[Organotropicity and the dynamics of the clearance of exogenous labelled TSH from the blood under conditions of stimulation and blockade of the thyrotropic function of the hypophysis].

Experiments were conducted on male Wistar rats. Incorporation into the kidney, the liver and the thyroid gland of I131-TSH and its elimination from the blood was studied. The rate of I131-TSH elimination from the blood plasma varied depending on the level of the endogenous TSH in the circulating blood of the recipient rats. The half-elimination period of the I131-TSH from the blood plasma of the intact rats constituted 10.4 minutes. In these animals the labeled hormone accumulated in the thyroid gland only 30 minutes after its administration. In case of an increase of the blood level of endogenous TSH following thyroidectomy the period of half-elimination of the I131-TSH from the plasma fell to 3.6 minutes; with reduction of the endogenous hormone level due to the block of the hypophysial secretion by triiodothyronine the period of the I131-TSH half-elimination rose to 39.4 minutes. In the latter case the labeled hormone failed to be incorporated into the thyroid gland. A conclusion was drawn on a possibility of assessing the level of the thyrotropic activity of the hypophysis on the basis of the changes in the period of the I131-TSH half-elimination from the blood plasma of the recipient animals.