[In vitro effects of 1,25-dihydroxycholecalciferol on alkaline phosphatase and gamma-glutamyltransferase activity in hypophysectomized rats].

Effects in vitro of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) on alkaline phosphatase (PAL), gamma-glutamyltransferase (gamma-GT) and acid phosphatase (PAC) activities were investigated on renal cortex from hypophysectomized rats. In these animals the biosynthesis of 1,25-(OH)2D3 and the specific activities of kidney PAL and gamma-GT were decreased. The course of these effects was determined from 45 min to 8 h. In the presence of 1,25-(OH)2D3 (2 x 10(-6) M) a delayed (5h) but simultaneous stimulation of the three enzymes was observed. It reached a maximum at 6h and disappeared at 8h. The dose-response relation was studied at 6h. In the presence of 1,25-(OH)2D3 (5 x 10(-7) M), the three enzymes were activated. The effect was maximal at 10(-6) M; it was +22% for PAL, +17% and +15% respectively for gamma-GT and PAC compared with controls. Cycloheximide suppressed the induction of PAL but not of gamma-GT activity. The effects of the secosteroid on renal enzymes seems to be a pharmacological more than a physiological one.