Continuous ultraslow microdialysis and ultrafiltration for subcutaneous sampling as demonstrated by glucose and lactate measurements in rats

Classical microdialysis has some drawbacks. Two main issues in this respect are the time-consuming calculations (due to partial recovery of an analyte) and depletion near the sampling site. In this paper we describe a sampling method, called ultraslow microdialysis (usMD), and compare this with ultrafiltration (UF) at flow rates between 100 and 300 nL/min. As an example of an application of this method, we conducted a dual-enzyme analysis for simultaneous measurement of the glucose and lactate concentrations, demonstrating these sampling techniques in the subcutaneous tissue of the rat. For UF, the flow rates in vitro and in vivo were the same. For usMD, the recovery for glucose and lactate at the applied flow rates was 100%, in contrast to conventional microdialysis. Both sampling techniques have the potential of on-line in vivo monitoring, as well as the measurement of time profiles of analytes by continuous collection and off-line analysis afterward.