Decreased inhibin tone and increased activin A secretion characterize reproductive aging in women.

OBJECTIVE: We hypothesized that the increased FSH noted in older reproductive-aged women is due to both decreased inhibin and increased activin A secretion.
DESIGN: Comparative clinical study.
SETTING: An academic research center. PATIENT(S): Five cycling women, aged 43 to 47, were compared to five midreproductive women, aged 19 to 38. INTERVENTION(S): Specimens taken every 2 to 3 days were assayed for inhibin A and B and activin A. MAIN OUTCOME MEASURE(S): Integrated concentrations of inhibin A, inhibin B, and activin A in the follicular phase, luteal phase, and whole cycle. RESULT(S): Follicular inhibin B was reduced in older versus younger women (504 +/-82 versus 748+/-72 total pg). Luteal inhibin A was reduced in older versus younger women (668 +/-72 versus 1152+/-216 total pg). Activin A was elevated throughout the cycle of older versus younger women, without within-cycle fluctuations (21+/-2 versus 11+/-1 total ng). CONCLUSION(S): Lack of restraint by inhibin A and inhibin B contributes to the FSH rise associated with reproductive aging. This loss of restraint occurs in a tandem fashion, with inhibin B reduction before ovulation and inhibin A reduction after ovulation. Activin A may also play an endocrine role in maintaining elevated FSH in older reproductive-aged women.