Decreased serum inhibin levels in normal elderly men: evidence for a decline in Sertoli cell function with aging

Compared to young men, normal elderly men have decreased sperm production despite elevated serum gonadotropin levels. To determine whether the seminiferous tubule defect in elderly men includes decreased Sertoli cell function, we measured serum immunoreactive inhibin concentrations in young and elderly men before and after clomiphene citrate (CC) administration. Thirty-eight healthy men, 19 young (aged 22-35 yr) and 19 elderly (aged 65-85 yr), were studied before CC administration. The mean baseline serum inhibin level was significantly lower (P less than 0.001) in the elderly men than in the young men [416 +/- 22 (+/- SE) vs. 588 +/- 30 U/L], while serum immunoreactive FSH and LH levels were higher in the older men, and bioactive FSH levels were similar in the two age groups. Eleven young men and 13 elderly men were studied after 1 week of CC administration. The mean serum inhibin level increased by 71%, from 566 +/- 36 to 970 +/- 82 U/L, in the young men, but it increased by only 24%, from 421 +/- 26 to 520 +/- 38 U/L, in the elderly men. Serum immunoreactive LH and bioactive and immunoreactive FSH concentrations increased to similar levels in both groups after CC administration. We conclude that the seminiferous tubule defect of elderly men includes decreased Sertoli cell function.