FREE-RADICALS AND THE ISCHEMIA-EVOKED EXTRACELLULAR ACCUMULATION OF AMINO-ACIDS IN RAT CEREBRAL-CORTEX

The effects of free radical generating systems on basal and ischemia/r eperfusion-evoked release of amino acids into cortical superfusates wa s examined in the rat using the cortical cup technique. Xanthine oxida se plus xanthine significantly enhanced GABA levels 358 fold over cont rols during 20 min of four vessel occlusion. Glutamate and phosphoetha nolamine release following reperfusion were also elevated. Prostagland in synthase plus arachidonic acid significantly enhanced the ischemia- evoked release of all amino acids (aspartate 360 fold; glutamate 433 f old; glycine 6 fold; GABA 689 fold; phosphoethanolamine 69 fold) and i ncreased the pre-ischemic levels of glutamate, glycine and phosphoetha nolamine. Administration of H2O2 plus ferrous sulfate significantly el evated both pre-ischemic amino acid release and ischemia-evoked releas e. A role for free radical generating systems in the development of is chemic injury is supported by the ability of superoxide dismutase plus catalase to reduce ischemia-evoked amino acid efflux into cortical su perfusates. Thus, the species of free radical produced, as well as the amount generated, may alter the pattern of amino acid release under b oth ischemic and non-ischemic conditions.