Background: Microdialysis is a method appropriate for monitoring blood flow and analyte concentrations in interstitium of different tissues.In order tomeasure the changes in tissue blood flow in ratsweused microdialysis with a flow-marker added. The lower the output concentration of flow marker in microdialysis solution the higher the tissue blood flow is. Ethanol is usually used for the purpose in spite of its known disadvantages (volatile, complicated analysis etc.). We tried lithium and gentamicin instead. The aim of this study was to find out changes in the interstitial blood flow in selected tissues in rats before and after partial hepatectomy (PH) or nephrectomy (PN). Methods: After institutional approval 32 Wistar rats (initial body weight 170–230 grams) were divided into 4 groups according to different treatment they underwent: Group 1: microdialysis probe CMA 20 (CMA Microdialysis, Solna, Sweden, cut off 20 20.000, the length of dialysis membrane 4 mm) was inserted into a skeletal muscle on a medial side of the quad and into an intact liver. Group 2: microdialysis probe was inserted into a skeletal muscle, and into liver remnant after 67% partial hepatectomy. Group 3: microdialysis probe was inserted into a skeletal muscle and an intact kidney. Group 4: microdialysis probe was inserted into a skeletal muscle and kidney remnant after 5/6 nephrectomy. The concentration of the lithium (Flame photometer EFOX 5053) and gentamicin (Axsym – FPIA) was then measured. All described procedures on rats were done under general pentobarbital anesthesia. SigmaStat software (Jandel Scientific Corporation) was used for statistical data evaluation. Results: The concentration of lithium in microdialysate from liver was higher in the first group than in the secondgroup.According to lithium microdialysateconcentration,the blood flow afterPHincreased.Theopposite happened in the third and fourth group where the lithium concentration in microdialysate from kidney was higher than in the third group, so that the blood flow after PN decreased. There were no significant differences between microdialysate lithium concentrations from skeletal muscle from rats before and after PH and PN, i.e. blood flow was the same. The blood flow according to the concentration of gentamicine was different than expected. The concentration of gentamicin in microdialysate was higher than its concentratio in perfusion fluid. These results indicate that gentamicin diffusion throughmicrodialysatemembranewasmore difficult than water diffusion. Conclusion: Our results indicate that gentamicin is not suitable as a flow-marker. Lithium is an appropriate flow-marker. Based on lithium microdialysate concentrations we can conclude that after PH the blood flow in liver interstitium increased. In contrast after PN the blood flow in kidney interstitium decreased.

        Key words: partial hepatectomy, partial nephrectomy, rat, gentamicin, lithium, microdialysis.