[Effect of thyrotropic hormone on the ultrastructure of the endothelium of thyroid gland perifolicular capillaries].

Under study was the alteration in the ultrastructure of the thyroid epithelium and endothelium of perifollicular capillaries influenced by exogenous thyrotropic hormone. The results obtained show that there is a direct relationship between the dosage of the injected thyrotopic hormone, the degree of the ultrastructural changes in the time of their appearance. It has been established that the alterations in the perifollicular capillary endothelium ultrastructure make their appearance and become maximum practically simulataneously with the alterations in the thyroid epithelium ultrastructure. The increased functional activity of the endothelium, thinner walls of capillaries and the appearnace of a greater amount of fenestrations against the background of the thyroid stimulation are likely to be factors contributing to penetration of non-hormonal iodine products (iodine tyrosines and products of incomplete hydrolysis of thyroglobulins) into the circulation, which can be observed under certain pathological conditions accompanied by increased thyrotropic stimulation--such as diffused toxic goiter and diffuse non-toxic goiter.