[The effect of one-time external low- and high-dose gamma-irradiation on rat thyroid structure at the acute and remote periods].

A study of the morphological structure of the thyroid was made at the acute (1, 3, 6 hours) and remote periods (1, 4, 24, 48 weeks) following the external gamma-irradiation at doses of 0.25-5.0 Gy using histologic and electron microscopic methods. At the acute period, morphological changes prevailed, which reflect the functional alterations (changes of the nucleic and of the follicular diameters and of the colloid density). Frequently they hare a non-synchronous character. At more remote periods, destructive (colloidorrhage, desquamation, hemorrhage) and reparative changes reveal in thyroid, which and by the development of the sclerotic processes and of the morphological signs of decreased functional activity of the gland (increased follicular size and colloidal density, flatness of follicular epithelium and pronounced decreasing of the thyrocytes ultra structure number). The presence of such morphological changes after high and low-dose irradiation (<1.0 Gy) shows high sensitivity of the thyroid to single external radiation.

[Functional and morphological characterization of rat thyroid gland at remote periods following single high and low dose radiation exposure]. / Funktional'no-morfologicheskaia kharakteristika shchitovidnoi zhelezy krys v otdalennye sroki posle odnokratnogo vozdeistviia radiatsionnogo izlucheniia v bol'shikh i malykh dozakh.

A study of the morphological structure and functional activity of the rat thyroid gland was carried out after 22 months following a single exposure to external radiation. The 3-month-old animals were irradiated with doses of 0.25, 0.5, 1.0, 2.0 and 5.0 Gy. Blood was assayed for thyroxin (T4) and triiodothyronine (T3) levels, while liver tissue--for NADP-MDH activity and thyroid tissue--for thyroperoxidase activity. The thyroid was studied histologically, morphometrically and by electron microscope. The decreased T4 concentrations 2.59-fold in the 5.0 Gy group, the increased T3/T4 in the 2.0 and 0.25 Gy groups, the reduced diameter of cellular nuclei and follicles, the flat follicular epithelium and diminished number of thyrocyte ultrastructures indicate thyroid hypofunction in the irradiated animals. The morphological changes are characterized by enhanced diffuse and focal sclerotic changes in thyroid, most pronounced at high irradiation doses (1.0-5.0 Gy), whereas the hemosiderosis foci suggest that the structural changes are consequences of radiation-induced destructive injuries in the gland parenchyma. Two of the thyroids (0.5 Gy) demonstrate foci with pronounced lymphoid infiltration, while follicular carcinomas were detected in 4 thyroids (2.0 Gy), and in one thyroid (0.5 Gy) in one thyroid (5.0 Gy). The remote effects of radiation were dose-dependent destructive, sclerotic and atrophic processes, decreased functional activity, stimulation of development of autoimmune aggression and carcinogenesis in thyroid.