Preconditioning in immature rabbit hearts: role of KATP channels. (1/1173)

BACKGROUND: The protective effects of ischemic preconditioning have been shown to occur in adult hearts of all species studied. We determined whether immature hearts normoxic or chronically hypoxic from birth could be preconditioned, the time window or memory of the cardioprotective effect, and the involvement of the KATP channel. METHODS AND RESULTS: Isolated immature rabbit hearts (7 to 10 days old) were subjected to 0, 1, or 3 cycles of preconditioning consisting of 5 minutes of global ischemia plus 10 minutes of reperfusion. This was followed by 30 minutes of global ischemia and 35 minutes of reperfusion. Normoxic hearts (FIO2=0.21) subjected to 1 cycle of preconditioning recovered 70+/-7% of left ventricular developed pressure compared with 43+/-8% recovery in nonpreconditioned controls. Three cycles of preconditioning did not result in additional recovery (63+/-8%). Hearts from rabbits raised from birth in hypoxic conditions (FIO2=0.12) and subjected to 1 and 3 preconditioning cycles did not show increased recovery (68+/-8% and 65+/-5%) compared with nonpreconditioned hypoxic controls (63+/-9%), although the recovery was greater in chronically hypoxic hearts than in age-matched normoxic controls. Increasing the recovery period after the preconditioning stimulus from 10 to 30 minutes resulted in a loss of cardioprotection. Pretreatment of normoxic hearts for 30 minutes with the KATP channel blocker 5-hydroxydecanoate (300 micromol/L) completely abolished preconditioning (70+/-7% to 35+/-9%) but had no effect on nonpreconditioned hearts (40+/-8%). CONCLUSIONS: Immature hearts normoxic from birth can be preconditioned, whereas immature hearts hypoxic from birth cannot. Preconditioning in normoxic immature hearts is associated with activation of the KATP channel.  (+info)

Morphine preconditioning attenuates neutrophil activation in rat models of myocardial infarction. (2/1173)

Previous results from our laboratory have suggested that morphine can attenuate neutrophil activation in patients with acute myocardial infarction. To elucidate if morphine preconditioning (PC) has the same effects via activation of neutrophil endopeptidase 24.11 (NEP), we measured serum levels of intercellular adhesion molecule-1 (ICAM-1), gp100MEL14 and NEP in adult Wistar rats subjected to ten different protocols (n = 10 for each) at baseline, immediately after and 2 h after morphine PC. All groups were subjected to 30 min of occlusion and 2 h of reperfusion. Similarly, morphine-induced PC was elicited by 3-min drug infusions (100 micrograms/kg) interspersed with 5-min drug-free periods before the prolonged 30-min occlusion. Infarct size (IS), as a percentage of the area at risk (AAR), was determined by triphenyltetrazolium staining. Pretreatment with morphine increased NEP activities (9.86 +/- 1.98 vs. 5.12 +/- 1.10 nmol/mg protein in control group; p < 0.001). Naloxone (mu-opioid receptor antagonist) (4.82 +/- 1.02 nmol/mg protein) and phosphoramidon (NEP inhibitor) (4.66 +/- 1.00 nmol/mg protein) inhibited morphine-activated NEP, whereas glibenclamide (ATP-sensitive potassium channel antagonist) and chelerythrine (protein kinase C inhibitor) had no effects. The ICAM-1 and gp100MEL14 of the third sampling were lowest for those with morphine PC (280 +/- 30 ng/ml and 2.2 +/- 0.7 micrograms/ml; p < 0.001), but naloxone (372 +/- 38 ng/ml and 3.8 +/- 0.9 micrograms/ml) and phosphoramidon (382 +/- 40 ng/ml and 4.2 +/- 1.1 micrograms/ml) abolished the above phenomenon. IS/AAR were definitely lowest for those with morphine PC (24 +/- 7%; p < 0.05). Morphine preconditioning increases NEP activities to attenuate shedding of gp100MEL14 and to ICAM-1 and, thus, provides myocardial protection.  (+info)

Attenuation of myocardial injury due to oxygen free radicals (OFR) by pretreatment with OFR or calcitonin gene-related peptide. (3/1173)

AIM: To study the cardioprotective effects of oxygen free radicals (OFR) and calcitonin gene-related peptide (OGRP) pretreatment on myocardial damages due to OFR in isolated perfused rat heart. METHODS: The hearts were perfused in a Langendorff mode. OFR were generated by electrolysis of Krebs-Henseleit (K-H) solution. RESULTS: OFR pretreatment reduced the impairment of cardiac contractile function, the decrease of coronary flow and the increase of creatinine kinase (CK) release due to OFR, and the effect exhibited period dependence and cycle-dependence. 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), an inhibitor of protein kinase C, abolished the protection of OFR pretreatment (CK release = 110 +/- 7, 215 +/- 23, 169 +/- 14, 240 +/- 30, and 113 +/- 19 kU.L-1 for control, OFR, OFR pretreatment, OFR pretreatment plus H-7, and H-7, respectively). CGRP pretreatment also protected the myocardium damages elicited by OFR in isolated perfused rat heart. CONCLUSIONS: OFR or CGRP pretreatment protected myocardium against injury elicited by OFR, and the effect of OFR pretreatment was related to the activation of PKC.  (+info)

Cardioprotection by opening of the K(ATP) channel in unstable angina. Is this a clinical manifestation of myocardial preconditioning? Results of a randomized study with nicorandil. CESAR 2 investigation. Clinical European studies in angina and revascularization. (4/1173)

AIMS: To assess the anti-ischaemic and anti-arrhythmic effects and overall safety of nicorandil, an ATP sensitive potassium (K+) channel opener, with 'cardioprotective' effects, in patients with unstable angina. METHODS: In a multicentre, randomized, double-blind, parallel-group, placebo-controlled study, oral nicorandil 20 mg twice daily or a matching placebo was administered for a minimum of 48 h to patients admitted with unstable angina. Treatment was standardized to include, where tolerated, oral aspirin, a beta-blocker and diltiazem. Continuous Holter ECG monitoring was performed for 48 h to assess the frequency and duration of transient myocardial ischaemia and any tachyarrhythmia, as the predefined end-points of the study. A pain chart recorded the incidence and severity of chest pain throughout the study period. Patients with myocardial infarction identified retrospectively from troponin-T analysis were excluded. RESULTS: Two hundred and forty-five patients were recruited into the study. Forty-three patients were excluded with an index diagnosis of myocardial infarction, two were not randomized and 12 had unsatisfactory tape data. In the remaining 188 patients, six out of 89 patients (6.7%) on nicorandil experienced an arrhythmia, compared with 17 out of 99 patients (17.2%) on placebo (P=0.04). Three nicorandil patients experienced three runs of non-sustained ventricular tachycardia compared to 31 runs in 10 patients on placebo (P=0.087 patients; P<0.0001 runs). Three nicorandil patients had four runs of supraventricular tachycardia, compared to 15 runs in nine patients on placebo (P=0.14 patients; P=0.017 runs). Eleven (12.4%) patients on nicorandil had 37 episodes of transient myocardial ischaemia (mostly silent) compared with 74 episodes in 21 (21.2%) patients on placebo (P=0.12 patients; P=0.0028 episodes). In the overall safety analysis, which included all patients who received at least one dose of study medication, there were no significant differences in the rates of myocardial infarction or death between the nicorandil or placebo-treated groups. CONCLUSIONS: Nicorandil, added to aggressive anti-anginal treatment for unstable angina, reduces transient myocardial ischaemia, non-sustained ventricular, and supraventricular arrhythmia compared to placebo. The anti-arrhythmic activity with nicorandil is probably a secondary effect resulting from its anti-ischaemic action and we suggest that this may be related to its effect on the ATP sensitive potassium channel causing pharmacological preconditioning.  (+info)

Mechanisms of isoflurane-induced myocardial preconditioning in rabbits. (5/1173)

BACKGROUND: Isoflurane has cardioprotective effects that mimic the ischemic preconditioning phenomenon. Because adenosine triphosphate-sensitive potassium channels and adenosine receptors are implicated in ischemic preconditioning, the authors wanted to determine whether the preconditioning effect of isoflurane is mediated through these pathways. METHODS: Myocardial infarct size was measured in seven groups of propofol-anesthetized rabbits, each subjected to 30 min of anterolateral coronary occlusion followed by 3 h of reperfusion. Groups differed only in the pretreatments given, and controls received no pretreatment. An ischemia-preconditioned group was pretreated with 5 min of coronary occlusion and 15 min of reperfusion. An isoflurane-preconditioned group was pretreated with 15 min end-tidal isoflurane, 1.1%, and then 15 min of washout. An isoflurane-plus-glyburide group was administered 0.33 mg/kg glyburide intravenously before isoflurane pretreatment. An isoflurane plus 8-(p-sulfophenyl)-theophylline (SPT) group received 7.5 mg/kg SPT intravenously before isoflurane. Additional groups were administered identical doses of glyburide or SPT, but they were not pretreated with isoflurane. Infarct size and area at risk were defined by staining. Data were analyzed by analysis of variance or covariance. RESULTS: Infarct size, expressed as a percentage of the area at risk (IS:AR) was 30.2+/-11% (SD) in controls. Ischemic preconditioning and isoflurane preexposure reduced myocardial infarct size significantly, to 8.3+/-5% and 13.4+/-8.2% (P<0.05), respectively. Both glyburide and SPT pretreatment eliminated the preconditioning-like effect of isoflurane (IS:AR = 30.0+/-9.1% and 29.2+/-12.6%, respectively; P = not significant). Neither glyburide nor SPF alone increased infarct size (IS:AR = 33.9+/-7.6% and 31.8+/-12.7%, respectively; P = not significant). CONCLUSIONS: Glyburide and SPT abolished the preconditioning-like effects of isoflurane but did not increase infarct size when administered in the absence of isoflurane. Isoflurane-induced preconditioning and ischemia-induced preconditioning share similar mechanisms, which include activation of adenosine triphosphate-sensitive potassium channels and adenosine receptors.  (+info)

Effects of K(ATP) channel blockade by glibenclamide on the warm-up phenomenon. (6/1173)

AIMS: The increased tolerance to myocardial ischaemia observed during the second of two sequential exercise tests, i.e. the warm-up phenomenon, has been proposed as a clinical model of ischaemic preconditioning. As ATP-sensitive K+ channels appear to be a mediator of ischaemic preconditioning in both experimental and clinical studies, the aim of this study was to investigate the role of K(ATP) channels in the warm-up phenomenon. METHODS AND RESULTS: Twenty-six patients with coronary artery disease were randomized to receive 10 mg oral glibenclamide, a selective ATP-sensitive K+ channel blocker, or placebo. Sixty minutes after glibenclamide or placebo administration, patients were given an infusion of 10% dextrose (8 ml x min(-1)) to correct glucose plasma levels or, respectively, an infusion of saline at the same infusion rate. Thirty minutes after the beginning of the infusions, both patient groups underwent two consecutive treadmill exercise tests, with a recovery period of 15 min to re-establish baseline conditions. Before exercise tests, blood glucose levels were similar in placebo and glibenclamide groups (96 +/- 10 vs 105 +/- 22 mg x 100 ml(-1), P=ns). After placebo administration, rate-pressure product at 1.5 mm ST-segment depression significantly increased during the second exercise test compared to the first (220 +/- 41 vs 186 +/- 29 beats x min(-1) x mmHg x 10(2), P<0.01), but it did not change after glibenclamide (191 +/- 34 vs 187 +/- 42 beats x min(-1) x mmHg x 10(2), P=ns), with a significant drug-test interaction (P=0.0091, at two-way ANOVA). CONCLUSIONS: Glibenclamide, at a dose previously shown to abolish ischaemic preconditioning during coronary angioplasty, prevents the increase of ischaemic threshold observed during the second of two sequential exercise tests. These findings confirm that ischaemic preconditioning plays a key role in the warm-up phenomenon and that in this setting is, at least partially, mediated by activation of ATP-sensitive K+ channels.  (+info)

Isoform-selective activation of protein kinase C by nitric oxide in the heart of conscious rabbits: a signaling mechanism for both nitric oxide-induced and ischemia-induced preconditioning. (7/1173)

Although isoform-selective translocation of protein kinase C (PKC) epsilon appears to play an important role in the late phase of ischemic preconditioning (PC), the mechanism(s) responsible for such translocation remains unclear. Furthermore, the signaling pathway that leads to the development of late PC after exogenous administration of NO in the absence of ischemia (NO donor-induced late PC) is unknown. In the present study we tested the hypothesis that NO activates PKC and that this is the mechanism for the development of both ischemia-induced and NO donor-induced late PC. A total of 95 chronically instrumented, conscious rabbits were used. In rabbits subjected to ischemic PC (six 4-minute occlusion/4-minute reperfusion cycles), administration of the NO synthase inhibitor Nomega-nitro-L-arginine (group III), at doses previously shown to block the development of late PC, completely blocked the ischemic PC-induced translocation of PKCepsilon but not of PKCeta, indicating that increased formation of NO is an essential mechanism whereby brief ischemia activates the epsilon isoform of PKC. Conversely, a translocation of PKCepsilon and -eta quantitatively similar to that induced by ischemic PC could be reproduced pharmacologically with the administration of 2 structurally unrelated NO donors, diethylenetriamine/NO (DETA/NO) and S-nitroso-N-acetylpenicillamine (SNAP), at doses previously shown to elicit a late PC effect. The particulate fraction of PKCepsilon increased from 35+/-2% of total in the control group (group I) to 60+/-1% after ischemic PC (group II) (P<0.05), to 54+/-2% after SNAP (group IV) (P<0.05) and to 52+/-2% after DETA/NO (group V) (P<0.05). The particulate fraction of PKCeta rose from 66+/-5% in the control group to 86+/-3% after ischemic PC (P<0.05), to 88+/-2% after SNAP (P<0.05) and to 85+/-1% after DETA/NO (P<0.05). Neither ischemic PC nor NO donors had any appreciable effect on the subcellular distribution of PKCalpha, -beta1, -beta2, -gamma, -delta, - micro, or -iota/lambda; on total PKC activity; or on the subcellular distribution of total PKC activity. Thus, the effects of SNAP and DETA/NO on PKC closely resembled those of ischemic PC. The DETA/NO-induced translocation of PKCepsilon (but not that of PKCeta) was completely prevented by the administration of the PKC inhibitor chelerythrine at a dose of 5 mg/kg (group VI) (particulate fraction of PKCepsilon, 38+/-4% of total, P<0.05 versus group V; particulate fraction of PKCeta, 79+/-2% of total). The same dose of chelerythrine completely prevented the DETA/NO-induced late PC effect against both myocardial stunning (groups VII through X) and myocardial infarction (groups XI through XV), indicating that NO donors induce late PC by activating PKC and that among the 10 isozymes of PKC expressed in the rabbit heart, the epsilon isotype is specifically involved in the development of this form of pharmacological PC. In all groups examined (groups I through VI), the changes in the subcellular distribution of PKCepsilon protein were associated with parallel changes in PKCepsilon isoform-selective activity, whereas total PKC activity was not significantly altered. Taken together, the results provide direct evidence that isoform-selective activation of PKCepsilon is a critical step in the signaling pathway whereby NO initiates the development of a late PC effect both after an ischemic stimulus (endogenous NO) and after treatment with NO-releasing agents (exogenous NO). To our knowledge, this is also the first report that NO can activate PKC in the heart. The finding that NO can promote isoform-specific activation of PKC identifies a new biological function of this radical and a new mechanism in the signaling cascade of ischemic PC and may also have important implications for other pathophysiological conditions in which NO is involved and for nitrate therapy.  (+info)

Is the development of myocardial tolerance to repeated ischemia in humans due to preconditioning or to collateral recruitment? (8/1173)

OBJECTIVES: The purpose of this study in patients with quantitatively determined, poorly developed coronary collaterals was to assess the contribution of ischemic as well as adenosine-induced preconditioning and of collateral recruitment to the development of tolerance against repetitive myocardial ischemia. BACKGROUND: The development of myocardial tolerance to repeated ischemia is nowadays interpreted to be due to biochemical adaptation (i.e., ischemic preconditioning). METHODS: In 30 patients undergoing percutaneous transluminal coronary angioplasty, myocardial adaptation to ischemia was measured using intracoronary (i.c.) electrocardiographic (ECG) ST segment elevation changes obtained from a 0.014-in. (0.036 cm) pressure guidewire positioned distal to the stenosis during three subsequent 2-min balloon occlusions. Simultaneously, an i.c. pressure-derived collateral flow index (CFI, no unit) was determined as the ratio between distal occlusive minus central venous pressure divided by the mean aortic minus central venous pressure. The study patients were divided into two groups according to the pretreatment with i.c. adenosine (2.4 mg/min for 10 min starting 20 min before the first occlusion, n = 15) or with normal saline (control group, n = 15). RESULTS: Collateral flow index at the first occlusion was not different between the groups (0.15 +/- 0.10 in the adenosine group and 0.13 +/- 0.11 in the control group, p = NS), and it increased significantly and similarly to 0.20 +/- 0.14 and to 0.19 +/- 0.10, respectively (p < 0.01) during the third occlusion. The i.c. ECG ST elevation (normalized for the QRS amplitude) was not different between the two groups at the first occlusion (0.25 +/- 0.13 in the adenosine group, 0.25 +/- 0.19 in the control group). It decreased significantly during subsequent coronary occlusions to 0.20 +/- 0.15 and to 0.17 +/- 0.13, respectively. There was a correlation between the change in CFI (first to third occlusion; deltaCFI) and the respective ST elevation shift (deltaST): deltaST = -0.02 to 0.78 x deltaCFI; r = 0.54, p = 0.02. CONCLUSIONS: Even in patients with few coronary collaterals, the myocardial adaptation to repetitive ischemia is closely related to collateral recruitment. Pharmacologic preconditioning using a treatment with i.c. adenosine before angioplasty does not occur. The variable responses of ECG signs of ischemic adaptation to collateral channel opening suggest that ischemic preconditioning is a relevant factor in the development of ischemic tolerance.  (+info)