SERTOLI-CELL FUNCTION DECLINES EARLIER THAN LEYDIG-CELL FUNCTION IN AGING JAPANESE MEN

In order to evaluate the age-related changes in Leydig cell and Sertol i cell function, we measured serum levels of total testosterone (TT), free testosterone (FT), inhibin, LH and FSH in 116 healthy Japanese me n, aged 24-92 years. Serum TT remained constant up to the age of 80 ye ars and decreased thereafter. Serum FT declined linearly with aging an d was significantly lower in men in their forties than in younger men (24-39 years old). Serum inhibin levels also declined with aging, with serum concentrations significantly lower in men older than 40 and mar kedly lower in men over 80 years old. LH and FSH were elevated in men over 60 and 40 years old, respectively. We also examined relationships between gonadotropins and gonadal hormones in these men divided into three age groups, young (24-39 years old), middle aged (40-59 years ol d) and aged (60-92 years old) men. Although there was a significant in verse correlation between LH and TT or FT for the entire population, s ubset analysis demonstrated that this inverse correlation was confined to men over 60 years old. In fact, in young men, TT and FT were posit ively correlated with LH. Overall, there was also an inverse correlati on between FSH and inhibin. In subset analysis this relationship was p resent in both middle aged and aged meg. These findings suggest that i n Japanese men testicular endocrine functions decline after the fourth decade of life, and that Sertoli cell function declines earlier than Leydig cell function.