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H F DeLuca

Publications and source records attributed to H F DeLuca.

At least 19 recordsLinked to original sources
PubMed1979

Characteristics of the rat liver microsomal enzyme system converting cholecalciferol into 25-hydroxycholecalciferol. Evidence for the participation of cytochrome p-450.

Properties of the rat hepatic cholecalciferol 25-hydroxylase have been studied. An assay system has been developed in which 25-hydroxycholecalciferol production is linear for at least 2h in both homogenates and microsomal fraction. Furthermore, the initial reaction velocity is linearly related to the amount of liver tissue or microsomal fraction. This enzyme system also metabolizes an analogue of cholecalciferol, namely dihydrotachysterol 3, into 25-hydroxydihydrotachysterol 3. The 25-hydroxylase is in the microsomal fraction and not in mitochondria. It has a Km of 44 nM for cholecalciferol and 360 nM for dihydrotachysterol 3. Its activity is not altered by dietary concentrations of calcium and phosphorus. Vitamin D-deficient rats have higher activities of the hepatic 25-hydroxylase than those receiving 25 ng of cholecalciferol daily. The 25-hydroxylase is inhibited by metyrapone. An atmosphere of CO/O2 (9:1, v/v) inhibits the reaction by 87%. This inhibition is partially reversed by white light. Additionally, cholecalciferol and 25-hydroxycholecalciferol competitively inhibit aminopyrine demethylase. These results support the idea that the cholecalciferol 25-hydroxylase is a cytochrome P-450-dependent mono-oxygenase.

Animals↗
PubMed1979

Target cells for 1,25-dihydroxyvitamin D3 in intestinal tract, stomach, kidney, skin, pituitary, and parathyroid.

After mature rats that had been fed on a vitamin D3-deficient diet were injected with tritium-labeled 1,25-dihydroxyvitamin D3, radioactivity became concentrated in nuclei of luminal and cryptal epithelium of the duodenum, jejunum, ileum, and colon; in nuclei of the epithelium of kidney distal tubules including the macula densa, and in podocytes of glomeruli; in nuclei of the epidermis including outer hairshafts and sebaceous glands; and in nuclei of certain cells of the stomach, anterior and posterior pituitary, and parathyroid. These results reveal cell types that contain receptors for 1,25-dihydroxyvitamin D3 or metabolites of this compound both in known or hypothesized target tissues and in tissues that were previously unknown to participate in vitamin D3 metabolism.

Animals↗
PubMed1979

25-Hydroxyvitamin D3 26,23-lactone: a new in vivo metabolite of vitamin D.

A major vitamin D metabolite was isolated in pure form from the blood plasma of chicks either maintenance levels or large doses of vitamin D3. The isolation involved methanol-chloroform extraction and five column chromatographic procedures. The metabolite purification and elution position on these columns were followed by a competitive protein binding assay. The metabolite was identified, using high- and low-resolution mass spectrometry, 270-MHz proton nuclear magnetic resonance spectrometry, ultraviolet absorption spectrophotometry, Fourier transform infrared spectrophotometry, and specific chemical reactions, as 3 beta,-25-dihydroxy-9,10-seco-5,7,10(19)-cholestatrieno-26,23-lactone. The trivial names 25-hydroxyvitamin D3 26,23-lactone or calcidiol 26,23-lactone are suggested for this compound.

Animals↗
PubMed1979

Isolation and characterization of 1 alpha-hydroxy-23-carboxytetranorvitamin D: a major metabolite of 1,25-dihydroxyvitamin D3.

The in vivo side-chain oxidation of 1 alpha,25-dihydroxyvitamin D3 was investigated by using a double-label radiotracer technique. Rats dosed with 1 alpha,25-dihydroxy-[3 alpha-3H]vitamin D3 and 1 alpha,25-dihydroxy[26,27-14C]vitamin D3 produced compounds with a high 3H/14C ratio. These compounds were found in sizable quantities in intestine and liver within 3 h after dosing. The major side-chain oxidized metabolite migrated as an acid on DEAE-Sephadex chromatography and contained no 14C. Methyl esterification of this compound with diazomethane proceeded in good yield and rendered the compound more amenable to chromatographic purification. The metabolite was isolated in several steps from rats dosed with 1 microgram of 1 alpha,25-dihydroxy[3 alpha-3H]vitamin D3. The metabolite was obtained in pure form as the methyl ester and was positively identified as 1 alpha,3 beta-dihydroxy-24-nor-9,10-seco-5,7,10(19)cholatrien-23-oic acid. The trivial name calcitroic acid is proposed for this major side-chain oxidized metabolite of 1,25-dihydroxyvitamin D3.

Animals↗
PubMed1979

Effect of ethane-1-hydroxy-1,1-diphosphonate and vitamin D on bone mineralization.

Administration of large quantities of ethane-1-hydroxy-1,1-diphosphonate to growing chicks resulted in a decrease in percent bone ash and an increase in percent osteoid. The degree of inhibition of bone mineral accumulation was a function of both duration and quantity of ethane-1-hydroxy-1,1-diphosphonic acid administration. The inhibition of bone mineral accumulation could be partially corrected with administration of 1,25-dihydroxyvitamin D3. Administration of high levels of ethane-1-hydroxy-1,1-diphosphonate also resulted in inhibition of intestinal calcium absorption. This could be reversed or prevented by the administration of 1,25-dihydroxyvitamin D3.

Animals↗
PubMed1979

Biological activity of 24,24-difluoro-25-hydroxyvitamin D3. Effect of blocking of 24-hydroxylation on the functions of vitamin D.

To examine the question of whether 24-hydroxylation plays and importance role in the physiological functions of vitamin D, the biological activity of 24,24-difluoro-25-hydroxyvitamin D was compared with that of 25-hydroxyvitamin D in vitamin D-deficient rats. These two compounds were found almost identically active in the stimulation of intestinal calcium transport, the mobilization of calcium from bone, the healing of rachitic epiphyseal plate cartilage, the elevation of serum inorganic phosphorus, the mineralization of rachitic bone, and in the prevention of rachitogenesis in rats. Little or no difference was detected in the time course of response of intestinal calcium transport or bone calcium mobilization to the two forms of vitamin D. Therefore, in the rat no support could be obtained for the idea that 24,25-dihydroxyvitamin D3 plays an important role in the known physiological responses to the vitamin.

Animals↗
PubMed1979

Metabolism and biological activity of 25-fluorocholecalciferol, 24-dehydrocholecalciferol and 25-dehydrocholecalciferol in the rat.

Three side-chain analogues of cholecalciferol (vitamin D3) modified at C-25, namely 25-fluorocholecalciferol, 24-dehydrocholecalciferol and 25-dehydrocholecalciferol, conceived as potential inhibitors of the cholecalciferol 25-hydroxylase have been prepared and tested in the rat. These compounds markedly diminish conversion in vivo of cholecalciferol into 25-hydroxycholecalciferol, but are not antagonists of vitamin D action, because they themselves possess significant biological activity in vivo. Each compound is capable of stimulating the intestinal transport of calcium and the mobilization of calcium from bone in vitamin D-deficient rats. Biological responses equivalent to those generated by a physiological dose of cholecalciferol (0.05 microgram) are produced, however, only when the analogues are administered at high doses (5-50 microgram). The biological activity of 24-dehydrocholecalciferol and 25-dehydrocholecalciferol is shown to result from conversion, in vivo, to the natural hormone, 1 alpha,25-dihydroxycholecalciferol, whereas 25-fluorocholecalciferol is metabolically activated in the rat by hydroxylation to 1 alpha-hydroxy-25-fluorocholecalciferol. This latter conversion is the first reported example of the 1 alpha-hydroxylation of a vitamin D compound lacking the 25-hydroxy group.

Animals↗
PubMed1979

Determination of vitamin D and its metabolites in plasma from normal and anephric man.

A multiple assay capable of reliably determining vitamins D(2) and D(3) (ergocalciferol and cholecalciferol), 25(OH)D(2) (25-hydroxyvitamin D(2)) and 25(OH)D(3) (25-hydroxyvitamin D(3)), 24,25(OH)(2)D (24,25-dihydroxyvitamin D), 25,26(OH)(2)D (25,26-dihydroxyvitamin D) and 1,25(OH)(2)D (1,25-dihydroxyvitamin D) in a single 3-5ml sample of human plasma was developed. The procedure involves methanol/methylene chloride extraction of plasma lipids followed by separation of the metabolites and purification from interfering contaminants by batch elution chromatography on Sephadex LH-20 and Lipidex 5000 and by h.p.l.c. (high-pressure liquid chromatography). Vitamins D(2) and D(3) and 25(OH)D(2) and 25(OH)D(3) are quantified by h.p.l.c. by using u.v. detection, comparing their peak heights with those of standards. 24,25(OH)(2)D and 25,26(OH)(2)D are measured by competitive protein-binding assay with diluted plasma from vitamin D-deficient rats. 1,25(OH)(2)D is measured by competitive protein-binding assay with diluted cytosol from vitamin D-deficient chick intestine. Values in normal human plasma samples taken in February are: vitamin D 3.5+/-2.5ng/ml; 25(OH)D 31.6+/-9.3ng/ml; 24,25(OH)(2)D 3.5+/-1.4ng/ml; 25,26(OH)(2)D 0.7+/-0.5ng/ml; 1,25(OH)(2)D 31+/-9pg/ml (means+/-s.d.). Values in two normal human plasma samples taken in February after 1 week of high sun exposure are: vitamin D 27.1+/-7.9ng/ml; 25(OH)D 56.8+/-4.2ng/ml; 24,25(OH)(2)D 4.3+/-1.6ng/ml; 25,26(OH)(2)D 0.5+/-0.2ng/ml. Values in anephric-human plasma are: vitamin D 2.7+/-0.8ng/ml; 25(OH)D 36.4+/-16.5ng/ml; 24,25(OH)(2)D 1.9+/-1.3ng/ml; 25,26(OH)(2)D 0.6+/-0.3ng/ml; 1,25(OH)(2)D was undetectable.

Animals↗
PubMed1979

25-Azavitamin D3, an inhibitor of vitamin D metabolism and action.

25-Azavitamin D3 inhibited both the bone calcium mobilization and intestinal calcium transport responses of rats to vitamin D3 but not to 25-hydroxyvitamin D3. Although 25-azavitamin D3 had no effect on the response of bone to 1alpha,25-dihydroxyvitamin D3, it did diminish the response of the intestine to that metabolite. 25-Azavitamin D3 increased liver vitamin D content and reduced the concentration of 25-hydroxyvitamin D3 required to inhibit the metabolism of vitamin D3 (75 and 200 microgram) were similar to the doses of 25-azavitamin D3 required to inhibit the action of vitamin D3 in vivo (50 and 150 microgram). 25-Azavitamin D3 is thus a vitamin D antagonist, acting for the most part via inhibition of the liver 25-hydroxylation of vitamin D3.

Animals↗
PubMed1979

Vitamin D deficiency and reproduction in rats.

Female weanling rats from a colony maintained on a diet low in vitamin D were raised on a diet that was deficient in vitamin D but was otherwise adequate. Vitamin D deficiency was confirmed in the rats by hypocalcemia and the absence of vitamin D metabolites in blood. These females gave birth to litters that were slightly smaller than control litters from females maintained on a vitamin D-containing diet. The pups from the vitamin D-deficient mothers appeared normal throughout lactation, and at weaning had normal concentrations of calcium and phosphate in the plasma. These results indicate that vitamin D and its metabolites are not necessary for reproduction and fetal development in the rat.

Animals↗