POSTMENOPAUSAL AND CHRONOLOGICAL AGE HAVE DIVERGENT EFFECTS ON PITUITARY AND HYPOTHALAMIC FUNCTION IN EPISODIC GONADOTROPIN-SECRETION

OBJECTIVE Ageing is known to reduce gonadotrophin secretion in post-me nopausal women. To what extent the hypothalamus and pituitary are invo lved in this process is not clear. The aim of this study was to compar e pulse characteristics of FSH and LH in relation to chronological and post-menopausal age. Based on the gonadotrophin response to GnRH, we assessed the extent to which pituitary and/or hypothalamic ageing is r esponsible for the observed changes. DESIGN Blood samples were obtaine d from postmenopausal women every 10 minutes for 6 hours. Subsequently , 100 mu g GnRH was administered intravenously and blood samples taken after 30, 60 and 90 minutes. PATIENTS Twenty healthy women aged 47-72 years and between 1 and 30 years after the menopause. MEASUREMENTS Pl asma LH and FSH were measured by immunoradiometric assay. Pulses were identified by a computerized pulse detection program. End points were the mean number and amplitude of purses, the mean LH and FSH concentra tions during the 6-hour study period and the maximal LH and FSH increm ents following GnRH. RESULTS Mean LH and FSH levels did not change wit h chronological age but the LH pulse frequency declined significantly and the response to GnRH increased. Mean LH levels declined with postm enopausal age without alteration in LH pulse frequency but with a sign ificant decrease in pituitary LH response to GnRH. FSH levels remained unchanged. CONCLUSIONS Post-menopausal ageing seems to have a major s uppressive effect on pituitary gonadotroph function, while chronologic al ageing mainly affects the hypothalamic regulation of LH secretion.