Stimulatory action of endothelin-1 on rat Leydig cells: Involvement of endothelin-A subtype receptor and phospholipase A(2)-arachidonate metabolism system

In a previous report we have observed that endothelin-l (ET-1) is able to stimulate testosterone (T) production by rat Leydig cells revealing an interaction with human chorionic gonadotropin (hCG). The present study was designed to further characterize the stimulatory action of ET on testicular steroidogenesis, to evaluate which subtype of ET receptors is involved in this activity and to examine the role of phospholipase A(2) (PLA(2))-arachidonate metabolism system in ET-1 transduction mechanism. To this' purpose we investigated: i) the interaction of ET-1 with another secretagogue of T, like luteinizing hormone releasing hormone (LHRH); ii) the interference of ETA and ETB receptor antagonists (BQ-123 and BQ-788, respectively) and of inhibitors of PLA(2) (quinacrine) and arachidonate lipoxygenase pathway (nordihydroguaiaretic acid: NDGA) on ET-l-induced T and PGE(2) secretion from purified rat Leydig cells. Data obtained indicate that ET-I amplified T and PGE(2) response to LHRH and this secretagogue in turn potentiated testicular steroidogenesis stimulated by endothelin. The ETA antagonist, BQ-123, inhibited in a dose-related fashion ET-l-induced T production whereas ET antagonist, BQ-788, failed to affect T response to the peptide. Furthermore ET antagonist inhibited the stimulatory effect of ET-1 on hCG- or LHRH-induced T secretion and it was able to exert a dose-dependent inhibition of ET-l-stimulated PGE(2) output. Moreover, a PLA(2) inhibitor quinacrine inhibited the stimulatory action of ET-I on T production and suppressed basal and ET-l-induced PGE(2) release whilst a Lipoxygenase blocker NDGA did not modify T response to the peptide. Taken together these findings i) indicate additivity of effects between ET-1 and LHRH in stimulating T and PGE(2) production; ii) confirm that ETA subtype receptors mediate the stimulatory action of ET-1 on rat Leydig cells; iii) strongly suggest that PLA(2)-arachidonate metabolism system is involved in endothelin transduction mechanism.