THE GONADOTROPIN-SECRETION PATTERN IN NORMAL WOMEN OF ADVANCED REPRODUCTIVE AGE IN RELATION TO THE MONOTROPIC FSH RISE

OBJECTIVE: Women of advanced reproductive age are known to demonstrate subtle FSH elevations (monotropic FSH rise) while still retaining ovu latory function. The purpose of this study was to investigate the hypo thesis that the physiologic basis for the monotropic FSH rise is an al teration in the secretion pattern of the GnRH pulse generator. METHODS : The subjects were 11 normal women age 40-45 years who underwent 24 h ours of frequent blood sampling in the follicular (EF) and/or midlutea l (ML) phases of spontaneous menstrual cycles. The controls were 11 no rmal women age 20-25 years. The respective gonadotropin secretion patt erns were analyzed for LH pulse frequency, mean LH and FSH levels, and LH pulse amplitude. RESULTS: There were no differences between the gr oups for estradiol (E2) and progesterone when the respective cycle pha ses were compared. The 24-hour mean FSH level was significantly increa sed in the older women in both the EF and ML phases. There were no dif ferences between the groups in either cycle phase for LH pulse frequen cy, LH pulse amplitude, and mean LH levels. CONCLUSION: The results le nd no support to the hypothesis that a slowing or other alteration of the GnRH pulse generator is the basis for the monotropic FSH rise in o lder ovulatory women. Other possibilities include the dynamics of E2 s ecretion or changes in FSH-modulating peptides (ie, inhibin) in these women.