Hypothalamo-pituitary regulation of hepatic prolactin receptors in the rat

Abstract

The number of specific binding sites for 125I-labeled human prolactin (hPrl) in crude membrane fractions from rat liver is sexually differentiated. Livers from female rats specifically bound much more of added [125I]hPrl than male liver membrane fractions which bound little, if any, Prl. Hypophysectomy of female animals eliminated hepatic binding of Prl; the effect was reversed by a pituitary implant under the kidney capsule. Treatment of male rats with estradiol valerate induced hepatic hPrl receptors, but only in the presence of an intact pituitary. Anterior hypothalamic deafferentation at the retrochiasmatic level in male rats increased the hepatic hPrl receptor concentration to the female level 3-4 days following the operation. This induction of hPrl receptors was also seen in the absence of the gonads. A transection rostral to the suprachiasmatic nucleus had no effect on the concentration of hPrl receptors in male animals. Our results demonstrate that [125I]hPrl binds specifically to rat liver membranes and that the number of binding sites is regulated by the hypothalamo-pituitary system. The regulatory brain centre appears to be located in the anterior hypothalamus or adjacent areas. The receptor-inducing pituitary factor might possibly be related to the so-called 'feminizing factor' involved in pituitary control of liver enzymes that metabolize drugs and steroids.