Post-menopausal and chronological age have divergent effects on pituitary and hypothalamic function in episodic gonadotrophin secretion.

OBJECTIVE Ageing is known to reduce gonadotrophin secretion in post-menopausal women. To what extent the hypothalamus and pituitary are involved in this process is not clear. The aim of this study was to compare 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 responsible for the observed changes. DESIGN Blood samples were obtained from post-menopausal women every 10 minutes for 6 hours. Subsequently, 100 μg 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 Plasma 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 pulses, the mean LH and FSH concentrations during the 6-hour study period and the maximal LH and FSH increments following GnRH. RESULTS Mean LH and FSH levels did not change with chronological age but the LH pulse frequency declined significantly and the response to GnRH increased. Mean LH levels declined with post- menopausal age without alteration in LH pulse frequency but with a significant decrease in pituitary LH response to GnRH. FSH levels remained unchanged. CONCLUSIONS Post-menopausal ageing seems to have a major suppressive effect on pituitary gonadotroph function, while chronological ageing mainly affects the hypothalamic regulation of LH secretion.