Preconditioning does not attenuate cardiac dysfunction after global ischaemia in the guinea-pig

Ischaemic preconditioning reduces infarct size, but the effects on cardiac function after global ischaemia are more controversial. Additionally, species differences may exist. The present study investigates the effects of preconditioning on cardiac performance in the globally ischaemic, Langendorff-perfused guinea-pig heart. Hearts were stabilized for 25 min, and divided into the following groups: (1) (n = 8) control perfusion for 16 min before 30-min global ischaemia and 30-min reperfusion, (2) (n = 7) two episodes of 3-min ischaemia and 5-min reperfusion before global ischaemia, (3) (n = 7) 5-min ischaemia and 10-min reperfusion before ischaemia, (4) (n = 8) control perfusion before 40-min ischaemia and 30-min reperfusion, (5) (n = 8) Preconditioning as group 2 before ischaemia as group 4, (6) (n = 9) Control perfusion before 50-min ischaemia and 30-min reperfusion, (7) (n = 10) Preconditioning as group 2 before ischaemia as group 6. A dose-dependent reduction of left ventricular systolic pressure, and increase of end-diastolic pressure was observed during reperfusion after 30-, 40- and 50-min ischaemia. Preconditioning did not influence these changes, nor did it attenuate the incidence of severe reperfusion arrhythmias or reduction of coronary flow. In conclusion, ischaemic preconditioning does not improve cardiac function during reperfusion of the globally ischaemic, isolated guinea-pig heart.     

Endogenous nitric oxide attenuates hypoxic vasoconstriction of small pulmonary arteries and veins in anaesthetized cats

Ischaemic preconditioning has cardioprotective effects. Reactive oxygen species may be possible mediators. The present study investigated whether low doses of exogenous hydrogen peroxide could mimic preconditioning in isolated, Langendorff-perfused rat hearts. Hearts were subjected to two episodes of 3 min global ischaemia and 5 min reperfusion (n = 17), or were given 10 (n=15), 20 (n=10), 30 (n=20), 40 (n=18), 80 (n=17) or 160 μM (n=10) hydrogen peroxide for 10 min, followed by 10 min recovery, before 25 min global ischaemia and 60 min reperfusion, and compared with ischaemic controls of matching perfusion time (n=17 and n=23). Cardiac performance was assessed by heart rate, left ventricular systolic, end-diastolic and developed pressures, and coronary flow. Severe reperfusion arrhythmias occurred frequently in control hearts, and was attenuated by ischaemic preconditioning. All hearts pretreated with 160 μM hydrogen peroxide had severe arrhythmias throughout reperfusion, while these were not seen in any heart perfused with 20 μM hydrogen peroxide (P< 0.01 compared to controls). Ischaemia and reperfusion induced a minor decrease in heart rate, left ventricular systolic and developed pressures, and increased end-diastolic pressure. Ischaemic preconditioning attenuated the decrease of heart rate and the increase of end-diastolic pressure, and increased coronary flow, while hydrogen peroxide did not significantly attenuate these changes. In conclusion, a low dose of exogenous hydrogen peroxide before global ischaemia inhibited severe reperfusion arrhythmias, but had no other protective effects. The present work does not suggest that reactive oxygen species are important mediators of the preconditioning effects on stunning and arrhythmias in the rat heart.     

Various inotropic effects of angiotensin II in post-ischaemic rat hearts depending on ischaemic time with possible involvement of protein kinase C

AIMS: The present study investigated if the inotropic effect of angiotensin II (AngII) is altered during post-ischaemic reperfusion in hearts subjected to mild and severe ischaemia. The possible involvement of protein kinase C (PKC) in the change in the inotropic effect was also investigated. METHODS: Isolated Langendorff-perfused rat hearts were perfused under constant flow with oxygenated Krebs-Henseleit buffer and paced at 360 beats min(-1). A saline-filled balloon catheter inserted into the left ventricle was used for measurement of contractile force. In the first series of experiments, hearts were subjected to continuous perfusion, 15- or 25-min global ischaemia followed by 45-min reperfusion. At the end of reperfusion, 0.1 micromol L(-1) AngII was infused for 5 min. In a second series of experiments, AngII was infused in hearts subjected to 25-min ischaemia followed by 45-min reperfusion in the absence or presence of the PKC inhibitor chelerythrine chloride (5 micromol L(-1)). RESULTS: The current study demonstrates that AngII exerts a positive inotropic effect in normoxic hearts with an increase of left ventricular developed pressure (LVDP) by 11% (P<0.05 vs. prior to AngII infusion). In post-ischaemic hearts subjected to 15-min ischaemia no effect of AngII was observed. In hearts subjected to 25 min of ischaemia, however, AngII evoked a negative inotropic response with a decrease of LVDP by 18% (P<0.05 vs. prior to AngII infusion). The negative inotropic effect of AngII was inhibited by the PKC inhibitor chelerythrine chloride. CONCLUSIONS: AngII exerts negative inotropic effect in severely injured post-ischaemic heart, possibly through the PKC pathway.     

Relationship between ischaemic time and ischaemia/reperfusion injury in isolated Langendorff-perfused mouse hearts

Myocardial functional recovery and creatine kinase (CK) release following various periods of ischaemia were investigated in isolated mouse hearts. The hearts were perfused in the Langendorff mode with pyruvate-containing Krebs-Hensleit (KH) buffer under a constant perfusion pressure of 80 mmHg, and were subjected to either continuous perfusion or to 5, 15, 20, 25, 30, 45 or 60 min of global ischaemia followed by 45 min of reperfusion. In hearts subjected to ischaemic periods of 5, 15 or 20 min, there was a transient reduction in the left ventricular (LV) dP/dt max during the early phase of reperfusion, while the recovery at the end of reperfusion reached a level similar to that in hearts subjected to continuous perfusion. In hearts subjected to longer ischaemic periods, i.e. 25, 30, 45 or 60 min, the decrease in the cardiac performance was more pronounced and persistent, with significantly lower recovery in LV dP/dt max and higher LV end diastolic pressure (LVEDP) at the end of reperfusion than in the non-ischaemic hearts. There were no significant differences in the recoveries in coronary flow or in heart rate (HR) between groups. Similarly to the functional recovery, the release of CK showed a clear ischaemic length-related increase. In conclusion, the Langendorff-perfused isolated mouse heart could be a valuable model for studies of myocardial ischaemia/reperfusion injury. Future studies using gene-targeted mice would add valuable knowledge to the understanding of myocardial ischaemia/reperfusion injury.     

Various inotropic effects of angiotensin II in post‐ischaemic rat hearts depending on ischaemic time with possible involvement of protein kinase C

Aims: The present study investigated if the inotropic effect of angiotensin II (AngII) is altered during post‐ischaemic reperfusion in hearts subjected to mild and severe ischaemia. The possible involvement of protein kinase C (PKC) in the change in the inotropic effect was also investigated. Methods: Isolated Langendorff‐perfused rat hearts were perfused under constant flow with oxygenated Krebs–Henseleit buffer and paced at 360 beats min^?1. A saline‐filled balloon catheter inserted into the left ventricle was used for measurement of contractile force. In the first series of experiments, hearts were subjected to continuous perfusion, 15‐ or 25‐min global ischaemia followed by 45‐min reperfusion. At the end of reperfusion, 0.1 μmol L^?1 AngII was infused for 5 min. In a second series of experiments, AngII was infused in hearts subjected to 25‐min ischaemia followed by 45‐min reperfusion in the absence or presence of the PKC inhibitor chelerythrine chloride (5 μmol L^?1). Results: The current study demonstrates that AngII exerts a positive inotropic effect in normoxic hearts with an increase of left ventricular developed pressure (LVDP) by 11% (P < 0.05 vs. prior to AngII infusion). In post‐ischaemic hearts subjected to 15‐min ischaemia no effect of AngII was observed. In hearts subjected to 25 min of ischaemia, however, AngII evoked a negative inotropic response with a decrease of LVDP by 18% (P < 0.05 vs. prior to AngII infusion). The negative inotropic effect of AngII was inhibited by the PKC inhibitor chelerythrine chloride. Conclusions: AngII exerts negative inotropic effect in severely injured post‐ischaemic heart, possibly through the PKC pathway.     

Relationship between ischaemic time and ischaemia/reperfusion injury in isolated Langendorff‐perfused mouse hearts

Myocardial functional recovery and creatine kinase (CK) release following various periods of ischaemia were investigated in isolated mouse hearts. The hearts were perfused in the Langendorff mode with pyruvate‐containing Krebs–Hensleit (KH) buffer under a constant perfusion pressure of 80 mmHg, and were subjected to either continuous perfusion or to 5, 15, 20, 25, 30, 45 or 60 min of global ischaemia followed by 45 min of reperfusion. In hearts subjected to ischaemic periods of 5, 15 or 20 min, there was a transient reduction in the left ventricular (LV) dP/dt max during the early phase of reperfusion, while the recovery at the end of reperfusion reached a level similar to that in hearts subjected to continuous perfusion. In hearts subjected to longer ischaemic periods, i.e. 25, 30, 45 or 60 min, the decrease in the cardiac performance was more pronounced and persistent, with significantly lower recovery in LV dP/dt max and higher LV end diastolic pressure (LVEDP) at the end of reperfusion than in the non‐ischaemic hearts. There were no significant differences in the recoveries in coronary flow or in heart rate (HR) between groups. Similarly to the functional recovery, the release of CK showed a clear ischaemic length‐related increase. In conclusion, the Langendorff‐perfused isolated mouse heart could be a valuable model for studies of myocardial ischaemia/reperfusion injury. Future studies using gene‐targeted mice would add valuable knowledge to the understanding of myocardial ischaemia/reperfusion injury.     

Remote vs. local ischaemic preconditioning in the rat heart: infarct limitation,suppression of ischaemic arrhythmia and the role of reactive oxygen species

The unmet clinical need for myocardial salvage during ischaemia–reperfusion injury requires the development of new techniques for myocardial protection. In this study the protective effect of different local ischaemic preconditioning (LIPC) and remote ischaemic preconditioning (RIPC) protocols was compared in the rat model of myocardial ischaemia–reperfusion, using infarct size and ischaemic tachyarrhythmias as end‐points. In addition, the hypothesis that there is involvement of reactive oxygen species (ROS) in the protective signalling by RIPC was tested, again in comparison with LIPC. The animals were subjected to 30‐min coronary occlusion and 90‐min reperfusion. RIPC protocol included either transient infrarenal aortic occlusion (for 5, 15 and 30 min followed by 15‐min reperfusion) or 15‐min mesenteric artery occlusion with 15‐min reperfusion. Ventricular tachyarrhythmias during test ischaemia were quantified according to Lambeth Conventions. It was found that the infarct‐limiting effect of RIPC critically depends on the duration of a single episode of remote ischaemia, which fails to protect the heart from infarction when it is too short or, instead, too prolonged. It was also shown that RIPC is ineffective in reducing the incidence and severity of ischaemia‐induced ventricular tachyarrhythmias. According to our data, the infarct‐limiting effect of LIPC could be partially eliminated by the administration of ROS scavenger N‐2‐mercaptopropionylglycine (90 mg/kg), whereas the same effect of RIPC seems to be independent of ROS signalling.     

Preconditioning of the Small Intestine to Ischemia in Rats

Measures reflecting the state of the small intestine were studied in rats after ischemia lasting 90 min produced by clamping the superior mesenteric artery and reperfusion for 30 min. Preconditioning of the intestine to ischemia was induced by producing intestinal ischemia for 10 min followed by 10 min of reperfusion (ischemic preconditioning), 30-min limb ischemia with 15-min reperfusion (distant ischemic preconditioning), and i.v. L-arginine. The smallest amount of damage to the intestine after 90 min of ischemia and 30 min of reperfusion was seen in the group of rats subjected to ischemic preconditioning. The protective effect of ischemic preconditioning was partially blocked by administration of N--nitro-L-arginine (a blocker of NO synthesis). Doses of L-arginine also had protective effects, though these were smaller than those of ischemic preconditioning. Preliminary ischemia-reperfusion of the limb had no effect on the state of the intestine. Thus: 1) ischemic preconditioning of the intestine is partially associated with activation of nitric oxide synthesis, and 2) distant ischemic preconditioning did not protect the intestine.     

Cariporide enhances lactate clearance upon reperfusion but does not alter lactate accumulation during global ischaemia

Cariporide (HOE 642) inhibits the Na⁺/H⁺ exchanger and would be expected to reduce lactate accumulation during ischaemia and stimulate lactate/H⁺ co-transporter upon reperfusion. The aim of this study was to determine the effect of cariporide on lactate production during global ischaemia and release during reperfusion. Guinea-pig hearts perfused in the Langendorff mode were exposed to 45 min global ischaemia and 30 min reperfusion with or without cariporide (5 or 10 mol/l). Cardiac function was assessed by measurement of left ventricular developed pressure (LVDP). Lactate and pH were measured in coronary effluent before ischaemia and throughout reperfusion. Tissue metabolites (lactate, adenine nucleotides, guanine nucleotides and purine) were measured in ventricular biopsy samples collected at the beginning and end of ischaemia. Cariporide significantly improved recovery of LVDP (from 66% for control to 88% and 93% for 5 and 10 mol/l cariporide, respectively). During ischaemia, only 10 mol/l cariporide produced a small (10%) but significant preservation of ATP and GTP compared to control. This was associated with significant reduction (25%) in ischaemic contracture. Cariporide did not influence lactate accumulation during ischaemia but significantly increased lactate efflux (18%) during the first 60 s of reperfusion. In conclusion, cariporide does not alter lactate accumulation during ischaemia but enhances lactate efflux upon reperfusion, which may have implications for its cardioprotective action.     

Involvement of endogenous adenosine in ischaemic preconditioning in swine

Adenosine release and the subsequent activation of adenosine receptors are involved in ischaemic preconditioning in dogs and rabbits. In the present study, we investigated whether adenosine also mediates ischaemic preconditioning in swine. Swine were used since, due to the lack of an innate collateral circulation, infarct development in this species most closely resembles that observed in humans. In 36 enflurane-anaesthetized swine the impact of increased adenosine breakdown with exogenous porcine adenosine deaminase (5 IU/ml blood/min) on global and regional myocardial function (sonomicrometry), subendocardial blood flow (ENDO, microspheres) and infarct size (IS, triphenyl tetrazolium chloride staining following 90 min ischaemia and 120 min reperfusion) were analysed. Low-flow ischaemia for 90 min at an ENDO of 0.09±0.04 (mean±SD) ml/min/g caused an IS of 13.2±9.7% (n=8) of the area at risk. Ischaemic preconditioning by a cycle of 10 min low-flow ischaemia followed by 15 min reperfusion prior to the 90-min ischaemic period (ENDO=0.06±0.03 ml/min/g) reduced IS to 2.6±3.0% (n=11, P<0.05). The interstitial adenosine concentration (microdialysis) increased from 1.60±0.87 nmol/ml to above 10 M during ischaemia; with intracoronary adenosine deaminase, the interstitial adenosine concentration fell from 1.65±0.23 to 0.12±0.07 nmol/ml and did not increase during ischaemia. Adenosine deaminase per se did not alter IS after 90 min ischaemia (n=7, ENDO=0.08±0.04 ml/min/g, IS=12.1±6.9%) but abolished the beneficial effect of ischaemic preconditioning (n=10, ENDO=0.06±0.03 ml/min/g, IS=8.8±5.8%). For any given ENDO, IS was significantly reduced in the ischaemic preconditioned group compared with the other three groups. Global and regional myocardial function were comparable among all groups of swine. We conclude that endogenous adenosine mediates ischaemic preconditioning also in swine.     

No protection of the porcine kidney by ischaemic preconditioning

One or more episodes of sublethal ischaemia and reperfusion delay infarct development during subsequent, sustained ischaemia in the heart and skeletal muscle. The present study tested whether or not such ischaemic preconditioning (IP) also protects the kidney. Enflurane-anaesthetized pigs underwent 60 min of right renal vessel occlusion (RVO), followed by 8 h of reperfusion without (placebo group, n = 8) or with three preceding cycles of 10 min RVO and 10 min reperfusion (IP group, n = 8). After 8 h of reperfusion, kidneys were oliguric in both groups (placebo group: 23 +/- 21 ml x h(-1), IP group: 24 +/- 27 ml x h(-1)). A transient polyuric phase occurred in the IP group at 2 h reperfusion. The reperfused kidneys did not excrete inulin, creatinine or urea in both groups, although renal blood flow during reperfusion was similar to baseline. Morphological damage ranged in both groups from single cell necrosis to disseminated patchy necrosis; the number of pyknotic cells tended to be higher in the IP group than in the placebo group (27.0 +/- 7.1 vs. 15.6 +/- 5.6%, n.s.). In anaesthetized pigs, IP did not therefore attenuate renal dysfunction and morphological damage resulting from 60 min of renal normothermic ischaemia followed by 8 h of reperfusion.     

Renal denervation abolishes the protective effects of ischaemic preconditioning on function and haemodynamics in ischaemia‐reperfused rat kidneys

Studies were conducted to investigate the role of renal sympathetic nerves in the process of acquiring ischaemic tolerance in ischaemic preconditioned ischaemia‐reperfused rat kidneys. Two periods of 3‐min occlusion of bilateral renal arteries was performed prior to 30‐min bilateral ischaemia and 90‐min reperfusion in acute renal denervated or innervated kidneys. The glomerular filtration rate (GFR), fractional excretion of sodium (FENa) and lithium (FELi), and renal blood flow (RBF) were assessed in reperfused kidneys. Ischaemic preconditioning significantly improved values for all these parameters as compared with no treated ischaemia‐reperfused kidneys. Denervation caused slight increase in GFR, diuresis and natriuresis without improving RBF after reperfusion. However, protecting effects of ischaemic preconditioning on renal function were disappeared in denervated kidneys, while in innevated kidneys the effects of ischaemic preconditioning were maintained. These results clearly showed that ischaemic preconditioning pre‐treatment protects kidneys against ischaemia–reperfusion injury, and the effects are, at least in part, mediated by sympathetic nerves, as the protective effects were abolished by denervation.     

Temperature preconditioning of isolated rat hearts – a potent cardioprotective mechanism involving a reduction in oxidative stress and inhibition of the mitochondrial permeability transition pore

We investigate whether temperature preconditioning (TP), induced by short-term hypothermic perfusion and rewarming, may protect hearts against ischaemic/reperfusion injury like ischaemic preconditioning ( IP ). Isolated rat hearts were perfused for 40 min, followed by 25 min global ischaemia and 60 min reperfusion (37°C). During pre-ischaemia, IP hearts underwent three cycles of 2 min global ischaemia and 3 min reperfusion at 37°C, whereas TP hearts received three cycles of 2 min hypothermic perfusion (26°C) interspersed by 3 min normothermic perfusion. Other hearts received a single 6 min hypothermic perfusion (SHP) before ischaemia. Both IP and TP protocols increased levels of high energy phosphates in the pre-ischaemic heart. During reperfusion, TP improved haemodynamic recovery, decreased arrhythmias and reduced necrotic damage (lactate dehydrogenase release) more than IP or SHP. Measurements of tissue NAD⁺ levels and calcium-induced swelling of mitochondria isolated at 3 min reperfusion were consistent with greater inhibition of the mitochondrial permeability transition at reperfusion by TP than IP; this correlated with decreased protein carbonylation, a surrogate marker for oxidative stress. TP increased protein kinase Cɛ (PKCɛ) translocation to the particulate fraction and pretreatment with chelerythrine (PKC inhibitor) blocked the protective effect of TP. TP also increased phosphorylation of AMP-activated protein kinase (AMPK) after 5 min index ischaemia, but not before ischaemia. Compound C (AMPK inhibitor) partially blocked cardioprotection by TP, suggesting that both PKC and AMPK may mediate the effects of TP. The presence of N -(2-mercaptopropionyl) glycine during TP also abolished cardioprotection, indicating an involvement of free radicals in the signalling mechanism.     

Renal denervation abolishes the protective effects of ischaemic preconditioning on function and haemodynamics in ischaemia-reperfused rat kidneys

Studies were conducted to investigate the role of renal sympathetic nerves in the process of acquiring ischaemic tolerance in ischaemic preconditioned ischaemia-reperfused rat kidneys. Two periods of 3-min occlusion of bilateral renal arteries was performed prior to 30-min bilateral ischaemia and 90-min reperfusion in acute renal denervated or innervated kidneys. The glomerular filtration rate (GFR), fractional excretion of sodium (FENa) and lithium (FELi), and renal blood flow (RBF) were assessed in reperfused kidneys. Ischaemic preconditioning significantly improved values for all these parameters as compared with no treated ischaemia-reperfused kidneys. Denervation caused slight increase in GFR, diuresis and natriuresis without improving RBF after reperfusion. However, protecting effects of ischaemic preconditioning on renal function were disappeared in denervated kidneys, while in innervated kidneys the effects of ischaemic preconditioning were maintained. These results clearly showed that ischaemic preconditioning pre-treatment protects kidneys against ischaemia-reperfusion injury, and the effects are, at least in part, mediated by sympathetic nerves, as the protective effects were abolished by denervation.     

Validity of the microdialysis technique for experimental in vivo studies of myocardial energy metabolism

OBJECTIVES: The validity of the microdialysis technique for experimental in vivo studies of myocardial energy metabolism is not known. To address this question interstitial levels of energy-related metabolites (lactate, adenosine, inosine and hypoxanthine) obtained by the microdialysis technique were compared with corresponding metabolites from myocardial biopsies at given intervals in a porcine heart model using different protocols of ischaemia and reperfusion. METHODS: In an open chest porcine heart model, interstitial levels of energy-related metabolites were monitored using the microdialysis technique. All animals (n = 23) were subjected to 120-min pretreatment followed by 40 min of regional ischaemia and 120 min of reperfusion. Tissue biopsies were obtained in the beginning, middle and at the end of the 40-min ischaemic period and at the end of the reperfusion period. Pretreatment consisted of either rest (group 1, n = 7), or rest for 90 min and one ischaemia/reperfusion (10 + 20 min) cycle (group 2, n = 9), or four ischaemia/reperfusion cycles (10 + 20 min each) (group 3, n = 7). RESULTS: Interstitial levels of energy-related metabolites monitored by the microdialysis technique correlated with tissue biopsy levels of lactate (r = 0.90, P < 0.001), adenosine (r = 0.89, P < 0.001), inosine (r = 0.88, P < 0.001) and hypoxanthine (r = 0.91, P < 0.001), respectively, which were obtained by tissue biopsies at given time intervals. These significant correlations were valid regardless of the functional state of the myocardium. CONCLUSION: We observed significant correlations between microdialysis probe levels and tissue biopsy levels of energy-related metabolites in both ischaemic and non-ischaemic tissue. These data assess the validity of the microdialysis technique (in the current setting) for studying dynamic changes of myocardial energy metabolism.     

Reversibility of mild to moderate ischemic injuries in the isolated rat heart. A characterization by 31P-NMR and by physiological and ultrastructural indices.

We have studied cardiac function, metabolism, and ultrastructure during reperfusion after global ischemia of short duration (6 and 12 minutes) in isolated rat hearts. Our aim was to obtain more detailed information on the reversibility of changes following presumedly mild and moderate ischemic injuries by use of multiple time-based indices. In a modified Langendorff perfusion system, hearts were subjected to 24 minutes of control perfusion and 6 or 12 minutes of ischemia followed by 1.5 or 24 minutes of reperfusion. During the experiments we monitored left ventricular developed pressure (LVDP), heart rate, and coronary flow rate, and intracellular phosphocreatine (PCr), inorganic phosphate (P(i)), pH, and ATP by 31P nuclear magnetic resonance spectroscopy. The number of cells with sarcolemmal and nuclear injuries was counted. Our main findings during 24 minutes of reperfusion following 6 and 12 minutes of ischemia were 80% versus 53% recovery of LVDP at the end of reperfusion, an increased PCr, 80% versus 65% recovery of ATP, and a rapid versus slower recovery of pH. Ultrastructural examination revealed sarcolemmal and unclear abnormalities at the end of ischemia, these alterations being fully (rapidly versus more slowly) reversible during reperfusion. According to these findings, there was a dissociation between an essentially normal ultrastructure, and a depressed recovery of LVDP, reduced ATP, and an overshoot of PCr upon 24 minutes of reperfusion after 12 minutes of ischemia. This may indicate a postischemic dysfunction closely related to stunning.     

Changes in catecholamine, angiotensin converting enzyme and adenosine triphosphatase in ischemic preconditioning rat hearts

Changes in catecholamine ,angiotensin converting enzy me and adenosine triphosphatase in ischemic preconditioning rat hearts     

Post-ischaemic dysfunction does not correlate with release of cardiac troponin T in isolated rat hearts.

Cardiac troponin T (cTnT) is a highly sensitive and specific serum marker of irreversible cardiomyocyte injury. It is not clear whether cTnT also is a suitable marker of subtle, reversible injury. In the present investigation the relationship between cTnT release and function during the first 30 min of reperfusion after 30 min of global ischaemia, was investigated in isolated, retrogradely perfused rat hearts. Left ventricular systolic (LVSP), end-diastolic (LVEDP) and developed (LVDP) pressures, heart rate (HR), and coronary flow (CF) were measured. In one series of experiments (n=7) the kinetics of cTnT release during 30 min of reperfusion was investigated. An early, short-lasting peak of cTnT release appeared after 30 s of reperfusion. Then cTnT release gradually increased with a maximum after 20 min (from 0.08 +/- 0.03 before ischaemia to 2.16 +/- 0.40 ng min-1) (mean +/- SEM). In a second series of experiments (n=52) the relationship between cTnT release and cardiac function was investigated after 20 min of reperfusion. At this time point LVEDP increased (0 to 62 +/- 3 mmHg) and LVDP decreased (84 +/- 2 to 33 +/- 3 mmHg), but without any correlation with cTnT release. cTnT release was positively correlated to LVSP (P < 0.04, r=0.29), and negatively correlated to HR (P < 0.03, r=-0.31). cTnT concentration in the coronary effluent increased in parallel to increasing CF (P < 0.03, r=0.31). In conclusion, during the early reperfusion period there was no consistent correlation between cTnT release and dysfunction after global ischaemia in the isolated rat heart. Release of cTnT and post-ischaemic function appear to provide supplementary information in this particular model.     

Inotropic and chronotropic effects of ischemic postconditioning on the model of isolated heart

The effects of global ischemia (45 min) and reperfusion (30 min) on left-ventricular developed pressure (LVDP), HR, and end-diastolic pressure were studied on isolated perfused rat heart. The following postconditioning protocols were used: 1) 3 cycles of reperfusion (10 sec) and ischemia (10 sec), total cycle duration 20 sec; 2) 6 cycles reperfusion of reperfusion (10 sec) and ischemia (10 sec), total cycle duration 20 sec; 3) 3 cycles of reperfusion (20 sec) and ischemia (20 sec), total cycle duration 40 sec; 4) 6 cycles of reperfusion (20 sec) and ischemia (20 sec), total cycle duration 40 sec; 5) 3 cycles of reperfusion (30 sec) and ischemia (30 sec), total cycle duration 60 sec. The use of several cycles of a total duration of 20 sec had no effect on LVDP, but reduced EDP throughout the reperfusion period. Postconditioning protocol consisting of three 40-sec cycles promoted LVDP recovery during the reperfusion, but had no effect on EDP and decelerated HP normalization. Six 40-sec cycles had no effect on LVDP and EDP, but impeded HR recovery during the reperfusion period. Postconditioning protocol consisting of three 60-sec cycles promoted LVDP increase during the reperfusion and reduced contracture, but these transient effects were accompanied by decelerated HP normalization.     

Additive protective effects of late and early ischaemic preconditioning are mediated by the opening of KATP channels in vivo

We investigated whether a combination of ischaemic late preconditioning (LPC) and ischaemic early preconditioning (EPC) induces additive myocardial protection in vivo, and the role of ATP-sensitive K (KATP) channels in ischaemic LPC and in LPC + EPC. Sixty rabbits were divided into seven groups. Anaesthetized animals were subjected to 30 min of coronary artery occlusion and 120 min of reperfusion (I/R). Controls (CON, n = 9) were not preconditioned. LPC (n = 10) was induced in conscious rabbits by a 5-min period of myocardial ischaemia 24 h before I/R. The KATP channel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg) was given 10 min before I/R with (LPC + 5-HD, n = 9) or without LPC (5-HD, n = 8). EPC (n = 8) was induced by a 5-min period of myocardial ischaemia 10 min before I/R. Animals received LPC and EPC without (LPC + EPC, n = 8) or with 5-HD (LPC + EPC + 5-HD, n = 8). LPC reduced infarct size (IS, triphenyltetrazolium staining) from 57 +/- 11% (MW +/- SD, CON) of the area at risk to 31 +/- 19% (LPC, P = 0.004). 5-HD did not affect IS (5-HD: 60 +/- 12%, P = 0.002 versus LPC), but abolished the cardioprotective effects of LPC (LPC + 5-HD: 62 +/- 18%, P = 0.001 versus LPC). EPC reduced IS to 18 +/- 8%. Additional LPC led to a further reduction to 8 +/- 4% (LPC + EPC, n = 8; P = 0.005 versus EPC; P = 0.004 versus LPC). 5-HD abolished this additional cardioprotective effect of LPC + EPC (LPC + EPC + 5-HD, n = 8; 46 +/- 11%, P < or = 0.001 versus LPC + EPC). We conclude that the combination of ischaemic LPC and EPC induces additive cardioprotection. KATP channel opening mediates the cardioprotective effects of ischaemic LPC and LPC + EPC.