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AN EXPERIMENTAL STUDY OF THE IRRADIATION EFFECTS ON THE THYROID TISSUE IN THE ALBINO RATS

This study was undertaken to observe the histopathological changes in the thyroidtissue of the albino rats when exposed to single and fractionated dose of Cobalt-60 irradiation. Fifty-six albino rats of a Sprague-Dawley strain, weighing approximately 180 gram, about 3 to 4 month old, were divided into the control group and 3 experimental groups. Irradiation was carried out using 1.25 MeV.RAC-120 Cobalt-00 Teletherpy Unit with exposure dose rate 84.3 rads/min, field size 4×5 cm, measured at 80 cm from source. In experimental groups, Group I was irradiated 1200 rads weekly of total dose 4800 rads for a period of 4 weeks, Group II was irradiated1500 rads with single dose and Group III was irradiated 2000 rads with single dose. The animals were sacrified at lst,3rd, 7th, 10th, 14th, 21th, and 28th day after each irradiations. Each specimen was fixed with 10% Formalin solution. The specimen was embedded in paraffin and sectioned serially 6μ in thickness. All specimens were stained with Hematoxylin-Eosin and examined in the usual methods. Following results were obtained; 1. The histological changes buck as the increase of the cell height, pyknosis and vacuolization were seen in the thyroid cells of all experimental groups. 2. The histological changes such as the decrease of the follicular size, destruction of the thyroid follicles, formation of the island principle, release of the thyroids colloid, vascular congestion, except the lymphocytic infiltration and fibrosis were seen in the thyroid follicles as well as in the stroma of the all experimental groups. 3. The regenerative changes were Been from the 7th day of the Group Ⅰ,Ⅱ, but it were slight in the 10th day of the Group Ⅲ. 4. The compensatory hypertrophy against the irradiation to the thyroid gland was seen as the increase of the cell height in the all experimental groups. 5. Comparing Group I with Group Ⅱ,Ⅲ, the histopathological changes were not affected by the irradiation means. 6. The malignant change may be produced when the long term irradiation were used under the fact that squamous metaplasia was observed in the 10th day of experimental Group Ⅱ.