Comparison of the metabolic and endocrine effects of 3,5,3'-triiodothyroacetic acid and thyroxine.
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.
Bracco
D
D
Institute of Physiology, University of Lausanne, Switzerland.
Morin
O
O
Schutz
Y
Y
Liang
H
H
Jéquier
E
E
Burger
A G
AG
D001481:Basal Metabolism / Q000187:drug effects; D002784:Cholesterol / Q000097:blood; D004734:Energy Metabolism / Q000187:drug effects; D006207:Half-Life; D006801:Humans; D007700:Kinetics; D008297:Male; D012119:Respiration / Q000187:drug effects; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism; D012890:Sleep / Q000502:physiology; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013974:Thyroxine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D014284:Triiodothyronine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D014285:Triiodothyronine, Reverse / Q000097:blood
D012738:Sex Hormone-Binding Globulin; D014284:Triiodothyronine; C010642:3,3',5-triiodothyroacetic acid; D014285:Triiodothyronine, Reverse; D013972:Thyrotropin; D002784:Cholesterol; D013974:Thyroxine