Involvement of inducible nitric oxide synthase in stress-impaired testicular steroidogenesis

The immobilization stress induces an acute inhibition of testicular steroid ogenesis that is mediated by the nitric oxide (NO) signaling pathway. Here we compared the effects of 2-h immobilization stress on in vivo and in vitr o rat steroidogenesis at two time points, 0 h and 6 h after the end of the stress session. As expected, serum androgens and human chorionic gonadotrop in (hCG)-stimulated progesterone and testosterone production by testicular tissue were inhibited at 0 h, and also at the 6-h time point. Both the acut e and sustained inhibitions of in vitro steroidogenesis were accompanied by a significant increase in nitrite, a stable oxidation product of NO. To cl arify which subtype of NO synthase (NOS) (constitutive (cNOS) or inducible (iNOS)) participates in down-regulation of testicular steroidogenesis, amin oguanidine hydrochloride (AG), a selective iNOS inhibitor, was employed. In tratesticular injection of AG prevented the sustained, but not the acute, s tress-induced decrease in serum testosterone. When added in vitro, it also prevented the sustained decrease in steroid production and increase in nitr ite production by testicular tissue, both in a dose-dependent manner and wi th EC50 of about 50 mu M. Furthermore, AG added in vivo and in vitro effect ively blocked the sustained decrease in 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) and 17 alpha-hydroxylase/C17-20 lyase (P450c17) activities. I n all concentrations employed, AG did not affect serum androgens and in vit ro steroid and nitrite production in unstressed animals. These results indi cate that the NO signaling pathway participates in acute and sustained stre ss-induced down-regulation of testicular steroidogenesis, presumably throug h its direct action on 3 beta HSD and P450c17. The acute NO production is c ontrolled by cNOS and the sustained production of this messenger is control led by iNOS.