The effect of ovarian steroid feedback upon radioimmunoreactive luteinizing hormone releasing hormone in the hypothalamus

Abstract

A radioimmunoassay (RIA) method for luteinizing hormone (LH) releasing hormone (RH) utilizing rabbit antiserum against synthetic (Glu1)-LH-RH coupled with human serum albumin at the N-terminus, is described. This assay system for LH-RH also cross-reacted with several LH-RH analogues or fragments, but not with pituitary trophic hormones. The assay was performed on the hypothalamic extracts of adult ovariectomized rats and female immature rats which had been treated with estradiol. The FSH and LH levels in the pituitary gland and serum of the same animals were determined by RIA. The radioimmunoreactive LH-RH content of the stalk median eminence markedly increased seven days after ovariectomy. The serum levels and the pituitary contents of FSH and LH of the same rats were also significantly augmented. In immature rats, the hypothalamic content of LH-RH, as measured by RIA, was significantly increased one hour after the injection of estradiol. The FSH and LH levels in the pituitary showed a significant rise after 7 hours.

PIP: To determine hypothalamic luteinizing hormone-releasing hormone (LH-RH) content and possible steroid feedback effects from the ovary, female rats were ovariectomized and killed 7 days later; another group was injected sc with 50 mcg estradiol benzoate and killed 1 hour or 7 hours later. The LH-RH content of the stalk median eminence of the hypothalamus as well as the levels of follicle stimulating hormone (FSH) and LH in the pituitary were measured by radioimmunoassay. In the castrated group there were significant increases in the LH-RH content of the median eminence (p less than .001) and in the LH and FSH levels in the serum and pituitary glands. Rats given the estradiol injection showed a significant increase in hypothalamic LH-RH 1 hour postinjection and in pituitary LH 7 hours postinjection.