The effect of hypothalamic luteinizing hormone releasing hormone (LH-RH) on plasma gonadotrophin levels in normal subjects

The release of gonadotrophin following the injection of synthetic LH‐RH (Hoechst) was studied in various physiological and experimental circumstances. In the male, 25 μg 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 μg of LH‐RH led to a clear‐cut release of FSH and a small release of LH 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 non‐sequential hormonal contraceptives blocked FSH and LH release normally produced by the injection of 50 μg of LH‐RH. There was no effect when a dose of 100 μg was injected. In post‐menopausal women, only LH rose following the administration of 25 μg of LH‐RH. After 5 days of treatment with 200 μg ethinyl oestradiol the same dose of LH‐RH led to simultaneous release of LH and of FSH. From the above studies it can be concluded that the secretory response of the gonadotrophins 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 gonadotrophins. Copyright © 1974, Wiley Blackwell. All rights reserved