Development and maintenance of the brown adipocytes phenotype in the adipose organ has great metabolic significance and experimental conditions capable to increase the number of brown adipocytes reduce insulin resistance and obesity. Sympathetic nervous system (SNS) plays a role in the brown adipocytes recruitment and a massive activation of the SNS was described during physical activity. We investigated the effect of endurance training ( approximately 60% of VO2max, 5 days/week, both for 1 and 6 weeks) on brown- (BAT) and white adipose tissue (WAT) of young Sprague Dawley male rats to clarify the role of exercise training on the activity and recruitment state of brown cells.

Running training affected the morphology, sympathetic tone and vascularization of BAT. Functionally, exercise could be considered a weakly effective stimulus for BAT thermogenesis and a new function of BAT could be supposed.

Only 1 week of running training was enough to reduce the size of the white adipocytes in both the visceral depots (rpWAT and eWAT). Some clusters of paucilocular and multilocular adipocytes appeared in the rpWAT but not in eWAT in all the exercised rats, most of the brown-like cells were UCP-1 immunostained and showed rare fine TH i.r. fibers. The quantification of the UCP-1 i.r. adipocytes in rpWAT demonstrated that the number of brown cells was 8-fold higher in exercised rats, suggesting that exercise could be a new physiological stimulus to counteract obesity by an adrenergic-regulated brown recruitment of adipocytes.