MSH Activity in Pituitary Glands of Rats Treated with Tranquilizing Drugs1

Abstract
The MSH content of rat pituitary glands was found to decrease after treatment with the tranquilizing drugs that cause frogs to darken. Injection of purified MSH-release inhibiting factor (MIF) or exogenous MSH to rats which had been pretreated with tranquilizers resulted in pituitary MSH levels greater than those found in rats treated with tranquilizers only. It is suggested that tranquilizing drugs probably exert their principal effect upon the hypothalamic factor which inhibits MSH release from the pituitary gland.