Role of calcium channel blockers in experimental exercise-induced ischemia

Enhancement of amlodipine cardioprotection by quercetin in ischaemia/reperfusion injury in rats

Objectives

To investigate the possible modification of the cardioprotective effect of amlodipine when co-administered with quercetin in myocardial ischaemia/reperfusion-induced functional, metabolic and cellular alterations in rats.

Methods

Oral doses of amlodipine (15 mg/kg) and quercetin (5 mg/kg), alone or in combination, were administered once daily for 1 week. Rats were then subjected to myocardial ischaemia/reperfusion (35min/10min). Heart rates and ventricular arrhythmias were recorded during ischaemia/reperfusion progress. At the end of reperfusion, activities of plasma creatine kinase (CK) and cardiac myeloperoxidase were determined. In addition, cardiac contents of lactate, ATP, thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and total nitrate/nitrite (NOx) were estimated. Finally, histological examination was performed to visualize the protective cellular effects of different pretreatments.

Key findings

Combined therapy provided significant improvement in the amlodipine effect toward preserving cardiac electrophysiologic functions, ATP and GSH contents as well as reducing the elevated plasma CK, cardiac TBARS and NOx contents.

Conclusion

Quercetin could add benefits to the cardioprotective effect of amlodipine against injury induced in the heart by ischaemia/reperfusion.

Calcium channel antagonists in the treatment of coronary artery disease: fundamental pharmacological properties relevant to clinical use

Calcium channel antagonists are a diverse group of drugs with clinical antianginal and antihypertensive properties. They have as a common property the capacity to lessen the rate of calcium ion entry through a specific type of calcium channel, namely the voltage-gated L-type channel. They do not bind to all the pore molecules; therefore, there is still some residual entry of calcium ions. Variables determining the clinical efficacy of the different drugs include the binding sites involved, the tissue specificity of the drug, the duration of action, and (closely related) the degree of counter-regulatory neurohumoral activation. Inhibitory effects on the calcium channels of vascular smooth muscle explain the antihypertensive effect and the reduction of afterload, one of the antianginal mechanisms common to all of the drugs. In general, the dihydropyridines, such as nifedipine, are more vascular-selective than the non-dihydropyridines, such as verapamil and diltiazem. The latter owe part of their antianginal activity to more prominent effects on the calcium channels in the sinoatrial node (decreased heart rate) and the myocardium (negative inotropic effect). In addition, calcium channel antagonists are coronary artery vasodilators. Whether the latter effect confers on these drugs any specific advantage in the therapy of anginal syndromes is controversial.

Calcium channel antagonists in the management of anginal syndromes: changing concepts in relation to the role of coronary vasospasm

Despite the increasing evidence that alterations in coronary vascular tone can and do occur in patients with anginal syndromes, only in a minority of such patients with Prinzmetal's angina is there decisive evidence that the coronary vasodilation induced by calcium channel antagonists (CCAs) plays a specific therapeutic role. CCAs may also give therapeutic benefit in a number of conditions in which coronary vasoconstriction may contribute to ischemia, such as hyperventilation, cold-induced angina, or silent ischemia not caused by an increase in heart rate. Thus, the decision of whether or not to use CCAs in angina syndromes will often have to be made on grounds other than what appears to be a minor role of vasospasm in the overall spectrum of angina. There are preliminary indications that the long-term prognosis may be different among different categories of CCAs.

Investigation of therapeutic mechanisms of atenolol and diltiazem in patients with variable-threshold angina

The effects of beta-adrenoreceptor and calcium channel-blocking agents on the balance of myocardial oxygen supply and demand were studied in 15 patients (2 women and 13 men), aged 46 to 69 (mean 62) years, with variable-threshold angina. An exercise test was performed before therapy was begun, and 24-hour ambulatory ECG monitoring was performed after 1 week of long-acting nitrate therapy, in the third week after random assignment to either atenolol or diltiazem, and in the third week after crossover. All exercise tests were positive except in one patient taking diltiazem. The exercise time to 0.1 mV ST change was 4.2 +/- 1.7 minutes with no therapy, 5.1 +/- 1.6 minutes with nitrates, 6.6 +/- 0.8 minutes with diltiazem, and 6.5 +/- 2.1 minutes with atenolol. The rate-pressure product at 0.1 mV ST change was 20.9 +/- 4.6 with no therapy and 21.2 +/- 5.7 and 22 +/- 4.6 with nitrates and diltiazem, respectively, but fell to 15 +/- 3.9 beats.min.-1 mm Hg 10(-3) after atenolol (p < 0.01). There was no significant difference in the number of anginal attacks or in nitroglycerin consumption per week. The heart rate at the onset of ST-segment change during the exercise test and during ambulatory ECG monitoring was significantly lower during atenolol than during diltiazem treatment. Both atenolol and diltiazem were of similar efficacy in increasing nonischemic exercise duration in patients with variable-threshold angina and acted primarily by slowing the resting heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial actions of amlodipine in the multiple-stunned canine myocardium

The effects of the long-acting dihydropyridine calcium-entry blocker, amlodipine, on subendocardial segment shortening (%SS), regional myocardial blood flow (radioactive microspheres), and tissue high-energy phosphate levels were compared with those of a saline-treated group of barbital-anesthetized dogs subjected to nine 5-minute coronary artery occlusions interspersed with 15 minutes of reperfusion and finally by 1 hour of reperfusion (multiple stunned myocardium). Saline or amlodipine (200 micrograms/kg, IV) were administered 15 minutes prior to the first coronary occlusion. There were no major differences between groups in ischemic bed size or hemodynamics throughout the experiment. Subendocardial collateral blood flow was significantly increased in the amlodipine-treated group during coronary occlusion 1; however, tissue blood flow in the ischemic region was not significantly different between groups during occlusion 9. Following each occlusion, %SS in the ischemic region was equally reduced in both groups and passive systolic lengthening resulted. In spite of similar decreases in %SS during occlusion, the amlodipine-treated dogs showed a marked improvement in myocardial segment function (%SS) of the ischemic-reperfused region at 15 minutes following each occlusion (1-9) and at 15, 30, and 60 minutes of reperfusion following occlusion 9, as compared to saline-treated animals. In addition, amlodipine attenuated the loss of adenine nucleotides in the ischemic-reperfused area at 1 hour of reperfusion. These results suggest that amlodipine has a favorable effect on the functional and metabolic recovery of the multiple-stunned myocardium and may have potential as a cardioprotective agent for the treatment of myocardial reperfusion injury.

Effects of amlodipine on myocardial ischemia-reperfusion injury in dogs

The effects of the dihydropyridine calcium channel blocker amlodipine on subendocardial segment shortening (%SS), regional myocardial blood flow, myocardial high-energy phosphate levels and tissue water content were compared with those of a saline-treated group of barbital-anesthetized dogs subjected to a 45-minute coronary artery occlusion followed by 60 minutes of reperfusion. Saline or amlodipine (200 micrograms/kg administered intravenously) was given 15 minutes before coronary occlusion. There were no significant differences between groups in ischemic bed size or hemodynamics although dP/dt was higher after amlodipine administration. Subepicardial collateral blood flow was higher in the amlodipine group during coronary occlusion. After occlusion, %SS in the ischemic region was markedly decreased in both series and passive systolic lengthening resulted. Despite similar decreases in %SS during occlusion, the amlodipine-treated dogs showed a marked improvement in myocardial segment function of the ischemic reperfused region throughout 60 minutes of reperfusion compared with saline-treated dogs. In addition, amlodipine prevented the rebound increase in phosphocreatine and attenuated the loss of adenine nucleotides and increase in tissue water in the ischemic reperfused area at 60 minutes of reperfusion. These results suggest that amlodipine has a favorable effect on the functional and metabolic recovery of the ischemic reperfused myocardium and may have potential as a therapeutic agent for the treatment of coronary artery disease. The mechanism of action of amlodipine in this model is unknown but may be partially related to a drug-induced increase in coronary collateral blood flow or a decrease in afterload.

Effect of amlodipine on myocardial functional and metabolic recovery following coronary occlusion and reperfusion in dogs

The effects of the dihydropyridine calcium-channel blocker, amlodipine, on subendocardial segment shortening (%SS), regional myocardial blood flow, myocardial high-energy phosphate levels and tissue water content were compared to those of a saline-treated group of barbital-anesthetized dogs subjected to a 45-minute coronary artery occlusion followed by 60 minutes of reperfusion. Saline or amlodipine (200 micrograms/kg, IV) were administered 15 minutes prior to coronary occlusion. There were no significant differences between groups in ischemic bed size or hemodynamics, although dP/dt was higher following amlodipine. Subepicardial collateral blood flow was higher in the amlodipine group during coronary occlusion. Following occlusion, %SS in the ischemic region was markedly decreased in both series and passive systolic lengthening resulted. In spite of similar decreases in %SS during occlusion, the amlodipine- treated dogs showed a marked improvement in myocardial segment function (%SS) of the ischemic-reperfused region throughout 60 minutes of reperfusion as compared to saline-treated animals. In addition, amlodipine prevented the rebound increase in phosphocreatine and attenuated the loss of adenine nucleotides and the increase in tissue water in the ischemic-reperfused area at 60 minutes of reperfusion. These results suggest that amlodipine has a favorable effect on the functional and metabolic recovery of the ischemic-reperfused myocardium, and may have potential as a therapeutic agent for the treatment of coronary artery disease. The mechanism of action of amlodipine in this model is unknown but may be partially related to a drug-induced increase in coronary collateral blood flow.

Pharmacology of acute effort angina

From the pharmacologic point of view, each of the major types of antianginal agents--calcium antagonists, beta-blockers, and nitrates--seem to act at least in part by an improvement of the myocardial blood supply. The recently elucidated mechanism of action of nitrates, acting on a common pathway with the endothelium-derived relaxation factor (EDRF), suggests an important role for guanylate cyclase and cyclic GMP in maintaining coronary artery patency in patients with coronary atheroma. The efficacy of calcium antagonists, even in effort-induced angina, is in accord with a current hypothesis that physical exercise in the presence of coronary stenosis can cause relative coronary vasoconstriction, or at the least, failure of full dilation. Therefore, calcium antagonists all act, at least in part, on the "supply" side of the supply-demand equation. Beta-adrenergic blockers appear to have as their major mode of action a reduction of heart rate, which not only reduces the oxygen demand but, through an anti-ischemic effect, also appears to improve the endocardial blood supply (in relation to the heart rate). Thus beta-blockade indirectly enhances the supply side of the equation. The intriguing situation arises whereby all three major types of antianginal compounds may also act by a common mechanism of anginal relief, namely, improvement in the coronary blood supply, in addition to the diverse mechanisms specific to each type of compound. That conclusion does not mean the the "demand" side of the equation can be ignored. Rather, the critical importance of a reduced myocardial blood supply in the production of anginal syndromes is highlighted.

Calcium channel antagonists. Part II: Use and comparative properties of the three prototypical calcium antagonists in ischemic heart disease, including recommendations based on an analysis of 41 trials

An analysis of 41 trials of angina of all varieties confirms that calcium antagonists are an important advance and are now established therapy for these syndromes. In effort angina, verapamil in a dose of 360-480 mg daily is better than propranolol in standard doses. Although nifedipine is highly effective against vasospastic angina, its use in threatened myocardial infarction or severe unstable angina is not supported by recent studies, unless combined with a beta-blocker. Diltiazem has recently been tested with apparent benefit in non-Q-wave myocardial infarction. Otherwise, these calcium antagonist agents all seem to have approximate equipotency in clinical ischemic syndromes including effort and vasospastic angina. Subjective side effects seem most troublesome in the case of nifedipine. All three calcium antagonists, especially nifedipine, have been successfully combined with beta-blocker therapy, yet occasional additive negative inotropic or chronotropic or dromotropic interactions may occur when verapamil or diltiazem is added to beta-blockade, and occasionally the direct negative inotropic potential of nifedipine may become evident. The choice between the calcium antagonists is determined not only by the clinical picture but also by the anticipated side effects in a given patient and by the overall cardiovascular status. In patients with supraventricular tachycardias or sinus tachycardia, verapamil or diltiazem is preferred, whereas in patients with a resting bradycardia or borderline heart failure nifedipine is likely to be chosen.