Effect of varying vitamin D status in the body on intestinal absorption and metabolism of vitamin D in the rat liver

: The absorption of [3H]-vitamin D3 in the intestine and its hydroxylation in the liver were higher in vitamin D-deficient rats than in vitamin D-treated ones. The higher is the vitamin content in the organism, the greater part of the label is occupied by unchanged vitamin D3. It is supposed that both absorption of the vitamin in the intestine and its 25-hydroxylation in hepatocytes may decrease with a rise of the vitamin D3 amount. This activates a mechanism of protection from the vitamin D redundancy.