The Effect of Ovarian Steroid Feedback upon Radioimmunoreactive Luteinizing Hormone Releasing Hormone in the Hypothalamus

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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 hypothalamic extracts of adult ovariectomized rats and female immature rats which had been treated with estradiol. The FSH (follicle stimulating hormone) and LH levels in the pituitary gland and serum of the same animals were determined by radioimmunoassay. The immunoreactive LH-RH content of the stalk median eminence markedly increased 7 days after ovariectomy. The serum levels and the pituitary contents of FSH and LH of the same rats were also augmented. In immature rats, the hypothalamic content of LH-RH, as measured by RIA, was significantly increased 1 h after injection of estradiol. The FSH and LH levels in the pituitary showed a significant rise after 7 h.