Physiology of 24,25-dihydroxyvitamin D3 in normal human subjects.
We determined the metabolic clearance and production rates of 24,25-dihydroxyvitamin D3 in four normal healthy adults. We also examined the excretion of radioactivity in stool, urine, and bile after the intravenous administration of 24,25-[3H]dihydroxyvitamin D3 to human subjects. 24,25-Dihydroxyvitamin D3 is rapidly cleared from the plasma with a half-life of approximately 390 +/- 25 min (mean +/- SE). The metabolic clearance rate of 24,25-dihydroxyvitamin D3 was 9.2 +/- 1.5 liters/day with a production rate of 26.4 +/- 7.2 micrograms/day (mean +/- SE). Within 1 day 13.0 +/- 4.2% (mean +/- SE) of the administered dose had appeared in the stool; by day 7, 48.8 +/- 2.7% of the dose had appeared in the feces. Within 24 hr, 6.4 +/- 0.8% of the administered dose appeared in the urine; 7.4 +/- 1.8% of the dose had appeared in the urine within 2 days. The biliary excretion of 24,25-dihydroxyvitamin D3 was studied in two subjects. By 8 h, 15.3 +/- 1.3% of the administered dose had appeared in the bile. The metabolites present in bile, feces, and urine were much more polar than 24,25-dihydroxyvitamin D3. These results demonstrate that 24,25-dihydroxyvitamin D3 is rapidly cleared from plasma and is excreted in the feces (probably via the bile) and urine of normal human subjects.
D015650:24,25-Dihydroxyvitamin D 3; D000328:Adult; D000818:Animals; D001646:Bile / Q000032:analysis; D002117:Calcitriol / Q000378:metabolism; D002645:Chickens; D004100:Dihydroxycholecalciferols / Q000378:metabolism*; D005243:Feces / Q000032:analysis; D006207:Half-Life; D006801:Humans; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D008928:Mitochondria / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D014316:Tritium
D004100:Dihydroxycholecalciferols; D014316:Tritium; D015650:24,25-Dihydroxyvitamin D 3; D002117:Calcitriol