Myocardial reactive hyperemia in experimental chronic heart failure: evidence for the role of K+ adenosine triphosphate-dependent channels and cyclooxygenase activity.

BACKGROUND: Several studies suggest that coronary perfusion is abnormal in heart failure. The fact that these deficits may results in an altered coronary reserve remains controversial. Therefore, coronary adaptability to short-duration ischemia and the resultant myocardial reactive hyperemia were investigated in a model of chronic heart failure. METHODS AND
RESULTS: Experiments were performed in normal and failing hamster hearts (UM-X7.1, aged > 225 days). Heart rate, left ventricular developed pressure, and coronary flow were recorded continuously before and after each 30-second ischemia in isolated perfused heart preparations. Studies were conducted under control conditions and in the presence of four inhibitors of potential mediators of the reactive hyperemia response: the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (30 microM), the adenosine antagonist 8-(p-sulfophenyl)theophylline (50 microM), the K+ cyclic adenosine triphosphate-dependent channel antagonist glibenclamide (10 microM), and the cyclooxygenase inhibitor indomethacin (10 microM). Baseline hemodynamic parameters were all significantly impaired in failing hearts. Under control conditions, failing hearts were able to respond adequately to a 30-second ischemia: repayment-to-debt ratio averaged 1.02 +/- 0.09 as compared with 1.10 +/- 0.09 in normal hearts (P = NS). All inhibitors significantly reduced basal coronary perfusion except for indomethacin. Of the four inhibitors of potential mediators of the myocardial reactive hyperemic response, only glibenclamide and indomethacin impaired the repayment-to-debt ratio. In their presence, repayment-to-debt ratio was reduced by 40% of the baseline response (P < .01) without significant difference between normal and failing hearts. On the contrary, NG-nitro-L-arginine methyl ester and 8-(p-sulfophenyl)theophylline did not alter the repayment-to-debt ratio.
CONCLUSIONS: These observations demonstrate the capacity of the failing heart to tolerate short-duration ischemia despite the presence of significant alterations in its basal coronary perfusion. In addition, results suggest that activation of K+ adenosine triphosphate-dependent channels and the presence of cyclooxygenase by-products are important determinants of coronary adaptation to short-duration ischemia in this model of chronic heart failure.