Superoxide production in experimental brain injury.

The appearance of superoxide anion radicals in cerebral extracellular space during and after experimental fluid-percussion brain injury was investigated in anesthetized cats equipped with cranial windows. Superoxide was detected by demonstrating the presence of superoxide dismutase (SOD)-inhibitable reduction of nitroblue tetrazolium (NBT). The SOD-inhibitable rate of reduction of NBT was 3.52 +/- 0.72 nM/min/sq cm during brain injury and 4.11 +/- 0.74 nM/min/sq cm 1 hour after injury. No significant superoxide production was detected in control animals. The sustained arteriolar dilation and reduced responsiveness to the vasoconstrictor effects of arterial hypocapnia observed 30 minutes after brain injury were eliminated by after-treatment with topical SOD (60 U/ml) and catalase (40 U/ml). The results show that experimental brain injury causes the generation and appearance in extracellular fluid space of superoxide. Superoxide production continues for at least 1 hour following injury. The sustained dilation and abnormal responsiveness of cerebral arterioles after injury are due to the continued generation of superoxide and other radicals derived from it. These functional changes can be reversed by after-treatment with appropriate scavenging agents.