Preservation of high-energy phosphates by verapamil in reperfused myocardium

To determine whether verapamil prevents depletion of adenine nucleotides during and after severe myocardial ischemia, dogs were subjected to 15 min occlusions of the left anterior descending coronary artery followed by 240 min of reperfusion. One hour before occlusion, dogs were randomly assigned to a treatment group (n = 10) to which an infusion of intravenous verapamil was given until the onset of reperfusion or to an untreated saline group (n = 9). Verapamil reduced mean aortic pressure and heart rate. After 15 min of ischemia, endocardial adenosine triphosphate (ATP) level, determined by needle biopsy, decreased in the untreated group from 34.7 ± 2.0 to 24.4 ± 2.7 nmol·mg protein^-1 (p < .005 vs preocclusion) and in the verapamil group from 32.8 ± 1.5 to 30.3 ± 1.5 nmol·mg protein^-1 (NS vs preocclusion). Dogs receiving verapamil had significantly higher ATP levels than untreated animals after 90 and 240 min of reperfusion. In untreated animals the sum of inosine and hypoxanthine levels increased during occlusion from very low levels to 4.6 ± 1.1 nmol·mg protein^-1 in the epicardium and to 6.8 ± 1.5 nmol·mg protein^-1 in the endocarcium (p < .05 compared with preocclusion values). In verapamil-treated dogs inosine and hypoxanthine levels increased to only 1.2 ± 0.3 (epicardium) and 1.9 ± 0.6 nmol·mg protein^-1 (endocardium) (both NS compared with preocclusion values). After 90 min of reperfusion the sum of ATP, adenosine disphosphate, adenosine monophosphate, inosine, and hypoxanthine levels was decreased in the endocardium by 10.2 nmol·mg protein^-1 in the untreated group, but no change was observed in verapamil-treated animals. We conclude that breakdown of ATP to inosine and hypoxanthine during severe ischemia is reduced by verapamil, resulting in higher ATP concentrations during occlusion and reperfusion and decreased washout of the diffusible purines inosine and hypoxanthine during reperfusion.