Measurement of interstitial albumin in human skeletal muscle and adipose tissue by open-flow microperfusion

The absolute concentration of albumin was measured in the interstitial flui d of subcutaneous adipose tissue and skeletal muscle in six healthy volunte ers by combining the method of open-flow microperfusion and the no-net-flux calibration technique. By use of open-flow microperfusion, four macroscopi cally perforated double lumen catheters were inserted into the tissue regio ns of interest and constantly perfused. Across the macroscopic perforations of the catheters interstitial fluid was partially recovered in the perfusi on fluid. Catheters were perfused with five solutions, each containing diff erent concentrations of albumin. Absolute interstitial albumin concentratio ns were calculated by applying Linear regression analysis to perfusate vs, sampled albumin concentration (no-net-flux calibration technique). Intersti tial albumin concentrations were significantly lower (P < 0.0001) in adipos e tissue (7.36 g/l; r = 0.99, P < 0.0003; range: 43-10.7 g/l) and in skelet al muscle (13.25 g/l; r = 0.99, P < 0.0012; range: 9.7 to 15.7 g/l) compare d with the serum concentration (48.9 +/- 0.7 g/l) mean +/- SE, n = 6; range : 46.4-50.4 g/l). Furthermore, interstitial albumin concentrations were sig nificantly higher in skeletal muscle compared with adipose tissue (P < 0.01 ). The study indicates that open-flow microperfusion allows stable sampling of macromolecules from the interstitial space of peripheral tissue compart ments. Moreover, the present data report for the first time in healthy huma ns in vivo the true albumin concentrations of interstitial fluid of adipose tissue and skeletal muscle.