Coronary and cardiac sensitivity to the vasoselective benzothiazepine-like calcium antagonist, clentiazem, in experimental heart failure

Recent evidence suggests that newer vasoselective dihydropyridine calcium antagonists are not cardiodepressant and may be useful in the treatment of heart failure. No data are available on the efficacy of clentiazem, a vasoselective benzothiazepine-like calcium antagonist, in this pathological condition. Therefore, our objective was to assess coronary and cardiac sensitivity to clentiazem in an experimental model of chronic heart failure (cardiomyopsthic hamster, UM-X7.1, >200 day old). Left ventricular developed pressure (LVP) and coronary flow changes were assessed in isolated, perfused failing hearts and in normal Syrian hamster hearts. Clentiazem dose-response curves for both coronary dilation and negative inotropic effects were determined under control conditions and in the presence of the nitric oxide (NO) synthase inhibitor, N-G-nitro-L-arginine (L-NAME, 30 mu M), and the cyclooxygenase inhibitor, indomethacin (10 mu M). Baseline hemodynamics indicate a significant reduction in both LVP and coronary perfusion in failing hearts. Cardiac sensitivity to the negative inotropic effects of clentiazem were similar in normal and failing hearts (IC50 = 677 nM and 734 nM, respectively). However, the clentiazem-induced increase in coronary flow was significantly attenuated in failing hearts (EC50 = 56 +/- 9 nM vs. 15 +/- 3 nM in normal hearts, p < 0.01). To better characterize the reduced coronary sensitivity to clentiazem in the presence of heart failure, the contributions of the NO synthase and the cyclooxygenase pathways were evaluated. Although coronary sensitivity to clentiazem was significantly reduced in the presence of L-NAME, this attenuation was of the same magnitude in normal and failing hearts, suggesting that coronary ''desensitization'' to clentiazem in failing hearts does not involve the NO synthase pathway. Experiments carried in the presence of indomethacin indicate that the reduced coronary sensitivity to clentiazem observed in failing hearts does not involve the cyclooxygenase pathway. In conclusion, reduced coronary sensitivity to the vasoselective calcium antagonist clentiazem was observed in the failing hamster heart, while no exacerbation of clentiazem's cardiodepressant actions was present. Although the mechanisms involved in the vascular desensitization to clentiazem are still unknown, our findings may provide an additional explanation for the variable efficacy of calcium antagonists in the treatment of heart failure.