Involvement of the endothelin system in experimental critical hind limb ischemia

Background: Endothelin-1 (ET-1) is involved in the pathogenesis of several ischemic diseases. We investigated the hypotheses that ET-1 is involved in the pathogenesis of experimental critical hind limb ischemia and that ET-1 receptor antagonists have a protective effect. Materials and Methods: Critical hind limb ischemia was achieved by exclusio n of the femoral artery and embolization of collateral vessels in rats. The induction of endothelin system components by ischemia was analyzed by reve rse transcription-polymerase chain reaction (RT-PCR) (mRNAs) and immunoassa y (peptides) in the plasma and ischemic muscles 5 hr (H5), 5 days (D5) and 14 days (D14) after ischemia. Two groups of rats received 100 mg/kg/day of either Bosentan, a mixed ETA/B receptor antagonist (n = 12), or LU 135252, a selective ETA receptor antagonist (n = 9), and a control group without tr eatment (n = 12) served as control. Muscle blood flow and ischemia were mon itored in the ischemic limb by laser Doppler and phosphorylase activity, re spectively. Results: The procedure induced an 80% decrease in muscle blood now and comp lete suppression of phosphorylase activity without necrosis. At day 14, the tissue blood flow remained reduced by 70% and phosphorylase activity was s uppressed completely. There was up-regulation of preproendothelin-1, prepro ET-3, endothelin converting enzyme-1, and ETA. ETB receptor mRNAs in ischem ic muscle at day 5 and day 14 was accompanied by an increase in muscle conc entration of ET-1 at day 5, without significant changes in plasma endotheli n. Treatment with Bosentan and LU 135252 increased tissue blood flow and re duced muscle ischemia at day 14. Conclusions: Tissue production of ET-1 is up-regulated in experimental crit ical hind limb ischemia. Inhibition of the endothelin system by a mixed ETA /B receptor antagonist may protect, at least in part, against muscle injury .