The effect of chronic (3-9 months) therapy with metoclopramide on serum levels of pituitary and thyroid hormones was studied in 4 males and 1 female. The mean serum prolactin concentration during metoclopramide therapy was significantly higher than after discontinuation of metoclopramide. Serum prolactin concentrations increased acutely after each dose of metoclopramide, and gradually returned to normal by 6-12 h. There were no significant differences in the serum TSH, T₃, T₄, GH, and gonadotrophin levels during and after metoclopramide administration. In the male subjects the mean serum testosterone was normal, but significantly lower during metoclopramide therapy.

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The thyromimetic activity of 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT), a nonhalogenated thyroid analog, was studied in adult men using suppression of TRH-induced TSH release to assess this activity. In nine men, aged 30-58 yr, the TSH increment after 500 microgram TRH iv was compared to the TSH response to TRH 24 h after oral administration of 1 mg DIMIT. Eight euthyroid subjects had normal baseline TSH levels of 1.5 +/- 0.2 (SE) microunit/ml that fell significantly to 0.7 +/- 0.2 microunit/ml 24 h after DIMIT (P less than 0.005). Their TSH increments after TRH fell from 15.3 +/- 2.8 to 6.7 +/- 1.6 microunit/ml 24 h after DIMIT (P less than 0.001). One subject with probable Hashimoto's thyroditis had an elevated TSH of 18 microunit/ml, with an exaggerated TSH response to TRH of 72 microunit/ml. His basal TSH fell to 7.6 and his TSH increment fell to 14.3 microunit/ml 24 h after DIMIT. The suppression of TSH was relatively prolonged. In four subjects, the TSH response to TRH was still blunted from 5-12 days after DIMIT. In one subject, the TSH increment returned to normal 15 days after DIMIT. DIMIT had no significant effect on PRL secretion. There was no evidence of toxicity in patients receiving DIMIT. DIMIT has effective thyromimetic activity in man, as shown by its significant and prolonged suppression of TSH secretion.