Purine modulation of the hormonal response of the rat Sertoli cell in culture.

To investigate the possibility that purines modulate the response of testicular cells to gonadotropin, binding of adenosine analogs and biological responses to adenosine were evaluated in Sertoli cell-enriched cultures. The adenosine analog cyclohexyladenosine bound specifically to a crude particulate fraction prepared from such cultures. Binding was saturable, and steady state studies showed the presence of a high affinity binding site (Kd = 2.1 +/- 0.3 nM; n = 4) and a receptor density of 200-300 fmol/mg protein. The bound radioactive ligand was displaced by N6-phenylisopropyladenosine (PIA), adenosine, and methylisobutylxanthine. In addition to the presence of a specific binding site, purines modulated the biological function of the Sertoli cell. The adenosine analog PIA inhibited both the FSH-dependent cAMP response and the FSH-stimulated androgen aromatization. Under all experimental conditions, the IC50 of PIA was 1-3 nM, and maximal effects were observed at 10-100 nM PIA. Adenosine itself inhibited the FSH-dependent response of the Sertoli cell, but was less potent than PIA. In addition, purine inhibition of the FSH response was antagonized by methylisobutylxanthine, while the nonxanthine phosphodiesterase inhibitor Ro 20-1724 [4-(3-butoxy-4-methoxybenzyl)2-imidazolidinone] was without effect. Purine modulation was evident not only when cells were stimulated with FSH, but also when the androgen aromatization was augmented by the beta-adrenergic agonist isoproterenol, cholera toxin, and forskolin. On the contrary, the purines had no effect when cells were stimulated with (Bu)2cAMP. The data reported are consistent with the presence of purine inhibitory receptors in Sertoli cell-enriched cultures and show that purines can regulate the response of the immature Sertoli cell in vitro.