A comparison of the effect of propylthiouracil on the respiration of thyroid slices from humans, chickens and rats.

1. The QO2 of thyroid slices from hyperthyroid patients treated with propylthiouracil (PTU) was 140% that of slices from euthyroid patients. Similar results were obtained using thyroid slices from PTU fed and control chickens. 2. PTU feeding caused thyroid hyperplasia, increased QO2 more than could be accounted for by the hyperplasia but neither increased QO2 of muscle, cerebral cortex or spleen nor altered serum T4 levels. 3. PTU in drinking water increased the size and vascularity of thyroids from control but not hypophysectomized rats and had no effect on QO2. 4. The observations made on human, chicken and rat thryoid apparently reflect the effects of TSH rather than a direct action of PTU.