Metabolic Activities of Thyroid Glands from Tapazole Treated Rats

Thyroid glands from rats treated with tapazole (0.1% in drinking water) for a four-week period show, as opposed to the controls, a significant increase in some metabolic activities which are known to be stimulated rather early by TSH, i. e. glucose oxidation, phospholipid metabolism and the hydrolysis of thyroglobulin. This stimulation cannot be affected to any further degree by the addition of thyrotropin in vitro. Moreover, the treatment with tapazole, unlike the addition of TSH to normal glands in vitro, increased the incorporation of a labelled amino acid into thyroglobin as well as other thyroglobulin-like proteins. — The results obtained indicate that the metabolic changes produced by tapazole on rat thyroid glands can all be ascribed to an increased secretion of TSH, and that in all probability, the thyroid cell receptor for the hormone is saturated with it. Furthermore, the results support the hypothesis that the effect of TSH on the biosynthesis of TGB is only of a delayed type.