Synergistic effect of nifedipine and propranolol on adenosine (catabolite) release from ischemic rat heart

Effect of antiarrhythmics on the release of adenosine in rat hearts with coronary occlusion and reperfusion

In isolated perfused rat hearts the left coronary artery was occluded for 5 min, with subsequent reperfusion for 20 min. During the reperfusion severe tachyarrhythmias were observed, with ventricular fibrillation occurring in all hearts. Simultaneously, large amounts of adenosine and its degradation products inosine, hypoxanthine, xanthine and uric acid were released into the coronary perfusate. The antiarrhythmics quinidine, lidocaine and gallopamil significantly decreased the release. The effect of quinidine and lidocaine was linked with the antifibrillatory action of these drugs. Also the interruption of fibrillation immediately after its appearance by potassium chloride decreased the release of adenosine and its metabolites in a highly significant way. The effect of gallopamil on the release was independent of an antifibrillatory action. The findings indicate that different kinds of antiarrhythmic drugs can affect the release of nucleosides and oxypurines in hearts with ischaemia and reperfusion.

Absence of beneficial effect of intravenous metoprolol given during angioplasty in patients with single-vessel coronary artery disease

In a double-blind, randomized, placebo-controlled trial, the possible anti-ischemic effect of metoprolol during percutaneous transluminal coronary angioplasty was tested. Electrocardiograms, hemodynamics, and metabolism were studied in 27 patients with a stenosis in the left anterior descending coronary artery. Measurements took place before angioplasty, after each of four 1-minute occlusions and 15 minutes after the last balloon deflation. Patients were randomly given placebo or metoprolol (15 mg as a bolus intravenously, followed by an infusion of 0.04 mg/kg/hr). At the end of the procedure, the rate-pressure product had decreased by 15% (NS) and 23% (p = 0.001) in the placebo and metoprolol groups, respectively, mainly due to similar decreases in heart rate. Metoprolol tended to lower chest pain and reduce precordial ST-segment elevation due to angioplasty, but the effects were not statistically significant. Lactate, hypoxanthine, and urate release immediately after deflation was similar in both groups. Metoprolol reduced arterial plasma hypoxanthine throughout the procedure by about 30% (p < or = 0.02 vs. placebo). Thus, intravenous infusion of metoprolol did not significantly attenuate chest pain and ST-segment elevation, and failed to decrease cardiac lactate and oxypurine release. It did, however, reduce arterial hypoxanthine concentrations during angioplasty, possibly indicating that the beta-blocker inhibits extracardiac ATP catabolism.

Effects of calcium-channel blockers on myocardial preservation during experimental acute myocardial infarction

Calcium antagonists have become accepted agents for the attenuation of myocardial ischemia when it becomes manifest as angina pectoris. However, it is not known whether these agents can protect ischemic myocardium during the early evolution of an acute myocardial infarct. Calcium antagonists could potentially improve myocardial perfusion, by relieving coronary spasm or improving collateral blood flow, and reduce the energy demands of the ischemic myocardium either directly or by reducing heart rate or contractility. In some studies, calcium antagonists have decreased the rate of adenosine triphosphate depletion in ischemia and reduced functional or structural indexes of ischemic injury after relatively brief periods (up to 2 hours) of injury. We have assessed the ability of verapamil to protect severely ischemic myocardium in dogs with a 40-minute test period of circumflex occlusion followed by reperfusion. After 4 days of recovery, infarcts were sized by histologic methods. Untreated dogs had subendocardial infarcts (the more moderately ischemic subepicardial region being salvaged by reperfusion). Pretreatment with verapamil reduced the size of these subendocardial infarcts from 34 +/- 8 to 8 +/- 3% of the ischemic circumflex vascular bed (anatomic area at risk). Thus, verapamil prevented cell death in a substantial proportion of the severely ischemic subendocardial region that otherwise would have died as a result of the 40-minute test period of ischemia. To establish whether verapamil could prevent cell death for a longer period of time in the less severely ischemic subepicardial region, a 3-hour period of coronary occlusion with reperfusion was studied.

Calcium antagonists--drug interactions

Evaluations of drug interactions should be done with caution. One needs to be aware of the reported interactions and apply the information on an individual basis. This review may therefore serve as a guide to the more common drug interactions and when drug therapy should be monitored closely in clinical practice. Major drug interactions with calcium antagonists are summarized in Table 2.