3,5,3'-Triiodothyroacetic acid (TRIAC) effects on pituitary thyroid regulation and on peripheral tissue parameters.

The effects of TRIAC on peripheral thyroid hormones, TSH incretion and peripheral tissue parameters were investigated in 13 mildly obese patients (group I) and 10 volunteers of normal body weight (group II). TRIAC was administered 3 x 1 mg daily over a period of 8 days to both groups. In group I (on a 400 kcal low caloric diet) bTSH and fT4 decreased significantly whereas TT4 decreased only insignificantly. TT3 and fT3 rose significantly due to the cross-reactivity of the employed antibody. The peripheral tissue parameters cholesterol, ankle jerk and systolic time interval did not reveal any changes suggesting an increase in metabolic rate. The increase in heart frequency was not significant either. The significant rise in sex-hormone binding globulin was most probably associated with the weight reduction of 3.1 +/- 1.2 kg per week. In group II (on normal diet) bTSH and fT4 decreased significantly whereas TT4 decreased only insignificantly. As in group I, TT3 and fT3 rose significantly. Also in group II TRIAC did not cause alterations in the peripheral tissue parameters. In contrast to the obese group the volunteers in group II showed no significant rise in sex-hormone binding globulin and no reduction of body weight. Side effects such as nervousness, tremor or palpitations were not observed. Thus, TRIAC does not induce an increase in peripheral metabolic rate, not even under a TSH-suppressive dose as high as 3 x 1 mg per day.