INCREASED PROLACTIN AND THYROTROPHIN SECRETION FOLLOWING ORAL METOCLOPRAMIDE: DOSE-RESPONSE RELATIONSHIPS

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Abstract
Four normal men received 1, 5, 10 and 20 mg doses of oral metoclopramide, a dopamine receptor antagonist, or placebo to determine the effect of this drug on anterior pituitary hormone secretion. Increases in serum prolactin (PRL) occurred even after the 1 mg tablet (P < 0.01) while maximal responses were observed 60 min after ingestion of the 20 mg tablet (mean 27.8 ng/ml; range 25.6-30.3 ng/ml). Serum PRL levels peaked 60-90 min after ingestion of any dose of metoclopramide and values remained significantly elevated (P < 0.05) for up to 8 h after the tablet. Increases in serum thyrotropin (TSH) occurred after the 10 and 20 mg doses of metoclopramide. Peak responses were seen at 120-180 min, with significant elevation (P < 0.05) persisting from 60-240 min after ingestion. No consistent changes in serum FSH [follicle-stimulating hormone], LH [luteinizing hormone] or GH [growth hormone] were observed and no side-effects were reported. Metoclopramide apparently elevated serum PRL and TSH. The threshold dose of metoclopramide required for these effects was different for the 2 hormones; their peak responses occurred at different times and the duration of the elevation was dissimilar, suggesting a mechanism other than the release of hypothalamic thyrotropin-releasing hormone (TRH).