Amounts of Interstitial Cell-Stimulating Hormone and Follicle-Stimulating Hormone Required for Follicular Development, Uterine Growth and Ovulation in the Hypophysectomized Rat1

Abstract

Female rats of the Sprague- Dawley strain were hypophysectomized at 28 days of age; 7 days later, subcutaneous injections of ovine ICSH and/or ovine FSH were initiated. Injected alone, neither gonadotropin stimulated the release of sufficient estrogen to cause uterine development. As little as 0.05 μg of ICSH injected together with 3 μg of FSH for a period of 3 days effected small increases, and 0.5 μg in combination with the same dosage of FSH substantial increases in the uterine weights. A daily dose of 1 μg of FSH neither promoted follicular development nor stimulated an increase in the weights of the ovaries; this dose level likewise was ineffective in stimulating estrogen secretion, even when combined with as much as 20 μg of ICSH. A dose of 3 μg of FSH injected together with 1 pg of ICSH once daily for a period of 3 days tripled the weights of the ovaries; developing follicles contained large antra and many showed evidence of luteinization. The same combination of FSH and ICSH injected once daily at 24-hr intervals, followed 8 hr after the third injection by 20 μg of ICSH or 20 μg of FSH, induced ovulation in 100 % of the hypophysectomized rats. In summary, ICSH was essential together with FSH for estrogen secretion and follicular growth in the rat, but not for ovulation; no additional gonadotropin was required for corpus luteum formation in animals in which ovulation had been effected with ICSH. (Endocrinology79: 991, 1966)