The role of endothelin-B receptors in myocardial and endothelial reperfusion injury after heart transplantation

Expression of endothelin-1 system in a pig model of endotoxic shock

Endothelin (ET)-1 is a potent vasoconstrictive peptide and it is involved in the pathogenesis of septic shock. Blockade of ET-1 receptors abolishes the LPS-induced pulmonary hypertension and worsens the LPS-dependent systemic hypotension, but the role of ET-1 in sepsis remains uncertain. To determine the role of ET-1 in cardiovascular and respiratory derangement in a porcine model of endotoxemic shock we evaluated ET-1 plasma levels and ET-1 mRNA and protein levels in lung, liver, and heart as well as Endothelin Converting Enzyme-1, ET(A) and ET(B) receptors mRNA in the same tissues. Twelve piglets were randomised to sham operated or to LPS-treated (40 microg/kg/h for 4 h) groups. During the experiment, respiratory and circulatory parameters have been recorded and blood samples collected. At the end of the experiment the animals were sacrificed and tissue samples collected for real-time quantitative PCR and ELISA test. LPS infusion evokes a large increase in ET-1 plasma concentration, and in tissues mRNA levels, associated with an increase in pulmonary arterial pressure, as well as in pulmonary and systemic vascular resistances, and a decrease in stroke volume. LPS infusion caused also a derangement of respiratory mechanics, evidenced by an increase in resistance and a decrease in compliance of the respiratory system. ET(A) and ET(B) receptor mRNA levels were markedly decreased in liver and lung and slightly increased in heart, evidencing that ET receptor subtypes were differentially regulated in the major organs of endotoxin treated pigs. In conclusion our data show the presence of a continuative and differentially regulated stimulating mechanism of ET-1 expression during pig endotoxaemia as well as a fundamental role of ET-1 system in the cardiovascular and respiratory derangement.

Differentiated and dose-related cardiovascular effects of a dual endothelin receptor antagonist in endotoxin shock

OBJECTIVE

To evaluate the effects of endothelin receptor antagonism on cardiac performance in endotoxin shock.

DESIGN

Prospective, experimental study.

SETTING

A university-affiliated research institution.

SUBJECTS

Domestic anesthetized landrace pigs.

INTERVENTIONS

Thirty-seven pigs were anesthetized and subjected to echocardiography, coronary sinus catheterization, and monitoring of central and regional hemodynamics in order to assess cardiac performance. All animals received endotoxin for 5 hrs. Twenty pigs served as endotoxin controls. Tezosentan, a dual endothelin-A and -B receptor antagonist, was administered during established endotoxemic shock. Seven pigs received an infusion of tezosentan of 1 mg x kg(-1) x hr(-1) (tezo1), and an additional ten pigs received a higher dose of 10 mg x kg(-1) x hr(-1) (tezo10).

MEASUREMENTS AND MAIN RESULTS

Endotoxemia evoked a state of shock with pulmonary hypertension and metabolic acidosis. A decrease in stroke volume and coronary perfusion pressure as well as an increase in troponin I was also noted. Tezosentan administration resulted in a significant increase in cardiac index, stroke volume index, left ventricular stroke work index, and left ventricular end-diastolic area index. Decreases in systemic and pulmonary vascular resistance indexes were also evident after intervention. This was achieved without changes in heart rate or systemic arterial or pulmonary artery occlusion pressures in tezo, animals compared with controls. In addition, metabolic variables were improved by tezosentan. These effects were sustained only in the tezo, group. In the higher dosage, tezosentan resulted in a deterioration of cardiac performance and 50% mortality rate. The endotoxin-induced increase in troponin I was attenuated in the tezo, group compared with controls.

CONCLUSIONS

In this porcine model of volume-resuscitated, endotoxemic shock, endothelin-receptor blockade with tezosentan improved cardiac performance. However, the effect was not sustained with higher doses of tezosentan, possibly due to reduced coronary perfusion pressure. These findings show differentiated, dose-dependent effects by dual endothelin receptor blockade on endotoxin-induced cardiovascular dysfunction.

Myocardial Protection with the Non-Selective Endothelin Receptor Antagonist L-753,037 Following Acute Coronary Artery Occlusion in the Dog

SUMMARY

Efficacy of a new, potent non-selective endothelin antagonist, l-753037, was examined in a model of canine coronary artery occlusion and reperfusion to assess whether blockade of both ETA and ETB receptors would enhance or reduce myocardial ischemic injury. Instrumented dogs were randomized to receive vehicle (n = 9) or l-753037 (0.1 microg/kg/min, n = 9) by intracoronary infusion 30 minutes before a 90-minute LCx coronary artery occlusion and through 4 hours of reperfusion. After 4 hours of reperfusion, plasma ET-1 levels rose significantly in both groups: 24 +/- 3 fmol/ml in vehicle animals (P < 0.01) versus 42 +/- 5 fmol/ml with l-753037 (P < 0.05). Treatment with l-753037 normalized total LCx flow and regional myocardial flow after 4 hours of reperfusion in all regions. LCx flow was reduced 16% from pre-occlusion baseline (P = 0.45) with treatment compared with 35% with vehicle (P < 0.01). Endocardial flow in the risk region returned to baseline values with l-753037 treatment but was reduced approximately 50% in vehicle animals. l-753037 treatment was associated with a 38% reduction in infarct size (24.1 +/- 3.9% AAR with l-753037 treatment versus 38.7 +/- 3.1% with vehicle, P < 0.01). Thus, a non-selective endothelin antagonist provides significant myocardial protection primarily by improving regional myocardial flow distribution following reperfusion and demonstrated no detrimental effects associated with blockade of the ETB receptor.