VARIATION IN LH AND FSH RESPONSE TO LH‐RELEASING HORMONE DURING THE MENSTRUAL CYCLE

Abstract

Summary Synthetic luteinizing hormone‐releasing hormone (LRH) was injected intravenously in a dose of 100 μg. to test the capacity of the pituitary to respond to LRH with a release of luteinizing hormone (LH) and follicle‐stimulating hormone (FSH) in 16 healthy regularly menstruating women. A total of 28 LRH tests were performed during different stages of the menstrual cycle. Venous blood was obtained before and at frequent intervals during the first two hours after the LRH injection and assayed for LH, FSH and in five tests also for thyrotrophic (TSH) and growth hormone (GH). No consistent change of TSH or GH was observed after LRH. In all the 28 LRH tests there was a significant increase of LH and in tests also of FSH. The mean LH and FSH increase was 292 and 40 per cent, respectively. The maximum response was usually observed after 30 to 45 minutes. There was a pronounced variation in the response to LRH in the course of the menstrual cycle. During the late follicular phase the average LH response was 4‐ to 6‐fold that obtained in the early and mid‐follicular phase. An increased pituitary responsiveness was also found in the luteal phase. It was suggested that this variation in the response to LRH is due to the changes of the ovarian secretion of oestrogens during the menstrual cycle. In one amenorrhoeic woman exogenous oestrogen was found to enhance the LH response to LRH.