Reproductive failure in aged CBF1 male mice: interrelationships between pituitary gonadotropic hormones, testicular...

Circulating pituitary gonadotropins and testicular function were examined in aged CBF1 male mice using two experimental designs: a) a longitudinal analysis of 2 to 30-month-old males, and b) a direct comparison of weight-matched, sexually-active vs. sexually-inactive 24-month-old males, all of whom were relatively robust. Measurements included serum concentrations of testosterone, follicle stimulating hormone, and luteinizing hormone, gonadotropic responsiveness to castration, success in a 4-day mating test, testicular sperm content, and reproductive organ weights. The longitudinal analysis showed progressive losses in mating success and sperm production between 18 and 30 months, changes which were correlated with decreased levels of serum LH and testosterone but not with FSH. The direct comparison of robust, sexually-active vs.-inactive males provided a better design for identifying reproductive-specific effects of aging, as opposed to debilitative changes that are general to several supporting systems. Such comparisons in 24-month-old CBF1 males suggest the existence of a subpopulation of mice in which reproductive failure is specifically correlated with a loss in the episodic release of LH.