Effects of the endothelin receptor antagonist Bosentan on ischaemia/reperfusion injury in rat skeletal muscle

We examined the role of endothelin in ischaemia/reperfusion injury in skele tal muscle. using the endothelin receptor antagonist Bosentan. In the rat h indlimb tourniquet ischaemia model, one hindlimb was rendered ischaemic for 2 h at 36 degreesC. then blood flow was re-established for either 24 h to assess muscle survival or 1.5 h for a study of capillary perfusion. In the first set of rats, the gastrocnemius muscle was removed from the postischae mic limb and assessed for viability histochemically using the nitro blue te trazolium stain. Tissue water content (a measure of oedema) and myeloperoxi dase activity (a measure of neutrophil accumulation) were also assessed in the ischaemic muscle, the contralateral non-ischaemic muscle and the lungs. In the second set of rats, the hind limb was infused with India ink after 2-h ischaemia and 1.5-h reperfusion and the muscle was harvested, fixed and cleared. In control rats, muscle viability was 17 +/- 2% (S.E.M.). In rats treated with Bosentan (10 mg/kg, i.p.) 30 min before release of the tourni quet, muscle viability (48 +/- 7%) was significantly increased compared to the control group (P < 0.01). Bosentan treatment had no significant effect on tissue water content or myeloperoxidase activity in the ischaemic muscle , the contralateral non-ischaemic muscle or the lung. Immunoreactive endoth elin levels in serum increased to a peak at 90 min of reperfusion and retur ned to control levels by 24-h reperfusion. India ink studies demonstrated a significantly increased functional capillary density in postischaemic Bose ntan-treated muscles compared with postischaemic control muscles ( P < 0.05 ). These results suggest that endothelin plays an important role in the nec rosis which results from a period of ischaemia and reperfusion in skeletal muscle, by mediating a decrease in postischaemic microvascular perfusion. ( C) 2001 Elsevier Science B.V. All rights reserved.