CONICET | Buscador de Institutos y Recursos Humanos

Involvement of NO in the mechanism of histamine-induced inhibition of leydig cell steroidogenesis Mondillo C; Pagotto R; Reche CG; Patrignani ZJ; Cymeryng CB; Pignataro OP The present study was conducted to shed light on the so far unexplored intracellular mechanisms underlying negative modulation of Leydig cell steroidogenesis by histamine (HA). Using MA-10 cells line and purified rat Leydig cells, we examined the effect of the amine on biochemical steps known to be modulated by HA, or involved in LH/hCG action. HA at 10 ìM showed a potent inhibitory effect on hCG-stimulated steroid synthesis. Moreover, HA not only decreased hCG-induced cAMP production but also steroid synthesis stimulated by db-cAMP. HA was almost equally effective at inhibiting db-cAMP-stimulated steroid synthesis. Considering the site(s) of action of HA, HA inhibited db-cAMP-stimulated steroidogenic acute regulatory (StAR) protein expression, as well the conversion of cholesterol to pregnenolone by cholesterol side-chain cleavage enzyme (CYP11A). The antisteroidogenic action of HA was blocked by addition of the PLC-inhibitor U73122, and HA significantly augmented IP3 production, suggesting a major role for the PLC/IP3 pathway in HA-induced inhibition of Leydig cell function. Finally, HA increased nitric oxide synthase (NOS) activity, and the NOS inhibitor L-NG-nitro-arginine methyl ester (L-NAME) markedly attenuated the effect of the amine on steroid synthesis. On the basis of our findings, HA antagonizes the gonadotropin action in Leydig cells at steps both pre- and post-cAMP formation. NOS activation is the main intracellular mechanism by which HA exerts its antisteroidogenic effects.