Protection of regional mechanics and mitochondrial oxidative phosphorylation by amlodipine in transiently ischemic myocardium

Effects of first and second generation calcium channel blockers on diastolic function of the failing hamster heart: relationship with coronary flow changes

Calcium channel blockers (CCBs) have variable efficacy in the treatment of heart failure. We hypothesized that modulation of left ventricular diastolic pressure (LVDP) may play a role in the variable efficacy of CCBs in this condition. Isolated perfused hearts from 200- to 250-day-old UM-X7.1 cardiomyopathic hamsters (failing hearts) and age-matched Syrian hamsters (normal hearts) were studied. After recording of heart rate, coronary flow (CF), LVDP and left ventricular systolic pressure (LVSP), hearts were exposed either to verapamil or diltiazem (1 nM-10 microM), mibefradil (1 nM-1 microM) or clentiazem (1 nM-10 microM). Mechanical increase in CF (+2 to +10 ml/min) was carried out using a roller pump. Mechanically-augmented flow led to an increase in coronary perfusion pressure (+40 to +90 mm Hg), LVSP (+5 to +40 mm Hg) and LVDP (+5 to +25 mm Hg). CCBs-induced increment of coronary flow led to a difference in their cardiac response. In normal hearts, the negative inotropic response was more important with diltiazem and verapamil. Failing hearts did not demonstrate increased inotropic sensitivity to first-generation CCBs. On the contrary, at clinically relevant concentrations, verapamil resulted in the most pronounced impairment of LVDP followed by diltiazem while mibefradil and clentiazem, at clinically relevant concentrations, preserved LVDP. Such findings provide an additional explanation for the variable efficacy of CCBs in heart failure.

Amlodipine dynamic effects and myocardial pharmacokinetics in the isolated and perfused guinea-pig heart

Myocardial dynamic effects and pharmacokinetics of amlodipine were studied in the isolated retrogradely perfused and spontaneously beating guinea-pig heart. Pharmacokinetic analysis of drug accumulation showed one-compartment characteristics with an half-life of 76 min. Whereas disposition exhibited two-compartment characteristics with phasic half-lives of 25 and 174 min., respectively. Myocardial drug accumulation was increased by 600 times at steady-state compared to the perfusion liquid. Dynamic effect parameters were studied during increasing amlodipine concentrations from 0.16 to 220 nM. Dynamic steady-states developed within 20 min. Coronary flow-rate increased with an Emax of 119% and an EC50 of 1.2 x 10(-8) M. Amlodipine produced inhibitory effects on contraction amplitude and velocities of contraction and relaxation. Observed Emax-values and curve-fitted EC50-values were: 97, 97 and 94% and 1.10(-8), 7.7 x 10(-9) and 2.1 x 10(-8) M, respectively. Heart frequency was not changed. Oxygen consumption increased markedly to a maximum of 44% at 3 x 10(-8) M amlodipine and then decreased to nearly initial values. The frequency-corrected QT-interval decreased to a maximal extent of 20% at the three highest concentrations. Myocardial efficiency expressed as the ratio of contraction velocity times frequency to oxygen consumption exhibited a progressive decline to about 2% of initial values. The PQ-interval was not changed and the QRS-interval showed only a small but significant decrease at the highest amlodipine concentration. No arrythmogenic effects were observed. The study demonstrated a very slow accumulation and disposition of amlodipine in the guinea-pig heart with a steady-state myocardial drug concentrating accumulation of 600 times. Marked increase in coronary flow-rate and oxygen consumption accompanied by a progressive negative inotropic effect were observed.

Calcium channel blockers in veterinary medicine

Calcium channel blockers are becoming increasingly popular in veterinary medicine for the treatment of systemic hypertension, cardiac arrhythmias, and hypertrophic cardiomyopathy. Calcium is vital to many cellular functions and thus stringent regulation of intracellular calcium concentrations is required. Pharmacologic manipulation of the regulatory mechanisms has the potential to alter cellular function in all body systems. In human medicine, calcium channel blockers are being evaluated for, among other things, use in treating glaucoma, deep vein thrombosis, and pulmonary hypertension, in renal transplantation, and for prevention of reperfusion injury. The potentially beneficial effects of these drugs have often been overshadowed by adverse effects including hypotension, inappetence, bradycardia, conduction abnormalities, and decreased cardiac output. With the introduction of sustained-release formulations (diltiazem) and 2nd generation calcium channel blockers (amlodipine) many of these effects have been attenuated or eliminated. This paper will review the functions of calcium and the calcium channels as well as discussing the classes and current and potential uses of the various calcium channel blockers.

Effects of azelnidipine, a dihydropyridine calcium antagonist, on myocardial stunning in dogs

Effects of azelnidipine, a dihydropyridine derivative, on stunned myocardium were examined in anesthetized open-chest dogs. The left anterior descending (LAD) coronary artery was ligated for 20 min and then released for 60 min. Dimethyl sulfoxide (DMSO), the solvent of azelnidipine, or azelnidipine (0.03, 0.1 or 0.3 mg/kg) was injected i.v. 20 min before ligation. Segment shortening was determined by sonomicrometry. The levels of high-energy phosphate were measured in 60-min reperfused hearts. Azelnidipine at 0.1 and 0.3 mg/kg significantly decreased diastolic blood pressure and increased % segment shortening. The increase in % segment shortening due to azelnidipine appeared to be abolished by propranolol and atropine pretreatment. Ischemia significantly decreased % segment shortening in all groups. The % segment shortening that had been decreased by ischemia recovered during reperfusion, but did not reach its preischemic level in each group. In the 0.1 and 0.3 mg/kg of azelnidipine-treated dogs, a significant enhancement of % segment shortening recovery during reperfusion was observed, as compared with that in the DMSO-treated dogs. Azelnidipine did not affect the high-energy phosphate levels in 60-min reperfused hearts. In conclusion, azelnidipine improved the contractile dysfunction in stunned myocardium, without any preservation of high-energy phosphate.

Stunned myocardium and the attenuation of stunning by calcium antagonists

Myocardial "stunning" is characterized by a reversible postischemic contractile dysfunction despite full restoration of blood flow. The underlying mechanisms are not clearly understood. Inadequate energy supply and impaired sympathetic neurotransmission may have been excluded. Potential mechanisms, which are not mutually exclusive, may include damage to membranes and enzymes by free radicals, an increase in free cytosolic calcium during ischemia and reperfusion, and a lower calcium sensitivity of myofibrils. The equally pronounced increases in regional contractility in normal and stunned myocardium during postextrasystolic potentiation and the infusion of calcium or the calcium-sensitizing agent AR-L-57, however, suggest an unchanged calcium sensitivity in reperfused myocardium. Pretreatment with calcium antagonists before ischemia attenuates myocardial stunning. This effect is probably related to a lessened myocardial calcium overload during early ischemia. The potential benefit of treatment with calcium antagonists after reperfusion is established remains controversial.

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.

Calcium antagonists and stunned myocardium: importance for clinicians?

Experimental evidence indicates that calcium antagonists enhance the recovery of contractile function in canine myocardium stunned by a brief, 15-minute episode of transient coronary artery occlusion. In fact, both nifedipine and verapamil have been shown to improve systolic contraction, even when treatment was delayed, that is, when the agents were administered 30 minutes after reperfusion. The beneficial effects of delayed treatment were not a consequence of myocardial high-energy phosphate preservation. Furthermore, as low-dose intracoronary nifedipine enhanced the recovery of function in the absence of systemic hemodynamic or coronary vasodilatory effects, the improved function associated with delayed administration of calcium antagonists could not be attributed solely to afterload reduction or increased coronary blood flow. These data suggest that calcium-channel blockers exert a direct effect on the previously ischemic tissue, perhaps by subtle modulation of calcium transport or flux within the stunned myocytes. Although the precise mechanism of action of these agents remain unresolved, these intriguing experimental results raise the possibility that calcium antagonists may provide a clinically useful means of attenuating postischemic dysfunction of viable myocardium salvaged by thrombolysis, angioplasty, or cardiopulmonary bypass. The potential role of calcium-channel blockers in these clinical instances of stunned myocardium awaits further evaluation.

Amlodipine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in cardiovascular disease

Amlodipine, a basic dihydropyridine derivative, inhibits the calcium influx through 'slow' channels in peripheral vascular and coronary smooth muscle cells, thus producing marked vasodilation in peripheral and coronary vascular beds. Short to medium term clinical trials indicate that amlodipine is effective as both an antianginal agent in patients with stable angina pectoris and an antihypertensive agent in patients with mild to moderate hypertension. In small comparative studies amlodipine was at least as effective as 'standard' agents, including atenolol, verapamil, hydrochlorothiazide or captopril in hypertension, and diltiazem or nadolol in angina pectoris. Amlodipine is well tolerated, and does not appear to cause some of the undesirable effects often associated with other cardiovascular agents (e.g. adverse changes in serum lipid patterns, cardiac conduction disturbances, postural hypotension). The most common adverse effects associated with amlodipine therapy--oedema and flushing--are related to the vasodilatory action of the drug, and are generally mild to moderate in severity. Thus, amlodipine seems to provide a useful alternative to other agents currently available for the treatment of essential hypertension and chronic stable angina pectoris, with certain pharmacodynamic and tolerability properties that should be advantageous in many patients.