VALIDATION OF THE INTERNAL REFERENCE TECHNIQUE FOR CALIBRATING MICRODIALYSIS CATHETERS IN-SITU

In vivo calibration of microdialysis catheters with [H-3]glucose as in ternal reference was done in rat (n = 17) and human (n = 12) subcutane ous tissue. The estimated interstitial glucose level was compared with the glucose concentration in venous plasma which, in turn, has been s hown to be identical to the interstitial glucose concentration. In sub cutaneous tissue of anaesthetized male Sprague-Dawley rats, interstiti al glucose was significantly overestimated (43%, P < 0.005, n = 8, and 19%, P < 0.005, n = 9, in normoglycaemic and hyperglycaemic animals, respectively). Furthermore, fractional outflux of [3H]glucose decrease d continuously during prolonged perfusion of the microdialysis cathete r. In contrast, in human subcutaneous tissue microdialysed with two ca theters, correct measurements of interstitial glucose could be achieve d and the precision was comparable to that obtained with equilibration calibration in vivo. The average relative error of the mean result of two catheters was 8.9% at a perfusate flow rate of 1 mu L min(-1). It may be suggested that calibration in vivo of microdialysis catheters with internal references may be used in human subcutaneous tissue. How ever, it is necessary to validate the calibration technique in each di fferent tissue under reproducible experimental conditions since accumu lation of the reference substance in the tissue may create artefactual results.