Effect of an anti PMS serum on ovulation and estrogen secretion in the PMS treated hamster

Abstract

Hamsters injected s.c. on day 1 (metestrus) of the cycle with 0, 5, 15 30, or 60 IU pregnant mare serum (PMS) ovulated, respectively, 11.7, 15.2, 36.9, 52.0 and 62.8 ova. This number represents the combined contribution of a maximum of 20 developing follicles, growing under the influence of endogenous gonadotropins and 50 reserve follicles, maturing in response to PMS. A single i.p. injection of 25 μl of antiserum (As) to PMS on days 1-3 resulted in the ovulation of only 10-15 ova, which indicates that the continued presence of PMS is required for the maturation of the reserve follicles. When the As injection was deferred until the morning of day 3 all of the PMS treated groups showed a consistent 1 day increase in cycle length. At 1600 hr of day 3, control hamsters had estradiol (E2) levels of 69 pg/ml. Animals injected on day 1 with 30 IU PMS had 929 pg/ml of E2 but the normal cycle length of 4 days was still maintained. When As was given at 0900 hr of day 3 to the 30 IU PMS group, a drastic fall in E2 levels was observed 7 hr later (20.8 pg/ml). However, similar treatment of animals injected with 5 or 15 IU PMS dropped E2 levels to the range of the controls (73-80 pg/ml). When animals injected with 5 or 15 IU PMS were hypophysectomized on day 1 (which eliminates the developing follicles) As injection on day 3 lowered E2 values to 11-27 pg/ml. Based on these results it is suggested that with lower doses of PMS both developing and reserve follicles contribute to the estrogen pool. However, with 30-60 IU PMS the reserve follicles produce most of the E2 thus accounting for the very drastic effects of As on peripheral estrogen levels.