INTERLEUKIN-1-BETA SUPPRESSES APOPTOSIS IN RAT OVARIAN FOLLICLES BY INCREASING NITRIC-OXIDE PRODUCTION

A growing body of evidence suggests that intraovarian interleukin-1 be ta (IL-1 beta) may play an intermediary role in the ovulatory process. Furthermore, induction of nitric oxide (NO) by IL-1 beta has been rep orted in a wide variety of tissues. As the majority of ovarian follicl es undergo an atretic degeneration process involving apoptotic cell de ath, we set out to determine whether IL-1 beta rescues follicles from apoptosis and the possible involvement of NO. Preovulatory follicles o btained from PMSG-primed rats were cultured for 24 h in serum-free med ium with or without hormone treatments. After culture, follicular apop totic DNA fragmentation was analyzed by autoradiography of size-fracti onated DNA labeled at 3'-ends with [P-32]dideoxy-ATP. Follicular NO pr oduction was also determined by a colorimetric method. Treatment with IL-1 beta dose-dependently suppressed the spontaneous onset of apoptos is in cultured follicles, but stimulated NO production. In contrast, t he addition of IL-1 receptor antagonist eliminated both effects of IL- 1 beta, confirming receptor mediation. Follicles treated with sodium n itroprusside, a NO generator, or an analog of cGMP, the second messeng er for NO, also showed decreased follicle apoptosis. Moreover, the add ition of N-G-monomethyl-L-arginine, a NO synthase inhibitor, reversed both IL-1 beta stimulation of NO production and suppression of apoptos is, suggesting a mediatory role of NO in these IL-1 beta effects. Gona dotropins also prevent follicle apoptosis. Of interest, treatment with hCG stimulated NO production, and the hCG suppression of follicle apo ptosis and stimulation of NO production were partially blocked by cotr eatment with IL-1 receptor antagonist; indicating the mediation of end ogenous IL-1 beta. Treatment with IL-1 beta also stimulated a small in crease in the production of cAMP, estrogen, and progesterone. Taken to gether, these findings suggest that IL-1 beta is a survival factor for ovarian follicles, and its action is partially mediated via NO and cG MP generation, Moreover, part of the suppressive action of gonadotropi ns on follicle apoptosis is mediated by endogenously produced IL-1 bet a.