Prolactin secretion by metoclopramide in man.

Six men and nine women were given intravenous injections of 2.5 mg of metoclopramide to assess its potential as a stimulus to prolactin release. Following the administration of metoclopramide, there was prompt increase in serum prolactin to a peak response of 38.2 +/- 3.9 ng/ml in men and 103 +/- 10.2 ng/ml in women. The prolactin response to metoclopramide in men was compared with the response to 400 mug of TRH in 10 men. The peak response after TRH was 22.4 +/- 2.2 ng/ml, which was significantly less than that observed after metoclopramide. Pretreatment with 500 mg of L-dopa suppressed the prolactin response to metoclopramide in 6 men to a mean response of 16.3 +/- 4.3 ng/ml. We have concluded that metoclopramide is a safe, reliable, and potent stimulus of prolactin secretion and exerts this effect by blocking dopamine receptors in the hypothalamus and decreasing prolactin inhibiting factor. It is free of side effects and is a useful alternative to chlorpromazine.