Action of different doses of 131I on thyroid gland, its tissue distribution and elimination in adult male rats

Adult male Wistar rats were administered 4, 37, 74 or 185 MBq/kg 131I i.p. Activities were measured in the thyroid gland or region, blood plasma (total and protein bound), salivary glands, cerebral cortex, skin, liver, spleen, small intestine, kidney, heart and skeletal muscle after 1-30 (36) days. Beginning 8 days after radiothyroidectomy the remaining or possibly regenerated thyroid function was tested with a test dose of 185 kBq/kg i.p. After administration of 4 MBq/kg 131I the thyroid gland showed a regeneration within 30 days, but not after treatment with higher doses. The time course of tissue distribution of activity is dose dependent: after 4 MBq/kg 131I increasing activities after the 3rd-8th day are observed in skin, brain, salivary glands, intestine, spleen, kidney, heart and skeletal muscle. After 37 MBq/kg 131I only in skin, brain, liver and intestine increasing activities between the 8th and 30th day have been observed. After 185 MBq/kg 131I only in skin, spleen and intestine increasing activities after the 15th day were measured. Thyroid gland activity 24 hs after administration of 185 kBq/kg 131I showed during the experimental period of 50 days considerable variation with a factor of 4 for thyroid gland, 8 for protein-bound and about 10 for total plasma 131I activity. (author)