title: Synthesis of [3 beta-3H]-3-epivitamin D3 and its metabolism in the rat.
abstract: 3-Epivitamin D3, the 3 alpha epimer of vitamin D3, was synthesized, and its biological activity in the rat was evaluated. It was found to be approximately 4 times less active on a weight basis than vitamin D3 with respect to intestinal calcium transport, bone calcium mobilization, and calcification score as determined by the line-test assay. Tritiated 3-epivitamin D3 was prepared, and its metabolism in the rat was compared with that of vitamin D3 to investigate the reasons for this diminished activity. 3-Epivitamin D3 was converted to two polar metabolites, for which the chromatographic properties and the origin of biosynthesis (in the liver and kidney, respectively) correspond to 25-hydroxy-3-epivitamin D3 and 1 alpha,25-dihydroxy-3-epivitamin D3. The fact that the concentration of 1 alpha,25-dihydroxy-3-epivitamin D3 in the intestine is half that of 1 alpha,25-dihydroxyvitamin D3 may be one explanation for the reduced biological activity of this epimer.
mesh_terms: D000818:Animals; D001681:Biological Assay; D002118:Calcium / Q000378:metabolism; D002762:Cholecalciferol / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D004386:Duodenum / Q000187:drug effects / Q000378:metabolism; D007408:Intestinal Absorption / Q000187:drug effects; D007553:Isotope Labeling / Q000379:methods; D008099:Liver / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D051381:Rats; D013053:Spectrophotometry; D013237:Stereoisomerism; D014316:Tritium
chemical_list: D014316:Tritium; D002762:Cholecalciferol; D002118:Calcium