STUDIES OF THYROID HORMONE SYNTHESIS IN EXPERIMENTAL AUTOIMMUNE THYROIDITIS

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Abstract
Thyroid hormone synthesis in rabbits with experimentally induced thyroiditis is compared with hormone synthesis in normal rabbits and in immunized rabbits receiving thyroid stimulating hormone. The immunized rabbits showed decreased thyroidal accumulation rates for 131I, T. S. H. administration produced an increase in the accumulation rate of immunized animals, but this increase was smaller than that obtained in normal rabbits stimulated with T. S. H. None of the rabbits'' thyroids discharged iodide with the administration of potassium thiocyanate. Twenty-four and 48 hours after 131I was administered, chromatography was performed on digested extracts of the thyroid glands. In the digested extracts of thyroids removed from normal rabbits the monodiiodotyrosine ratio was greater than 1.0 whereas the extracts of thyroids removed from immunized rabbits and normal rabbits stimulated with T. S. H. consistently had a ratio of less than 1.0. Thyroxine was not always present in the thyroids of normal rabbits but was consistently found in the thyroids of the immunized and T. S. H. treated animals. The findings suggest that the remaining thyroid cells in the glands of immunized rabbits are operating under increased T. S. H. stimulation. The experimental thyroiditis of immunized rabbits was similar to Hashimoto''s thyroiditis in respect to histological alteration and the presence of anti-thyroid antibodies. 131I accumulation rates, response to potassium thiocyanate, and chromatography studies revealed no correlation between the two groups.