Negative Feedback Effects of Ovarian Steroids in the Chronically Ovariectomized Hamster

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Abstract
In a series of experiments using ovariectomized hamsters, we have examined the serum gonadotropin levels during the transition period to 14 days after ovariectomy, serum concentrations throughout Day 14, negative feedback effects of estradiol and progesterone, and the effects of gonadotropin releasing hormone (GNRH) on Day 14 after ovariectomy. LH levels continue to increase during this transition period while FSH is at a maximum by Day 2. On Day 14 after ovariectomy, no statistical changes in LH or FSH are seen throughout the day; prolactin decreases significantly by midnight. Progesterone (100, 500 or 1000 μg s.c. in oil) is not as effective as estradiol (10, 50 or 100 μg s.c. in oil) or estradiol + progesterone in suppressing serum FSH and LH on Day 14 postovariectomy. Estradiol causes reductions in LH within 3 h. GNRH injections cause significant increases in LH and FSH in chronically ovariectomized hamsters. In a group of females ovariectomized and serially bled over a period of 28 weeks, serum LH continues to increase for 12 weeks while FSH and prolactin do not show significant changes.