Studies on obesity. III. Effect of triiodothyronine (T 3) on thyroglobulin autoantibodies in euthyroid obese subjects

Effect of T 3 therapy on tanned red cell agglutinating thyroglobulin (TRC-TG) antibodies in 10 obese subjects without apparent thyroid disease was investigated. Six other obese subjects without thyroid dysfunction and of approximately the same mean age who also had circulating TRC-TG antibodies served as control subjects and were untreated. In vitro thyroid tests (TSH, total and free T 4) performed before T 3 therapy, as well as clinical examination, showed thyroid function to be normal in all subjects, and there was no evidence of thyroiditis. TRC-TG antibodies were present in low to moderate titers of 40–1280 in control subjects as well as in subjects selected for T 3 treatment. Therapy with T 3 was started at 50 μg/day and gradually increased to a maximum of 250 μg/day, depending on clinical needs. T 3-treated as well as untreated obese control subjects were all maintained on a high protein, low fat, low carbohydrate diet. Duration of T 3 therapy varied from 2–8 mo, and in all but one T 3-treated subject, TRC-TG antibodies completely disappeared. In the one exceptional case, TRC-TG antibody titer decreased from 1280 to 80 after 7 mo of therapy. In non-T 3-treated obese control subjects, antibody titers remained at the same levels throughout the observation period, thereby indicating a lack of spontaneous regression of circulating immune response. Therapy with T 3, by inhibiting TSH, may have caused regression of inapparent immunologic thyroid lesion, thus leading to the disappearance of circulating TRC antibodies; alternatively, T 3 specifically may have accelerated catabolism of thyroid antibodies. The latter possibility is favored in the absence of clinical and laboratory evidence of thyroiditis in T 3-treated subjects.