IN-VIVO, CONTINUOUS AND AUTOMATIC MONITORING OF EXTRACELLULAR ASCORBIC-ACID BY MICRODIALYSIS AND ONLINE LIQUID-CHROMATOGRAPHY

A system for in vivo, automatic, continuous monitoring of organ extrac ellular ascorbic acid in anesthetized rat is described. This system in volves microdialysis perfusion and a LC system equipped with an electr ochemical detector. Microdialysate, eluted from a microdialysis probe implanted in the brain cortex or in the left ventricular myocardium of anesthetized rats was collected in the sample loop of an on-line inje ctor for direct injection onto the LC system. This automated method pr ovides a shortened sample processing time. This system was utilized to investigate the effect of cerebral ischemia on cortex extracellular a scorbic acid and the effect of myocardial ischemia on left ventricular myocardium extracellular ascorbic acid in anesthetized rats. Basal as corbic acid concentrations in the cortex and left ventricular myocardi um ranged from 9.7 to 15.4 mu M (mean+/-S.D., 12.7+/-2.5 mu M from the results of eight rats) and from 9.3 to 36.0 mu M (mean+/-S.D., 24.3+/ -8.9 mu M from the results of twelve rats), respectively. Cerebral isc hemia significantly elevated ascorbic acid levels in the cortex extrac ellular space, while myocardial ischemia did not significantly alter a scorbic acid levels in the left Ventricular myocardium extracellular s pace.