RESUMEN
INTRODUCTION: Endothelin (ET) and nitric oxide (NO) act as opponents in the regulation of the hepatic microcirculation. During ischemia/reperfusion (I/R) ET levels are increased, whereas no rise in NO levels is observed. This imbalance may be responsible for microcirculatory disturbances. The aim of this study was to restore the delicate ET/NO balance to maintain the integrity of the hepatic microcirculation and to reduce I/R injury. METHODS: Ischemia was induced by crossclamping of the hepatoduodenal ligament for 30 min with portal decompression using a splenocaval shunt (56 Wistar rats, 200-250 g). Sham operation, ischemia and treatment groups with the endothelin receptor antagonist (ERA) bosentan (1 mg/kg body weight i.v.) and the NO donor L-arginine (400 mg/kg body weight i.v.) were performed. For assessment of the microcirculation, sinusoidal perfusion rate, diameters of sinusoids and postsinusoidal venules, leukocyte endothelium interactions and velocity of free-flowing leukocytes were investigated by means of in vivo microscopy 30-90 min after reperfusion. Local hepatic tissue PO2 was measured prior to ischemia, 30 min and 60 min after reperfusion and aspartate aminotransferase (AST)/alanine aminotransferase (ALT) levels were investigated 2 h and 6 h after reperfusion. RESULTS: After ischemia, sinusoidal and venular diameters were reduced to 76% and 85%, respectively, of sham operation group values (P<0.05), but were maintained at baseline in ERA (98/102%) and NO (102/105%) groups (P<0.05). Increased postischemic leukocyte sticking in sinusoids (144%) and venules (435%) was reduced by therapy to 110/253% (ERA) and 111/ 324% (NO), respectively (P<0.05). Perfusion rate was increased to 93% and 94% compared with 82% in the ischemia group (P<0.05). Concomitant with the improved microcirculation in therapy groups, local hepatic tissue pO2 was improved 30 min after reperfusion in the ERA (11.0 mmHg) and the L-arginine group (11.5 mmHg) relative to the ischemic group (6.9 mmHg) (P<0.05). In addition, postischemic AST/ALT increase was reduced by therapy. CONCLUSION: Our results indicate that maintenance of ET/NO balance by blocking ET receptors, as well as providing a NO donor, protects the liver microcirculation and reduces hepatic I/R injury.
Asunto(s)
Endotelinas/metabolismo , Hígado/irrigación sanguínea , Óxido Nítrico/metabolismo , Daño por Reperfusión/metabolismo , Alanina Transaminasa/sangre , Animales , Arginina/farmacología , Aspartato Aminotransferasas/sangre , Bosentán , Antagonistas de los Receptores de Endotelina , Femenino , L-Lactato Deshidrogenasa/sangre , Microcirculación/fisiología , Donantes de Óxido Nítrico/farmacología , Ratas , Ratas Wistar , Sulfonamidas/farmacologíaRESUMEN
UNLABELLED: Hepatic ischemia followed by reperfusion evokes an imbalance between the vasoregulatory compounds endothelin and nitric oxide (NO) followed by constriction of the vascular bed, leading to microcirculatory disturbances and reduced blood flow, thereby causing hypoxia and liver damage. The aim of this study was to protect the liver microcirculation by maintaining this delicate balance. MATERIAL AND METHODS: In an in vivo ischemia/reperfusion model with portal decompression by a splenocaval shunt, hepatic ischemia was induced for 30 min by Pringle's maneuver. The effect of the NO donor L-arginine (400 mg/kg b.w. i.v.) was assessed by in vivo microscopy. Microhemodynamic studies, including the sinusoidal perfusion rate, diameters of hepatic sinusoids and postsinusoidal venules, leukocyte endothelium interactions and leukocyte velocity were performed. Microcirculatory data were compared with local tissue pO2 and serum transaminase levels. RESULTS: After ischemia the diameters of sinusoids and postsinusoidal venules were significantly reduced to 76+/-7 and 86+/-10% respectively in the nontreatment group, but dilated to 102+/-3 and 105+/-7% in the group treated with L-arginine (p < 0.001). The percentage of permanently adherent leukocytes in sinusoids and venules was increased by ischemia, but L-arginine reversed this increase (p < 0.001). Perfusion rate was improved to 90+/-2 compared with 83+/-5% in the untreated group (p < 0.01). Systemic arterial blood pressure was not affected by administration of the NO donor. The postischemic increase in serum transaminase levels was diminished in the treatment group (ASAT: p < 0.05). Local postischemic hepatic tissue pO2 was significantly decreased to 45% of basal values after 30 min and to 55% after 60 min of reperfusion (p < 0.05). Administration of L-arginine results in a significant increase in local tissue pO2 to 86 and 106% of basal values respectively (p < 0.05). CONCLUSION: These data indicate that L-arginine improves hepatic microcirculation after warm ischemia by increasing sinusoidal perfusion rate and by diminishing leukocyte endothelium interactions. Maintained integrity of microcirculation is associated with sufficient oxygen supply and improved hepatocellular function.
Asunto(s)
Arginina/farmacología , Isquemia/prevención & control , Circulación Hepática/efectos de los fármacos , Daño por Reperfusión/prevención & control , Animales , Femenino , Hígado/metabolismo , Microcirculación/efectos de los fármacos , Oxígeno/metabolismo , Presión Parcial , Ratas , Ratas Wistar , Transaminasas/metabolismoRESUMEN
Elevated levels of endothelin (ET) are measured during ischemia and reperfusion, but no adequate increase of nitric oxide (NO) can be observed. Thus, the balance of both substances, which occurs under physiological conditions and regulates microcirculatory vessel widths, is disturbed. This leads to microcirculatory damages. As well ET receptor blocking using a mixed ET receptor antagonist as increase of NO production after L-arginine treatment influenced this pathomechanism. The preischemic sinusoidal diameters were maintained and leukocyte endothelial interactions reduced. Concomitantly, sinusoidal perfusion rate and local hepatic tissue pO2 were increased. Because of significant reduced hepatocellular damage in both therapy groups both therapeutical ways might exert beneficial effects to attenuate ischemia/reperfusion induced microvascular and tissue injury.
Asunto(s)
Endotelinas/fisiología , Hígado/irrigación sanguínea , Óxido Nítrico/fisiología , Daño por Reperfusión/fisiopatología , Animales , Femenino , Isquemia/fisiopatología , Microcirculación/fisiopatología , Ratas , Ratas Wistar , Resistencia Vascular/fisiologíaRESUMEN
Endothelin evokes strong and longlasting constriction of postischemic sinusoids, leading to microcirculatory disturbances and local hypoxia, thereby causing liver damage. The aim of the study was to avoid the constrictive response of sinusoids by blocking endothelin receptors. In an in vivo ischemia-reperfusion model (21 female Wistar rats, 250-300 g) with portal decompression by a splenocaval shunt, hepatic ischemia was induced for 30 min by cross clamping of the hepatoduodenal ligament. The endothelin receptor antagonist bosentan (10 mg/kg bw IV) was administered before ischemia. The effect of the receptor antagonist was assessed by serum levels of aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT) that were determined prior to ischemia, 2 and 6 h postoperatively. The local tissue pO2 was measured prior to inducing ischemia, 30 and 60 min after reperfusion. Application of 10 mg/kg bw endothelin receptor antagonist (ERA) intravenously did not influence the systemic blood pressure. The postischemic increase in serum ASAT and ALAT levels was diminished after receptor antagonist treatment (ASAT: p < .05). Local postischemic hepatic tissue pO2 was significantly decreased to 45% of basal values after 30 min and to 54.8% after 60 min of reperfusion (p < .05). Application of ERA results in a significant increase in local tissue pO2 to 110.9% of basal values after 30 min and to 90.7% after 60 min of reperfusion (p < .05). These data indicate that the endothelin receptor antagonist treatment results in a prevention of postischemic sinusoidal constriction avoiding hypoxia and leading to improved hepatocellular recovery.
Asunto(s)
Antagonistas de los Receptores de Endotelina , Hígado/irrigación sanguínea , Oxígeno/sangre , Daño por Reperfusión/tratamiento farmacológico , Sulfonamidas/farmacología , Animales , Presión Sanguínea , Bosentán , Femenino , Hígado/cirugía , Ratas , Ratas Wistar , Daño por Reperfusión/sangre , Vasoconstrictores/farmacologíaRESUMEN
UNLABELLED: One mechanism evoked by ischemia is endothelin mediated vasoconstriction of the hepatic vascular bed. Postischemic sinusoidal constriction leads to microcirculatory disturbances and reduced blood flow, thereby causing local hypoxia and liver damage. The aim of the study was to avoid the constrictive response of sinusoids by blocking endothelin receptors. MATERIAL AND METHODS: In an in vivo ischemia-reperfusion-model (21 Wistar rats, 250-300 g) with portal decompression by a splenocaval shunt, hepatic ischemia was induced for 30 min by cross clamping of the hepatoduodenal ligament. The effect of the endothelin receptor antagonist bosentan (10 mg/kg bw i.v.) injected before ischemia was assessed by in vivo microscopy. Microhemodynamic studies, including the sinusoidal perfusion rate, diameters of hepatic sinusoids and postsinusoidal venules, leukocyte endothelium interactions and leukocyte velocity were performed. RESULTS: After ischemia sinusoidal diameters and diameters of postsinusoidal venules were significantly reduced to 76 +/- 7% and 86 +/- 10%, respectively, in the non-treatment group, but dilated to 109 +/- 6% and 118 +/- 8% in the group treated with endothelin receptor antagonist (p < 0.001). Increased percentage of postischemic permanent adherent leukocytes could be diminished in sinusoids and more markedly in venules by therapy (p < 0.001). Leukocyte velocity was decreased to 69 +/- 9% in the treatment group ( p < 0.001). Perfusion rate could be improved to 90 +/- 2% compared to 83 +/- 5% in the untreated group (p < 0.01). Systemic arterial blood pressure was not affected by administration of the receptor antagonist. CONCLUSION: These data indicate that the endothelin receptor antagonist treatment results in prevention of postischemic sinusoidal constriction. Perfusion rate could be improved due to dilation of sinusoids and diminished leukocyte adhesion, but leukocyte velocity was reduced by 31%.