The mechanisms of regulation of vitamin D metabolism in the kidney.

Recently, the 24-hydroxylase enzyme of 25-hydroxyvitamin D3 was purified from rat and chick kidney, and its complementary DNA was cloned. The length of the rat 24-hydroxylase gene is about 15 kbp with 12 exons. Cloning of the 24-hydroxylase gene made it possible to examine the mechanism of regulation of vitamin D metabolism at the gene level. Expression of renal 24-hydroxylase mRNA is regulated by a balance of plasma parathyroid hormone and 1 alpha,25-dihydroxyvitamin D3 levels, whereas intestinal 24-hydroxylase mRNA is regulated mainly by plasma 1 alpha,25-dihydroxyvitamin D3. This article reviews recent progress in understanding the molecular aspects of vitamin D metabolism.