Endothelin Receptor Blockade as a Therapeutic Strategy in Ameliorating Postischemic Damage to the Liver Microcirculation

Ischemia leads to profound endothelin- (ET) related constriction of hepatic microvessels, causing disturbances in blood and oxygen supply. The aim of the study was to modulate hepatic microvascular diameters by blocking ET receptors to find the optimal therapeutic vessel width for reduction of ischemia-reperfusion injury. In an in vivo model (84 female Wistar rats, 250-300 g) with portal decompression by means of a splenocaval shunt, normothermic hepatic ischemia was induced for 30 min by crossclamping of the hepatoduodenal ligament. The ET receptor antagonist (ERA) bosentan was administered before induction of ischemia in different dosages [0.1, 1.0 and 10.0 mg/kg body weight (BW) i.v. and 10 mg/kg BW intraportally (i.p.)]. The effect on microcirculation was assessed by in vivo microscopy and influence on hepatocellular function by measurement of aspartate aminotransferase (AST) levels. Sinusoidal diameters were reduced as a result of ischemia to 76.3 +/- 7.4% compared with values received from sham-operated animals. After application of 0.1 mg/kg of bosentan, sinusoids remained constricted (89.7 +/- 9.9%, AST 255.0 +/- 12.8 U/l). Blocking ET receptors with 1 mg/kg bosentan avoided sinusoidal constriction (99.0 +/- 8.8%, p0.05) and led to the most effective reduction of AST level peak after 6 h of reperfusion (244.0 +/- 34.2 U/l vs 422.9 +/- 163.3 U/l in untreated ischemia). Bosentan (10 mg/kg i.v.) caused an increase in sinusoidal diameter to 109.1 +/- 6.4% (AST 311.7 +/- 33.6 U/l) and 10 mg/kg i.p. to 136.8 +/- 19.3% and even increase AST levels (618.90 +/- 209.32 U/l). After intravenous application of 1 and 10 mg/kg BW bosentan the perfusion rate was significantly increased and sticking of leukocytes in sinusoids and venules reduced (p0.05). In our model, diameters of sinusoids and postsinusoidal venules could be regulated gradually. We conclude that the avoidance of constriction, but not an excessive vasodilation leads to increased perfusion rate and hence improved hepatocellular function.