Age, sex and gonadal influences on oestrogen receptor content in the rat liver.

Liver cytosol oestrogen receptor (OR) content of intact and gonadectomized male and female rats of defined age (1-18 months) was measured by the controlled pore glass bead assay. The OR content of animals of both sexes aged 3 weeks was low to insignificant (0.12 +/- 0.04 (S.E.M.) pmol/g wet wt liver). In the intact animal, liver OR reached maximum levels at an earlier age in the male (1.35 +/- 0.12 pmol/g at 28-32 weeks) than in the female (4.89 +/- 0.17 pmol/g at 44-52 weeks). In the mature female the OR is thus maintained at a level threefold greater than in males of comparable age. Levels of OR in the gonadectomized male tended to be higher, at all ages, than those in the intact male but this difference was not statistically significant. Ovariectomy was associated with a decreased OR content in rats aged less than 6 months and an increase in the older rats, but these effects (of ovariectomy) were not statistically significant. In the females, regression analysis of pooled data, combining all ages, indicated a significant positive correlation between OR and liver wet weight, independent of gonadal status; no such relationship was found with the males. The results indicate that factors influencing liver cytosol OR content include maturity, age and sex whereas the gonads have little obvious effect. These findings lend further support to the concept that sex differences exist in the liver.