Defibrotide reduces infarct size in a rabbit model of experimental myocardial ischaemia and reperfusion.

1. Defibrotide, a single-stranded polydeoxyribonucleotide obtained from bovine lungs, has significant anti-thrombotic, pro-fibrinolytic and prostacyclin-stimulating properties. 2. The present study was designed to evaluate the effects of defibrotide on infarct size and regional myocardial blood flow in a rabbit model of myocardial ischaemia and reperfusion. 3. Defibrotide (32 mg kg-1 bolus + 32 mg kg-1 h-1, i.v.) either with or without co-administration of indomethacin (5 mg kg-1 x 2, i.v.) was administered 5 min after occlusion of the left anterior-lateral coronary artery and continued during the 60 min occlusion and subsequent 3 h reperfusion periods. 4. Defibrotide significantly attenuated the ischaemia-induced ST-segment elevation and abolished the reperfusion-related changes (R-wave reduction and Q-wave development) in the electrocardiogram. In addition, defibrotide significantly improved myocardial blood flow in normal and in ischaemic, but not in infarcted sections of the heart. The improvement in blood flow in normal perfused myocardium, but not in the ischaemic area was prevented by indomethacin. 5. Although the area at risk was similar in all animal groups studied, defibrotide treatment resulted in a 51% reduction of infarct size. Indomethacin treatment abolished the reduction of infarct size seen with defibrotide alone. 6. The data demonstrate a considerable cardioprotective effect of defibrotide in the reperfused ischaemic rabbit myocardium. This effect may be related, at least in part, to a stimulation of endogenous prostaglandin formation. Other possible mechanisms are discussed.     

Cardioprotective and endothelial protective effects of [Ala-IL8]77 in a rabbit model of myocardial ischaemia and reperfusion.

1 We studied the effects of a form of interleukin-8 (i.e., [Ala-IL8]77) on endothelial dysfunction and myocardial injury in rabbits. Pentobarbitone-anaesthetized rabbits were subjected to 1.5 h occlusion of the marginal coronary artery and 3.5 h reperfusion. [Ala-IL8]77 (50 micrograms or its vehicle) was given i.v. as a bolus 10 min prior to reperfusion. [Ala-IL8]77 was also studied in isolated perfused hearts of rabbits. 2 Myocardial ischaemia plus reperfusion in untreated rabbits produced severe endothelial dysfunction and myocardial injury, including marked myocardial necrosis, elevated cardiac myeloperoxidase (MPO) activity in ischaemic cardiac tissue, and loss of response of marginal coronary rings to the endothelium-dependent vasodilators, acetylcholine (ACh) and A23187. 3 Administration of [Ala-IL8]77 10 min prior to reperfusion resulted in significant protective effects in post-ischaemic reperfusion. Compared with untreated rabbits, [Ala-IL8]77 caused a reduced necrotic zone (P less than 0.01), lower MPO activity in the necrotic zone (P less than 0.05), and significantly preserved vasorelaxant responses of marginal coronary artery rings to endothelium-dependent vasodilators, ACh (P less than 0.001) and A23187 (P less than 0.001). 4 These results indicate that myocardial ischaemia and reperfusion result in a severe endothelial dysfunction and myocardial injury which involved the interaction of neutrophils and endothelial cells. However, [Ala-IL8]77 did not appear to exert a direct endothelial protective effect in the absence of neutrophils in rabbit isolated perfused hearts. 5 Inhibition of neutrophil accumulation in the myocardium, perhaps by prevention of endothelial dysfunction resulting from [Ala-IL8]77, leads to significant protective effects in ischaemia and reperfusion in rabbits.     

Endothelin-1-induced reduction of myocardial infarct size by activation of ATP-sensitive potassium channels in a rabbit model of myocardial ischaemia and reperfusion.

1. This study examined whether endothelin-1 (ET-1) reduces infarct size in a rabbit model of acute coronary artery occlusion (60 min) and reperfusion (120 min). In addition, we investigated whether the observed cardioprotective effect of ET-1 was due to the activation of ATP-sensitive potassium (KATP) channels by using two selective antagonists, glibenclamide and sodium 5-hydroxydecanoate (5-HD). 2. In the anaesthetized rabbit, infarct size (expressed as a percentage of the area at risk) after 60 min of coronary artery occlusion followed by 2 h of reperfusion was 55 +/- 4% (n = 11). ET-1 (0.3 nmol kg-1), administered as a bolus injection into the left ventricle, had no effect on infarct size (62 +/- 2%, n = 4). A lower dose of ET-1 (0.03 nmol kg-1) resulted in a significant reduction in infarct size (infarct size 43 +/- 3%; P < 0.05, n = 16). The higher dose (0.3 nmol kg-1), but not the lower dose of ET-1 caused a significant rise in blood pressure, pressure rate index and hence, myocardial oxygen consumption. 3. The reduction in infarct size afforded by ET-1 (0.03 nmol kg-1) was abolished by pretreatment of rabbits with the KATP channel inhibitors, glibenclamide (0.3 mg kg-1) and 5-HD (5 mg kg-1), (infarct size 59 +/- 3 and 63 +/- 4% respectively; n = 4-9). 4. We propose that ET-1 reduces infarct size by opening KATP channels.     

The effects of the endothelin ETA receptor antagonist, FR 139317, on infarct size in a rabbit model of acute myocardial ischaemia and reperfusion.

1. The effects were investigated of the ETA receptor antagonist, FR 139317, on endothelin-1 (ET-1)-induced coronary vasoconstriction in the isolated perfused heart of the rabbit. In addition, this study examined whether FR 139317 reduced infarct size in a rabbit model of coronary artery occlusion and reperfusion. 2. In the rabbit isolated perfused heart, ET-1 (1-100 pmol) elicited a dose-dependent increase in coronary perfusion pressure (CPP). For example, 30 pmol ET-1 caused CPP to rise by 22 +/- 8 mmHg and 100 pmol ET-1 by 47 +/- 10 mmHg (n = 8). Infusion of FR 139317 (1 microM) significantly attenuated the increase in CPP caused by ET-1 (30 pmol: 3 +/- 1 mmHg, 100 pmol: 8 +/- 2 mmHg; n = 8). 3. In the anaesthetized rabbit, infarct size (expressed as a percentage of the area at risk) after 45 or 60 min of coronary artery occlusion followed by 2 h of reperfusion was 47 +/- 6% (n = 6) and 55 +/- 7% (n = 5), respectively. A continuous infusion of FR 139317 (0.2 mg kg-1 min-1 preceded by a loading dose of 1.0 mg kg-1, i.v.; n = 5-6) had no effect on the extent of the myocardial infarct size (45 min: 47 +/- 6%; 60 min: 49 +/- 7%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prevention of myocardial enzyme release by ranolazine in a primate model of ischaemia with reperfusion.

In control anaesthetized baboons subjected to 30 min occlusion of the left anterior descending coronary artery, followed by 5.5 h reperfusion, total plasma levels for creatine kinase (CK) and lactate dehydrogenase (LDH) were markedly elevated in a time-related manner. In a second group of baboons pretreated 10 min prior to ischaemia with ranolazine [(+/-)-N-(2,6-dimethyl-phenyl)-4[2-hydroxy-3-(2-methoxyphenoxy)propyl]-1 - piperazine acetamide dihydrochloride; RS-43285-193] at 500 micrograms kg-1 i.v., followed by continuous infusion of 50 micrograms kg-1 min-1, neither enzyme was significantly elevated at any time point. Similarly, serum levels of the cardiospecific isoenzyme CK2 were 8 fold greater in the controls than in the ranolazine-treated animals at 6 h. The results indicate that ranolazine pretreatment abolished cardiac enzyme release over a 5.5 h reperfusion period, indicating a potential protective effect.     

Stereospecific antiarrhythmic effects of naloxone against myocardial ischaemia and reperfusion in the dog.

1. The effects of both the (-)- and (+)-stereoisomers of naloxone in anaesthetized dogs with arrhythmias induced by acute coronary artery occlusion followed by reperfusion were investigated. 2. Following coronary artery occlusion and reperfusion, all dogs in the control group developed ischaemia- and reperfusion-induced cardiac arrhythmias, bradycardia and hypotension. 3. The opiate antagonist (-)-naloxone prevented the arrhythmias, bradycardia and hypotension due to myocardial ischaemia and reperfusion. 4. The (+)-stereoisomer of naloxone, which is inactive as an opiate antagonist, was without beneficial effects. 5. These results indicate a possible involvement of endogenous opioid peptides in the cardiac effects due to myocardial ischaemia and reperfusion, mediated by opiate receptors through opiate antagonism.     

The relationship between calcium and increased sensitivity of rabbit aortae four hours after reserpine.

1 Four hours after reserpine, rabbit aortic strips were supersensitive to acetylcholine, isoprenaline and noradrenaline. The threshold concentration of the drugs necessary to induce a response was less and the maximum tension developed by the tissues was greater than in control strips. 2 Reserpine-treatment potentiated the contractile responses to CaCl2. 3 Reserpine-treatment resulted in an increase in calcium uptake and an increase in the slow component of 45Ca2+ efflux. 4 After resperine-treatment, the rate of relaxation from a potassium-induced contraction was decreased. 5 It is concluded that reserpine-induced supersensitivity is related to an enhanced ability of the tissue to retain and utilize calcium.     

Cilostazol protects the heart against ischaemia reperfusion injury in a rabbit model of myocardial infarction: focus on adenosine, nitric oxide and mitochondrial ATP-sensitive potassium channels

1. The present study examined whether or not cilostazol reduces the myocardial infarct size, and investigated its mechanism in a rabbit model of myocardial infarction. 2. Japanese white rabbits underwent 30 min of coronary occlusion, followed by 48 h of reperfusion. Cilostazol (1 and 5 mg/kg) or vehicle was given intravenously 5 min before ischaemia. 8-p-sulfophenyl theophylline (8SPT; an adenosine receptor blocker, 7.5 mg/kg), Nω-nitro-L-arginine methylester (l-NAME; an NOS inhibitor, 10 mg/kg) or 5-hydroxydecanoic acid sodium salt (5-HD; a mitochondrial ATP-sensitive potassium (KATP) channel blocker, 5 mg/kg) was given intravenously 5 min before cilostazol injection. Infarct size was determined as a percentage of the risk area. 3. The myocardial interstitial levels of adenosine and nitrogen oxide (NOx) during ischaemia and reperfusion, and the intensity of myocardial dihydroethidium staining were determined. 4. Infarct size was significantly reduced in the cilostazol 1 mg/kg (38.4% (2.9%)) and cilostazol 5 mg/kg (30.7% (4.7%)) groups compared with that in the control group (46.5% (4.2%)). The infarct size-reducing effect of cilostazol was completely abolished by 8SPT (46.6% (3.5%)), L-NAME (49.0% (5.5%)), or 5HD (48.5% (5.1%)). 8SPT, L-NAME or 5HD alone did not affect the infarct size. Cilostazol treatment significantly increased myocardial levels of adenosine and NOx during ischaemia, and attenuated the intensity of dihydroethidium staining during reperfusion. 5. These findings show that cilostazol reduces the myocardial infarct size by increasing adenosine and NOx levels, attenuating superoxide production and opening the mitochondrial KATP channels. Cilostazol might provide a new strategy for the treatment of coronary heart disease.     

An antiarrhythmic effect of adenosine during myocardial ischaemia and reperfusion

Adenosine (10 micrograms kg-1 min-1, infused into the lumen of the left ventricle) and dipyridamole (0.25 mg kg-1 intravenously, a dose that potentiated markedly the fall in arterial pressure in response to bolus doses of adenosine) each reduced the number of extrasystoles which occurred during the first 30 minutes following coronary artery occlusion in anaesthetised greyhound dogs (from 786 +/- 115 in control dogs to 156 +/- 44 in those treated with adenosine and to 388 +/- 167 with dipyridamole). Intracoronary adenosine (1 microgram kg-1 min-1, infused into the ischaemic area) however appeared to increase the number of extrasystoles to 1230 +/- 214. Left ventricular infusion of adenosine reduced the incidence of ventricular fibrillation (from 88 to 43%) when the ischaemic myocardium was perfused at the end of a 40 min occlusion period. In the dose used in this study (10 micrograms kg-1 min-1) adenosine caused a sustained fall in blood pressure but did not alter blood gases. In control dogs the levels of purine derivatives in blood draining the myocardium rendered ischaemic by coronary artery occlusion (local coronary venous samples) increased gradually during the ischaemic period (from 9 +/- 3 microM pre-occlusion to 25 +/- 7 microM post-occlusion). Dipyridamole increased the resting plasma concentration of purines prior to occlusion by approximately 90%; these remained raised for the occlusion period. These results support the suggestion that adenosine may act as a locally produced endogenous antiarrhythmic agent.     

The cardioprotective efficacy of TVP1022 in a rat model of ischaemia/reperfusion

BACKGROUND AND PURPOSE

Because myocardial infarction is a major cause of morbidity and mortality worldwide, protecting the heart from the ischaemia and reperfusion (I/R) damage is the focus of intense research. Based on our in vitro findings showing that TVP1022 (the S-enantiomer of rasagiline, an anti-Parkinsonian drug) possesses cardioprotective effects, in the present study we investigated the hypothesis that TVP1022 can attenuate myocardial damage in an I/R model in rats.

EXPERIMENTAL APPROACH

The model consisted of 30-min occlusion of the left anterior descending artery followed by 4 or 24 h reperfusion. In addition, we investigated the possible mechanisms of cardioprotection in H9c2 cells and neonatal rat ventricular myocytes (NRVM) exposed to oxidative stress induced by H₂O₂.

KEY RESULTS

TVP1022 (20 and 40 mg·kg⁻¹) administered 5 min before reperfusion followed by an additional dose 4 h after reperfusion reduced the infarct size and attenuated the decline in ventricular function. TVP1022 also attenuated I/R-induced deterioration in cardiac mitochondrial integrity evaluated by mitochondrial swelling capacity. In vitro, using H9c2 cells and NRVM, TVP1022 attenuated both serum free- and H₂O₂-induced damage, preserved mitochondrial membrane potential and Bcl-2 levels, inhibited mitochondrial cytochrome c release and the increase in cleaved caspase 9 and 3 levels, and enhanced the phosphorylation of protein kinase C and glycogen synthase kinase-3β.

CONCLUSIONS AND IMPLICATIONS

TVP1022 provided cardioprotection in a model of myocardial infarction, and therefore should be considered as a novel adjunctive therapy for attenuating myocardial damage resulting from I/R injuries.     

The effect of body temperature on myocardial protection conferred by ischaemic preconditioning or the selective adenosine A1 receptor agonist GR79236, in an anaesthetized rabbit model of myocardial ischaemia and reperfusion

1 The cardioprotective effect of N-[(1S, trans)-2-hydroxycyclopentyl]adenosine (GR79236), an adenosine A1 receptor agonist, was compared with that produced by ischaemic preconditioning in an anaesthetized rabbit model of myocardial ischaemia and reperfusion. In addition, we examined the effect of different body core temperatures on GR79236- or ischaemic preconditioning-induced cardioprotection when administered prior to ischaemia, and on cardioprotection induced by GR79236 administered 10 min prior to the onset of reperfusion. 2 When rabbits were subjected to 30 min occlusion of the left coronary artery, followed by 2 h reperfusion, GR79236 (3 x 10(-8) mol kg-1 i.v. (10.5 microg kg-1 i.v.)) or ischaemic preconditioning (5 min ischaemia followed by 5 min reperfusion), administered or applied 10 min prior to the occlusion, significantly limited the development of infarction. The cardioprotective effect of ischaemic preconditioning was significantly greater than that seen after administration of GR79236. Pre-treatment with the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 3.3 x 10(-6) mol kg-1 (1 mg kg-1 i.v.)), prevented the cardioprotective effect of GR79236, but not that of ischaemic preconditioning. 3 Maintaining body core temperature at 38.5 degrees C rather than at 37.0 degrees C did not influence infarct size in control groups of rabbits, but reduced the cardioprotective effect of GR79236 when administered 10 min prior to occlusion or 10 min prior to the onset of reperfusion. The cardioprotective effect of ischaemic preconditioning was not temperature-dependent. 4 In conclusion, myocardial protection conferred by GR79236 in anaesthetized rabbits is mediated via adenosine A1 receptors. Myocardial protection can be conferred when GR79236 is administered before the onset of ischaemia or reperfusion, and is reduced when body core temperature is maintained at 38.5 degrees C rather than at 37.0 degrees C. In contrast, myocardial protection conferred by ischaemic preconditioning is not reduced by adenosine A1 receptor blockade, or by maintaining body core temperature at 38.5 degrees C rather than at 37.0 degrees C. These findings point to distinct differences in the mechanisms of induction of myocardial protection by adenosine A1 receptor agonist and ischaemic preconditioning. They also highlight the need for careful control of body core temperature when investigating the phenomenon of cardioprotection.     

Mechanism of myocardial protective action of dilazep during ischaemia and reperfusion

The aim of this study was to investigate if dilazep is able to reduce with a direct protective action on the myocardium the deleterious effects caused by ischaemia and reperfusion. For this purpose we used an isolated rabbit heart preparation. The hearts were either perfused aerobically or made totally ischaemic for 60 min (by abolishing coronary flow) or made ischaemic for 60 min and then reperfused for 30 min. Ischaemic and reperfusion damage was measured in terms of alteration in mechanical function, lactate and CPK release, mitochondrial function and tissue content of Adenosine Triphosphate (ATP), Creatine Phosphate (CP) and calcium. Dilazep (10(-5) M) was administered in the perfusate either 20 minutes before ischaemia or only during post-ischaemic reperfusion. Ischaemia induced a decline of the endogenous stores of ATP and CP, followed by an alteration of calcium homeostasis with increase of diastolic pressure, mitochondria calcium overload and impairment of the oxidative phosphorylating capacities. On reperfusion, tissue and mitochondrial calcium increase the capacity of the mitochondria to use O2 for state III respiration was further impaired and the ATP-generating capacity reduced. Diastolic pressure increased and there was only a small recovery of active tension generation associated with massive CPK release. Administration of dilazep before ischaemia induced a negative inotropic effect which, in turn, resulted in a slowing of the rate of CP and ATP depletion during ischaemia. This protected the hearts against the ischemic, and reperfusion-induced decline in the ATP-generating and O2-utilizing capacities of the mitochondria. In addition, there was a less marked increase in tissue and mitochondrial Ca++, CPK and lactate release were reduced and the recovery of developed pressure on reperfusion was significantly increased. Administration of dilazep during reperfusion failed to modify the exacerbation of ischaemic damage caused by the readmission of coronary flow. These data suggest that dilazep benefits the ischaemic myocardium via an ATP sparing action.     

Allopurinol and amlodipine improve coronary vasodilatation after myocardial ischaemia and reperfusion in anaesthetized dogs.

1. We have assessed the effect of allopurinol, amlodipine and propranolol pretreatment on both endothelium-dependent and endothelium-independent coronary vasodilatation in vivo, by comparing pre-ischaemic responses with those measured after 60 min of coronary artery occlusion and 30 min of reperfusion in anaesthetized dogs. 2. In 15 untreated dogs ischaemia and reperfusion attenuated the increases in coronary blood flow produced by either acetylcholine (0.01-0.05 micrograms kg-1, i.a.) or glyceryl trinitrate (0.05-0.2 micrograms kg-1, i.a.), to an average of 39 +/- 4% and 42 +/- 5% of the pre-ischaemic control response, respectively (both P < 0.05). 3. In 5 dogs treated with allopurinol (25 mg kg-1, orally, 24 h previously, plus 50 mg kg-1, i.v., 5 min before occlusion), the increases in coronary blood flow after ischaemia and reperfusion (acetylcholine: 78 +/- 12%, glyceryl trinitrate: 60 +/- 3% of pre-ischaemic response) were significantly larger than post-ischaemic responses in untreated dogs (both P < 0.05). 4. Similarly, amlodipine treatment (3 micrograms kg-1 min-1, i.v., starting 90 min before occlusion) in 5 dogs improved post-ischaemic increases in blood flow (acetylcholine: 58.5%, glyceryl trinitrate: 66 +/- 6% of pre-ischaemic response, significantly greater than post-ischaemic responses in untreated dogs, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardioprotective actions of oligotide, a single stranded polydeoxyribonucleotide complex, in myocardial ischaemia and reperfusion injury.

1. The efficacy of oligotide, a single stranded polydeoxyribonucleotide complex, was examined in a feline model of myocardial ischaemia (MI: 90 min) and reperfusion (R: 270 min). Oligotide (15 mg kg-1 bolus) was administered intravenously 80 min after occlusion of the left anterior descending (LAD) coronary artery (i.e., 10 min prior to R) and continued for an additional 280 min (10 mg kg-1 h-1 infusion). 2. Oligotide-treated cats showed significantly smaller myocardial necroses and lower cardiac myeloperoxidase activities (significantly lower neutrophil infiltration) in the necrotic zone as compared to MI+R cats receiving only vehicle. 3. LAD coronary arteries isolated from MI+R cats exhibited a significant endothelial dysfunction (i.e., reduced endothelium-dependent relaxation), and significantly increased adherence of polymorphonuclear neutrophils (PMNs) ex vivo. However, oligotide significantly preserved endothelial function and attenuated PMN adherence in ischaemic LAD coronary arteries. 4. Oligotide attenuated P-selectin expression on thrombin-stimulated platelets as well as PMN adherence to thrombin-stimulated coronary endothelium. Immunohistochemical examination in vivo revealed that oligotide treatment also significantly inhibited coronary endothelial P-selectin expression after 90 min MI and 20 min R. 5. Oligotide exerted a significant cardioprotection in MI+R injury. The mechanism appears to be related to attenuation of PMN-endothelial interaction and eventual infiltration into the ischaemic myocardium.     

Inhibition of post-ischaemic inflammation as a therapeutic approach to myocardial ischaemia reperfusion injury

Reperfusion injury of the heart remains an untreated condition even though reperfusion strategies have been successfully implemented in the clinical standard. Accordingly, low or no reflow phenomena with subsequent myocardial infarction, myocardial and endothelial stunning as well as arrhythmias remain aspects of reperfusion injury of the heart. Since leukocyte recruitment has been linked to these phenomena, inhibition of leukocyte adhesion and of the subsequent post-ischaemic inflammation of the heart has emerged as a therapeutic goal. Around 40 patents from 1997 to the first quarter of 2000 are implicitly or explicitly aimed at myocardial reperfusion injury.     

Cardioprotective effects of N-hydroxyguanidine PR5 in myocardial ischaemia and reperfusion in rats

1. The potential for the N-hydroxyguanidine compound PR5 (N-(3, 4-dimethoxy-2-chlorobenzylideneamino)-N'-hydroxyguanidine) as a cardioprotective agent in heart ischaemia and reperfusion injury was investigated using rat models. 2. Administration of 1-10 mg kg-1 of PR5 5 min before 10 min of left coronary artery occlusion, followed by 20 min reperfusion, strongly inhibited reperfusion burst of arrhythmias and markedly improved the survival of the animals (e.g. ventricular fibrillation incidence 93 vs 43% (P<0.05); mortality 47 vs 0% (P<0.05), for controls and for 3 mg kg-1 of PR5, respectively). 3. Administration of 3 mg kg-1 of PR5 1 min before reperfusion to rats subjected to 10 min occlusion, 20 min reperfusion was most effective in reducing arrhythmias and decreasing mortality (43 vs 0%, P<0.05), but effects were also seen when PR5 was administered 0, 1 and 5 min after start of reperfusion. 4. Coronary occlusion/reperfusion (10 - 20 min) increased malondialdehyde (MDA) of rat hearts (0.88+/-0.13 for sham vs 1.45+/-0.12 nmol mg-1 protein for ischaemic; P<0.05). In rats where 3 mg kg-1 PR5 were administered 1 min before reperfusion the increase was attenuated (MDA being 1.04+/-0.12; P<0.05 vs ischaemic). 5. PR5 caused a substantial reduction of the infarction size in rats subjected to 180 min left coronary artery occlusion, followed by 120 min of reperfusion; the necrotic zone being 326+/-32 mg for controls vs 137+/-21 mg for animals treated with 3x3 mg kg-1 of PR5 (P<0.01). 6. PR5 reduced the elevation of the ST-segment of the ECGs, as well as caused pronounced attenuation of the rapid blood pressure drop seen at the start of reperfusion following coronary artery occlusion. 7 We conclude that the N-hydroxyguanidine PR5 provides remarkable protection against ischaemia and reperfusion induced myocardial necrosis and life-threatening arrhythmias. These effects of PR5 are discussed in relation to a recently discovered ability of N-hydroxyguanidines to function as electron acceptors at the xanthine oxidase enzyme.     

The effects of timolol on arrhythmias and prostanoid release during canine myocardial ischaemia and reperfusion

Timolol (50 micrograms kg-1), administered intravenously to chloralose-anaesthetized open-chest greyhounds 30 min prior to occlusion of the left anterior descending coronary artery, reduced heart rate and mean arterial blood pressure. This dose caused a 20 fold increase in the dose of isoprenaline required to increase heart rate by 25 beats min-1. During the first 30 min of myocardial ischaemia the number of extrasystoles in the timolol-treated dogs (327 +/- 179) was less than in the control group (888 +/- 168) and none of the dogs that received timolol fibrillated. The haemodynamic changes induced by coronary artery occlusion (decreased cardiac output and stroke volume, increased peripheral vascular resistance) were similar in both control and timolol-treated dogs as were the increases in PCO2 and decreases in PO2 and pH in blood draining from the ischaemic myocardium. Timolol did not alter the release during myocardial ischaemia, of either thromboxane B2 or prostacyclin (measured as 6-keto PGF1 alpha). Reperfusion-induced ventricular fibrillation occurred in 7 out of 8 control dogs and in 5 out of 10 timolol-treated dogs. The overall survival following occlusion and reperfusion was improved by 10% to 50% by timolol.     

Cardioprotective actions of human superoxide dismutase in two reperfusion models of myocardial ischaemia in the rat.

1. In rats under ether anaesthesia, the left coronary artery was ligated and reperfused after 10 min of ischaemia. Forty-eight hours later the myocardium was analyzed for creatine kinase (CK) activity. 2. Human superoxide dismutase (h-SOD) given 1 min after occlusion and again 6 h later significantly improved survival and retarded the loss of myocardial CK. 3. In rat isolated hearts perfused at 15% of normal flow for 30 min followed by re-establishment of normal flow for 20 min, perfusion pressure increased by 72% and myocardial CK decreased by 44%. No significant changes occurred in wet-to-dry heart weight ratio. 4. Administration of h-SOD at 2.5 or 5.0 mg, significantly attenuated the elevated post-ischaemic perfusion pressure and the loss of myocardial CK activity in rat perfused hearts. 5. h-SOD appears to be an effective anti-ischaemic agent in the intact animal as well as the isolated perfused heart of the rat subjected to low flow followed by reperfusion at normal flow. The mechanism of this cardioprotective effect is not totally dependent upon the formed elements of the blood, but may be partially due to a direct cytoprotective effect.     

Delayed protection against ventricular arrhythmias by monophosphoryl lipid-A in a canine model of ischaemia and reperfusion.

Bacterial endotoxin reduces the severity of ventricular arrhythmias which occur when a coronary artery is occluded several hours later. We have now examined in anaesthetised dogs the effects on ischaemia and reperfusion-induced arrhythmias, of a non-toxic derivative component of the endotoxin molecule of the lipid-A (monophosphoryl lipid-A). This was given intravenously, in doses of 10 and 100 microg kg(-1), 24 h prior to coronary artery occlusion. Arrhythmia severity was markedly reduced by monophosphoryl lipid-A. During ischaemia, ventricular premature beats were reduced from 315+/-84 in the vehicle controls to 89+/-60 (with the lower dose of monophosphoryl lipid-A) and 53+/-23 (P<0.05) with the higher dose. The incidence of ventricular tachycardia was reduced from 75% to 25% (P<0.05) and 31% (P<0.05), and the number of episodes of ventricular tachycardia from 13.4+/-4.9 per dog to 1.1+/-1.1 (P<0.05) and 1. 2+/-0.9 (P<0.05) after doses of 10 and 100 microg kg(-1), respectively. The incidence of ventricular fibrillation during occlusion and reperfusion in the control group was 96% (15/16), i.e., only 6% (1/16) dogs survived the combined ischaemia-reperfusion insult. Monophosphoryl lipid-A (100 microg kg(-1)) significantly reduced the incidence of occlusion-induced ventricular fibrillation (from 50% to 7%; P<0.05), and increased survival following reperfusion to 54% (P<0.05). Monophosphoryl lipid-A also significantly reduced ischaemia severity as assessed from ST-segment elevation recorded from epicardial electrodes as well as the degree of inhomogeneity of electrical activation within the ischaemia area. There were no haemodynamic differences prior to coronary occlusion between vehicle controls and monophosphoryl lipid-A-treated dogs. These results demonstrate that monophosphoryl lipid-A reduces arrhythmia severity 24 h after administration. Although the precise mechanisms are still unclear, there is some evidence that nitric oxide and prostanoids (most likely prostacyclin) may be involved because the dual inhibition of nitric oxide synthase and cyclooxygenase enzymes by administration of aminoguanidine and meclofenamate abolished the marked antiarrhythmic protection resulted from monophosphoryl lipid-A treatment 24 h previously.     

Importance of myocardial blood flow changes in the protective action of diltiazem in a new model of myocardial ischaemia.

The effect of diltiazem was studied in a new model of myocardial ischaemia in which in addition to a critical constriction of the left circumflex branch (LCX), the left anterior descending coronary artery (LAD) was suddenly occluded. This model is probably more relevant to the clinical situation in which multivessel coronary artery disease is common. In this model diltiazem exerted a beneficial effect, manifested by an increase in myocardial blood flow (MBF) within the stenosed area of the LCX; by a marked reduction of the enhanced preload (LVEDP); by a diminution of the inhomogeneity of electrical activation and by a decrease in ST-segment elevation. Diltiazem also caused a significant reduction both in the number of extrasystoles and in the incidence of ventricular fibrillation. Increased MBF within the stenosed area was associated with enhanced blood flow to the ischaemic myocardium, i.e. diltiazem directed flow to the ischaemic zone by improvement of the collateral circulation. The beneficial electrophysiological changes caused by diltiazem are probably at least partly due to the drug-induced improvement of myocardial blood supply to the ischaemic area.