Study of the direct effect of LHRH agonist on testicular 17-hydroxylase and 5 alpha-reductase activities in non-hypophysectomized adult rats treated with an anti-luteinizing hormone serum

In order to study both direct and pituitary-mediated mechanisms of action of the LHRH analogue D-Ser(TBU)6, des-Gly-NH2(10)]LHRH ethylamide upon testicular steroidogenesis in adult rat, we compared the effects of the agonist when administered alone or concomitantly with an anti-LH serum to non-hypophysectomized rats. Testicular steroid contents and in vitro progesterone and testosterone metabolism were determined. Anti-LH serum administration was able to prevent 5 alpha-reductase stimulation by the agonistic peptide, but not the inhibition of 17-hydroxylase activity. These data suggest that modulation of 17-hydroxylase involves both direct and pituitary-mediated processes, while 5 alpha-reductase stimulation is mainly if not only due to a pituitary-mediated mechanism.