Abstract
Besides being a strong vasoconstrictor, endothelin-1 (ET-1) also causes severe ventricular arrhythmias. The aim of our study was to differentiate between the vasoconstrictor and arrhythmogenic actions of ET-1 by using the selective endothelin-A-(ETA) receptor antagonist LU 135.252 (LU). A bolus injection of 5 mg/kg LU was administered to 10 anesthetized mongrel dogs in group A. The 30 min intracoronary ET-1 infusion was started 20 min after the LU bolus at a rate of 60 pmol/min. In the control group (group B, n = 8) only ET-1 was administered (60 pmol/min). The left anterior descending coronary artery blood flow (CBF), cardiac output, electrocardiograph (ECG) and arterial blood pressure were monitored. Two monophasic action potential duration (MAPD) catheters were placed onto the left ventricular epicardium (LVEP) and into the right ventricular endocardium (RVEND) to follow electrophysiologic changes. No significant changes were observed in blood pressure (0 min vs 30 min: group A, 99.0 +/- 4.5 vs 90.0 +/- 5.2 mmHg, p = NS; group B, 103 +/- 6 vs 104 +/- 3 mmHg, p = NS), cardiac output (0 min vs 30 min: group A, 3.5 +/- 0.7 vs 3.2 +/- 0.8 l/min, p = NS; group B, 3.6 +/- 0.4 vs 3.3 +/- 0.3 l/min, p = NS), and MAPD90 (0 min vs 30 min: group A, LVEP, 241 +/- 11 vs 260 +/- 14 ms; RVEND, 233 +/- 5 vs 239 +/- 8 ms, p = NS), whereas a significant decrease was observed in CBF (deltaCBF 30 min: group A, -28 +/- 2%, p < 0.05; group B, -32 +/- 3%, p < 0.05). In group A ventricular fibrillation (VF) occurred once. Ventricular premature contractions (VPCs) and short, nonsustained ventricular tachycardias (nsVTs) were observed in seven cases. Early after depolarizations and a MAPD90 increase were observed in the control group B (0 min vs 30 min: LVEP, 244 +/- 10 vs 292 +/- 12 ms; RVEND, 255 +/- 9 vs 290 +/- 8 ms) accompanied by VPCs, incessant nsVTs. Sustained VT and VF were evident in seven cases. Our results indicate, that the applied single bolus injection of LU effectively prevents ET-1-induced major ventricular arrhythmias, whereas it has no effect on coronary vasoconstriction. These data support the notion that ET-1 possesses a direct arrhythmogenic action.
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