1. Biochemical mechanisms of ischaemia were investigated in rabbit skin flaps subjected to 2 h of primary ischaemia then, 24 h later, to 4 h of secondary ischaemia. During secondary ischaemia, flaps underwent either total ischaemia (arterial and venous blood supply occluded) or partial ischaemia (vein only occluded). Some of these flaps were treated at the time of reperfusion with the free-radical scavenger superoxide dismutase (EC and/or the thromboxane synthetase inhibitor UK-38,485.

2. After 30 min of reperfusion, superoxide dismutase treatment significantly reduced blood thromboxane levels, elevated during ischaemia. Superoxide dismutase also reduced tissue levels of malonyldialdehyde and xanthine oxidase, indicators of free-radical damage, and restored the depleted tissue levels of superoxide dismutase.

3. UK-38,485 treatment failed to significantly alter any of these tissue free-radical parameters, although this agent significantly reduced blood thromboxane levels.

4. Combined superoxide dismutase plus UK-38,485 treatment was not significantly better than either treatment alone with respect to any parameter.

5. Partial ischaemia led to consistently higher levels of tissue free radicals and blood thromboxane than did total ischaemia. Thus partial ischaemia appears to result in greater free-radical damage than total ischaemia.

6. These results are consistent with the hypothesis that thromboxane acts as a mediator for free-radical damage in the ischaemic changes within the flap.

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