Effect of an Anti-PMS Serum on Ovulation and Estrogen Secretion in the PMS-Treated Hamster

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Abstract
Hamsters injected SC 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 ip 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 h 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 h 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.

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