Effect of temperature on the kinetics of lactate production and clearance in a rat model of forebrain ischemia.

To investigate the effect of brain temperature on metabolic perturbations during and following forebrain ischemia, localized 1H magnetic resonance spectroscopy was used to measure the kinetics of lactate production and clearance in a rat model of 12- or 20-min forebrain ischemia (two-vessel occlusion with hypotension) at a brain temperature of either 34.5 +/- 0.5 degrees C or 37.5 +/- 0.5 degrees C. During ischemia, lactate production was modeled with apparent first order kinetics. Hypothermia did not affect the rate or the extent of lactate production during ischemia. Upon reperfusion, a delay in the decrease of the cerebral lactate level was found in the normothermia groups. Such a delay was absent in hypothermia groups, which may reflect faster resumption of cerebral oxidative metabolism upon reperfusion in the hypothermic animals. The rate constant for lactate clearance postischemia was larger for normothermic animals and for the 20-min ischemia groups, perhaps because of increased blood-brain barrier permeability following more severe ischemia.