Brain tissue concentrations of ATP, phosphocreatine, lactate, and tissue pH in relation to reduced cerebral blood flow following experimental acute middle cerebral artery occlusion.

Local CBF (LCBF) was compared with the corresponding local tissue concentration of ATP, phosphocreatine (PCr), and lactate in anaesthetized baboons subjected to focal ischaemia produced by middle cerebral artery occlusion (MCAO). LCBF hydrogen electrodes were implanted in cortical regions where MCAO had been previously shown to produce severe and penumbral ischaemia and in posterior regions where blood flow is not altered. Metabolites were assayed in small tissue samples collected either by cryoprobe biopsy in the regions where LCBFs were measured (series 1) or by sampling appropriate regions of the rapidly frozen brain (series 2). Subsequent topographical study of brain tissue pH with umbelliferone was performed in this latter series. The results from these two series are compared and discussed in terms of the more appropriate way to perform simultaneous electrode measurements and analysis of tissue samples for studying focal ischaemia in the primate brain. They confirm that the concentrations of ATP and PCr decrease, and that lactate level increases, with decreasing blood flow. These metabolites tended to change more rapidly below a blood flow threshold, rather than showing a steady decrease as the blood flow was reduced, although the variability of the data precluded us from establishing this with confidence. Topographical study of tissue pH often showed sharp boundaries between zones of very low pH and regions with normal pH.