Growth hormone induces in vitro maturation of follicle- and cumulus-enclosed rat oocytes.

The aim of this study was to assess the possible role of growth hormone (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 of GH to the cultures significantly accelerated maturation in both follicle- and cumulus-enclosed oocytes while no effect was seen on denuded oocytes maturation. Also, GH accelerated meiotic maturation in follicle-enclosed oocytes from immature untreated rats. The GH action was not mediated by lactogenic receptors since prolactin (Prl) did not affect the maturation process while it was mediated by insulin growth factor-I (IGF-I) as suggested by the block of GH action observed in the presence of antibodies anti-IGF-I. Finally, no GH effect was found when dbcAMP was added to the cultures. Our results demonstrate that GH is capable 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 relevance of GH in the reproductive biology.