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G F Baxter

Publications and source records attributed to G F Baxter.

At least 37 records · Page 2Linked to original sources
PubMed2000

Caspase inhibition and limitation of myocardial infarct size: protection against lethal reperfusion injury.

Ischaemia-reperfusion injury causes cell death by both necrosis and apoptosis. Caspase activation is a major event in apoptosis. We therefore examined the effect of caspase inhibitors during reperfusion upon myocardial infarction. Rat isolated hearts were subjected to 35 min coronary occlusion and 120 min reperfusion. Treatment groups were perfused with caspase inhibitors during early reperfusion. We assessed a non-selective caspase inhibitor (Z-VAD. fmk, 0.1 microM), a caspase-8 inhibitor (Z-IETD.fmk, 0.07 microM), a caspase-9 inhibitor (Z-LEHD.fmk, 0.07 microM) and a caspase-3 inhibitor (Ac-DEVD.cmk, 0.07 microM). All caspase inhibitors limited infarct size (infarct-risk ratio per cent: control 38.5+/-2.6; Z-VAD. fmk 24.6+/-3.4; Z-LEHD.fmk 19.3+/-2.4; Z-IETD.fmk 23.0+/-5.4; Ac-DEVD.cmk 27.8+/-3.3; P<0.05 when compared with control value, 1-way ANOVA). We conclude that caspase inhibition during early reperfusion protects myocardium against lethal reperfusion injury.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Quantitative assessment of cardiac myocyte apoptosis in tissue sections using the fluorescence-based tunel technique enhanced with counterstains.

Apoptosis is a distinct form of cell death, induced, for example, by ischaemia/reperfusion injury, that results in characteristic alterations in cell morphology and fate. In tissue sections, the most commonly used technique to detect apoptosis is terminal deoxynucleotidyl transferase mediated nick end labelling (TUNEL) staining which labels the ends of DNA strand breaks characteristic of the apoptotic process. However, without the employment of additional staining, TUNEL is only a qualitative procedure that gives no information about the proportion of negative cells nor the cell type undergoing apoptosis. We have utilised propidium iodide (PI) as a counterstain to visualise TUNEL negative nuclei together with anti-desmin antibody in order to assess quantitatively apoptosis in specific cell types. The procedure has been evaluated in tissue sections from isolated perfused rat hearts subjected to ischaemia and reperfusion. Hearts were cross-sectioned into four 2.5 mm thick slices which were fixed in 4% formaldehyde and embedded in paraffin. Serial sections (5 microns) were cut, dewaxed and pretreated by incubation with trypsin at 37 degrees C for 30 min. After the employment of the TUNEL assay, sections were labelled with anti-desmin antibody, counterstained with PI and finally examined by confocal fluorescent microscopy. Apoptosis was not seen in sections from hearts subjected to ischaemia alone nor in control hearts. After 35 min of ischaemia the percentages of TUNEL positive cells were very low both in myocytes (0.1%) and in non-myocytes (0.3%). In ischaemic-reperfused hearts, the number of TUNEL positive cells was only significantly higher in vascular cells (44+/-5%) and cardiac myocytes (6+/-2%). This simple method therefore allows quantification of apoptosis in myocytic and non-myocytic cells in tissue sections. Use of alternative immunohistochemical markers would permit adaptation of the method to the quantitative assessment of apoptosis in other tissues.

Animals↗
PubMed1999

ATP-sensitive K+ channels mediate the delayed cardioprotective effect of adenosine A1 receptor activation.

Adenosine A1 receptor stimulation increases myocardial resilience to ischaemia many hours later but the mechanism of protection is unclear. We hypothesized that A1 receptor-induced delayed cardioprotection is mediated by KATP channel opening. Rabbits were pretreated with saline or the selective A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA), 0.1 mg/kg i.v. After 24 h, they were anaesthetized and subjected to 30 min left coronary artery occlusion (CAO) and 120 min reperfusion. Twenty minutes before CAO, either glibenclamide 0.3 mg/kg, sodium 5-hydroxydecanoate (5-HD) 5 mg/kg, or a corresponding volume of vehicle solution were given i.v. Infarct size as a percentage of ischaemic risk volume (I/R%) was assessed by triphenyltetrazolium. In the absence of either glibenclamide or 5-HD, CCPA pretreatment resulted in significant limitation of infarction (I/R 23.4+/-3.3%vs 39.6+/-2.6% in saline pretreated animals, P<0.01). Administration of glibenclamide before CAO abolished this delayed protective effect of CCPA (I/R 37.4+/-4. 7%), as did 5-HD (I/R 48.8+/-3.7%). Neither glibenclamide nor 5-HD significantly modified I/R in saline pretreated animals. Risk volume was similar in all groups (0.8-1.1 cm3). Systemic haemodynamic variables were not markedly different between any of the groups immediately before or during the ischaemia-reperfusion protocol. Thus, delayed protection following transient A1 receptor activation was abolished by pre-ischaemic treatment with either glibenclamide or 5-HD, providing pharmacological evidence that KATP channel opening mediates A1 agonist-induced delayed myocardial protection. The inhibitory effect of 5-HD suggests specific involvement of mitochondrial KATP but the mechanisms of sub-acute regulation of KATP function following A1 receptor stimulation remain to be determined.

Adenosine Triphosphate↗
PubMed1999

Reperfusion injury revisited: is there a role for growth factor signaling in limiting lethal reperfusion injury?

Myocardial reperfusion injury represents an important therapeutic target. The ability of several peptide growth factors, including transforming growth factor-beta1, insulin, insulin-like growth factor-1, cardiotrophin-1 and fibroblast growth factors, to modify reperfusion injury has been examined in recent studies. The protective effects of these agents may be related to the inhibition of apoptosis, especially during reperfusion, probably through p42/p44 MAP kinase and PI3-kinase/Akt signaling. Growth factor signaling may therefore represent a novel approach for the development of pharmacological strategies that attenuate reperfusion injury in the heart.

Animals↗
PubMed1999

Mibefradil, a T-type and L-type calcium channel blocker, limits infarct size through a glibenclamide-sensitive mechanism.

Mibefradil is a novel calcium channel blocker with activity at both L-type and T-type calcium channels. There are data suggesting that this compound can protect the ischemic/reperfused myocardium in spite of the fact that there is a very low abundance of T-type calcium channels within ventricular tissue. The aims of this study were two-fold. First, we wished to study the protective effect of mibefradil on ischemia/reperfusion injury in the isolated rat heart using infarct size as the endpoint of injury. In this respect, we compared mibefradil with amlodipine, a well-known and potent L-type calcium channel blocker, and with ischemic preconditioning, an intervention known to reduce infarct size consistently. Secondly, we investigated the possible mechanisms through which protection was achieved. For this second purpose, we examined the effects on protection of glibenclamide (an ATP-dependent K+ channel blocker) and chelerythrine (a protein kinase C inhibitor). Isolated rat hearts were perfused in the Langendorff mode at constant pressure. Control, mibefradil-treated (0.3 microM), mibefradil plus glibenclamide (50 microM), and mibefradil plus chelerythrine (10 microM) treated hearts underwent 35 minutes regional ischemia followed by 120 minutes reperfusion. At the end of the experiments, infarct size was determined with triphenyltetrazolium chloride and was expressed as a percentage of the ischemic risk zone (I/R%). A significant reduction in infarct size with mibefradil treatment was observed (I/R 11.1 +/- 2.1% vs. 35.5 +/- 3.1% in controls). This was comparable with the infarct reduction seen with two 5-minute cycles of ischemic preconditioning (17.7 +/- 2.5%). Amlodipine 0.1 microM, a concentration that caused equivalent coronary vasodilatation as that produced by mibefradil treatment, had no significant effect on infarct size (I/R 29.7 +/- 3.5%). The protective effect of mibefradil was not significantly modified by the presence of the PKC inhibitor chelerythrine 10 microM (I/R 19.1 +/- 4.9%) but was abolished when glibenclamide 50 microM was coadministered with mibefradil prior to ischemia (I/R 28.1 +/- 4.7%). Neither chlelerythrine nor glibenclamide alone had any influence on infarct size. We conclude from these data that mibefradil, unlike amlodipine, markedly reduces infarct size in the rat isolated heart. This protection is sensitive to inhibition by glibenclamide, suggesting that KATP channel opening may be an important additional and novel mechanism of mibefradil's action.

Animals↗
PubMed1999

Pharmacological evidence that inducible nitric oxide synthase is a mediator of delayed preconditioning.

Brief periods of myocardial ischaemia preceding a subsequent more prolonged ischaemic period 24-72 h later confer protection against myocardial infarction ('delayed preconditioning' or the 'second window' of preconditioning). In the present study, we examined the effects of pharmacological modifiers of inducible nitric oxide synthase (iNOS) induction and activity on delayed protection conferred by ischaemic preconditioning 48 h later in an anaesthetized rabbit model of myocardial infarction. Rabbits underwent a myocardial preconditioning protocol (four 5 min coronary artery occlusions) or were sham-operated. Forty-eight hours later they were subjected to a sustained 30 min coronary occlusion and 120 min reperfusion. Infarct size was determined with triphenyltetrazolium staining. In rabbits receiving no pharmacological intervention, the percentage of myocardium infarcted within the risk zone was 43.9+5.0% in sham-operated animals and this was significantly reduced 48 h after ischaemic preconditioning with four 5 min coronary occlusions to 18.5+5.6% (P<0.01). Administration of the iNOS expression inhibitor dexamethasone (4 mg kg(-1) i.v) 60 min before ischaemic preconditioning completely blocked the infarct-limiting effect of ischaemic preconditioning (infarct size 48.6+/-6.1%). Furthermore, administration of aminoguanidine (300 mg kg(-1), s.c.), a relatively selective inhibitor of iNOS activity, 60 min before sustained ischaemia also abolished the delayed protection afforded by ischaemic preconditioning (infarct size 40.0+/-6.0%). Neither aminoguanidine nor dexamethasone per se had significant effect on myocardial infarct size. Myocardial risk zone volume during coronary ligation, a primary determinant of infarct size in this non-collateralized species, was not significantly different between intervention groups. There were no differences in systolic blood pressure, heart rate, arterial blood pH or rectal temperature between groups throughout the experimental period. These data provide pharmacological evidence that the induction of iNOS, following brief periods of coronary occlusion, is associated with increased myocardial tolerance to infarction 48 h later.

Animals↗
PubMed1998

Ischaemic preconditioning: present position and future directions.

Preconditioning the myocardium using short episodes of sublethal ischaemia will delay the onset of necrosis during a subsequent lethal ischaemic insult. This powerful protective adaptation of the myocyte has also been observed in other cell types. The potential for clinical application to benefit patients with a variety of pathological conditions has led to an expansion in our knowledge concerning the pathophysiology of ischemia-reperfusion injury and the regulatory mechanisms underlying cellular metabolism. We feel it is timely to assess the current position in this field and provide a critical appraisal to facilitate future research.

Animals↗
PubMed1998

Adaptation to myocardial stress in disease states: is preconditioning a healthy heart phenomenon?

Effective therapeutic strategies for protecting the ischaemic myocardium are much sought after. Ischaemic heart disease in humans is a complex disorder, often associated with other systemic diseases such as dyslipidaemia, hypertension and diabetes that exert multiple biochemical effects on the heart, independently of ischaemia. Ischaemic preconditioning of myocardium is a well-described adaptive response in which brief exposure to ischaemia markedly enhances the ability of the heart to withstand a subsequent ischaemic insult. The underlying molecular mechanisms of this phenomenon have been extensively investigated in the hope of identifying new rational approaches to therapeutic protection of the ischaemic myocardium. However, most studies have been undertaken in animal models in which ischaemia is imposed in the absence of other disease processes. In this article, Peter Ferdinandy, Zoltan Szilvassy and Gary Baxter review the ways in which systemic diseases might modify the preconditioning response and they emphasize the importance of further preclinical studies that specifically examine preconditioning in relation to complicating disease states.

Age Factors↗
PubMed1998

Prolonging the delayed phase of myocardial protection: repetitive adenosine A1 receptor activation maintains rabbit myocardium in a preconditioned state.

OBJECTIVES: This study was designed to examine whether the myocardium can be maintained in a protected state by extending the delayed phase of cardioprotection with chronic, intermittent adenosine A1 receptor activation. BACKGROUND: Several recent studies have explored the temporal characteristics of the protective effects of ischemic preconditioning. Two distinct phases of myocardial protection have been described: the short-lived immediate phase, or "classic" preconditioning, and the delayed phase, or "second window of protection" (SWOP). Previous studies have examined the potential for extending the duration of classic preconditioning by repeated application of the preconditioning stimulus. Pretreatment with either multiple episodes of ischemia or continuous infusion of a selective adenosine A1 receptor agonist, 2-chloro-N6-cyclopentyladenosine (CCPA), resulted in attenuation of the protective effects of preconditioning, implying downregulation of the receptors involved in triggering classic preconditioning. METHODS: Male New Zealand White rabbits were treated with repeated intravenous boluses of CCPA, 100 microg/kg body weight, or 0.9% saline at 48-h intervals. Forty-eight hours after the fifth dose (day 10), the animals were anesthetized and subjected to 30 min of coronary occlusion, followed by 120 min of reperfusion. Infarct size was determined as a percentage of myocardial risk volume using tetrazolium staining. To further explore whether the rabbits had developed tolerance to the effects of adenosine A1 receptor activation, a subgroup of animals were treated with a further bolus of CCPA, 100 microg/kg, at the end of the reperfusion period, and the hemodynamic response was monitored for 10 min before excision of the heart. RESULTS: Pretreatment with intermittent doses of CCPA resulted in a 42% reduction in the infarct to risk ratio compared with vehicle pretreatment (26.6+/-3.7% vs. 45.9+/-5.5%, p < 0.01). Furthermore, CCPA treatment at the end of reperfusion resulted in identical hypotension and bradycardia in both groups. CONCLUSIONS: We conclude that rabbits can be maintained in a protected state against myocardial infarction by repeated activation of adenosine A1 receptors, with no evidence of tachyphylaxis to the infarct-limiting or hemodynamic effects of CCPA. This finding suggests that adenosine A1 receptor activation may hold promise as a new approach to long-term cardioprotection.

Adenosine↗
PubMed1998

Myocardial protection afforded by nicorandil and ischaemic preconditioning in a rabbit infarct model in vivo.

We previously showed that preoperative nicorandil, a hybrid potassium channel opener and nitrate compound, conferred cardioprotective effects in a hypoxia/reoxygenation model of isolated human atrial muscle by using functional recovery as an end point, and that ischaemic preconditioning surprisingly abolished the protection afforded by nicorandil. In view of this paradoxic result, this study was undertaken to assess whether ischaemic preconditioning influences any protective effect of nicorandil by using infarct size as an end point. In addition, we investigated the underlying mechanisms of the protective action of nicorandil. Rabbits underwent a midline sternotomy under anaesthesia. A left coronary branch was occluded for 30 min followed by 120 min of reperfusion. Nicorandil (100 microg/kg bolus + 10 microg/kg/min) was given intravenously 30 min before coronary occlusion and continued to the time of reperfusion (early treatment) or 5 min before reperfusion and continued throughout reperfusion (late treatment). Ischaemic preconditioning was achieved by a single episode of 5-min coronary occlusion followed by 10-min reperfusion before the 30-minute occlusion in the presence or absence of nicorandil. Risk volume and infarct volume were determined by fluorescent microspheres and tetrazolium staining, respectively. Early treatment with nicorandil conferred a significant decrease in percentage of infarct size within the risk zone (24.9 +/- 2.9%) when compared with control (39.2 +/- 4.3%; p < 0.01). Late treatment with nicorandil had no effect on infarct size (43.5 +/- 3.4%). Ischaemic preconditioning also resulted in significant reduction in infarct size (13.4 +/- 4.3%; p < 0.01 vs. control). The combination of ischaemic preconditioning with nicorandil (early treatment) showed an intermediate protective efficacy between early treatment with nicorandil alone and ischaemic preconditioning alone (18.1 +/- 4.2%; p < 0.01 vs. control). Nitroglycerin (10 microg/kg bolus + 1 microg/kg/kg/min, i.v.) given before and during ischaemia tended to reduce infarct size, but the effect was not statistically significant (28.9 +/- 2.9%; p > 0.05 vs. control). Although an adenosine triphosphate (ATP)-sensitive potassium channel blocker, 5-hydroxydecanoate (5 mg/kg, i.v.) by itself had no effect on infarct size (38.8 +/- 3.6%), the protective effect of nicorandil was abolished by 5-hydroxydecanoate (37.7 +/- 5.8%; p < 0.05 vs. early treatment of nicorandil). There were no differences in area at risk or haemodynamics between groups. Our results show that nicorandil has a protective effect against myocardial infarction in our rabbit model when infused before and during ischaemia, but not during reperfusion, and the protective effect is abolished by an ATP-sensitive potassium channel blocker. Furthermore, the addition of ischaemic preconditioning does not detrimentally influence the effect of nicorandil. This suggests that nicorandil can confer an infarct-limiting effect by opening of ATP-sensitive potassium channels with or without intermittent ischaemia, as may happen in patients with unstable angina.

Animals↗
PubMed1998

Renal ischemia preconditions myocardium: role of adenosine receptors and ATP-sensitive potassium channels.

Brief renal ischemia-reperfusion is reported to precondition the myocardium; however, the underlying mechanisms are unknown. This phenomenon was, therefore, investigated using an in vivo rabbit model of acute myocardial infarction. Characterization of the mechanisms involved was performed using the nonselective adenosine receptor antagonist 8-(p-sulfophenyl)theophylline (8-SPT) and the ATP-sensitive potassium (KATP) channel blocker sodium 5-hydroxydecanoate (5-HD). Pentobarbital-anesthetized rabbits underwent a left thoracotomy and pericardiotomy. A laparotomy was then performed to expose the left renal artery. Animals were either preconditioned with a 10-min occlusion of the renal artery followed by 10 min of reperfusion or underwent a 20-min sham period of anesthesia. Subsequently, the left coronary artery was then occluded for 30 min and reperfused for 2 h. Infarct-to-risk ratio was limited from 32.7 +/- 4.0% (n = 12) in controls to 17.8 +/- 3.0% (n = 9; P = 0.002) in preconditioned hearts. Protection was abolished by 7.5 mg/kg iv 8-SPT (36.7 +/- 3.7%; n = 6) or 5 mg/kg iv 5-HD (33.1 +/- 4. 4%; n = 6) administered before preconditioning. 8-SPT (40.0 +/- 4. 4%; n = 6) or 5-HD (40.5 +/- 4.2%; n = 6) did not affect infarct-to-risk ratio in sham controls. Thus activation of both adenosine receptors and KATP channels appears to be involved in acute renal preconditioning of the myocardium.

Animals↗
PubMed1997

Genistein, a tyrosine kinase inhibitor, blocks the "second window of protection" 48 h after ischemic preconditioning in the rabbit.

We have previously reported a delayed or "second window of protection" against infarction 24-72 h after ischemic preconditioning in the rabbit. This phenomenon has also been associated with the protein kinase C signalling pathway. In the present study, we expanded our investigation to ascertain whether protein tyrosine kinase was in any way associated with this phenomenon in the rabbit heart. We found that 48 h after ischemic preconditioning with 4x5 min coronary occlusions the percentage of myocardium infarcting within the risk zone following a 30-min coronary occlusion and 120-min reperfusion (I/R) was reduced from 39. 6+/-3.3% to 18.0+/-3.7% (P<0.01). However, an i.v. bolus administration of genistein (5 mg/kg), a tyrosine kinase inhibitor, 5 min before ischemic preconditioning stimulus, abolished this protection (I/R=39.0+/-3.4%). Genistein per se had no significant effect on infarction 48 h later. Risk zone volume after coronary ligation was not significantly different between intervention groups. There were no differences in hemodynamic parameters between groups throughout the experimental period. We conclude that the second window of protection, 48 h after preconditioning, is mediated by tyrosine kinase activation in the rabbit heart.

Animals↗
PubMed1997

Attenuation of myocardial ischaemic injury 24 h after diacylglycerol treatment in vivo.

Previous work suggests that delayed protection against infarction following ischaemic preconditioning of rabbit myocardium may involve the activation of protein kinase C (PKC). Preconditioning in the presence of chelerythrine, an inhibitor of PKC, abolished the late anti-infarct effect of preconditioning. In the studies described here, we tested the hypothesis that direct PKC activation with an analogue of diacylglycerol, the physiological activator of PKC, would invoke an adaptive mechanism leading to enhanced myocardial tolerance to ischaemia 24 h later. Rabbits were treated with i.v. injections of 1,2-dioctanoyl-sn-glycerol (DiC8) 5 mg/kg or 15 mg/kg or an equivalent volume of vehicle solution. Twenty-four h after pretreatment, the animals were anaesthetised and underwent 30 min coronary artery occlusion with 120 min reperfusion. Infarct size was determined by triphenyltetrazolium staining. In vehicle pretreated rabbits, infarct-risk zone ratio was 32.8+/-2.6%. Pretreatment with DiC8 5 mg/kg did not significantly affect infarct size (26.3+/-4.0%), but pretreatment with DiC8 15 mg/kg resulted in a marked reduction in infarct size (18.0+/-3.4%, P<0.05, 1-way ANOVA). Reduction in infarct size with the higher dose of DiC8 was independent of myocardial risk zone size and systemic haemodynamic parameters during coronary occlusion. The haemodynamic effects of acute administration of DiC8 15 mg/kg were examined in a separate cohort of pentobarbitone-anaesthetised rabbits. The compound was found not to affect systolic blood pressure or heart rate under these conditions. We examined the possibility that increased ischaemic tolerance might be due to induction of the 27 and 72 kDa heat shock proteins (hsp27 and hsp70i) which are known to be cytoprotective and are upregulated by ischaemia and other stressful stimuli. Western blot analysis of left ventricular tissue revealed that neither protein was induced 24 h after treatment with DiC8 15 mg/kg. Thus, infarct limitation 24 h after DiC8 treatment did not appear to be due to increased tissue content of these proteins. The mechanisms of DiC8-induced delayed myocardial protection remain unclear. However, these data are compatible with the hypothesis that activation of PKC isoenzymes is an important intermediate signal of sub-acute cellular adaptation, and results in enhanced tolerance to ischaemia-reperfusion injury in myocardium many hours later.

Animals↗
PubMed1997

Protein kinase C is involved in resistance to myocardial infarction induced by heat stress.

Heat stress (HS) is known to protect against mechanical dysfunction and myocardial necrosis in myocardial ischemia-reperfusion models both in vivo and in vitro. However, the mechanisms involved in this form of cardioprotection remain unclear. Protein kinase C (PKC) and tyrosine kinase activation have both been shown to be involved in the delayed phase of protection following ischemic preconditioning, a phenomenon which appears to be analogous to HS-induced protection. Therefore, we investigated the role of PKC and tyrosine kinase in HS-induced resistance to myocardial infarction, in the isolated rat heart. The selective inhibitors chelerythrine (Che) and genistein (Gen) were used to inhibit PKC and tyrosine kinase, respectively. Rats were treated with Che (5 mg/kg, i.p.) or Gen (5 mg/kg, i.p.) or vehicle before they were either heat stressed (42 degrees C for 15 min) or sham anesthetized. Twenty-four h later their hearts were isolated, retrogradely perfused, and subjected to 35-min occlusion of the left coronary artery followed by 120-min of reperfusion. Infarct-to-risk ratio was significantly reduced in HS (19.9+/-1.1%) compared to sham (43.1+/-1.1%) hearts. This reduction in infarct size was abolished in chelerythrine-treated groups (43.8+/-1.9% in HS+Che v 44.9+/-2.0% in sham+Che), but was conserved in genistein-treated groups (17.7+/-0.9% in HS+Gen v 36.4+/-2.8% in sham+Gen). In order to confirm that genistein at this dose was effectively inhibiting tyrosine kinase activity, we observed the ability of the agent to prevent the hypoglycemic responses to insulin in a separate group of anesthetised rats receiving an i.v. insulin infusion. Western blot analysis of the myocardial hsp72 showed a HS-induced increase of this protein, which was modified by neither the PKC inhibitor, chelerythrine, nor the tyrosine kinase inhibitor, genistein. We conclude that the activation of PKC, but not of tyrosine kinase, appears to play a role in the functional cardioprotection associated with the heat stress response. Although protection appears to be dissociated from induction of hsp72, further work is required to explore the importance of hsp72 phosphorylation to cytoprotective activity of the protein.

Alkaloids↗
PubMed1997

Characterisation of the infarct-limiting effect of delayed preconditioning: timecourse and dose-dependency studies in rabbit myocardium.

The delayed phase ('second window') of protection induced by ischemic preconditioning in rabbit heart is observed as enhanced resilience to infarction 24 hours after repetitive brief cycles of ischemia. Here we provide a fuller physiological characterisation of this phenomenon in the open-chest rabbit model, examining temporal characteristics and dose-dependency of this adaptation. For examination of the timecourse of delayed protection, rabbits were pretreated with four 5 minute coronary artery occlusions (PC) or sham operation (SHAM). Twenty four, 48, 72 or 96 hours later, infarct size after 30 min coronary occlusion and 120 minutes reperfusion was assessed with TTC staining and expressed as a percentage of myocardial risk volume (I/R). I/R was reduced at 24 hours (SHAM 48.1 +/- 3.9% v PC 31.4 +/- 3.0%, P < 0.01), 48 hours (SHAM 41.9 +/- 3.0% v PC 19.6 +/- 6.3%, P < 0.01), and 72 hours (SHAM 39.8 +/- 3.4% v PC 17.2 +/- 2.5%, P < 0.01). No protection was observed 96 hours after preconditioning (SHAM 35.0 +/- 4.8% v PC 36.9 +/- 3.8%). In a further study, animals were pretreated with one, two or four 5 minute coronary occlusions (1 x 5 PC, 2 x 5 PC, 4 x 5 PC) and subjected to the infarction protocol 48 hours later. I/R was 44.5 +/- 4.3% in SHAM, 24.8 +/- 4.4% in 1 x 5 PC (P < 0.01), 27.4 +/- 2.9% in 2 x 5 PC (P < 0.05) and 24.4 +/- 4.8 in 4 x 5 PC (P < 0.01). Delayed protection in this rabbit model is prolonged, extending between 24 and 72 hours after the preconditioning stimulus. The threshold for eliciting the second window of protection in this model is as low as one 5 minute coronary occlusion.

Animals↗