AJP - Gastrointestinal and Liver Physiology, Vol 242, Issue 4 326-G332, Copyright © 1982 by American Physiological Society
Comparison of vitamin D and 25-hydroxyvitamin D absorption in the rat
M. D. Sitrin, K. L. Pollack, M. J. Bolt and I. H. Rosenberg
We have studied the intestinal absorption of physiological amounts of
vitamin D and 25-hydroxyvitamin D [25(OH)D3] in vivo from jejunal sacs in
rats with thoracic and bile duct cannulas. Under all test conditions,
absorption of 25(OH)D was greater than absorption of vitamin D. The
majority of absorbed vitamin D and 25(OH)D was transported from the
intestine in portal blood rather than lymph. When the luminal fluid
contained 2.5 mM oleic acid and monoolein, the presence of taurocholate did
not affect total intestinal absorption of vitamin D or 25(OH)D but
increased recovery of vitamin in lymph. When luminal fat content was
increased to 10 mM oleic acid and monoolein, total absorption of both
vitamin D and 25(OH)D was enhanced by taurocholate. No significant
metabolism of vitamin D or 25(OH)D occurred during absorption and transport
in lymph. Fifty-three percent of lymph vitamin D was found in the
chylomicron fraction, compared with only 13% of 25(OH)D. Inhibition of
chylomicron synthesis by cycloheximide decreased vitamin D absorption by
46% but diminished 25(OH)D absorption by only 30%. These differences in
behavior of vitamin D and 25(OH)D during absorption may explain the
superior absorption of 25(OH)D in patients with malabsorption.
