THE EFFECT OF HYPOTHALAMIC LUTEINIZING HORMONE RELEASING HORMONE (LH-RH) ON PLASMA GONADOTROPHIN LEVELS IN NORMAL SUBJECTS

The release of gonadotropin following the injection of synthetic LH- RH was studied in various physiological and experimental circumstances. In the male 25 mcg of LH-RH led to simultaneous release of FSH and LH prior to and during puberty. In adults on the other hand the same dose led only to an increase in LH while FSH levels remained unchanged. At higher doses there was FSH release and an increase in LH proportional to the amount of LH-RH injected. When FSH was released the increase was clearly less than that of LH and often occurred considerably later. In the female 25 mcg of LH-RH led to a clear-cut considerably later. In the female 25 mcg of prior to puberty. After the onset of puberty the degree of response was inverted; the increase in LH was greater than that of FSH. In normally menstruating women the FSH and LH response was greater during the luteal phase than during the preovulatory phase. Treatment with nonsequential hormonal contraceptives blocked FSH and LH release normally produced by the injection of 50 mcg of LH-RH. There was no effect when a dose of 100 mcg was injected. In postmenopausal women only LH rose following the administration of 25 mcg of LH-RH. After 5 days of treatment with 200 mcg ethinly estradiol the same dose of LH-RH led to simultaneous release of LH and of FSH. It is concluded that the secretory response of the gonadotropins to LH-RH is influenced by the endocrine equilibrium and more particularly by the interaction of the gonadal steroids which can alter the synthesis and/or the release of the pituitary gonadotropins.