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-17 beta, estradiol-17 alpha, testosterone, cortisol, progesterone, or the nonsteroidal estrogen diethyl stilbestrol (all at 10 microgram/ml) in defined medium that contained either BSA or dextran. Estradiol-17 beta 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-17 beta medium, resumed meiotic maturation. Oocytes took up 3H-estradiol-17 beta 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-17 beta or progesterone, nor were the oocytes saturated even when cultured in 10(-6) M estradiol-17 beta. Autoradiography of sectioned oocytes after culture in 3H-estradiol-17 beta 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-17 beta may not act at the level of the oocyte nucleus.

A progesterone binding component in porcine ovarian follicular fluid

“…Rondell (1974) suggested that increased levels of steroids may regulate the synthesis of enzymes required in the ovulatory process. We have reported that the meiotic maturation of porcine oocytes is specifically influenced by oestradiol and progesterone in vitro (McGaughey, 1977;Richter & McGaughey, 1979). Finally, the follicular retention of progesterone may prevent its interference in the release of LH necessary for ovulation (Rothchild, 1965), to serve as a reservoir of substrate for further steroidogenesis, or even to act upon the oviduct after ovulation.…”

Influence of dbcAMP on the inhibitory effect of cumulus cell factor(s)

“…Cyclic AMP can stimulate aromatase activity in cultured granulosa cells. Oestrogen may be implicated in the observed inhibition of pig oocyte maturation (Richter and McGaughey, 1979;Racowsky and McGaughey, 1982). In the light of these data we cannot exclude the possibility that steroids are at least partly involved in the action of inhibitory factor(s) produced by porcine cumulus cells.…”

Effects of estradiol on in vitro maturation of buffalo and goat oocytes

“…Estradiol has been shown to increase IVM of bovine oocytes 12,13 but Gliedt and colleagues have reported that estradiol negatively regulates cumulus expansion and in vitro embryo production in bovine 14 . It has also been reported that estradiol reduces the maturation of mouse oocytes 15,16 and that in vitro maturation of pig oocytes has been inhibited by estradiol 17 . A high concentration of estradiol (100 µg/mL) has also inhibited oocyte maturation in boer goats 18 .…”