Article: article from journal or magazin.
Comparison of the metabolic and endocrine effects of 3,5,3'-triiodothyroacetic acid and thyroxine.
Journal of Clinical Endocrinology and Metabolism
To test the hypothesis that 3,5,3'-triiodothyroacetic acid (Triac) is more active as a TSH suppressor than on peripheral parameters of thyroid hormone action, the following parameters were studied: basal metabolic rate, sleeping energy expenditure (SEE), sex hormone-binding globulin, and cholesterol. In a double blind trial, 14 subjects received during 3 weeks (phase 1) 180 micrograms T4 or 1700 micrograms Triac daily, divided into 3 doses, to suppress thyroidal secretion. The dosage was doubled for the next 3 weeks (phase 2). Under T4 treatment, TSH reached 0.11 mU/L during phase 1 and less than 0.03 mU/L during phase 2. With Triac, a marked TSH inhibition occurred after 1 week (0.17 mU/L), followed by an escape during the following 2 weeks (0.63 mU/L). During phase 2, an almost complete TSH suppression was obtained (0.03 mU/L). Both Triac doses suppressed endogenous thyroid hormone secretion, as evidenced by T4 and rT3 levels. Both substances induced a 2-fold stimulation of sex hormone-binding globulin during phase 2. Serum cholesterol decreased similarly, without affecting the high/low density lipoprotein ratio. T4 increased SEE by 4.1% and 8.5% during phases 1 and 2. Triac failed to induce the expected peripheral metabolic responses of the thyroid hormones, as demonstrated by an unchanged SEE and basal metabolic rate. These results clearly show a preferential action of Triac on TSH suppression.
Basal Metabolism/drug effects, Cholesterol/blood, Energy Metabolism/drug effects, Half-Life, Humans, Kinetics, Male, Respiration/drug effects, Sex Hormone-Binding Globulin/metabolism, Sleep/physiology, Thyrotropin/blood, Thyrotropin/secretion, Thyroxine/administration & dosage, Thyroxine/blood, Triiodothyronine/administration & dosage, Triiodothyronine/analogs & derivatives, Triiodothyronine, Reverse/blood
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