Specificity of inhibition by steroids of porcine oocyte maturation in vitro

Abstract

In order to examine the influence of several steroids on the process of oocyte maturation, denuded (adherent cumulus granulosa cells mechanically removed) and intact (cumulus granulosa cells left attached) porcine oocytes were cultured in the presence or absence of estradiol‐17β, estradiol‐17α, testosterone, cortisol, progesterone, or the nonsteroidal estrogen diethyl stilbestrol (all at 10 μg/ml) in defined medium that contained either BSA or dextran. Estradiol‐17β was the only steroid to exert a significant inhibitory effect on the maturation of denuded oocytes, and did so only in BSA supplemented medium. The inhibition was reversible in that oocytes, cultured in steroid‐free medium after initial culture in estradiol‐17β medium, resumed meiotic maturation. Oocytes took up ³H‐estradiol‐17β in both media, although less radiolabel entered oocytes in BSA supplemented medium. The majority of label in the oocytes, when cultured with either medium, was not displaced by excess radioinert estradiol‐17β or progesterone, nor were the oocytes saturated even when cultured in 10⁻⁶ M estradiol‐17β. Autoradiography of sectioned oocytes after culture in ³H‐estradiol‐17β has shown that there was no selective accumulation of silver grains over the germinal vesicle as was the case with granulosa cell nuclei. This observation suggests that estradiol‐17β may not act at the level of the oocyte nucleus.