Neonatal red cell superoxide dismutase enzyme levels: possible role as a cellular defense mechanism against pulmonary oxygen toxicity.

Red cell superoxide dismutase (SOD) enzyme activity was determined in 58 cord blood specimens obtained from infants over a range of gestational ages. An inverse relationship between red cell SOD activity and gestational age was demonstrated. Red cell SOD activity showed a progressive fall from 263.1 +/- 30.5 units/mg non-hemoglobin protein (NHP) in infants of less than 29 weeks of gestation to 168.9 +/- 21.3 units/mg NHP in infants of more than 36 weeks of gestation (P less than 0.05). Infants treated for RDS showed an increase in red cell SOD activity which reached significance at 72 hr when compared to cord blood levels from the same population (P less than 0.05). No similar significant difference could be demonstrated in gestational age-matched control subjects over the same time period. However, initial cord blood SOD enzyme levels were lower in premature infants with RDS (229.5 +/- 30.6 units/mg NHP) than in premature infants without RDS (264.0 +/- 38.0 units/mg NHP). When infants with RDS were examined for oxygen toxicity and survival, red cell SOD levels were noted to decrease over 24 hr in four of five infants who died, three of whom developed bronchopulmonary dysplasia. In the surviving infants, red cell SOD levels showed a significant increase by 48 hr (P less than 0.05). None developed bronchopulmonary dyplasia and all survived.