In vivo 31phosphorus spectroscopy during transient cerebral ischaemia in the gerbil

The depletion of the high energy phosphates; phosphocreatine and ATP, during cerebral ischaemia disrupts normal cellular function and can lead to cerebral infarction. Using in vivo nuclear magnetic resonance spectroscopy, the metabolic effects of the gerbil model of transient bilateral carotid artery occlusion were quantified. By examining the changes in the inorganic phosphate (Pi), phosphocreatine (PCr) and beta-ATP peaks, the PCr/Pi ratio, the PCr/beta-ATP ratio and intracellular pH (pHi) before, during and after an ischaemic insult were calculated. Preischaemic values for these parameters were: PCr/Pi = 2.466 +/- 0.130, PCr/beta-ATP = 1.691 +/- 0.053, pHi = 7.112 +/- 0.021. By the end of 20 min of global ischaemia, the PCr and beta-ATP peaks fell to levels similar to background in most animals. Calculated values were: PCr/Pi = 0.488 +/- 0.126, PCr/beta-ATP = 1.833 +/- 0.179, pHi = 6.551 +/- 0.258. With reperfusion, PCr/Pi increased rapidly back towards preischaemic levels but pHi improvement was delayed 10 min after that of PCr/Pi. By 1 h of reperfusion, both PCr/Pi and pHi were statistically equivalent to preischaemic values. During ischaemia, ATP was lost more rapidly than the storage form, PCr, but recovery of both was parallel. This suggested an intact ability to store such energy. These data indicate that the gerbil brain recovers normal high energy phosphate levels within an hour following a 20 min ischaemic insult, but that initial reperfusion does not immediately correct intracellular acidosis. Such a delay may prove a useful marker of those animals with more severe ischaemic injury.