Timely administration of nisoldipine essential for prevention of myocardial ATP catabolism

Time-dependent cardioprotection with calcium antagonism and experimental studies with clevidipine in ischemic-reperfused pig hearts: part II

The intracellular calcium level is increased during ischemia and early reperfusion. The aim of this study was to study the role of the calcium influx in the development of myocardial ischemic and reperfusion injury during the early and late phases of ischemia and during early reperfusion. An ultrashort-acting calcium antagonist, clevidipine, was used as a tool for this investigation. Pentobarbital-anesthetized pigs were subjected to 45 minutes of LAD occlusion followed by 240 minutes of reperfusion. In the first set of experiments, clevidipine (0.3 nmol/kg per minute) was infused over 5 minutes into the ischemic myocardium via a catheter in the LAD, starting at 5, 35, or 44 minutes following the onset of ischemia (n = 6 in each group). The area at risk and the infarct size were determined after 240 minutes of reperfusion by staining with Evans blue dye and triphenyl tetrazolium chloride (TTC), respectively. In a second set of experiments, two groups of animals (n = 6 in each) were subjected to the same periods of ischemia and reperfusion; one group received no infusion during ischemia, whereas the other group received vehicle infusion during a 5-minute period between 5 and 10 minutes of ischemia. In the first set of experiments, there were no significant differences between the groups with regard to hemodynamic variables. The area at risk expressed as a percentage of the left ventricle was of similar magnitude in all three clevidipine-treated groups (about 18%). The infarct size, expressed as a percentage of the area at risk, was significantly smaller in pigs given clevidipine after 5 minutes (58 +/- 17%; p < 0.01) and after 44 minutes (42 +/- 6%; p < 0.01) of ischemia than in pigs receiving clevidipine after 35 minutes of ischemia (85 +/- 4%). The difference in infarct size between pigs given clevidipine after 5 or 44 minutes of ischemia was not significant. In the second set of experiments, there was a similar area at risk and no significant difference in infarct size between the noninfusion group and the 5-minute vehicle infusion group, indicating that the LAD infusion per se did not affect infarct size. The present results demonstrate that blockade of calcium influx by the short-acting dihydropyridine calcium antagonist clevidipine during the early phase of ischemia and at the time of reperfusion, but not during a late phase of ischemia, limits infarct size induced by ischemia and reperfusion. This indicates that the pathophysiological importance of calcium influx varies according to the different phases of myocardial ischemia and reperfusion.

Calcium antagonist protects the myocardium from reperfusion injury by interfering with mechanisms directly related to reperfusion: an experimental study with the ultrashort-acting calcium antagonist clevidipine

To test the hypothesis that calcium antagonists protect the myocardium from reperfusion-induced damage by local myocardial mechanisms just at the time of reperfusion, the myocardioprotective effects of the dihydropyridine clevidipine were investigated, taking advantage of its ultrashort-acting effect. Pigs were subjected to 45 min of myocardial ischemia by occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. Either clevidipine (0.3 nmol/kg/min, n = 6) or the corresponding amount of vehicle (n = 6) was administered to the ischemic myocardium by retrograde coronary venous infusion over a 30-min period starting 10 min before reperfusion. Hemodynamic variables (heart rate, left ventricular systolic and end-diastolic pressure, max dP/dt, and mean arterial blood pressure) as well as coronary blood flow were measured throughout the experiment. At the end of reperfusion, the area at risk (percentage of left ventricle) was determined by infusion of Evans blue into the left atrium, and the infarct size, by triphenyl tetrazolium chloride (TTC) staining. The plasma level of endothelin-like immunoreactivity (ET-LI) was analyzed in blood from the aorta and the anterior coronary vein before ischemia and at different times during reperfusion. The area at risk was similar in the vehicle and the clevidipine groups. The infarct size, expressed as a percentage of the area at risk, was 80 +/- 9.2 in the vehicle group, whereas it was significantly reduced to 51 +/- 9.2% in the clevidipine group (p < 0.01). Clevidipine did not influence any of the hemodynamic variables measured throughout the study. A nonsignificant trend toward decreased total ET-LI overflow during 4-h reperfusion was observed in the clevidipine-treated pigs compared with vehicle-treated ones (5.3 +/- 1.4 vs. 7.1 +/- 3.4 pmol). These results demonstrate that, in this model of ischemia/reperfusion-induced myocardial infarction, clevidipine reduced the damage to the myocardium when given in association with reperfusion. The local administration of the compound together with its short blood half-life shows that clevidipine reduces reperfusion-induced damage by local mechanisms within the ischemic tissue rather than by peripheral mechanisms.

Beneficial effects of felodipine on myocardial and coronary function during low-flow ischemia and reperfusion

An acute coronary occlusion causes severe low-flow ischemia in the occluded region. Calcium antagonists have the potential to reduce the rate of ischemic injury by decreasing myocardial oxygen demand, as well as by other mechanisms, especially when given prior to the onset of ischemia. However, their clinical use may be limited by their negative inotropic effects. The purpose of this study was to assess the effects of felodipine as a potentially protective agent against myocardial ischemia and reperfusion injury, independent of any negative inotropic actions, when given after the onset of low-flow ischemia. Isolated isovolumic (balloon-in-LV), blood-perfused rabbit hearts, paced at a constant heart rate, were subjected to 90 minutes of low-flow ischemia at a coronary perfusion pressure of 10 mmHg, which reduced coronary blood flow to 22-24% of baseline. After 15 minutes of low-flow ischemia, hearts received 2 x 10(-6) M felodipine (n = 7) or no drug (controls, n = 8). Felodipine was given until 15 minutes of reperfusion. During low-flow ischemia both groups of hearts had identical coronary blood flow, heart rate, left ventricular (LV) developed pressure, lactate production, and O2 consumption. However, felodipine markedly protected against ischemic diastolic dysfunction. At the end of low-flow ischemia, LV end-diastolic pressure (LVEDP) had increased from 10 +/- 1 to 28 +/- 5 mmHg in the felodipine group, while in the controls LVEDP increased to 48 +/- 8 mmHg (p < 0.05). During 30 minutes of reperfusion, felodipine had a beneficial effect upon coronary blood flow (initial postischemic hyperemia 245 +/- 38% of baseline in the felodipine group vs. 124 +/- 18% in the controls; p < 0.01) Felodipine markedly improved the recovery of contractile function [LV developed pressure recovered from a baseline of 104 +/- 4 to 75 +/- 6 mmHg (72%) in the felodipine group vs. 34 +/- 10 mmHg (32%) in the control group; p < 0.01], as well as diastolic function (LVEDP = 25 +/- 4 mmHg in the felodipine group vs. 61 +/- 10 mmHg in the controls; p < 0.05), and ATP levels (8.5 +/- 1.4 mumoles/g d.w. in the felodipine group vs. 3.9 +/- 1.4 mumoles/g d.w. in the control group, p < 0.05). Felodipine, given after the onset of low-flow ischemia, protects the myocardium during both ischemia and reperfusion by mechanisms other than reducing myocardial oxygen demand.

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.

Improvement of ischemic myocardial dysfunction by nisoldipine

We examined the cardioprotective effect of nisoldipine against myocardial dysfunction during ischemia and reperfusion in Langendorff perfused rabbit hearts. Nisoldipine was administered to the hearts before 60 minutes of global ischemia. This agent inhibited the increase of end-diastolic pressure during ischemia and also improved the recovery of left ventricular developed pressure and coronary flow during reperfusion in a concentration-dependent manner. The maximal cardioprotective effect was observed in 10(-8) M nisoldipine. The beneficial effect was associated with an increase of coronary flow during reperfusion. Therefore, both the nisoldipine-increased coronary flow during reperfusion and the inhibition of ischemic contracture by nisoldipine seem to play a crucial role in improving myocardial dysfunction of ischemic-reperfused hearts.

Neuroprotective activity of fructose-1,6-bisphosphate following transient forebrain ischemia in the Mongolian gerbil

We examined the protective activity of fructose-1,6-bisphosphate (FBP) on mortality and delayed hippocampal cell death induced by transient cerebral ischemia in the Mongolian gerbil. Forebrain ischemia was produced by bilaterally occluding the common carotid arteries for 15 min using microaneurysm clips; then the blood supply to the brain was restored. The number of survivors was counted for 8 days, and the histopathological damage in the CA1 region of the hippocampus was scored according to the semiquantitative scale of Rudolphi and colleagues. When injected 15 min before the ischemic insult, FBP (100 and 333 mg/kg, i.v.) significantly reduced the rate of mortality during the 8-day observation period. Equivalent doses of fructose and fructose monophosphate did not improve survival, and neither did low doses (33 mg/kg) of FBP. FBP also produced a significant degree of protection against the CA1 pyramidal cell loss in comparison with its vehicle (distilled water). Conversely, when we administered the compound, at the same dose, 15 min after the release of the arterial occlusion, we observed neither a significant reduction of mortality nor significant protection against hippocampal CA1 pyramidal cell loss. These results suggest that FBP possesses salutary properties against the damages induced by transient cerebral ischemia, although they are evident only when the compound is administered before the resolution of the ischemic injury.

Myocardial infarction in rats: effects of metabolic and pharmacologic interventions

Myocardial infarction was induced in rats by ligation of the descending branch of the left coronary artery. The time course of changes in heart function was recorded within the first nine days. There was a progressive decline in LVSP, in LV dP/dtmax and in the pressure-rate-product. LVEDP was elevated. Cardiac output and stroke volume index were depressed after two days. The ATP content in the nonischemic region was lower than control, but recovered spontaneously toward the normal value within the first four days. Three metabolic and pharmacologic interventions known to affect cardiac adenine nucleotide metabolism were applied. Continuous i.v. administration of ribose which stimulates further adenine nucleotide biosynthesis attenuated the fall and promoted the restoration of ATP in the nonischemic myocardium within four days after coronary artery ligation. The elevation of LVEDP was attenuated with ribose after two and four days. The calcium antagonist gallopamil administered as i.v. infusion for two days led to a further reduction of all parameters of left heart function, but did not influence the increase in adenine nucleotide and protein synthesis that occurred in the nonischemic heart. Coenzyme Q10 had only slight effects on LVSP, LVEDP, and LV dP/dtmax, but attenuated significantly the fall in cardiac output and stroke volume index after two days following coronary artery ligation. Thus, all interventions affected differently the infarct-induced changes in heart and circulatory function. An improvement was observed with ribose and with coenzyme Q10.

Cardioplegia and calcium antagonists: a review

During open-heart operations, periods occur during which the blood supply to the heart is stopped. Myocardial damage can be limited by cooling and induction of electromechanical arrest (cardioplegia). Many animal studies and some clinical trials provide strong evidence for the use of calcium antagonists, such as nifedipine, verapamil hydrochloride, diltiazem hydrochloride, and lidoflazine, as adjuncts to cardioplegia to optimize the protection. Salutary effects of calcium antagonists are discussed in regard to possible mechanism of action, application time, and efficacy during hypothermia. A major conclusion is that virtually no negative effects on cardiac protection have as yet been described in experimental or clinical studies, apart from short-term negative inotropic responses, while there is an increasing body of positive evidence for their efficacy. A new development is the use of these drugs for regional cardioplegia during dilation of coronary arteries (transluminal angioplasty).