IMMUNOCYTOCHEMICAL LOCALIZATION OF PROLACTIN RECEPTORS IN RAT-LIVER CELLS .1. DEPENDENCE ON SEX AND SEX STEROIDS

The peculiarities of cellular and tissue distribution of prolactin rec eptors (PRLR) in the liver of female and male rats with different sex steroid status were investigated in paraplast-embedded tissue with the indirect immunoperoxidase technique. Two clones of antibodies directe d outside the PRL-binding site (U6) or to the PRL-binding site (T6) of the receptor were used. PRLR-specific immunoreactivity was identified essentially in hepatocytes. PRLR can be visualized in sinusoidal doma ins of cellular membranes, in cytoplasmic granules and sometimes in th e perinuclear area of hepatocytes. The staining characteristics were s imilar with both antibodies. There were no prominent differences in th e intensity of PRLR-positive staining among hepatocytes of different z ones of hepatic lobules with the exception of some hepatocytes around central veins. Sex differences in the intensity of immunostaining (str ong in females, and faint in males) but not in the amount and distribu tion of PRLR-containing cells were observed. Gonadectomy of animals ca used the disappearance of sex differences in the intensity of PRLR-pos itive staining as a result of its decrease in females and increase in males. The essential elevation in the intensity of PRLR-specific immun oreactivity was revealed in hepatocytes of gonadectomized females and males after prolonged estradiol administration (10 mu g for 14 days). The cytoplasmic staining of some hepatocytes surrounding central veins was much more pronounced in estrogenized animals. PRLR-specific immun oreactivity in the perinuclear area was identified in these cells. And rogen treatment (3 mg of testosterone-propionate for 3 days) of gonade ctomized animals caused a decrease in the intensity of hepatocyte PRLR -positive staining similarly in both sexes. It is concluded that sex s teroids regulate PRLR expression in all hepatocytes and do not influen ce the number of PRLR-containing cells. It is speculated that PRLR exh ibition in liver cells is not a factor of gradient expression of other sex-dependent proteins in hepatic lobules.