Assessment of ischemia reperfusion injury in skeletal muscle by macromolecular clearance.

Qualitative changes in skeletal muscle injury after ischemia are well known; however, quantitative assessments have not been well documented. We have determined microvascular permeability changes by measuring the clearance of fluorescein-labeled dextran of MW 150,000 (FITC-Dextran-150). The cremaster muscle of anesthetized rats was fashioned as a single layer, splayed on a lucite chamber and suffused with bicarbonate buffer solution at 35 degrees C. Clearance is the product of suffusion rate times the ratio of suffusate to plasma concentrations of FITC-Dx 150. After a 1-hr period of baseline data collection, ischemia was produced by cross-clamping the cremasteric vascular pedicle for periods of 30 min and 2 hr in separate experiments. Clearance of FITC-Dx 150 increased from a control value (mean +/- SE) of 8.3 +/- 2.7 to 29.9 +/- 8.1 microliters/min/g after reperfusion following a 30-min period of ischemia, and from a control value of 36.2 +/- 13.6 to 274 +/- 94.5 after 2 hr of ischemia. The differences were statistically significant (P less than 0.05). Our results show a significant increase in microvascular permeability occurring after only 30 min of ischemia. They also demonstrate a direct relationship between the extent of the permeability change and the duration of the ischemic period.