CHRONIC EFFECT OF INSULIN ON MONOAMINE-OXIDASE AND ANTIOXIDANT ENZYME-ACTIVITIES IN THE RAT BRAIN-STEM

It was shown that hydrogen peroxide (H2O2) is a possible intracellular second messenger in specific insulin action. Because its concentratio n in the cell depends on the activity of both antioxidant enzymes and monoamine oxidase (MAO), we studied the influence of different insulin doses (0.4 and 4.0 IU/kg body mass, i.p., daily injected over 3 days) on the activity of MAO, types A and B, copper zinc superoxide dismuta se (CuZnSOD), manganese superoxide dismutase (MnSOD), and catalase in the rat brainstem. Chronic insulin treatment significantly increased V -max of MAO-A and B activities (P < 0.05, P < 0.025, respectively) ind ependent of the dose applied. CuZnSOD activity was also increased (P < 0.025), but only when higher dose of hormone was injected. However, i nsulin had the opposite effect on MnSOD and catalase causing a decreas e in their activities (P < 0.005). The observed changes in the activit ies of the enzymes studied are possible compensations that potentially maintain an optimal H2O2 level in the brainstem, which might be impor tant for insulin action. (C) 1997 Elsevier Science Inc.