Effect of cimetidine on prolactin secretion in normal controls and hyperthyroid patients.

Nine healthy female controls and 10 hyperthyroid female patients were studied. The intravenous administration of 200 mg cimetidine, an H2-receptor antagonist, was followed by a significant and marked rise in serum prolactin levels in all control subjects. There was no significant difference in serum PRL response to cimetidine injection between the euthyroid controls and hyperthyroid patients. But max delta PRL, the change from basal to peak values, is significantly lower in the hyperthyroid patients than in the controls. There was a significant negative correlation between max delta PRL and serum T4 or T3 levels in hyperthyroid patients before and after treatment with MMI or PTU. It appears from our data that cimetidine induced PRL release was blunted in hyperthyroid patients.