Aging in brown fat: antioxidant defenses and oxidative stress.

Brown adipose tissue (BAT) responds to physiological stimulation with high rates of mitochondrial O2 consumption, and with high rates of lipid turnover. These are the most susceptible molecules to peroxidation. Thus, it is important to elucidate the changes in antioxidant defenses and lipid peroxidation that occur in this tissue during the lifetime of the individual. It is shown for the first time that during development from young (3 months) to mature adults (9 months) quantitatively important increases of all the antioxidant enzymes (superoxide dismutase, catalase, selenium dependent and independent glutathione peroxidases and glutathione reductase) take place in BAT. This is concordant with the much higher aerobic capacity and sensitivity to in vitro peroxidation of the tissue in mature adults than in the young. During aging (from 9 to 28 months of age), aerobic capacity is clearly reduced. Nevertheless, the sensitivity of BAT to in vitro peroxidation is maintained in old animals and, accordingly, the antioxidant defensive systems do not show important changes either.