AJP - Endocrinology and Metabolism, Vol 243, Issue 5 370-E374, Copyright © 1982 by American Physiological Society
Physiology of 24,25-dihydroxyvitamin D3 in normal human subjects
R. Kumar, R. Wiesner, M. Scott and V. L. Go
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.
