METABOLIC AND ANTIOXIDANT ENZYME-ACTIVITIES IN THE DIAPHRAGM - EFFECTS OF ACUTE EXERCISE

Disruption of cellular constituents including inhibition or ''downregu lation'' of metabolic enzyme activity has been associated with free ra dical stress in locomotor muscle with acute, strenuous exercise. Howev er, the effects of acute, strenuous exercise on important metabolic an d antioxidant enzyme activity levels in the diaphragm are unknown. Twe nty 4-month-old and twenty 24-month-old female Fischer-344 rats were d ivided at random into young exercised (YE; n = 10)/ old exercised (OE; n = 10); young control (YC; n = 10)/old control (OC; n = 10) groups. Animals in both young and old exercise groups ran on a treadmill (10% uphill grade) for 40 min at similar to 75% of age group V(O2)max. Imme diately following the treadmill run, both exercise and control groups were euthanized with sodium pentobarbital. Costal (COD) and crural dia phragm (CRD) were quickly removed and frozen in liquid nitrogen. Lipid peroxidation was significantly increased (P<0.05) in COD of YE vs. YC rats. Activity of the antioxidant enzyme glutathione peroxidase (GPX) was unaltered in the diaphragm by acute exercise (P>0.05) in both age groups. There was a significant increase in superoxide dismutase (SOD ) activity with exercise (P<0.05). Post-hocs revealed SOD activity was similar to 20% greater (P = 0.066) in YE CRD only. Activities of the metabolic enzymes phosphofructokinase (PFK), succinate dehydrogenase ( SDH), and citrate synthase (CS) were not affected by acute exercise in YE or OE. Strenuous exercise resulted in a small trend towards a decr ease in 3-hydroxyacyl-CoA dehydrogenase (HADH) activity in YE COD (P = 0.115) and YE CRD (P = 0.082). We conclude that the employed bout of exercise induces some free radical stress, while metabolic enzymes are protected, in the diaphragm.