STUDIES ON INTERACTIONS BETWEEN THE OVARY AND PITUITARY FOLLICLE-STIMULATING HORMONE IN THE GOLDEN HAMSTER

Abstract

SUMMARY During the first 3 days of the oestrous cycle of the hamster, pituitary follicle-stimulating hormone (FSH) is relatively constant. However, a decrease in concentration occurred between days 3 and 4. The drop in pituitary FSH—which was not statistically significant—coincided with a period of follicular atresia. After unilateral ovariectomy on day 1, the remaining ovary ovulates twice the normal number of ova. After semi-spaying, pituitary FSH increased over control values on days 2 and 3 and then decreased sharply by day 4. This suggests that the release of FSH between days 3 and 4 prevents atresia and is therefore responsible for compensatory ovulation. Bilateral ovariectomy on day 1 resulted on days 2 and 3 in pituitary FSH concentrations comparable to those in the unilaterally ovariectomized group. However, pituitary FSH increased markedly on day 4 in the bilaterally ovariectomized hamster. Superovulation of approximately 70 eggs occurs after the administration of 60 i.u. pregnant mare serum (PMS) on day 1. A drastic decrease in pituitary FSH took place on days 3 and 4, indicating reduced synthesis of the hormone. The decrease in pituitary FSH between days 2 and 3 is due to ovarian stimulation by PMS inasmuch as the decrease did not occur in animals bilaterally ovariectomized and injected with PMS. The existence of a 'short feedback loop' for FSH is demonstrated by the finding that the increase in pituitary FSH between days 3 and 4 was much greater in bilaterally ovariectomized females than in castrated animals injected with PMS.