Estrogens and cytosolic estrogen receptors in aged male rats

To determine whether estrogens may play a role in the decline in Leydig cell function in aged rats, plasma levels of testosterone, estradiol, and estrone; intratesticular concentrations of testosterone and estradiol; as well as cytosolic estrogen receptors were studied. Plasma and intratesticular testosterone levels were reduced in aged Sprague-Dawley rats, but circulating levels of estrone and estradiol, as well as intratesticular estradiol concentrations, were similar in aged and young-adult animals. Furthermore, in both testicular and kidney cytosol, the dissociation constants for estradiol and the concentrations of estradiol binding sites remained unchanged during aging. These data suggest that estrogens are unlikely to be important mediators of the reduced Leydig cell function in old rats.