Decrease in rat uterine estrogen receptors during aging: physio- and immunochemical properties.

Rat uterine estrogen receptors decrease in concentration by about 45% between maturity (6-12 months) and senescence (22-24 months). No change in binding affinity occurs over this period. No age differences were observed in the thermostability, hormone-induced stability, or specificity of binding for various steroids. Most importantly, immunochemical titration of receptors with specific antiserum revealed that the ratio of immunoreactive to functional receptor is not changed with age. Thus, the apparent loss of rat uterine estrogen receptors during aging does not seem to be due to the appearance of a nonfunctional receptor population detectable by presently available immunoreagents.