Adenosine Receptor-Mediated Effects by Nonmetabolizable Adenosine Analogs in Preovulatory Rat Granulosa Cells: A Putative Local Regulatory Role of Adenosine in the Ovary*

The influence of nonmetabolizable adenosine analogs on cAMP production was investigated in preovulatory rat granulosa cells. 5'-(N-ethyl)Carboxamido-adenosine (NECA), a stimulatory A2-adenosine receptor agonist, stimulated cAMP accumulation, and NECA and 2-chloro-adenosine also potentiated the response to FSH. The adenosine receptor antagonist 8-phenyltheophylline antagonized the effect of NECA, shown by a shift in the dose-response curve to the right. The stimulatory effect of NECA was also seen in an ovarian membrane preparation, where NECA stimulated adenylate cyclase in both the presence and absence of FSH. The stimulatory effect of NECA was also decreased by 8-phenyltheophylline in this preparation. The A1-receptor agonists N6-(R-phenyl-isopropyl)-adenosine (R-PIA) and N6-(S-phenyl-isopropyl)-adenosine (S-PIA) both inhibited FSH-stimulated cAMP accumulation. The inhibitory effects of R-PIA and S-PIA, but not the stimulatory effects of NECA, could be counteracted by dipyridamole, a nucleoside transport inhibitor. Furthermore, R-PIA and S-PIA inhibited adenosine uptake into granulosa cells. Thus, the inhibitory effects of R-PIA and S-PIA are not likely to be mediated via membrane-bound inhibitory A1-adenosine receptors. Neither the stimulatory effects of NECA nor the inhibitory effects of R- and S-PIA could be attributed to changes in ATP levels, since the ATP levels were unaffected by these analogs. The results of this study indicate the existence of stimulatory A2-adenosine receptors in preovulatory rat granulosa cells and suggest a membrane-associated modulatory role of adenosine in preovulatory granulosa cells.