"Antigonadal" activity of the neurohypophysial hormones in cultured rat testicular cells: abolition by pertussis toxin.

The intermediary role of the putative inhibitory regulatory membrane protein "Ni" in the "antigonadal" activity of the neurohypophysial hormones was investigated in vitro with the use of a primary culture of rat testicular cells. To this end, use was made of the pertussis toxin (PT) probe, an exotoxin of Bordetella pertussis presumed to modify and inactivate a membrane protein related to or identical with Ni. Testicular cells were pretreated with PT (70 ng/ml) for 24 h, a duration of exposure known to result in a maximal PT effect. Thereafter, the cells were cultured for an additional 48 h in the absence or presence of hCG (10 ng/ml), with or without a maximal inhibitory dose (10(-6) M) of the neurohypophysial principle arginine vasotocin (AVT). Although concomitant treatment of control cells with AVT produced a profound (95%) inhibition of hCG-stimulated testosterone accumulation, PT pretreatment resulted in a long-lasting (greater than 4 days) abolition of this "antigonadal" effect. Furthermore, pretreatment with PT resulted in significant (P less than 0.05) augmentation of the hCG-stimulated accumulation of extracellular cAMP (1.5- to 2.0-fold) and testosterone (1.7- to 3.8-fold), presumably as a result of abolition of the "basal" tonic inhibition of adenylate cyclase activity. Taken together, these findings constitute the first demonstration of the involvement of Ni in the "antigonadal" activity of the neurohypophysial hormones and in the regulation of testicular function, thereby raising the intriguing possibility that testicular Ni may serve as the coupling unit of inhibitory receptors other than those for the neurohypophysial hormones, integrating varied incoming signals of endocrine, paracrine or autocrine nature.