Ca2+/calmodulin-dependent protein kinase II and protein kinase G oxidation contributes to impaired sarcomeric proteins in hypertrophy model

Aims

Volume overload (VO) induced hypertrophy is one of the hallmarks to the development of heart diseases. Understanding the compensatory mechanisms involved in this process might help preventing the disease progression.

Methods and results

Therefore, the present study used 2 months old Wistar rats, which underwent an aortocaval fistula to develop VO‐induced hypertrophy. The animals were subdivided into four different groups, two sham operated animals served as age‐matched controls and two groups with aortocaval fistula. Echocardiography was performed prior termination after 4‐ and 8‐month. Functional and molecular changes of several sarcomeric proteins and their signalling pathways involved in the regulation and modulation of cardiomyocyte function were investigated.

Results

The model was characterized with preserved ejection fraction in all groups and with elevated heart/body weight ratio, left/right ventricular and atrial weight at 4‐ and 8‐month, which indicates VO‐induced hypertrophy. In addition, 8‐months groups showed increased left ventricular internal diameter during diastole, RV internal diameter, stroke volume and velocity‐time index compared with their age‐matched controls. These changes were accompanied by increased Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness in 8‐month VO rats compared with other groups. The altered cardiomyocyte mechanics was associated with phosphorylation deficit of sarcomeric proteins cardiac troponin I, myosin binding protein C and titin, also accompanied with impaired signalling pathways involved in phosphorylation of these sarcomeric proteins in 8‐month VO rats compared with age‐matched control group. Impaired protein phosphorylation status and dysregulated signalling pathways were associated with significant alterations in the oxidative status of both kinases CaMKII and PKG explaining by this the elevated Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness and perhaps the development of hypertrophy.

Conclusions

Our findings showed VO‐induced cardiomyocyte dysfunction via deranged phosphorylation of myofilament proteins and signalling pathways due to increased oxidative state of CaMKII and PKG and this might contribute to the development of hypertrophy.

Long-Term Endurance Exercise Training Alters Repolarization in a New Rabbit Athlete’s Heart Model

In the present study, the effect of long-term exercise training was investigated on myocardial morphological and functional remodeling and on proarrhythmic sensitivity in a rabbit athlete’s heart model. New-Zealand white rabbits were trained during a 12-week long treadmill running protocol and compared with their sedentary controls. At the end of the training protocol, echocardiography, in vivo and in vitro ECG recordings, proarrhythmic sensitivity with dofetilide (nM) were performed in isolated hearts, and action potential duration (APD) measurements at different potassium concentrations (4.5 and 2 mM) were made in the isolated papillary muscles. Expression levels of the slow component of delayed rectifier potassium current and fibrosis synthesis and degradation biomarkers were quantified. Echocardiography showed a significantly dilated left ventricle in the running rabbits. ECG PQ and RR intervals were significantly longer in the exercised group (79 ± 2 vs. 69 ± 2 ms and 325 ± 11 vs. 265 ± 6 ms, p < 0.05, respectively). The in vivo heart rate variability (HRV) (SD of root mean square: 5.2 ± 1.4 ms vs. 1.4 ± 0.2 ms, p < 0.05) and Tpeak-Tend variability were higher in the running rabbits. Bradycardia disappeared in the exercised group in vitro. Dofetilide tended to increase the QTc interval in a greater extent, and significantly increased the number of arrhythmic beats in the trained animals in vitro. APD was longer in the exercised group at a low potassium level. Real-time quantitative PCR (RT-qPCR) showed significantly greater messenger RNA expression of fibrotic biomarkers in the exercised group. Increased repolarization variability and higher arrhythmia incidences, lengthened APD at a low potassium level, increased fibrotic biomarker gene expressions may indicate higher sensitivity of the rabbit “athlete’s heart” to life-threatening arrhythmias.

Long-term endurance training-induced cardiac adaptation in new rabbit and dog animal models of the human athlete's heart

Sudden cardiac death in athletes is rare and most often unexpectable. For a better understanding of cardiac remodeling, this study presents the effects of chronic vigorous exercise on cardiac structure and electrophysiology in new rabbit and dog athlete's heart models. Rabbits and dogs were randomized into sedentary ('Sed'), exercised (subjected to 16 weeks chronic treadmill exercise ('Ex') groups, and a testosterone-treated ('Dop') group in dogs. Echocardiography and electrocardiogram were performed. Proarrhythmic sensitivity and autonomic responses were tested in conscious dogs. 'Ex' animals exhibited left ventricular enlargement with bradycardia (mean RR in 'Ex' vs. 'Sed' rabbits: 335 ± 15 vs. 288 ±19 ms, p ≤ 0.05, and in 'Dop' vs. 'Ex' vs. 'Sed' dogs: 718 ± 6 vs. 638 ± 38 vs. 599 ± 49 ms) accompanied by an increase of heart rate variability in both species (e.g. SD RR in 'Ex' vs. 'Sed' rabbits: 3.4 ± 0.9 vs. 1.4 ± 0.1 ms, p ≤ 0.05, and in 'Dop' vs. 'Ex' vs. 'Sed' dogs: 156 ± 59 vs. 163 ± 44 vs. 111 ± 49 ms) indicating an increased vagal tone. A lower response to parasympatholytic agent atropine and more pronounced QTc interval lengthening after dofetilide challenge were found in 'Ex' and 'Dop' dogs compared to the 'Sed' group. No morphological and functional changes were found after chronic steroid treatment in dogs. The structural-functional findings share more similarities with human athlete's heart. Slight repolarization sensitivity in the exercised dogs may indicate an increased risk of arrhythmias in athletes under different circumstances. These animal models might be useful for the further investigations of the cardiovascular effects of competitive training.

The Effect of a Novel Highly Selective Inhibitor of the Sodium/Calcium Exchanger (NCX) on Cardiac Arrhythmias in In Vitro and In Vivo Experiments

Background

In this study the effects of a new, highly selective sodium-calcium exchanger (NCX) inhibitor, ORM-10962 were investigated on cardiac NCX current, Ca²⁺ transients, cell shortening and in experimental arrhythmias. The level of selectivity of the novel inhibitor on several major transmembrane ion currents (L-type Ca²⁺ current, major repolarizing K⁺ currents, late Na⁺ current, Na⁺/K⁺ pump current) was also determined.

Methods

Ion currents in single dog ventricular cells (cardiac myocytes; CM), and action potentials in dog cardiac multicellular preparations were recorded utilizing the whole-cell patch clamp and standard microelectrode techniques, respectively. Ca²⁺ transients and cell shortening were measured in fluorescent dye loaded isolated dog myocytes. Antiarrhythmic effects of ORM-10962 were studied in anesthetized ouabain (10 μg/kg/min i.v.) pretreated guinea pigs and in ischemia-reperfusion models (I/R) of anesthetized coronary artery occluded rats and Langendorff perfused guinea pigs hearts.

Results

ORM-10962 significantly reduced the inward/outward NCX currents with estimated EC50 values of 55/67 nM, respectively. The compound, even at a high concentration of 1 μM, did not modify significantly the magnitude of I_CaL in CMs, neither had any apparent influence on the inward rectifier, transient outward, the rapid and slow components of the delayed rectifier potassium currents, the late and peak sodium and Na⁺/K⁺ pump currents. NCX inhibition exerted moderate positive inotropic effect under normal condition, negative inotropy when reverse, and further positive inotropic effect when forward mode was facilitated. In dog Purkinje fibres 1 μM ORM-10962 decreased the amplitude of digoxin induced delayed afterdepolarizations (DADs). Pre-treatment with 0.3 mg/kg ORM-10962 (i.v.) 10 min before starting ouabain infusion significantly delayed the development and recurrence of ventricular extrasystoles (by about 50%) or ventricular tachycardia (by about 30%) in anesthetized guinea pigs. On the contrary, ORM-10962 pre-treatment had no apparent influence on the time of onset or the severity of I/R induced arrhythmias in anesthetized rats and in Langendorff perfused guinea-pig hearts.

Conclusions

The present study provides strong evidence for a high efficacy and selectivity of the NCX-inhibitory effect of ORM-10962. Selective NCX inhibition can exert positive as well as negative inotropic effect depending on the actual operation mode of NCX. Selective NCX blockade may contribute to the prevention of DAD based arrhythmogenesis, in vivo, however, its effect on I/R induced arrhythmias is still uncertain.

High-dose Radiation Induced Heart Damage in a Rat Model

BACKGROUND/AIM

Radiation-induced heart disease (RIHD) is a concern during radiotherapy. For its comprehensive study, an in vivo selective heart irradiation model was developed.

MATERIALS AND METHODS

Sprague-Dawley rats were irradiated with 50 Gy and functional imaging, biochemical (circulating growth differentiation factor-15 (GDF-15), transforming growth factor-beta (TGF-beta) and morphological (picrosirius red staining of the heart) objectives were tested.

RESULTS

Signs and symptoms of RIHD occurred >12 weeks after irradiation with tachypnea, systolic and diastolic dysfunction, cardiac hypertrophy and body development retardation. Plasma GDF-15 was increased 3, 12 and 26, while plasma TGF-beta was increased 12 weeks after irradiation. At autopsy, extensive pleural fluid was found in the irradiated animals. Interstitial fibrosis could be reliably detected and quantified in irradiated hearts after a follow-up time of 19 weeks.

CONCLUSION

The studied parameters could be used in future experiments for testing protective agents for prevention of radiation heart injury.

Long-term pretreatment with desethylamiodarone (DEA) or amiodarone (AMIO) protects against coronary artery occlusion induced ventricular arrhythmias in conscious rats

The aim of this investigation was to compare the effectiveness of long-term pretreatment with amiodarone (AMIO) and its active metabolite desethylamiodarone (DEA) on arrhythmias induced by acute myocardial infarction in rats. Acute myocardial infarction was induced in conscious, male, Sprague–Dawley rats by pulling a previously inserted loose silk loop around the left main coronary artery. Long-term oral pretreatment with AMIO (30 or 100 mg·(kg body mass)−1·day−1, loading dose 100 or 300 mg·kg−1 for 3 days) or DEA (15 or 50 mg·kg−1·day−1, loading dose 100 or 300 mg·kg−1 for 3 days), was applied for 1 month before the coronary artery occlusion. Chronic oral treatment with DEA (50 mg·kg−1·day−1) resulted in a similar myocardial DEA concentration as chronic AMIO treatment (100 mg·kg−1·day−1) in rats (7.4 ± 0.7 μg·g−1 and 8.9 ± 2.2 μg·g−1). Both pretreatments in the larger doses significantly improved the survival rate during the acute phase of experimental myocardial infarction (82% and 64% by AMIO and DEA, respectively, vs. 31% in controls). Our results demonstrate that chronic oral treatment with DEA resulted in similar cardiac tissue levels to that of chronic AMIO treatment, and offered an equivalent degree of antiarrhythmic effect against acute coronary artery ligation induced ventricular arrhythmias in conscious rats.

Biomarkers and endogenous determinants of dofetilide-induced torsades de pointes in α(1) -adrenoceptor-stimulated, anaesthetized rabbits

BACKGROUND AND PURPOSE

Torsades de pointes (TdP) liability is a stochastic event, which indicates that unidentified factors have an important role in facilitating the initiation of TdP by increasing the probability of TdP occurrence. We sought to identify factors that facilitate drug-induced TdP.

EXPERIMENTAL APPROACH

We studied dofetilide-induced TdP in pentobarbital-anaesthetized, phenylephrine-sensitized rabbits, seeking biomarkers that discriminated between the animals that experienced TdP ('TdP+' animals) and those that did not ('TdP-' animals). As novel variables, the beat-to-beat variability and instability of ECG intervals were measured at preset times, irrespective of whether or not hearts were in stable sinus rhythm ('absolute' variability and instability). Autonomic activity was also determined.

KEY RESULTS

Dofetilide delayed repolarization and induced arrhythmias prior to TdP. The variability of the coupling interval and shape of arrhythmic beats before TdP were significantly greater in the 'TdP+' group than in the 'TdP-' group. Accordingly, the 'absolute' variability and instability of the ECG intervals were significantly elevated in the 'TdP+' group. Phenylephrine increased significantly the up-baroreflex sensitivity in the 'TdP+' group before dofetilide administration.

CONCLUSIONS AND IMPLICATIONS

'Preceding' arrhythmias have characteristics that permit prediction of TdP occurrence: the more chaotic the ventricular rhythm, the greater the probability of TdP initiation. This suggests that complexity of the arrhythmic beats may play an important mechanistic role in TdP genesis. The electrical instability quantified by the novel 'absolute' variability and instability parameters correlates with the probability of TdP occurrence. Baroreflex may contribute to TdP genesis in vivo.

Effects of 3-aminopyridine-induced seizures on platelet eicosanoid synthesis

We investigated the influence of recurrent epileptic seizures on the arachidonic acid (AA) cascade in platelets and brain microvessels, using [(14)C]AA as a tracer substrate and chromatographic determination. The recurrent epileptic seizures of male Wistar rats were induced every second day with 3-aminopyridine (3-AP, 25 mg/kg ip) for two weeks. In the chronic 3-AP model, the earlier epileptic insults resulted in a decreased incidence of limbic seizures and higher survival rate at later administration of 3-AP. After 3-AP treatment, the formation of lipoxygenase products was unchanged, but the total amount of cyclooxygenase (COX) metabolites was decreased both in platelets and brain microvessels. The reduction in COX-mediated eicosanoid synthesis after recurrent seizures was due to the decreased synthesis of vasodilator and vasoconstrictor COX metabolites. In platelets, the 3-AP-treatment reduced the synthesis of vasodilator prostacyclin (PGI(2)), prostaglandin E(2) (PGE(2)) and 12-L-hydroxy-5,8,10-heptadecatrienoic acid (12-HHT), while the synthesis of prostaglandin D(2) (PGD(2)) remained unchanged. In isolated brain capillaries, the PGD(2), PGE(2) and 12-HHT synthesis was decreased after recurrent seizures. As for the vasoconstrictor COX metabolites, both platelets and brain microvessels synthesized significantly lesser amount of prostaglandin F(2alpha) (PGF(2alpha)) and thromboxane A(2) (TxA(2)) upon 3-AP administration. Our results indicate that platelets and isolated brain capillaries synthesize significantly lesser amount of COX metabolites after chronic 3-AP treatment. The decreased conversion of AA into different COX products may play a role in the neuroprotective/preconditional adaptation of the brain against subsequent seizures.

Selective cardiac plasma-membrane KATP channel inhibition is defibrillatory and improves survival during acute myocardial ischemia and reperfusion

ATP-dependent potassium channels (K(ATP)) have been implicated in cardioprotection both during myocardial ischemia and reperfusion. We compared the effect of a non-selective K(ATP) inhibitor glibenclamide, a selective mitochondrial K(ATP) inhibitor 5-hydroxy-decanoate (5-HD) and a selective sarcolemmal K(ATP) blocker HMR 1883, on survival and incidence of arrhythmias during myocardial ischemia in conscious, and during ischemia-reperfusion in pentobarbitone anesthetized rats. Glibenclamide (5 mg/kg i.p.) or HMR 1883 (3 mg/kg i.v.) reduced ischemia-induced irreversible ventricular fibrillation and improved survival during myocardial ischemia (64% and 61% vs. 23% in controls, respectively). 5-HD (5 mg/kg i.v.) did not influence survival and the incidence of ventricular arrhythmias. The incidence of reperfusion-induced arrhythmias was reduced by both glibenclamide and HMR 1883 (3 or 10 mg/kg) resulting in improved survival during reperfusion (81%, 82% and 96% vs. 24% in controls, respectively) in anesthetized rats. 5-HD did not reduce the incidence of lethal reperfusion arrhythmias. Glibenclamide and HMR 1883 prolonged (89+/-4.6 and 89+/-4.9 ms vs. 60+/-2.4 ms in controls), while 5-HD did not change the QT interval. In conclusion, inhibition of sarcolemmal K(ATP) reduces the incidence of lethal ventricular arrhythmias and improves survival both during acute myocardial ischemia and reperfusion in rats. This beneficial effect correlates with the prolongation of repolarization. Inhibition of mitochondrial K(ATP) does not improve survival or reduce the occurrence of ischemia and/or reperfusion-induced arrhythmias and does not prolong the QT interval. The present results also suggest that the antiarrhythmic effect of K(ATP) inhibitors is not influenced by pentobarbitone anesthesia.

Relevance of anaesthesia for dofetilide-induced torsades de pointes in alpha1-adrenoceptor-stimulated rabbits

BACKGROUND AND PURPOSE

No information is available concerning the effects of anaesthetics in the most frequently used in vivo pro-arrhythmia model. Accordingly, in this study we examined the effect of pentobarbital, propofol or alpha-chloralose anaesthesia on the pro-arrhythmic activity of the class III anti-arrhythmic dofetilide in alpha(1)-adrenoceptor-stimulated rabbits.

EXPERIMENTAL APPROACH

Rabbits anaesthetized intravenously with pentobarbital, propofol or alpha-chloralose were infused simultaneously with the alpha(1)-adrenoceptor agonist phenylephrine (15 microg kg(-1) min(-1), i.v.) and dofetilide (0.04 mg kg(-1) min(-1), i.v.). The electrocardiographic QT interval, the T (peak)-T (end) interval and certain QT variability parameters were measured. The heart rate variability and the baroreflex sensitivity were utilized to assess the vagal nerve activity. The spectral power of the systolic arterial pressure was calculated in the frequency range 0.15-0.5 Hz to assess the sympathetic activity.

KEY RESULTS

Pentobarbital considerably reduced, whereas propofol did not significantly affect the incidence of dofetilide-induced torsades de pointes (TdP) as compared with the results with alpha-chloralose (40% (P=0.011) and 70% (P=0.211) vs 100%, respectively). In additional experiments, neither doubling of the rate of the dofetilide infusion nor tripling of the rate of phenylephrine infusion elevated the incidence of TdP to the level seen with alpha-chloralose. None of the repolarization-related parameters predicted TdP. The indices of the parasympathetic and sympathetic activity were significantly depressed in the alpha-chloralose and propofol anaesthesia groups.

CONCLUSIONS AND IMPLICATIONS

In rabbits, anaesthetics may affect drug-induced TdP genesis differently, which must be considered when results of different studies are compared.

Preconditioning Effects of Levosimendan in a Rabbit Cardiac Ischemia-Reperfusion Model

The preconditioning effects of levosimendan were investigated on ischemia-reperfusion induced morphological and functional cardiac damage. Langendorff-perfused rabbit hearts were reserved as controls or subjected either to global myocardial ischemic preconditioning or to perfusion with levosimendan (0.1 micromol/l) for two 5-minute cycles. After a washout period, all hearts were then subjected to 30 minutes of global ischemia and 120 minutes of drug-free reperfusion. Intraventricular pressure and coronary flow were measured, and infarct size determined after nitroblue-tetrazolium staining on completion of the experiments. Levosimendan pretreatment resulted in a significantly smaller elevation from the preischemic level in left ventricular end-diastolic pressure during reperfusion (37 +/- 17 mm Hg) compared with controls (56 +/- 14 mm Hg) and ischemia-preconditioned hearts (53 +/- 34 mm Hg). The left ventricular developed pressure-representing the functional recovery of the heart after ischemia-that was significantly improved by levosimendan pretreatment (38 +/- 6% vs 16 +/- 5% in controls, P < 0.05). In addition, contractility and relaxability parameters (+dP/dt and -dP/dt, respectively) were better preserved in the levosimendan hearts. The volume of infarcted myocardium after global ischemia-reperfusion was significantly (P < 0.05) decreased by both ischemic preconditioning (38 +/- 2%) or levosimendan pretreatment (45 +/- 2%) versus controls (52 +/- 2%). The results of this study suggest that levosimendan pretreatment is capable of decreasing infarct size in an ischemia-reperfusion model and improving recovery of cardiac function following ex vivo global ischemia.

Distinct modulation of angiotensin II-induced early left ventricular hypertrophic gene programming by dietary fat type

Long-term dietary fatty acid intake alters the development of left ventricular hypertrophy, but the linking signaling pathways are unclear. We studied the role and underlying signaling mechanisms of dietary fat intake in the early phase of the hypertrophic process. Rats assigned for 4 weeks of high-oil, high-fat, or standard diet were subjected to angiotensin II (Ang II; 33 microg/kg/h, subcutaneous) or vehicle infusion for 24 h. The Ang II-induced increase in left ventricular mRNA levels of hypertrophy-associated genes was higher in rats fed the high-oil diet compared with the standard diet. Western blotting revealed that, in parallel with changes in gene expression, the high-oil diet increased c-Jun N-terminal kinase phosphorylation (P < 0.001). Ang II increased p38 mitogen-activated protein kinase (MAPK) phosphorylation in rats fed the high-fat diet (3-fold; P < 0.01). The increase in transcription factor activator protein-1 (AP-1) DNA binding activity in response to Ang II was higher in rats fed the high-oil diet compared with those fed the standard diet (P < 0.001). Ang II downregulated inducible nitric oxide synthase mRNA levels in fatty acid-supplemented groups compared with the standard diet group. These results show that dietary fat type modulates the early activation of hypertrophic genes in pressure-overloaded myocardium involving the distinct activation of AP-1 and MAPK signal transduction pathways.

Effect of long-term oral pretreatment with levosimendan on cardiac arrhythmias during coronary artery occlusion in conscious rats

Heart failure is frequently associated with cardiac arrhythmias. The aim of the present study was to investigate the effect of levosimendan, a new cardiotonic drug for the treatment of congestive heart failure, on experimental ischaemic arrhythmias. Acute coronary artery occlusion was produced in conscious rats 7-10 days after placement of ligature around the left main coronary artery. Acute pretreatment with levosimendan (0.2 or 0.6 mg/kg orally 1 h before coronary artery occlusion) did not influence the incidence, onset and duration of arrhythmias. Long-term pretreatment with levosimendan (0.2 or 0.6 mg/kg orally twice a day for 2 weeks) increased the survival rate (50% and 81% vs. 44% in controls) and the number of animals without any arrhythmia (37% and 31% vs. 5% in controls). The present results demonstrate that chronic oral treatment with levosimendan could be beneficial in congestive heart failure and arrhythmias resulting from regional myocardial ischaemia.

Proarrhythmic effects of intravenous quinidine, amiodarone, D-sotalol, and almokalant in the anesthetized rabbit model of torsade de pointes

The proarrhythmic effects of four antiarrhythmic agents were examined during alpha1-adrenoceptor stimulation in chloralose-anesthetized rabbits. Each dose of almokalant (26, 88, and 260 microg/kg), D-sotalol, quinidine, or amiodarone (each 3, 10, and 30 mg/kg) was infused i.v. over 5 min and there was a 20-min interval between each infusion. D-sotalol and almokalant evoked torsade de pointes (TdP) and other arrhythmics, frequently. The incidences of TdP were 0, 50, and 40% after administering the first, second, and third doses of the nonselective I(Kr) inhibitor D-sotalol, respectively. Similarly, these values were 20, 40, and 33% after administering the first, second, and third doses, respectively, of the selective I(Kr) inhibitor almokalant. Quinidine elicited only a few arrhythmics, but not TdP. Quinidine, D-sotalol, and almokalant evoked conduction blocks in a dose-related manner (p < 0.05) and prolonged QT and QT(c) intervals (p < 0.05). Amiodarone neither prolonged QT and QT(c) nor evoked ventricular tachyarrhythmias, blocks, or other proarrhythmias. In conclusion, these results show no direct correlation between the occurrence of TdP and the infusion rate or dose of anti-arrhythmics. Furthermore, the lack of TdP with quinidine warns of false-negative results in the applied model.

Effect of glibenclamide and glimepiride treatment on the development of myocardial infarction in rats

The effect of glibenclamide and glimepiride, two orally active antidiabetic sulphonylurea derivatives, on the development of myocardial infarction has been compared. Permanent coronary artery ligation was induced in rats and the development of infarction was evaluated by a computer-assisted method after nitroblue-terazolium staining. Seven-day coronary ligation produced enlargement of the left ventricular cavity, scar thinning and thickening of the non-infarcted myocardium. Glibenclamide treatment (5 mg/kg b.i.d. intraperitoneally) decreased the infarct volume (29.1 +/- 3.5% vs. 39.1 +/- 3.2% in controls), that occurred primarily as a result of more significant thinning of the scar tissue (1.6 +/- 0.04 mm vs. 2.0 +/- 0.13 mm in controls). Glibenclamide also inhibited the thickening of the non-infarcted ventricular septum (2.1 +/- 0.10 mm vs. 2.9 +/- 0.10 mm in controls). In contrast to the effects of glibenclamide, glimepiride treatment (5 mg/kg b.i.d. intraperitoneally) inhibited the enlargement of the left ventricular cavity (15.2 +/- 1.1% vs. 19.9 +/- 1.2% of the left ventricular volume in controls), it did not precipitate scar thinning and did not influence the development of hypertrophy of the non-infarcted myocardium. These results suggest that glimepiride treatment might inhibit the development of left ventricular dilatation after myocardial infarction. Glibenclamide treatment, however, producing a thinning of the scar tissue may further precipitate morphological changes that can contribute to the development of heart failure.

Antiarrhythmic and electrophysiological effects of GYKI-16638, a novel N-(phenoxyalkyl)-N-phenylalkylamine, in rabbits

The effect of N-[4-[2-N-methyl-N-[1-methyl-2-(2, 6-dimethylphenoxy)ethylamino]-ethyl]-phenyl]-methanesulfonamide. hydrochloride (GYKI-16638; 0.03 and 0.1 mg/kg, i.v.), a novel antiarrhythmic compound, was assessed and compared to that of D-sotalol (1 and 3 mg/kg, i.v.) on arrhythmias induced by 10 min of coronary artery occlusion and 10 min of reperfusion in anaesthetized rabbits. Also, its cellular electrophysiological effects were studied in rabbit right ventricular papillary muscle preparations and in rabbit single isolated ventricular myocytes. In anaesthetized rabbits, intravenous administration of 0.03 and 0.1 mg/kg GYKI-16638 and 1 and 3 mg/kg D-sotalol significantly increased survival during reperfusion (GYKI-16638: 82% and 77%, D-sotalol: 75% and 83% vs. 18% in controls, P<0.05, respectively). GYKI-16638 (0.1 mg/kg) significantly increased the number of animals that did not develop arrhythmias during reperfusion (46% vs. 0% in controls, P<0.05). In isolated rabbit right ventricular papillary muscle, 2 microM GYKI-16638, at 1 Hz stimulation frequency, lengthened the action potential duration at 50% and 90% repolarization (APD(50-90)) without influencing the resting membrane potential and action potential amplitude (APA). It decreased the maximal rate of depolarization (V(max)) in a use-dependent manner. This effect was statistically significant only at stimulation cycle lengths shorter than 700 ms. The offset kinetics of this V(max) block were relatively rapid, the corresponding time constant for recovery of V(max) was 328.2+/-65.0 ms. In patch-clamp experiments, performed in rabbit ventricular myocytes, 2 microM GYKI-16638 markedly depressed the rapid component of the delayed rectifier outward and moderately decreased the inward rectifier K(+) current without significantly altering the slow component of the delayed rectifier and transient outward K(+) currents. These results suggest that in rabbits, GYKI-16638 has an in vivo antiarrhythmic effect, comparable to that of D-sotalol, which can be best explained by its combined Class I/B and Class III actions.

Comparison of the efficacy of glibenclamide and glimepiride in reperfusion-induced arrhythmias in rats

The effect of glibenclamide and glimepiride, two orally active antidiabetic sulphonylurea derivatives, was investigated on the development of reperfusion-induced arrhythmias and it was compared to their blood glucose lowering action. Arrhythmias were produced by reperfusion following 6 min coronary artery ligation in anaesthetised rats. Glimepiride pretreatment (0.001-0.01-0.1-5.0 mg/kg i.p., 30 min before coronary occlusion) significantly decreased the incidence of irreversible ventricular fibrillation and increased the survival rate during reperfusion (64%, 61%, 60%, and 67% vs. 27% in controls). Glibenclamide produced similar effect (81% survival) only in a dose of 5 mg/kg, while smaller doses were ineffective. The minimal hypoglycaemic dose and the dose required to inhibit significantly the oral glucose loading-induced hyperglycaemia were similar (1 and 0.1 mg/kg, respectively) after glibenclamide and glimepiride. It is concluded that although the blood glucose lowering potency of glibenclamide and glimepiride is rather similar, glimepiride appears to be more potent than glibenclamide in preventing reperfusion-induced cardiac arrhythmias.

Comparison of the antiarrhythmic and the proarrhythmic effect of almokalant in anaesthetised rabbits

In this study the antiarrhythmic and the proarrhythmic activities of almokalant, a selective class III antiarrhythmic agent, were compared. The antiarrhythmic effect of the drug was tested in pentobarbital-anaesthetised rabbits. Arrhythmia was evoked by occluding and releasing the left circumflex coronary artery. Almokalant in a dose of 250 nmol/kg i.v., significantly decreased the incidence of reperfusion induced ventricular fibrillation (21% vs. 75% in the control group) and increased the proportion of surviving animals during reperfusion (86% vs. 42%). The proarrhythmic effect of almokalant was examined during alpha1-adrenoceptor stimulation in chloralose-anaesthetised rabbits. Almokalant (75 nmol/kg per min) triggered torsade de pointes arrhythmias in 8 animals out of 11. The dose of almokalant (mean+/-S.E.M.) required to produce this effect was 1181+/-519 nmol/kg. It is concluded that, although almokalant is an effective antiarrhythmic agent against ischaemia-reperfusion induced arrhythmias, it has marked proarrhythmic activity during alpha1-adrenoceptor stimulation.

KATP channel modulators increase survival rate during coronary occlusion-reperfusion in anaesthetized rats

We investigated the effect of ATP-sensitive K+ channel (KATP) openers (pinacidil and cromakalim), and a KATP blocker (glibenclamide) on reperfusion-induced arrhythmias in pentobarbitone-anaesthetized rats. Arrhythmias were induced by reperfusion following a 6 min ligation of the left main coronary artery. Rats were pretreated with pinacidil (0.1 or 0.3 mg/kg), or cromakalim (28 or 56 micrograms/kg), or glibenclamide (5 mg/kg), or vehicle. Pinacidil and cromakalim produced dose-related reductions in blood pressure. Pinacidil (0.1 mg/kg) and cromakalim (56 micrograms/kg) significantly decreased the incidence of reperfusion-induced ventricular fibrillation and increased survival. Glibenclamide did not decrease ventricular fibrillation incidence, yet improved survival by increasing the possibility of recovery from ventricular fibrillation. The present study suggests that both opening and blocking KATP channels may increase survival during coronary occlusion and reperfusion in anaesthetized rats.

Influence of anesthetics on the incidence of reperfusion-induced arrhythmias and sudden death in rats

PURPOSE

We compared the influence of pentobarbital (P, 60 mg/kg), urethane (U, 1.8 g/kg), and a contribution of diazepam with ketamine hydrochloride (D+K, 10 + 100 mg/kg) anesthesia on the incidence of ischemia/ reperfusion-induced arrhythmias in rats. In anesthetized rats, myocardial ischemia was produced by a 6-min ligation of the left main coronary artery, followed by 5 min of reperfusion. The incidence of reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT) was markedly decreased in the D+K-anesthetized animals compared with the P-anesthetized group (VF, 46 vs. 89%; VT, 64 vs. 94%). The mean blood pressure (MBP) before coronary ligation was significantly lower in U-anesthetized animals (72 +/- 3.5 vs. 102 +/- 4.1 and 108 +/- 5.9 mm Hg in P and D+K, respectively). The MBP recovery was the best in the D+K-anesthetized group. In experimental work, pentobarbitone anesthesia may be recommended for studying arrhythmias, while the combination of diazepam and ketamine may be useful for hemodynamic investigations.

ATP-sensitive potassium channel modulators: both pinacidil and glibenclamide produce antiarrhythmic activity during acute myocardial infarction in conscious rats

We investigated the effects of pinacidil, an ATP-sensitive potassium channel opener, and of glibenclamide, an ATP-sensitive potassium channel inhibitor, on the incidence of arrhythmias and sudden cardiac death after coronary artery ligation in conscious rats. Occlusion of the left main coronary artery was produced by tightening a previously placed loose silk ligature. In the control group (n = 25) only 40% and 24% of the animals survived for 15 min and 16 hr after coronary artery ligation, respectively. Intravenous pretreatment with 0.1, 0.3 or 1 mg/kg pinacidil increased the survival rate to 67% (n = 15), 70% (n = 20) and 67% (n = 12) in the first 15 min and to 60%, 55% and 67% in the first 16 hr, respectively. Glibenclamide pretreatment (5.0 mg/kg i.p.) improved the survival rate at both time-points to 87% (n = 16). Both types of pretreatment significantly decreased the incidence of life-threatening arrhythmias and increased the number of animals that survived without developing any arrhythmia. In conclusion, the present findings demonstrate that in conscious rats, pretreatment with pinacidil and pretreatment with glibenclamide, although they obviously have different mechanisms of action, may result in a very similar final outcome with respect to arrhythmias and sudden cardiac death during the acute phase of experimental myocardial infarction.

Effect of glimepiride and glibenclamide, inhibitors of ATP-dependent K(+)-channel, on ischaemia-reperfusion induced arrhythmias in rats

Glibenclamide or glimepiride pretreatment (5 mg/kg i.p. 30 min prior to coronary ligation) significantly improved the survival rate during reperfusion after 6 min myocardial ischaemia in rats (82% or 67% vs. 17% in controls). Smaller dose of glibenclamide (0.01 mg/kg) did not influence the survival rate (31%), while glimepiride still offered a significant protection (61%). These results suggest that different KATP inhibitors may increase the chance to survive life-threatening arrhythmias during myocardial ischaemia-reperfusion.

Effect of almokalant a specific inhibitor of IKr on myocardial ischaemia-reperfusion induced arrhythmias in rabbits

The antiarrhythmic effect of almokalant, a new type III antiarrhythmic agent, was examined by occluding and releasing the left circumflex coronary artery for 10 min, respectively, in openchest, pentobarbital-anaesthetized albino rabbits. Almokalant pretreatment increased the number of animals developing no arrythmias (5/9 vs. 1/12 in controls), and decreased the incidence of ventricular fibrillation (1/9 vs. 9/12) during reperfusion. According to our results almokalant can protect the heart against arrhythmias induced by ischaemia and reperfusion.

Effect of moxonidine on arrhythmias induced by coronary artery occlusion and reperfusion

The aim of the present study was to investigate the influence of moxonidine, a representative of I1-imidazoline-receptor agonist, on arrhythmias induced by myocardial ischemia or reperfusion. Acute myocardial infarction was produced by tightening a previously placed loose silk loop around the coronary artery in conscious rats. Moxonidine (0.01, 0.03, or 0.10 mg/kg i.v., 10 min before coronary ligation) significantly decreased the incidence of ventricular tachycardia during the first 15 min of infarction (70 versus 100% in controls), and the number of animals that survived without developing any arrhythmia was increased (15, 20, and 25%, respectively, versus 0%). Reperfusion-induced arrhythmias were produced by releasing a snare after 6 min of myocardial ischemia in anesthetized, artificially ventilated rats. Reperfusion rapidly induced severe dysrhythmias in all of the control animals. Moxonidine pretreatment (0.03 and 0.10 mg/kg) decreased the incidence of ventricular fibrillation (25 and 30% versus 64%) and increased the number of animals that survived without developing any arrhythmia (20 and 25% versus 0%). We conclude that moxonidine offers significant protection against the development of arrhythmias induced by acute regional myocardial ischemia in conscious rats. Moxonidine pretreatment also provides a beneficial effect during reperfusion-induced arrhythmias that appear after a brief period of myocardial ischemia.

Effect of dietary sunflower seed oil on the severity of reperfusion-induced arrhythmias in anesthetized rats

Myocardial ischemia followed by reperfusion was produced in artificially respirated, open-chest rats. Coronary artery ligation for 6 min rarely evoked arrhythmias; however, reperfusion after this period rapidly produced severe dysrhythmias in all control animals. Reperfusion after 12 min of ischemia produced less frequent dysrhythmias than after coronary occlusion for 6 min. Feeding of a linoleic acid-rich diet, applying 12% sunflower seed oil in rat food pellet for 4 weeks, decreased the incidence of reperfusion-induced ventricular fibrillation both after 6 min (2/15 vs. 7/11) and 12 min (0/11 vs. 2/8) of myocardial ischemia and the incidence of other arrhythmias was also decreased. The number of animals developing no arrhythmias during reperfusion was increased (8/15 after 6 min of ischemia, 4/11 after 12 min of ischemia vs. 0/11 and 0/8 in controls, respectively). Our results indicate that increased dietary consumption of linoleic acid decreased the occurrence of life-threatening arrhythmias both during the acute phase of myocardial ischemia and during reperfusion in anesthetized rats.

Membrane phospholipid and fatty acid changes in the mitochondrial and sarcolemmal fractions of the heart in adjuvant arthritic rats

Adjuvant arthritis was found to induce changes in phospholipid and fatty acid composition as well as in membrane fluidity of mitochondrial and sarcolemmal fractions in the rat heart. In the sarcolemmal fraction, phosphatidylcholine content was decreased, while phosphatidylserine, phosphatidylinositol and the lysocompounds of phospholipids were increased. Mitochondria isolated from the heart of rats with adjuvant disease contained less linoleic acid than control samples. Docosatetraenoic acid and docosahexaenoic acid levels were shown to be increased in both mitochondrial and sarcolemmal fractions of the heart in treated animals. Electron spin resonance studies indicated that the break points of the curves obtained by plotting the order parameters against temperature changes were slightly shifted to lower temperature region in both subcellular fractions of arthritic rat hearts. As compared to the control values, membrane fluidity was increased both in mitochondrial and sarcolemmal fractions. The relationship of these alterations to our previous findings that adjuvant arthritis protected the rats against fatal post-infarctions arrhythmias needs further elucidation.

Effects of a combination of metoprolol and dazmegrel on myocardial infarct size in rats

The effects of acute pretreatment with metoprolol, dazmegrel and a combination of these two drugs has been examined on myocardial infarct size in rats. Ischaemic damage was assessed 4 h after coronary artery occlusion in anaesthetized rats and after 48 h of ischaemia in conscious rats. Infarct size was measured histochemically (by using periodic-acid-Schiff diastase reaction for glycogen) and by standard histological examination (haematoxylin and eosin stain). There was some evidence of protection of the myocardium by metoprolol following 4 h of ischaemia (determined histologically) but this was not apparent 48 h after occlusion. When given alone, dazmegrel had no significant effects on infarct size assessed by either method. A clear reduction in the extent of glycogen depletion and histological damage was observed with the combination of metoprolol and dazmegrel 48 h after the onset of ischaemia. This protection was seen to occur in the horizontal plane of the heart, preventing the extension of the infarct towards the posterior wall of the left ventricle and showing some salvage of the epicardial surfaces.

The effects of metoprolol and dazmegrel, alone and in combination, on arrhythmias induced by coronary artery occlusion in conscious rats

The effects of metoprolol and the thromboxane synthetase inhibitor dazmegrel, alone and in combination, were examined in a model of coronary artery occlusion in conscious rats. In a dose (2 mg kg-1), intravenously, that resulted in a marked bradycardia (of 50-80 beats min -1) metoprolol did not influence the incidence or severity of the ventricular arrhythmias that occur in the first 20 min following occlusion, nor did it improve survival (assessed at both 20 min and 16 h). In a dose (5 mg kg-1), intravenously, that in another conscious rat model involving tissue hypoperfusion inhibited thromboxane production, dazmegrel also did not modify ischaemic arrhythmias or survival. In contrast, metoprolol and dazmegrel (2 mg kg-1 and 5 mg kg-1 i.v.) when given together prior to coronary artery occlusion, produced a significant reduction in mortality both at 20 min and 16 h (e.g. from 60-75% in the control, metoprolol alone and dazmegrel alone groups and only 25% in the combined-treatment group). This was due to a decrease in the incidence of terminal ventricular fibrillation. The results suggest that a combination of beta-adrenoceptor blocking drug with a drug that inhibits thromboxane synthesis may offer more protection against ischaemia-induced ventricular fibrillation than either drug used alone. They suggest a role for both catecholamines and thromboxane in the genesis of ischaemia-induced ventricular fibrillation.

Actinomycin D suppresses the protective effect of dexamethasone in rats affected by global cerebral ischemia

Simultaneous occlusion of both common carotid arteries in female Sprague-Dawley CFY rats produced characteristic symptoms of global cerebral ischemia, such as staggering, circling, convulsions, followed by coma and death. A close correlation existed among these symptoms and the elevation of water and Na+ content, appearing at the stage of staggering; Evans blue extravasation and diminution of K+ content, detected at circling; and the increase in Ca2+ content in the total brain tissue, manifesting itself at the phase of convulsions, indicating the development of cerebral edema due to ischemia. Dexamethasone given subcutaneously in a single 2.0 mg kg-1 dose 5 hours prior to the induction of global cerebral ischemia reduced considerably the morbidity and mortality, the alterations in water and electrolyte content, and albumin leakage in the brain tissue. Actinomycin D, in a dose of 0.5 mg kg-1 injected intravenously 1 hour before steroid treatment, abolished the beneficial effect. This finding suggests that de novo protein synthesis is involved in the cerebroprotective effect of dexamethasone.

In vivo interaction of prostacyclin with an inhibitor of cyclic nucleotide phosphodiesterase, HL 725

Prostacyclin (PGI2) inactivates platelets by stimulation of adenylate cyclase, and its effect can be potentiated in vitro by simultaneous inhibition of cyclic AMP phosphodiesterase. The interaction of synthetic PGI2 and the potent phosphodiesterase inhibitor HL 725 was studied in a model of systemic platelet activation by intravenous injection of collagen. Platelet aggregate formation was evaluated by continuous on-line measurement of the circulating platelet count. Collagen injection in rabbits receiving vehicle caused a 30 +/- 3% decrease in the circulating platelet count. Infusion of PGI2 (0.05, 0.1 and 0.75 micrograms kg-1 min-1) dose-dependently inhibited this decrease. HL 725 (0.5, 1 and 3 micrograms kg-1 min-1) caused a slight but significant effect. Combinations of PGI2 and HL 725, respectively, at 0.25 + 1.0 and 0.1 + 0.5 micrograms kg-1 min-1 inhibited platelet aggregate formation to a greater extent than when either substance was used alone and produced a comparable inhibition to PGI2 at 0.75 micrograms kg-1 min-1. Collagen induced an acute fall in the mean arterial blood pressure (MABP) which also was inhibited by PGI2, HL 725 and their combinations. The infusion of a combination of PGI2 and HL 725 before collagen produced a decrease in the MABP which was greater than when either compound was used on its own. Thus, PGI2 and the phosphodiesterase inhibitor HL 725 interact in vivo to inhibit platelet aggregation and lower MABP.

Ischemia aggravating effects of platelet-activating factor in acute myocardial ischemia

The effect of platelet-activating factor (PAF) was studied during the acute phase of myocardial ischemia in cats. PAF infusion (0.75 micrograms/kg/h for 4.5h) in anesthetized, open-chest cat decreased arterial blood pressure, but did not influence heart rate or biochemical indices of cell integrity. The same dose of PAF, however, started 30 min after coronary ligation, resulted in a significantly higher elevation of plasma creatine phosphokinase (CK) activity and a reduced CK content in the region of the ischemic myocardium. Treatment with the thromboxane A2 synthetase inhibitor, CGS-13080, significantly attenuated the PAF-aggravated ischemic cellular damage. These experiments suggest that hypoxia-generated PAF may contribute to the aggravation of myocardial ischemia, part of which appears to be due to PAF-induced release of thromboxane A2.

Specificity of anti-leukotriene actions of nicardipine

The calcium channel blocker, nicardipine (100 ng/ml) markedly antagonized the coronary vasoconstrictor effect of the peptide leukotrienes LTC4 and LTD4 on the isolated perfused cat coronary artery. However, nicardipine even at 300 ng/ml failed to antagonize the leukotriene induced contraction of either tracheal or pulmonary parenchymal strips from guinea pigs. However, at higher concentrations (i.e., 10 micrograms/ml), nicardipine inhibited the production of peptide leukotrienes from minced cat lung incubated in the presence of A23187. Thus, nicardipine exerts some selectivity in its anti-leukotriene actions.

The possible mechanism of protection induced by dexamethasone against sudden death due to coronary ligation in conscious rats

Rat isolated peritoneal cells (10(7) cells ml-1) incubated in the presence of dexamethasone (3 X 10(-9) M, for 90 min) were shown to release some factor(s), having a mol. wt. of 15 k, as determined by size exclusion chromatography, which inhibited phospholipase A2 activity and offered significant protection against sudden death due to post-infarction arrhythmias in conscious rats pretreated with actinomycin D (0.5 mg kg-1 i.v. 4 h before coronary ligation). This observation suggests that the cardioprotective effect of glucocorticoids in acute myocardial infarction may result from the de novo synthesis of macrocortin, an antiphospholipase protein.

Coronary artery ligation, early arrhythmias, and determination of the ischemic area in conscious rats

A method for studying the acute phase of myocardial infarction in conscious rats has been developed. In preliminary surgery, a loose ligature of atraumatic silk was understitched around the left coronary artery. Its ends were pulled through a polyethylene tube placed within the thorax and fixed under the skin. Seven days later, coronary occlusion was performed by tightening the ligature in conscious animal. Lidocaine and pindolol pretreatment increased the survival rate and attenuated the life-threatening arrhythmias during the first 20 min, but did not influence the infarct size 16 hrs later. An ex vivo perfusion technique for determining the ischemic area has also been developed. 3, 6, and 20 min after coronary ligation, the hearts were excised and perfused with 4% formaldehyde. The ischemic area could not be perfused and remained dark red with a sharp border-line. At the 3rd and 20th min its size was as same as that of the 16-hr infarcted area; however at the 6th min it increased by 50%. Lidocaine and pindolol eliminated this transitory increase. These methods appear to be valuable for large-scale determination of drug effects on the acute phase of experimental myocardial infarction in conscious rats, and for estimating their action on the size of ischemic area very early after coronary occlusion.

Antiarrhythmic actions of meptazinol, a partial agonist at opiate receptors, in acute myocardial ischaemia

1 The intravenous administration, to anaesthetized rats, of meptazinol (1 and 2 mg kg-1), a partial agonist at opiate receptors, greatly reduced the incidence of ventricular extrasystoles that resulted from acute coronary artery occlusion. The incidence of ventricular fibrillation (VF) was reduced from 50% (in the controls) to 10% and the mortality from 30% to zero. 2 In similar doses, pretreatment with meptazinol also reduced ventricular arrhythmias, including fibrillation, in conscious rats subjected to coronary artery occlusion. In this model, survival at 16 h was increased from 27% in the controls to 50% and 83% respectively in rats pretreated with 1 and 2 mg kg-1 of the drug. 3 In antiarrhythmic doses, meptazinol had little effect on either heart rate or systemic arterial blood pressure. 4 Intracellular action potential recordings from papillary muscle removed from rats given meptazinol (2 mg kg-1) 15 min previously showed an increase in APD50 and APD90 of more than 40%. There was no effect on dV/dtmax. When superfused with meptazinol in vitro normal rat papillary muscle stimulated at 1 or 3 Hz showed an increase in APD90 and a decrease in dV/dtmax. 5 The antiarrhythmic effect of meptazinol in these models can probably be explained by direct actions on the cardiac muscle action potential (increase in APD) although effects on opiate receptors cannot be ruled out. It is suggested that meptazinol might be useful in relieving pain, and in reducing the severity of arrhythmias in the early stages of acute myocardial infarction.

Naloxone inhibits early arrhythmias resulting from acute coronary ligation

The intravenous administration of naloxone 15 min before acute coronary artery ligation in both anesthetized and conscious male rats markedly reduced the incidence and severity of the ventricular arrhythmias that occur within 30 min of the onset of myocardial ischaemia. The incidence of ventricular fibrillation was especially reduced and, in conscious rats, the survival 16 h after ligation was increased from 27% (in the controls) to 58 and 73% after 2 and 4 mg/kg naloxone respectively. One possible explanation of these results implies a detrimental effect of released endorphin in the early stages of myocardial ischaemia.

Experimental myocardial infarction in adjuvant arthritis rats

We studied the influence of various inflammatory reactions on the survival rate and occurrence of arrhythmias in the acute phase of experimental myocardial infarction in conscious male Sprague--Dawley CFY rats. Chronic disseminated inflammatory disease was induced by subplantar injection of Freund complete adjuvant, while chronic local inflammatory lesion was produced by carrageenan granuloma pouch method. An acute inflammatory response in the rat paw was evoked by carrageenan. Myocardial infarction was provoked by tightening a previously implanted silk loop around the left anterior descending coronary artery 14 days after the induction of adjuvant disease, and 7 days or 4 h after the production of granuloma pouch or foot edema. Carrageenan paw swelling was induced in rats showing expressed primary and slight secondary lesions due to Freund adjuvant. Adjuvant arthritis, but not granuloma pouch or acute paw edema, protected the rat against the fatal complications of coronary ligation. This effect was characterized by a significant increase in the survival rate from 30% to 63%, and a reduction in the occurrence of various types of dysrhythmias. Carrageenan paw edema was also less expressed and of shorter duration in rats with adjuvant disease. The level of cardiolopin was considerably increased in the arthritic group, while the other phospholipids showed no change. We conclude that chronic disseminated inflammation markedly alters the reactivity of conscious rats to experimental myocardial infarction. The alterations observed may be related to an increased energy supply and/or to accumulation of some endogenous antiinflammatory substances during adjuvant arthritis.

Effect of actinomycin D and cycloheximide on experimental myocardial infarction in rats

Actinomycin D, an inhibitor of DNA-directed RNA synthesis, or cycloheximide, a protein synthesis inhibitor, administered 24 h and 1 or 4 h respectively, before inducing coronary occlusion in conscious rats, offered marked protection against postinfarction ventricular fibrillation and sudden death. When actinomycin D was given 4 h prior to coronary ligation, the outcome of myocardial infarction was not influenced, the well-established cardioprotective effect of dexamethasone was however completely abolished. These results suggest that protein factors may be involved in the early events of myocardial infarction.

Effect of a linoleic acid-rich diet on the acute phase of coronary occlusion in conscious rats: influence of indomethacin and aspirin

We studied the effect of a long-term diet rich in linoleic acid (LAR diet) on the acute phase of experimental myocardial infarction. Male Sprague-Dawley CFY rats were fed a diet containing 12% sunflower seed oil or standard laboratory chow for 3 months. Gas-chromatographic determination of the fatty acid content in total heart phospholipids showed an increase in the n-6/n-3 fatty acid ratio, resulting from an elevated arachidonic acid content of the membrane. In parallel experiments in conscious animals, the left anterior descending coronary artery was ligated by a previously implanted silk loop. Long-term LAR diet increased the survival rate from 19 to 81% and reduced the occurrence of arrhythmias during the first 20 min after coronary ligation. Oral administration of 10 mg/kg indomethacin 1 hr prior to coronary ligation abolished the protective effect of the LAR diet, while 200 mg/kg aspirin did not. The prevention by indomethacin of the beneficial effect suggest the involvement of an increased prostaglandin synthesis in the protection offered by the diet. The ineffectiveness of aspirin in this respect is discussed. These results provide evidence that a long-term LAR diet may be of therapeutic value in the management of myocardial infarction.

Effect of non-steroid anti-inflammatory drugs in experimental myocardial infarction in rats

Four non-steroid anti-inflammatory drugs, sulfinpyrazone, acetylsalicylic acid, sodium salicylate and indomethacin were tested in the acute phase of experimental myocardial infarction in conscious rats. A single oral dose was administered, then 1 h later the occlusion of the left anterior descending coronary artery was made by using a previously implanted silk loop. It was found that each drug markedly increased the survival rate, reduced the occurrence of ventricular fibrillation and tachycardia, and delayed the appearance and shortened the duration of arrhythmias.