MEIOSIS-FACILITATING EFFECTS INVIVO OF ANTISERUM TO ESTRONE ON FOLLICULAR OOCYTES IN IMMATURE RATS TREATED WITH GONADOTROPINS

The effects of neutralization of endogenous estrogen with rabbit antiserum to estrone (antiestrone) on the resumption of meiosis of oocytes in small (<125 μm), intermediate (125-250 μm) and large (>250 μm) diameter follicles were investigated by a quantitative histological technique in immature rats treated with 5 IU pregnant mare's serum gonadotropin (PMS) alone or sequentially with 10 IU human chorionic gonadotropin (hCG). Effective neutralization of an hCG-induced rise of estradiol-17β with simultaneously administered anti-estrone was evidenced by an undetectable level of plasma estradiol-17β up to the time of autopsy. Treatment with PMS alone induced no appreciable change 74 hr later in the incidence of meiosis, while treatment with PMS and anti-estrone increased significantly the incidence of meiosis in intermediate and large follicles. Treatment with hCG in addition to PMS markedly increased the incidence of dividing ova in follicles 6 hr and 18 hr later. In animals given anti-estrone simultaneously with hCG, a significant increase in incidence of meiosis was noted only in intermediate follicles after 6 hr, whereas the incidence of meiosis increased significantly both in intermediate and large follicles after 18 hr. The increased incidence of meiosis in large follicles was interpreted as a false increase resulting from a reduction in the population of large follicles between 6 and 18 hr after hCG, due to the influence of anti-estrone. It is suggested that hCG-induced preovulatory estrogen has a localized inhibitory effect on the resumption of meiosis of oocytes predominantly in intermediate follicles counteracting the meiosis inducing action of hCG.