GROWTH-HORMONE INDUCES IN-VITRO MATURATION OF FOLLICLE-ENCLOSED AND CUMULUS-ENCLOSED RAT OOCYTES

The aim of this study was to assess the possible role of growth hormon e (GH) on rat oocyte maturation. This effect was analyzed in follicle- enclosed, cumulus-enclosed and denuded oocytes obtained from immature pregnant mare's serum gonadotropin (PMSG)-treated rats. The addition o f GH to the cultures significantly accelerated maturation in both foll icle- and cumulus-enclosed oocytes while no effect was seen on denuded oocytes maturation. Also, GH accelerated meiotic maturation in follic le-enclosed oocytes from immature untreated rats. The GH action was no t mediated by lactogenic receptors since prolactin (Prl) did not affec t the maturation process while it was mediated by insulin growth facto r-I (IGF-I) as suggested by the block of GH action observed in the pre sence of antibodies anti-IGF-I. Finally, no GH effect was found when d bcAMP was added to the cultures. Our results demonstrate that GH is ca pable of inducing maturation in oocytes from both primed and unprimed rats. Since the presence of physiological levels of GH in the ovary is now well established, the present data strongly suggest a potential r elevance of GH in the reproductive biology.