The effects of verapamil, quiescence, and cardioplegia on calcium exchange and mechanical function in ischemic rabbit myocardium

Regulation of cell death in the cardiovascular system

The adult heart is a post-mitotic terminally differentiated organ; therefore, beyond development, cardiomyocyte cell death is maladaptive. Heart disease is the leading cause of death in the world and aberrant cardiomyocyte cell death is the underlying problem for most cardiovascular-related diseases and fatalities. In this chapter, we will discuss the different cell death mechanisms that engage during normal cardiac development, aging, and disease states. The most abundant loss of cardiomyocytes occurs during a myocardial infarction, when the blood supply to the heart is obstructed, and the affected myocardium succumbs to cell death. Originally, this form of cell death was considered to be unregulated; however, research from the last half a century clearly demonstrates that this form of cell death is multifaceted and employees various degrees of regulation. We will explore all of the cell death pathways that have been implicated in this disease state and the potential interplay between them. Beyond myocardial infarction, we also explore the role and mechanisms of cardiomyocyte cell death in heart failure, myocarditis, and chemotherapeutic-induced cardiotoxicity. Inhibition of cardiomyocyte cell death has extensive therapeutic potential that will increase the longevity and health of the human heart.

Effects of intravenous diltiazem in a rat model of experimental coronary thrombotic microembolism

The aim of this study was to assess the feasibility of evaluating the therapeutic effects of intravenous diltiazem in a newly established rat model of coronary thrombotic micro-embolism (CME). CME was induced by injecting 0.199 ml saline containing 5 mg of automicrothrombotic particulates (∼10 μm) into the aorta of Sprague Dawley rats. The injection was carried out over 10 sec using a tuberculin syringe with a 28-gauge needle. The CME model rats were randomly divided into untreated (CME, n=38) and diltiazem-treated (CME+DIL, n=38) groups. Diltiazem (1 mg/ml, 50 μg/min/kg) was intravenously injected using an infusion pump through the tail vein for 175 min, 5 min following the injection of the automicrothrombotic particulates. Hemodynamic measurements, echocardiography and pathohistological examinations were performed at various time-points (3 h, 24 h and 7 and 28 days) postoperatively. Arteriolar thrombosis, multifocal myocardial necrosis, inflammatory cell infiltration with markedly increased myocardial tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) expression, reduced left ventricular (LV) systolic function and increased plasma von Willebrand factor (vWF), endothelin-1 (ET-1) and serum c-troponin I (c-TnI) levels (indicating vascular endothelial injury and myocardial necrosis) were observed in the CME model rats. These pathological responses in CME rats were partly attenuated by intravenous diltiazem treatment. The present CME model is suitable for evaluating the therapeutic effects of intravenous diltiazem; intravenous diltiazem treatment significantly improved cardiac function through alleviating inflammatory responses and microvascular thrombotic injury in this rat model of CME.

Mechanisms of vitexin preconditioning effects on cultured neonatal rat cardiomyocytes with anoxia and reoxygenation

This study was aimed at investigating the protective effect and mechanism of vitexin preconditioning (VPC) on cultured neonatal rat cardiomyocytes after anoxia and reoxygenation (A/R). An A/R model was established by using cultured neonatal rat cardiomyocytes. Cellular injury was evaluated by measuring cell viability, the releases of creatine kinase (CK), and lactate dehydrogenase (LDH). The apoptosis rate of cardiomyocytes after Anoxia/reoxygenation and the activities of extracellular signal-regulated protein kinases (ERKs) were measured. The intracellular calcium indicated by the fluorescence in cardiomyocytes was measured by the laser confocal microscope. Vitexin preconditioning (10, 30 and 100 microM) significantly enhanced the cell viability, markedly inhibited A/R-induced increases of LDH and CK release, obviously decreased the number of apoptotic cardiomyocytes and markedly decreased the fluorescence intensity value of [Ca(2+)](i) in cardiomyocytes. Exposure to anoxia or vitexin preconditioning significantly increased the phospho-ERK level, and the increase was markedly inhibited by PD98059, an inhibitor of the upstream kinase of ERK. These results suggest that vitexin preconditioning has a protective effect on cardiomyocytes A/R injury through the improvement of cell viability, decrease of LDH and CK release, such that the protective mechanism may relate to its ability to inhibit the cardiomyocytes apoptosis, reduce the cardiomyocytes calcium overload and increase the abundance of phosphor-ERK1/2 of the cardiomyocytes after anoxia and reoxygenation.

Importance of creatine kinase activity for functional recovery of myocardium after ischemia-reperfusion challenge

To define the relation between the phosphoryl transfer via creatine kinase and the ability to recover from an ischemia-reperfusion challenge, the authors chemically inhibited creatine kinase activity with iodoacetamide (IAm) and then measured myocardial recovery after 2, 10, or 30 min of global ischemia followed by 30 min of reperfusion in the isolated, arterially perfused interventricular septa of the rabbit heart. During normoxia, IAm (0.5 M perfused for 15 min) did not by itself modify developed tension, maximal rate of tension development, or resting tension. In ischemia, IAm pretreatment increased the rate of developed tension loss and highly diminished developed tension recovery after reperfusion for all the ischemia periods tested. Moreover, IAm significantly enhanced the maximal increase in the resting tension induced by 10 or 30 min of ischemia plus reperfusion. Lactate dehydrogenase activity in reperfusion was also significantly increased over untreated septa. On the basis of the present results, the authors suggest that the aggravating effects exhibited by IAm on the ischemic myocardium are compatible with its creatine kinase inhibition properties and that creatine kinase activity is essential for full recovery from an ischemia-reperfusion challenge.

Effects of dietary phytoestrogen on global myocardial ischemia-reperfusion injury in isolated female rat hearts

We investigated the effects of phytoestrogen on global myocardial ischemia-reperfusion injury in five groups of female rats. A high-phytoestrogen group (HPE) was ovariectomized (Ovx) and fed a diet containing soybean protein and a high-isoflavone soy extract. Another Ovx group of rats was fed the same diet as the HPE group but treated with the estrogen receptor blocker ICI-182,780 (HPE + ICI). A third group of Ovx rats was fed a diet containing soybean protein alone (low-phytoestrogen content; LPE). A fourth Ovx group was fed a diet free of phytoestrogen (Ovx). The fifth group of rats was sham ovariectomized (sham). Hearts from all rats were subjected to 30 min of global, hypothermic (4 degrees C), cardioplegic ischemia and 120 min of normothermic (37 degrees C) reperfusion with oxygenated Krebs-Henseleit buffer. Compared with either the sham or the HPE group, the Ovx and HPE + ICI groups had significantly decreased first derivative of left ventricular pressure (dP/dt), coronary flow rate (CFR), nitrite production and mitochondrial respiratory function and significantly increased Ca2+ accumulation and myocardial histological and ultrastructural injury. The CFR of the LPE group was significantly different from that of either Ovx or HPE + ICI group but the dP/dt, nitrite production, Ca2+ accumulation, and mitochondrial function were not. Our results indicate that diets containing phytoestrogen extract play a cardioprotective role in global myocardial ischemia-reperfusion in female rats.

Anesthetic modulation of myocardial ischemia and reperfusion injury in pigs: comparison between halothane and sevoflurane

PURPOSE

Halothane offers protection against the reperfusion injury of the myocardium. This study compared sevoflurane with halothane in its potential to modulate the effects of acute severe ischemia and reperfusion on the myocardium.

METHODS

Experiments were conducted on 25 pigs. Anesthesia consisted of thiopental, vecuronium and fentanyl. The lungs were mechanically ventilated with oxygen and nitrogen. Animals were randomly allocated to receive either I MAC halothane or sevoflurane. A control group received fentanyl and pentobarbital. Regional myocardial function was measured with sonomicrometers. The left anterior descending coronary artery was occluded for 15 min followed by 60 min reperfusion.

RESULTS

Neither halothane nor sevoflurane protected the heart against the effects of acute and severe regional myocardial ischemia. During reperfusion, 89% of the animals receiving sevoflurane suffered from ventricular fibrillation compared with 30% in the halothane group (P < 0.005). Five minutes into the reperfusion period the animals subjected to halothane anesthesia demonstrated an 88% recovery in regional myocardial systolic function while in the sevoflurane group the recovery was 40% of pre-ischemic control (P < 0.05).

CONCLUSION

Halothane is associated with less reperfusion arrhythmias and, in addition, recovery of regional myocardial function during reperfusion was more rapid in the presence of halothane than with sevoflurane.

Protective effects of cyclopiazonic acid on ischemia-reperfusion injury in rabbit hearts

The cardioprotective effects on myocardial ischemia of the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA) inhibitor, cyclopiazonic acid (CPA), were studied. We used the isolated arterially perfused interventricular septum of the rabbit heart submitted to 30-min global ischemia/30-min reperfusion. Mechanical [maximal increase in resting tension (MIRT), and the recovery of developed tension (RDT)], and biochemical parameters [creatine phosphokinase activity (CPK) in the effluent] were analyzed. CPA, 1 microM, perfused 30 min before the ischemia intervention significantly increased RDT by 54% and lessened MIRT by 66%. CPA also decreased CPK in the perfusate by 67.7 and 71.4% at 0-2 and 5-7 min of reperfusion, respectively. No additional benefits were shown either when the drug was perfused, both during ischemia and reperfusion, or with higher CPA concentrations (10-30 microM). The CPA cardioprotection was lost when the drug was present only during the reperfusion period. CPA exhibits functional and biochemical cardioprotective effects on myocardial ischemia. We postulated a decreased SR calcium contribution to the initial cytoplasmic calcium overload as the most probable mechanism involved.

Interrelationship between cellular calcium homeostasis and free radical generation in myocardial reperfusion injury

This review describes the interrelationship between two important biological factors, intracellular calcium overloading and oxygen-derived free radicals, which play a crucial role in the pathogenesis of myocardial ischemic reperfusion injury. Free radicals are generated during the reperfusion of ischemic myocardium, and polyunsaturated fatty acids in the membrane phospholipids are the likely targets of the free radical attack. On the other hand, activation of phospholipases can provoke the breakdown of membrane phospholipids which results in the activation of arachidonate cascade leading to the generation of prostaglandins, and oxygen free radicals can be produced during the interconversion of the prostaglandins. In conclusion, it has been emphasized that the two seemingly different causative factors of reperfusion injury, intracellular calcium overloading and free radical generation are, in fact, highly interrelated.

Global ischemia increases the density of voltage-dependent calcium channels in porcine cardiac sarcolemma

The objective of this work was to determine whether normothermic global cardiac ischemia in a porcine model was associated with a change in the density (Bmax) of voltage-dependent calcium channels in myocardial sarcolemmal membranes. Pigs were anesthetized, a thoracotomy was performed, and samples were taken of the left and right ventricles from control and ischemic hearts. Dihydropyridine-binding sites were quantified using [3H]isradipine, and 5'-nucleotidase activity was measured by the liberation of inorganic phosphate from adenosine monophosphate. Bmax and dissociation constants and 5'-nucleotidase activity for control and ischemic tissues, respectively, were compared by using Student's t-test for unpaired samples. After normothermic global ischemia, the Bmax of [3H]isradipine binding increased in the left ventricle by 81% (299% +/- 1.7% to 540% +/- 11% fmoles/mg, P < 0.01) and in the right ventricle by 33% (387% +/- 9.9% to 515% +/- 38% fmoles/mg, P < 0.01) compared with control. 5'-nucleotidase activity increased by 48% in the left ventricle and by 96% in the right ventricle (p < 0.05). Fifteen minutes of normothermic ischemia in the pig is associated with marked sarcolemmal abnormalities, including increases in specific dihydropyridine binding and 5'-nucleotidase activity, which reflect global changes in membrane function, which might contribute to the increase in myoplasmic calcium during ischemia.

Protective effect of l-cis-diltiazem on hypercontracture of rat myocytes induced by veratridine

The protective effect of l-cis-diltiazem, the stereoisomer of d-cis-diltiazem, was studied against the veratridine-induced hypercontracture of rat myocytes. Veratridine increased both [Na+]i and [Ca2+]i, but did not cause hypercontracture in the absence of extracellular Ca2+. Both l-cis-diltiazem (0.1-10 microM) and d-cis-diltiazem (10-30 microM) inhibited the hypercontracture and the increase in [Ca2+]i in a concentration-dependent manner. However, l-cis-diltiazem did not exert a negative inotropic effect in K+ (20 mM)-depolarized rat papillary muscles even at a dose of 10 microM. As seen in the case of tetrodotoxin, l-cis-diltiazem and d-cis-diltiazem also suppressed the increase in [Na+]i. The results show that l-cis-diltiazem prevents the veratridine-induced hypercontracture of myocytes by suppression of the [Ca2+]i increase. The attenuation of the [Ca2+]i increase by l-cis-diltiazem was not dependent on inhibition of Ca2+ channels, but was partly due to inhibition of excessive Na+ entry via veratridine-modified Na+ channels.

Effects of felodipine on the ischemic heart: insight into the mechanism of cytoprotection

To assess whether the administration of felodipine protects the myocardium in a dose-dependent manner against ischemia and reperfusion, isolated rabbit hearts were infused with three different concentrations of felodipine: 10(-10), 10(-9), and 10(-8) M. Diastolic and developed pressures were monitored; coronary effluent was collected and assayed for CPK activity and for noradrenaline concentration; mitochondria were harvested and assayed for respiratory activity; and ATP production and calcium content and tissue concentration of ATP, creatine phosphate (CP), and calcium were determined. The occurrence of oxidative stress during ischemia and reperfusion was also monitored in terms of tissue content and release of reduced (GSH) and oxidized (GSSG) glutathione. Treatment with felodipine at 10(-10) and 10(-9) M had no effect on the hearts when perfused under aerobic conditions, whilst the higher dose reduced developed pressure from 57.7 +/- 2.6 to 30.0 +/- 2.6 mmHg (p < 0.01). On reperfusion treated hearts recovered better than the untreated hearts with respect to left ventricular performance, replenishment of ATP and CP stores, and mitochondrial function. Recovery of developed pressure was 100% at 10(-8) M, 55% at 10(-9) M, and 46% at 10(-10) M. The reperfusion-induced tissue and mitochondrial calcium overload, release of CPK and noradrenaline, and oxidative stress were also significantly reduced. The effects of felodipine were dose dependent. Felodipine inhibited the initial rate of ATP-driven calcium uptake but failed to affect the initial rate of mitochondrial calcium transport. It is concluded that felodipine infusion provides dose-dependent protection of the heart against ischemia and reperfusion. Because this protection also occurred at 10(-9) M and 10(-10) M in the absence of a negative inotropic effect during normoxia and of a coronary dilatory effect during ischaemia, it cannot be attributed to an energy-sparing effect or to improvement in oxygen delivery. From our data we can envisage two other major mechanisms-(1) membrane protection and (2) reduction in oxygen toxicity. The ATP-sparing effect occurring at 10(-8) M is likely to be responsible for the further protection.

Prevention of reoxygenation-induced arrhythmias in guinea pig papillary muscles

Effects of various agents on reoxygenation-induced arrhythmias, action potentials, and tension of guinea pig papillary muscles were recorded to investigate the site of action. Triggered activities due to delayed afterdepolarizations (DADs) and aftercontractions were elicited on reoxygenation after 60-min substrate-free hypoxia. Low extracellular Ca2+ (0.1 mM) abolished arrhythmias, and high Ca2+ (4.9 mM) increased the amplitudes of DADs and aftercontractions. D-600 at the high concentration (20 microM) decreased the incidence of arrhythmias (p < 0.05 vs. no drug) and decreased the recovery of developed tension after reoxygenation (p < 0.001). Ryanodine (1 microM) abolished aftercontractions and arrhythmias but did not affect the recovery of developed tension. Tetrodotoxin (TTX 3 microM) and nicorandil (100 microM) decreased the incidence of arrhythmias (p < 0.05), but did not affect the recovery of developed tension or the amplitudes of aftercontractions. TTX caused only a slight decrease in Ca2+ transients in a fluo-3-loaded guinea pig ventricular myocyte. The Ca2+ entry through the Ca2+ channels apparently synchronized Ca2+ release from the sarcoplasmic reticulum, and D-600 at the high concentration apparently decreased the incidence of arrhythmias. TTX and nicorandil decreased arrhythmias, probably by decreasing the Na+ current or by increasing the ATP-sensitive K+ current, respectively.

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.

Lack of platelet-activating factor release on acute myocardial ischemia in the isolated interventricular septum of rabbit heart

The effects of platelet-activating factor (PAF) on myocardial injury after 1 h global ischemia-30 min reperfusion were investigated in isolated arterially perfused interventricular septum of rabbit heart. PAF did not significantly affect developed tension, +/- dT/dtmax, resting tension and the times of active state in non-ischemic septa. The recovery of developed tension was significantly reduced by PAF (100 nM), after an ischemia-reperfusion challenge, from the control value of 20.9 +/- 3.5% to 10.5 +/- 1.8%, without a change in the resting tension (15.7 +/- 2.8 vs. 15.6 +/- 1.3 g). BN 52021 (20 microM), alone did not modify either parameter of ischemic damage, but antagonized the aggravating effect of PAF. Evidence of PAF activity was not found in any of the samples of the effluent perfusate obtained from ischemic control experiments. On the basis of the present results, we suggest a direct role for PAF in aggravating the myocardial damage induced by ischemia, and discard heart cells as the source of PAF in this state.

The adverse effects of long-term cassava (Manihot esculenta Crantz) consumption

Cassava (Manihot esculenta Crantz) is an important dietary staple for more than 500 million people in developing countries. People eat 60% of the cassava produced and one third of the harvest feeds animals. All cultivars of cassava contain the cyanogenic glucoside, linamarin, but in different concentrations. The roots of those cultivars with high cyanogenic content are processed to reduce the level of linamarin, because linamarin is hydrolysed in the intestinal tract of both men and animals by microbial flora and HCN is released. Researchers have implicated the sublethal levels of HCN produced on ingestion in the development of a number of metabolic diseases in both man and animals when cassava-based diets are consumed over a long period of time but the release of HCN cannot fully explain the metabolic effects of ingested linamarin. A significant amount of linamarin remains intact and is excreted in the urine. It appears that the intact linamarin inhibits Na+K+ATPase causing electrolyte imbalance within the cell. This phenomenon is exacerbated by free radicals generated by the hypoxia/normoxia cycles created by cyanide released from linamarin, which cause lipid peroxidation and cell membrane damage. When the supply of endogenous thiosulphate is adequate, cyanide plays a very minor role in the development of lesions. The amount of damage is related to the quantity of linamarin routinely ingested at sublethal levels. There appears to be species differences in the rate of the development of diseases and the intensity.

Down-regulation of protein kinase C attenuates the oxidant hydrogen peroxide-mediated activation of phospholipase A2 in pulmonary vascular smooth muscle cells

Exposure of rabbit pulmonary vascular smooth muscle cells to H2O2 dose-dependently stimulates the cell membrane associated protein kinase C (PKC) activity, phospholipase A2 (PLA2) activity, phospholipase A2 (PLA2) activity, and arachidonic acid (AA0) release. Pretreatment of the cells with staurosporine (an inhibitor of PKC) prevents AA release and PLA2 activity caused by H2O2. Treatment of the cells with 4 beta-PMA (an active phorbol ester), or 4 alpha-PMA (an inactive phorbol ester) does not affect basal AA release. In contrast, 4 beta-PMA significantly stimulates the cell membrane associated PKC activity. Treatment of the cells with 4 beta-PMA for a short time (up-regulation of PKC) augments PLA2 activity and AA release caused by a sub-optimal dose of H2O2 (0.4 mM). Under this condition, staurosporine prevents the stimulatory effects of 4 beta-PMA on membrane PLA2 activity, and AA release. In contrast to the up-regulation, pretreatment with 4 beta-PMA for a longer time (down-regulation of PKC) does not appreciably augment PLA2 activity and AA release caused by 0.4 mM H2O2. Treatment of the cells with an intracellular Ca2+ antagonist TBM-8 prevents H2O2 induced membrane PLA2 activity and AA release without affecting membrane PKC activity. Treatment of the cells with TMB-8 before addition of 4 beta-PMA (up-regulation of PKC) followed by incubation with 0.4 mM H2O2 does not augment PLA2 activity and AA release, although membrane PKC activity increases under this condition.

31P nuclear magnetic resonance study of the effects of the calcium ion channel antagonist fantofarone on the rat heart

The biochemical and mechanical effects of a new calcium ion channel antagonist, fantofarone ((2-isopropyl-1-((4-(3-(N-methyl-N-(3,4-dimethoxy-beta-phenethyl)-amino) propyloxy)benzenesulfonyl))-indolizine), on isovolumic perfused rat heart have been assessed by using 31P nuclear magnetic resonance (NMR) spectroscopy together with simultaneous monitoring of myocardial mechanical function. Cytosolic pH and phosphocreatine, adenosine triphosphate and inorganic phosphate contents were monitored by using 31P NMR. Heart rate, coronary flow and left ventricular developed pressure were measured routinely to assess mechanical function. Perfusion with 10 nM, 100 nM or 1 microM fantofarone for a period of 48 min did not cause any measurable metabolic changes. However, coronary vasodilatation and a partial positive inotropic effect were noted. A 15-min pretreatment with 100 nM did not protect against the deleterious effects of an 18-min period of normothermic, zero-flow ischemia. In contrast, a 20-min pretreatment period with 1 microM fantofarone significantly improved the recovery of mechanical performance, metabolic activity and pH after the same 18 min of ischemia. While only a slight protection of the ATP pool was noted during the ischemic period, major beneficial effects were observed during the reperfusion period, such that reflow was characterized by high recoveries of left ventricular pressure and rate pressure product (70-80%), low end diastolic pressure (< 10 mm Hg), significant recovery of ATP content (to 55%), a complete repletion of the phosphocreatine pool and a fast return of cytosolic pH to normal value.

Attenuation of myocardial reperfusion injury by reducing intracellular calcium overloading with dihydropyridines

The effects of three different dihydropyridine (DHP) calcium channel antagonists, nisoldipine, nimodipine, and nifedipine, on myocardial ischemic and reperfusion injury were studied using isolated rat hearts subjected to ischemia and reperfusion. Hearts were perfused with Krebs-Henseleit bicarbonate buffer containing 0, 4, 16, 64 and 100 nM concentrations of the above dihydropyridines for 15 min. Global ischemia was then induced by terminating the aortic flow for 30 min at 37 degrees, followed by 30 min of reperfusion. Left ventricular (LV) functional (LV developed pressure, its first derivative and coronary flow) and biochemical parameters (creatine kinase release) were monitored prior to ischemia and during reperfusion. In separate group of hearts, intracellular free Ca2+ ([Ca2+]i) was monitored with an intracellular calcium analyzer using a fluorescent Ca2+ indicator (Fura-2 AM). Tissue Ca2+ was also measured by atomic absorption spectroscopy after perfusing the hearts with ion-free cold buffer to wash out extracellular Ca2+. Significant recovery of the coronary flow was observed in all hearts treated with a high concentration (100 nM) of DHPs compared with the control group (P < 0.05), while a lower dose of nisoldipine (16 nM) and nifedipine (64 nM) also improved the coronary flow effectively. Reduction of myocardial creatine kinase release and improvement of the recovery of LV developed pressure, dp/dtmax, were achieved by DHPs in a concentration-dependent manner. A higher concentration of DHPs also decreased the formation of myocardial thiobarbituric acid reactive substances, although these compounds did not possess direct free radical scavenging effects in vitro. Tissue Ca2+ content was reduced significantly in treated groups. The rise of [Ca2+]i during ischemia and reperfusion appeared to be attenuated by these DHPs. The concentration-response study of the three DHPs showed the effective concentrations for reducing [Ca2+]i to be 16, 64 and 100 nM nisoldipine, nifedipine and nimodipine, respectively, in this experimental setting. The above results indicate that pretreatment with DHPs can attenuate the myocardial reperfusion injury by modulating Ca2+ overloading and decreasing the susceptibility of the membrane to free radical attack.

The effects of calcium channel antagonist treatment and oxygen radical scavenging on infarct size and the no-reflow phenomenon in reperfused hearts

Calcium antagonists reduce ischemic injury, and anti-free-radical interventions may reduce reperfusion injury. However, the effects of treatment with both interventions have never been investigated. In the present study, anesthetized rabbits underwent 30 minutes of coronary artery ligation, which was followed by 5.5 hours of reflow. Eight animals in each group received: (1) the calcium antagonist gallopamil during ischemia, (2) the oxygen radical scavenger superoxide dismutase during reperfusion, (3) combined treatment with gallopamil and superoxide dismutase, and (4) saline solution. All groups were similar with respect to collateral flow during ischemia and extent of risk region. Infarct size averaged 60.2% +/- 5.5% of risk region in controls and was significantly smaller (p < 0.001) in rabbits that were treated with either gallopamil (28.1% +/- 3.4%) of superoxide dismutase (29.3% +/- 3.2%). Little further reduction in infarct size was observed with combination therapy (22.9% +/- 3.2% of risk region; p = NS). Superoxide dismutase had no effects on hemodynamics, whereas gallopamil significantly reduced heart rate, mean arterial pressure, and rate-pressure product. However, the reduction in infarct size that was observed in gallopamil-treated rabbits significantly exceeded the expected value in this group after corrections were made for changes in these determinants of ischemic injury. Therefore we investigated whether other factors may have contributed to the beneficial effects of gallopamil. In vitro the drug had no oxygen radical scavenging activity, nor did it exert antioxidant effects. In addition, gallopamil did not affect neutrophil function. In conclusion, in this acute model myocardial cell necrosis was significantly reduced either by administration of a calcium antagonist during ischemia or by removing oxygen radicals during reperfusion. However, superoxide dismutase administration did not further reduce infarct size when given to animals that had been treated with gallopamil. Since gallopamil has no direct effect on several mechanisms of reperfusion injury, these data suggest that calcium antagonists, by decreasing myocardial oxygen demand during ischemia, may indirectly reduce oxygen radical damage during subsequent reperfusion.

Activation of ATP-sensitive K+ channels by cromakalim. Effects on cellular K+ loss and cardiac function in ischemic and reperfused mammalian ventricle

Pharmacological modulation of [K+]o accumulation and action potential changes during acute myocardial ischemia is under evaluation as a promising new antiarrhythmic and cardioprotective strategy during myocardial ischemia and reperfusion. We studied the effects of cromakalim, a K+ channel opener that activates ATP-sensitive K+ channels, in isolated arterially perfused rabbit interventricular septa subjected to ischemia and reperfusion and, through use of the patch clamp technique, in inside-out membrane patches excised from guinea pig ventricular myocytes. During aerobic perfusion, 5 microM cromakalim shortened action potential duration (APD) from 217 +/- 7 to 201 +/- 10 msec, had no effect on [K+]o, and reduced tension by 17 +/- 3% (n = 11). During ischemia, pretreatment with 5 microM cromakalim resulted in 1) more rapid APD shortening (71 +/- 9 versus 166 +/- 7 msec at 10 minutes and 63 +/- 12 versus 122 +/- 8 msec at 30 minutes), 2) similar [K+]o accumulation after 10 minutes (8.9 +/- 0.3 versus 9.6 +/- 0.5 mM) but a trend toward increased [K+]o accumulation after 30 minutes (11.0 +/- 1.7 versus 9.6 +/- 1.0 mM), and 3) similar times for tension to decline to 50% of control (2.14 +/- 0.16 versus 2.14 +/- 0.19 minutes) but shorter time to fall to 20% of control (4.34 +/- 0.33 versus 4.90 +/- 0.22 minutes; p = 0.003). After 60 minutes of reperfusion following 30 minutes of ischemia, recovery of function was similar, with a trend toward better recovery of developed tension (to 58 +/- 9% versus 39 +/- 10% of control; p = 0.18) and tissue ATP levels in cromakalim-treated hearts but no differences in APD or rest tension. Thus, 5 microM cromakalim had mild effects in normal heart but greatly accelerated APD shortening during ischemia without markedly increasing [K+]o accumulation, possibly because the more rapid APD shortening reduced the time-averaged driving force for K+ efflux through ATP-sensitive K+ channels. A significant cardioprotective effect during 30 minutes of ischemia plus 60 minutes of reperfusion could not be demonstrated in this model. In excised membrane patches studied at room temperature, the ability of cromakalim to activate ATP-sensitive K+ channels was significantly potentiated by 100 microM but not 15 microM cytosolic ADP, suggesting that in addition to the modest fall in cytosolic ATP during early ischemia, the rapid increases in cytosolic ADP may further sensitize cardiac ATP-sensitive K+ channels to activation by cromakalim.(ABSTRACT TRUNCATED AT 400 WORDS)

Moderation of myocardial ischemia reperfusion injury by calcium channel and calmodulin receptor inhibition

Intracellular Ca2+ accumulation is implicated in the pathogenesis of myocardial reperfusion injury. To study approaches designed to modify Ca2+ uptake during coronary revascularization after acute infarction, a pig heart surgical infarct model (left anterior descending artery occlusion for 60 min) was subjected to 60 min hypothermic potassium cardioplegic arrest, followed by 60 min of global reperfusion. Four groups of six hearts each were studied in a randomized manner, i.e., cardioplegia alone (control), cardioplegia + 10 microM diltiazem (Ca2+ slow channel blocker), cardioplegia + 10 microM trifluoperazine (TFP), (a Ca(2+)-calmodulin antagonist), and cardioplegia+diltiazem (10 microM) + TFP (10 microM). Left ventricular contractility (global and segmental), metabolism (coronary blood flow and O2 consumption), and creatine kinase generation were measured during reperfusion. Both the Ca2+ channel blocker, diltiazem, and the calmodulin antagonist, TFP, improved myocardial global and regional function as well as myocardial metabolism. While diltiazem better restored global and regional contractility, trifluoperazine had a greater effect on coronary blood flow and myocardial oxygen consumption. Enzyme release and lipid peroxidation were equally moderated by both drugs. From this study it can be concluded that Ca2+ influx does play a role in ischemic and reperfusion injury. The mechanisms of its effect are complex, but can be successfully antagonized by Ca2+ blockers as well as by calmodulin antagonists, with improved myocardial preservation.

Myocardial fatty acid oxidation during ischemia and reperfusion

Inhibition of fatty acid oxidation is an early event in myocardial ischemia that most likely contributes to tissue injury by the accumulation of potentially toxic intermediates such as acylCoA and acylcarnitine. After reperfusion both myocardial oxygen consumption and fatty acid oxidation may rapidly recover to preischemic levels, even when contractile function remains depressed. The mechanisms underlying the apparent dissociation between contractile function and oxidative metabolism early during reperfusion are still controversial. In isolated rat hearts subjected to 60 min of no-flow ischemia myocardial oxygen consumption and oxidation of palmitate were lowered during reperfusion by 3 mM of NiCl2 and by 6 microM of ruthenium red. The results provide indirect evidence for the hypothesis that intracellular calcium transport may be involved in the mechanisms responsible for the high oxidative metabolic rate early after reperfusion.

Myocardial Na+ during ischemia and accumulation of Ca2+ after reperfusion: a study with monensin and dichlorobenzamil

The intracellular cation contents were determined in isolated perfused rat heart using cobaltic EDTA as a marker of the extracellular space. In hearts in which Na+ accumulation was induced with monensin, a Na+ ionophore, during 20 min-ischemia which otherwise did not result in accumulation of Na+, the levels of Na+ and Ca2+ were significantly higher after reperfusion with a significant decrease in K+. While the recovery of the cardiac mechanical function (CMF) was complete after reperfusion in control hearts, the recovery was incomplete in monensin-hearts. Dichlorobenzamil (DCB), the most specific inhibitor of Na(+)-Ca2+ exchanger, infused for 10 min before induction of ischemia in a dose of 10(-5) M, which produced a definite suppression of CMF (over 80%), inhibited the accumulation of Ca2+ and Na+ and the loss of K+ and ATP after 40 min-ischemia and reperfusion. The same dose of DCB given for 3 min before induction of ischemia and after reperfusion, which produced a less than 20% inhibition of CMF, failed to prevent the Ca2+ accumulation after 40 min-ischemia and reperfusion. These findings are at variance with the idea that the accumulation of Na+ during ischemia and the consequent augmented operation of Na(+)-Ca2+ exchange is responsible for accumulation of Ca2+ after reperfusion.

The leakage of fatty acid binding protein from cultured myocardial cells during hypoxia

Fatty-acid binding protein (FABP) is thought to play an important role as a carrier protein of fatty acids in cells. It may leak from damaged cells, because its molecular weight is low (mol wt 14000) and it accounts for several percent of soluble protein. In this experiment we attempted to use FABP as a marker of cell injury under hypoxia in cultured myocytes. Newborn-rat myocytes were incubated under hypoxic treatment for 6 hours, and then the releases of FABP and CPK were measured. The cell-death ratio during hypoxygenation increased from 4 hours and rose to 80% at 6 hours, but it was only 8% under aerobic conditions. FABP in medium was detected at 1 hour, and rapidly increased and reached a plateau at 4 hours. On the other hand, CPK in medium was negligible during the 3 hours, then slightly increased. Ca antagonists and a beta 1-adrenergic blocking agent inhibited the release of FABP and prevented cell death. But the alpha 1-adrenergic blocking agent had little effect on preventing FABP leakage and cell death. These results show that FABP is of use as a marker of myocardial cell injury and revealed that the Ca antagonist and beta 1-adrenergic blocking agent are useful drugs for the protection of myocardial cell injury in hypoxia.

Effect of cardioplegic preservation on intracellular calcium transients

Intracellular Ca2+ ([Ca2+]i) plays a pivotal role in the regulation of cardiac function. We investigated the effect of cardioplegic preservation on [Ca2+]i transients in the isolated and perfused guinea pig heart loaded with a fluorescent Ca2+ indicator (fura-2). The measurements of [Ca2+]i transients and isovolumetric left ventricular pressure revealed that [Ca2+]i transients and mechanical responses to [Ca2+]i were markedly altered during 15 minutes of normothermic global ischemia and after reperfusion. First, [Ca2+]i transients remained during ischemia without generation of active force of contraction. Such a manifestation of depressed sensitivity of the myofilaments to Ca2+ persisted for the first 5 minutes after reperfusion. Second, the amplitude of [Ca2+]i was diminished during ischemia and reperfusion. Third, diastolic [Ca2+]i was increased during ischemia and especially at the onset of reperfusion. Bolus infusion of cold St. Thomas' Hospital solution abolished [Ca2+]i transients and left ventricular pressure development at an end-diastolic level. Moreover, improved recovery of left ventricular function during reperfusion afforded by the hypothermic cardioplegia was intimately related to its ability to modulate impaired [Ca2+]i transients and mechanical responses to [Ca2+]i; improvement of systolic left ventricular function appears to be produced by restoration of Ca2+ sensitivity of the myofilaments and the amplitude of [Ca2+]i transients, whereas better diastolic compliance of the left ventricle is ascribed to significantly lower diastolic [Ca2+]i. These results may provide new insight into the mechanism of cardioplegic preservation on the basis of [Ca2+]i transients.

Phospholipid metabolism and prostacyclin synthesis in hypoxic myocytes

We observed that in hypoxic myocardial cells prostacyclin and arachidonic acid release increased and that during hypoxia phospholipid degradation also occurred. In order to clarify the mechanism of phospholipid degradation, we determined the activity of phospholipases A2 and C. We found that phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were markedly decreased and that lysophosphatidylcholine and lysophosphatidylethanolamine were increased. In contrast, there was only slight phosphatidylinositol degradation and no lysophosphatidylinositol elevation was observed. These results show that phospholipase A2 was activated in hypoxic myocytes and had substrate specificity towards PC and PE. To study phospholipase C activity, membrane phospholipids were labeled with [3H]choline, [3H]inositol or [3H]ethanolamine. The release of inositol was observed, but neither choline nor ethanolamine was released. In hypoxia, myocardial-cell phospholipase C has high substrate specificity towards phosphatidylinositol. The activation of phospholipases is closely related to the intracellular Ca2+ concentration; it is though that inositol polyphosphatides may regulate intracellular Ca2+. We determined how Ca2+ influx occurs in hypoxia. beta-Adrenergic blockade and Ca2+ antagonists markedly suppressed Ca2+ influx, phospholipase A2 activity, phospholipase C activity and cell death. However, the alpha 1-adrenergic blockade was less effective in suppressing these phenomena. These results suggest that in hypoxic myocardial cells Ca2+ influx mediated by beta-adrenergic stimulation activates phospholipases A2 and C, and that phospholipid degradation and prostacyclin release then occur.

Role of timing of administration in the cardioprotective effect of iloprost, a stable prostacyclin mimetic

We administered iloprost, a stable prostacyclin mimetic, 27 nM, to isolated and perfused rabbit hearts submitted, after 60 min of equilibration, to an ischaemic period (60 min at a coronary flow of 1 ml/min) followed by a period of reperfusion (30 min at a coronary flow of 25 ml/min). Iloprost was delivered at different times during the experimental protocol: 60 min before ischaemia, at the onset and after 30 min of ischaemia and only during reperfusion. The iloprost cardioprotective effect was evaluated in terms of recovery of left ventricular pressure developed during reperfusion, creatine phosphokinase (CPK) and noradrenaline release, mitochondrial function (expressed as yield, RCI (respiratory control index), QO2, ADP/O), ATP and creatine phosphate (CP) tissue contents, calcium homeostasis and by measuring several parameters of oxidative stress: reduced and oxidized glutathione release and tissue contents, Mn and Cu-Zn superoxide dismutase activities; glutathione reductase and peroxidase activities. Our data show that the cytoprotective action of iloprost is closely related to the time of administration. Optimal myocardial preservation was achieved when it was given before or at the onset of ischaemia. Iloprost administration 30 min after the onset of ischaemia was still beneficial, although to a lesser extent. Iloprost lost its protective effect when given only on reperfusion. The data suggest that the iloprost cardioprotective effect is related to maintainance of membrane integrity.

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.

Comparison of dihydropyridine and phenylalkylamine calcium antagonists in patients with coronary heart disease

To evaluate possible differences between dihydropyridine and phenylalkylamine calcium antagonists in the setting of chronic stable angina, 2 placebo-controlled, double-blind, crossover trials were conducted comparing the effects of gallopamil and nifedipine on exercise tolerance and ischaemic ST depression, using standard as well as slow release formulations. In the first study, 30 patients received standard formulations of gallopamil (50mg 3 times daily) and nifedipine (20mg 3 times daily). This trial was stopped after 9 patients had been enrolled, because of severe exacerbation of angina in 3 nifedipine recipients. 21 patients then entered a second protocol in which the nifedipine dose was reduced to 10mg 3 times daily. Compared with the preceding placebo periods, time to angina onset and total exercise time were statistically significantly (p less than 0.01) prolonged by gallopamil (by 30 and 18%, respectively), and nonsignificantly prolonged by nifedipine (by 20 and 13%, respectively), after 4 weeks' treatment. Increases in heart rate and rate-pressure product at maximal comparable workloads were less with gallopamil than with nifedipine (p less than 0.01). In contrast to nifedipine, gallopamil was associated with very few side effects. The second trial comprised 24 patients who received slow release formulations of gallopamil (100mg twice daily) and nifedipine (20mg twice daily) over 2 weeks. Again, both drugs exhibited significant anti-ischaemic efficacy, as evidenced by reductions in ST depression at maximal comparable workloads and increases in exercise time compared with placebo, but the differences between the treatments were not statistically significant. Side effects were more frequent with nifedipine, but less severe than with the standard formulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitochondria, oxygen and reperfusion damage

Reperfusion of the ischaemic or hypoxic heart elicits a number of oxygen dependent processes such as cell lysis and Ca2+ uptake. It is known that the energisation of mitochondria, which requires oxygen, plays a key role in these processes and that the organelle actively sequesters Ca2+ under these circumstances. In this brief review we discuss how oxidants derived from mitochondrial electron transport may perturb mitochondrial calcium handling on reoxygenation of the hypoxic myocardium. In addition we show that the immunosuppressive agent cyclosporin has little or no effect on the oxygen dependent increase in total cell Ca2+ which occurs when hypoxic myocytes are reoxygenated. This result suggests that the Ca2+ dependent mitochondrial pore, which is known to function under conditions of oxidative stress, does not play a major role in the perturbation of Ca2+ homeostasis which occurs on reoxygenation of hypoxic hearts.

Cardioprotective effects of amlodipine on ischemia and reperfusion in two experimental models

The cardioprotective effect of amlodipine, a long-acting dihydropyridine derivative, was studied in 2 experimental models of ischemia and reperfusion. Isolated and blood-perfused feline hearts were made globally ischemic for 60 minutes and then reperfused for 60 minutes. Alterations of left ventricular developed pressure and compliance were monitored in both amlodipine-treated hearts and saline-treated control animals. Changes in perfusion pressure indicated that amlodipine significantly reduced myocardial oxygen consumption and coronary vascular resistance. Furthermore, a progressive increase in resting left ventricular diastolic pressure indicated that amlodipine, administered before the onset of global ischemia, attenuated the development of ischemic contracture. Return of contractile function 60 minutes after reperfusion and maintenance of tissue concentrations of electrolytes were significantly better in the amlodipine-treated group than in the control animals. In intact canine hearts, regional myocardial ischemia was induced for 90 minutes, followed by 6 hours of reperfusion. Although the hemodynamic variables and the size of the region of risk did not differ significantly between treated animals and control animals, the infarct size was significantly smaller in the amlodipine-treated group than in the control animals, and a gradual reduction in coronary blood flow was observed in the control group that was prevented in the amlodipine group. A comparison of these findings with those observed with oxygen radical scavengers also is discussed. A detailed report of these studies was published in The American Journal of Cardiology (1989;64:101I-116I). This review is included here to maintain continuity of the symposium for the convenience of the reader.

Protecting the vasculature: an eye toward the future

Although calcium antagonists were originally developed for use in the management of patients with angina pectoris, they are now used in the management of other cardiovascular disorders, including hypertension. More recently, the calcium antagonists have been under investigation for their potential protective role in atherosclerosis. Coupled with these new possibilities for therapeutic use are the development of new, long-acting, tissue-specific calcium antagonists. Amlodipine belongs to this group, and although it is a dihydropyridine-based calcium antagonist, its pharmacologic profile differs from that of other dihydropyridine-based calcium antagonists. Differences include: different pH optimum for receptor binding, different rates of association and dissociation, and differences in allosteric interaction with the diltiazem and verapamil binding sites. Amlodipine, when given orally to rabbits receiving a high-cholesterol diet, reduces atheroma formation. Evidence of its ability to protect the vasculature is provided by its ability to significantly increase (p less than 0.001) survival in stroke-prone hypertensive rats.

Advantages of beta blockers versus antiarrhythmic agents and calcium antagonists in secondary prevention after myocardial infarction

Patients who have sustained greater than or equal to 1 myocardial infarcts are at high risk for sudden death or reinfarction; the risk is highest for those with lowest ventricular ejection fraction, continuing myocardial ischemia and asymptomatic high-density and complex premature ventricular contractions. At present, beta blockers when given prophylactically are the only agents that reduce the incidence of sudden death and reinfarction in survivors of myocardial infarction (MI) in the first 2 years. The beneficial effect was shown to correlate with a reduction in heart rate, the effect being absent or deleterious with beta blockers with marked sympathomimetic activity. The effects of beta blockers on ventricular fibrillation appeared to be dissociated from those on premature ventricular contractions. Trials with calcium antagonists indicate that these drugs had no effect or increased the mortality rate. The divergent effect of beta blockers and calcium antagonists is unexplained but may be due in part to a lack of bradycardiac effect of calcium antagonists; there were no differences in effect among different calcium antagonists. Data from trials involving class I antiarrhythmic agents indicate that agents acting by depression of cardiac conduction are either devoid of effect or produce a modest increase in mortality. Results of the Cardiac Arrhythmia Suppression Trial, employing the newer class I agents flecainide and encainide, were used to determine whether the suppression of premature ventricular contractions in the survivors of acute MI reduces mortality. Flecainide and encainide suppressed premature ventricular contractions greater than 80%, but resulted in an increased mortality rate undoubtedly due to a marked proarrhythmic effect. Whether these data can be extrapolated to all class I agents is uncertain. Preliminary data with class III antiarrhythmic agents suggest that these agents, especially amiodarone, similarly to beta blockers, have the potential to reduce mortality in survivors of MI. Evolving data suggest that in the secondary prevention of morbid events in the survivors of acute MI, the focus must shift away from antiarrhythmic agents that delay conduction and toward beta blockers and antifibrillatory actions resulting from a prolongation of refractoriness.

Beneficial effect of tan-shen, an extract from the root of Salvia, on post-hypoxic recovery of cardiac contractile force

The present study was undertaken to elucidate the possible effects of tanshinone VI, one of the extracts from the root of Salvia, on post-hypoxic recovery of cardiac contractile force. For this purpose, rat hearts were perfused for 45 min under reoxygenated conditions following 20-min hypoxic perfusion, and changes in tissue high-energy phosphates and calcium contents, and release of ATP metabolites and creatine kinase were examined. Post-hypoxic recovery of cardiac contractile force was augmented when hearts were treated with 42 nM tanshinone VI during hypoxia. This beneficial recovery was accompanied by enhanced restoration of myocardial high-energy phosphates, depression of hypoxia- and reoxygenation-induced increase in tissue calcium content, and suppression of release of ATP metabolites such as adenosine, inosine and hypoxanthine from the perfused heart. The results suggest that tanshinone VI is beneficial for the recovery of cardiac contractility after a certain period of oxygen-deficiency, possibly through mechanisms involving improvement of myocardial energy production upon oxygen-replenishment and/or inhibition of calcium accumulation in the cardiac cell.

Effects of amiloride on metabolism and contractility during reoxygenation in perfused rat hearts

Myocardial recovery after hypoxia may be determined not only by the extent of metabolic depression during the hypoxic period but also by changes in cation contents as well. Calcium overload during reoxygenation, mediated in part by Na-Ca exchange and supported by the rise in cell sodium during hypoxia, may be one factor. The effects of amiloride (0.1 mM), a diuretic that inhibits Na(+)-H+ and Na-Ca exchanges in cardiac sarcolemma and mitochondria preparations, were studied during hypoxia-reoxygenation in the isovolumic, isolated rat heart. During hypoxia, cell sodium, measured using potassium ethylenediamine tetraacetate cobaltate as an extracellular marker, increased in amiloride and amiloride-free hearts, but there was no increase in cell calcium (3.3 +/- 0.3 vs. 3.6 +/- 0.9 mumol/g dry wt; p = NS). Amiloride did not alter developed pressure (DP), end-diastolic pressure (EDP), pH, or integrated areas of adenosine triphosphate (ATP) and phosphocreatine (PCr) (determined by phosphorus-31-nuclear magnetic resonance spectroscopy) during hypoxia or normal perfusion conditions. Forty minutes after reoxygenation, however, cell calcium was significantly lower in the amiloride (5.1 +/- 1.3 mumol/g dry wt) than in the amiloride-free group (10.4 +/- 1.8 mumol/g dry wt; p less than 0.001), and there was improved recovery of DP (percent of initial) (72 +/- 12% vs. 41 +/- 12%; p less than 0.001), PCr (99 +/- 9% vs. 70 +/- 14%; p less than 0.001), and pH (7.17 +/- 0.17 vs. 6.88 +/- 0.16; p less than 0.001) in the amiloride group. To determine whether this dose of amiloride inhibits the manifestations of sodium-mediated calcium gain in the same model during normoxia, the metabolic and functional sequelae of lithium-substituted low sodium (50 mM) perfusion were studied. Amiloride significantly limited the manifestations of sodium-mediated calcium gain as indexed (all expressed as percent of control) by a lower peak DP (221 +/- 25% vs. 284 +/- 20%) at 3 minutes, improved preservation of PCr (85 +/- 10% vs. 68 +/- 9%) and ATP (104 +/- 12% vs. 84 +/- 9%), lower rise in inorganic phosphate (201 +/- 74% vs. 332 +/- 106%), and a smaller fall in intracellular pH (7.01 +/- 0.04 vs. 6.70 +/- 0.15, p less than 0.05) for all metabolic parameters during a 20-minute period.(ABSTRACT TRUNCATED AT 400 WORDS)

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 on phosphate metabolism in ischemic and reperfused myocardium using phosphorus31 nuclear magnetic resonance spectroscopy in vivo

Diltiazem may provide a protective effect to ischemic and reperfused myocardium through preservation of high-energy phosphate metabolism. To test this hypothesis, rabbits had a 1.3 cm solenoidal coil placed over the myocardium to be rendered ischemic. Data were acquired with a 22 cm bore nuclear magnetic resonance spectrometer at 2.0 T. Animals were treated with diltiazem (200 micrograms/kg intravenous bolus of drug followed by a 15 micrograms/kg/min continuous intravenous infusion, n = 10) or by an equal volume of saline (n = 6). The left circumflex artery was occluded and reperfused using a reversible snare while electrocardiogram-gated spectra were accumulated. Levels of phosphocreatine were decreased during occlusion in both groups; however, this decrease was attenuated in the diltiazem treated animals compared to control (in relative percent area: 7.8 +/- 1.0 to 2.5 +/- 0.5, p less than 0.01). Levels of phosphocreatine promptly returned to baseline following reperfusion and there was no difference between the two groups. The inorganic phosphate metabolites of high-energy phosphate consumption increased with occlusion, though more so in the control group compared with the diltiazem-treated rabbits (in relative percent area: 72.5 +/- 0.9 to 55.4 +/- 1.3, p less than 0.01). With reperfusion, levels of inorganic phosphates returned toward baseline in both groups; however, the diltiazem group had a more complete recovery relative to control (in relative percent area: 38.8 +/- 2.1 to 47.6 +/- 2.7, p less than 0.05). Levels of adenosine triphosphate decreased in both groups relative to baseline; however, the amount of decrease was similar in the two groups. With reperfusion there was a definite though incomplete recovery of levels of adenosine triphosphate in the diltiazem-treated group (in relative percent area: 10.7 +/- 1.0 at occlusion, 12.3 +/- 0.4 during reperfusion, p less than 0.05), but in the control group levels of adenosine triphosphate remained depressed (in relative percent area: 9.8 +/- 0.6 at occlusion, 9.8 +/- 0.8 during reperfusion, p = NS). During ischemia there was a trend toward attenuation of intracellular acidosis in the diltiazem group; however, this trend did not reach statistical significance. These data indicate that diltiazem provides a protective effect on myocardial high-energy phosphate metabolism during regional ischemia and reperfusion in the intact animal.

Verapamil preserves myocardial performance and energy metabolism in left ventricular hypertrophy following ischemia and reperfusion. Phosphorus 31 magnetic resonance spectroscopy study

While calcium entry blockers have a beneficial influence on the postischemic recovery of the nonhypertrophied heart, their influence on the hypertrophied heart has not been determined. The aim of this study was to assess postischemic recovery of myocardial performance and energy metabolites in rat hearts with left ventricular hypertrophy pretreated either chronically or acutely with verapamil. Left ventricular hypertrophy was induced by suprarenal constriction of the abdominal aorta. Hemodynamics and phosphorus 31 magnetic resonance spectra were monitored simultaneously in the isolated hearts during control perfusion, after 30 minutes of global ischemia, and after 30 minutes of reperfusion. All hypertrophied hearts had significantly higher rate-pressure products than normal hearts. Compared with normal hearts, oxygen consumption was significantly lower in all hypertrophied hearts, especially untreated hypertrophied hearts. Also, before ischemia all normal or hypertrophied hearts (treated or untreated) began with comparable phosphorylation potentials (i.e., the supply of energy was not significantly different). Postischemic recovery was not related to energy supply-oxygen demand before onset of ischemia. Furthermore, it was not related to energy levels or intracellular pH during ischemia. For postischemic recovery, the rate-pressure product was 40 +/- 5% in the hypertrophied heart, 83 +/- 5% in the normal, 100 +/- 3% in the hypertrophied heart chronically treated with verapamil, and 82 +/- 5% in the hypertrophied heart acutely treated with verapamil. The degree of recovery was related to coronary flow both before and after ischemia. The latter is important for flushing deleterious metabolites and ions from the interstitial space as well as for delivery of oxygen and substrate to the myocardium.

Cardioprotective effects of amlodipine in the ischemic-reperfused heart

Amlodipine is a dihydropyridine derivative belonging to the group of pharmacologic calcium entry blocking agents and is characterized as having a slow onset and relatively long duration of action with minimal effects on cardiac electrophysiology and myocardial contractility. The protective effect of amlodipine was studied in isolated blood-perfused feline hearts made globally ischemic for 60 minutes followed by reperfusion for 60 minutes. Ischemic-induced alterations of left ventricular developed pressure and complicance were monitored. In 11 control and 7 drug-treated hearts, amlodipine produced significant decreases in myocardial oxygen consumption (6.2 +/- 0.4 to 4.4 +/- 0.4 ml oxygen/min/100 g) and coronary vascular resistance, as assessed by changes in perfusion pressure (120 +/- 1 to 100 +/- 4 mm Hg). Amlodipine administered before the onset of global ischemia decreased the development of ischemic contracture as reflected by a progressive increase in resting left ventricular diastolic pressure. The return of contractile function, 60 minutes afer reperfusion, improved significantly in the amlodipine-treated group compared with controls, and there was better maintenance of the tissue concentration of Na+, Ca2+ and K+. A canine model of regional myocardial ischemia (90 minutes) followed by 6 hours of reperfusion was used to assess the cardioprotective effects of amlodipine, 150 micrograms/kg, administered 15 minutes before reperfusion. Infarct size, expressed as a percentage of the area at risk, was smaller in the amlodipine-treated group (n = 10) than in the control group (n = 10) (34.5 +/- 3.8% vs 45.9 +/- 2.8%, p = 0.027). Risk region size did not differ between groups and both groups were comparable with respect to the hemodynamic parameters of heart rate, blood pressure and rate-pressure product. Amlodipine prevented the gradual reduction in coronary blood flow observed in the control group. It is concluded that amlodipine reduces myocardial ischemic injury by mechanism(s) that may involve a reduction in myocardial oxygen demand as well as by positively influencing transmembrane Ca2+ fluxes during ischemia and reperfusion.

Amlodipine pretreatment and the ischemic heart

Amlodipine is a long-acting dihydropyridine-based Ca2+ channel blocker, developed for use on a once-daily basis. Experiments using hearts from amlodipine-pretreated rats were undertaken to further test the hypothesis that Ca2+ channel blockers can be used as prophylactic therapy to reduce the severity of the mechanical and biochemical consequences of ischemia and reperfusion. Amlodipine was given intravenously, 0.25 mg/kg, 5 hours before excising the hearts. Ischemia (global) was induced at 37 degrees C for 10, 30 or 60 minutes, and was followed by reperfusion. Protection was quantitated in terms of functional recovery, adenosine triphosphate and creatine phosphate retention, tissue acidosis and Ca2+ gain. The results show that amlodipine pretreatment supplied protection, provided that the ischemic episode did not exceed 30 minutes. The protection resulted in improved recovery of peak developed tension on reperfusion, reduced Ca2+ gain, retention of tissue adenosine triphosphate and creatine phosphate, and reduced acidosis.

Effect of D-600 on ischemic and reperfused rabbit myocardium: relation with timing and modality of administration

In this study we have investigated the possibility that D-600, a phenylalkylamine calcium antagonist, protects the isolated rabbit heart against ischemia and reperfusion-induced damage. D-600 was either subcutaneously injected (2mg/kg, twice daily for 5 to 6 days) in the rabbit before isolation of the heart, or delivered to the isolated hearts in the perfusate (10(-7) M), either at the onset of ischemia and during reperfusion, or only during post-ischemic reperfusion. Ischemia (90 min) was induced by reducing coronary flow from 25 to 1 ml/min, followed by 30 min of reperfusion. Myocardial damage was determined in terms of mechanical function, release of creatine phosphokinase (CPK) and noradrenaline, mitochondrial function, calcium homeostasis, and endogenous stores of ATP and creatine phosphate (CP). Administration of D-600 to the rabbits or to the isolated hearts at the time of ischemia exerted protection. There are four groups of evidence in support of this conclusion: 1) the rise in diastolic pressure during ischemia was diminished with greater recovery of developed pressure during reperfusion; 2) CPK and noradrenaline release during reperfusion were reduced; 3) the oxygen consumption and ATP generating capacities of mitochondria were better maintained; and 4) associated with this preservation of mitochondrial function was the maintenance of near normal calcium homeostasis and of endogenous ATP and CP stores. The two different modalities of administration did not produce substantially different results. When administered to the isolated hearts after the ischemic period, D-600 failed to improve mechanical recovery and release of endogenous substances. However, it reduced mitochondrial calcium overload and improved ATP production. The mechanism of the protective effect of D-600 seems to be multiple: energy-sparing effect, reduction of the toxicity mediated by endogenous catecholamines, and direct inhibition of mitochondrial calcium transport.