Title: 82 CEREBRAL NITRIC OXIDE SYNTHETASE ACTIVITY FOLLOWING HYPOXIA IN NEWBORN PIGLETS
Abstract: Recent studies in animal models suggest, that nitric oxide (NO), produced by nitric oxide synthetase (NOS) during conversion of L-arginine into L-citrulline, is a source of free radicals following hypoxia. The present study tested the hypothesis that NOS was altered in cortical tissue after one hour of cerebral hypoxia. Newborn piglets (6 hypoxia, 6 normoxia) were anesthetized and ventilated; hypoxia was induced by lowering the FiO2 to 0.05-0.07 in the hypoxia group, and was maintained for one hour. Cerebral cortical tissue obtained from each piglet was homogenized and dialyzed for 6 hours to remove endogenous arginine. The activity of NOS was assessed using the conversion of 3H-L-arginine into 3H-L-citrulline in the presence of calcium and NADPH, followed by counting the amount of 3H-L-citrulline formed after removal of 3H-L-arginine by ion-exchange. Due to NOS activity NO and 3H-L-citrulline are formed on an equimolar basis. Results showed, that NOS activity was present in both groups: normoxia: 265±85, hypoxia: 230±165 fmol NO/mg protein/min. Differences between the hypoxia and normoxia groups were not significant. The results indicate that cerebral NOS in newborn piglets is resistant to hypoxia. The present in vitro data do not preclude, that NOS activity is increased in vivo during hypoxia by a cellular influx of calcium, thereby possibly contributing to the formation of free radicals and membrane lipid peroxidation following hypoxia. Funded by NIH #HD-20337, USA and Ter Meulen Fund, the Netherlands.