RAT DIAPHRAGM OXIDATIVE CAPACITY, ANTIOXIDANT ENZYMES, AND FATIGUE - NEWBORN VERSUS ADULT

Little is known about the antioxidant capacity and oxidant-generating potential of newborn muscle, or how these properties compare with the adult and relate to fatigue resistance. We determined the 1) antioxida nt enzyme activities [superoxide dismutase (SOD), catalase, glutathion e peroxidase], 2) glutathione content, 3) oxidative capacity [indexed by succinic dehydrogenase activity], 4) extracellular cytochrome c red uction, and 5) efficacy of exogenously administered SOD in amelioratin g fatigue in vitro of newborn and adult diaphragm (DIA). Newborn and a dult DIA SOD activities were not different, whereas new-born catalase activity was greater, and newborn glutathione peroxidase activity and glutathione content less than adult DIA. Succinic dehydrogenase activi ty was similar to 2-fold greater in the adult compared with the neonat e. Repetitive contractions led to a significant decline in newborn and adult DIA force; this decline was greater in the adult (78 +/- 4% dec rement in force at 2 min) compared with newborn DIA (28 +/- 8% decreme nt in force at ? min). Extracellular cytochrome c reduction was greate r in adult as compared with newborn DIA during fatiguing contractions. Exogenous SOD attenuated fatigue in the adult, but had no effect on n ewborn DIA. We conclude that the oxidative capacity of the adult DIA i s greater than that of the newborn and not matched by a concomitant in crease in SOD activity. Our data suggest that the increased oxidative capacity relative to SOD activity in adult DIA may lead to oxidative s tress and an enhanced susceptibility to fatigue.