PHARMACOLOGICAL MANIPULATION OF GASTROCNEMIUS-MUSCLE BLOOD-FLOW IN AN ANIMAL-MODEL OF REPERFUSION INJURY

Despite technically satisfactory surgery for acute lower limb ischaemia reperfusion injury may result in failure of limb salvage and the need for amputation. An animal model using the rat hind limb has been developed which demonstrates this complication. A tourniquet was applied to one hind limb for 6 h and then released. Gastrocnemius muscle blood flow in both hind limbs was assessed using radiolabelled microspheres and a perfusion index calculated between the revascularized and normal hind limbs and the results compared with similar measurements in control animals and rats with a tourniquet still in situ (ischaemic). Following 10 min the median perfusion index in reperfused animals was significantly less than that in control animals (0.12 +/- 2 inter-quartile range 0.02-0.43) versus 1.05 (0.68-1.18), P < 0.01) but similar to the results in rats with a tourniquet still in situ [0.04 (0.00-0.07), ns], thus demonstrating low reflow following tourniquet release. After 120 min revascularization a phase of relative reperfusion occurred with perfusion indices becoming higher than those in animals with a tourniquet in situ (0.48 (0.11-0.70) versus 0.02 (0.01-0.07), P < 0.05) but remaining lower than those in control rats [0.97 (0.79-1.13), P < 0.05]. Finally after 240 min, reperfusion injury occurred with perfusion being similar to that in animals with a tourniquet applied [0.05 [0.01-0.38) versus 0.03 (0.00-0.07), ns] and less than that in the normal rats [1.01 (0.73-1.16), P < 0.01]. Attempts to modify these reductions in muscle perfusion pharmacologically have demonstrated that a superoxide radial scavenger (superoxide dismutase and catalase) abolished low reflow (0.94 (0.54-1.12) versus 0.12 (0.02-0.43), P < 0.01). In contrast dimethylthiourea, an hydroxyl radical scavenger, prevented the phase of relative reperfusion (0.04 (0.02-0.21) versus 0.48 (0.11-0.70), P < 0.01. Sodium nitroprusside, a vasodilator, increased perfusion at 240 min [0.41 (0.11-1.22] versus 0.05 (0.01-0.38], P < 0.05] with 6 out of 15 rats having a normal perfusion index at the time when reperfusion injury would be expected to occur.