Effect of steroids on oocyte maturation and atresia in mouse ovarian fragments in vitro.

Ovaries from pubertal mice were dissected into fragments containing 1-4 antral follicles which were cultured on the surface of a chemically defined, modified Eagle's Minimum Essential Medium (MEM). After 17-20 h oocytes were released from the cultured follicles and their meiotic status recorded. In the presence and absence of exogenous gonadotrophins, oocytess in these cultures behaved meiotically as expected if they had been studied in vivo. Medium containing progesterone (10 microM), testosterone (100 microM), or androstenedione (100 microM) increased the incidence of oocytes remaining meiotically inactive compared to follicles cultured in steroid-free medium. Lower concentrations of the above steroids or pregnenolone (1-100 microM) did not affect the meiotic status of cultured follicle-enclosed oocytes. Most (61%) of the dictyate oocytes released from steroid-treated follicles resumed and/or completed the first meiotic division when cultured further in steroid-free medium. Progesterone (100 microM) caused atresia of oocytes and follicle cells which increased as the period of follicular exposure to progesterone was increased.