Acute Negative Feedback Effects of Ovarian Steroid Removal and Replacement in the Cyclic Female Hamster

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Abstract
Bilateral ovariectomy of hamsters [Mesocricetus auratus] on any day of the 4 day cycle caused a rapid decrease in serum estradiol and progesterone (Day 1 = day ovulation, Day 4 = proestrus). Serum prolactin was not affected by ovariectomy. Increases in serum LH [lutropin] and FSH [follitropin] were evident within 3-6 h. The proestrous surge of LH still occurred after ovariectomy, but was decreased in magnitude. The proestrous surge of FSH increased in magnitude when compared to controls. Replacement of 10 .mu.g estradiol or 100 .mu.g progesterone after ovariectomy on day 1 or 3 of the cycle revealed that estradiol was more effective in negative feedback regulation of gonadotropins than progesterone. The rapid changes in serum estradiol and LH following ovariectomy in the hamster are different from those reported for cyclic female rats. Apparently, there is little adrenal contribution to serum estradiol or progesterone or adrenal negative feedback regulation of gonadotropins in female hamsters.