine has a low K t (i.e. a high affinity) not readily demonstrable by kinetic analysis. 5. The results suggest that mediated uptake of l-valyl-l-valine is the result of at least two processes, uptake of intact peptide by a mechanism or mechanisms shared with glycylsarcosine and also hydrolysis followed by uptake of free l-valine; estimates of the proportions of intact valine and of free valine taken up by mediated transport suggest that at pH 5 uptake of intact peptide varies from 25% at low concentrations to 55% at high concentrations. They do not explain why l-valyl-l-valine is a stronger inhibitor of uptake of glycylsarcosine than the more lipophilic l-leucyl-l-leucine, but do suggest how such a situation could arise.

1. Water absorption rates by small intestine in vitro and the incidence of diarrhoea in vivo were estimated after 5-fluorouracil was injected into rats at various times of day and night. 2. Impairment of water absorption and the incidence of diarrhoea were minimal in rats on a normal dietary regimen when the 5-fluorouracil was injected at around 02.00 hours. 3. the DNA content of the mucosa of the small intestine from uninjected animals also showed a diurnal variation, with a maximum at around 03.00 hours. 4. Manipulation of the time of injections (possibly in relation to feeding time) provides a potential means for increasing the therapeutic value of 5-fluorouracil.

1. In the present investigation with rings of everted rat small intestine, carbohydrate gelling agents (plant polysaccharides) such as guaran, pectin, tragacanth, carubin and carrageenan were employed to study their direct effect on intestinal absorption of α-methyl-d-glucoside, d-galactose, l-leucine and l-phenylalanine. 2. Inhibition was found to correlate with the viscosity of the incubation medium, a function only of the polysaccharide concentration, and was independent of other properties of the carbohydrate gelling agents. 3. Reversal of this inhibition was achieved either by washing the tissue free of polysaccharide or by raising tissue agitation. 4. Uptake kinetics in polysaccharide-containing solutions revealed a marked increase of the apparent Michaelis constant although the maximal transport capacity remained essentially unaltered. 5. Since there was no binding of the substrate by the polysaccharides under experimental conditions as judged by a membrane filtration technique, it is concluded that carbohydrate gelling agents may impair intestinal absorption by means of an increased unstirred layer resistance.

1. This paper reports an investigation of whether the dipeptides glycylsarcosine and l-lysyl-l-lysine share a single mediated transport mechanism into hamster jejunum, or whether one of these peptides is taken up in part by a mediated mechanism unavailable to the other. The investigation, using rings of everted jejunum in vitro , was carried out at pH 5 in order to reduce brush border and/or intramedium hydrolysis of lysyl-lysine. 2. The kinetics of uptake of each peptide was studied over a wide range of concentrations. Estimates of the simple diffusion component in uptake of each peptide were made by the method of self-inhibition of transport as previously described. After correction for simple diffusion, uptake of each peptide conformed to Michaelis-Menten kinetics, and values for K t and V max. were obtained. 3. It was found that each peptide was capable, at infinitely high concentration, of complete inhibition of mediated uptake of the other. The inhibitory effect was competitive. We concluded that glycylsarcosine and lysyl-lysine were taken up by a common mediated mechanism (or possibly mechanisms), neither peptide being taken up by a mediated mechanism unavailable to the other. 4. A previous paper showed that l-glutamyl-l-glutamic acid and glycylsarcosine were taken up by a common mediated mechanism, and this paper shows that l-lysyl-l-lysine and glycylsarcosine are taken up by a common mediated mechanism. It is therefore postulated that the neutral dipeptide glycylsarcosine, the acidic dipeptide glutamyl-glutamic acid and the basic dipeptide lysyl-lysine all share a common mediated mechanism for uptake. This suggests that peptide uptake differs from amino acid uptake in that it is indifferent to the net charge on the amino acid side chain(s).

1. There are two saturable transport processes in the monkey small intestine for glycyl-l-leucine, one with K max 1 μmol min −1 g −1 wet weight of tissue and an affinity constant ( k t ) of 5 mmol/l, and the other with V max. 3·9 μmol min −1 g −1 wet weight of tissue and k t 33 mmol/l. 2. Glycyl-l-leucine uptake is inhibited by a wide variety of amino acids, although to a variable extent. The inhibition was shown to be competitive with leucine used as the representative amino acid. Phenylalanine, methionine, alanine and leucine are the most potent in their inhibitory action. 3. The effect of various amino acids on the hydrolysis of glycyl-l-leucine by particulate and cytosol fractions of monkey small intestine was studied. All the amino acids, except glycine, proline, alanine and glutamic acid, inhibit both the particulate and cytosol glycyl-l-leucine hydrolase activities. In general, the cytosol enzyme is more susceptible to amino acid inhibition than the particulate enzyme. 4. There is no correlation between the effects of amino acids on glycyl-l-leucine uptake and hydrolysis of glycyl-l-leucine by either particulate or cytosol fraction.

1. Hydrolase activities against three dipeptides were measured in mucosal cytoplasm in unperfused intestines and in mucosal cytoplasm, luminal effluents and serosal secretions after perfusion in vitro and in vivo for 1 h. Intestines in vitro were prepared both from anaesthetized rats and from freshly killed rats. 2. Only 0·6–1·9% of the initial cytoplasmic activity was recovered in the luminal effluent when intestines in vitro were prepared from anaesthetized rats. Recoveries in luminal effluents were similar (1·3–3·3%) during perfusion in vivo. 3. Losses of dipeptidases into the luminal effluent were four to eight times greater when intestines in vitro were prepared from freshly killed animals. 4. Similar losses of dipeptidases into the secretion on to the serosal surface were observed; they too were much greater when intestines were prepared from freshly killed animals. 5. Small losses of mucosal DNA during perfusion were also observed; however, losses of cytoplasmic peptidases were consistently slightly greater. 6. Enzyme loss therefore probably occurs both by sloughing of whole cells and by a more specific process which is greatly influenced by experimental procedure. Caution is necessary in the interpretation of peptide transport experiments in vitro , although the possibility that intraluminal hydrolysis is of physiological significance must not be excluded.

1. Water absorption and cytoplasmic dipeptidase activities were determined in isolated rat small intestine after animals had fed on various ‘elemental’ diets or a standard rat diet and after a single injection of 5-fluorouracil. 2. Vivonex diets were associated with a decrease in dry weight of the small intestine and an increase in glucose and water absorption in vitro. 3. The nature of the dietary nitrogen profoundly affects the activities of intestinal peptidases. 4. Water absorption was severely depressed 3 days after 5-fluorouracil administration: the extent of depression was independent of the diet. Thus, any ameliorative effects of ‘elemental’ diets on 5-fluorouracil toxicity are unlikely to be mediated by direct protection of intestinal absorption.

1. This paper describes an investigation of the kinetics of influx of the dipeptide glycylsarcosine and the amino acids glycine and l-leucine into rings of everted hamster small intestine in vitro , in proximal and distal small intestine (jejunum and ileum). Results were expressed per unit wet weight of intestine. 2. At all concentrations studied (0·1–100 mmol/l), influx of glycylsarcosine was more rapid in the jejunum than in the ileum. In contrast, at all concentrations studied, influx of glycine and leucine was more rapid in the ileum than the jejunum. 3. Estimates of the simple diffusion component in total influx were made. This component became increasingly large as the substrate concentration was raised. After correction for simple diffusion, transport of all three substrates conformed to Michaelis-Menten kinetics in both jejunum and ileum. Values for simple diffusion, apparent K t and V max. are reported. 4. Possibly physiological implications of the results are discussed, and it is pointed out that under experimental conditions similar to our own, simple diffusion is too large a component in total influx to be ignored.

1. This paper reports an investigation of whether the dipeptides glycylsarcosine and l-glutamyl-l-glutamic acid share a single mediated transport mechanism into hamster jejunum, or whether one of these peptides is transported in part by a transport mechanism unavailable to the other. It describes the kinetics of influx of glycylsarcosine and of l-glutamyl-l-glutamic acid into rings of everted hamster jejunum in vitro , incubations being carried out at pH 5 in order to minimize brush-border and intra-medium hydrolysis of l-glutamyl-l-glutamic acid, so that peptide transport rather than a mixture of peptide transport and transport of free glutamic acid was studied. With glycylsarcosine, brush-border and intra-medium hydrolysis are negligibly small. 2. Estimates of the simple diffusion component in transport of each peptide were made by treating each of the substrates as a competitive inhibitor of its own mediated transport (assuming that mediated transport conforms to simple Michaelis-Menten kinetics), extrapolating the observed inhibitory effect over a range of concentrations to an infinitely high concentration of inhibitor, and estimating the transport component remaining at such a concentration. This component in transport would be expected to represent transport by simple diffusion, and this assumption was supported by the observation that for glycylsarcosine the uninhibitable component in transport was linearly proportional to substrate concentration; with l-glutamyl-l-glutamic acid the observations were too few to provide this demonstration. Estimates of apparent K t and V max. for mediated transport of both peptides are given. Before correction for simple diffusion, linearizing plots were clearly biphasic for both peptides; after correction for simple diffusion, they became linear, providing no evidence for transport of either peptide by more than one mediated transport system, though not excluding the possibility of multiple systems. 3. Measurement of influx of [ 14 C]Gly-Sar over a range of concentrations both alone and in the presence of a constant concentration of Glu-Glu showed that after correction for the non-mediated component in influx of Gly-Sar (simple diffusion), influx of this peptide conformed to Michaelis-Menten kinetics and the inhibitory effect of Glu-Glu on influx of Gly-Sar appeared to be competitive. The extent of inhibition corresponded well with that predicted from the K t values of the two peptides. 4. Measurement of influx of [ 14 C]Gly-Sar (1 mmol/l) in the presence of a range of concentrations of Glu-Glu, with extrapolation of the inhibitory effect of Glu-Glu to an infinitely high concentration of this peptide, showed that at such a concentration mediated influx of Gly-Sar was completely abolished, influx being reduced to the simple diffusion component in total influx of [ 14 C]Gly-Sar. Measurement of influx of [ 14 C]Glu-Glu (1 mmol/l) in the presence of a range of concentrations of Gly-Sar, with extrapolation of the inhibitory effect of Gly-Sar to an infinitely high concentration of this peptide, showed that at such a concentration mediated influx of Glu-Glu was completely abolished, influx being reduced to the simple diffusion component in total influx of [ 14 C]Glu-Glu. 5. The results are compatible with the conclusion that Gly-Sar and Glu-Glu are taken up by the absorptive cells by a single mediated mechanism. They do not exclude the possibility that these peptides are taken up by multiple common mechanisms, but they do appear to exclude the possibility that at the substrate concentration used (1 mmol/l) there is appreciable uptake of one of the peptides by a system unavailable to the other.

1. Enterocytes, isolated from the proximal jejunum and distal ileum of normal and prednisolone-treated rats, were homogenized and fractionated by isopycnic centrifugation on sucrose density gradients. The distributions of marker enzymes for the principal subcellular organelles, RNA and protein were determined and related to the activities per enterocyte. 2. In enterocytes from the jejunum and ileum of prednisolone-treated animals the activities of particulate brush-border enzymes and of both soluble and mitochondrial malate dehydrogenase were increased compared with those of the control system. The equilibrium density of the brush borders was enhanced in the prednisolone-treated jejunum. The modal densities of the other organelles were unaltered by prednisolone administration. 3. There was a large increase in the total RNA content of enterocytes from the jejunum and ileum of prednisolone-treated animals. This was predominantly associated with a distinct particulate component, indicative of a proliferation of the rough endoplasmic reticulum and consistent with an enhanced rate of protein synthesis. 4. Studies of latent brush-border enzyme activities, the mechanical fragility of isolated brush borders and electron microscopy suggest that steroid administration results in no marked alterations in the gross conformation of the brush- border membrane or in the orientation of the enzymes within the membrane.

1. Enterocytes, isolated from the proximal jejunum and distal ileum of the rat, were homogenized and their organelles separated by isopycnic centrifugation on continuous sucrose density gradients. The distributions of marker enzymes for the principal organelles, RNA and protein were determined in the sucrose gradients and related to the activities per enterocyte. 2. In the jejunum the modal equilibrium densities of the various organelles were: brush borders (1.20), lysosomes (1.20), peroxisomes (1.19), mitochondria (1.17) and basal-lateral membranes (1.13). These values were not significantly different in the ileum. The activities of brush-border enzymes, soluble and mitochondrial malate dehydrogenase, soluble and membrane-associated lactate dehydrogenase and particulate protein content, however, were greater in the jejunal than the ileal enterocytes. 3. Detergent exposed latent alkaline phosphatase activity in jejunal enterocytes and indicated that this enzyme is present not only in the brush border but also in the basal-lateral membrane and soluble fractions of the cell. 4. Isolated jejunal brush-border preparations showed latent activities of both alkaline phosphatase and γ-glutamyltransferase whereas the activities of α-glucosidase and leucyl-β-naphthylamidase were not affected by detergent. Mechanical disruption of these preparations suggested the presence of two forms of alkaline phosphatase in the brush border and provides a technique to assess membrane fragility.

1. Glucose absorption, water absorption and dipeptide hydrolase activities have been determined in isolated rat small intestine at 1, 3, 5 and 21 days after a single intraperitoneal injection of 5-fluorouracil. 2. Absorption rates and enzyme activities were elevated 1 day after treatment, but were reduced to 40% of control values at 3 and 5 days. Changes were seen regardless of whether absorption was expressed per unit length or per unit dry weight of intestine. 3. There were highly significant positive correlations between glucose or water absorption rates and peptidase activities, especially in proximal jejunum. The most significant correlation was observed between water absorption rate and jejunal l-Leu-Gly hydrolase activity. 4. Malabsorption may account for some of the gastrointestinal side effects associated with treatment with 5-fluorouracil. Enzyme measurements may be useful as an index of intestinal function.

1. Gliadin from which carbohydrate was removed by treatment with carbohydrase from Aspergillus niger was fed to three coeliac patients in remission. 2. Xylose absorption, mucosal morphology and brush-border enzymes were used to assess the toxicity of the carbohydrase-treated gliadin. 3. Gliadin treated with carbohydrases did not damage the intestinal mucosa of the coeliac patients. 4. The primary structure of the gliadin proteins was not altered by the enzyme treatment.

1. Absorption of [ 3 H]glycine and [ 14 C]-glycyl-l-proline at concentrations between 0·5 and 4 mmol/l was studied by perfusion in vivo of rat jejunal and ileal segments. Absorption was defined as net removal of radioisotope from the perfusate. Radioactivity assays and amino acid analyses were performed on perfusates and on mucosal tissue samples obtained from the perfused segments. 2. At the concentrations studied, absorption rates of glycine and glycylproline were proportional to concentration. Ileal rates were approximately 60% of jejunal rates. Glycylproline absorption was slightly faster than glycine absorption and was associated with the appearance in the perfusate of free glycine and proline in the ratio approximately 3:1. Intraluminal hydrolysis was insufficient to account for the amounts of free amino acids found and glycylproline hydrolase activity at the brush border is known to be minimal. 3. Glycylproline absorption apparently occurred by transport of the intact peptide followed by its intracellular hydrolysis. However, more than one-third of absorbed glycine and one-eighth of absorbed proline returned to the lumen as free amino acid. This reflux of glycine and proline was not proportional to their concentrations in the mucosa.

1. To study the relative contributions of luminal nutrition, bile and pancreatic secretions and hormonal factors in intestinal adaptation, lactation hyperphagia was chosen as a model for increased luminal nutrition, either alone (intestinal transection control group) or in combination with (i) exclusion of bile and pancreatic secretions from the jejunum (by transposition of the jejunum above the Ampulla of Vater) or (ii) exclusion of bile, pancreatic secretions and exogenous luminal nutrition from the jejunum (proximal Thiry—Vella by-pass group). 2. The results confirm that in lactation there is mucosal hyperplasia with increases in villus height and crypt depth, and in small-bowel wet and defatted dry-tissue weights per unit length of intestine. 3. There are corresponding changes in absorptive function with increased glucose and water absorption per unit length of intestine. 4. These structural and functional adaptive changes are proportionately greater in ileum than in jejunum. 5. The exclusion of exogenous luminal nutrition, bile and pancreatic secretions from the jejunum did not diminish the degree of intestinal mucosal hyperplasia and functional adaptation seen in lactation. 6. Diversion to the ileum of greater than normal amounts of bile, pancreatic secretions and luminal nutrition did not further increase the degree of mucosal hyperplasia and enhanced absorption seen in the lactating intestinal transection control group. 7. Unlike other models of intestinal adaptation, the changes in small-bowel mucosal structure and function seen in lactation are problaby due to hormonal factors.

1. The absorption in vivo of d-galactose by the rat small intestine has been examined in proximal jejunum and distal ileum by use of a recirculation—perfusion technique. 2. Multiple sequential perfusions over 4 h produced no subsequent functional or morphological damage in the perfused segments. 3. Absorption of galactose from 8 and 64 mmol/l solutions was found to be independent of flow rate over the range 1·0–6·5 ml/min. 4. Galactose absorption in both the jejunum and the ileum exhibited saturation kinetics of the Michaelis—Menten type, and phlorrhizin sensitivity. Sorbose was only absorbed minimally. These observations demonstrate that galactose is absorbed by carrier-mediated transport and that there is no significant passive diffusive component in vivo. 5. Under the stated experimental conditions, the maximum absorptive capacity was 4·5 times greater in the jejunum than in the ileum. The Michaelis constant for galactose was higher in the jejunum than in the ileum. 6. Enterocytes were isolated from perfused segments and quantified by DNA assay with a correction for yield. In this manner, the absorptive capacity per enterocyte was calculated. 7. The maximum absorptive capacity per enterocyte was 3·5 times greater in the jejunum than in the ileum.

1. The effects in rats of an oral pharmacological dose of prednisolone on mucosal function, enzymology, lysosomal membrane fragility, morphology and cell kinetics have been examined in proximal jejunum and distal ileum. 2. The maximum absorptive capacity for galactose was significantly greater in both the jejunum and the ileum of the steroid-treated animals. This was due to an increase in carrier-mediated transport in the individual enterocytes and not to a change in the cell population. The Michaelis constant for galactose was not significantly altered by prednisolone. 3. Activities of brush-border and mitochondrial enzymes and of RNA were increased in isolated enterocyte preparations from the jejunum and ileum of the steroid-treated group. 4. Lysosomal membrane fragility was unaltered in the prednisolone-treated group. 5. Morphometrical observations confirmed that the size of the enterocyte population was unaltered by prednisolone. Studies on cell kinetics indicate that the effects of prednisolone are due to a direct action on the enterocyte and not secondary to changes in migration rate.

1. Enterocytes were isolated from rat jejunum and characterized morphologically. 2. Attempts to separate the enterocyte subcellular organelles, characterized by their marker enzymes, with isopycnic centrifugation were unsuccessful but good separation of peroxisomes, lysosomes and mitochondria was achieved by sedimentation through a shallow sucrose density gradient with a superimposed inverse gradient of low-molecular-weight dextran. 3. The properties and enzyme activities of the principal subcellular organelles in rat liver cells and enterocytes were compared.

1. Ammonia, bicarbonate and pH were measured in samples of faecal dialysate from thirteen healthy subjects taking free diets. To observe the effect of marked changes in faecal pH, three subjects were also studied while taking 25 mmol/day of MgCO 3 or Na 2 SO 4 by mouth. Both salts increased stool weight without causing diarrhoea, but stool pH was significantly increased by MgCO 3 and decreased by Na 2 SO 4 . 2. The total ammonia concentration and pH of faecal dialysate were very variable, but showed a highly significant negative correlation similar to that already established in man between urinary excretion of ammonia and urine pH. This relationship was more marked when individual subjects were studied while faecal pH was deliberately varied by administration of MgCO 3 and Na 2 SO 4 . 3. Faecal bicarbonate concentrations were positively correlated with pH. Faecal P co 2 was usually in the range 40–120 mmHg, the higher P co 2 values being found in the more acid samples. Faecal total ammonia concentrations were negatively correlated with faecal bicarbonate. 4. These findings suggest that passive non-ionic diffusion is the main mechanism by which ammonia is absorbed by the colon, but do not exclude a minor contribution from diffusion of ionized ammonium. Colonic secretion of bicarbonate facilitates non-ionic diffusion of ammonia by providing an anion which is also absorbed by non-ionic diffusion, so maintaining an alkaline intraluminal reaction that continues to generate unionized ammonia.

1. The effects of intestinal ammonia in uraemia have been studied by administering a urease inhibitor, acetohydroxamic acid, to bilaterally nephrectomized rats. 2. Ammonia concentration was significantly decreased in the colon although it remained slightly higher than in normal animals. Caecal ammonia concentration was not altered. Total ammonia content was decreased in both colon and caecum. 3. A study in vitro indicated that ammonia production could be totally inhibited by acetohydroxamic acid. This suggests that the failure to suppress ammonia production in vivo is due to failure of the inhibitor to reach the site of urease production in sufficient concentration. 4. The animals treated with high doses of acetohydroxamic acid survived for a shorter time. Blood urea was higher and total serum protein lower in the treated group. The incidence of colitis was not affected.