Deiodinating activity in the brown adipose tissue of rats following short cold exposure after strenuous exercise.

Interscapular brown adipose tissue (IBAT) activity is controlled by the sympathetic nervous system, and factors that influence thermogenesis appear to act centrally to modify the sympathetic outflow to IBAT. Cold exposure produces a rise in IBAT temperature as a result of the increase in sympathetic outflow to IBAT. This is associated with an increased thyroid activity. 3,5,3'-triiodothyronine (T3) and T4 levels increase during strenuous exercise, and, at the end of the exercise bout, a decrease of T3 and T4 levels, with an increase in TSH during the following 4-5 days, is seen. We evaluated the effect of strenuous exercise on 5'-deiodinase (5'-D) activity in IBAT in normal environmental conditions and after short (30 min) cold exposure. 5'-D activity is lower in rats at basal condition. Short cold exposure (SCE) increases 5'-D in IBAT both in exercising rats and in sedentary rats. However, this increase is lower in exercising animals. Strenuous exercise can reduce 5'-D activity in normal environmental conditions and after SCE. Probably, other compensatory mechanisms of heat production are active in exercising rodents.