Influence of Complete and Pronounced Incomplete Cerebral Ischemia and Subsequent Recirculation on Cortical Concentrations of Oxidized and Reduced Glutathione in the Rat

The influence of complete and pronounced incomplete cerebral ischemia on cortical concentrations of reduced (GSH) and oxidized (GSSG) glutathione was studied in lightly anaesthetized (70% N 2 O) rats. GSH was extracted with HCl‐methanol‐perchloric acid and GSSG with trichloroacetic acid in the presence of N ‐ethylmaleimide and measured fluorometrically, giving normal concentrations in cortical tissue of about 2 and 0.01 μmol.g −1 respectively. Reversible complete ischemia was induced by increasing the intracranial pressure to above the systolic blood pressure by infusing mock CSF into the cisterna magna. Reversible pronounced incomplete ischemia was induced by bilateral carotid artery clamping combined with hypovolemic hypotension. Whether complete or incomplete, a 30‐min ischemic period caused a similar decrease in cortical GSH concentration (to about 90% of control) without any concomitant accumulation of GSSG in the tissue (or in CSF). Prolongation of the ischemic period (complete ischemia) to maximally 120 min caused an almost linear decrease of the tissue glutathione concentration to 45% of the preischemic value. During subsequent recirculation following a 30 min period of either complete or pronounced incomplete ischemia, there was a further decrease in cortical GSH concentrations without a reciprocal increase in GSSG concentrations. Lipid peroxidation (verified by determination of malondialdehyde production) induced in brain cortical tissue in vitro caused oxidation of tissue GSH with accumulation of GSSG. As the observed decrease in GSH during brain ischemia in vivo was not accompanied by any reciprocal increase in GSSG the results fail to support the hypothesis that peroxidative damage occurs during or following brain ischemia. The finding of an unchanged GSSG concentration does, however, not exclude the possibility of an increased turnover rate in the glutathione reductase reaction. It is concluded that the observed decrease in tissue GSH concentration mainly reflects a decrease in the glutathione pool size, due to an imbalance between breakdown and synthesis secondary to tissue energy failure.