Assessment of transcapillary glucose exchange in human skeletal muscle and adipose tissue

1 Department of Biophysics, Institute of Biomedical Engineering, Graz University of Technology; and Departments of 2 Biochemical Analysis and Mass Spectrometry and 3 Internal Medicine, Diabetes and Metabolism, Karl Franzens University Graz, A-8010 Graz, Austria Submitted 9 August 2002 ; accepted in final form 5 April 2003 We studied the kinetics of glucose exchange between plasma and interstitial fluid (ISF) in human skeletal muscle and adipose tissue under fasting conditions. Five normal human subjects received an intravenous [6,6- 2 H 2 ]glucose infusion in a prime-continuous fashion. During the tracer infusion, the open-flow microperfusion technique was employed to frequently sample ISF from quadriceps muscle and subcutaneous adipose tissue. The tracer glucose kinetics observed in muscle and adipose tissue ISF were found to be well described by a capillary-tissue exchange model. As a measure of transcapillary glucose exchange efficiency, the 95% equilibrium time was calculated from the identified model parameters. This time constant was similar for skeletal muscle and adipose tissue (28.6 ± 3.2 vs. 26.8 ± 3.6 min; P = 0.60). Furthermore, we found that the (total) interstitial glucose concentration was significantly lower ( P < 0.01) in muscle (3.32 ± 0.46 mmol/l) and adipose tissue (3.51 ± 0.17 mmol/l) compared with arterialized plasma levels (5.56 ± 0.13 mmol/l). Thus the observed gradients and dynamic relationships between plasma and ISF glucose in muscle and adipose tissue provide evidence that transcapillary exchange of glucose is limited in these two tissues under fasting conditions. open-flow microperfusion; interstitial fluid; capillary-tissue exchange model Address for reprint requests and other correspondence: W. Regittnig, Dept. of Biophysics, Institute of Biomedical Engineering, Graz Univ. of Technology, Krenngasse 37, A-8010 Graz, Austria (E-mail: werner.regittnig{at}healthgate.at ).