The effect of intracarotid (ic) or intravenous infusion of extracts of rat hypothalamus (SME) or brain cortex (CE) on serum prolactin levels was investigated in rats anesthetized with sodium pentobarbital (Nembutal, 35 mg/kg) pretreated with perphenazine (10 mg/kg) and Nembutal, reserpine (0.2 mg) and Nembutal, or subjected to ablation of the medial hypothalamus. Thirty minutes following injection of Nembutal, serum prolaction levels were significantly increased. Injection of perphenazine or reserpine prior to Nembutal injection induced a marked rise in serum prolactin one hour and five hours, respectively, after injection. However, the magnitude of the rise evoked by reserpine was considerably less than that induced by perphenazine and not significantly different from that produced by Nembutal only. Surgical ablation of the medial hypothalamus increased serum prolactin levels 2 hrs after the operation and serum prolactin levels were still elevated 18 days later. In Nembutal-anesthetized rats, infusion of either 3 SME or CE extract foi 30 min markedly decreased serum prolactin levels. In contrast, in the pharmacologically blocked oi surgically ablated animals, neither the infusion of CE or SME resulted in a significant reduction of serum prolactin. These results suggest that the observed decrease in prolactin levels following infusion of SME or CE in Nembutal-anesthetized rats may reflect the release of endogenous PRIF, evoked by the tissue extracts, and not a direct inhibitory action on pituitary prolactin secretion.
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