17β-Estradiol treatment increases the levels of estrogen receptor and its mRNA in male rat liver

Abstract

This study examined estrogen receptor dynamics in the livers of male obses rats ( SHHF Mcc-cp ) treated for two weeks with a continuous, low dose of 17β-estradiol compared with untreated controls. An increased binding capacity for tritiated 17β-estradiol in the cytosol, consistent with binding to the estrogen receptor, was demonstrated in treated males relative to control males ( P < 0.01). These observations were confirmed using curve-peeling techniques with saturation analysis, ammonium sulfate precipitation/fractionation of cytosol protein, and chromatographic techniques to isolate the high-affinity binding from other interfering factors. Increased hepatic nuclear estrogen receptor levels in treated males (112.3 ± 8.3 fmol/g liver) compared with controls (64.1 ± 6.8 fmol/g liver) suggested that the liver was under estrogenic influences. This interpretation was supported by an increase in serum triglyceride levels, reflecting increased very low density lipoprotein secretion by the liver. Reductions in testosterone levels and in the weights of seminal vesicles and the testes in treated males indicated detrimental effects on reproduction. An interpretation of increased synthesis of estrogen receptor with 17β-estradiol treatment was supported by the observation of an increase in the mRNA for estrogen receptor. Taken together, these observations indicate that continuous, low-dose 17β-estradiol treatment induces estrogenic action in the livers of male rats and also increases hepatic estrogen receptor, probably indirectly, via an increase in its mRNA.