Interscapular brown adipose tissue (IBAT) hyperplasia involves a new metabolic and structural profile, resulting from acclimation of animals to a cold environment. Cold-induced changes of several antioxidative defense (AD) components in IBAT and their interrelationship with uncoupling protein 1 (UCP1), sympathetic innervation and apoptosis were studied using cold-acclimated adult rat males (4 +/- 1 degrees C, 45 days). Their age-matches were maintained at 22 +/- 1 degrees C serving as the controls. In cold-adapted rats, activities of CuZn- and Mn-superoxide dismutase (SOD) and apoptosis were reduced, while catalase (CAT), glutathione peroxidase (GSH-Px), glutathione S-transferase (GST) activities and glutathione (GSH) content were increased compared to the control. IBAT mass, protein content, plasma free fatty acid (FFA) concentration, sympathetic innervation and UCP1 level were significantly increased in cold-acclimated group compared to the corresponding control. These results suggest that decreased CuZn and MnSOD activities in IBAT represent an adaptive response due to UCP1-induced mitochondrial uncoupling. Additionally, intensive fatty acid oxidation led to an increased H(2)O(2) production which resulted in increased CAT, GSH-Px and GST activities and GSH level. Generally speaking, cold-induced changes of AD in the IBAT are closely connected with newly established metabolic profile in this tissue, thus making an important part of the entire tissue homeostasis including cell survival.