INFLUENCE OF PERFUSATE GLUCOSE-CONCENTRATION ON DIALYSATE LACTATE, PYRUVATE, ASPARTATE, AND GLUTAMATE LEVELS UNDER BASAL AND HYPOXIC CONDITIONS - A MICRODIALYSIS STUDY IN RAT-BRAIN

The aim of this study was to evaluate the influence of perfusion media with different glucose concentrations on dialysate levels of lactate, pyruvate, aspartate (Asp), and glutamate (Glu) under basal and hypoxi c conditions in rat brain neocortex. Intracerebral microdialysis was p erformed with the rat under general anesthesia using bilateral probes (o.d. 0.3 mm; membrane length, 2 mm) perfused with artificial CSF cont aining 0.0 and 3.0 mM glucose, respectively. Basal dialysate levels we re obtained 2 h after probe implantation in artificially ventilated an imals. Dialysate levels of glucose were also measured for the two diff erent perfusion fluids. The mean absolute extracellular concentration of glucose was estimated by a modification of the no-net-flux method t o be 3.3 mmol/L, corresponding to an average in vivo recovery of 6% fo r glucose. Hypoxia was induced by lowering the inspired oxygen concent ration to 3%. Hypoxia caused a disturbance of cortical electrical acti vity, evidenced by slower frequency and lower amplitudes on the electr oencephalogram compared with prehypoxic conditions. This was associate d with significant elevations of lactate, Asp, and Glu levels. There w ere no statistically significant differences in dialysate metabolite l evels between the two perfusion fluids, during either normal or hypoxi c conditions. We conclude that microdialysis with glucose-free perfusi on fluid does not drain brain extracellular glucose in anesthetized ra ts to the extent that the dialysate lactate, pyruvate, Asp, and Glu le vels during basal or hypoxic conditions are altered.