title: Metabolism and excretion of 3H-1,25-(OH)2-vitamin D3 in healthy adults.
abstract: The synthesis of very high specific activity 25-OH-vitamin D3 (78 Ci/mmol) has made possible the study of the metabolism and plasma disappearance of 3H after a single dose of 3H-1,25-(OH)2-D3 in quantities that are only 10-20% of the endogenous plasma pool. We studied seven healthy adults who were given doses of 1,25-(OH)2-D3 ranging from 30-2300 pmol. Plasma disappearance was rapid with only 14 +/- 2% of administered 3H remaining in the plasma pool 4 h after labeling. Plasma metabolite profiles during the first 4 h showed only 1,25-(OH)2-D3. Thereafter, significant amounts of other metabolites were detected. The 6-day cumulative excretion of 3H in urine and feces (virtually all associated with metabolites of 1,25-(OH)2-D3) averaged 16 +/- 3% and 49 +/- 11% of the dose, respectively. Compartmental analysis of the isotope data for two subjects who received the smallest doses of 1,25-(OH)2-D3 indicated that endogenous renal 1,25-(OH)2-D3 synthesis rates approximate 0.8-2.4 nmol/day (0.3-1.0 microgram/day).
mesh_terms: D000328:Adult; D002112:Calcifediol; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000652:urine; D005243:Feces / Q000032:analysis; D005260:Female; D006801:Humans; D006887:Hydroxycholecalciferols / Q000652:urine; D007408:Intestinal Absorption; D007700:Kinetics; D008274:Magnesium / Q000652:urine; D008297:Male; D010710:Phosphates / Q000652:urine
chemical_list: D006887:Hydroxycholecalciferols; D010710:Phosphates; D002117:Calcitriol; D008274:Magnesium; D002112:Calcifediol; D002118:Calcium