triiodothyronine deiodinating activity in brown adipose tissue after short cold stimulation test in trained and untrained rats interscapular brown adipose tissue ibat activity is controlled by sympathetic nervous system and factors that influence thermogenesis appear to be centrally connected to the sympathetic outflow to ibat cold exposure produces a rise in bat temperature which is associated with an increased thyroid activity elevated serum levels of 353triiodothyronine t3 and an increased rate of t3 production this study evaluated the effect of swimming training on 5triiodothyronine deiodinase 5d activity in ibat under normal environmental conditions and after short 30 min cold exposure tst stimulation test 5d activity is lower in trained rats at basal condition and tst increases 5d in ibat of both untrained and trained rats however this increase is lower in trained rats training reduces the deiodinating activity in normal environmental conditions as well as after short cold exposure probably other compensatory mechanisms of heat production are active in trained rodents