Studies on the mechanism controlling growth hormone release induced by chlorpromazine in the anesthetized rat

In intact urethane-anesthetized rats, plasma growth hormone (GH) levels were low but increased significantly following intravenous injection of chlorpromazine. Plasma GH levels were significantly elevated in rats with hypothalamic cuts such as complete deafferentiation, anterior cut and antero-lateral cut, whereas plasma GH levels in rats with posterior cut or postero-lateral cut were not significantly different from those in rats with sham-operation. Intravenous injection of chlorpromazine caused an increase of plasma GH in rats with any type of hypothalamic cut. However, the maximum increments of plasma GH following chlorpromazine were larger in rats with antero-lateral cut and smaller in rats with posterior cut than in rats with sham-operation. These results suggest that extrahypothalamic inhibiting and stimulating neurons influence the regulatory mechanism of rat GH secretion through anterior and posterior routes to the hypothalamus respectively.