Comparison of metoclopramide with other dynamic tests of prolactin secretion.

Metoclopramide, a derivative of procainamide, was compared with thyrotropin releasing hormone (TRH), N3im-methyl-TRH and chlorpromazine as a prolactin (PRL) releaser in 11 euthyroid males. The peak response of serum PRL and the maximum increment of serum PRL (max deltaPRL) were greater (P less than 0.0005) after the administration of metoclopramide (deltaPRL 24.1 +/- 1.5 (SE) ng/ml) than after either TRH (14.9 +/- 1.5 ng/ml) or chlorpromazine (7.0 +/- 2.1 ng/ml). There were no significant differences between the peak and max deltaPRL responses to metoclopramide or N3im-methyl-TRH. Metoclopramide produced a small increase in serum thyrotropin and small reductions of serum growth hormone, luteinizing hormone and follicle-stimulating hormone. Metoclopramide may be useful for dynamic testing of PRL release. It offers the advantage of oral administration; a 10 mg dose produces a larger, more sustained increment in serum PRL than other agents used to evaluate prolactin reserve.