Oxygen free radicals potentiate tissue injury in critically ill newborns who are exposed to high concentrations of oxygen. Superoxide dismutase (SOD), an antioxidant, protects tissues from damage by oxygen free radicals. Extracellular SOD (EC-SOD) is bound to the vascular extracellular matrix by heparan sulfate. In adults, high doses of H competitively releases EC-SOD from the vascular matrix into the blood, where it is rapidly degraded. The purpose of this study is to determine whether exogenous H can release EC-SOD from the extracellular matrix of human umbilical cord veins. Blood was removed from cord veins by flushing with Dulbecco's Phosphate Buffered Saline (DPBS). The cords were clamped in half. One half of the vein was incubated with DPBS at 37°C, while the other half was incubated with an equal volume of DPBS containing H (175 H units/ml). Levels of EC-SOD (expressed as mean SOD units/ml ± S.D., n = 5) were measured by the cytochrome C method in samples taken at 10 min and at 24 hr: Table H resulted in up to a 2.5 fold increase in EC-SOD. These data suggest that high doses of H administered to neonates may increase their vulnerability to damage by oxygen free radicals by releasing EC-SOD from the vascular extracellular matrix.

Table 1
Full size table