Effect of glucocorticoids on vitamin D metabolism

Abstract

Vitamin Da is hydroxylated in the liver and other tissues to 25hydroxycholecalciferol((25OH)Da) [l] and further converted by the kidney to 1,25dihydroxycholecalciferol((1,25-OH),Da) the hormonal form of vitamin Da [2]. Evidence has been presented to show that the calcium and phosphorus content of the diet [3,4] 1,25(OH)?Da itself [5], parathyroid hormone [6] and prolactin [7,8] regulate the production of (1,25OH)zDs by the kidney. Recently Kenny [9] suggested that steroid hormones stimulate the 25.hydroxycholecalciferol-lo-hydroxylase, the enzyme responsible for the production of (1,25-Ol$Da and Tanaka et al. [lo] reported that large doses of oestrogens in the presence of androgens have a profound stimulatory effect on the activity of this enzyme. Our results are slightly different since we found that the presence of androgens is not essential for oestrogens to exert their effect. Thus oestrogens alone, or when combined with androgens or even with progesterone, markedly stimulate lo-hydroxylase activity [ 1 l] . The purpose of this report is to present evidence that glucocorticoids also have a profound stimulatory effect on the activity of la-hydroxylase.