Endocrine aging in CBA mice: characterization of uterine cytosolic and nuclear sex steroid receptors.

We examined the evidence of alterations with age in sex steroid hormone/receptor interaction in the uteri of CBA mice. The mean affinity for estrogens and progesterone that we observed in uterine cytosols and nuclei of old (16-18 months) mice were no different than those observed in young (4-8 months) animals. Whereas the total number of unoccupied estrogenic receptor sites in old uteri did not differ significantly from that observed in uteri of young mice, aging was accompanied by a 3-fold and significant decrease in mean nuclear binding sites when standardized as mg of DNA (p less than 0.05). Contrary to estrogen receptors, aging uteri showed a 3-fold and significant decrease in the total number of uterine progesterone receptor concentration (p less than 0.05) which was manifested by a decrease of progesterone binding sites in both the cytosol and the nucleus. These results suggest that aging CBA mice present a profile of altered hormone-receptor interaction which is only partly dependent on ovarian steroids.