Effect of carvedilol in comparison with metoprolol on myocardial collagen postinfarction.

OBJECTIVES: We sought to compare the effects of two different beta-blockers, carvedilol and metoprolol, to an angiotensin-converting enzyme (ACE) inhibitor (captopril) on myocardial collagen deposition during healing and ventricular remodeling after myocardial infarction (MI).
BACKGROUND: Beta-adrenergic blockade has been shown to be beneficial post-MI and in chronic heart failure. Carvedilol is a new-generation vasodilating beta-blocker with additional alpha1-adrenoceptor antagonism and an antiproliferative action, but it is not known if it is more beneficial than standard selective beta-blockers.
METHODS: Using a rat model of MI, induced by left coronary ligation, we studied the effects of 11 weeks of therapy with oral carvedilol, metoprolol or captopril on hemodynamics, tissue weights, collagen volume fraction and hydroxyproline content.
RESULTS: Both beta-blockers caused similar decreases in heart rate and LVEDP compared with untreated post-MI rats. At equivalent beta-adrenoceptor blocking doses, however, carvedilol, but not metoprolol, attenuated the increase in collagen content in noninfarcted regions and prevented the increase in right ventricular weight/body weight (all p < 0.05), and its effect was similar to captopril. Metoprolol treatment tended to increase right ventricular weight and heart weight (p < 0.05). There were no differences in infarct size between the groups.
CONCLUSIONS: Long-term treatment with both beta-blockers, as well as an ACE inhibitor, benefited the healing process in rats post-MI. At equivalent myocardial beta-adrenoceptor blocking doses, however, carvedilol significantly reduced myocardial collagen in the noninfarcted myocardium and cardiac hypertrophy in the right ventricle, whereas metoprolol had no effect on myocardial collagen deposition.