Factors Affecting the Postovulatory Surge of FSH in the Rabbit1

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Abstract
Serum levels of luteinizing hormone and FSH were measured by radioimmunoassay in rabbits before and after ovulation. Coitus led to 2 distinct surges of FSH; before ovulation with a peak at .apprx. 2 h postcoitum (p.c.) (6.4 .+-. 0.8 ng/ml) and a 2nd peak after ovulation with maximal values at 24 h p.c. (6.0 .+-. 1.6 ng/ml). The ovulation rate in mated animals was 11.7 .+-. 0.7 corpora lutea/rabbit. Injection of a single ovulatory dose of hCG [human chorionic gonadotropin] caused large follicles to ovulate (12.5 .+-. 1.3 corpora lutea/rabbit) and led to the postovulatory FSH peak at 24 h after mating (3.7 .+-. 0.5 ng/ml). Pentobarbital blocked all gonadotropin release and ovulation when given immediately before mating (1.5 .+-. 0.5 ng/ml at 24 h p.c.) but not when given immediately after mating (4.5 .+-. 1.0 ng FSH/ml at 24 h p.c., 5.7 .+-. 2.0 corpora lutea/rabbit). Injection of hCG into pentobarbital-blocked rabbits does fully restored ovulation (11.3 .+-. 1.0 corpora lutea/rabbit) as well as the postovulatory FSH surge (3.9 .+-. 0.2 ng/ml). Evidently the postovulatory FSH surge is observed only in animals which ovulate. The postovulatory FSH surge appears to be dependent on the presence of the ovary or on ovulation. Blockage of the preovulatory gonadotropin surge prevents ovulation and may, thereby, prevent the postovulatory release of FSH.