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Biomedical subjects

F Bronner

Publications and source records attributed to F Bronner.

At least 55 records · Page 3Linked to original sources
PubMed1978

Vitamin D metabolism and expression in rats fed on low-calcium and low-phosphorus diets.

1. Cholecalciferol, radioactively labelled with both (14)C and (3)H, was administered weekly for 7 weeks to rats that had been depleted of vitamin D for 4 weeks before repletion with the radioactive vitamin. This permitted measurement of the steady-state effect on vitamin D metabolism of low-calcium and low-phosphorus regimens, as compared with a normal mineral intake. These dietary manoeuvres were carried out during the last 3 weeks of repletion. Cholecalciferol, 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol were determined in plasma, intestine, kidney and bone. Ca(2+)-binding-protein content was measured in intestine and kidneys of comparable animals. 2. In rats on the low-calcium diets, 1,25-dihydroxycholecalciferol concentration was elevated in plasma, bone, kidney and intestine, and intestinal Ca(2+)-binding protein was increased to over twice the concentration found in the control animals. 3. The low-phosphorus regimens led to a decrease in plasma phosphate and 1,25-dihydroxycholecalciferol in all tissues studied, for the latter to the point where it was undetectable in plasma and bone. Intestinal and renal concentrations of Ca(2+)-binding protein were unchanged in the low-phosphate-intake group and decreased in the very-low-phosphate-intake group. 4. It is concluded that in the rat, unlike in the chick, hypophosphataemia is not associated with a stimulation of the production of 1,25-dihydroxycholecalciferol or its expression in the synthesis of Ca(2+)-binding protein. Therefore the plasma phosphate concentration does not appear to be directly involved in the regulation of the functional metabolism of vitamin D.

Animals↗
PubMed1976

Vitamin D deficiency and rickets.

Classical experimental rickets in the rat is a dual deficiency, resulting from both phosphate and vitamin D deficiency, with many of the features of rickets reproducible by simple phosphorus deficiency. Simple vitamin D deficiency differs markedly from experimental rickets, with only the absence of the vitamin D-dependent calcium-binding proteins common to both situations. The expression at the bone level of vitamin D deficiency differs in the two conditions, with rickets leading to profound structural and metabolic changes, whereas simple vitamin deficiency primarily compromises the regulatory function of bone, without obvious structural alterations. It is proposed that human nutritional rickets is the result of a nutritional vitamin D deficiency that aggravates the expression of a pre-existing metabolic defect in phosphate transport. Simple nutritional vitamin D deficiency, unaccompanied by rickets, may occur, but probably has always been rare.

Animals↗
PubMed1975

Stimulation in vitro by 1,25-dihydroxy-vitamin D3 of intestinal cell calcium uptake and calcium-binding protein.

Treatment of duodenal tissue from rats deficient in vitamin D with 1,25-dihydroxy-vitamin D3 [1,25-(OH)2-D3] led to more than a doubling of calcium uptake by the isolated cells and the appearacne in those cells of previously undetectable calcium-binding protein (CaBP). Treatment with the precursor, 25-hydroxy-vitamin D3, was without effect on calcium uptake or CaBP. Cells from vitamin D-replete animals took up three and a half times more calcium than cells from deficient animals. This rapid (90-minute) effect of in vitro treatment with a physiological dose (4.7 X 10(-8)M) of 1,25-(OH)2-D is the first such report and is in accord with the regulatory role of the hormone-like sterol.

Animals↗
PubMed1975

Vitamin D -- induced changes in the renal membrane ATPase system.

Ca-dependent and Mg-dependent ATPase activity was found to be depressed significantly in renal membrane preparations from vitamin D-deficient as compared to normal rats. Administratiin of 2000 i.u. vitamin D2 to deficient rats 30 hours before sacrifice restored the membrane enzyme activity to normal. ATP binding by enzymes was also reduced in vitamin D deficiency and raised by repletion. Vitamin D may therefore be required for normal Ca-and Mg-dependent ATPase activity.

Adenosine Triphosphatases↗
PubMed1975

Vitamin D-dependent calcium-binding protein from rat kidney.

A calcium-binding protein has been partially purified from rat kidney. It is found in the cortex, but not in the medulla. It is Vitamin D-dependent, as it occurs in normal, but not in Vitamin D-deficient rats. The molecular weight is 28 000, more than twice that of the Vitamin D-dependent calcium-binding proteins from rat intestinal mucosa. The apparent dissociation constant of the partially purified renal calcium-binding protein is approx. 10-5 M.

Animals↗
PubMed1975

Regulation of intestinal calcium-binding protein calcium intake in the rat.

Analytical gel electrophoresis of the vitamin D-dependent intestinal calcium-binding protein (CaBP) has demonstrated two protein bands (1 and 2) of similar molecular weight and similar specific binding activity. The mucosal concentration of CaBP, measured by a quantitative competitive binding assay, has been shown to vary reproducibly and inversely with calcium intake and the mucosal calcium concentration. These same factors also influence the relationship of bands 1 and 2. When animals on a high-calcium diet were placed on a low-calcium diet, their CaBP increased by 35% in 24 h and by 48% in 48 h and reached a level typical of animals on a low-calcium diet. Measurement of the diurnal variation of CaBP and mucosal calcium in animals allowed access to feed only at night revealed significant, but inverse, oscillations. These observations are interpreted as reflecting a regulation of CaBP by the mucosal calcium concentration, which appears to reflect absorbed calcium in transit.

Calcium↗
PubMed1975

Intestinal CaBP: a new quantitive index of vitamin D deficiency in the rat.

Rats raised from weaning on regiments adequate in calcium and phosphorus but deficient in vitamin D will have no detectable intestinal calcium-binding proteins (CaBP), whether or not they show other signs of vitamin D deficiency, such as hypocalcemia. When hypocalcemic, vitamin D-deficient animals were treated with 25-hydroxycholecalciferol, a vitamin D metabolite, they showed a dose-dependent increase in plasma calcium and CaBP; both responses can be described by a single linear relationship, which appears to apply whether the metabolite is 25-hydroxycholecalciferol or dihydrotachysterol. Since vitamin D status is only one determinant of plasma calcium, whereas CaBP (or its expression) appears to depend on vitamin D quantitatively, CaBP may be used as an index of vitamin D status, provided calcium intake is controlled.

Animals↗
PubMed1974

Bacterial calcium transport: energy-dependent calcium uptake by membrane vesicles from Bacillus megaterium.

Membrane vesicles capable of energy-dependent calcium uptake have been prepared from Bacillus megaterium cells in log-phase growth or when undergoing sporulation. The uptake is dependent on the calcium concentration and appears saturable in vesicles from cells in log-phase growth. Both ascorbate and phenazine methosulfate are needed as a source of electrons for the energy-dependent increase in calcium uptake. Addition of 8 mM sodium cyanide inhibited the energy-dependent uptake. If this calcium uptake mechanism is a component of the sporulation-specific calcium accumulation process, the latter's functional expression would appear to be inhibited during log-phase growth.

Ascorbic Acid↗