1. The renal handling of glucose was determined in male X-linked hypophosphataemic ( Hyp/Y ) mice and in control littermates (+/ Y ) aged 4 months. Plasma glucose concentration and urinary glucose excretion were measured before and during stepwise increase in glycaemia induced by an acute infusion of glucose. The relationship between plasma glucose concentration and urinary glucose excretion was monitored per ml of glomerular filtrate in mice fed high and low phosphate diets. 2. Hyp/Y mice fed the high phosphate diet showed a significantly higher glucosuria compared with +/ Y littermates. When glycaemia was increased, Hyp/Y mice developed frank glucosuria earlier than +/ Y animals. In Hyp/Y mice we could not find a threshold below which virtually no glucose was excreted in the urine, whereas this was clearly visible in +/ Y mice. These differences persisted in animals fed the low phosphate diet. 3. Using the acute response to the glucoregulatory hormones, glucagon and insulin, administered exogenously, we found that the regulation of plasma glucose concentration did not differ between Hyp/Y and +/ Y mice. 4. The significantly lower plasma glucose concentration observed in Hyp/Y as compared with +/ Y mice decreased further during fasting. 5. We conclude that the renal reabsorptive capacity for glucose is defective in Hyp/Y mice and their low plasma glucose concentration may be explained by the renal leak. Therefore the X-linked phosphataemic mouse appears not only to be characterized by a defect in renal phosphate and calcium reabsorption but also by an altered glucose reabsorption.

1. It has been suggested that a dominant mutation in the mouse is a suitable model for the most frequent form of human vitamin D-resistant rickets, X-linked hypophosphataemia. The mutant mice have reduced tubular reabsorption of phosphate, hypophosphataemia, rachitic bone lesions, moderate dwarfism and mild hypocalcaemia. 2. The present work shows that male hypophosphataemic (HYP/Y) mice have a decrease in the tubular capacity to reabsorb calcium as compared with normal littermates (+/Y). This decrease appears to be related to the phosphate status of the animals, since it is much more pronounced when the animals are fed on a low phosphorus diet. 3. The decrement in the tubular reabsorption and plasma concentration of calcium in HYP/Y mice is not accompanied by an augmentation in the absolute urinary excretion of calcium. It is associated with an increase in the urinary excretion of cyclic AMP. Furthermore, removal of the thyroparathyroid glands leads to much larger fall in the plasma concentration of calcium in HYP/Y than in +/Y mice. 4. Thus HYP/Y mice, when compared with normal littermates, have decreased tubular reabsorption of calcium with no apparent increase in the mobilization of calcium from intestinal and body sources as reflected by the absence of an augmentation in the absolute amount of calcium excreted in the urine. These findings could account for a propensity to hypocalcaemia which would be partially compensated by secondary hyperparathyroidism. This could explain the increase in urinary cyclic AMP excretion and the exaggerated hypocalcaemic response to removal of the parathyroid glands observed in murine X-linked hypophosphataemia.

1. The effect of long-term administration of parathyroid hormone (PTH) on whole-body calcium and ash weight of individual bones has been studied in normal and osteoporotic adult female rats in order to examine whether such a treatment could induce a positive calcium balance. 2. Osteoporosis was induced by calcium restriction during pregnancy and lactation. Sequential measurements of whole-body calcium were made by neutron activation. 3. In non-osteoporotic intact and thyroparathyroidectomized rats a daily dose of 75 units of human PTH 1–34 given subcutaneously for 3 weeks increased whole-body calcium. 4. In osteoporotic animals 25–50 units of either bovine PTH 1–84 or human PTH 1–34 given subcutaneously twice daily for 6 weeks increased both whole-body calcium and ash weight of individual bones. Microradiographic examination of the tibiae indicates, however, that PTH administration does not result in the restoration of individual trabeculae lost during the development of osteoporosis. 5. The results show that PTH can enhance skeletal mass in both normal and osteoporotic rats. In osteoporotic animals the restoration of whole-body calcium and ash weight of individual bones is not accompanied by a return of the morphological structure of the tibia to normal.

1. Protein-binding assays have been used to measure plasma 1,25-dihydroxy-vitamin D [1,25-(OH) 2 D] as well as 25-hydroxy-vitamin D [25-(OH)D] in rats given 10 mg of phosphorus (P) day −1 kg −1 as ethane-1-hydroxy-1,1-diphosphonate (EHDP). 2. In control animals given a normal laboratory chow plasma 25-(OH)D and 1,25-(OH) 2 D were about 40 nmol/l and 300 pmol/l respectively. 3. EHDP produced a decrease of plasma 1,25-(OH) 2 D to below 50 pmol/l in 2 days. 4. Both in control and in EHDP-treated rats plasma 1,25-(OH) 2 D increased when dietary calcium (Ca) was restricted to 0.1%, or dietary P to 0.2%, indicating that the well-known stimulatory effect of Ca or P deprivation was at least partially effective in EHDP-treated rats. 5. In response to an increase of the oral supply of vitamin D 3 to 65 nmol/day the plasma level of 25-(OH)D rose in both control and EHDP groups. Plasma 1,25-(OH) 2 D was not increased above the normal value in control rats. In EHDP-treated rats, however, plasma 1,25-(OH) 2 D rose to a level equal to that in controls, suggesting that the effect of EHDP on plasma 1,25-(OH) 2 D can be overcome at high precursor concentration.

1. Previous studies have shown that in thyroparathyroidectomized rats injection of disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) at doses that inhibit bone mineral retention (0.16 mmol = 10 mg of phosphorus/kg body wt. per day subcutaneously) leads to a decrease in the net tubular reabsorption of phosphate. 2. In the present work the tubular response to EHDP (0.16 mmol/kg body wt.) injected subcutaneously for 9 days has been localized by free-flow micropuncture in thyroparathyroidectomized rats. 3. The results show that the net tubular reabsorption of phosphate along the first portion of the (early) proximal tubule was markedly depressed in the EHDP-injected thyroparathyroidectomized rats compared with that in the pair-fed thyroparathyroidectomized control animals. In this latter group the delivery of phosphate to the distal tubule was larger than in the final urine, confirming previous reports. In the EHDP-injected thyroparathyroidectomized rats no difference in delivery of phosphate was found between the distal tubule and the final urine, suggesting that diphosphonate inhibited net reabsorption of phosphate in the terminal nephron. 4. The sites of the EHDP-induced changes in the tubular handling of phosphate were similar to those previously determined for the adaptive response to an increase in the supply of phosphate.

1. Chronic administration of 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] can normalize plasma calcium in human hypoparathyroidism and in thyroparathyroidectomized animals. The effect of 1,25(OH) 2 D 3 on plasma calcium is associated with an increase in urinary calcium excretion. In an attempt to prevent this increase, thyroparathyroidectomized rats receiving 1,25(OH) 2 D 3 were also treated with hydrochlorothiazide for 9–11 days. 2. Calcium clearance studies show that hydrochlorothiazide stimulated the tubular reabsorption of calcium in thyroparathyroidectomized rats treated with 1,25(OH) 2 D 3 . 3. Calcium balance and kinetic studies indicated that hydrochlorothiazide decreased 1,25(OH) 2 D 3 -induced hypercalciuria in thyroparathyroidectomized rats. Hydrochlorothiazide did not affect the 1,25(OH) 2 D 3 -induced increase in plasma calcium. The hypocalciuric effect of hydrochlorothiazide was not associated with significant changes in calcium deposition into or release from bone. 4. In thyroparathyroidectomized rats treated with 1,25(OH) 2 D 3 the hypocalciuric effect of hydrochlorothiazide was associated with a fall in intestinal calcium absorption. Overall, the calcium balance was unaffected. 5. Thus it appears that hydrochlorothiazide reduces the 1,25(OH) 2 D 3 -induced hypercalciuria in parathyroid hormone-deficient animals by decreasing intestinal calcium absorption. Despite the decreased absorption, hydrochlorothiazide does not reduce the 1,25(OH) 2 D 3 -induced increase in plasma calcium.

1. The short- and longer-term effects of ethane-1-hydroxy-1,1-diphosphonate (EHDP), an inhibitor of crystal growth and potential preventive agent against urinary tract stones in man, have been studied. 2. Measurement of urinary excretion of EHDP was used to define the best dosage regimen. When 4·4 mmol of EHDP was given daily in four divided doses the urinary concentration of EHDP achieved was high enough (10 −5 mol/l) to inhibit the crystallization of calcium crystals throughout the day. 3. Nine patients with recurrent calcium stones were given this dose of EHDP daily for 12 months and seven were then studied for a further 12 months under placebo. During treatment with EHDP, inhibitory activity in urine towards precipitation of calcium phosphate was restored from low values to greatly above normal. This could be accounted for by the inhibitory effect of EHDP itself, coupled with an increase in urinary inorganic pyrophosphate. After stopping EHDP the excretion of EHDP rapidly fell to undetectable levels but the excretion of pyrophosphate remained elevated throughout the 12 months of placebo treatment. EHDP also induced a rise in plasma phosphate and an increase in the urinary excretion of oxalic acid and uric acid, but these changes were all fully reversible when EHDP was stopped. 4. The average rate of stone formation per patient per year decreased from 2·4 to 0·2 during treatment with EHDP and remained low during the following 24 months. However, the dose needed for this effect is known to affect bone turnover and mineralization.

1. The uptake of inorganic pyrophosphate (PPi) from blood to bone was investigated in the rat in vivo. 2. PPi is taken up by the bone, where it appears both as PPi and as inorganic orthophosphate (Pi). The latter is due at least partly to local hydrolysis. 3. The fraction of injected PPi taken up by bone, measured as total Pi, was in the same range as that of technetium—tin—PPi, diphosphonates, technetium—tin—ethane-1-hydroxy-1,1-diphosphonate and Pi, but lower than that of calcium. 4. The plasma half-life of PPi is in the same order of magnitude as that of technetium—tin—PPi, diphosphonates, technetium—tin—ethane-1-hydroxy-1,1-diphosphonate, Pi and calcium. 5. PPi, diphosphonates and their technetium complexes are only partly ultrafiltrable in plasma. 6. It appears that the technetium complexes behave in a similar fashion to free PPi or diphosphonate.

1. In order to assess the relative importance of possible pathogenetic factors in the formation of calcium-containing renal stones, a group of 18 patients (12 men, six women) with active, recurrent stone disease were compared with 16 age-matched control subjects (10 men, six women) given an identical diet. 2. Fifteen (83%) of the patients showed at least one, eight (44%) showed two, and one (6%) patient showed three abnormalities that might predispose to stone formation. 3. Increased urinary calcium excretion was the most common abnormality (11 patients, 61%), particularly in the women (83%). 4. A diminished excretion of inhibitors of crystal formation of calcium phosphate was the next most common abnormality, which occurred in eight patients (44%), all of whom were men. It was largely attributable to a diminished excretion of inorganic pyrophosphate (PP i ). The PP i /orthophosphate ratios were also lower in the stone-formers. Significant differences in residual inhibitory activity after enzymatic removal of PP i between control subjects and stone-formers could not be found in 24 h urine samples but were present during certain times of the day. Pyrophosphate showed a higher inhibitory activity in urine than in control solutions, this enhancement being absent in stone-formers. 5. Nine (50%) of the patients, but only one of the control subjects, produced crystal aggregates greater than 50 μm in diameter after an oral load of oxalate.

1. The urinary excretion of inorganic pyrophosphate (PP 1 ), a known inhibitor of the growth and aggregation of crystals of calcium phosphate and calcium oxalate, increases after ingestion of orthophosphate (P 1 ). This effect may contribute to the apparent ability of oral phosphate to reduce the formation of urinary stones in man. This paper is a study of the mechanism by which P 1 increases PP 1 excretion, investigated by renal clearance techniques in man and renal arterial infusion in dogs. PP 1 in plasma was measured by an isotope-dilution method after ion-exchange chromatography. 2. The mean renal clearance of endogenous PP 1 in ten men was 7·9 ± 1·7 (se) ml/min, and the mean ratio of PP 1 clearance to creatinine clearance was 008 ±002 (se). The oral ingestion of P 1 increased the urinary excretion and renal clearance of PP 1 about threefold, without significantly changing its concentration in plasma. 3. In dogs, the infusion of P 1 into one renal artery caused a greater increase in urinary PP 1 from the infused than from the non-infused kidney, an effect that could be accentuated by simultaneous intravenous infusion of PP 1 . In dogs, only 1–3% of an injected or infused dose of PP 1 appeared intact in the urine, regardless of whether it was infused into the systemic or renal circulation. 4. These results suggest that P 1 has a direct effect on the kidney to increase the excretion of PP 1 . It is possible that P 1 either interferes with tubular reabsorption of PP 1 , perhaps by competing for a common tubular transport mechanism, or that P 1 diminishes the intrarenal hydrolysis of PP 1 .

1. The diphosphonates, disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) and disodium dichloromethylene diphosphonate (Cl 2 MDP), inhibit bone resorption in animals and in explanted bone in tissue culture. The possibility that these effects might be due to inhibition of skeletal adenylate cyclase has been studied. 2. EHDP and Cl 2 MDP, added for 30 mm to the incubation medium at concentrations known to inhibit bone resorption, had no effect on basal content of adenosine 3′:5′-cyclic monophosphate (cyclic AMP) of mouse calvaria incubated in vitro , nor did they inhibit the rise in cyclic AMP induced by bovine parathyroid hormone. 3. Pretreatment of mice for 3 days with Cl 2 MDP also had no effect on cyclic AMP under basal conditions or after incubation of explanted calvaria with parathyroid hormone in vitro. EHDP under similar conditions slightly inhibited the increase induced by parathyroid hormone but had no effect on basal concentrations of cyclic AMP. 4. It is suggested that the inhibition of adenylate cyclase is not an essential feature of the reduction of bone resorption by diphosphonates, which may act by direct inhibitory effects on the dissolution of hydroxyapatite and perhaps by other unidentified effects on bone cells.

1. The existence of tubular secretion of inorganic phosphate (P i ) in the mammalian kidney has been investigated by studying the renal response of rats infused with sodium phosphate by three different techniques. 2. Clearance studies indicate that, in anaesthetized rats, the net tubular reabsorption decreases markedly in response to P i infusion. In conscious rats, the clearance of P i slightly exceeded that of inulin at high plasma P i concentration. 3. Free-flow micropuncture in control rats showed a net tubular reabsorption of P i along the proximal tubule, and probably between the end of the distal tubule and the ureteral urine. In phosphate-loaded rats, whether receiving parathyroid hormone or not, an apparent net secretion of P i was observed between the end of the distal tubule and the ureteral urine. In the phosphate-loaded group receiving parathyroid hormone, net secretion was also observed very early in the proximal tubule followed by a predominant reabsorption along this segment. Thus the early proximal tubule and probably also the terminal nephron can be the site of either net reabsorption or net secretion. 4. Microperfusions of proximal tubules show a fall in the specific radioactivity of the perfused radioactive P i solution, indicating entry of P i into the lumen.

1. Ligated intestinal segments from rats treated with disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) at the daily dose of 16 μmol (1 mg of phosphorus)/kg subcutaneously for 7 days show an increased rate of calcium absorption. 2. This dose of EHDP enhances the intestinal accumulation of a vitamin D 3 metabolite with the chromatographic characteristics of 1,25-dihydroxycholecalciferol.

1. Bladder stones composed of calcium hydrogen phosphate dihydrate, calcium oxalate mono- and di-hydrate and magnesium ammonium phosphate hexahydrate (struvite) were successfully induced in rats by various dietary manipulations and by implanting zinc pellets in the bladder. 2. The effect of a diphosphonate, disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP), given in the drinking water at concentrations of 0·0025, 0·05 and 0·5% (w/v), on the size and composition of these stones was examined. 3. All the concentrations of EHDP decreased the weight of the calcium oxalate calculi. In contrast, only the highest concentration of EHDP inhibited calcium hydrogen phosphate stone formation and the magnesium ammonium phosphate stones were unaffected. 4. The difference between the effects on calcium oxalate and magnesium ammonium phosphate stones is consistent with the finding that EHDP inhibited the precipitation of calcium oxalate from solution in vitro but had only a slight effect on magnesium ammonium phosphate precipitation. 5. It is suggested that EHDP might be of use in the prevention of some types of urinary stones in man.