Perfusate oxygen and carbon dioxide concentration influence basal microdialysate levels of striatal glucose and lactate in conscious rats.

O(2) concentration ([O(2)]) in air equilibrated solutions at room temperature is three fold higher than that in brain extracellular fluid (ECF), and CO(2) concentration ([CO(2)]) is 100 times lower. Using microdialysis the ECF is routinely dialyzed against glucose free isotonic perfusates containing 200 microM O(2) and 10 microM CO(2). In conscious rats, 2 days after probe implantation, decreasing perfusate [O(2)] from 200 to 68 microM (physiologic level) for 60 min, while maintaining a low [CO(2)] (10 microM), increased striatal dialysate glucose and lactate by 12% and 33%, respectively. The same protocol on the third day essentially had no effect on monoamine metabolites. Decreasing [O(2)] concurrent with increasing [CO(2)] to 1.3 mM (physiologic level) for 60 min increased glucose and lactate by 17% and 37%, respectively. This study demonstrates for dialysis studies of glucose and lactate, perfusates that mimic physiologic ECF [O(2)] and [CO(2)] are more appropriate.