Involvement of phosphodiesterase in the refractoriness of the Sertoli cell

Gonadotropin treatment of the Sertoli cell produces a marked refractory state of the cell to subsequent hormonal stimulation. Because FSH also stimulates the phosphodiesterase activity of these cells, the possible involvement of an altered cAMP catabolism during refractoriness was investigated in an in vitro model. Sertoli cells, after 3 days of culture in a defined medium, were exposed to FSH or isoproterenol for 1-24 h. After this pretreatment, cells were stimulated for 1 h with a maximal FSH dose, and the responsiveness was measured in terms of cAMP accumulation. Sertoli cells previously treated with hormone entered a refractory state, a second exposure being ineffective in elevating intracellular or extracellular cAMP. Addition of the phosphodiesterase inhibitor 3-isobutyl-methylxanthine in the second incubation partially restored the ability of the cell to accumulate cAMP in the presence of hormone. This phosphodiesterase inhibitor also caused an apparent decrease in the potency of FSH to induce the refractory state. Such an impairment of response developed in the intact cell in 4 h, and was accompanied by a partial desensitization of the adenylate cyclase and an increase in phosphodiesterase activity. The stimulation of phosphodiesterase activity, but not the desensitization of adenylate cyclase, was inhibited by cycloheximide. The inhibition of protein synthesis also prevented the onset of the refractory state of the intact Sertoli cell. Pretreatment of the Sertoli cells with either FSH or isoproterenol rendered the cell refractory to a second stimulation with either agonist; in contrast, the adenylate cyclase desensitization in the homogenate was apparent only for the agonist employed in the preincubation. These results indicate that phosphodiesterase regulation is involved in the control of Sertoli cell responsiveness to hormone. Thus, the net decrease in cAMP production of the FSH-treated cells is the result of a decreased adenylate cyclase stimulation and an increased cAMP catabolism mediated by phosphodiesterase. The latter phenomenon appears to be the predominant cause of the partial refractoriness induced by low doses of gonadotropin.