Gonadotropin releasing hormone agonists stimulate meiotic maturation of follicle-enclosed rat oocytes in vitro.

Although the principal function of gonadotropin releasing hormone (GnRH) is to stimulate the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH), there is evidence that agonistic analogues of GnRH directly inhibit steroidogenesis in the testis and ovary. On the other hand, Clark et al. have demonstrated that GnRH and two agonists have a marked stimulatory effect on prostaglandin synthesis by granulosa cells isolated from immature rats treated with pregnant mare's serum gonadotropin (PMSG). Stimulation by these compounds was distinct from that by LH in that no changes in cyclic AMP production were detected. Thus it seems important to investigate the effect of these peptides on other aspects of ovarian function, for example oocyte maturation. Mammalian oocytes are arrested in the dictyate stage of the first meiotic prophase, and meiosis (oocyte maturation) normally resumes in preovulatory follicles as a consequence of the surge of LH and FSH. This maturation can also be initiated in vitro by the addition of gonadotropins to isolated preovulatory follicles, and is accompanied by an increase in the production of lactate. We now report that GnRH and two potent agonists stimulate meiosis in vitro in follicle-enclosed oocytes in a dose-dependent and specific manner, and also cause an increase of lactate accumulation during incubation.