Exercise suppression of thermoregulatory thermogenesis in warm- and cold-acclimated rats

An evaluation was made of the effects of an acute exercise bout on (i) nonshivering thermogenesis (NST) in cold-acclimated rats (4 °C for 6 weeks) and (ii) shivering thermogenesis in 24 °C-acclimated rats (24 °C for 6 weeks). Assessment techniques included indirect calorimetry during treadmill running and brown adipose tissue (BAT) mitochondrial guanosine diphosphate (GDP) binding immediately following a treadmill run. Calorimetric results for 24 °C-acclimated rats running at 4 °C indicated total substitution of shivering thermogenesis by exercise-derived heat. No difference in GDP-binding, an index of BAT nonshivering thermogenic activity, was observed between exercised and nonexercised 24 °C-acclimated rats. Calorimetric results for cold-acclimated rats running at 4 °C indicated a total suppression in the energy cost associated with NST, exercise-derived heat replacing or substituting for NST. Examining BAT properties in the exercised cold-acclimated rats revealed a significant 40% decrease in BAT mitochondrial GDP-binding. These results suggest that during running, metabolic heat due to the exercise (i) totally replaces shivering in 24 °C-acclimated rats and (ii) totally replaces BAT nonshivering thermogenesis in cold-acclimated rats.