ISCHEMIA-REPERFUSION INDUCED MICROVASCULAR DYSFUNCTION IN SKELETAL-MUSCLE - APPLICATION OF INTRAVITAL VIDEO MICROSCOPY

Video microscopy of red cell Row in capillaries at the surface of skel etal muscle provided the opportunity to quantitate ischemia-reperfusio n (I-R) induced microcirculatory changes, in vivo. Extensor Digitorum Longus (EDL) muscles of 22 male Wistar rats (300-400 g), anesthetized with sodium pentobarbital (Somnotol, 65 mg kg,(-1) IP), were used to m easure the number of perfused capillaries (CDper: mm(-1)) crossing lin es drawn perpendicular to the muscle axis, and red blood cell velocity (V-RBC: mm/s) within individual capillaries from controls (n = 6), an d after 2 hr (n = 4), 3 hr (n = 4), and 4 hr (n = 5) of no-how ischemi a with the muscle temperature maintained at its normal value of 32 deg rees C. Ischemia was induced by tightening a tourniquet placed around the limb above the EDL muscle. Measurements were made after 30, 60, an d 90 min of reperfusion. To test the usefulness of this skeletal muscl e model for evaluating proposed interventions in I-R, the effect of hy pothermia (24 degrees C) on the microcirculation following 4 hr ischem ia (n = 3) was measured. Edema formation was estimated from the wet/dr y weight ratio of the ischemic and contralateral control EDL muscles. Capillary perfusion at the surface of the control muscles was remarkab ly stable over the 5 hr period studied, while significant changes occu rred following the ischemic periods. Significantly lower CDper was mea sured 30 min following all periods of normothermic ischemia. However, unlike the 2 and 4 hr ischemic periods 3 hr normothermic ischemia resu lted in a progressive decline in CDper throughout the reperfusion peri od. V-RBC showed evidence of a hyperemic response following 2 hr normo thermic ischemia (control: 0.12 mm/s +/- 0.19 compared to 0.26 mm/s +/ - 0.03 following 90 min reperfusion; mean +/- sem). However, no such h yperemia was measured following either 3 or 4 hr normothermic ischemia (i.e., 3 hr control: 0.24 mm/s +/- 0.01 compared to 0.07 mm s +/- 0.0 03 following 90 min reperfusion). In fact, V-RBC was essentially zero 90 min following 4 hr normothermic ischemia (0.01 mm/s +/- 0.01). Howe ver, when the muscle was allowed to cool to 24 degrees C during 4 hr i schemia no significant change in either V-RBC or CDper was measured co mpared to pre-ischemic controls. Evidence of edema was found after 3 a nd 4 hr normothermic ischemia. This study establishes a skeletal muscl e model of I-R, which may be useful in testing hypotheses regarding me chanisms of I-R injury, and effectiveness of proposed treatments of I- R.