ACTIVITIES OF ANTIOXIDANT ENZYMES AND MONOAMINE OXIDASE-A IN THE RAT INTERSCAPULAR BROWN ADIPOSE-TISSUE - EFFECTS OF INSULIN AND 6-HYDROXYDOPAMINE

The effects of different doses of insulin (INS) (0.4 or 4.0 IU/kg body mass, i.p., for 3 hr) and 6-hydroxydopamine (6-HDA) (100 mg/kg., i.p. ) on the activities of antioxidant enzymes-copper-zinc superoxide dism utase (CuZnSOD), manganese superoxide dismutase (MnSOD), catalase (CAT ) and catecholamine degrading enzyme monoamine oxidase (MAO-A)-in the rat interscapular brown adipose tissue (IBAT) were studied. In vivo 6- HDA administration, which induces the destruction of sympathetic nerve s, markedly reduced IBAT CuZnSOD activity but did not change MnSOD and CAT activities. However, the low dose of INS, which did not induce hy poglycemia, significantly increased the activity of both IBAT mitochon drial enzymes (MnSOD and MAO-A) of control rats. This INS effect on Mn SOD was abolished by 6-HDA. On the contrary, CuZnSOD activity was mark edly reduced under the influence of INS in both control and 6-HDA-trea ted rats, whereas for the maintenance of the control level of this enz yme activity, the intact sympathetic nervous system (SNS) is necessary . INS, independent of the dose applied, did not. affect CAT activity i n control rats, whereas only low INS dose increased the activity of th is enzyme in 6-HDA-treated rats. The results indicate that the stimula tory effect of INS on the IBAT mitochondrial enzymes studied is dose d ependent and in the case of MnSOD is mediated by SNS. However, the dep ression in the activity of CuZnSOD is independent of the above-mention ed factors. (C) 1997 Elsevier Science Inc.