Endothelin receptor subtype A blockade selectively reduces pulmonary pressure after cardiopulmonary bypass.

BACKGROUND: The bioactive peptide endothelin-1 is elevated during and after cardiopulmonary bypass and exerts cardiovascular effects through its 2 receptor subtypes, endothelin-1A and endothelin-1B. Increased endothelin-1A receptor stimulation after cardiopulmonary bypass can cause increased pulmonary vascular resistance and modulate myocardial contractility. However, whether and to what degree selective endothelin-1A blockade influences these parameters in the postbypass setting is not completely understood. OBJECTIVES: Our objective was to measure left ventricular function and hemodynamics in a porcine model of cardiopulmonary bypass after selective blockade of endothelin-1A. METHODS: Adult pigs (n = 23) underwent 90 minutes of cardiopulmonary bypass and were randomized 30 minutes after bypass to receive a selective endothelin-1A antagonist (TBC 11251, 10 mg/kg; n = 13) or saline vehicle (n = 10). RESULTS: After bypass and before randomization, pulmonary vascular resistance rose nearly 4-fold, and left ventricular preload recruitable stroke work fell to one third of baseline values (both P <.05). In the vehicle group pulmonary vascular resistance continued to rise, and preload recruitable stroke work remained reduced. However, after endothelin-1A blockade, the rise in pulmonary vascular resistance was significantly blunted compared with that in the vehicle group. Moreover, the reduction in pulmonary vascular resistance with endothelin-1A blockade was achieved without a significant change in systemic perfusion pressures. CONCLUSIONS: The present study demonstrated that increased activity of the endothelin-1A receptor likely contributes to alterations in pulmonary vascular resistance in the postbypass setting. Selective endothelin-1A blockade may provide a means to selectively decrease pulmonary vascular resistance without significant effects on systemic hemodynamics.

Temporal endothelin dynamics of the myocardial interstitium and systemic circulation in cardiopulmonary bypass.

OBJECTIVE: Increased systemic levels of the bioactive peptide endothelin 1 during and after cardioplegic arrest and cardiopulmonary bypass have been well documented. However, endothelin 1 is synthesized locally, and therefore myocardial endothelin 1 production during and after cardiopulmonary bypass remains unknown. METHODS: Pigs (n = 11) were instrumented for cardiopulmonary bypass, and cardioplegic arrest was initiated. Myocardial interstitial and systemic arterial levels of endothelin 1 were measured before cardiopulmonary bypass, throughout bypass and cardioplegic arrest (90 minutes), and up to 90 minutes after separation from bypass. Myocardial interstitial endothelin 1 was determined by microdialysis and radioimmunoassay. RESULTS: Baseline myocardial endothelin 1 levels were higher than systemic endothelin 1 levels (25.6 +/- 6.7 vs 8.3 +/- 1.1 fmol/mL, P <.05). With the onset of bypass, myocardial endothelin 1 increased by 327% +/- 92% from baseline (P <.05), which preceded the increase in systemic endothelin 1 levels. CONCLUSION: Myocardial compartmentalization of endothelin 1 exists in vivo. Cardiopulmonary bypass and cardioplegic arrest induce temporal differences in endothelin 1 levels within the myocardial interstitium and systemic circulation, which, in turn, may influence left ventricular function in the postbypass period.