The unusual estrogen-binding protein (UEBP) of rat liver: The role of sex steroids and hypophysis in its regulation

Abstract

The number of estradiol(E 2) binding sites of rat liver unusual estrogen-binding protein (N UEBP) was measured, using a novel modification of the quantitative method of specific UEBP determination. In liver cytosol of mature male and female rats, N UEBP amounted to 6.83 ± 0.49 and < 0.05pmol/mg protein, respectively. Neonatal administration of testosterone-propionate (TP) and TP injections at later periods of ontogenesis increased N UEBP in female rat liver in a similar fashion. The elevated N UEBP was found in the liver of mature ovariectomized females 30 days after cessation of TP injections. Hypophysectomy (but not adrenalectomy or thyroidectomy) prevented TP induction of elevated N UEBP in pubertal females. E 2 injections reversibly decreased N UEBP in the liver of all animals under study except of hypophysectomized males. A stimulating regulatory effect of TP on N UEBP in male rat liver was observed only in the case of endogenous androgen deficiency and low N UEBP. TP prevented the E 2-dependent decrease of N UEBP upon their simultaneous injections and increased the E 2-reduced N UEBP when injected after E 2. Hypophysectomy led to a decrease of N UEBP in pubertal males but only slightly affected that in castrated animals. After TP injections to hypophysectomized males, N UEBP returned to a level next to the initial one. It was concluded that estrogen-androgen regulation of the UEBP level led to the maintenance of sex differences in the UEBP content.