Protein metabolism in hypo- and hyperstimulated rat thyroid glands. II. Degradation of newly formed thyroidal proteins.

The rate of degradation of total thyroidal proteins is modified in differently stimulated glands. It is slowed down in hypostimulated thyroids and accelerated in hyperstimulated ones. Comparative evaluation of the rates of degradation (either in absolute terms - DPM/mg of tissue or as specific activity) of different proteins shows that a modified hormonal state affects the degradation of the thyroglobulin much more significantly than the degradation of non-thyroglobulin proteins. In the absence of thyrotropic hormone (TSH) the degradation of thyroglobulin is almost completely inhibited, while with excess of hormone it is dramatically accelerated. Comparing the TSH action on the synthesis with its effect on the degradation of thyroglobulin, it appears that it has a much stronger effect on the process of degradation than on the process of synthesis. This means that TSH significantly modifies the turnover of thyroglobulin. This effect of TSH leads, in chronically hypo- or hyperstimulated glands to the new levels of colloidal thyroglobulin which are highly increased in hypostimulated and significantly decreased in hyperstimulated glands. These results are in perfect agreement with the classical morphological description of hypo- and hyperstimulated glands.