Suppression of prolactin secretion by L-dopa in the stalk-sectioned rhesus monkey

The effects of iv administration of L-dopa on serum prolactin were studied in both normal female rhesus monkeys and in monkeys in which the pituitary stalk had been previously sectioned. Revascularization of the pituitary gland was prevented by the insertion of a silastic barrier over the diaphragma sellae. Prolactin secretion was increased in all stalk-sectioned monkeys and, in contrast to intact animals, chlorpromazine administration was ineffective in further releasing prolactin. In both normal and stalk-sectioned monkeys, iv administration of L-dopa (3-120 mg) significantly inhibited prolactin release from the pituitary (P less than .005 normal; P less than .001 stalk section). L-dopa also suppressed the TRH-induced release of prolactin in both groups. These results indicate that L-dopa or dopamine may act directly on the anterior pituitary to inhibit prolactin secretion.