AJP - Gastrointestinal and Liver Physiology, Vol 242, Issue 5 522-G532, Copyright © 1982 by American Physiological Society
Biliary excretion of [3H]-25-hydroxyvitamin D3 in the vitamin D-depleted rat
M. Gascon-Barre
The biliary excretion of [3H]-25-hydroxyvitamin D3 ([3H]25(OH)D3) was
studied in vitamin D-depleted female rats over a 3-h period after
intravenous or intraduodenal administration of intact [3H]25(OH)D3 and
after the intraduodenal readministration of the [3H]25(OH)D3-derived
biliary material. In each group four doses of 25(OH)D3 were administered
(0.25, 2.5, 25, and 250 nmol/100 g). Over the dose range studied, the
biliary excretion of [3H]25(OH)D3 could not be saturated, indicating that
the biliary excretion of 25(OH)D3 is a reliable detoxification mechanism in
circumstances of 25(OH)D3 intoxication. Analysis of plasma, liver, and bile
suggests that the canalicular membrane seems to be rate limiting in the
biliary excretion of 25(OH)D3. The intraduodenal administration of biliary
excretion compounds derived from [3H]25(OH)D3 showed that they are
efficiently reexcreted in newly secreted bile, confirming the existence of
an enterohepatic circulation for 25(OH)D3. In this group of animals,
however, the plasma analysis indicates that these compounds reach the
systemic circulation in insignificant quantities, suggesting that the
enterohepatic circulation probably plays a limited role in the body
25(OH)D3 economy.
