| Abstract: | Because of prominent age-related changes in the responses to stress and in steroid metabolism and excretion, the effect of age on fractionated liver glucocorticoid-binding proteins was studied in C57BL/6J male mice. When cytosol, pre-labeled with [3H]corticosterone, was chromatographed on Sephadex G-100, 4 peaks were obtained. Peak 1 (excluded), peak 2 (corresponding to plasma transcortin), and peak 3 corresponding to glucocorticoid receptors isolated from nuclei) showed no significant age differences. This finding is consistent with reports that glucocorticoid-mediated induction of hepatic tyrosine aminotransferase is not altered by aging in rodents. However, there was a striking age-related decrease (80%) in peak 4 (apparent MW 29,000). Competition studies imply that peak 4 binds aldosterone, testosterone, progesterone, and corticosterone (delta4-3-keto steroids), but not estradiol or dt a plasma component. Although the function of peak 4 is not identified, the pattern of highest competition with delta4-3-keto steroids suggests that it is a steroid ring "A" reductase. |
