Biology of Reproduction, Vol 25, 530-535, Copyright © 1981 by Society for the Study of Reproduction

Factors Affecting the Postovulatory Surge of FSH in the Rabbit

¹ Department of Endocrinology, Medical College of Georgia, Augusta, Georgia 30912

Serum levels of LH and FSH were measured by RIA in rabbits before and after ovulation. Coitus led to two distinct surges of FSH; one before ovulation with a peak at 2 h postcoitum (p.c.) (6.4 ± 0.8 ng/ml) and a second 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 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 does fully restored ovulation (11.3 ± 1.0 corpora lutea/rabbit) as well as the postovulatory FSH surge (3.9 ± 0.2 ng/ml). These results demonstrate that 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.

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ACKNOWLEDGMENTS The authors wish to express appreciation to Mr. Robert Gerardot for his excellent technical assistance. We also wish to thank Kay Mills for typing the manuscript.