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Biomedical subjects

H F DeLuca

Publications and source records attributed to H F DeLuca.

At least 397 records · Page 22Linked to original sources
PubMed1980

1,25-Dihydroxyvitamin D3 stimulated increase of 7,8-didehydrocholesterol levels in rat skin.

A convenient, accurate assay was developed for determining skin cholesta-5,7-dien-3 beta-ol (7,8-didehydrocholesterol) concentrations. Ultraviolet spectrophotometry provided quantitation of the sterol from rat skins following saponification and chromatography on Lipidex and high-performance liquid chromatography. Correction for recoveries was accomplished by using 7,8-didehydro[3 alpha-3H]cholesterol as an internal standard. Chronic dosing of vitamin D-deficient rats with 1,25-dihydroxyvitamin D3 caused a 4-fold increase in skin 7-dehydrocholesterol content. This rise was not the result of changes in food consumption, body weight, or plasma calcium. Cholesterol concentrations were not significantly elevated although some of the other nonsaponifiable lipid components found in the high-performance liquid chromatogram appeared to be increased by the treatment. These results suggest that the vitamin D hormone 1,25-(OH)2D3 may exert a positive feedback regulation on the production of vitamin D3 in skin.

Animals↗
PubMed1980

In vivo and in vitro inhibition of rat liver vitamin D3-25-hydroxylase activity by 19-hydroxy-10(S),19-dihydrovitamin D3.

Rats treated with varying amounts of 19-hydroxy-10(S),19-dihydrovitamin D3 prior to administration of physiologic doses of vitamin D3 exhibit normal intestinal calcium transport but are unable to mobilize bone calcium. In contrast, 19-hydroxy-10(R),19-dihydrovitamin D3 had no inhibitory activity. Circulating serum levels of 25-hydroxy[3H]vitamin D3 and 1 alpha, 25-dihydroxy[3H]vitamin D3 are markedly suppressed but not totally eliminated in animals predosed with 19-hydroxy-10(S),19-dihydrovitamin D3 before [3H]vitamin D3. Hepatic 25-hydroxy[3H]vitamin D3 levels were approximately equal in both 19-hydroxy-10(S),19-dihydroviotamin D3 treated and untreated rats. However, the rate of conversion of [3H]vitamin D3 to 25-hydroxyvitamin D3 in vivo is greatly reduced in the treated rats. The inhibitory vitamin analogue was also show to block hepatic microsomal 25-hydroxylation in vitro. These results indicate that 19-hydroxy-10(S),19-dihydrovitamin D3 is a specific inhibitor for a hepatic microsomal vitamin D3-25-hydroxylase system.

Animals↗
PubMed1980

Characterization of a specific, high affinity binding macromolecule for 1 alpha, 25-dihydroxyvitamin D3 in cultured chick kidney cells.

Cytosol prepared from vitamin D3-deficient kidney cells in culture contains a 3.7 S protein that specifically binds 1,25-dihydroxyvitamin D3 with high affinity and low capacity. Whole kidney homogenate cytosol preparations are shown to possess two 1,25-dihydroxyvitamin D3 binding macromolecules. One of the binding proteins sediments at 3.5 to 3.7 S while the second sediments at 6.0 S. The 6.0 S component has a greater affinity for 25-dihydroxyvitamin D3 than for 1,25-dihydroxyvitamin D3. Cultured cell cytosol was found to have little 6.0 S 25-hydroxyvitamin D3 binding protein. Scatchard analysis of the cultured cell cytosol reveals an equilibrium binding constant (KD) of 5.6 x 10 (-11) with 57 fmol of sites/mg of protein. The receptor-like protein has a Mr = 72,000 and as with other steroid receptors it aggregates in the presence of low potassium concentrations. Analog competition for receptor binding reveals the following potency order: 1,25-dihydroxyvitamin D3 > 25-hydroxyvitamin D3 > 1 alpha-hydroxyvitamin D3 > 24(R),25-dihydroxyvitamin D3; the receptor had no detectable affinity for vitamin D3. The kidney cells respond to 1,25-dihydroxyvitamin D3 by diminishing 25-hydroxyvitamin D3 1 alpha-hydroxylation and increasing 24R-hydroxylation. Cultured cells provide a preparation of cytosol which has allowed extensive characterization of the renal 1,25-dihydroxyvitamin D3 receptor and should facilitate investigations into the role this receptor plays in renal control of vitamin D3 metabolism.

Animals↗
PubMed1980

Metabolites of 1 alpha, 25-dihydroxyvitamin D3 in rat bile.

Metabolites of 1 alpha, 25-dihydroxy[3 alpha-3H]vitamin D3 in rat bile were studied. The water-soluble metabolites (77-91% of the total bile radioactivity) are predominantly acids (retained by DEAE-Sephadex chromatography) that become chloroform soluble after methylation with diazomethane. Calcitroic acid was isolated from this fraction (after conversion to the methyl ester) and unambiguously identified by chromatographic and mass spectrometric studies. The chloroform phase of extracted bile contains small amounts (1.1-8.1% of the metabolites in bile, dependent on dose given) of unchanged 1 alpha, 25-dihydroxyvitamin D3 and no 1 alpha, 24(R),25-trihydroxyvitamin D3. In addition, the chloroform phase contained a mixture of 24-dehydro- and 25-dehydro-1 alpha-hydroxyvitamin D3 and calcitroic acidmethyl ester. The latter compound was shown to be an artifact resulting from the use of methanol as part of the advent mixture for the initial bile extractions.

Animals↗
PubMed1980

Direct chemical synthesis of 1 alpha,25-dihydroxy[26,27-3H]vitamin D3 with high specific activity: its use in receptor studies.

The first direct chemical synthesis of radiolabeled 1 alpha,25-dihydroxyvitamin D3 is reported. Unlike all previous syntheses, the new approach does not rely on enzymatic 1 alpha-hydroxylation of radiolabeled precursors. Rather, isotope is introduced in the last synthetic step by reaction of [3H]-methylmagnesium bromide with methyl 1 alpha-hydroxy-26,27-dinorvitamin D3-25-carboxylate to give 1 alpha,25-dihydroxy-[26,27-3H]vitamin D3 with a specific activity of 160 Ci/mmol. Mass spectroscopy confirmed that the radiohormone consists of a single isomer with six tritium atoms bound to carbons 26 and 27. Synthetically produced 1 alpha,25-dihydroxy[26,27-3H]vitamin D3 is indistinguishable from 1 alpha,25-dihydroxy-[26,27-3H]vitamin D3 obtained from the enzymatic 1 alpha-hydroxylation of 25-hydroxy[26,27-3H]vitamin D3 (160 Ci/mmol) by high-pressure liquid chromatography analysis and in the competitive binding assay using chick intestinal cytosol as the receptor source. Equilibrium dissociation constant measurements with the high specific activity radiohormone indicate a Kd of 8.2 x 10(-11) M for the chick intestinal cytosol 1 alpha,25-dihydroxyvitamin D3 receptor--a value considerably lower than the constants in the range of (1-5) x 10(-9) M previously reported.

Animals↗
PubMed1980

A specific 1,25-dihydroxyvitamin D3 binding macromolecule in chicken bone.

Cytosol prepared from homogenates of bone from vitamin D3-deficient chicks contains a 3.7 S macromolecule having high affinity and low capacity for 1,25-dihydroxyvitamin D3. Employing 1,25-dihydroxy-[26,27-3H]vitamin D3 (160 Ci/mmol) an apparent Kd has been calculated to be 7.6 x 10(-11) M while the association and dissociation rate constants for the binding process at 25 degrees C were determined to be 9.5 x 10(8) M-1 min-1 and 2.3 x 10(-2) min-1, respectively. A 5.5 S molecule is also present which binds 1,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 but appears to prefer 25-hydroxyvitamin D3 and is increased by the addition of chick serum to cytosol. The 3.7 S material is neither a serum contaminant nor a component of the 5.5 S molecular species and is likely of intracellular origin. Under low salt conditions the 3.7 S macromolecule migrates to 4.3 S and 5.5 S regions on sucrose gradients suggesting aggregation of the protein. Several vitamin D3 metabolites are capable of specifically binding to the 3.7 S macromolecule. The relative order of potency for several analogs causing displacement of specifically bound 1,25-dihydroxy-[26,27-3H]vitamin D3 is: 1,25-dihydroxyvitamin D3 greater than 1 alpha-hydroxyvitamin D3 greater than or equal to 25-hydroxyvitamin D3 greater 24(R),25-dihydroxyvitamin D3. It is concluded that chick bone cytosol contains a macromolecule of high affinity and low capacity for 1,25-dihydroxyvitamin D3 which may function as a receptor for some physiological events in bone.

Animals↗
PubMed1980

5,6-epoxyretinoic acid is a physiological metabolite of retinoic acid in the rat.

5,6-Epoxyretinoic acid was detected in small intestine, kidney, liver, testes and serum of vitamin A-deficient rats 3 h after a single physiological dose of [3H]retinoic acid. The maximum concentration of 5,6-epoxide in intestinal mucosa was observed 3 h after intrajugular administration of retinoic acid. However, at 7 h post administration, no 5,6-epoxyretinoic acid was detected in mucosa, demonstrating the rapid intestinal metabolism or excretion of this metabolite. No 5,6-epoxy[3H]retinoic acid was detected in mucosa, liver or serum of retinoic acid-repleted rats 3 h after administration of 2 micrograms of [3H]retinoic acid.

Animals↗
PubMed1980

Vitamin D homeostasis in the perinatal period: 1,25-dihydroxyvitamin D in maternal, cord, and neonatal blood.

To investigate vitamin D homeostasis in term pregnancy, we measured 1,25-dihydroxyvitamin D (1,25(OH)2D) in serum samples from 19 term pregnant women and in samples from the placental veins of their infants. Samples were obtained from 14 neonates at 24 hours of age. At delivery, maternal concentrations of 1,25(OH)2D were elevated above normal adult values; placental-vein concentrations in the infants were significantly lower than adult normal or maternal values and bore no relation to maternal values. By the time the infants reached 24 hours of age, their serum concentrations had reached normal adult values, concomitant with a decrease in serum concentration of ionized calcium. We speculate that low 1,25(OH)2D concentrations in utero suggest that there is no need for intestinal calcium absorption in the fetus. Postnatal increase of 1,25(OH)2D may result from its production as a prerequisite to extrauterine requirements for intestinal absorption of calcium and phosphorus.

Adult↗
PubMed1980

Serum 1,25-dihydroxyvitamin D levels in normal children and in vitamin D disorders.

Using a precise assay for 1,25-dihydroxyvitamin D in serum, the levels in 103 children, aged 13 months to 16 years, were found to be 43 +/- 2 pg/mL (mean +/- SE). This value is higher than reported values in adults and in neonates. Age-related changes in 1,25-dihydroxyvitamin D levels during childhood were also evident. Older children have significantly higher levels than children less than 11 years, possibly indicating changes with puberty and the adolescent growth spurt. The values were significantly reduced in childhood uremia (13 +/- 5 pg/mL), in hypoparathyroidism (16 +/- 1 pg/mL), and in children with Fanconi's syndrome. Treatment with oral calcitriol in these three groups of patients led to increased serum levels.

Adolescent↗
PubMed1980

Supranormal 25-hydroxyvitamin D and subnormal 1,25-dihydroxyvitamin D: their role in X-linked hypophosphatemic rickets.

Serum 25-hydroxyvitamin D (25-OH-D) and 1,25-dihydroxyvitamin D (1,25-(OH)2D) and bone mineral content by the photon-absorption technique were determined in eight patients with X-linked hypophosphatemic rickets treated for at least 24 months with oral sodium phosphate and high-dosage ergocalciferol (vitamin D2). Mean 25-OH-D2 level was 129.5 +/- 67.5 ng/mL (mean +/- SD); the level of 25-OH-D3 was 10.5 +/- 5.8 ng/mL. These values were significantly higher than in normal subjects (total 25-OH-D mean of 27 +/- 10 ng/mL). Serum 1,25-(OH)2D was 16.9 +/- 8.5 pg/mL (mean +/- SD) in the eight patients, significantly lower than 47 +/- 16 pg/mL in 27 age-matched controls. Values indicative of significant demineralization were found in seven of the eight phsophate-treated patients, who had no radiologic evidence of rickets. These results suggest that any theory of the pathogenesis of this disorder must account for inappropriate renal vitamin D metabolism and for renal hyperphosphaturia. The failure of high-dosage oral phosphate and ergocalciferol to fully correct demineralization may suggest a role for calcitriol (1,25-(OH)2D3) as a therapeutic agent.

Absorption↗
PubMed1980

Thyrotropes in the pituitary are target cells for 1,25 dihydroxy vitamin D3.

In the anterior pituitary of the rat, target cells of 1,25 (OH)2 vitamin D3 are identified as those that secrete thyroid stimulating hormone by means of a combined technique of thaw-mount autoradiography and immunohistochemistry. The results for the first time provide evidence that suggests a central effect of 1,25 (OH)2 vitamin D3 on the modulation of thyrotropin secretion in a manner similar to that of other steroid hormones at the level of the pituitary.

Animals↗
PubMed1980

Target cells for 1,25 dihydroxyvitamin D3 in the pancreas.

Mature rats raised on a vitamin D deficient diet were injected with tritium labeled, 1,25 dihydroxyvitamin D3. Concentration of radioactivity, which is prevented by pretreatment with unlabeled 1,25 dihydroxyvitamin D3, is found in nuclei of cells that are centrally located in pancreatic islets. The central location of these cells and supportive evidence from the literature suggest that they are B-cells, and that 1,25 dihydroxyvitamin D3 has a direct and genomic action on B-cell functions including insulin secretion.

Animals↗