PubMed Health⌕ Search

Biomedical subjects

D M Yellon

Publications and source records attributed to D M Yellon.

At least 19 recordsLinked to original sources
PubMed2006

Leptin, the obesity-associated hormone, exhibits direct cardioprotective effects.

BACKGROUND AND PURPOSE: Protection against ischaemia-reperfusion (I/R) injury involves PI3K-Akt and p44/42 MAPK activation. Leptin which regulates appetite and energy balance also promotes myocyte proliferation via PI3K-Akt and p44/42 MAPK activation. We, therefore, hypothesized that leptin may also exhibit cardioprotective activity. EXPERIMENTAL APPROACH: The influence of leptin on I/R injury was examined in perfused hearts from C57Bl/6 J mice that underwent 35 min global ischaemia and 35 min reperfusion, infarct size being assessed by triphenyltetrazolium chloride staining. The concomitant activation of cell-signalling pathways was investigated by Western blotting. The effect of leptin on mitochondrial permeability transition pore (MPTP) opening was studied in rat cardiomyocytes. KEY RESULTS: Leptin (10 nM) administered during reperfusion reduced infarct size significantly. Protection was blocked by either LY294002 or UO126, inhibitors of Akt and p44/42 MAPK, respectively. Western blotting confirmed that leptin stimulated p44/42 MAPK phosphorylation significantly. Akt phosphorylation was also enhanced but did not achieve statistical significance. Additionally, leptin treatment was associated with a significant increase in p38 phosphorylation. By contrast, leptin caused downregulation of phosphorylated and non-phosphorylated STAT3, and of total AMP-activated kinase. Cardiomyocytes responded to leptin with delayed opening of the MPTP and delayed time until contracture. CONCLUSIONS AND IMPLICATIONS: Our data indicate for the first time that the adipocytokine, leptin, has direct cardioprotective properties which may involve the PI3-Akt and p44/42 MAPK pathways.

Animals↗
PubMed2005

Representational difference analysis of cDNA identifies novel genes expressed following preconditioning of the heart.

Preconditioning of the myocardium rapidly induces a number of transcription factors, which are likely to be responsible for a cascade of transcriptional changes underlying the development of delayed adaptation. Identifying these changes provides insight into the molecular pathways elicited by sub-lethal ischaemia and the mechanism leading to delayed adaptation. Genes up-regulated in rabbit myocardium in vivo by ischaemic preconditioning following reperfusion for 2 h, 4 h and 6 h post-treatment were identified by representational difference analysis of cDNA (cDNA. RDA). The area of the left ventricle rendered ischaemic by preconditioning or the equivalent area of sham-treated animals was isolated and cDNA.RDA performed. Three novel genes and six genes with known function where identified, including the TGFbeta receptor interacting protein 1, the alpha isoform of the A subunit of PP2 and the cap binding protein NCBP1. To determine whether expression of these genes correlated with preconditioning per se, expression was measured in myocardium after both ischaemic as well as heat shock induced preconditioning following 2 h, 4 h, and 6 h reperfusion. These genes were induced in rabbit myocardium in vivo by both ischaemia and heat shock, consistent with a fundamental role in the development of delayed adaptation. The well described role of PP2 in modulating the mitogen-activated protein kinase pathway and promoting cell survival is consistent with our previous work, which identified the reperfusion injury salvage kinase pathway in mediating the protective effects of ischaemic preconditioning. Expression of Trip1 and Ncbp1 also implicates TGFbeta signalling pathways and RNA processing and transport in delayed adaptation to stress in the myocardium.

Animals↗
PubMed2005

Erythropoietin protects the myocardium against reperfusion injury in vitro and in vivo.

OBJECTIVE: Erythropoietin (EPO) is a hormone that is currently used to treat patients with renal failure and anaemia. However, it has also been shown to protect against ischaemia/reperfusion injury; this protection occurring via activation of the ERK 1/2 and PI3K pathways. Since we have previously shown activation of ERK 1/2 and PI3K to be important for protection against reperfusion-induced injury in the myocardium, this study was designed to investigate its effect in the myocardium using both an isolated perfused rat heart and an in vivo rat recovery model of ischaemia-reperfusion. METHODS: Using an in vitro isolated rat heart model of 35 minutes ischaemia and 2 hours reperfusion, EPO (50 ng/ml) was administered to the rat myocardium 5 minutes prior to reperfusion for 20 minutes. The in vivo open-chest rat model consisted of 40 minutes ischaemia followed by 24 hours reperfusion with EPO (5000 U/kg) being administered at the point of reperfusion. RESULTS: In the isolated perfused heart studies 50 ng/ml EPO was found to provide protection with a % I/R of 22.9% +/- 6.4 vs 54.5% +/- 7.4 for the ischaemic control group. To examine the mechanistic pathways involved in EPO-mediated protection, we co-administered the ERK 1/2 inhibitor, U0126 (10 uM) or the PI3K inhibitors, wortmannin, (100 nM) and LY294002 (15 microM) at reperfusion. U0126, wortmannin and LY294002 all abrogated EPO-mediated protection (% I/R 49.2% +/- 5.6, 46.1% +/- 5.5 and 49.9% +/- 6.1 respectively, p < 0.05). In the in vivo open-chest rat model, the % I/R was significantly attenuated in EPO-treated animals from 53.6 % +/- 3.7 in the control to 32.5% +/- 2.9 (p < 0.05). Likewise, wortmannin abrogated EPO-mediated protection (% I/R 50.7 +/- 2.3 v EPO 32.5% +/- 2.9, p < 0.05). CONCLUSION: We demonstrate that EPO, administered at the point of reperfusion, reduced infarct size in an isolated perfused rat heart, in an ERK and PI3K dependent manner; in addition the mechanism was also confirmed in a whole animal model of ischaemia-reperfusion. These results suggest that EPO may be able to directly protect the myocardium against lethal reperfusion-induced injury and so offer the myocardium an additional clinical advantage over and above its ability to improve the oxygen carrying capacity of the blood.

Animals↗
PubMed2004

Omapatrilat limits infarct size and lowers the threshold for induction of myocardial preconditioning through a bradykinin receptor-mediated mechanism.

Bradykinin is an important endogenous trigger of myocardial ischemic preconditioning (IPC). Through simultaneous inhibition of neutral endopeptidase and angiotensin converting enzyme, omapatrilat prevents enzymatic degradation of bradykinin. The aim of this study was to investigate if omapatrilat, through its ability to augment bradykinin levels, can augment a subthreshold IPC stimulus (Sub-IPC) and to compare the action of omapatrilat with the angiotensin-converting enzyme inhibitor, captopril. Langendorff perfused rat hearts were subjected to 35 min left coronary artery occlusion and 120 min reperfusion. Full IPC was induced with 5 min global ischemia/10 min reperfusion and substantially limited infarct size (21.5 +/- 3.5% of risk zone vs 53.4 +/- 2.0% in controls, P < 0.01). Sub-IPC (2 min global ischemia/10 min reperfusion) did not limit infarct size (48.4 +/- 3.8%). Omapatrilat (10 micromol/L) or captopril (200 micromol/L) were administered alone or in conjunction with Sub-IPC. Reduced infarct size comparable to that observed with the full IPC protocol was seen when sub-IPC was combined with either omapatrilat (19.7 +/- 2.5%) or captopril (20.3 +/- 4.9%). Omapatrilat alone caused modest reduction of infarct size (34.6 +/- 1.5%, P < 0.01 v control), an effect not observed with captopril. Hoe140, a selective kinin B(2) receptor antagonist, eliminated the cardioprotective effect of omaptrilat alone or in combination with sub-IPC. We conclude that omapatrilat elicits cardioprotection via inhibition of bradykinin degradation and that dual inhibition of angiotensin-converting enzyme and neutral endopeptidase may have beneficial effects beyond standard angiotensin-converting enzyme inhibitor therapy in patients with acute coronary syndromes who are at risk of myocardial infarction.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2002

The effect of preconditioning (ischemic and pharmacological) on myocardial necrosis following coronary artery bypass graft surgery.

OBJECTIVES: Ischemic preconditioning is known to protect the human heart from ischemic injury during coronary artery bypass graft (CABG) surgery but is not practised routinely. Adenosine A1 receptor agonists may confer protection in this setting by mimicking preconditioning. The aim of this study was to compare preconditioning, by ischemia or an adenosine A1 receptor agonist (GR79236X), with an established method of myocardial protection in CABG, namely intermittent cross-clamp fibrillation. METHODS: In this prospective double-blind study, 30 CABG patients were randomised to receive: (a) intermittent cross-clamp fibrillation (control), (b) pharmacological preconditioning (GR79236X), or (c) ischemic preconditioning (two 3-min periods of ischemia, each followed by 2 min of reperfusion). Surgery was performed under standardised conditions by one surgeon (WBP). The primary endpoint was cardiac troponin T release. RESULTS: Mean cardiopulmonary bypass time was 91+/-11.6 (S.D.) min. Mean ischemic time was 33+/-5.5 (S.D.) min with no inter-group difference. Mean troponin T at 72 h was highest in the control group (1.32+/-0.99 (S.D.) microg/l), similar in the GR79236X group (1.22+/-1.22 (S.D.) microg/l; P=0.85) and significantly reduced in the ischemic preconditioning group (0.58+/-0.40 (S.D.) microg/l; P=0.04). CONCLUSIONS: Ischemic preconditioning is superior to the other techniques at limiting myocardial necrosis during CABG. Pharmacological preconditioning may confer some benefit but this was not statistically shown using a specific adenosine A1 agonist (GR79236X).

Adenosine↗
PubMed2002

A comparison between ischemic preconditioning, intermittent cross-clamp fibrillation and cold crystalloid cardioplegia for myocardial protection during coronary artery bypass graft surgery.

The aim of this study was to compare ischemic preconditioning (IPC) with two established methods of myocardial protection, namely cold crystalloid cardioplegia and intermittent cross-clamp fibrillation (ICCF), in coronary artery bypass graft (CABG) surgery. This was a prospective randomised study. Thirty CABG patients were randomised to receive: (a) St Thomas' cardioplegia solution no. 2; (b) ICCF; or (c) IPC (two 3-min periods of ischemia with 2-min of reperfusion). Surgery was performed under standardised conditions by one surgeon (WBP). The primary endpoint was cardiac troponin T release during the first 72 h after surgery. Mean troponin T at 72 h was significantly lower in the IPC group (0.5 microg/l; p=0.05, ANOVA) compared with the cardioplegia and ICCF groups (2.1 and 1.3 microg/l respectively). This suggests that ischemic preconditioning is superior at limiting myocardial necrosis during CABG, but there is no difference between cold crystalloid cardioplegia and intermittent cross-clamp fibrillation.

Aorta, Thoracic↗
PubMed2001

Myocardial protection by insulin at reperfusion requires early administration and is mediated via Akt and p70s6 kinase cell-survival signaling.

The "metabolic cocktail" comprising glucose-insulin-potassium administrated at reperfusion reduces infarct size in the in vivo rat heart. We propose that insulin is the major component mediating this protection and acts via Akt prosurvival signaling. This hypothesis was studied in isolated perfused rat hearts (measuring infarct size to area of risk [%]) subjected to 35 minutes regional myocardial ischemia and 2 hours reperfusion. Insulin administered at the onset of reperfusion attenuated infarct size by >/=45% versus control hearts (P<0.001). Insulin-mediated cardioprotection was found to be independent of the presence of glucose at reperfusion. Moreover, the cell survival benefit of insulin is temporally dependent, in that insulin administration from the onset of reperfusion and maintained for either 15 minutes or for the duration of reperfusion reduced infarct size. In contrast, protection was abrogated if insulin administration was delayed until 15 minutes into reperfusion. Pharmacological inhibition of both upstream and downstream signals in the Akt prosurvival pathway abolished the cardioprotective effects of insulin. Here coadministration of insulin with the tyrosine kinase inhibitor lavendustin A, the phosphatidylinositol3-kinase (PI3-kinase) inhibitor wortmannin, and mTOR/p70s6 kinase inhibitor rapamycin abolished cardioprotection. Steady-state levels of activated/phosphorylated Akt correlated with insulin administration. Finally, downstream prosurvival targets of Akt including p70s6 kinase and BAD were modulated by insulin. In conclusion, insulin administration at reperfusion reduces myocardial infarction, is dependent on early administration during reperfusion, and is mediated via Akt and p70s6 kinase dependent signaling pathway. Moreover, BAD is maintained in its inert phosphorylated state in response to insulin therapy.

Animals↗
PubMed2001

Ischemic and pharmacological preconditioning in Girardi cells and C2C12 myotubes induce mitochondrial uncoupling.

Pharmacological uncoupling of mitochondrial oxidation from phosphorylation promotes preconditioning-like cardioprotection in the isolated rat heart. We hypothesized that modest mitochondrial uncoupling may be a critical cellular event in orchestrating preconditioning. Human-derived Girardi cells and murine C2C12 skeletal myotubes were preconditioned using simulated ischemia, adenosine, and diazoxide. Cell viability after 6 hours of simulated ischemia was measured using lactate dehydrogenase release and propidium iodide uptake. Mitochondrial inner membrane potential (DeltaPsim) was investigated by flow cytometry, cellular ATP by recombinant firefly-luciferase bioluminescence, and cellular oxygen consumption using oximetry. Preconditioning enhanced cell viability with attenuation of lactate dehydrogenase release (>/=30%, P<0.05 versus ischemic controls) and a reduction in propidium iodide uptake by >/=26% versus ischemic controls after simulated ischemia in both cell lines. In Girardi cells, preconditioning induced the following phenotype immediately before index ischemia: (1) decreased DeltaPsim (JC-1: simulated ischemia 90+/-3%, adenosine 82+/-7%, diazoxide 87+/-4%, versus control 100%, P<0.05); (2) attenuation in cellular ATP levels (CTL 0.21+/-0.03 nmol/L ATP/microg protein, simulated ischemia 0.12+/-0.02, adenosine 0.15+/-0.02, diazoxide 0.11+/-0.02, P<0.05); and (3) enhanced cellular oxygen consumption (control 2.3+/-0.1 nmol/L oxygen/min/1x10(6) cells, simulated ischemia 3.1+/-0.1, adenosine 3.1+/-0.3, diazoxide 2.6+/-0.2, P<0.05). Cytoprotection, mitochondrial depolarization, and enhanced oxygen consumption were attenuated by the putative mitochondrial K(ATP)-channel antagonist 5-hydroxydecanoate. The uncoupled phenotype in response to preconditioning was similarly observed in C2C12 myotubes. The present study suggests that modest mitochondrial uncoupling represents a unifying cellular response which may be important in directing preconditioning-mediated cytoprotection.

Adenosine↗
PubMed2001

Cardiotrophin-1 can protect cardiac myocytes from injury when added both prior to simulated ischaemia and at reoxygenation.

OBJECTIVE: The cytokine cardiotrophin-1 (CT-1) has previously been shown to protect cultured cardiocytes from cell death induced by serum removal or hypoxia when administered prior to the damaging stimulus. We wished to test whether a similar protective effect could be observed if CT-1 was added after the ischaemic period and to investigate the signalling pathways involved in the protective effect when CT-1 is given prior to or after ischaemia. METHODS: We therefore examined the protective effect of CT-1 in cultured rat cardiocytes exposed to simulated ischaemia followed by reoxygenation when CT-1 was administered either prior to simulated ischaemia or at reoxygenation. RESULTS: We show that CT-1 can exert a protective effect against the damaging effects of simulated ischaemia/reoxygenation both when added after the simulated ischaemia at reoxygenation (P<0.05 in trypan blue, TUNEL and annexin V assays) or when added prior to the simulated ischaemia (P<0.05). In both cases, these protective effects are blocked by an inhibitor of the p42/p44 MAPK pathway (P<0.05 in all assays). CONCLUSION: CT-1 can protect cardiac cells when added either prior to simulated ischaemia or at the time of reoxygenation following simulated ischaemia and these effects are dependent upon its ability to activate the p42/p44 MAPK pathway. Hence CT-1 may have therapeutic potential when added at the time of reperfusion following ischaemic damage.

Animals↗
PubMed2001

Glimepiride, a novel sulfonylurea, does not abolish myocardial protection afforded by either ischemic preconditioning or diazoxide.

BACKGROUND: The sulfonylurea glibenclamide (Glib) abolishes the cardioprotective effect of ischemic preconditioning (IP), presumably by inhibiting mitochondrial K(ATP) channel opening in myocytes. Glimepiride (Glim) is a new sulfonylurea reported to affect nonpancreatic K(ATP) channels less than does Glib. We examined the effects of Glim on IP and on the protection afforded by diazoxide (Diaz), an opener of mitochondrial K(ATP) channels. METHODS AND RESULTS: Rat hearts were Langendorff-perfused, subjected to 35 minutes of regional ischemia and 120 minutes of reperfusion, and assigned to 1 of the following treatment groups: (1) control; (2) IP of 2x 5 minutes each of global ischemia before lethal ischemia; or pretreatment with (3) 30 micromol/L Diaz, (4) 10 micromol/L Glim, (5) 10 micromol/L Glib, (6) IP+Glim, (7) IP+Glib, (8) Diaz+Glim, or (9) Diaz+Glib. IP limited infarct size (18.5+/-1% vs 43.7+/-3% in control, P<0.01) as did Diaz (22.2+/-4.7%, P<0.01). The protective actions of IP or Diaz were not abolished by Glim (18.5+/-3% in IP+Glim, 22.3+/-3% in Diaz+Glim; P<0.01 vs control). However, Glib abolished the infarct-limiting effects of IP and Diaz. Patch-clamp studies in isolated rat ventricular myocytes confirmed that both Glim and Glib (each at 1 micromol/L) blocked sarcolemmal K(ATP) currents. However, in isolated cardiac mitochondria, Glim (10 micromol/L) failed to block the effects of K(ATP) opening by GTP, in contrast to the blockade caused by Glib. CONCLUSIONS: Although it blocks sarcolemmal currents in rat cardiac myocytes, Glim does not block the beneficial effects of mitochondrial K(ATP) channel opening in the isolated rat heart. These data may have significant implications for the treatment of type 2 diabetes in patients with ongoing ischemic heart disease.

Animals↗
PubMed2001

Angiotensin-converting enzyme inhibition enhances a subthreshold stimulus to elicit delayed preconditioning in pig myocardium.

OBJECTIVES: We assessed the effect of angiotensin-converting enzyme (ACE) inhibition in combination with a subthreshold preconditioning (PC) stimulus to elicit delayed preconditioning against infarction in pig myocardium. BACKGROUND: Bradykinin triggers early PC. Angiotensin-converting enzyme inhibitors increase local bradykinin levels via inhibition of kinin breakdown and have been shown in experimental studies to augment early protection afforded by PC. A role for bradykinin in eliciting delayed PC has not so far been identified. METHODS: We used a two-day protocol. On day 1 (closed chest), pigs were either sham-operated (group 1) or preconditioned, using balloon catheter inflation of the left anterior descending (LAD) coronary artery, with either a full (4 x 5 min PC, group 2) or subthreshold PC stimulus (2 x 2 min PC, group 3). Additional groups were pre-treated with perindoprilat (0.06 mg/kg i.v.) before sham (group 4) or subthreshold PC (group 5). On day 2 (open chest), all pigs were subjected to 40 min occlusion of the LAD followed by 3 h of reperfusion. Infarct size was determined by tetrazolium staining. RESULTS: Group 1 had a mean infarct size of 42.8+/-3.2% of the risk zone. Preconditioning with 4 x 5 min reduced the infarct size to 19.5+/-3.9% (p < 0.05). Groups 3 and 4 had infarct sizes not statistically different from group 1. However, combining perindoprilat with subthreshold PC resulted in a significant limitation of the infarction (18.4+/-3.1% p < 0.05), comparable with group 2. CONCLUSIONS: This is the first study to show that ACE inhibition can augment a mild ischemic stimulus to induce a protected state 24 h later.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Backtable heat-enhanced preconditioning: a simple and effective means of improving function of heart transplants.

BACKGROUND: Cardiac harvest teams are usually committed to immediately transfer the explanted donor heart into its cold storage solution. We tested the opposite hypothesis that a brief prestorage episode of heat-enhanced ischemic preconditioning could be protective. METHODS: Fifty-three isolated isovolumic rat hearts underwent 4 hours of cold (4 degrees C) storage in the Celsior preservation solution and 2 hours of reperfusion. Control hearts were immediately immersed after arrest. In the 3 treated groups, 2 customized thermal probes were first applied onto the left ventricular free wall of the explanted heart at 22 degrees C, 37 degrees C or 42.5 degrees C for 15 minutes before immersion. Each of the selected temperatures were monitored at the probe-tissue interface by a thermocouple. RESULTS: Whereas base line end-diastolic pressure was set at = 8 mm Hg in all groups, it increased during reperfusion (mean +/- SEM) to 28+/-3, 27+/-3, 17+/-1, and 18+/-2 mm Hg in control, 22 degrees C, 37 degrees C and 42.5 degrees C-heated hearts, respectively (37 degrees C and 42.5 degrees C: p < 0.05 versus controls and 22 degrees C). Slopes of pressure-volume curves featured similar patterns. Likewise, reperfusion dP/dT (mm Hg/s(-1)) was significantly lower in control and 22 degrees C hearts (1,119+/-114 and 1,076+/-125, respectively) than in those undergoing prestorage heating to 37 degrees C and 42.5 degrees C (1,545+/-109 and 1,719+/-111, p < 0.05 and p < 0.01 versus controls and 22 degrees C, respectively). Western blot analysis of LV samples did not demonstrate any upregulation of HSP 72 in either group. Conversely, the involvement of preconditioning was evidenced by the loss of protection in the 42.5 degrees C-heated hearts when, in 2 additional groups, the storage solution was supplemented with either the protein kinase C and tyrosine kinase inhibitors chelerythrine (5 micromol/L) and genistein (50 micromol/L) or the mitochondrial K(ATP) channel inhibitor 5-hydroxydecanoate (200 micromol/L). CONCLUSIONS: A brief period of postexplant ischemia with enhancement by topical heating ("backtable preconditioning") could be a simple and effective means of improving the functional recovery of heart transplants.

Animals↗
PubMed2001

Mitochondrial K(ATP) channel opening protects a human atrial-derived cell line by a mechanism involving free radical generation.

OBJECTIVES: The mechanism by which the mitochondrial K(ATP) channel openers confer protection against ischemia/reperfusion injury is debated. Evidence suggests that rather than solely being an end effector, opening of these channels may act by a trigger mechanism. We examined the effects of the mitochondrial K(ATP) channel opener, diazoxide on parameters of mitochondrial function with specific reference to reactive oxygen species (ROS) generation in a human atrial derived cell line model of simulated ischemia/reperfusion (LSI/R). METHODS AND RESULTS: Propidium iodide (PI) exclusion was used to assess survival. Diazoxide treatment conferred protection against LSI/R (13.9+/-0.9% vs. 36.9+/-4.5% controls) that was abolished by pre-treatment with the mitoK(ATP) channel blocker, 5-hydroxydecanoate (5-HD) (33.3+/-3.6%) and with the free radical scavenger, 2-mercaptopropionylglycine (MPG) (29+/-4.0%). Diazoxide caused increased oxidation of the ROS probe, reduced mitotracker orange (1.3 vs. 1.0 arbitrary units for control; P<0.01 vs. control) that was abrogated by either 5-HD or MPG (1.07 and 1.07 arbitrary units, respectively). At the same time there was no change in orange fluorescent signal from the membrane potential sensitive probe, JC-1 indicating no change in mitochondrial membrane potential. Changes in light scattering, reflecting changes in mitochondrial volume, occurred during treatment with diazoxide. CONCLUSION: These results demonstrate for the first time that the mitoK(ATP) channel opener diazoxide can act as a trigger of preconditioning by a mechanism involving mitochondrial swelling and the generation of ROS.

Analysis of Variance↗
PubMed2001

The contribution of endothelial nitric oxide synthase to early ischaemic preconditioning: the lowering of the preconditioning threshold. An investigation in eNOS knockout mice.

Nitric oxide (NO) is implicated in triggering and mediating delayed preconditioning. However, the role of NO and endothelial nitric oxide synthase (eNOS) in early ischaemic preconditioning is controversial. To investigate the role of eNOS in this paradigm further, the response of hearts isolated from either eNOS knockout (KO) or eNOS wild type (WT) mice to various ischaemic-preconditioning stimuli were studied. To determine whether eNOS is pivotal to early ischaemic preconditioning, hearts from both groups were subjected to a robust ischaemic-preconditioning stimulus consisting of four cycles of 5 min ischaemia and reperfusion (4PC) prior to an injurious ischaemia/reperfusion insult. Both WT and KO animals demonstrated significant attenuation of infarct size from 34.91+/-2.14 to 21.32+/-2.53% and from 30.92+/-1.87 to 22.60+/-2.98%, respectively. Whilst eNOS/NO appears not to be pivotal to early ischaemic preconditioning, NO can nonetheless mediate protection in both WT and KO hearts, as the NO donor, S-nitroso N-acetyl penicillamine (2 microM), was seen to mimic preconditioning protection. Therefore, it appears that the targets for NO mediated protection exist in both WT and KO hearts. Reducing the number of preconditioning cycles from four to three to two continued to result in significant attenuation of infarct size in WT hearts (26.30+/-2.86 and 26.70+/-1.95%). However, early ischaemic preconditioning failed in the KO hearts with any preconditioning stimulus less robust than the four cycle protocol used in the initial experiments (3PC 32.51+/-3.04%, 2PC 28.64+/-2.55%). Therefore, whilst eNOS is not essential for robust early ischaemic preconditioning, NO can be shown to be cardioprotective in its own right, and, moreover, eNOS and thus nitric oxide synthesis may contribute to early ischaemic preconditioning by lowering the ischaemic threshold for protection.

Analysis of Variance↗
PubMed2001

Delayed or second window preconditioning induced by adenosine A1 receptor activation is independent of early generation of nitric oxide or late induction of inducible nitric oxide synthase.

Transient adenosine A1 receptor (A1R) activation induces a second window or delayed preconditioning against myocardial infarction 24-72 h later. Early generation of nitric oxide and delayed induction of nitric oxide synthase have been implicated in mediating delayed cardioprotection after ischemic preconditioning in rabbits. Recent evidence indicates that some of the regulatory roles of adenosine in cardiac tissue may be mediated by A1R-induced generation of nitric oxide. This study examined the role of nitric oxide in the mediation of A1R-induced delayed preconditioning against infarction. Pharmacologic preconditioning of rabbits with the selective A1R agonist 2-chloro-N6-cyclopentyladenosine 100 microg/kg (CCPA) significantly reduced myocardial infarct size compared with control animals, after 30 min regional ischemia and 2 h reperfusion in vivo 24 h later (27.3+/-4.7 vs. 46.0+/-3.7%, respectively; p = 0.001). Nonselective inhibition of nitric oxide synthase with N(G)-nitro-L-arginine methyl ester (10 mg/kg) before administration of CCPA did not affect this infarct limitation at 24 h. Selective inhibition of inducible nitric oxide synthase before the prolonged ischemic insult on day 2, with two structurally independent inducible nitric oxide synthase inhibitors, L-N(6)-(1-iminoethyl)-lysine (10 mg/kg) or aminoguanidine (300 mg/kg), did not abrogate the reduction in infarction observed by pharmacologic preconditioning with CCPA 24 h earlier. These results suggest that the second window or delayed protection against myocardial infarction observed 24 h after pharmacologic preconditioning with an adenosine A1 agonist occurs independently of either early generation of nitric oxide or subacute induction of inducible nitric oxide synthase.

Adenosine↗
PubMed2001

Cardioprotective effects of transforming growth factor-beta1 during early reoxygenation or reperfusion are mediated by p42/p44 MAPK.

Apoptosis contributes to myocardial cell death during ischemia and reperfusion, especially during reperfusion. Growth factor "survival" signaling attenuates apoptosis. We therefore examined the effects of transforming growth factor-beta1 (TGF-beta1) on reperfusion injury and assessed the role of p42/p44 MAPK signaling in TGF-beta1-induced protection. Rat ventricular myocytes were subjected to hypoxia and reoxygenation. TGF-beta1 (0.2 ng/ml) was applied to cells during reoxygenation and the extent of apoptosis was determined by TUNEL and annexin V binding assays. Further studies were conducted in intact rat hearts subjected to regional ischemia and reperfusion. TGF-beta1 (0.2 ng/ml) was perfused during early reperfusion. In cells, incubation with TGF-beta1 (0.2 ng/ml) during reoxygenation attenuated the extent of cell membrane damage (trypan blue uptake) and also reduced the numbers of TUNEL-and annexin V-positive cells. Reduction of apoptosis was abrogated by PD98059 (5 microM), an inhibitor of p42/p44 MAPK activation. TGF-beta1 activated p42/p44 MAPK transiently in normoxic myocytes. When intact hearts received TGF-beta1 (0.2 ng/ml) during early reperfusion, infarct size was reduced from 39.4 +/- 3.1% to 17.3 +/- 3.1% (p < 0.01). This protective action of TGF-beta1 was abrogated by PD98059. These studies are the first to show that TGF-beta attenuates cardiac myocyte apoptosis during early reperfusion and limits infarct size through p42/p44 MAPK activation.

Animals↗
PubMed2001

Exercise directly enhances myocardial tolerance to ischaemia-reperfusion injury in the rat through a protein kinase C mediated mechanism.

OBJECTIVE: To determine whether exercise is capable of protecting the myocardium from experimental infarction and to explore the involvement of protein kinase C, a key signalling protein, in the development of any protection observed. METHODS: Rats were exercised on a treadmill for 30 minutes at 23-27 m/min. Sham treated animals were placed on the stationary treadmill but not exercised. Twenty four hours later, hearts were Langendorff perfused and subjected to 35 minute left main coronary artery occlusion followed by 120 minute reperfusion. Infarct size was determined by tetrazolium staining and expressed as a percentage of the risk zone (I/R%). To examine the potential signalling pathway, animals were treated with either the selective protein kinase C inhibitor chelerythrine, 5 mg/kg intraperitoneally, or with vehicle 10 minutes before the exercise or sham treadmill period. RESULTS: In the non-exercised group, mean (SEM) I/R was 48.4 (3.0)%. In the exercised group, infarct size was reduced to 17.3 (3.0)% (p < 0.01). Infarct size limitation induced by exercise was abolished by chelerythrine (I/R 45.0 (6.0)%). Chelerythrine pretreatment alone did not have any effect on infarct size (I/R 51.1 (3.9)%). Differences in infarct size were independent of risk zone size and myocardial contractile function during ischaemia-reperfusion. CONCLUSIONS: Experimental moderate exercise induces protection against myocardial infarction 24 hours later. Protein kinase C activation during exercise appears to be an important signal mediator of this protective response.

Alkaloids↗