Increased Suppression of Luteinizing Hormone Secretion by Chronic and Acute Estradiol Administration in Underfed Adult Female Rats1

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Abstract
These studies attempted to educidate the relationship between estradiol and luteinizing hormone (LH) secretion in chronically underfed (R) adult female rats. Examination of the response to ovariectomy revealed a significant delay in the onset of the postcastration increase in LH secretion in R females compared to control (C) animals. Chronic estrogen treatment in the form of Silastic capsules containing varying doses of 17.beta.-estradiol (E2) prevented the postcastration rise of LH secretion in R animals at all doses of E2. The response of C females was dose-dependent, ranging from complete suppression at 10 .mu.g E2/animal to an absence of inhibition at 2.4 .mu.g E2/animal. The acute response of LH secretion to E2 administration in the ovariectomized female indicated an increased suppression of plasma LH at 6 and 24 h after a single s.c. injection of estradiol benzoate (EB) in R compared to C animals. There was no difference between R and C rats in the ratio of free to protein-bound estradiol in the serum. The results of these studies suggest that the negative feedback efficacy of estrogen on LH secretion is significantly enhanced by reduced food intake in adult female rats and may be responsible for the loss of reproductive cyclicity in these animals.

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