Effect of gonadectomy and exogenous sex hormone administration on the concentrations of hepatic oestrogen receptors and hepatic atypical sex hormone binding protein (HASP) in the rat.

The concentrations of hepatic oestrogen receptors and atypical sex hormone-binding protein are regulated by sex hormones in different manners. Ovariectomy of female rats leads to a significant increase in the concentration of hepatic oestrogen receptors, which can be reversed following administration of either androgens or oestrogens. No differences are observed between total binding site and unoccupied receptor concentrations. Intact male rats contain significantly lower total binding site concentrations and these are not affected by either testectomy or subsequent androgen administration. However, treatment of male castrates with oestradiol leads to the induction of typical female levels. It is not possible to determine the concentrations of unoccupied receptors in intact or gonadectomized males, or rats of either sex treated with androgens, due to masking by the moderate affinity, high capacity oestradiol binder (hepatic atypical sex hormone-binding protein, HASP). Oestradiol binding to this protein is not affected by testectomy nor subsequent androgen administration, but is reduced pressed following treatment with oestradiol. It is also induced in ovariectomized rats by androgens. Oestradiol binding to this protein can be prevented by inclusion of sodium thiocyanate in the assay buffer, thereby permitting unhindered measurement of the oestrogen receptor concentrations.