Modulation of gonadotropic and purinergic responsiveness by islet activating protein in sertoli cells from immature rats.

In the present study we have examined the effects of islet activating protein (IAP) on the regulatory effects of FSH, glucagon and (-)N6-(R)-phenyl-isopropyladenosine (PIA), an adenosine A1 receptor agonist, on the formation of cAMP and estradiol-17 beta (E2) in Sertoli cell cultures isolated from immature (19-day-old) rats. FSH (NIH-FSH-S-15) (1.25 micrograms/ml) caused a more than 10-fold stimulation of the level of both cAMP and E2 in the spent media from Sertoli cell cultures during an 18 h incubation. Both responses were reduced by 80% in the presence of PIA (10(-6) M). When the cultures were preincubated for 24 h with increasing concentration of IAP, the inhibitory effects of PIA were counteracted in a concentration-dependent manner. Moreover, preincubation with IAP (> 20 ng/ml) caused a significant stimulation of FSH-stimulated cAMP production even in the absence of PIA. PIA inhibited FSH-stimulated cAMP production in a concentration dependent manner. However, when the cells were preincubated with IAP (100 ng/ml) for 24 h, the inhibitory effects of PIA were completely abolished, and PIA now actually caused a slight stimulation of cAMP production. Both FSH and glucagon stimulated cAMP production in a concentration-dependent manner. Preincubation with IAP (100 ng/ml for 24 h) resulted in an increase in maximal stimulation of cAMP production for both FSH and glucagon. When adenylyl cyclase (AC) activity was measured directly in isolated membrane particles from Sertoli cells cultured in the presence of IAP (100 ng/ml) for 24 h, both basal and FSH-stimulated AC activity were significantly higher than in membrane particles from control cells. These results provide a further characterization of the functional Gi component coupled to the AC complex in cultured rat Sertoli cells, mediating the inhibitory effects of adenosine and possibly other endogenous substances on cAMP production.