Comparison of calibration by delivery versus no net flux for quantitative in vivo microdialysis sampling Original Research Article

Various approaches to calibrating microdialysis probes were investigated both in vitro and in vivo in muscle and brain tissue. No differences were found between calibration by recovery, delivery or no net flux experiment in vitro. There was no concentration dependence of the extraction efficiency determined by recovery and the perfusate concentration in vitro. Calibration by delivery experiment was then compared to calibration by no net flux in vivo. No differences were found between the two approaches in muscle tissue for either acetaminophen or caffeine. In the brain, the extraction efficiency determined by delivery was higher for caffeine and lower for acetaminophen than the extraction efficiency determined by no net flux. For caffeine this was determined to be due to saturable active transport across the blood–brain barrier. This active transport resulted in the extraction efficiency being dependent upon the concentration of caffeine in the brain.