Frontal deafferentation at the retrochiasmatic and suprachiasmatic level resulted in a complete "feminization" of hepatic steroid metabolism in male rats. Such an effect was also seen when lesions involving mainly the anterior periventricular hypothalamic area and the suprachiasmatic nucleus were performed in male rats. No effects were seen in analogous lesions in female rats in any of the cases studied. The present findings suggest that a region including the anterior hypothalamic periventricular area. the suprachiasmatic nucleus and adjacent areas is involved in the control of hepatic steroid metabolism. It is postulated that the neuronal cell bodies that produce a factor with an inhibitory effect on the secretion of "feminizing factor" have their origins in this area of the hypothalamus, or alternatively, may send axons through this area to the basal hypothalamus and thus directly or indirectly influence the anterior pituitary gland. With liver membranes from female rats. 6-8% of totally added 125I-hPrl was specifically bound, whereas in male liver membrane fractions the specific Prl binding was very low or absent. 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. A transection rostral to the suprachiasmatic nucleus had no effect on the concentration of hPrl receptors in male animals. Our results demonstrate that the number of hPrl receptors is regulated by the hypothalamo-pituitary system. The receptor-inducing pituitary factor might be related to the "feminizing factor".
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