Effects of castration, sex steroids, LHRH and glucocorticoids on LHRH binding in the anterior pituitary of male rats.

In the present study we have examined the effects of gonadotrophin releasing hormone (LHRH), sex steroids and glucocorticoids on the binding of LHRH to receptors in the pituitary of male intact and castrated rats. In intact rats, LHRH (10 microgram/day) treatment for 11 days caused a significant increase in LHRH binding, whereas testosterone (500 microgram/day) or oestradiol (50 microgram/day) were inhibitory. 17-hydroxyprogesterone and dexamethasone were without effects. In castrated rats, LHRH caused a marginal decrease in LHRH binding. Much greater inhibition was observed with testosterone and oestradiol. 17-hydroxyprogesterone reduced binding to that of intact controls, whereas dexamethasone was ineffective. When different doses of sex steroids were tested, both oestradiol, testosterone and 5 alpha-dihydrotestosterone inhibited LHRH in a dose-dependent manner. The lowest doses of steroids causing significant inhibition of LHRH binding in castrated animals were 0.5, 50 and 500 microgram/day for oestradiol, 5 alpha-dihydrotestosterone and testosterone, respectively. The present study shows that pituitary receptors for LHRH are regulated both by sex steroids and LHRH itself.