Plasma lactate is widely used as a biomarker in critical illness. The aims of the present study were to elucidate the usefulness of a three-compartment model for muscle lactate kinetics in humans and to characterize the response to an exogenous adrenaline challenge. Repeated blood samples from artery and femoral vein together with blood flow measurements and muscle biopsies were obtained from healthy male volunteers ( n =8) at baseline and during an adrenaline infusion. Concentrations of lactate and enrichment of [ 13 C]lactate were measured and kinetics calculated. Mitochondrial activity, glycogen concentration, oxygen uptake and CO 2 release were assessed. The adrenaline challenge increased plasma lactate 4-fold as a result of a greater increase in the rate of appearance ( R a ) than the increase in the rate of disappearance ( R d ). Leg muscle net release of lactate increased 3.5-fold, whereas intramuscular production had a high variation but did not change. Mitochondrial state 3 respiration increased by 30%. Glycogen concentration, oxygen uptake and CO 2 production remained unchanged. In conclusion a three-compartment model gives additional information to the two-compartment model but, due to its larger variation and invasive muscle biopsy, it is less likely to become a regularly used tool in clinical research. Hyperlactataemia in response to adrenergic stimuli was driven by an elevated lactate release from skeletal muscle most probably due to a redirection of a high intramuscular turnover rather than an increased production.

Arginine deficiency in sepsis may impair nitric oxide (NO) production for local perfusion and add to the catabolic state. In contrast, excessive NO production has been related to global haemodynamic instability. Therefore, the aim of the present study was to investigate the dose–response effect of intravenous arginine supplementation in post-absorptive patients with septic shock on arginine-NO and protein metabolism and on global and regional haemodynamics. Eight critically ill patients with a diagnosis of septic shock participated in this short-term (8 h) dose–response study. L -Arginine-HCl was continuously infused [intravenously (IV)] in three stepwise-increasing doses (33, 66 and 99 μmol·kg −1 ·h −1 ). Whole-body arginine-NO and protein metabolism were measured using stable isotope techniques, and baseline values were compared with healthy controls. Global and regional haemodynamic parameters were continuously recorded during the study. Upon infusion, plasma arginine increased from 48±7 to 189±23 μmol·l −1 (means±S.D.; P <0.0001). This coincided with increased de novo arginine ( P <0.0001) and increased NO production ( P <0.05). Sepsis patients demonstrated elevated protein breakdown at baseline ( P <0.001 compared with healthy controls), whereas protein breakdown and synthesis both decreased during arginine infusion ( P <0.0001). Mean arterial and pulmonary pressure and gastric mucosal-arterial partial pressure of carbon dioxide difference ( P r-a CO 2 ) gap did not alter during arginine infusion ( P >0.05), whereas stroke volume (SV) increased ( P <0.05) and arterial lactate decreased ( P <0.05). In conclusion, a 4-fold increase in plasma arginine with intravenous arginine infusion in sepsis stimulates de novo arginine and NO production and reduces whole-body protein breakdown. These potential beneficial metabolic effects occurred without negative alterations in haemodynamic parameters, although improvement in regional perfusion could not be demonstrated in the eight patients with septic shock who were studied.

The aim of the present study was to investigate the acute effect of CABG (coronary artery bypass graft) surgery on the rates of synthesis of muscle protein, the positive acute-phase protein fibrinogen and the negative acute-phase protein albumin. Synthesis rates of muscle protein, fibrinogen and albumin were measured simultaneously before and 4 h after the end of surgery from the incorporation of L -[ 2 H 5 ]phenylalanine (given at 43 mg/kg of body weight) in 12 patients undergoing CABG surgery. Surgery was performed either with the use of extracorporeal circulation with cardiopulmonary bypass (on-pump; n =5) or with the beating heart procedure without cardiopulmonary bypass (off-pump; n =7). Post-surgical muscle protein fractional synthesis rates were decreased by 36±6.5% compared with pre-surgical values (1.59±0.10 compared with 0.97±0.08%/day respectively; P <0.001). In contrast, the synthesis rates of both fibrinogen (36±4 compared with 100±11 mg·day −1 ·kg −1 of body weight; P <0.0001) and albumin (123±12 compared with 178±19 mg·day −1 ·kg −1 of body weight; P <0.001) were both significantly increased after surgery. No significant differences were found between surgery performed with or without cardiopulmonary bypass. In conclusion, the results demonstrate that CABG surgery has a profound effect on protein metabolism, with a differential response of protein synthesis in muscle and liver.

We have described recently that cancer patients have low plasma arginine concentrations, even without weight loss being present, suggesting that decreased arginine availability may be a specific feature of the presence of tumour. As arginine is important in post-operative repair, we hypothesized that abnormalities in arginine metabolism in cancer lead to an aberrant post-operative response in arginine and NO metabolism. To investigate this, we studied post-operative alterations in arginine and NO production and the acute-phase response in MCA (methylcholanthrene) sarcoma-bearing mice. Controls, mice with small MCA tumours (<15% of carcass weight) and large MCA tumours (>15% of carcass weight) were studied, either with or without undergoing laparotomy. The stable isotopes L -[guanidino- 15 N 2 - 2 H 2 ]arginine and L -[ureido- 15 N]citrulline were used to study whole-body arginine and NO production rates. SAP (serum amyloid P component) concentrations were measured to assess the acute-phase response. Significance was tested using Mann–Whitney U test. In healthy FVB mice, laparotomy significantly increased whole-body arginine production (from 42±3 to 54±3 nmol·10 g −1 of carcass weight·min −1 ), NO production (from 1.1±0.1 to 1.4±0.2 nmol·10 g −1 of carcass weight·min −1 ) and levels of SAP (from 4±1 to 115±23 ng/ml), whereas in all MCA tumour-bearing mice baseline values of arginine metabolism and SAP concentration were already elevated and the response to laparotomy was absent. In conclusion, MCA tumour-bearing mice had a disturbed post-operative metabolic response, as evidenced by attenuated post-operative arginine and NO production, concomitant with an attenuated acute-phase response. This indicates that altered arginine metabolism may be an important characteristic of the metabolic changes in cancer.

The general perception that catabolism and inflammation are associated with a high synthesis rate of total liver protein and a low albumin synthesis rate has been challenged in recent years by several studies in man, indicating that the synthesis rate of albumin in response to a catabolic insult is increased rather than decreased. Thus changes in liver protein synthesis rates in conjunction with catabolism and acute inflammation in man need to be characterized better. The aim of the present study was to measure protein synthesis rates of total liver protein and albumin during a state of acute inflammation. Patients ( n =10) undergoing acute laparoscopic cholecystectomy due to acute cholecystitis were investigated. FSRs (fractional synthesis rates) of total liver protein (liver biopsy specimens) and albumin (plasma samples) were investigated as early as possible during the surgical procedure, using a flooding dose of L -[ 2 H 5 ]phenylalanine. The results were compared with a reference group of patients without cholecystitis undergoing elective laparoscopic cholecystectomy ( n =17). FSR of total liver protein was 60% higher ( P <0.001) and the FSR of albumin was 45% higher ( P <0.01) in the cholecystitis patients compared with the control group. In conclusion, the synthesis rates of total liver protein and albumin are both increased in patients with an acute general inflammatory reaction undergoing laparoscopic cholecystectomy.

In the present study, we have investigated the use of 1-[ 13 C]glucose and GC/combustion/isotope-ratio MS as an alternative to 6,6-[ 2 H 2 ]glucose and GC/MS in the determination of parameters of glucose metabolism using the IVGTT (intravenous glucose tolerance test) interpreted by labelled (hot) minimal models. The study has been done in four populations, normoglycaemics (subdivided into lean and obese individuals), subjects with impaired glucose tolerance and those with diabetes mellitus. Although the use of carbon label may in some circumstances be compromised by substrate recycling, our hypothesis was that this would not be an issue under the condition of suppression of hepatic glucose production during the short timescale of an IVGTT. In all four groups, we found that the methodology employing the carbon label gave equivalent results to those obtained using the conventional deuterated material, but the sensitivity of the measurement technique in the new approach was sufficient to allow an approx. 15-fold reduction in the quantity of isotope administered. In addition to the clear cost advantages, this represents a significant scientific advance in that true tracer status is more nearly attained in these measurements with near-physiological tracee loads.

Muscle protein catabolism is a considerable clinical problem following surgery. However, the impact of surgical trauma on muscle protein synthesis is not well characterized. In this pilot study, we therefore investigated whether the severity of surgical trauma is related to a decrease in muscle protein synthesis rate in humans. Metabolically healthy patients ( n =28) were included in the study. Eight of the patients were day-care patients undergoing minor breast surgery (defined as minor surgery). The other 20 patients were subjected to major abdominal surgery and were therefore scheduled to stay overnight in the recovery room during the first postoperative night (defined as major surgery). Protein FSRs (fractional synthesis rates) in skeletal muscle were determined during a measurement period of 90 min before surgery and immediately after termination of surgery. FSR in skeletal muscle of the minor surgery patients was 1.72±0.25%/24 h before surgery and 1.67±0.29%/24 h after surgery ( P =0.68). In the major surgery group, FSR was 1.62±0.30%/24 h before surgery and 1.57±0.40%/24 h ( P =0.59) immediately following surgery. The observations made in this pilot study could not confirm a size-related decrease in muscle protein synthesis immediately following minor and major surgery. This finding is discussed in relation to confounders, postoperative course and to muscle protein degradation. The shortage of knowledge in this field is emphasized.

The objective of the present study was to investigate the validity of using holmium as a faecal marker in a copper absorption study using a highly enriched 65 Cu stable isotope label. Ten volunteers (nine female, one male) aged 24-55 years were recruited from the Norwich area to take part in a free-living study. The study was conducted in the Human Nutrition Unit at the Institute of Food Research, Norwich, U.K., and involved feeding breakfast test meals containing foods labelled intrinsically or extrinsically with a highly enriched 65 Cu stable isotope label. A 1mg oral dose of the rare earth element holmium was administered to volunteers simultaneously with an oral dose of highly enriched 65 Cu stable isotope as a label in the breakfast test meal. Complete faecal collections were made for 10 days after dosing, and the mean percentage holmium recovery (±S.D.) was 105±15%. After correcting for re-excreted copper label, the labelled copper and holmium had similar excretory profiles. It was concluded that holmium is a valid faecal marker in adult human copper absorption studies using stable isotopes.

We aimed to investigate the metabolism of chylomicron remnants in the postabsorptive state employing a new stable isotope breath test in centrally obese men without overt hyperlipidaemia. Groups of 12 centrally obese and 12 non-obese men of similar age and with similar plasma cholesterol and triacylglycerol (triglyceride) levels were studied. The catabolism of chylomicron remnants was measured using an intravenous injection of a remnant-like emulsion containing cholesteryl [ 13 C]oleate. Isotopic enrichment of 13 CO 2 in breath was determined using isotope-ratio mass spectrometry, and a multi-compartmental model (SAAM II program) was used to estimate the fractional catabolic rate (FCR) of the chylomicron remnant-like particles. The plasma concentrations of low-density lipoprotein (LDL)-cholesterol, non-high-density lipoprotein (HDL)-cholesterol and insulin were significantly higher ( P < 0.05) in the obese than the control subjects. The obese subjects had significantly lower HDL-cholesterol ( P < 0.05) and, in particular, a decreased FCR of the remnant-like particles compared with lean subjects (0.061±0.014 and 0.201±0.048pools/h respectively; P = 0.016). In the obese group, the FCR of remnant-like particles was inversely associated with the waist/hip ratio, and with plasma triacylglycerol, cholesterol, LDL-cholesterol and non-HDL-cholesterol levels. In multiple regression analysis, the waist/hip ratio was the best predictor of the FCR of the emulsion. In conclusion, this new test suggests that postabsorptive chylomicron remnant catabolism is impaired in centrally obese subjects without overt hyperlipidaemia. This defect may be due to the degree of adiposity.

1. The stimulation and depression of peripheral blood lymphocytes has previously been studied in vitro , showing an immune depression postoperatively; however, it is difficult to interpret these in vitro findings. Therefore, an in vivo technique has been established for determination of the fractional protein synthesis rate, as an index of metabolic activity in human peripheral blood lymphocytes, by using a stable isotope technique. 2. The rate of protein synthesis was calculated from the increase in enrichment of l-[ 2 H 5 ]phenylalanine in protein of a mixed population of mononuclear leucocytes, isolated by density gradient, after an intravenous flooding dose of l-[ 2 H 5 ]phenylalanine. A linear time course of isotopic incorporation into the cells was demonstrated. 3. The fractional rate of protein synthesis of a mixed population of mononuclear leucocytes was studied in relation to surgical interventions and to potential modifiers of the response. The fractional synthesis rate increased 24 h after open and laparoscopic cholecystectomy (49 ± 19% and 40 ± 14% respectively, P > 0.02), irrespective of postoperative total parenteral nutrition or preoperative glucose infusion. In contrast to surgery, insulin did not stimulate protein synthesis in peripheral mononuclear leucocytes.

1. The effects of fasting for 12, 36 and 72 h were examined in 19 normal subjects. Each subject was studied before and during a euglycaemic (4 mmol/l) hyperinsulinaemic (100 m-units min −1 m −2 ) clamp. Measurements were made of palmitate turnover and oxidation, glucose disposal, thermogenesis, intermediary metabolites and cardiovascular variables. 2. Basal respiratory exchange ratio fell from 0.78 ± 0.01 to 0.75 ± 0.01 to 0.72 ± 0.01 with fasting ( P < 0.001). In response to the clamp it rose to 0.91 ± 0.02, 0.83 ± 0.01 and 0.77 ± 0.01 after 12, 36 and 72 h respectively. Metabolic rate rose during the clamp by 0.41 ± 0.06, 0.11 ± 0.03 and 0.14 ± 0.04 kJ/min respectively ( P < 0.001 for 36- and 72-h values versus that at 12 h). 3. Fasting reduced total insulin-mediated glucose disposal rates from 42.6 ± 2.5, to 31.0 ± 1.8 to 21.3 ± 1.5 μmol min −1 kg −1 body weight after 12, 36 and 72h respectively ( P < 0.001). Glucose oxidation fell from 16.9 ± 1.1 to 8.7 ± 1.7 to 0.2 ± 1.3 μmol min −1 kg −1 body weight over the same period ( P < 0.001). Non-oxidative glucose disposal rates did not change significantly. 4. Basal plasma palmitate turnover increased with duration of fasting, being 1.16 ± 0.08, 1.72 ± 0.17 and 2.30 ± 0.35 μmol min −1 kg −1 body weight. In response to the clamp, palmitate turnover fell to 0.42 ± 0.05, 0.69 ± 0.08 and 1.28 ± 0.45μmol min −1 kg −1 body weight. Plasma palmitate oxidation was 0.58 ± 0.04, 0.75 ± 0.06 and 1.13 ± 0.11 μmol min −1 kg −1 body weight basally, and fell to 0.16 ± 0.02, 0.28 ± 0.04 and 0.43 ± 0.13 μmol min −1 kg −1 body weight by the end of the clamp. The proportion of total lipid oxidation represented by plasma non-essential fatty acid oxidation was not affected by fasting, but fell in response to the clamp. 5. Fasting caused a progressive resistance to the effects of insulin and glucose on oxidative glucose disposal and on forearm glucose uptake. Insulin-mediated glucose storage was unaffected by fasting, but the apparent cost of this storage was reduced by fasting.

1. The short-term (120 min) kinetics of Zn turnover has been studied in control subjects and patients with alcoholic liver disease after intravenous injection of 0.5 mg of 96.5% enriched 70 ZnCl 2 . 2. The 70 Zn enrichment of plasma was found closely to obey two-compartment kinetics and the derived two-component decay equation has been used to calculate the size and turnover of the initial two rapidly exchanging pools of body Zn. 3. In normal subjects isotopic Zn appears initially to equilibrate with the whole of the plasma Zn which comprises the first metabolic compartment, pool a. This has a size of 0.72 ± 0.1 μmol/kg. 70 Zn equilibration then occurs with a second compartment, pool b, consistent with a rapidly exchanging liver Zn pool of size 3.60 ± 0.93 μmol/kg. The fractional turnover rate of pool b was found to be fivefold slower than that of pool a. 4. In the alcoholic group an expansion of pool a was observed (1.63 ± 0.39 μmol/kg), but the size of the second pool was not significantly different from that of control subjects (5.55 ± 1.0 μmol/kg), although its fractional turnover was significantly increased ( K ab : control subjects, 0.018 ± 0.002 min −1 , alcoholic patients, 0.031 ± 0.006 min −1 ). 5. These data therefore demonstrate that kinetic studies using stable isotopes of Zn can provide novel information on exchangeable Zn pools in man, but provide no support for the possibility of an underlying Zn depletion in patients with alcoholic liver disease.

1. Iron absorption has been quantitatively measured as the incorporation of physiological doses of stable iron isotopes into erythrocytes. Five milligrams of 57 Fe (orally) and 250 μg of 58 Fe (intravenously) were given to five healthy women on 2 consecutive days. Fourteen days later the changes in the 57 Fe/ 56 Fe and 58 Fe/ 56 Fe ratios in the erythrocytes of each subject were measured using an inductively coupled plasma mass spectrometer. Isotope ratios were also measured in two subjects who were not given any enriched isotope. Concomitant measurements of plasma volume using a dye-dilution technique enabled the estimation of body iron mass and the calculation of iron absorption. 2. The mean coefficients of variation for the 57 Fe/ 56 Fe ratio and the 58 Fe/ 56 Fe ratio were 0.22% and 0.47%, respectively. This precision allowed enrichments of basal ratios to be reliably detected in all cases. The mean change in the 57 Fe/ 56 Fe ratio was 0.00116 ( sd 0.00052, P <0.001) and the mean change in the 58 Fe/ 56 Fe ratio was 0.00035 ( sd 0.00004, P <0.001). Control subjects showed no enrichment. 3. The calculated iron absorption ranged from 10% to 34%, and the amount of absorption was related to the iron stores of the subjects. Percentage iron absorption was identical when estimates of the plasma volume (derived from a body mass equation) were used instead of the plasma volume determined by dye-dilution measurements. Incorporation of intravenous iron into erythrocytes was on average 81% (range 68–93%). 4. The method is especially applicable to the study of iron absorption during pregnancy when incorporation into erythrocytes cannot be predicted.

1. Albumin fractional synthetic rate was determined in five non-pregnant subjects and five normal pregnant subjects in late gestation after an overnight fast by simultaneous prime and intravenous infusion of two precursor amino acids, [ 15 N]glycine and l -[1- 13 C]leucine, with additional priming of the large but, slowly turning over, urea pool with [ 15 N 2 ]urea. 2. The two tracers yielded similar values of albumin fractional synthetic rate: 6.1 and 6.0%/day in nonpregnant subjects and 7.3 and 7.6%/day in pregnant subjects, for glycine and leucine, respectively. While plasma volume was greater and serum albumin concentration was significantly reduced during pregnancy, the calculated intravascular albumin mass was significantly increased in pregnant subjects. 3. The amount of albumin synthesized in the intravascular compartment was significantly greater at 8.8 and 9.5 g/day in pregnant subjects compared with 6.4 and 6.3 g/day in non-pregnant control subjects (glycine and leucine methods, respectively). Calculated whole-body protein turnover using glycine was not different between the two subject groups, but leucine flux was higher in pregnant subjects. Partitioning of nitrogenous products in urine revealed that pregnant subjects excreted less urea, less ammonia and less creatinine than the non-pregnant control subjects. 4. These findings suggest that whereas the serum albumin concentration decreases during pregnancy secondary to the large increase in plasma volume, there is an increase in albumin synthesis such that total intravascular albumin mass is increased in late pregnancy.

1. The simultaneous effects of an intravenous glucose infusion on plasma urea, glucose and alanine kinetics were investigated in normal post-absorptive man. 2. The primed constant intravenous infusion of compounds labelled with stable isotopes, [ 15 N 2 ]urea, [6- 2 H]glucose and [3- 13 C]alanine, was used. 3. The rate of appearance of glucose and urea in the plasma was rapidly reduced by the 17.7 μUmol min −1 kg −1 glucose infusion. 4. In contrast, during the glucose infusion there was an increased rate of appearance of alanine in the plasma, and an increased percentage of glucose carbon atoms derived from alanine. 5. Reduced production of glucose and urea during the glucose infusion was not due to decreased gluconeogenesis from alanine.