Hepatic nuclear estrogen receptor concentrations in the rat—influence of age, sex, gestation, lactation and estrous cycle

Abstract

Nuclear estrogen receptor concentrations in rat liver were determined by exchange assay. The concentration of estrogen receptors in nuclei from vehicle-treated male and female rats show agedependent, but not sex-dependent variations in the course of life. Levels are highest during the perinatal period (~ 1500 binding sites/nucleus), whereafter they decrease towards the onset of puberty (~ 300 binding sites/nucleus) before rising again to reach the postpuberal maximum (~ 800 binding sites/nucleus). Pregnancy further raised receptor concentrations in the last week of gestation when they reach ~ 1200 binding sites/nucleus. Studies with ethynylestradiol-treated rats demonstrated that virtually no translocation can be detected before the onset of puberty; thereafter the number of translocated receptors increases dramatically reaching a maximum (9000 binding sites/nucleus) between day 80 and 87 of life. The extractability of the nuclear receptors with 0.4 M KC1 varies during the course of life. Extractability is very high (~90%) up to about day 12 of life, but then decreases markedly (to ~70% in vehicle-treated and to ~ 50% in ethynylestradiol-treated rats) before the onset of puberty.