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CARDIOVASCULAR

Bradycardic Therapy Improves Left Ventricular Function and Remodeling in Dogs with Coronary Embolization-Induced Chronic Heart Failure

The Institute of Molecular and Experimental Therapeutics, East China Normal University, Shanghai, People's Republic of China (Y.C., J.W.); Departments of Surgery, Division of Cardiothoracic Surgery (I.G., J.M., M.C.O.), and Department of Medicine, Division of Cardiology (Y.C., G.-H.Y., S.R., A.G., Y.K.T., S.Q., K.-L.H., I.H., K.Y., D.B., J.W.), Columbia University College of Physicians and Surgeons, New York, New York; Department of Cardiac-Nephrology, Chinese PLA General Hospital, Beijing, People's Republic of China (K.-L.H.); Jack Skirball Center for Cardiovascular Research, Orangeburg, New York (J.W.); and Department of Biomedical Engineering, Columbia University, New York, New York (J.H.)

Both -adrenergic blockade and bradycardia may contribute to the therapeutic effect of -blockers in chronic heart failure (CHF). This study tested the relative importance of bradycardia by comparing cilobradine (Cilo), a sinus node inhibitor, with a -blocker, metoprolol (Meto), in an established canine model of CHF. Dogs were chronically instrumented for hemodynamic and left ventricular (LV) volume measurements. CHF was created by daily coronary embolization via a chronically implanted coronary (left anterior descending coronary artery) catheter. After establishment of CHF, control (n = 6), Meto (30 mg/day, n = 5), Cilo (low) (1 mg/kg/day, n = 5), or Cilo (high) (3 mg/kg/day, n = 5) was given orally for 12 weeks. Systemic hemodynamics, echocardiography, and pressure volume analysis were measured at baseline, at CHF, and 3 months after treatment in an awake state. Protein levels of cardiac sarcoplasmic reticulum calcium-ATPase (SERCA2a), ryanodine receptor (RyR2), and Na⁺-Ca²⁺ exchanger (NCX1) were measured by Western blot. RyR2 protein kinase A (PKA) phosphorylation was determined by back-phosphorylation. After 12 weeks, Meto and Cilo (high and low) produced similar bradycardic effects, accompanied by a significantly improved LV dP/dt versus control [Meto, 2602 ± 70; Cilo (low), 2517 ± 45; Cilo (high), 2579 ± 78; control, 1922 ± 115 mm Hg/s; p < 0.05]. Both Meto and Cilo (high) normalized protein levels of SERCA2a and NCX1 and reversed PKA hyperphosphorylation of RyR2, in contrast to controls. High-dose cilobradine effectively produced bradycardia and improved cardiac function after CHF, comparable with metoprolol. Restored protein levels of SERCA2a and improved function of RyR2 may be important mechanisms associated with cilobradine therapy.

Address correspondence to: Dr. Jie Wang, The Jack H. Skirball Center for Cardiovascular Research, Cardiovascular Research Foundation, 8 Corporate Drive, Orangeburg, NY 10962. E-mail: jwang{at}crf.org

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