Biology of Reproduction, Vol 24, 820-830, Copyright © 1981 by Society for the Study of Reproduction

Effects of Estradiol and Progesterone on Plasma Gonadotropins, Prolactin, and LHRH in Specific Brain Areas of Ovariectomized Rats

¹ Department of Physiology, School of Medicine, University of Maryland, Baltimore, Maryland 21201

We examined the effects of physiological concentrations of estradiol (E₂) and progesterone (P) on plasma LH, FSH, and prolactin (PRL) and on LHRH concentrations in several microdissected brain regions in ovariectomized (OVX) rats. One week after ovariectomy (Day 0), rats received Silastic capsules containing only sesame oil or 37.5, 75.0 or 150 µg E₂/ml of oil s.c. The E₂ capsules produced plasma estrogen concentrations of 7.0, 9.6, or 15.4 pg/ml, respectively, on Day 2 whereas oil-treated controls had 5.4 pg/ml of E₂ in plasma. All three E₂ -treated groups of rats had LH surges of comparable magnitude during the afternoon of Day 2. Two Silastic capsules of P (50 mg/ml) were implanted at 0900 h on Day 2 into E₂ -treated rats. In animals in which E₂ levels were 7.0 or 9.6 pg/ml, P only moderately amplified the LH surges. However, when plasma E₂ concentrations reached 15 pg/ml, P treatment evoked a massive release of LH and advanced the time of release by 1 h. In contrast, the stress of inserting oil capsules into ether-anesthetized E₂-treated rats at 0900 h on Day 2 had no effect on afternoon LH surges in these animals. FSH surges occurred only in rats receiving both E₂ and P. PRL surges were induced using the highest concentrations of E₂ and were advanced in time by P. When the highest dose of E₂ was used, LHRH concentrations in the median eminence (ME) increased prior to and decreased during the E₂ P-induced surge. These changes were not paralleled by any changes in the other anterior brain regions we examined (suprachiasmatic preoptic nucleus, suprachiasmatic nucleus, medial preoptic nucleus, anterior hypothalamic nucleus, and retrochiasmatic area). No changes in LHRH concentrations were observed under any other steroid treatment regimen. Higher plasma E₂ concentrations induced by the 150 µg/ml E₂ capsule were correlated with higher LHRH concentraions in the median eminence concomitant with a parallel trend in some of the anterior brain areas: MPN (P<0.06), SPN (P<0.06), and RCA (P<0.03).

Note:
ACKNOWLEDGMENTS The authors gratefully acknowledge the gifts of RIA material (LH, FSH, PRL) made by Dr. A. F. Parlow, the NIAMDD, Dr. T. Nett (anti-LHRH), Dr. G. D. Niswender (anti-ovine LH; anti-P), Dr. G. Collins (anti-E₂) and Dr. L. Reichert (ovine LH). We thank Ms. Patricia Capogrossi, Viktoria Reck-Malleczewen, and Ruth Caldwell for their excellent technical assistance.

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