NEURONAL NITRIC-OXIDE SYNTHASE INHIBITION REDUCES NEURONAL APOPTOSIS AFTER HYPOTHERMIC CIRCULATORY ARREST

Background. Neurologic injury, including choreoathetosis and learning and memory deficits, occurs after prolonged hypothermic circulatory ar rest (HCA). Apoptosis, or programmed cell death, is a possible cause o f the neurologic injury seen after HCA. However, the mechanism of apop tosis is unknown. Hypothermic circulatory arrest causes glutamate exci totoxicity, resulting in increased nitric oxide production. We therefo re hypothesized that nitric oxide mediates apoptosis. The purpose of t his study was to determine if neuronal nitric oxide synthase inhibitio n reduces neuronal apoptosis in an established canine model of HCA. Me thods. Fourteen male hound dogs (weight, 20 to 27 kg) were placed on c losed-chest cardiopulmonary bypass, subjected to 2 hours of HCA at 18 degrees C, rewarmed to normothermia, and sacrificed 8 hours after HCA. Group 1 (n = 7) dogs were treated with the neuronal nitric oxide inhi bitor 7-nitroindazole, 25 mg/kg intraperitoneally, before arrest and e very 2 hours until sacrifice. Group 2 (n 7) dogs received vehicle only . The brains were analyzed histopathologically. Apoptosis, identified by hematoxylin-eosin staining, was confirmed by DNA terminal deoxynucl eotidyltransferase-mediated dUTP-biotin nick end-labeling assay and el ectron microscopy. Apoptosis was scored by a blinded neuropathologist from 0 (normal) to 100 (severe injury). Results. Apoptosis occurred ea rly after HCA in select neuronal populations, including the hippocampu s, stria terminalis, neocortex, and entorhinal cortex. Apoptotic neuro ns showed a characteristic shrunken cytoplasm and nuclear chromatin co ndensation. 7-Nitroindazole significantly inhibited apoptosis (group 1 versus 2: 19.17 +/- 14.39 versus 61.11 +/- 5.41; p < .001). Conclusio ns. Our results provide evidence that apoptosis is associated with the neurologic injury that occurs after HCA and that nitric oxide mediate s the apoptosis that occurs after HCA. Strategies for cerebral protect ion during HCA may include the inhibition of neuronal nitric oxide syn thase. (C) 1997 by The Society of Thoracic Surgeons.