IN VITRO INDUCTION OF PHYSIOLOGICAL MATURATION IN RANA PIPIENS OOCYTES REMOVED FROM THEIR OVARIAN FOLLICLES

Full-grown oocytes dissected from their ovarian follicles can be induced to undergo physiological maturation by exposure, in vitro, to the steroid hormones progesterone and deoxycorticosterone or to homoplastic pituitary suspensions. Evidence for the occurrence of physiological maturation includes (1) a positive response to an activation stimulus and (2) the ability to undergo cleavage and subsequent development. While all the hormones tested are capable of inducing maturation, the steroids are most effective. Exposure of afolliculate oocytes to progesterone (1 μg/ml) for 1 hour is routinely successful in inducing maturation in 100% of the cases at virtually any time of the year. The effectiveness of pituitary preparations did not reach 100%, varied considerably, and exhibited seasonal dependence. These results support the hypothesis that steroids act directly on the oocyte to induce maturation whereas pituitary hormones act through the mediation of follicular tissue. © 1968.