Postcoital Patterns of Secretion of Pituitary Gonadotropin and Ovarian Progestin in the Rabbit

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Abstract
Progestin (20αhydroxy-pregn-4-en-3-one) secretion by the rabbit ovary increases rapidly postcoitally, remains elevated for about 8 hr, and drops to nondetectable levels by the time of follicular rupture. Circulating endogenous or exogenous gonadotropin can be assessed by the progestin responses elicited by the blood when infused intraarterially through ovaries of recipient rabbits in vivo. Following mating the gonadotropic potency of peripheral blood rises immediately and a high level is sustained for about 6 hr before dropping to nonmeasurable values. These high and low levels of circulating gonadotropin thus correspond to the pattern of progestin release from the donor rabbit's ovaries between coitus and ovulation. When exogenous luteinizing hormone is administered intravenously to a donor rabbit, one half the original potency still remains in the circulation after 4 hr. From these and related data it is calculated that the postcoital release of pituitary gonadotropin continues for about 2 hr and that the tropin remains in the circulation as a potential ovarian stimulator for an additional 4 hr. (Endocrinology75: 957, 1964)