Thermogenic effect of triiodothyroacetic acid at low doses in rat adipose tissue without adverse side effects in the thyroid axis

Instituto de Investigaciones Biomédicas Madrid and Centro de Investigación Biomédica en Red (CIBER) Fisiopatologia Obesidad y Nutricion, Instituto Salud Carlos III, Madrid, Spain Submitted 2 July 2007 ; accepted in final form 12 February 2008 Triiodothyroacetic acid (TRIAC) is a physiological product of triiodothyronine (T 3 ) metabolism, with high affinity for T 3 nuclear receptors. Its interest stems from its potential thermogenic effects. Thus this work aimed 1 ) to clarify these thermogenic effects mediated by TRIAC vs. T 3 in vivo and 2 ) to determine whether they occurred predominantly in adipose tissues. To examine this, control rats were infused with equimolar T 3 or TRIAC doses (0.8 or 4 nmol·100 g body wt –1 ·day –1 ) or exposed for 48 h to cold. Both T 3 doses and only the highest TRIAC dose inhibited plasma and pituitary thyroid-stimulating hormone (TSH) and thyroxine (T 4 ) in plasma and tissues. Interestingly, the lower TRIAC dose marginally inhibited plasma T 4 . T 3 infusion increased plasma and tissue T 3 in a tissue-specific manner. The highest TRIAC dose increased TRIAC concentrations in plasma and tissues, decreasing plasma T 3 . TRIAC concentrations in tissues were