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Biomedical subjects

Gary F Baxter

Publications and source records attributed to Gary F Baxter.

18 recordsLinked to original sources
PubMed2007

Rho kinase activation plays a major role as a mediator of irreversible injury in reperfused myocardium.

Intracellular signal transduction events in reperfusion following ischemia influence myocardial infarct development. Here we investigate the role of Rho kinase (ROCK) activation as a specific injury signal during reperfusion via attenuation of the reperfusion injury salvage kinase (RISK) pathway phosphatidylinositol 3-kinase (PI3K)/Akt/endothelial nitric oxide (NO) synthase (eNOS). Rat isolated hearts underwent 35 min of left coronary artery occlusion and 120 min of reperfusion. Phosphorylation of the ROCK substrate protein complex ezrin-radixin-moesin, assessed by immunoblotting and immunofluorescence, was used as a marker of ROCK activation. Infarct size was determined by tetrazolium staining, and terminal dUTP nick-end labeling (TUNEL) positivity was used as an index of apoptosis. The ROCK inhibitors fasudil or Y-27632 given 10 min before ischemia until 10 min after reperfusion reduced infarct size (control, 34.1 +/- 3.8%; 5 microM fasudil, 18.2 +/- 3.1%; 0.3 microM Y-27632, 19.4 +/- 4.4%; 5 microM Y-27632, 9.2 +/- 2.9%). When 5 microM Y-27632 was targeted specifically during early reperfusion, robust infarct limitation was observed (14.2 +/- 2.6% vs. control 33.4 +/- 4.4%, P<0.01). The protective action of Y-27632 given at reperfusion was attenuated by wortmannin (29.2 +/- 6.1%) and N(omega)-nitro-L-arginine methyl ester (30.4 +/- 5.7%), confirming a protective mechanism involving PI3K/Akt/NO. Ezrin-radixin-moesin phosphorylation in risk zone myocardium confirmed early and sustained ROCK activation during reperfusion and its inhibition by Y-27632. Inhibition of ROCK activation at reperfusion reduced the proportion of TUNEL-positive nuclei in the infarcted region. In conclusion, ROCK activation occurs specifically during early reperfusion. Inhibition of ROCK at reperfusion onset limits infarct size through an Akt/eNOS-dependent mechanism, suggesting that ROCK activation at reperfusion may be deleterious through suppression of the RISK pathway.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed2006

Attenuated cardioprotective response to bradykinin, but not classical ischaemic preconditioning, in DOCA-salt hypertensive left ventricular hypertrophy.

Hypertensive left ventricular hypertrophy (LVH) co-exists frequently with ischaemic heart disease. While ischaemic preconditioning (IPC) is known to protect against ischaemia-reperfusion injury in LVH, it is not known if other cardioprotective manoeuvres are effective. Bradykinin, a key autacoid mediator in IPC, is protective in normal hearts but its ability to protect against ischaemia-reperfusion injury in LVH is unknown. Hypertensive LVH was induced in male rats by 4 weeks treatment with deoxycorticosterone acetate (DOCA) and salt drinking fluid. Hearts were Langendorff perfused, subjected to 35 min coronary artery occlusion and 120 min reperfusion, and infarct size (AN/RZ %) was determined by tetrazolium staining. The effects of IPC with 2 x 5 min cycles of global ischaemia or 10 min pretreatment with bradykinin were assessed. DOCA-salt rats were markedly hypertensive and left ventricle/body weight ratio was 26% greater than in normotensive controls. Baseline coronary flow and risk zone/LV ratio were similar in normotensive hearts and DOCA-salt hearts, and infarct size was similar (AN/RZ 50.6+/-3.2% and 47.0+/-3.1%, respectively). IPC was equally protective in normotensive and DOCA-salt hearts (AN/RZ 18.6+/-3.3% and 18.4+/-2.3%, respectively, P < 0.01 versus corresponding control). Bradykinin 0.1, 0.2 or 0.5 microM pretreatment produced concentration-dependent infarct limitation in normotensive hearts (bradykinin 0.5 microM AN/RZ, 9.5+/-3.6%, P < 0.01 versus normotensive control), but the effect in DOCA-salt hearts was attenuated (bradykinin 0.5 microM AN/RZ, 23.4+/-3.8%). Further, the pre-ischaemic coronary vasodilator response to bradykinin was abrogated in DOCA-salt hypertensive hearts. We conclude that the cardioprotective action of bradykinin is markedly attenuated in moderate LVH and coronary vasodilator effect is lost. The reasons for reduced sensitivity to bradykinin in the hypertensive heart are unknown but these findings may have implications for the application of preconditioning-mimetic interventions in LVH.

Animals↗
PubMed2006

A critical cytoprotective role of endogenous adrenomedullin in acute myocardial infarction.

Exogenous administration or transfection of adrenomedullin (AM) affords protection against ischaemia-reperfusion injury. Here we have examined the role of endogenous AM in regulating the development of myocardial infarction. Wild type (WT) and AM(+/-) mice underwent 30 min regional myocardial ischaemia and 120 min reperfusion. In AM(+/-) hearts, tetrazolium-determined infarct size was greater than in WT controls (27.9 +/- 2.0 vs. 17.7 +/- 2.4%, P < 0.01) and mortality rate was increased (35% vs. 14%, P < 0.05). Treatment with exogenous recombinant AM (200 ng/kg) prior to coronary occlusion rescued the ischaemia-reperfusion intolerant phenotype of AM(+/-) mice and further limited infarct development in WT mice. Administration of recombinant AM was associated with augmented phosphorylation of Akt and eNOS in early reperfusion suggesting a role for AM in regulating this survival pathway. These studies provide the first evidence that expression of AM is a critical factor regulating myocardial tolerance to ischaemia-reperfusion injury.

Adrenomedullin↗
PubMed2005

Exogenous hydrogen sulfide (H2S) protects against regional myocardial ischemia-reperfusion injury--Evidence for a role of K ATP channels.

Hydrogen sulfide (H2S) is a gaseous mediator, produced by the metabolic pathways that regulate tissue concentrations of sulfur-containing amino acids. Recent studies indicate that endogenous or exogenous H2S exerts physiological effects in the cardiovascular system of vertebrates, possibly through modulation of K ATP channel opening. The present study was undertaken to examine the hypothesis that H2S is cytoprotective against myocardial ischemia-reperfusion injury and that this protective action is mediated by K ATP opening. Rat isolated hearts were Langendorff-perfused and underwent 30 min left main coronary artery occlusion and 120 min reperfusion. The resulting injury was assessed as infarct size, determined by tetrazolium staining. Treatment of hearts with the H2S-donor, NaHS, commencing 10 min prior to the onset of coronary occlusion and maintained until 10 min reperfusion, resulted in a concentration-dependent limitation of infarct size (control, 41.0 +/- 2.6% of risk zone; NaHS 0.1 microM, 33.9 +/- 2.1%, [0.05 > P < 0.1]; NaHS 1 microM, 20.2 +/- 2.1% [P < 0.01]). Pretreatment with the K ATP channel blockers glibenclamide 10 microM or sodium 5-hydroxydecanoate (5HD) 100 microM led to abrogation of the infarct-limiting effect of NaHS 1 microM (glibenclamide + NaHS 42.5 +/- 3.6%; 5HD + NaHS 44.7 +/- 2.2%). No statistically significant effects of NaHS treatment on coronary flow, heart rate or left ventricular developed pressure were observed in this experimental preparation. These data provide the first evidence that exogenous H2S protects against irreversible ischemia-reperfusion injury in myocardium and support the involvement of K ATP opening in the mechanism of action. Further work is required to elucidate the potential role of endogenous H2S as a cytoprotective mediator against myocardial ischemia-reperfusion injury, the mechanisms regulating its generation, and the nature of its interaction with protein targets such as the K ATP channel.

Adenosine Triphosphate↗
PubMed2005

Adrenomedullin: regulator of systemic and cardiac homeostasis in acute myocardial infarction.

During and following acute myocardial infarction, a variety of endogenous mediators are elevated, one of which is adrenomedullin (AM). AM is a multifunctional peptide that has been identified as having a putative beneficial role following an ischemic insult at both systemic and local levels. Classically described as a potent vasodilator, natriuretic, and diuretic agent, experimental infarct models also demonstrate AM to exhibit antiproliferative and antiapoptotic functions in the myocardium, counterregulating the effects of mediators such as angiotensin-II and endothelin-1. Less well documented are the angiogenic and inflammatory modulating potentials of AM, which may also contribute toward reducing adverse ventricular remodeling. The review examines clinical and experimental studies, looking at the effects of AM and cellular mechanisms that could be involved in mediating cardioprotective effects and ultimately optimizing left ventricular remodeling. Finally, the possibility of enhancing endogenous actions of AM by pharmacological intervention is considered.

Adrenomedullin↗
PubMed2004

Effect of radiofrequency catheter ablation on the biochemical marker ischemia modified albumin.

Ischemia-modified albumin (IMA) levels were measured after radiofrequency (RF) catheter ablation to evaluate the effect of direct myocardial necrosis on IMA formation. IMA levels have been shown to increase in patients after RF catheter ablation compared with those who undergo diagnostic electrophysiologic studies. The results of this study suggest that IMA may be a marker of myocardial injury.

Adult↗
PubMed2004

The natriuretic peptides.

The natriuretic peptides are a family of widely distributed, but evolutionarily conserved, polypeptide mediators that exert a range of actions throughout the body. In cardiovascular homeostasis, the endocrine roles of the cardiac-derived atrial and B-type natriuretic peptide (ANP and BNP) in regulating central fluid volume and blood pressure have been recognised for two decades. However, there is a growing realisation that natriuretic peptide actions go far beyond their volume regulating effects. These pleiotropic actions include local (autocrine/paracrine) regulatory actions of ANP and BNP within the heart, and of another natriuretic peptide, CNP, within the vessel wall. Effects on function and growth of the local tissue environment are likely to be of great importance, especially in disease states where tissue and circulating levels of ANP and BNP rise markedly. At present, the relevance of other natriuretic peptides (notably uroguanylin and DNP) to human physiology and pathology remain uncertain. Other articles in this issue of Basic Research in Cardiology review the molecular physiology of natriuretic peptide signalling, with a particular emphasis on the lessons from genetically targetted mice; the vascular activity of natriuretic peptides; the regulation and roles of natriuretic peptides in ischaemic myocardium; and the diagnostic, prognostic and therapeutic roles of natriuretic peptides in heart failure.

Animals↗
PubMed2004

Natriuretic peptides and myocardial ischaemia.

In both experimental and clinical myocardial ischaemia, release of BNP occurs rapidly from ventricular myocardium, prompting speculation that the early activation of the natriuretic peptide receptor/cGMP signalling system may be an important autocrine/paracrine response to ischaemia. Among the growing list of pleiotropic actions of natriuretic peptides is the attenuation of tissue susceptibility to ischaemic injury. BNP and other natriuretic peptides limit the extent of tissue infarction during ischaemia and reperfusion. The mechanism of cytoprotection is related to cGMP accumulation and opening of ATP-sensitive K(+) channels. The effects of longer-term upregulation of natriuretic peptide expression in the heart following myocardial infarction could include the suppression of growth and proliferative responses in myocytes and fibroblasts. Thus, chronic elevation of natriuretic peptide expression in infarcted myocardium probably represents a negative regulatory system to counter the pro-hypertrophic and pro-fibrotic signalling activated by other mediators such as angiotensin II and catecholamines. The acute and chronic actions of natriuretic peptides in myocardial ischaemia suggest a profile of activity that may be therapeutically beneficial in the management of patients with acute coronary syndromes and for the optimisation of post-infarction remodelling.

Animals↗
PubMed2004

Autocrine and paracrine actions of natriuretic peptides in the heart.

The natriuretic peptides, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), are a family of polypeptide mediators exerting numerous actions in cardiovascular homeostasis. ANP and BNP are cardiac derived, being secreted and up-regulated in myocardium in response to many pathophysiological stimuli. CNP is an endothelium-derived mediator. The classical endocrine effects of ANP and BNP on fluid homeostasis and blood pressure, especially in conditions characterised by left ventricular dysfunction, are well recognised and extensively researched. However, there is accumulating evidence that, in addition to endocrine actions, ANP and BNP exhibit important autocrine and paracrine functions within the heart and coronary circulation. These include regulation of myocyte growth, inhibition of fibroblast proliferation and extracellular matrix deposition, a cytoprotective anti-ischaemic (preconditioning-like) function, and influences on coronary endothelium and vascular smooth muscle proliferation and contractility. Most if not all of these actions can be ascribed to particulate guanylyl cyclase activation because the ANP/BNP receptor, natriuretic peptide receptor (NPR)-A, has an intracellular guanylyl cyclase domain. Subsequent elevation of the intracellular second messenger cGMP may exert diverse physiological effects through activation of cGMP-dependent protein kinases (cGK), predominantly cGK-I. However, there appear to be other contributory mechanisms in several of these actions, including the augmentation of nitric oxide synthesis. These diverse actions may represent counterregulatory mechanisms in the pathophysiology of many cardiovascular diseases, not just those typified by left ventricular dysfunction. Ultimately, insights from the autocrine/paracrine actions of natriuretic peptides may provide routes to therapeutic application in cardiac diseases of natriuretic peptides and drugs that modify their availability.

Animals↗
PubMed2004

Acute actions of natriuretic peptides in coronary vasculature and ischaemic myocardium.

The natriuretic peptides are a family of widely distributed polypeptide mediators that exert a range of actions in several body systems. In cardiovascular homeostasis, the endocrine roles of the cardiac-derived atrial and B-type natriuretic peptide (ANP and BNP) in regulating central fluid volume and blood pressure have been recognised for two decades. However, there is a growing realisation that natriuretic peptide actions go far beyond their endocrine effects and that local (autocrine/paracrine) regulatory actions within the heart and coronary vasculature may be of comparable importance, especially in disease states where tissue and circulating levels of the peptides rise markedly. In acute myocardial ischaemia, release of BNP occurs rapidly from ventricular myocardium, prompting speculation that the early activation of the natriuretic peptide receptor/cGMP signalling system may be an important autocrine/paracrine response in cardiac ischaemia. The autocrine/paracrine actions include inotropic effects, the acute regulation of coronary vascular tone and the attenuation of the susceptibility of myocardium to ischaemic injury. The effects of longer-term upregulation of natriuretic peptide expression in the heart could include the suppression of growth and proliferative responses in a variety of myocardial and vascular cells. In a variety of preparations, acute exposure of epicardial coronary arteries to pharmacological concentrations of natriuretic peptides evokes vasorelaxation, although in coronary microvessels, evidence for a vasorelaxant action of the peptides is less consistent. The mechanisms of the coronary vasorelaxant action are unclear but limited evidence suggests an endothelium-dependent component. In ischaemic myocardium, acute treatment with BNP prior to and during coronary artery occlusion exerts a markedly protective, concentration-dependent infarct-limiting action. This cytoprotective effect of the natriuretic peptide signalling pathway might conceivably represent an alternative endogenous salvage pathway in myocardium which is potentially exploitable therapeutically. Taken together, the acute actions of natriuretic peptides on the coronary vasculature and in myocardial ischaemia suggest a profile of activity that may be therapeutically beneficial in the management of patients with acute coronary syndromes.

Animals↗
PubMed2003

B-type natriuretic peptide limits infarct size in rat isolated hearts via KATP channel opening.

B-type natriuretic peptide (BNP) has been reported to be released from the myocardium during ischemia. We hypothesized that BNP mediates cardioprotection during ischemia-reperfusion and examined whether exogenous BNP limits myocardial infarction and the potential role of ATP-sensitive potassium (K(ATP)) channel opening. Langendorff-perfused rat hearts underwent 35 min of left coronary artery occlusion and 120 min of reperfusion. The control infarct-to-risk ratio was 44.8 +/- 4.4% (means +/- SE). BNP perfused 10 min before ischemia limited infarct size in a concentration-dependent manner, with maximal protection observed at 10(-8) M (infarct-to-risk ratio: 20.1 +/- 5.2%, P < 0.01 vs. control), associated with a 2.5-fold elevation of myocardial cGMP above the control value. To examine the role of K(ATP) channel opening, glibenclamide (10(-6) M), 5-hydroxydecanoate (5-HD; 10(-4) M), or HMR-1098 (10(-5) M) was coperfused with BNP (10(-8) M). Protection afforded by BNP was abolished by glibenclamide or 5-HD but not by HMR-1098, suggesting the involvement of putative mitochondrial but not sarcolemmal K(ATP) channel opening. We conclude that natriuretic peptide/cGMP/K(ATP) channel signaling may constitute an important injury-limiting mechanism in myocardium.

Animals↗
PubMed2003

Second window of protection following myocardial preconditioning: an essential role for PI3 kinase and p70S6 kinase.

Ischaemic preconditioning (IPC) protects the heart against myocardial infarction acutely as well as several hours later (e.g. 24-48 h). The mechanism of the profound cardioprotection is not completely explored. We hypothesized that PI3K/PDK1/Akt/mTOR/p70S6K-mediated pro-survival pathway is involved in delayed cardioprotection induced by IPC. Under Hypnorm-Diazepam anaesthesia, male New Zealand White rabbits were either sham-operated (SC) or preconditioned by four cycles of 5-min ischaemia and 10-min reperfusion on day 1. Twenty-four hours after recovery, the animals were anaesthetized with sodium pentobarbitone and subjected to 30-min ischaemia followed by 180-min reperfusion. Wortmannin (0.6 mg/kg, i.v.), an irreversible PI3 kinase (PI3K) inhibitor, rapamycin (0.25 mg/kg, i.v.), which prevents the phosphorylation of p70S6 kinase (p70S6K), or DMSO (control vehicle) was given 15 min prior to IPC. IPC significantly reduced infarct size compared to the control group (SC) (31.9 +/- 5.8% (n = 7) vs. 54.9 +/- 2.9% (n = 6), P < 0.05). Wortmannin and rapamycin alone had no effect on infarct size (56.3 +/- 1.6% (n = 6) and 54.7 +/- 3.8% (n = 6), respectively). However, when wortmannin or rapamycin were given prior to IPC the protection was completely abolished (49.9 +/- 2.8% (n = 6), 45.1 +/- 4.6% (n = 7), P < 0.05 vs. IPC). Western blot analysis showed that wortmannin, at a dose of 0.6 mg/kg, and rapamycin, at a dose of 0.25 mg/kg, were sufficient to prevent phosphorylation of Akt and p70S6K, respectively, when the inhibitors were given prior to IPC. We conclude that PI3K/PDK1/Akt/mTOR/p70S6K-signalling pathway plays an essential role in the development of the cardioprotection against infarction in rabbits.

Androstadienes↗
PubMed2003

Role of nuclear factor-kappa B activation in acute ischaemia-reperfusion injury in myocardium.

(1) Our aims were to characterize activation of the transcription factor, nuclear factor kappa-B(NF-kappaB), during myocardial ischaemia-reperfusion and to assess its functional role in the evolution of acute ischaemia-reperfusion injury in intact myocardium in vivo. (2) Under pentobarbitone anaesthesia, rabbits underwent sham operation, 30 min left coronary artery occlusion followed by 0, 10 or 180 min reperfusion. Saline or NF-kappaB inhibitor diethyldithiocarbamic acid (DDTC, 50, 100 or 200 mg kg(-1)) was given intravenously 5 min prior to reperfusion. (3) Electromobility shift assay revealed that 30 min ischaemia alone did not activate NF-kappaB compared to time-matched sham-operated controls (85+/-13% vs 100+/-28%, respectively). However, ischaemia plus 10 min reperfusion markedly increased activation of NF-kappaB (295+/-77%). DDTC 50 mg kg(-1) did not inhibit NF-kappaB activation (278+/-67%) but at the higher doses complete inhibition was observed (54+/-20%, 31+/-16%, respectively). (4) Infarct to risk ratio was determined by triphenyltetrazolium chloride staining after 30 min ischaemia and 180 min reperfusion. DDTC 50 or 100 mg kg(-1) significantly reduced infarct size compared to the saline-treated control group (34.9+/-5.2%, 37.1+/-5.9%, vs 51.3+/-3.6%, P<0.05, respectively), whereas there was no protection with 200 mg kg(-1) (45.6+/-5.3%). (5) We conclude that ischaemia alone does not activate NF-kappaB, but post-ischaemic reperfusion robustly activates NF-kappaB in the myocardium. DDTC limited irreversible injury at low doses, but this effect appears to be dissociated from inhibition of NF-kappaB. Thus, activation of NF-kappaB during reperfusion does not appear to play a role in the evolution of myocardial infarction during the early phase of reperfusion.

Animals↗
PubMed2002

Inhibiting mitochondrial permeability transition pore opening: a new paradigm for myocardial preconditioning?

OBJECTIVE: We propose that ischemic preconditioning (IPC) and mitochondrial K(ATP) channel activation protect the myocardium by inhibiting mitochondrial permeability transition pore (MPTP) opening at reperfusion. METHODS: Isolated rat hearts were subjected to 35 min ischemia/120 min reperfusion and assigned to the following groups: (1) control; (2) IPC of 2x5 min each of preceding global ischemia; (3,4,5) 0.2 micromol/l cyclosporin A (CsA, which inhibits MPTP opening), 5 micromol/l FK506 (which inhibits the phosphatase calcineurin without inhibiting MPTP opening), or 20 micromol/l atractyloside (Atr, a MPTP opener) given at reperfusion; (6,7) pre-treatment with 30 micromol/l diazoxide (Diaz, a mitochondrial K(ATP) channel opener) or 200 nmol/l 2 chloro-N(6)-cyclopentyl-adenosine (CCPA, an adenosine A1 receptor agonist); (8) IPC+Atr; (9) Diaz+Atr; (10) CCPA+Atr. The effect of mitochondrial K(ATP) channel activation on calcium-induced MPTP opening in isolated calcein-loaded mitochondria was also assessed. RESULTS: IPC, CsA when given at reperfusion, and pre-treatment with diazoxide or CCPA all limited infarct size (19.9+/-2.6% in IPC; 24.6+/-1.9% in CsA, 18.0+/-1.7% in Diaz, 20.4+/-3.3% in CCPA vs. 44.7+/-2.0% in control, P<0.0001). Opening the MPTP with atractyloside at reperfusion abolished this cardio-protective effect (47.7+/-1.8% in IPC+Atr, 42.3+/-3.2% in Diaz+Atr, 51.2+/-1.6% in CCPA+Atr). Atractyloside and FK506, given at reperfusion, did not influence infarct size (45.7+/-2.1% in Atr and 43.1+/-3.6% in FK506 vs. 44.7+/-2.0% in control, P=NS). Diazoxide (30 micromol/l) was shown to reduce calcium-induced MPTP opening by 52.5+/-8.0% in calcein-loaded mitochondria. 5-Hydroxydecanoic acid (100 micromol/l) was able to abolish the cardio-protective effects of both diazoxide and IPC. CONCLUSION: One interpretation of these data is that IPC and mitochondrial K(ATP) channel activation may protect the myocardium by inhibiting MPTP opening at reperfusion.

Adenosine↗
PubMed2002

The neutrophil as a mediator of myocardial ischemia-reperfusion injury: time to move on.

Granulocytes, especially neutrophils, are recruited in myocardium during the evolution of acute myocardial infarction. Because the neutrophil reaction is most intense during reperfusion and because these cells are a rich source of toxic oxidant species and proteolytic enzymes, it has become a widely held view that neutrophils are an important mechanism of myocardial injury extension during reperfusion. However, on close examination the evidence underlying this contention is equivocal. The basic experimental situation can be summarised thus. (1) All forms of reperfusion injury (i.e., cytotoxic or lethal cell injury, myocardial stunning, endothelial dysfunction, and reperfusion-induced arrhythmias) can be observed in neutrophil-free conditions. (2) "Anti-neutrophil" interventions (e.g., anti-inflammatory drugs, adenosine, anti-neutrophil antisera, leukocyte filters and inhibitors of the various pathways of neutrophil adhesion) do not consistently prevent reperfusion injury and they certainly do not consistently limit infarct size. (3) The time course of neutrophil accumulation in post-ischaemic myocardium may be different to the time course of injury. (4) Despite more than two decades of research, no double-blind, randomised controlled clinical trial assessing an anti-neutrophil therapy in myocardial infarction has yet reported a positive benefit that is attributable to inhibition of neutrophil recruitment. The evidence weighs against a pivotal role of neutrophils as a causal factor in most forms of ischemia-reperfusion injury. An exception may be microvascular injury and capillary plugging leading to the "no-reflow" phenomenon but even here the evidence suggests that the extent of neutrophil accumulation and microvascular injury is determined by, rather than a cause of, myocyte necrosis.

Humans↗
PubMed2002

Nitrate tolerance does not increase production of peroxynitrite in the heart.

Clinical studies have suggested that long-term nitrate treatment does not improve and may even worsen cardiovascular mortality, and the possible role of nitrate tolerance has been suspected. Nitrate tolerance has been recently shown to increase vascular superoxide and peroxynitrite production leading to vascular dysfunction. Nevertheless, nitrates exert direct cardiac effects independent from their vascular actions. Therefore, we investigated whether in vivo nitroglycerin treatment leading to vascular nitrate tolerance increases cardiac formation of nitric oxide (NO), reactive oxygen species, and peroxynitrite, thereby leading to cardiac dysfunction. Nitrate tolerance increased bioavailability of NO in the heart without increasing formation of reactive oxygen species. Despite elevated myocardial NO, neither cardiac markers of peroxynitrite formation nor cardiac mechanical function were affected by nitroglycerin treatment. However, serum free nitrotyrosine, a marker for systemic peroxynitrite formation, was significantly elevated in nitroglycerin-treated animals. This is the first demonstration that, although the systemic effects of nitroglycerin may be deleterious due to enhancement of extracardiac peroxynitrite formation, nitroglycerin does not result in oxidative damage in the heart.

Animals↗
PubMedDate not supplied

Limitation of myocardial reperfusion injury by AMP579, an adenosine A1/A2A receptor agonist: role of A2A receptor and Erk1/2.

AMP579, an adenosine A(1)/A(2A) receptor agonist, protects against myocardial infarction when given at the onset of reperfusion. However, it is unclear which receptor subtype mediates its protective actions. Anaesthetised rabbits were subjected to 30 min regional ischaemia/180 min reperfusion in vivo. AMP579 (30 microg kg(-1) bolus + 3 microg kg(-1) min(-1) for 70 min) reduced heart rate and mean arterial blood pressure with the latter being abolished with ZM241385 (a selective A(2A) receptor antagonist). AMP579 reduced infarct size from 46.0 +/- 3.4% in vehicle control hearts to 29.6 +/- 3.5% (P < 0.05), an effect that was attenuated in the presence of ZM241385, in a dose-dependent manner (38.2 +/- 4.9% at 1 mg kg(-1); 45.1 +/- 4.2% at 2.5 mg kg(-1)). CGS21680 (a selective A(2A) agonist, 30 microg kg(-1) bolus + 3 microg kg(-1) min(-1) for 70 min), or CCPA (a selective A(1) agonist, 50 microg kg(-1)), alone or in combination showed no protection (44.7 +/- 5.8%; 39.8 +/- 2.8%; 39.1 +/- 5.1%, respectively) when given at the commencement of reperfusion. Furthermore, we hypothesized that the prosurvival MEK1/2-Erk1/2 pathway was involved in the downstream mechanism of cardioprotection afforded by AMP579. PD098059, an inhibitor of MEK1/2 showed a dose dependent attenuation on infarct size (39.9 +/- 5.3% at 2 mg kg(-1); 48.3 +/- 5.7% at 4 mg kg(-1), i.v., respectively). PD098059 alone had no effect on infarct size (44.7 +/- 5.8%, 2 mg kg(-1), i.v.). We conclude that AMP579 limits myocardial infarction by activating A(2A) adenosine receptors that might be linked to further downstream kinases such as Erk1/2.

Adenosine A1 Receptor Agonists↗