Effect of oxytocin on testosterone production by isolated rat Leydig cells is mediated via a specific oxytocin receptor.

The effect of the neurohypophysial hormones oxytocin and arginine vasopressin (AVP) on testicular steroidogenesis was reevaluated by use of short-term (< 10 h) cultures of isolated adult rat Leydig cells. Oxytocin at 10(-9), 10(-7), and 10(-5) M concentrations significantly increased basal testosterone production in a dose-dependent manner but had no effect on LH-stimulated testosterone production. The specificity of the effect was determined by use of the specific oxytocin receptor antagonist (OTA). OTA from 10(-9) to 10(-5) M concentrations inhibited the oxytocin-stimulated increase in testosterone production. Furthermore, the oxytocin agonist Thr4 Gly7 oxytocin also induced a dose-dependent increase in basal testosterone production. In contrast, AVP from 10(-9) to 10(-5) M concentrations did not consistently affect basal testosterone production by isolated Leydig cells, but significantly decreased LH-stimulated testosterone production. Inclusion of 10(-7) and 10(-5) M OTA with 10(-7) M AVP did not alter the inhibitory effect of the AVP. These data show that oxytocin and AVP have different effects on testosterone production by Leydig cells in vitro and support the hypothesis that oxytocin acts in the testis through a specific oxytocin receptor.