Control of renal vitamin D hydroxylases in birds by sex hormones.

Abstract

Kidney homogenates from adult male Japanese quail [Coturnix coturnix] or chickens [Gallus domesticus] demonstrated hydroxylase activity predominantly for the 24 rather than the 1 position of 25-hydroxyvitamin D3 (25-hydroxycholecalciferol). A single injection of 5 mg of estradiol-17.beta. into a male bird completely suppressed the 24-hydroxylase and greatly increased the 1-hydroxylase activity. Immature males did not respond well to estrogen alone, but they did respond well to estradiol plus testosterone. Testosterone alone had little or no effect on the hydroxylases of either species. Castrated male chickens showed an estradiol response only when testosterone was also given. Optimal 24 h responses to 5 mg of estradiol/kg in the castrate male were obtained with about 12 mg of testosterone/kg. These optimal amounts of estradiol and testosterone increased the activity of 25-hydroxyvitamin D3-1-hydroxylase approximately 225-fold [this enzyme is also known as 25-hydroxycholecalciferol 1-monooxygenase; 25-hydroxycholecalciferol, NADPH: oxygen oxidoreductase (hydroxylating), EC 1.14.13.13]. These results demonstrated a strong regulation by the sex hormones of the renal vitamin D hydroxylases in birds.