Diltiazem administered before or during myocardial ischemia decreases adenine nucleotide catabolism

The role of aldosterone inhibitors in cardiac ischemia-reperfusion injury

Myocardial ischaemia-reperfusion (I/R) injury is a well-known term for exacerbation of cellular destruction and dysfunction after the restoration of blood flow to a previously ischaemic heart. A vast number of studies that have demonstrated that the role of mineralocorticoids in cardiovascular diseases is based on the use of pharmacological mineralocorticoid receptor (MR) antagonists. This review paper aimed to summarize current knowledge on the effects of MR antagonists on myocardial I/R injury as well as postinfarction remodeling. Animal models, predominantly the Langendorff technique and left anterior descending coronary artery occlusion, have confirmed the potency of MR antagonists as preconditioning and postconditioning agents in limiting infarct size and postinfarction remodeling. Several preclinical studies in rodents have established and proved possible mechanisms of cardioprotection by MR antagonists, such as reduction of oxidative stress, reduction of inflammation, and apoptosis, therefore limiting the infarct zone. However, the results of some clinical trials are inconsistent, since they reported no benefit of MR antagonists in acute myocardial infarction. Due to this, further studies and the results of ongoing clinical trials regarding MR antagonist administration in patients with acute myocardial infarction are being awaited with great interest.

Role of Calcium Channel Blockers in Myocardial Preconditioning

Coronary heart disease is the leading cause of mortality and morbidity worldwide. The effects of coronary heart disease are usually attributable to the detrimental effects of acute myocardial ischaemia-reperfusion injury. Newer strategies such as ischaemic or pharmacological preconditioning have been shown to condition the myocardium to ischaemia-reperfusion injury and thus reduce the final infarct size. This review investigates the role of calcium channel blockers in myocardial preconditioning. Additionally, special attention is given to nicorandil whose mechanism of action may be associated with the cardioprotective effects of preconditioning. There are still many uncertainties in understanding the role of these agents in preconditioning, but future research in this direction will certainly help reduce coronary heart disease.

Calcium antagonist verapamil and reperfusion injury of the heart

OBJECTIVE

An experimental study to examine the effect of verapamil, given into a coronary artery, on reperfusion injury.

DESIGN

The study was randomized but not blinded.

SETTING

This study was conducted in the animal laboratory of the Department of Anesthesiology and Critical Care in an academic institution.

PARTICIPANTS

The study was performed in an anesthetized open-chest pig model.

INTERVENTIONS

Left anterior coronary artery (LAD) occlusion for 15 minutes followed by 90 minutes of reperfusion. Verapamil or saline was given into the LAD artery either at the time the coronary artery was occluded (ie, during acute severe ischemia or during the reperfusion period).

MEASUREMENTS

LAD artery blood flow, regional myocardial function, and metabolism were assessed by the end-systolic pressure length relationship, regional systolic shortening, postsystolic shortening, regional myocardial oxygen consumption, and local cardiac vein lactate.

CONCLUSIONS

Verapamil given during ischemia resulted in a shorter period of regional myocardial stunning when compared with saline or verapamil during reperfusion. The difference in the verapamil strategies (ie, verapamil administered during ischemia versus verapamil during the reperfusion period) can probably be explained by a difference in the effective dose of the drug present in the heart at the time reperfusion started rather than the period of administration per se.

Clinical L-type Ca(2+) channel blockade prevents ischemic preconditioning of human myocardium

Although Ca(2+) channel blockers are commonly used to control both blood pressure and angina in patients with coronary artery disease, clinical trials have associated the use of L-type Ca(2+) channel blockers with increased cardiovascular mortality. Recent evidence has implicated Ca(2+) entry through the L-type Ca(2+) channel during transient ischemia as a proximal stimulus for ischemic preconditioning (IPC) in experimental animals. We therefore hypothesized that clinical L-type Ca(2+) channel blockade prevents IPC in human myocardium. Human atrial trabeculae were suspended in organ baths, field simulated at 1 Hz, and force development was recorded. Following 90 min equilibration, trabeculae from control patients and patients taking L-type Ca(2+) channel blockers were subjected to simulated ischemia/reperfusion (I/R: 45/120 min) with or without 5 min of simulated ischemia (IPC stimulus) prior to I/R. IPC increased post-ischemic developed force in control patients from 14.6+/-2.6 to 43.1+/-3.5% baseline developed force (%BDF P<0.05 I/R vs IPC). Whereas IPC failed to increase post-ischemic developed force in myocardium from patients taking L-type Ca(2+) channel blockers (15. 1+/-1.9 vs 16.6+/-1.7 %BDF, P>0.05 L-type I/R v L-type IPC). We conclude that: (1) atrial muscle can be preconditioned by transient ischemia; (2) atrial muscle from patients taking L-type Ca(2+) channel blockers cannot be preconditioned by transient ischemia; and (3) the increased cardiovascular mortality historically associated with the use of Ca(2) channel blockers in patients with coronary artery disease may be, in part, due to the pharmacological inhibition of ischemic preconditioning.

New perspectives on the cardioprotective phosphonate effect of the spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide: an hemodynamic and 31P NMR study in rat hearts

The spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO) is an improved ESR probe to assess superoxide (O2*-) formation in the postischemic heart. We recently found that DEPMPO pretreatment improves recovery of cardiac function with the concomitant inhibition of postischemic O2*- production. By perfusing diethyl methylphosphonate MeP(O)(OEt)2 to ischemic-reperfused isolated rat hearts, we provide hemodynamic evidence that this preservation, which exerts during ischemia, is in fact specific to the phosphonate group. Using 31P NMR on intact rat hearts, it was also found that the "phosphonate effect" of DEPMPO is related to the preservation of ATP levels during ischemia, when compared to 5,5-dimethyl-1-pyrroline N-oxide. This mechanism may be a means of reducing the potency of cardiac tissue to produce O2*- during reperfusion.

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.

Cardiac depressant effects of oxygen free radicals

In many clinical situations, including cardiac ischemia/reperfusion, elective cardiac arrest, and renal dialysis, the chances of increased production of oxygen free radicals (OFR) exist. OFR have been implicated as a causative factor of cell damage in several pathologic conditions. The effects of exogenous OFR, generated by xanthine plus xanthine oxidase, in the absence and in the presence of OFR scavenger (superoxide dismutase [SOD]) on the contractility of isolated perfused heart of rabbit were studied. OFR produced concentration-dependent decreases in the contractility of perfused heart. SOD prevented the OFR-induced decreases in the left ventricular contractility. Xanthine produced an increase in the contractility of isolated perfused rabbit's heart. Xanthine oxidase produced a marked decrease in the left ventricular contractility. Repeated administration of xanthine oxidase produced accelerated and greater decreases in the contractility of perfused heart when compared with that of the initial administration of the drug. Effects of xanthine or xanthine oxidase on the cardiac function and contractility were also studied in anesthetized dogs. Xanthine alone had no significant effect on the cardiac function and indices of myocardial contractility. However, xanthine oxidase produced a marked decrease in the mean aortic pressure, left ventricular work index, heart rate, cardiac index, left ventricular systolic pressure, left ventricular end-diastolic pressure, (+) and (-) dp/dt of left ventricular pressure, and other indices of myocardial contractility [(dp/dt)/PAW (pulmonary arterial wedge pressure)]; and an increase in the total systemic and pulmonary vascular resistance. Repeated administration of xanthine oxidase in anesthetized dogs had lesser effects on the cardiovascular system when compared with those from the initial dose of the drug. These results suggest that OFR are cardiac depressant. Clinical situations wherein there is an increased production of OFR or increased formation of xanthine and xanthine oxidase may be associated with decreased cardiac function and contractility. Scavengers of OFR may protect the heart from the deleterious effects of OFR in such clinical conditions.

Effects of K+ channel openers on ischemic dysfunction and metabolic disturbance in isolated perfused rat heart

The effects of two structurally different K+ channel openers, KRN2391 and cromakalim, on cardiac mechanisms during ischemia and reperfusion were studied in isolated perfused rat hearts. Isolated buffer-perfused rat hearts pretreated with KRN2391, cromakalim and vehicle were subjected to 25 min of ischemia followed by 30 min of reperfusion. Before ischemia, KRN2391 (1-10 microM) and cromakalim (1-10 microM) increased coronary flow, but did not modify cardiac function or biochemical parameters (adenine nucleotides, energy charge potential: ECP, lactate). During ischemia, KRN2391 (3, 10 microM) and cromakalim (10 microM) significantly accelerated the reduction in cardiac function and attenuated the decreased levels of ATP and ECP, but did not change the lactate content. After 30 min of reperfusion, pretreatment with KRN2391 and cromakalim resulted in a significant improvement in cardiac function, ischemic contracture and biochemical parameters. Thus, both KRN2391 and cromakalim have beneficial effects on biochemical parameters during ischemia and reperfusion, effects which may be related to cardiodepression during ischemia.

Effects of TA-3090, a new calcium channel blocker, on myocardial substrate utilization in ischemic and nonischemic isolated working fatty acid-perfused rat hearts

Experimental studies have shown that calcium channel blockade has a protective effect on the ischemic myocardium. Although these agents may act by decreasing intracellular Ca2+ accumulation during reperfusion or to reduce oxygen requirements by decreasing myocardial work load, recent evidence suggests that calcium blockers may also favorably alter energy substrate metabolism in ischemic and reperfused myocardium. In this study, TA-3090, a new calcium channel blocker with minimal effect on myocardial work load, was used to study the effect of calcium channel blockade on both myocardial substrate utilization and reperfusion recovery of ischemic hearts. Isolated working rat hearts were perfused at an 11.5 mm Hg preload and an 80 mm Hg afterload with Krebs-Henseleit buffer containing 11 mM glucose, 1.2 mM palmitate, and 500 microunits/ml insulin. In aerobically perfused spontaneously beating hearts, a 0.5 microM dose of TA-3090 had a mild depressant effect on heart rate but no effect on peak systolic pressure development. In paced hearts (250 beats/min), 0.5 microM TA-3090 had no effect on either peak systolic pressure development or contractility. Fatty acid and glucose oxidation was determined by measuring 14CO2 production in hearts perfused with either [14C]palmitate or [14C]glucose, respectively, whereas glycolysis was determined by measuring 3H2O production from [3H]glucose. Under aerobic conditions, fatty acid oxidation was not altered by TA-3090, but a significant decrease in glucose oxidation and glycolytic rates was observed. If hearts were subjected to a 30-minute period of no-flow ischemia, the addition of 0.5 microM TA-3090 to the perfusate before ischemia significantly improved reperfusion recovery of mechanical function. The protective effects of TA-3090 were not observed if TA-3090 was added at the time of reperfusion and were not related to a depression of function before ischemia. TA-3090, added before ischemia, significantly reduced glycogen and ATP depletion during no-flow ischemia and also significantly decreased glycolytic rates in hearts subjected to low-flow ischemia (coronary flow = 0.5 ml/min). Combined, our data suggest that the beneficial effects of calcium channel blockade on the ischemic myocardium are not related solely to a decrease in myocardial work load or metabolic demand before ischemia, but rather may in part be related to a decrease in myocardial energy demand during ischemia itself, resulting in preservation of ATP and a decrease in glycolysis. The decrease in glycolytic rates during ischemia may also result in a reduction of glycolytic product accumulation during ischemia.

Bay K 8644, modifier of calcium transport and energy metabolism in rat heart mitochondria: a new intracellular site of action

1. The dihydropyridine Ca2+ channel agonist Bay K 8644 (10-200 microM) produced a concentration-dependent increase in State 4 respiration in the rat heart mitochondria with the highest concentration (200 microM) increasing the rate from 33.1 +/- 0.7 to 187.0 +/- 13.3 ng atoms O2 consumed min-1 mg-1 protein. 2. Bay K 8644 (200 microM) reduced State 3 respiration from 247.2 +/- 11.7 to 174.4 +/- 0.06 ng atoms O2 min-1 mg-1 protein, reduced the respiratory control index (RCI) from 5.3 +/- 0.45 to 1.1 +/- 0.03 and reduced the ADP:O ratio from 2.75 +/- 0.03 to 1.3 +/- 0.15. 3. A similar, but smaller, stimulation of State 4 respiration was seen with nitrendipine (25-200 microM), the rate increasing from 22.6 +/- 1.0 to 33.1 +/- 1.8 ng atoms O2 consumed min-1 mg-1 protein in the presence of 200 microM nitrendipine. 4. Bay K 8644 (10-60 microM) increased the total Ca2+ uptake into rat heart mitochondria, the total increasing from 248.8 +/- 8.4 to 406.9 +/- 17.6 ng Ca2+ mg-1 protein at 60 microM Bay K 8644 (EC50 = 18.9 +/- 1.4 microM). 5. Bay K 8644 (10-60 microM) produced a concentration-dependent reduction in the Ca2+ influx rate (IC50 = 52.5 +/- 2.8 microM). Similar effects were seen with (+)-Bay K 8644 and (-)-Bay K 8644. 6. Nitrendipine (40-120 microM) stimulated Ca2+ efflux from mitochondria preloaded with the ion; the efflux rate increasing from 2.9 +/- 0.05 to 114.2 +/- 6.2 nmol Ca2+ min-1 mg-1 protein (EC50 = 57.3 +/- 1.3 microM). 7. These data indicate dihydropyridine-induced changes in the activity of the mitochondrial Na+/Ca2 . antiporter pathway; nitrendipine causing stimulation and Bay K 8644 causing inhibition.

Myocardial protection by intravenous diltiazem during angioplasty of single-vessel coronary artery disease

The possible cardioprotective effect of diltiazem during ischemia caused by percutaneous transluminal coronary angioplasty was tested. Electrocardiograms and myocardial lactate, hypoxanthine and urate production were determined in 26 patients with a stenosis in the left anterior descending artery without angiographically demonstrable collaterals. Measurements took place before angioplasty, after each of 4 occlusions and 15 minutes after the last balloon inflation. Patients were randomly given placebo or DL-diltiazem (0.4 mg/kg as a bolus intravenously, followed by an infusion of 15 mg/hr). During angioplasty the ST-segment elevation for the anterior wall leads V2, V4 and V6, and the intracoronary lead was similar for both groups, as was lactate release. Diltiazem significantly reduced cardiac hypoxanthine release immediately after angioplasty from 63 to 88% (p less than 0.05). The drug diminished urate production after the last dilatation by 82% (p less than 0.05). In conclusion, intravenous infusion of diltiazem reduced cardiac adenosine triphosphate breakdown during angioplasty as shown by diminished hypoxanthine and urate production. In contrast, diltiazem was unable to attenuate ST-segment elevation and lactate release.

Differential enhancement of postischemic segmental systolic thickening by diltiazem

Prolonged depression of segmental systolic thickening after brief coronary artery occlusion may result principally from events during reperfusion rather than during the ischemic interval. Thus, cellular calcium overload at reperfusion may be a mediator of contractile dysfunction after brief ischemia, and reduction of calcium entry by diltiazem, a calcium channel antagonist, may enhance recovery of systolic thickening after brief periods of ischemia. Thirteen awake unsedated dogs instrumented with hemodynamic catheters, left anterior descending coronary artery occluders and five to six pairs of intramyocardial sonomicrometers underwent two 15 min coronary artery occlusions with 24 h reperfusion. The order of infusion of diltiazem (15 micrograms/kg per min) or saline solution was alternated. Systolic thickening, hemodynamic variables and regional myocardial blood flow were measured serially over 24 h. Despite equally severe ischemic dysfunction during coronary occlusion, diltiazem-treated segments with systolic thinning during ischemia recovered control segmental thickening significantly earlier than saline solution-treated segments (at 30 versus 180 min of reperfusion). Blood pressure was mildly decreased during diltiazem treatment; therefore, a second group of 10 dogs underwent a similar occlusion and reflow period during infusion of nitroprusside to lower mean arterial pressure equivalently. Decreases in blood pressure in this group resulted in some improvement in segmental systolic function; however, this did not reach statistical significance at any time. Regional myocardial blood flows were similar in the saline solution- and diltiazem-treated groups during ischemia and reflow. Thus, it is concluded that 1) diltiazem infusion significantly enhanced recovery of segmental systolic thickening after 15 min of ischemia and 24 h of reperfusion; 2) the enhancement in segmental systolic function could not entirely be attributed to decreased mean arterial pressure; 3) improvement in postischemic segmental ventricular function was seen only in those segments with systolic thinning during ischemia; thus, segments with the most severe ischemic dysfunction benefited most; and 4) there were no important differences in regional myocardial blood flow during ischemia and reperfusion between saline- and diltiazem-treated animals.

Effects of diltiazem upon globally ischemic rat hearts

Addition of diltiazem (0.0, 0.95, 2.5 or 7.5 microM) to isolated working rat hearts before and during ischemia, produced a concentration-dependent increase in recovery of contractile function. Recovery of post-ischemic pressure-rate product showed a strong relationship with depression of pre-ischemic pressure-rate product, primarily from decreased heart rate before ischemia and increased pressure development following reperfusion. Increased recovery in treated hearts was associated with higher ATP and adenine nucleotide levels (ADN), but no relationship was observed between energy levels and degree of recovery of function or concentration of diltiazem. Hearts made ischemic for 20 min without reperfusion had increased ATP and decreased lactic acid accumulation when treated with 7.5 microM diltiazem. The results indicate contractile-dependent mechanisms of action of diltiazem in global ischemic hearts which can only be partly explained by preservation of ATP and ADN, but also are associated with reduced lactic acid accumulation.

Calcium channel blockers and cardiac surgery

Calcium channel blockers have an important role in the pharmacotherapy of cardiovascular disorders. These agents act by inhibiting the slow inward current into excitable cells, exert direct negative inotropic, chronotropic, and dromotropic activity, and are potent vasodilators. These direct effects are modified by reflex autonomic stimulation and by pathologic states. Serious adverse effects of the calcium channel blockers are most frequently observed in patients with ventricular dysfunction, conduction system disease, or concomitant beta blockade. Calcium channel blockers are indicated in the treatment of angina pectoris, supraventricular arrhythmias, and hypertension. The use of these agents in patients with hypertrophic cardiomyopathy, congestive heart failure, and pulmonary hypertension is investigational. The calcium channel blockers are gaining increased importance in the management of patients undergoing cardiac surgery. Verapamil is indicated for the treatment of post-cardiac-surgical atrial flutter and fibrillation; however, the calcium antagonists are not effective as prophylaxis against postoperative supraventricular arrhythmias. Laboratory studies have shown that drug interactions exist between calcium channel blockers and inhalational anesthetics and nondepolarizing neuromuscular blocking agents; clinical studies have demonstrated that these interactions are rarely significant. Perioperative coronary spasm can be effectively treated with the calcium channel blockers. The timing of calcium antagonist withdrawal prior to surgery is controversial, but continuation of therapy until surgery is usually safe. The clinical significance of platelet function inhibition by the calcium antagonists is unknown. Protection of ischemic myocardium by calcium channel blockers has been demonstrated. Important interactions between the calcium antagonists, hypothermia, and the ionic constituents of cardioplegia require further study before the role of these agents as adjuncts to clinical cardioplegia is defined. Expanded indications and the introduction of new calcium channel blockers will result in increased use of these agents in the future.

Effects of calcium antagonists on infarcting myocardium

Numerous studies have been conducted over the past 10 years on the effects of calcium antagonists on regional myocardial ischemia and infarct size. Verapamil, for example, reduced the degree of adenosine triphosphate degradation during 15 minutes of coronary occlusion followed by reperfusion in an anesthetized canine preparation. It also preserved the ultrastructural appearance of mitochondria in myocardium subjected to 1 hour of ischemia. Using an 8-hour permanent coronary artery occlusion model in which risk zone was assessed with radioactive microspheres and infarct size determined by tetrazolium staining, verapamil, administered 1 hour after occlusion, resulted in a modest decrease in infarct size. In a reperfusion model in which anesthetized dogs were subjected to 3 hours of coronary artery occlusion followed by 3 hours of reperfusion, verapamil decreased infarct size when it was administered during the period of ischemia, but failed to decrease infarct size when administered only during the reperfusion phase, i.e., after 3 hours of ischemia. Although verapamil is known to have negative inotropic effects, the newer calcium antagonist agent nisoldipine is less negatively inotropic, and might therefore be preferable in the situation of compromised hemodynamics. In a 6-hour permanent coronary artery occlusion model, nisoldipine decreased infarct size without decreasing left ventricular contractility. Most published reports support the concept that calcium antagonists decrease infarct size in models of experimental infarction. Of 4 major clinical studies, only 1 has shown that calcium antagonists are capable of reducing infarct size in man. However, in most of these studies, drug therapy commenced relatively late--4 or more hours after symptoms. In order for these drugs to demonstrate beneficial effects, the risk zone may have to be small and the degree of collateral flow adequate, the drug may have to be given very early or even before coronary occlusion (in a prophylactic fashion) and administration of the drug may have to be coupled to early coronary reperfusion.

Temperature-specific effects of adjuvant diltiazem therapy on myocardial energetics following potassium cardioplegic arrest

Adjuvant slow calcium channel blockade theoretically minimizes the calcium influx attendant to potassium-induced cardioplegic arrest, particularly if clinically acceptable levels of cardiac hypothermia are not maintained. The present study assessed the efficacy of diltiazem therapy in ameliorating perturbations of myocardial oxygen consumption that could be attributable to postischemic intracellular calcium accumulation. In 30 canine hearts, myocardial oxygen consumption was determined during incremental isovolumic pressure-volume loading before and 30 minutes after 2 hours of either 20 or 28 degrees C potassium cardioplegic arrest. The intracoronary perfusate in randomized hearts was modified by the addition of diltiazem, 150 micrograms/kg. Although systolic performance (as defined by peak developed pressure as compared with balloon volume curves) was unchanged after 20 degrees C ischemia, adjuvant diltiazem therapy prevented the 44 +/- 2% (p less than .01) decrease in peak developed pressure after 28 degrees C arrest. Moreover, the 39% augmentation of postischemic myocardial oxygen consumption at specific peak developed pressure following both 20 and 28 degrees C ischemia was attenuated with diltiazem only after the warmer ischemic interval. This difference was characterized by a larger (35 +/- 2 vs. 26 +/- 2%; p less than .025) decrease in postischemic oxygen extraction despite a comparable hyperemia. These data suggest that adjuvant diltiazem therapy during potassium-induced cardioplegic arrest preserves energy-efficient pump function only after warmer ischemia, thereby limiting the clinical application of this myoprotective regimen.

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).

The effect of diltiazem on myocardial recovery after regional ischemia in dogs

The effect of diltiazem on post-ischemic metabolic and functional recovery was investigated in regionally ischemic dog hearts. The duration of ischemia was 60 min, followed by 60 min of reperfusion. Diltiazem (bolus injection of 0.1 mg X kg-1 body weight prior to ischemia, followed by a continuous infusion of 0.1 mg X kg-1 X h-1) had no effect on residual coronary flow in the centre of the ischemic area, but blunted the reactive hyperemia response after restoration of flow. The drug partially prevented the depletion of ATP and glycogen in the severely underperfused subendocardial layers, i.e. when residual flow was below 0.1 ml X min-1 X g-1. Reduction of the content of these substances in the subepicardial layers was moderate and not influenced by diltiazem. Segment shortening in the subepicardial layers disappeared whereas segment lengthening was observed in the subendocardial layers during the ischemic period. Diltiazem did not prevent the loss of contractile function. Despite an initial restoration of contractile function within 10 min after reperfusion, no significant beneficial effect of diltiazem treatment on mechanical function of the reperfused area was present thereafter.

Timely administration of nisoldipine essential for prevention of myocardial ATP catabolism

Calcium entry blockers can effectively preserve high-energy phosphates in ischemic heart. However, little is known about the optimal timing of drug therapy. The moment of nisoldipine administration in relation to its protective efficacy during ischemia and reperfusion was studied in rat hearts. Nisoldipine (50 nM), given some time before a reduction of about 90% in coronary flow diminished ATP-catabolite efflux during both ischemia and reperfusion by up to 85%. In contrast, drug administration at the onset of ischemia, or during ischemia or during reperfusion was completely without protective effect. Similarly, early nisoldipine application gave rise to ischemic ATP, adenylate charge and creatine phosphate values higher than those in untreated or late-treated hearts. Nisoldipine decreased the tension developed before ischemia by up to 66%, without affecting (post)ischemic function. Nisoldipine spares energy effectively only if administered to the heart prior to ischemia. This presumably has to do with its negative inotropy before flow reduction.

An effect of ischemia on myocardial dihydropyridine binding sites

The [3H]nitrendipine binding activity of sarcolemmal fragments isolated from aerobically perfused or ischemic rat hearts was studied. After 90 min aerobic perfusion, two populations of binding sites were detected--high affinity sites with KD of 0.24 +/- 0.04 nM and Bmax 313 +/- 110 fmol/mg protein, and low affinity sites with KD of 47.6 +/- 8.7 nM and Bmax 12.4 +/- 1.88 pmol/mg protein. Sixty minutes global ischemia significantly reduced the KD of the low (15.8 +/- 2.9 nM, P less than 0.03) but not of the high (0.22 +/- 0.05 nM) affinity sites. Under these same conditions the Bmax of both the high (82.4 +/- 14.5 fmol/mg protein, P less than 0.03) and low (6.1 +/- 1.7 pmol/mg protein, P less than 0.01) affinity binding sites was reduced but the sites retained their selectivity, with nifedipine displacing bound [3H]nitrendipine more potently than D600. Bay K 8644, when added upon reperfusion, promoted a dose-related increase in Ca2+ entry which was reduced by nifedipine, indicating that dihydropyridine binding sites can be activated after 60 min ischemia.

Measurement of adenosine metabolites and metabolism in isolated tissue preparations

Several pitfalls have been encountered in setting up methodology for the study of adenosine metabolism and quantitation of adenosine metabolites in isolated tissue preparations. Quantitation of metabolites by high-performance liquid chromatography (HPLC) methods has shown that: 1. significant absorbtion of purines to some types of thread (used to tie up tissues in tissue baths) occurs; 2. without particular care in the preparation of tissue baths and medium, significant microbiological contamination can occur; 3. stimulation of guinea pig ileum preparations at 0.2 Hz is associated with weight loss of the tissue and release of purine-degrading enzymes into the bathing medium; 4. stability of purine analogs is dependent on the tissue and species. A method for the measurement of the purines uric acid, xanthine, hypoxanthine, inosine, adenosine, adenine nucleotides, and various substituted nucleotides in medium and tissue samples following incubations of rat vas deferens and guinea pig ileum is presented.