Estrogen modulation of gonadotropin secretion in the underfed female laboratory rat
A 50% reduction in food intake results in the cessation of regular estrous cycles in the female rat. These studies examine the relationship between estradiol (E2) and gonadotropin secretion in the acyclic underfed female rat. The first experiments test the negative feedback response of luteinizing hormone (LH) to E2 in ovariectomized underfed (R) females. Subcutaneous injection of estradiol benzoate (EB) resulted in increased suppression of plasma LH levels at 6 and 24 hours in R compared to ad libitum fed (C) animals. Subcutaneously implanted silastic capsules containing a range of estrogen doses prevented the postcastration rise in LH secretion in the R animal for at least 12 days; the response of C females was dose dependent. No statistical difference in the clearance of estradiol from the circulation of C or R females was observed following intra-arterial injection of EB. There was no difference between C and R females in the ratio of free to protein-bound estradiol, as determined by ultrafiltration. Additional experiments examined the positive feedback response of gonadotropins to E2 in underfed females. Silastic capsules containing 100 $\mu$g E2 were implanted subcutaneously at ovariectomy. Capsules of this size produced daily LH and follicle-stimulating hormone (FSH) surges in C females. Initially, underfed females were much more responsive than were C animals; however, LH surges after day 2 were greatly attenuated or absent, possibly as a result of reduced pituitary stores of LH. FSH surges were greater in R than in C animals on days 2-6, and comparable on day 8, reflecting similar total pituitary FSH content. In conclusion, these results demonstrate an increased sensitivity to estrogen inhibition rather than an increased availability of estrogen is responsible for the enhanced suppression of LH by estradiol in the underfed female rat. Underfeeding also increases the efficacy of estrogen stimulation of gonadotropin secretion. This change in estrogen modulation must be, at least in part, responsible for the loss of cyclicity associated with undernutrition.
Sherrie A Sprangers,
"Estrogen modulation of gonadotropin secretion in the underfed female laboratory rat"
(January 1, 1987).
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