Estrogen Receptor in Liver of Male and Female Rats: Endocrine Regulation and Molecular Properties1

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Abstract
Estrogen receptors from livers of adult male and female rats were compared. Hepatic cytosol estrogen receptors from both sexes were similar using the criteria of percent of saturation with ammonium sulfate required for precipitation, and isoelectric point (pI) of the receptor. The estrogen receptor from male or female rat liver cytosol was maximally precipitated with ammonium sulfate at 30% of saturation (30% AS ppt). As previously described, demonstration of the estrogen receptor in liver cytosol of male rats required this partial purification step because of the presence of an additional sex hormone binder with unusual properties. The pI of the liver cytosol receptor from females was 6.9. After 30% AS ppt, the p1 of the cytosol receptor from male or female rat livers was 4.7. Liver estrogen receptors from male or female rats had similar affinity (Kd = 1 x 10-10 M), capacity (2 fmoles/mg liver) (confirming previous results) and pattern of binding specificity for active estrogens. The liver cytosol estrogen receptors in both female (confirming previous reports) and male rats were reduced to 10% of control values following hypophysectomy (Hx); the Kd was unaffected. Receptor levels in female rat livers were not substantially restored following treatment with prolactin or growth hormone. Treatment of intact female rats with bromocriptine (a blocker of prolactin secretion) did not change the hepatic cytosol estrogen receptor level. The pituitary factor required for receptor maintenance remains to be elucidated. After gonadectomy (Gx), the liver cytosol from males or females was increased to 150% of control values; the Kd remained unchanged. A gonadal factor appears to regulate receptor levels negatively in the intact animal. The recently described, male-specific, nonreceptor [3H]-E2 binding sites in liver cytosol were reduced to 10% of control values by Hx and to 30% of control values by Gx. The estrogen receptors found in the livers of male and female rats were similar on the basis of physical properties, binding properties for [3H]-E2 and endocrine regulation.