Nitric oxide signaling in ischemic heart

Cardioprotective effects of an aminothiazole compound on isoproterenol-induced myocardial injury in mice

Dendrodoine analogue (DA), an aminothiazole compound derived from dendrodoine, present in a marine tunicate, has been shown to possess many beneficial properties. This study was aimed to evaluate its cardioprotective effect against isoproterenol (ISO)-induced myocardial damage in mice. Swiss mice were pretreated with DA for 7 days and then treated with ISO (5 mg/kg BW, for 2 consecutive days). Biochemical assessment of myocardial injury was carried out by measuring marker enzymes, antioxidant enzymes and levels of lipid peroxidation. Histological studies of hearts were also carried out. ISO administration increased the activities of creatine kinase-MB, lactate dehydrogenase and aspartate aminotranferase (AST) in serum. Prior administration of DA restored the levels of these enzymes and the heart coefficient close to normal levels. DA at a concentration of 5 mg/kg BW was most effective in reducing AST, and this concentration was used for further studies. DA also gave significant protection against lipid peroxidation in the heart besides restoring histopathological alterations. DA showed significant reactivity towards superoxide radicals. In conclusion our study indicates that DA can protect mouse myocardium against damage and one of the possible reasons behind this protective effect can be attributed to its antioxidant property.

The cardioprotective effect of different doses of vasopressin (AVP) against ischemia-reperfusion injuries in the anesthetized rat heart

The aim of the present study was to investigate the protective effect of various doses of exogenous vasopressin (AVP) against ischemia-reperfusion injury in anesthetized rat heart. Anesthetized rats were randomly divided into seven groups (n=4-13) and all of them subjected to prolonged 30 min regional ischemia and 120 min reperfusion. Group I served as saline control with ischemia, in treatment groups II, III, IV and V, respectively different doses of AVP (0.015, 0.03, 0.06 and 1.2 μg/rat) were infused within 10 min prior to ischemia, in group VI, an AVP-selective V1 receptor antagonist (SR49059, 1mg/kg, i.v.) was administrated prior to effective dose of AVP injection and in group VII, SR49059 (1 mg/kg, i.v.) was only administrated prior to ischemia. Various doses of AVP significantly prevented the decrease in heart rate (HR) at the end of reperfusion compared to their baseline and decreased infarct size, biochemical parameters [LDH (lactate dehydrogenase), CK-MB (creatine kinase-MB) and MDA (malondialdehyde) plasma levels], severity and incidence of ventricular arrhythmia, episodes and duration of ventricular tachycardia (VT) as compared to control group. Blockade of V1 receptors by SR49059 attenuated the cardioprotective effect of AVP on ventricular arrhythmias and biochemical parameters, but partially returned infarct size to control. AVP 0.03 μg/rat was known as effective dose. Our results showed that AVP owns a cardioprotective effect probably via V1 receptors on cardiac myocyte against ischemia/reperfusion injury in rat heart in vivo.

Sulfaphenazole protects heart against ischemia-reperfusion injury and cardiac dysfunction by overexpression of iNOS, leading to enhancement of nitric oxide bioavailability and tissue oxygenation

The objective of this study was to establish the cardioprotective effect of sulfaphenazole (SPZ), a selective inhibitor of cytochrome P450 2C9 enzyme, in an in vivo rat model of acute myocardial infarction (MI). MI was induced by 30 min ligation of left anterior descending coronary artery, followed by 24 h reperfusion (I/R). The study used 6 groups: I/R (control); SPZ; L-NAME; L-NAME + SPZ; 1400W (an inhibitor of iNOS); 1400W + SPZ. The agents were administered orally through drinking water for 3 days prior to induction of I/R. Myocardial oxygenation (pO(2)) at the I/R site was measured using EPR oximetry. The preischemic pO(2) value was 18 +/- 2 mm Hg in all groups. At 1 h of reperfusion, the SPZ group showed a significantly higher hyperoxygenation when compared to control (45 +/- 1 vs. 34 +/- 2 mm Hg). The SPZ group showed a significant improvement in the contractile functions and reduction in infarct size. Histochemical staining of SPZ-treated hearts exhibited significantly lower levels of superoxide and peroxynitrite, and markedly increased levels of iNOS activity and nitric oxide. Western blot analysis indicated upregulation of Akt and attenuation of p38MAPK activities in the reperfused myocardium. The study established that SPZ attenuated myocardial I/R injury through overexpression of iNOS, leading to enhancement of nitric oxide bioavailability and tissue oxygenation.

Cardioprotection by Sulfaphenazole, a Cytochrome P450 Inhibitor: Mitigation of Ischemia-Reperfusion Injury by Scavenging of Reactive Oxygen Species

Cytochrome P450 (P450) enzymes play a significant role in promoting myocardial ischemia-reperfusion (I/R) injury. CYP2C9, an isoform of P450, is known to generate superoxide radicals in the reperfused heart. Sulfaphenazole (SPZ), a CYP2C9 inhibitor, has been shown to decrease I/R injury; however, the mechanism of cardioprotection by SPZ is not well elucidated. The objective of this study was to test whether SPZ mitigates myocardial I/R injury by scavenging reactive oxygen species (ROS). Isolated rat hearts were subjected to 30 min of global ischemia followed by 45 min of reperfusion. Hearts were perfused with SPZ and/or N(omega)-nitro-L-arginine methylester (L-NAME). Coronary flow (CF), left-ventricular developed pressure (LVDP), and rate-pressure product (RPP) were monitored. Superoxide and nitric oxide (NO) generation in the reperfused tissue was determined using fluorescence methods. Myocardial infarct size was measured using triphenyltetrazolium chloride staining. The SPZ-treated group showed a significant recovery of cardiac function compared with the untreated I/R group (CF, 53 versus 45%; LVDP, 48 versus 22%; RPP, 51 versus 20%). The infarct size was significantly reduced in the SPZ-treated group (15%) compared with the I/R control (42%). Coadministration of L-NAME with SPZ significantly attenuated the beneficial effects of SPZ. In addition, SPZ treatment showed significantly decreased superoxide levels and enhanced NO bioavailability in the reperfused heart. In conclusion, the protective effect of SPZ against I/R-mediated myocardial damage appears to be due to a reduction in the superoxide level caused by its inhibition of CYP2C9, as well as scavenging of oxygen free radicals generated in the reperfused heart.

Determination of nitric oxide in hydrophytes using poly(methacrylic acid-ethylene glycol dimethacrylate) monolith microextraction coupled to high-performance liquid chromatography with fluorescence detection

Nitric oxide (NO) is a bioactive molecule that has recently emerged as a cellular messenger in numerous physiological processes in plants. A novel high-performance liquid chromatography (HPLC) method combined with poly(methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith microextraction (PMME) is developed for sensitive determination of NO in hydrophytes. NO is derivatized using a fluorescent probe, 1,3,5,7-tetramethyl-8-(3',4'-diaminophenyl)-difluoroboradiaza-s-indacene (DAMBO), and then the derivatives are extracted with PMME and analyzed by high-performance liquid chromatography (HPLC) with fluorescence detection. The conditions for the derivatization and the subsequent extraction of NO derivatives are optimized in detail. The detection limit (S/N=3) of NO is determined to be 2x10(-12)mol L(-1). Close correlation coefficient and excellent method reproducibility are obtained for the analyte over a linear range of 9x10(-11)-4.5x10(-8)mol L(-1). The inter- and intraday relative standard deviations (R.S.D.s) are less than 5%. The proposed method is successfully applied to the determination of NO levels in hydrophytes samples.

Myocardial release of nitric oxide during ischaemia and reperfusion: effects of L-arginine and hypercholesterolaemia

AIMS

Nitric oxide (NO) may modulate myocardial ischaemia/reperfusion (I/R) injury, but effects of hypercholesterolaemia on myocardial NO release during I/R are unknown.

METHODS

A NO-specific carbon fibre electrode continuously measured coronary sinus [NO] during 60 min low-flow ischaemia (1 ml/min) and 60 min free reperfusion (I/R) in isolated rabbit hearts. Experimental groups (n=7 per group) were control, L-arginine supplement (200 microM), N-nitro-L-arginine methyl ester (L-NAME) treatment (8 microM) and hypercholesterolaemic.

RESULTS

During early I, NO release decreased markedly in control (-1356+/-286 pmol/min/g) and L-arginine (-1972+/-172) groups, but less in L-NAME (-441+/-89) and hypercholesterolaemic (-602+/-164) groups (both p<0.01 vs. controls). No increase in NO release during I was seen in any group. After R, NO release increased above baseline in control (+2333+/-591 pmol/min/g) and L-arginine (+1048+/-278) groups and hypercholesterolaemic (+1100+/-478) (p<0.05 vs. pre-ischaemia each group). There was little increase in NO release in the L-NAME group (+436+/-247 pmol/min/g, p<0.05 vs. controls). In each group, myocardial NO release declined towards pre-ischaemic levels during 60 min R. Hearts treated with L-arginine had similar NO release but better functional recovery than controls (p<0.01). Treatment with L-NAME was also associated with better functional recovery than in controls or hypercholesterolaemic hearts.

CONCLUSION

Myocardial NO release declines rapidly during ischaemia, but increases above baseline during early reperfusion. Improved function after L-arginine treatment appears to be independent of effects upon NO release. Hypercholesterolaemia is associated with reduced myocardial NO release, under both baseline conditions and during ischaemia and reperfusion.

Proposed mechanisms for red palm oil induced cardioprotection in a model of hyperlipidaemia in the rat

High-cholesterol diets alter myocardial and vascular NO-cGMP signaling and have been implicated in ischaemic/reperfusion injury. We investigated the effects of dietary red palm oil (RPO) containing fatty acids, carotonoids, tocopherols and tocotrienols on myocardial ischaemic tolerance and NO-cGMP pathway function in the rat. Wistar rats were fed a standard rat chow+/-RPO, or a standard rat chow+cholesterol+/-RPO diet. Myocardial mechanical function and NO-cGMP signaling pathway intermediates were determined before, during and after 25 min ischaemia. RPO-supplementation improved aortic output recovery and increased myocardial ischaemic cGMP concentrations. Simulated ischaemia (hypoxia) increased cardiomyocyte nitric oxide levels in the two RPO supplemented groups, but not in control non-supplemented groups. RPO supplementation also increased hypoxic nitric oxide levels in the control diet fed, but not the cholesterol fed rats. These data suggest that dietary RPO may improve myocardial ischaemic tolerance by increasing bioavailability of NO and improving NO-cGMP signaling in the heart.

Cardioprotective effect of resvaratrol pretreatment on myocardial ischemia–reperfusion induced injury in rats

OBJECTIVE

The major objective of the present study was to examine the cardioprotective effect of resveratrol, an antioxidant presents in red wine, in the rat after ischemia-reperfusion (I/R).

DESIGN

The left coronary artery was in occlusion for 30 min followed by a 120 min reperfusion in anesthetized rats. Animals were pretreated with and without resveratrol before occlusion. The post-ischemic ventricular function (left ventricle maximum systolic pressures and the maximal first derivative of developed pressure) and myocardial infarct size and myocardial nitric oxide (NO) and malonaldehyde (MDA) content were compared.

RESULTS

Resveratrol pretreatment had dramatic cardioprotective effects on post-ischemic ventricular functional recovery and decreasing myocardial infarct size. Resveratrol pretreatment also increased NO and decreased MDA content in myocardium.

CONCLUSIONS

Resveratrol has cardioprotective properties in I/R rats. The cardioprotective effects in the I/R rats may be correlated with its antioxidant activity and upregulation of NO production.

Cardioprotective effect of grape seed proanthocyanidins on isoproterenol-induced myocardial injury in rats

PURPOSE

To investigate whether grape seed proanthocyanidins (GSP) might protect the heart against myocardial injury (MI) induced by isoproterenol (ISO), in a rat model.

METHODS

GSP was administered orally to Wistar albino rats (150-180 g) in three different doses, by gastric gavage (50, 100 and 150 mg kg(-1) GSP), 6 days a week for 5 weeks. At the end of this period, all the rats, except the normal untreated rats that served as the control group, were administered ISO, 85 mg kg(-1) subcutaneously, for 2 consecutive days to induce myocardial injury. After 48 h, rats (n=6 per group) were anaesthetized with anesthetic ether, sacrificed and the levels of biochemical and histological observations of the heart tissues were performed.

RESULT

Our results suggest that prior administration of GSP maintained the levels of the marker enzymes (AST, ALT, LDH and CK) in all the treatment groups (GSP-50-ISO, GSP-100-ISO and GSP-150-ISO) when compared to ISO-injected rats. The entire baseline groups also showed no significant alterations in serum marker enzyme levels in comparison to that of control group. Interestingly, in this study, there was no significant change in the basal levels of myocardial TBARS, GST, SOD and CAT on administration of GSP in all the three dosages (GSP-50-BL, GSP-100-BL and GSP-150-BL). However, a significant decrease occurred in the levels of GSH and GPx in group GSP-50-BL, which in the absence of any cellular injury (as evidenced by histological studies), is considered to be non-lethal. In the ISO-injected group there was a significant rise in TBARS and a significant decrease in GSH, GPx, GST, SOD and CAT when compared to group control. The administration of GSP maintained the activities of these enzymes close to normal levels when compared to group ISO, which proves the stress stabilizing action of GSP. The biochemical and histological evidence from this study shows that 100 and 150 mg kg(-1) of GSP protected against ISO-induced myocardial injury.

CONCLUSION

This study demonstrates that GSP has a significant effect in the protection of heart against MI induced by ISO. We believe that pretreatment with GSP may contribute to developing novel strategies in the prevention and treatment of cardiotoxic effects of elevated levels of catecholamine.

Protective effect of nitric oxide pathway in resveratrol renal ischemia-reperfusion injury in rats

BACKGROUND

Nitric oxide (NO), synthesized from L-arginine by the enzyme nitric oxide synthase (NOS), seems to play an ambiguous role during tissue ischemia-reperfusion (I/R) injury. This study was designed to investigate the effects of resveratrol, a polyphenolic phytoalexin, in renal ischemia reperfusion (RIR) injury in rats.

METHODS

Forty-eight rats were randomized into six groups. Group 1: sham operated (C); group 2: right nephrectomy (UNI); group 3: UNI + 45 min of ischemia and 24 h of reperfusion in the contralateral kidney; group 4: UNI + RIR + L-NAME (10 mg/kg, i.p.); group 5: UNI + RIR + resveratrol (5 mg/kg, p.o.); group 6: UNI + RIR + resveratrol + L-NAME. At the end of the reperfusion period, rats were sacrificed. Thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) levels, catalase (CAT), and superoxide dismutase (SOD) activities were determined in renal tissue. Serum creatinine and blood urea nitrogen (BUN) were measured for the evaluation of renal function. Tissue and urine nitrite levels were measured to assess total nitric oxide levels.

RESULTS

Ischemic control animals demonstrated severe deterioration of renal function, altered renal morphology, reduced total nitric oxide levels and a marked renal oxidative stress.

CONCLUSIONS

Pretreatment of animals with resveratrol markedly attenuated renal dysfunction, morphological alterations, improved nitric oxide levels, reduced elevated TBARS levels and restored the depleted renal antioxidant enzymes, However, treatment with L-NAME attenuated this protection afforded by resveratrol indicating that resveratrol exerts its protective effect through NO release.

COX-2 mediates morphine-induced delayed cardioprotection via an iNOS-dependent mechanism

Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) have been shown to be mediators of cardioprotection induced by ischemic preconditioning and opioids. However, it is not known whether COX-2 is involved in morphine-induced cardioprotection accompanied with iNOS. Therefore, we investigated the role of COX-2 in morphine-induced cardioprotection and the effect of iNOS on COX-2. Myocardial ischemia was induced by a 45-min coronary artery occlusion in mice. Infarct size (IS) as a percentage of the area at risk (AAR) was determined by triphenyltetrazolium chloride staining. The COX-2-selective inhibitor NS-398 was used to investigate the role of COX-2. Expression of COX-2 was assessed by Western blotting, and the myocardial prostaglandin (PG)E2 and 6-keto-PGF(1alpha) contents were measured using enzyme immunoassays. The iNOS-selective inhibitor SMT and iNOS gene-knockout mice were used to investigate the effect of iNOS on COX-2. IS/AAR was reduced significantly 1 and 24 h after morphine preconditioning. The infarct-sparing effect 24 h after morphine administration, but not the cardioprotection 1 h later, was completely abolished by NS-398. Marked enhancement of myocardial COX-2 expression was measured 24 h after morphine preconditioning associated with up-regulation of myocardial contents of PGE2 and 6-keto-PGF(1alpha). Neither the level of COX-2 nor the contents of PGE2 and 6-keto-PGF(1alpha) were enhanced 1 h later. Administration of SMT and targeted abrogation of iNOS gene blocked the enhancement of myocardial PGE2 and 6-keto-PGF(1alpha) 24 h after morphine administration but did not inhibit the up-regulation of COX-2 expression. We concluded that COX-2 mediates morphine-induced delayed cardioprotection via an iNOS-dependent pathway.

Mechanisms by which KATP channel openers produce acute and delayed cardioprotection

Mitochondria are being increasingly studied for their critical role in cell survival. Multiple diverse signaling pathways have been shown to converge on the K+-sensitive ATP channels as the effectors of cytoprotection against necrosis and apoptosis. The role of potassium channel openers in regulation and transformation of cell membrane excitability, action potential and electrolyte transfer has been extensively studied. Cardiac mitoK(ATP) channels are the key effectors in cardioprotection during ischemic preconditioning, as yet with an undefined mechanism. They have been hypothesized to couple myocardial metabolism with membrane electrical activity and provide an excellent target for drug therapy. A number of K(ATP) channel openers have been characterized for their beneficial effects on the myocardium against ischemic injury. This review updates recent progress in understanding the physiological role of K(ATP) channels in cardiac protection induced by preconditioning and highlights relevant questions and controversies in the light of published data.

Dietary red palm oil improves reperfusion cardiac function in the isolated perfused rat heart of animals fed a high cholesterol diet

It has been shown that dietary red palm oil (RPO) supplementation improved reperfusion function. However, no exact protective cellular mechanisms have been established. Our aim was to search for a possible cellular mechanism and a role for fatty acids. Rats were fed a standard rat chow, plus cholesterol and/or RPO-supplementation for 6 weeks. Functional recovery, myocardial phospholipid and cAMP/cGMP levels were determined in isolated rat hearts subjected to 25 min of normothermic total global ischaemia. Dietary RPO in the presence of cholesterol improved aortic output (AO) recovery (63.2+/-3.06%, P<0.05) vs. cholesterol only (36.5+/-6.2%). The improved functional recovery in hearts supplemented with RPO vs. control was preceded by an elevation in the cGMP levels early in ischaemia (RPO 132.9+/-36.3% vs. control 42.7+/-24.4%, P<0.05). Concurrently, cAMP levels decreased (RPO -8.3+/-6.9% vs. control 19.9+/-7.7%, P<0.05). Our data suggest that dietary RPO-supplementation improved reperfusion AO through mechanisms that may include activation of the NO-cGMP and inhibition of the cAMP pathway.

Cardioprotection with resveratrol pretreatment: improved beneficial effects over standard treatment in rat hearts after global ischemia

OBJECTIVE

The major objective of the present study is to evaluate the potential role of resveratrol (RVT), a natural antioxidant found in grapes and red wine, in protecting the myocardium from the deleterious effects of ischemia-reperfusion (I/R) injury using isolated rat hearts.

METHODS

Langendorff perfused isolated rat hearts were subjected to 60 min of global ischemia following 60 min of reperfusion. RVT was given according to chronic pretreatment and/or acute treatment protocols. Animals received RVT at the dose of 20 mg/kg via an intragastric tube for 14 days before the experiment and/or at the infusion concentration of 10 microM for 30 min before the onset of ischemia. The myocardial postischemic recovery was compared using hemodynamic data (peak systolic pressure, end diastolic pressure, and +dP/dtmax), coronary flow, biochemical parameters (LDH, CK-MB, cTnI, myoglobin) from coronary effluent, and oxidative stress markers (MDA, GSH, carbonyl) from heart tissue homogenates in each group.

RESULTS

RVT pretreatment and treatment protocols have provided increased preservation in myocardial recovery following global ischemia compared to a non-treated group. Furthermore, the ischemic damage of myocardium was significantly lower in chronic pretreated rats than in the acutely treated group. In contrast, no significant difference was observed in cardioprotective effects of RVT between the only pretreated group, and both the pretreated and treated group throughout reperfusion.

CONCLUSION

The findings from this study indicate that RVT has potent cardioprotective properties against I/R injury in rat hearts. The study also highlighted that the administration of RVT, as pretreatment, has amplified the beneficial effects over the standard treatment.

Vasopressin effects on the coronary circulation after a short ischemia in anesthetized goats

To examine the coronary effects of arginine-vasopressin during reperfusion after a short ischemia, left circumflex coronary artery flow was electromagnetically measured, and 15 min total occlusion of this artery followed by reperfusion was induced in anesthetized goats (five nontreated, five treated with the inhibitor of nitric oxide synthesis Nomega-nitro-L-arginine methyl ester (L-NAME) and five treated with the inhibitor of cyclooxygenase meclofenamate). The vasoactive drugs and L-NAME were intracoronarily injected, and meclofenamate by i.v. route. At 60 min of reperfusion, coronary vascular conductance was not changed significantly in nontreated and was decreased by 35% (P<0.01) in L-NAME-treated and by 30% (P<0.01) in meclofenamate-treated animals. During reperfusion, the coronary vasodilatation with acetylcholine (3-100 ng) and sodium nitroprusside (1-10 microg) was not altered in nontreated animals, and the vasodilatation with acetylcholine but not with sodium nitroprusside was partially decreased in L-NAME--but not in meclofenamate-treated animals. The vasoconstriction in response to arginine-vasopressin (0.03-0.3 microg) was increased during reperfusion in nontreated, was not changed in L-NAME-treated and was decreased in meclofenamate-treated animals. Therefore, it is suggested that during reperfusion after a short ischemia: (1) the coronary vasodilator reserve is preserved; (2) the coronary vasodilatation with acetylcholine is also preserved, but in this vasodilatation, the role of nitric oxide may be attenuated and prostanoids may be not involved; and (3) the coronary vasoconstriction with arginine-vasopressin is increased, probably due to both attenuation of the modulatory role of nitric oxide and the release of vasoconstrictor prostanoids.

Real-time measurement of nitric oxide by luminol-hydrogen peroxide reaction in crystalloid perfused rat heart

The objective of this study was to develop an assay system that allows continuous monitoring of nitric oxide (NO) released from crystalloid perfused hearts. We utilized chemiluminescence reaction between NO and luminol-H(2)O(2) to quantify the NO level in coronary effluent. Isolated rat hearts were subjected to ordinary Langendorff's perfusion, and the right ventricle was cannulated to sample coronary effluent. After equilibration, the coronary flow rate was set constant and the hearts were paced at 300 bpm. Coronary effluent was continuously sampled and mixed with the chemiluminescent probe containing 0.018 mmol/l luminol plus 10 mmol/l H(2)O(2). Chemiluminescence from the mixture of coronary effluent and the probe was continuously measured. NO concentration was calibrated by various concentrations (0.5-400 pmol/l) of standard NO solution. The lower detection limit of NO was 1 pmol/l. Basal NO release from isolated perfused rat heart was 0.41 +/- 0.17 pmol/min/g of heart weight, and that was significantly suppressed by 0.1 mmol/l of L-NAME to 0.18 +/- 0.10 pmol/min/g of heart weight (n = 7). Application of 0.1 and 0.3 micromol/l acetylcholine increased NO level in the coronary effluent, in a concentration-dependent manner, from 6.6 +/- 1.7 in a baseline condition to 16.3 +/- 7.4 and 30.3 +/- 16.1 pmol/l at each peak, respectively. Thrombin at 1 and 10 U/ml also increased NO level from 17.6 +/- 4.3 in control to 35.5 +/- 10.4 and 48.7 +/- 8.7 pmol/l at each peak, respectively (n = 7). Thus, this assay system is applicable to the continuous real-time measurement of NO released from crystalloid perfused hearts, and it may be useful for the study of physiological or pathophysiological role of NO in coronary circulation.

Coronary reactivity to endothelin-1 during partial ischemia and reperfusion in anesthetized goats. Role of nitric oxide and prostanoids

To examine the coronary reactivity to endothelin-1 and its interaction with nitric oxide or prostanoids during partial coronary ischemia and reperfusion, left circumflex coronary artery flow was electromagnetically measured, and partial occlusion of this artery was induced for 60 min, followed by reperfusion in anesthetized goats (eight non-treated, six treated with N(w)-nitro-L-arginine methyl esther (L-NAME) and five treated with meclofenamate). During partial occlusion, coronary vascular conductance was reduced by 24-37% (P<0.01), and the coronary vasodilatation in response to acetylcholine (3-100 ng) and sodium nitroprusside (1-10 microg) was much decreased in every case; the vasoconstriction in response to endothelin-1 (1-10 microg) was depressed in non-treated animals, and this depression was reversed by L-NAME and was accentuated by meclofenamate. At 30 min of reperfusion coronary vascular conductance remained decreased by 22-27% (P<0.01), and the vasodilatation in response to acetylcholine (3-100 ng) and sodium nitroprusside (1-10 microg), as well as the vasoconstriction with endothelin-1 (1-10 microg), were as in the control and comparable in the three groups of animals. These results suggest: (a) that during ischemia, the coronary vasodilator reserve is greatly reduced, and the vasoconstriction with endothelin-1 is blunted, with preservation of the modulatory role of nitric oxide and involvement of vasoconstrictor prostanoids in this vasoconstriction, and (2) that during reperfusion, the coronary vasodilator reserve and the coronary reactivity to acetylcholine and endothelin-1 recover, but the modulatory role of nitric oxide in this reactivity may be attenuated.

Redox signaling in vascular angiogenesis

Angiogenesis is thought to be regulated by several growth factors (EGF, TGF-alpha, beta-FGF, VEGF). Induction of these angiogenic factors is triggered by various stresses. For instance, tissue hypoxia exerts its pro-angiogenic action through various angiogenic factors, the most notable being vascular endothelial growth factor, which has been mainly associated with initiating the process of angiogenesis through the recruitment and proliferation of endothelial cells. Recently, reactive oxygen species (ROS) have been found to stimulate angiogenic response in the ischemic reperfused hearts. Short exposure to hypoxia/reoxygenation, either directly or indirectly, produces ROS that induce oxidative stress which is associated with angiogenesis or neovascularization. ROS can cause tissue injury in one hand and promote tissue repair in another hand by promoting angiogenesis. It thus appears that after causing injury to the cells, ROS promptly initiate the tissue repair process by triggering angiogenic response.

Cardiovascular responses and nitric oxide production in cerebral ischemic rats

We investigated that the role of nitric oxide (NO) on ischemic rats in brain and heart. Ischemia was induced by both common carotid arteries (CCA) occlusion for 24h following reperfusion. Then tissue samples were removed and measured NOx. In brain, NOx was increased by about 40% vs. normal and it was significantly inhibited by aminoguanidine, selective iNOS inhibitor. This result showed that NOx concentration was increased by iNOS. We investigated the role of Ca2+ during ischemia. Nimodipine, L-type calcium channel blocker, didn't inhibit the increases of NOx concentration during ischemia. It suggested that increased NOx was due to calcium-independent NOS. MK-801, which N-methyl-D-aspartate (NMDA) receptor antagonist, didn't significantly prevent the increases of NOx. In heart, ischemia caused NOx decrease and it is inconsistent with NOx increase in brain. Aminoguanidine and nimodipine didnt affect on NOx decrease. But MK-801 more lowered NOx concentration than those of ischemia control group. It seemed that Ca2+ influx in heart partially occurred via NMDA receptor and inhibited by NMDA receptor antagonist. The mean arterial pressure (MAP) in ischemic rats after 24h of CCA occlusion was decreased when compared to normal value, whereas the heart rates (HR) was not different between two groups. Aminoguanidine or MK801 had no effect on MAP or HR, but nimodipine reduced MAP. There was no difference the effects of aminoguanidine, nimodipine, or MK-801, on MAP and HR between normal rats and ischemic rats. In summary, ischemic model caused an increase of NOx concentration, suggesting that this may be produced via iNOS, which is calcium independent in brain. However in heart, ischemia decreased NOx concentration and NMDA receptor was partially involved. The basal MAP was decreased in ischemic rats but HR was not different from normal control, suggesting that increased NOx in brain of ischemic rat may result in the hypotension.

Quinaprilat during cardioplegic arrest in the rabbit to prevent ischemia-reperfusion injury

OBJECTIVES

This study evaluated intracardiac angiotensin-converting enzyme inhibition as an adjuvant to cardioplegia and examined its effects on hemodynamic, metabolic, and ultrastructural postischemic outcomes.

METHODS

The experiments were performed with an isolated, erythrocyte-perfused, rabbit working-heart model. The hearts excised from 29 adult New Zealand White rabbits (2950 +/- 200 g) were randomly assigned to four groups. Two groups received quinaprilat (1 microg/mL), initiated either with cardioplegia (n = 7) or during reperfusion (n = 7). The third group received l-arginine (2 mmol/L) initiated with cardioplegia (n = 7). Eight hearts served as a control group. Forty minutes of preischemic perfusion were followed by 60 minutes of hypothermic arrest and 40 minutes of reperfusion.

RESULTS

All treatments substantially improved postischemic recovery of external heart work (62% +/- 6%, 69% +/- 3%, and 64% +/- 5% in quinaprilat during cardioplegia, quinaprilat during reperfusion, and l-arginine groups, respectively, vs 35% +/- 5% in control group, P <.001) with similarly increased external stroke work and cardiac output. When administered during ischemia, quinaprilat significantly improved recovery of coronary flow (70% +/- 8%, P =.028 vs quinaprilat during reperfusion [49% +/- 5%] and P =.023 vs control [48% +/- 6%]). l-Arginine (55% +/- 7%) showed no significant effect. Postischemic myocardial oxygen consumption remained low in treatment groups (4.6 +/- 1.2 mL. min(-1). 100 g(-1), 6.0 +/- 2.2 mL. min(-1). 100 g(-1), and 4.7 +/- 1.6 mL. min(-1). 100 g(-1) in quinaprilat during cardioplegia, quinaprilat during reperfusion, and l-arginine groups, respectively, vs 4.2 +/- 0.8 mL. min(-1). 100 g(-1) in control group), even though cardiac work was markedly increased. High-energy phosphates, which were consistently elevated in all treatment groups, showed a significant increase in adenosine triphosphate with quinaprilat during ischemia (2.24 +/- 0.14 micromol/g vs 1.81 +/- 0.12 micromol/g in control group, P =.040). Ultrastructural grading of mitochondrial damage revealed best preservation with quinaprilat during ischemia (100% [no damage], P =.001 vs control).

CONCLUSION

These experimental findings have clinical relevance regarding prevention of postoperative myocardial stunning and low coronary reflow in patients undergoing heart surgery.

[Nitric oxide synthases and peripheral cardiovascular system]

The synthesis of nitric oxide (NO) is catalysed by nitric oxide synthases which exist in at least three distinct isoforms. These enzymes catalyse the oxidation of the amino acid L-arginine to give rise to L-citrulline and NO. The different cell types comprising cardiac muscle express one or more of the three isoforms (neuronal, inductible, endothelial) of NO synthases. Recently, a mitochondrial nitric oxide synthase has been isolated. A complexity of NO synthase exists with distinct domains and multitude of cofactors. NO synthases are able to produce not only NO but also superoxide O2-. (uncoupled reaction). These two products can react together extremely rapidly to form the potent oxidant peroxynitrite. The formation of peroxynitrite has been implicated in the pathology of a large number of conditions involving oxidative stress such as atherosclerosis and heart failure.

Effects of defibrotide, a novel oligodeoxyribonucleotide, on ischaemia and reperfusion injury of the rat liver

1. The purpose of this study was to investigate the protective effects of defibrotide, a single-stranded polydeoxyribonucleotide, on ischaemia-reperfusion injury to the liver using a rat model. 2. Ischaemia of the left and median lobes was created by total inflow occlusion for 30 min followed by 60 min of reperfusion. Hepatic injury was assessed by the release of liver enzymes (alanine transferase, ALT and lactic dehydrogenase, LDH). Hepatic oxidant stress was measured by superoxide production, lipid peroxidation and nitrite/nitrate formation. Leukocyte-endothelium interaction and Kupffer cell mobilization were quantified by measuring hepatic myeloperoxidase (MPO), polymorphonuclear leukocyte adherence to superior mesenteric artery (SMA) and immunostaining of Kupffer cell. 3. Defibrotide treatment resulted in a significant inhibition of postreperfusion superoxide generation, lipid peroxidation, serum ALT activity, serum LDH activity, MPO activity, serum nitrite/nitrate level, leukocyte adherence to SMA, and Kupffer cell mobilization, indicating a significant attenuation of hepatic dysfunction. 4. A significant correlation existed between liver ischaemia/reperfusion and hepatic injury, suggesting that liver ischaemia/reperfusion injury is mediated predominantly by generation of oxygen free radicals and mobilization of Kupffer cells. 5. We conclude that defibrotide significantly protects the liver against liver ischaemia/reperfusion injury by interfering with Kupffer cell mobilization and formation of oxygen free radicals. This study provides strong evidence that defibrotide has important beneficial effects on acute inflammatory tissue injury such as that occurring in the reperfusion of the ischaemic liver.

Mitochondrial K(ATP) channel as an end effector of cardioprotection during late preconditioning: triggering role of nitric oxide

Nitric oxide (NO) has been implicated in the "second-window" of ischemic preconditioning (PC). However, the identity of the end effector after initiation of preconditioning by NO is not known. It is likely that NO is involved in opening of mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels. We hypothesized that NO is an important trigger for the opening of mitoK(ATP) channels in the late phase of preconditioning and inducible nitric oxide synthase (iNOS) up-regulation via NF kappa B plays a critical role in diazoxide-induced cardioprotection. To examine this, diazoxide (7 mg/kg) was administered to wild-type (WT) mice and mice lacking the gene 24 hours before 40 minutes of global ischemia. Hearts were perfused in a Langendorff mode and effects of activation of mitoK(ATP) channel and other interventions on functional, biochemical and pathological changes in ischemic hearts were assessed. In hearts from WT mice treated diazoxide, left-ventricular-developed pressure, end-diastolic pressure and coronary flow were significantly improved after ischemia/reperfusion (I/R); lactate dehydrogenase (LDH) release was also significantly decreased, while ATP contents were significantly higher. Administration of 5-HD, a specific blocker of mitoK(ATP) channel or l -NAME, an inhibitor of iNOS before I/R, during diazoxide-pretreatment completely blocked the late cardioprotection against ischemia. Late cardioprotection was also blocked by inhibition of either PKC- delta by rottlerin or NF kappa B by DDTC before diazoxide pretreatment. Diazoxide pretreatment significantly increased nuclear translocation of p65 which was blocked by protein kinase C (PKC) or nitric oxide synthase (NOS) inhibition. Diazoxide was totally inefffective in iNOS knockout mice. These results suggest that diazoxide activates NF kappa B via PKC signaling pathway and that leads to iNOS up-regulation after 24 hours. NO which is generated upon ischemic stress triggers the opening of mitoK(ATP)channel as an end effector of cardioprotection during late PC.

Cardioprotection from ischemia and reperfusion injury by an endothelin A-receptor antagonist in relation to nitric oxide production

It has previously been shown that endothelin (ET)-receptor antagonists protect the myocardium from ischemia and reperfusion (I/R) injury. The mechanism behind this effect is unclear. The aim of this study was to elucidate the possible interaction between ET(A)-receptor antagonism and nitric oxide (NO) during I/R. Anesthetized pigs were subjected to 45-min ligation of the left anterior descending coronary artery (LAD) followed by 4 h of reperfusion. Vehicle (n = 7), the ET(A)-receptor antagonist LU 135252 (LU; 0.1 mg/kg, n = 7), the combination of LU and the NO precursor L-arginine (15 mg/kg, n = 7; LU + L-arg), the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA; 0.2 mg/kg, n = 6), or the combination of LU and L-NMMA (LU + L-NMMA; n = 6) were injected into the LAD during the last 10 min of ischemia and the first 5 min of reperfusion. There were no significant differences in coronary flow, pulmonary capillary wedge pressure, mean arterial pressure, or heart rate between the groups before ischemia or at the end of reperfusion. The area at risk was similar in all five groups. The infarct size of the vehicle group was 79 +/- 6% of the area at risk. LU and LU + L-arginine (L-arg) reduced the infarct size to 39 +/- 6% and 35 +/- 8%, respectively (p < 0.001 vs. vehicle). L-NMMA completely prevented the infarct-limiting effect of LU. Thus the infarct size in the LU + L-NMMA group was 83 +/- 4% (p < 0.001 vs. LU alone); L-NMMA did not affect infarct size per se (79 +/- 4%). ET immunoreactivity increased threefold in the I/R myocardium of the vehicle group. The increase in ET immunoreactivity was significantly attenuated in the LU and LU + L-arg groups (p < 0.001), but not in the groups given L-NMMA or LU + L-NMMA. In conclusion, ET(A)-receptor blockade results in cardioprotection and attenuation of the increase in myocardial ET levels after I/R. Both effects were inhibited by NO synthase blockade, suggesting that they are dependent on maintained production of NO.

Reduction in the level of cardiac cyclic GMP worsens contractile delay in myocardial stunning

We tested the hypothesis that a reduction in the level of myocardial cyclic GMP would worsen the contractile delay associated with myocardial stunning. Two groups of 12 anesthetized open-chest New Zealand white rabbits were utilized. Myocardial stunning was produced by two 15-min occlusions of the left anterior descending coronary artery followed by 15 min of reperfusion. Either control vehicle (saline + 1% DMSO) or 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ 10(-4) M, a guanylate cyclase inhibitor) was topically applied to the left ventricular surface of the rabbit hearts. Left ventricular and aortic pressures along with wall thickness parameters were determined. Coronary blood flow (microspheres) and O(2) extraction (microspectrophotometry) were used to determine myocardial O(2) consumption. Myocardial stunning was observed in the control group through an increased delay in onset of wall thickening (46.2 +/- 7.3 vs 76.6 +/- 17.5 ms). There was no significant effect of stunning on the rate of wall thickening (21.8 +/- 9.5 vs 18.1 +/- 3.4 mm/s) or O(2) consumption (stun 4.6 +/- 0.6, control 4.8 +/- 0.4 ml O(2)/min/100 g). After treatment with ODQ 10(-4) M, both delay (43.9 +/- 9.6 vs 134.1 +/- 30.0 ms) and myocardial O(2) consumption (stun 5.9 +/- 0.6, control 5.9 +/- 0. 7) increased significantly compared to control. There was no significant change in the rate of wall thickening. We conclude that decreasing cyclic GMP worsens stunning by increasing delay in onset of wall thickening and increasing local O(2) costs in the stunned region.

Cyclic GMP reduces ventricular myocyte stunning after simulated ischemia-reperfusion

We tested the hypothesis that the second messenger activated by nitric oxide, cyclic GMP, would reduce the effects of myocyte stunning following simulated ischemia-reperfusion and that this was related to cyclic GMP protein kinase. Ventricular cardiac myocytes were isolated from New Zealand White rabbits (n = 8). Cell shortening was measured by a video edge detector and protein phosphorylation was determined autoradiographically after SDS gel electrophoresis. Cell shortening data were acquired at: (i) baseline followed by 8-Bromo-cGMP 10(-6) M (8-Br-cGMP) and then KT 5823 10(-6) M (cyclic GMP protein kinase inhibitor) and (ii) simulated ischemia (20 min of 95% N(2)-5% CO(2) at 37 degrees C) followed by simulated reperfusion (reoxygenation) with addition of 8-Br-cGMP 10(-6) M followed by KT 5823 10(-6) M, (iii) addition of 8-Br-cGMP prior to ischemia followed by the addition of KT 5823 10(-6) M after 30 min of reoxygenation. In the control group, 8-Br-cGMP 10(-6) M decreased percentage shortening (%short) (5.0 +/- 0.6 vs 3.8 +/- 0. 4) and the maximum velocity (V(max), microm/s) (48.6 +/- 6.9 vs 40.2 +/- 6.4). KT 5823 10(-6) M added after 8-Br-cGMP partially restored %short (4.6 +/- 0.5) and V(max) (46.6 +/- 8.0). After stunning, baseline myocytes had decreased %short (3.4 +/- 0.2) and V(max) (36. 0 +/- 4.2). After the addition of 8-Br-cGMP, the %short (2.7 +/- 0. 2) and V(max) (27.6 +/- 2.5) decreased further. The addition of KT 5823 did not change either the %short or the V(max). The myocytes with 8-Br-cGMP during ischemia had increased %short (4.2 +/- 0.2) and V(max) (37.2 +/- 3.4) when compared to the stunned group. The addition of KT 5823 did not significantly alter %short (3.3 +/- 0.4) or V(max) (29.2 +/- 5.0) in the myocytes pretreated with 8-Br-cGMP. Protein phosphorylation was increased by 8-Br-cGMP in control and stunned myocytes. KT 5823 blocked this effect in control but not stunned myocytes, suggesting some change in the cyclic GMP protein kinase. Ischemia-reperfusion produced myocyte stunning that was reduced when 8-Br-cGMP was added prior to but not after ischemia.

Myocardial ischemia/reperfusion injury in the inducible nitric oxide synthase knockout mice

Inducible nitric oxide synthase (iNOS) plays an important role in the inflammatory process of certain major cardiac disorders including myocardial infarction and allograft rejection. However, the role of iNOS in acute myocardial ischemia has not been well defined. We determined the effects of genetically disruption of the intact iNOS system on cardiac tolerance to ischemia/reperfusion injury. Adult male wild-type (WT) and iNOS knockout (KO) B6,129 mice were subjected to 20 min global ischemia and 30 min reperfusion in a Langendorff isolated perfused heart model (37 degrees C, n = 10/each group). Ventricular contractile function, heart rate, coronary flow, and leakage of intracellular enzymes (CK and LDH) were not significantly different between the groups during pre-ischemia as well as reperfusion period (P > 0.05). Myocardial infarct size was also not significantly different between WT (20.2+/-2.0% of risk area) and KO mice (23.5+/-3.8%; Mean+/-SEM, P > 0.05). However, the post-ischemic heart rate was significantly preserved in KO as compared to WT (P < 0.05). We conclude that disruption of iNOS gene does not exacerbate ischemia/ reperfusion injury in the heart.

The red wine antioxidant resveratrol protects isolated rat hearts from ischemia reperfusion injury

The consumption of red wine has been reported to impart a greater benefit in the prevention of coronary heart disease than the consumption of other alcoholic beverages. This beneficial effect is increasingly being attributed to certain antioxidants comprising the polyphenol fraction of red wine such as transresveratrol. In the present study, we investigated the potential cardioprotective effects of resveratrol in the face of ischemia reperfusion (I/R) injury. Isolated perfused working rat hearts after stabilization were perfused with Krebs-Henseleit Bicarbonate buffer (KHB) either in the presence or absence of transresveratrol (RVT) at a concentration of 10 microM for 15 min prior to subjecting them to 30 min of global ischemia followed by 2 h of reperfusion. Left ventricular functions were monitored at various timepoints throughout the reperfusion period to assess the extent of postischemic recovery in comparison with baseline values. Coronary perfusate samples were also collected to determine malonaldehyde (MDA) levels. The results demonstrated that RVT exhibited significant myocardial protection. This was evidenced by improved recovery of post-ischemic ventricular function including developed pressure and aortic flow as compared to the control group (KHB). Values for developed pressure in the RVT-treated group were significantly higher than those in the control group throughout the reperfusion period (71.09+/-4.88 mm Hg vs. 58.47+/-3.88 mm Hg, 68.87+/-5.07 mm Hg vs. 49.74+/-2.65 mm Hg and 51.67+/-3.95 mm Hg vs. 30.50+/-4.80 mm Hg at reperfusion timepoints R-15, R-60, and R-120, respectively). From R-30 onwards, aortic flow was markedly higher in the RVT treated group as compared with the control group, the differences being most significant at R-90 (32.45+/-2.19 ml/min vs. 19.83+/-1.62 ml/min) and R-120 (27.15+/-2.27 ml/min vs. 14.10+/-1.69 ml/min). In contrast to the KHB treated group, the RVT-treated group displayed significant reduction in MDA formation especially in the immediate early reperfusion period (63.71+/-8.19 pM/ml vs. 130.86+/-4.76 pM/ml, 63.84+/-15.62 pM/ml vs. 156.99+/-18.93 pM/ml, 71.29+/-2.80 pM/ml vs. 129.5+/-10.30 pM/ml and 56.25+/-5.79 pM/ml vs. 127.99+/-3.50 pM/ml at timepoints R-1, R-3, R-5, and R-7, respectively) indicating a reduction in I/R injury related oxidative stress. Infarct size was markedly reduced in the RVT group when compared with the control group (10.57+/-0.35% vs. 36.27+/-5.28%). In vitro studies revealed RVT to be a potent scavenger of peroxyl radicals suggestive of a probable mechanism involved in the protective ability of RVT. The results of this study indicate that resveratrol possesses cardioprotective effects which may be attributed to its peroxyl radical scavenging activity.

Interaction of bradykinin with angiotensin, prostacyclin, and nitric oxide in myocardial preservation

This review focuses on the importance of bradykinin in myocardial preservation during ischemic arrest. Bradykinin is released from the heart spontaneously in response to ischemic stress, which may be viewed as a survival signal of the heart against ischemia. Bradykinin appears to function as a signaling molecule by controlling the release of other intracellular modulators, such as prostacyclins and nitric oxide, which also exert beneficial effects on the ischemic myocardium.

Nitric oxide and endothelin-1 in coronary and pulmonary circulation

Since the discovery of the vasorelaxant properties of nitric oxide and the vasoconstrictor effect of endothelin-1, there have been many studies of the distribution and functional significance of these agents in various vascular beds. In the coronary and pulmonary circulation nitric oxide and endothelin-1 actions have been largely investigated in terms of an imbalance between the opposing effects of these vasoactive agents leading to pathophysiological conditions. This article review functional and immunocytochemical studies with emphasis on the ultrastructural localization of nitric oxide synthase and endothelin-1 in the coronary and pulmonary vascular beds. Localization of nitric oxide synthase (type III or I or II) has been shown in endothelial cells, smooth muscle, and perivascular nerves of the coronary and pulmonary vascular beds and in the neurons, nerve fibers, and the small granule-containing cells within cardiac ganglia. Endothelin-1 was mainly localized in subpopulations of coronary and pulmonary endothelial cells. These immunocytochemical studies provide information about the sources of nitric oxide and endothelin-1 that contribute to the vasomotor control of cardiac and pulmonary circulation under normal and pathophysiological conditions.

Coordinated role of vasoactive intestinal peptide and nitric oxide in cardioprotection

The present study sought to examine the interrelationship between nitric oxide (NO) and vasoactive intestinal peptide (VIP) in myocardial protection. Isolated rat hearts were perfused for 15 min with buffer only (Group I); 0.3 mM VIP (Group II); 3 mM L-arginine (a precursor of NO) (Group III); VIP and aminoguanidine (iNOS blocker) (Group IV); or L-arginine plus VIP 10-28 (VIP inhibitor) (Group V). Each heart was then made globally ischemic for 30 min followed by 2 h reperfusion. Both VIP and NO were found to provide cardioprotection during ischemia and reperfusion. However, the beneficial effects of VIP and NO were reduced by inhibition of NO and VIP, respectively, suggesting that cardioprotection by VIP is modulated by NO and vice versa. The results of this study suggested a coordinated regulation by cardioprotection by NO and VIP.

L-arginine, a nitric oxide precursor, attenuates ischemia-reperfusion injury by inhibiting inositol-1,4,5-triphosphate

OBJECTIVE

We evaluated the effect of pretreatment with nitric oxide precursor before ischemia on recovery with reperfusion in rat hearts.

METHODS

Isolated rat hearts were perfused with Krebs-Henseleit buffer without (C group) or with 3 mmol/L L-arginine (A group) before 30 minutes of ischemia. The left ventricular function, including heart rate, developed pressure, maximal dp/dt, and coronary flow, were measured before pretreatment and after 10 and 30 minutes of reperfusion. Cyclic guanosine monophosphate (by radioimmunoassay), calcium (by absorption spectrophotometry), and inositol 1,4,5-triphosphate synthesized from tritiated myo-inositol (by ion-exchange chromatography preceding counting) were measured at the same times and immediately after ischemia.

RESULTS

Recovery of ventricular function was significantly greater in the A group than in the C group. Pretreatment increased postischemic cyclic guanosine monophosphate content compared with the preischemic level (from 1.06 +/- 0.12 to 1.94 +/- 0.09 pmol/mg protein, p < 0.05). No change in cyclic guanosine monophosphate was evident in the C group. In the C group, inositol triphosphate content increased after 10 minutes of reperfusion beyond the preischemic level (from 0.53 +/- 0.023 to 1.15 +/- 0.045 cpm x 10(-3)/gm, p < 0.05) as did calcium at 30 minutes (from 4.12 +/- 0.164 to 6.86 +/- 0.544 mmol/gm dry weight). In the A group, both of these increases were significantly attenuated.

CONCLUSION

These data suggest that L-arginine pretreatment may reduce calcium overload by increasing cyclic guanosine monophosphate production, which in turn downregulates inositol triphosphate synthesis during reperfusion.

Angiotensin II as a stimulator of Na(+)-dependent Ca2+ efflux from freshly isolated adult rat cardiomyocytes

In cardiac tissues, angiotensin II causes inotropic and chronotropic effects on the heart. It is indicated that the mechanism of the inotropic effect of angiotensin II is attributed to an increase in cytosolic free calcium ([Ca2+]i) in cardiomyocytes. However, increased [Ca2+]i should be restored to a physiological level because cumulative elevation in [Ca2+]i leads to irreversible injury in cardiomyocytes. Whereas it is known that angiotensin II causes the increase in [Ca2+]i in cardiac cells, little is known about the mechanisms of decrease in [Ca2+]i in cardiomyocytes upon angiotensin II stimulation. In the present study, we examined the effect of angiotensin II on Ca2+ efflux from freshly isolated adult rat cardiomyocytes. Angiotensin II stimulated the efflux of 45Ca2+ from the cells in a concentration-dependent manner (10(-7)-10(-5) M). The 45Ca2+ efflux from the cells was inhibited by type 1 angiotensin II receptor inhibitor. The angiotensin II-stimulated 45Ca2+ efflux was not affected by deprivation of the extracellular Ca2+, but was dependent on the presence of extracellular Na+. These results indicate that angiotensin II stimulates extracellular Na(+)-dependent 45Ca2+ efflux from freshly isolated adult rat cardiomyocytes, probably through its stimulatory effect on the plasma membrane type 1 angiotensin II receptors which may couple to Na+/Ca2+ exchange.

Delayed protection against ischaemia-induced ventricular arrhythmias and infarct size limitation by the prior administration of Escherichia coli endotoxin

1. Bacterial endotoxin (lipopolysaccharide derived from Escherichia coli) was injected intraperitoneally in conscious rats in doses ranging from 0.5 to 2.5 mg kg-1. At various times afterwards the animals were anaesthetized and subjected to a 30 min period of left coronary artery occlusion. 2. Under these conditions the severity of ventricular arrhythmias was markedly suppressed, in comparison with saline-injected controls, but this was particularly marked with the higher doses (1.5 and 2.5 mg kg-1); the number of ventricular premature beats was reduced from 1687 +/- 227 over the 0.5 h coronary artery occlusion period to 190 +/- 46 in those rats administered 2.5 mg kg-1 endotoxin 8 h previously (P < 0.05). The duration of ventricular tachycardia was also significantly reduced (138 +/- 26 s to 8.9 +/- 4.2 s; P < 0.01) and there was a reduction in the incidence of ventricular fibrillation (from 56% to 10%). 3. The time course of this protection was studied following the administration of a single dose of 2.5 mg kg-1 of endotoxin by anaesthetizing rats 4, 8 or 24 h later. Protection was apparent at each time but was particularly marked at 8 h. 4. No rat given the highest dose of endotoxin (32 in all) died as a result of ventricular fibrillation, or from any other cause, during an occlusion, in contrast to a 26% mortality in the controls (P < 0.01). 5. Infarct size, measured following a 30 min period of coronary artery occlusion followed by a 3 h reperfusion period, was reduced both 8 and 24 h after the administration of 2.5 mg kg-1 endotoxin (reductions of 24.3 and 23.1% respectively; P < 0.05). Endotoxin had no significant effect on the area at risk. 6. The beneficial effects of endotoxin on infarct size and on ventricular arrhythmias were markedly attenuated by the prior administration of dexamethasone, 3 mg kg-1 given 1 h prior to endotoxin administration. Dexamethasone itself reduced infarct size (P < 0.05) but had no direct effect on arrhythmia severity following coronary artery occlusion. 7. The mechanisms of this "cross-tolerance' induced by bacterial endotoxin against ischaemia-reperfusion injury remain to be elucidated but the most likely mechanisms appear to be the induction of protective enzymes or proteins (e.g. nitric oxide synthase, cyclo-oxygenase (COX) 2) probably mediated by cytokine release.

Nicorandil suppressed ventricular arrhythmias in a canine model of myocardial ischaemia

These experiments were designed to explore the possibility that a K+ channel opener which also donates nitric oxide to the myocardium (nicorandil) may modify ischaemia-induced ventricular arrhythmias in a large animal model. In mongrel dogs anaesthetised with chloralose-urethane and thoracotomised, a side branch of the left anterior descending artery was catheterised for the local intracoronary infusion of nicorandil (2.5 micrograms kg-1 min-1 for 20 min prior to coronary artery occlusion and then continuing throughout the 25 min occlusion period). In this dose, nicorandil had no haemodynamic effects, increased coronary blood flow by up to 16% and significantly reduced the severity of ischaemia-induced arrhythmias (e.g. from nearly 500 ventricular premature beats in the controls to 160 +/- 60 in the nicorandil group). There was a significant reduction in the number of episodes of ventricular tachycardia during the ischaemic period and a reduced incidence of ventricular fibrillation following reperfusion resulting in a 42% survival from the combined ischaemia-reperfusion insult (cf. 0% in the control; P < 0.05). The marked changes that occurred in ST-segment elevation (mapped with epicardial electrodes) and in the inhomogeneity of electrical activation within the ischaemic area in control dogs was markedly reduced in those dogs administered nicorandil. We conclude that the local intracoronary administration of nicorandil reduces the severity of both ischaemia and the life-threatening arrhythmias that result from an abrupt reduction in coronary blood flow in this canine model. Possible mechanisms include an increase in coronary blood flow, a reduction in the severity of myocardial ischaemia and an ability of the compound to "donate' nitric oxide to the ischaemic area.