Dose-Response Relationships Between Hypothalamic PIF and Prolactin Release by Rat Pituitary Tissue in Vitro

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Abstract
A negative log-dose relationship was demonstrated when different amounts of rat hypothalamic extract containing prolactin- inhibiting activity (PIF) were incubated with rat anterior pituitary tissue, and the amounts of prolactin released were measured. Use of male rat pituitary glands in the incubation system proved to be more sensitive and showed less variability in response than when female rat pituitary tissue was incubated with hypothalamic extract. Rat cerebral extract at several dose levels had no significant effect on pituitary prolactin release in vitro. These results indicate that PIF exists as a specific hormone in the hypothalamus, and that the in vitro method is suitable for measuring changes in hypothalamic PIF content produced by different physiological states.