Potent adenylate cyclase agonist forskolin restores myoprotective effects of ischemic preconditioning in rat hearts after myocardial infarction

BACKGROUND: The purpose of this study was to determine whether ischemic preconditioning (IPC) provides myoprotective effects in post-myocardial infarction (MI) hearts, and whether beta adrenergic signaling is involved in IPC. METHODS: Rats were subjected to either ligation of the left anterior descending coronary artery (LAD) resulting in MI, or a sham operation. Two weeks later, hearts were isolated and perfused. Six groups (n = 7 each) were studied: group 1, control (sham operation); group 2, sham operation + IPC; group 3, post-MI; group 4, post-MI + IPC; group 5, post-MI + forskolin; group 6, post-MI + forskolin + IPC. IPC consisted of two cycles of 5 minutes of global ischemia. The adenylate cyclase agonist forskolin (1.0 x 10(-5) M) was administered in post-MI hearts either alone (group 5) or for 5 minutes before IPC (group 6). All hearts were then subjected to 20 minutes of global ischemia followed by 120 minutes of reperfusion, after which infarct size was measured. Concentrations of endogenous catecholamines and myocardial mRNA expression of beta 2 adrenergic receptor were measured in the post-MI model. RESULTS: (1) IPC reduced infarct size in shams, from 34.7 +/- 5.2% in group 1 to 21.4 +/- 3.8% in group 2, but did not affect infarct size in post-MI hearts (group 3 versus group 4). (2) Forskolin combined with IPC reduced infarct size in post-MI hearts to 29.3 +/- 3.4% (group 6), but not in group 5 where the value was 39.3 +/- 4.8%. (3) Beta 2 adrenergic receptor mRNA expression in post-MI hearts was significantly decreased as compared with sham-operated animals. CONCLUSIONS: The results indicate that downregulation of beta adrenergic receptors in post-MI hearts may be associated with ineffectiveness of IPC, and that beta adrenergic signaling, especially in relation to adenylate cyclase activation, may be required to generate the IPC response in post-MI hearts.     

Differences in prolonged ischemia length using ischemic preconditioning in the rabbit heart. Tolerable limitation time for surgically induced myocardial ischemia during normothermic cardiac operation

BACKGROUND: To determine the effect of the tolerable limitation time of prolonged ischemia after ischemic preconditioning on postischemic functional recovery and infarct size reduction in the rabbit heart. METHODS: White rabbits (n=30) were used for Langendorff perfusion. Control hearts were perfused at 37 degrees C for 180 min; 30 min global ischemia hearts (30GI) received 30 min global ischemia and 120 min reperfusion; IPC+30GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 30 min global ischemia; 20 min global ischemia hearts (20GI) received 20 min global ischemia and 120 min reperfusion; IPC+20GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 20 min global ischemia. RESULTS: Infarct size in the 30GI hearts was 33.5+/-4.0% and 1.7+/-0.5% in the control hearts. The 20GI hearts and IPC+30GI hearts decreased infarct size, as compared with the 30GI hearts (13.0+/-1.8% and 16.6+/-1.7%, respectively; p<0.001, 20GI vs 30GI; p<0.01, IPC+30GI vs 30GI; p>0.05, 20GI vs IPC+30GI) but did not enhance postischemic functional recovery. The IPC+20GI hearts (3.5+/-0.6%) significantly decreased infarct size as compared with the 20GI hearts (p<0.05, IPC+20GI vs 20GI), and there was no significant difference between the IPC+20GI and the control hearts (p>0.05), but the IPC+20GI hearts did not enhance postischemic functional recovery. CONCLUSIONS: A 20 min ischemia may be the tolerable limitation time of prolonged ischemia after ischemic preconditioning in an isolated rabbit heart model.     

Mitochondrial ATP-sensitive potassium channel plays a dominant role in ischemic preconditioning of rabbit heart

BACKGROUND: The ATP-sensitive potassium (K(ATP)) channel has been shown to be important in the ischemic preconditioning (IPC) response. Recently, the mitochondrial rather than the sarcolemmal K(ATP) channel has been focused on due to its energy-modulating property. Hence, this study was undertaken to elucidate the role of the mitochondrial K(ATP) channel in IPC by modulating the mitochondrial K(ATP) channel in isolated perfused rabbit hearts. METHODS: Seven hearts served as a control with no interventions. Seven hearts underwent IPC consisting of two 5-min cycles of global ischemia followed by 5 min of reperfusion. Seven hearts received the selective mitochondrial K(ATP) channel blocker 5-dehydroxydecanoate (5-HD, 100 microM) for 5 min before IPC, and 7 hearts received the selective mitochondrial K(ATP) channel opener diazoxide (50 microM) for 5 min. Then, all hearts were subjected to 1 h of left anterior descending coronary artery ischemia and 1 h of reperfusion. Left ventricular pressures, monophasic action potentials and coronary flow were measured throughout the experiment and infarct size was detected at the end of experiment. RESULTS: (1) The mitochondria-selective K(ATP) channel opener diazoxide reduced infarct size as compared to control (p < 0.05); (2) IPC reduced infarct size and preserved postischemic diastolic function as compared to control (p < 0.05), and (3) the mitochondria-selective K(ATP) channel blocker 5-HD reversed these effects. CONCLUSION: The mitochondrial ATP-sensitive potassium channel may be a potential site of cardioprotection.     

Does adenosine administration during the early reperfusion period affect ischemic preconditioning?

We hypothesized that the adenosine administration during the early reperfusion period might affect ischemic preconditioning (IPC) and might reduce infarct size and enhance post-ischemic functional recovery. Twenty-four anesthetized rabbits underwent 30 min. normothermic global ischemia with 120 min. reperfusion in a buffer-perfused isolated, paced heart model and divided into four groups. Global ischemic hearts (GI, n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n=6) were subjected to perfusion without ischemia. Ischemic preconditioned hearts (IPC, n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. IPC + Ado hearts (n=6) received IPC and adenosine administration (100 m mol/L) during 3 min. early reperfusion period. Post-ischemic functional recovery was better in IPC + Ado hearts as compared to GI and IPC hearts, but the effect of post-ischemic functional recovery in IPC + Ado hearts became weaker during 120 min. reperfusion after prolong ischemic insult. Infarct size wre 1.0 ± 0.3% in Control hearts, 32.9 ± 5.1% in GI hearts, 13.8 ± 1.3% in IPC hearts and 8.1 ± 0.9% in IPC + Ado hearts. Infarct size in IPC hearts was significantly decreased (p<0.01) as compared to GI hearts. The reduction rate against myocardial necrosis in IPC + Ado hearts versus GI hearts was higher as compared to IPC hearts versus GI hearts (p<0.001, IPC+Ado hearts vs GI hearts; p<0.01, IPC hearts vs GI hearts; p = ns, IPC + Ado hearts vs Control hearts). These data suggest that adenosine administration during the early reperfusion period reinforce IPC effect and reduce myocardial reperfusion injury. Cardiomyoprotective effects of IPC and exogenous adenosine are exerted during early reperfusion after coronary occlusion in the isolated perfused rabbit hearts.     

Oral hypoglycemic sulfonylurea glimepiride preserves the myoprotective effects of ischemic preconditioning

BACKGROUND: To investigate whether the sulfonylurea glimepiride affects the myoprotective effects of ischemic preconditioning (IPC), isolated rabbit hearts were perfused with Krebs-Henseleit solution. METHODS: Eight hearts underwent IPC consisting of two cycles of 5 min global ischemia and reperfusion. Six hearts received a 5-min infusion of 10 microM glimepiride, six hearts received a 5-min infusion of 50 microM glimepiride, and seven hearts received a 5-min infusion of 10 microM glibenclamide before IPC. Seven hearts received a 5-min infusion of the selective mitochondrial K(ATP) channel opener diazoxide (50 microM). Other hearts received a 5-min infusion of 10 microM glimepiride (n = 6), 50 microM glimepiride (n = 6), or 10 microM glibenclamide (n = 7) before diazoxide. Seven hearts served as a control. All groups then were subjected to 1 h of regional ischemia, followed by 1 h of reperfusion. LV pressures, monophasic action potential duration (APD(50)), and infarct size were measured. RESULTS: Both IPC and diazoxide significantly prolonged APD(50) and preserved diastolic function at 60 min of reperfusion compared to control. In addition, both groups reduced infarct size compared to control. Glibenclamide, but not glimepiride reversed these effects. CONCLUSION: Glimepiride offers less cardiovascular effects than glibenclamide, possibly due to its lower affinity for the mitochondrial K(ATP) channels.     

Amrinone preconditioning in the isolated perfused rabbit heart

BACKGROUND: Ischemic preconditioning (IPC) reduces infarct size in experimental preparations. IPC, however, is not without detrimental effects. We studied amrinone as a possible alternative to IPC. METHODS: Isolated perfused rabbit hearts were given a 5-minute infusion of 10 micromol/L amrinone followed by a 5-minute washout (n = 6). The anterior descending artery was then occluded for 1 hour and reperfused for 1 hour. Six hearts underwent IPC, with two episodes of 5-minute global ischemia followed by 5-minute reperfusion before LAD occlusion; eight control hearts received no preconditioning. Left ventricular pressure and ischemic zone epicardial monophasic action potentials were continuously monitored. RESULTS: IPC but not amrinone reduced peak pressure before anterior descending artery occlusion. Peak pressure fell significantly during ischemia and reperfusion in all hearts. End diastolic pressure rose significantly during reperfusion in control and IPC hearts but not in amrinone hearts. Action potentials shortened during ischemia in all hearts. They returned to preocclusion values in control hearts but lasted beyond preocclusion values in IPC and amrinone hearts. Both the incidences of ventricular fibrillation and infarct size were significantly reduced in amrinone hearts but not in IPC hearts. CONCLUSIONS: Amrinone is not only a useful inotropic agent but is also a superior preconditioning agent when compared to IPC.     

Sevoflurane preconditioning before moderate hypothermic ischemia protects against cytosolic [Ca(2+)] loading and myocardial damage in part via mitochondrial K(ATP) channels

BACKGROUND: Brief sevoflurane exposure and washout (sevoflurane preconditioning [SPC]) before 30-min global ischemia at 37 degrees C is known to improve cardiac function, decrease cytosolic [Ca(2+)] loading, and reduce infarct size on reperfusion. It is not known if anesthetic preconditioning (APC) applies as well to hypothermic ischemia and reperfusion and if K(ATP) channels are involved. The authors examined in guinea pig isolated hearts the effect of sevoflurane exposure before 4-h global ischemia at 17 degrees C on cardiac function, cytosolic [Ca(2+)] loading, and infarct size. In addition they tested the potential role of the mitochondrial K(ATP) channel in eliciting the cardioprotection by SPC. METHODS: Hearts were randomly assigned to (1) a nontreated hypothermic ischemia group (CON), (2) a group given 3.5 vol% sevoflurane for 15 min with a 15-min washout before hypothermic ischemia (SPC), and (3) an SPC group in which anesthetic exposure was bracketed with 200 microm 5-hydroxydecanoate (5-HD) from 5 min before until 5 min after sevoflurane (SPC + 5-HD). Cytosolic [Ca(2+)] was measured in the left ventricular (LV) free wall with the intracellularly loaded fluorescence probe indo-1. RESULTS: Initial reperfusion in CON hearts markedly increased systolic and diastolic [Ca(2+)] and reduced contractility (dLVP/dt(max)), relaxation (diastolic LVP, dLVP/dt(min)), myocardial oxygen consumption (MvO(2)), and cardiac efficiency. In SPC hearts, cytosolic [Ca(2+)] overloading (especially diastolic [Ca(2+)]) was decreased with increased myocardial [Ca(2+)] influx (d[Ca(2+)]/dt(max)) and efflux (d[Ca(2+)]/dt(min)), improved contractility, relaxation, coronary flow, MvO(2), cardiac efficiency, and decreased infarct size. In SPC + 5HD hearts, the reduction in infarct size was antagonized by 5-HD, but functional return was less affected by 5-HD. CONCLUSIONS: Anesthetic preconditioning occurs after long-term hypothermic ischemia, and the infarct size reduction is the result, in part, of mitochondrial K(ATP) channel opening.     

Sevoflurane mimics ischemic preconditioning effects on coronary flow and nitric oxide release in isolated hearts.

BACKGROUND: Like ischemic preconditioning, certain volatile anesthetics have been shown to reduce the magnitude of ischemia/ reperfusion injury via activation of K+ adenosine triphosphate (ATP)-sensitive (K(ATP)) channels. The purpose of this study was (1) to determine if ischemic preconditioning (IPC) and sevoflurane preconditioning (SPC) increase nitric oxide release and improve coronary vascular function, as well as mechanical and electrical function, if given for only brief intervals before global ischemia of isolated hearts; and (2) to determine if K(ATP) channel antagonism by glibenclamide (GLB) blunts the cardioprotective effects of IPC and SPC. METHODS: Guinea pig hearts were isolated and perfused with Krebs-Ringer's solution at 55 mm Hg and randomly assigned to one of seven groups: (1) two 2-min total coronary occlusions (preconditioning, IPC) interspersed with 5 min of normal perfusion; (2) two 2-min occlusions interspersed with 5 min of perfusion while perfusing with GLB (IPC+GLB); (3) SPC (3.5%) for two 2-min periods; (4) SPC+GLB for two 2-min periods; (5) no treatment before ischemia (control [CON]); (6) CON+GLB; and (7) no ischemia (time control). Six minutes after ending IPC or SPC, hearts of ischemic groups were subjected to 30 min of global ischemia and 75 min of reperfusion. Left-ventricular pressure, coronary flow, and effluent NO concentration ([NO]) were measured. Flow and NO responses to bradykinin, and nitroprusside were tested 20-30 min before ischemia or drug treatment and 30-40 min after reperfusion. RESULTS: After ischemia, compared with before (percentage change), left-ventricular pressure and coronary flow, respectively, recovered to a greater extent (P<0.05) after IPC (42%, 77%), and treatment with SPC (45%, 76%) than after CON (30%, 65%), IPC+GLB (24%, 64%), SPC+GLB (20%, 65%), and CON+GLB (28%, 64%). Bradykinin and nitroprusside increased [NO] by 30+/-5 (means +/- SEM) and 29+/-4 nM, respectively, averaged for all groups before ischemia. [NO] increased by 26+/-6 and 27+/-7 nM, respectively, in SPC and IPC groups after ischemia, compared with an average [NO] increase of 8+/-5 nM (P<0.01) after ischemia in CON and each of the three GLB groups. Flow increases to bradykinin and nitroprusside were also greater after SPC and IPC. CONCLUSIONS: Preconditioning with sevoflurane, like IPC, improves not only postischemic contractility, but also basal flow, bradykinin and nitroprusside-induced increases in flow, and effluent [NO] in isolated hearts. The protective effects of both SPC and IPC are reversed by K(ATP) channel antagonism.     

Sevoflurane Mimics Ischemic Preconditioning Effects on Coronary Flow and Nitric Oxide Release in Isolated Hearts

Background: Like ischemic preconditioning, certain volatile anesthetics have been shown to reduce the magnitude of ischemia/ reperfusion injury viaactivation of K+ adenosine triphosphate (ATP)-sensitive (KATP) channels. The purpose of this study was (1) to determine if ischemic preconditioning (IPC) and sevoflurane preconditioning (SPC) increase nitric oxide release and improve coronary vascular function, as well as mechanical and electrical function, if given for only brief intervals before global ischemia of isolated hearts; and (2) to determine if KATP channel antagonism by glibenclamide (GLB) blunts the cardioprotective effects of IPC and SPC.

Methods: Guinea pig hearts were isolated and perfused with Krebs-Ringer's solution at 55 mmHg and randomly assigned to one of seven groups: (1) two 2-min total coronary occlusions (preconditioning, IPC) interspersed with 5 min of normal perfusion; (2) two 2-min occlusions interspersed with 5 min of perfusion while perfusing with GLB (IPC+GLB); (3) SPC (3.5%) for two 2-min periods; (4) SPC+GLB for two 2-min periods; (5) no treatment before ischemia (control [CON]); (6) CON+GLB; and (7) no ischemia (time control). Six minutes after ending IPC or SPC, hearts of ischemic groups were subjected to 30 min of global ischemia and 75 min of reperfusion. Left-ventricular pressure, coronary flow, and effluent NO concentration ([NO]) were measured. Flow and NO responses to bradykinin, and nitroprusside were tested 20-30 min before ischemia or drug treatment and 30-40 min after reperfusion.

Results: After ischemia, compared with before (percentage change), left-ventricular pressure and coronary flow, respectively, recovered to a greater extent (P < 0.05) after IPC (42%, 77%), and treatment with SPC (45%, 76%) than after CON (30%, 65%), IPC+GLB (24%, 64%), SPC+GLB (20%, 65%), and CON+GLB (28%, 64%). Bradykinin and nitroprusside increased [NO] by 30 +/- 5 (means +/- SEM) and 29 +/-4 nM, respectively, averaged for all groups before ischemia. [NO] increased by 26 +/- 6 and 27 +/- 7 nM, respectively, in SPC and IPC groups after ischemia, compared with an average [NO] increase of 8 +/- 5 nM (P < 0.01) after ischemia in CON and each of the three GLB groups. Flow increases to bradykinin and nitroprusside were also greater after SPC and IPC.     

Supplementing preservation solution with mitochondria‐targeted H2S donor AP39 protects cardiac grafts from prolonged cold ischemia–reperfusion injury in heart transplantation

Heart transplant has been accepted as the standard treatment for end‐stage heart failure. Because of its susceptibility to ischemia–reperfusion injury, the heart can be preserved for only 4 to 6 hours in cold static preservation solutions. Prolonged ischemia time is adversely associated with primary graft function and long‐term survival. New strategies to preserve donor hearts are urgently needed. We demonstrate that AP39, a mitochondria‐targeting hydrogen sulfide donor, significantly increases cardiomyocyte viability and reduces cell apoptosis/death after cold hypoxia/reoxygenation in vitro. It also decreases gene expression of proinflammatory cytokines and preserves mitochondria function. Using an in vivo murine heart transplant model, we show that preserving donor hearts with AP39‐supplemented University of Wisconsin solution (n = 7) significantly protects heart graft function, measured by quantitative ultrasound scan, against prolonged cold ischemia–reperfusion injury (24 hours at 4°C), along with reducing tissue injury and fibrosis. Our study demonstrates that supplementing preservation solution with AP39 protects cardiac grafts from prolonged ischemia, highlighting its therapeutic potential in preventing ischemia–reperfusion injury in heart transplant.     

Sevoflurane Preconditioning before Moderate Hypothermic Ischemia Protects against Cytosolic [Ca2+] Loading and Myocardial Damage in Part via Mitochondrial KATP Channels

Background: Brief sevoflurane exposure and washout (sevoflurane preconditioning [SPC]) before 30-min global ischemia at 37[degrees]C is known to improve cardiac function, decrease cytosolic [Ca2+] loading, and reduce infarct size on reperfusion. It is not known if anesthetic preconditioning (APC) applies as well to hypothermic ischemia and reperfusion and if KATP channels are involved. The authors examined in guinea pig isolated hearts the effect of sevoflurane exposure before 4-h global ischemia at 17[degrees]C on cardiac function, cytosolic [Ca2+] loading, and infarct size. In addition they tested the potential role of the mitochondrial KATP channel in eliciting the cardioprotection by SPC.

Methods: Hearts were randomly assigned to (1) a nontreated hypothermic ischemia group (CON), (2) a group given 3.5 vol% sevoflurane for 15 min with a 15-min washout before hypothermic ischemia (SPC), and (3) an SPC group in which anesthetic exposure was bracketed with 200 [mu]m 5-hydroxydecanoate (5-HD) from 5 min before until 5 min after sevoflurane (SPC + 5-HD). Cytosolic [Ca2+] was measured in the left ventricular (LV) free wall with the intracellularly loaded fluorescence probe indo-1.

Results: Initial reperfusion in CON hearts markedly increased systolic and diastolic [Ca2+] and reduced contractility (dLVP/dtmax), relaxation (diastolic LVP, dLVP/dtmin), myocardial oxygen consumption (Mvo2), and cardiac efficiency. In SPC hearts, cytosolic [Ca2+] overloading (especially diastolic [Ca2+]) was decreased with increased myocardial [Ca2+] influx (d[Ca2+]/dtmax) and efflux (d[Ca2+]/dtmin), improved contractility, relaxation, coronary flow, Mvo2, cardiac efficiency, and decreased infarct size. In SPC + 5HD hearts, the reduction in infarct size was antagonized by 5-HD, but functional return was less affected by 5-HD.     

Preconditioning the diabetic heart: the importance of Akt phosphorylation

Conflicting evidence exists whether diabetic myocardium can be protected by ischemic preconditioning (IPC). The phosphatidylinositol 3-kinase (PI3K)-Akt pathway is important in IPC. However, components of this cascade have been found to be defective in diabetes. We hypothesize that IPC in diabetic hearts depends on intact signaling through the PI3K-Akt pathway to reduce myocardial injury. Isolated perfused Wistar (normal) and Goto-Kakizaki (diabetic) rat hearts were subjected to 1) 35 min of regional ischemia and 120 min of reperfusion with infarct size determined; 2) preconditioning (IPC) using 5 min of global ischemia followed by 10 min of reperfusion performed one, two, or three times before prolonged ischemia; or 3) determination of Akt phosphorylation after stabilization or after one and three cycles of IPC. In Wistar rats, one, two, and three cycles of IPC reduced infarct size 44.7 +/- 3.8% (P < 0.05), 31.4 +/- 4.9% (P < 0.01), and 34.3 +/- 6.1% (P < 0.01), respectively, compared with controls (60.7 +/- 4.5%). However, in diabetic rats only three cycles of IPC significantly reduced infarction to 20.8 +/- 2.6% from 46.6 +/- 5.2% in controls (P < 0.01), commensurate with significant Akt phosphorylation after three cycles of IPC. To protect the diabetic myocardium, it appears necessary to increase the IPC stimulus to achieve the threshold for cardioprotection and a critical level of Akt phosphorylation to mediate myocardial protection.     

Pharmacological preconditioning with the adenosine triphosphate-sensitive potassium channel opener pinacidil

BACKGROUND: Ischemic preconditioning (IPC) decreases infarct size after global or regional ischemia. Potassium channel openers also precondition but are subject to dose-limiting vasodilation. We compared the mechanical and electrophysiological effects of ischemic and pharmacological preconditioning in an isolated rabbit heart model. METHODS: Rabbit hearts were preconditioned with either 10 micromol/L pinacidil alone (P-), 10 micromol/L pinacidil with 10 micromol/L phenylephrine (P+), or two cycles of global ischemia and reperfusion (IPC) before 1 hour of LAD occlusion. Left ventricular pressure, epicardial monophasic action potential duration (APD) and coronary flow were monitored throughout. Infarct size was determined at the end of reperfusion. RESULTS: Regional ischemia uniformly decreased APD (p<0.05). During reperfusion, APDs were prolonged beyond preischemic values in all preconditioned groups (p<0.05). P- and P+ reduced the incidence of fibrillation. P- significantly increased coronary flow (+15%, p = 0.001), whereas IPC and P+ did not. However, IPC and P- significantly decreased systolic function (p<0.05) but P+ did not. In addition, IPC depressed diastolic function (p<0.05) but P- and P+ did not. Infarct size was reduced by all methods (p<0.05). CONCLUSIONS: Pinacidil presents a safe and effective alternative to IPC for preserving the heart during regional ischemia. Its coronary vasodilatory effects are safely and effectively reversed by the addition of phenylephrine.     

Deletion of endothelial nitric oxide synthase exacerbates myocardial stunning in an isolated mouse heart model

BACKGROUND: While endothelial nitric oxide synthase (eNOS) is an important regulator of vascular tone, it is also constitutively expressed in cardiac myocytes and contributes to the regulation of myocardial function. The role of eNOS in ischemia-reperfusion is uncertain, however, with some studies showing beneficial effects while other studies demonstrate increased cardiac injury. We hypothesized that the beneficial effects of eNOS would predominate, and thus that targeted deletion of eNOS would exacerbate myocardial dysfunction following ischemia-reperfusion. MATERIALS AND METHODS: ENOS knockout and wild-type mouse hearts were Langendorff-perfused using Krebs bicarbonate buffer and subjected to 20 min of global normothermic ischemia followed by 30 min of reperfusion. Myocardial function was measured using a ventricular balloon to determine time to onset of contracture, left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP), and rate-pressure product (RPP). RESUKTS: Heart rate and coronary resistance were similar in both groups during baseline and reperfusion periods. Diastolic function as determined by peak LVEDP during ischemia and final LVEDP after reperfusion were worse in the eNOS knockout group vs wild-type (114 and 31 mmHg vs 92 and 18 mmHg, P <.05). Although RPP (heart rate x LVDP), measured as an index of systolic function, was initially better in eNOS knockouts (24216 vs 16353), wild-type hearts recovered more function than did eNOS knockout hearts by the end of 30 min of reperfusion (30892 vs 20522, P <.05). CONCLUSIONS: These data suggest that the deletion of eNOS results in increased myocardial dysfunction following ischemia-reperfusion in an isolated heart model.     

In vivo chronic carvedilol treatment in rats attenuates ex vivo regional infarction of the heart

OBJECTIVE: Carvedilol is an alpha-and beta-blocking agent with antioxidant properties. We examined if treatment with carvedilol in vivo protected the heart against ischemic injury ex vivo. METHODS: Isolated hearts from treated rats (80 mg/kg/day) were subjected to 30 min regional ischemia. Hearts from non-treated animals received either no drug, 10 min carvedilol (1 microM) acute or ischemic preconditioning (IP) by 5 min ischemia +5 min reperfusion prior to regional ischemia. In separate experiments isolated hearts were subjected to 15 min global ischemia and 30 min reperfusion. RESULTS: Infarct size was significantly reduced by ischemic preconditioning or by chronic carvedilol treatment (9.0+/-0.9% and 7.2+/-1.9% of risk zone infarcted, respectively, vs. 33.8+/-6.4% in control hearts, mean+/-SEM, p < 0.05). Recovery of left ventricular developed pressure after global ischemia was not improved by carvedilol. Post-ischemic rise in left ventricular end diastolic pressure was, however, attenuated by chronic carvedilol treatment. CONCLUSION: Chronic in vivo but not acute ex vivo pretreatment with carvedilol significantly limited infarct size in isolated rat hearts.     

Increasing heart size and age attenuate anesthetic preconditioning in guinea pig isolated hearts

Anesthetic preconditioning (APC) reduces myocardial ischemia/reperfusion injury. Recent investigations have reported that older hearts are not susceptible to APC. We investigated if increasing heart size with age determines the susceptibility to APC in young guinea pigs. Langendorff-prepared guinea pig hearts of different weights (1.1-2.2 g) and ages (2-7 wks) were exposed to 1.3 mM sevoflurane for 15 min followed by 30 min washout (APC; n = 20) before 30 min global ischemia and 120 min reperfusion. Control hearts (n = 20) were not subject to APC. Left ventricular pressure was measured isovolumetrically and infarct size was determined by triphenyltetrazolium staining. Functional data were not different between groups at the beginning of the experiments nor did they correlate with heart weight or age. At 120 min reperfusion, left ventricular pressure, coronary flow, and tissue viability showed significant negative correlations with increasing heart weight and age in APC but not in control hearts; i.e., APC improved function and attenuated infarct size better in smaller/younger hearts than in larger/older hearts. Thus, increasing age and heart size attenuate the susceptibility for APC even in younger guinea pigs. This may have important implications for further basic science research and the possible clinical applicability of APC in humans.     

Reduced efficacy of volatile anesthetic preconditioning with advanced age in isolated rat myocardium

BACKGROUND: Ischemic preconditioning and anesthetic preconditioning (APC) are reported to decrease myocardial infarct size during ischemia-reperfusion injury. However, the beneficial effects of ischemic preconditioning have been shown to decrease with advancing age. Although the mechanisms of ischemic preconditioning and APC are thought to be similar, it is not known whether the beneficial effects of APC are also reduced in the aged myocardium. METHODS: Male Fischer 344 rats of three age groups (2-4, 10-12, and 20-24 months) were used. Hearts were Langendorff perfused. Six hearts in each age group were pretreated with 10 min of sevoflurane and a 5-min washout before 25 min of ischemia and 60 min of reperfusion. Six control hearts in each age group received no treatment before ischemia. Nuclear magnetic resonance was used to measure intracellular Na, intracellular Ca, and intracellular pH, respectively. Left ventricular developed pressure, creatine kinase, and infarct size were measured. RESULTS: Ischemia decreases intracellular pH and increases intracellular Na and intracellular Ca in all age groups. APC blunts the pH decreases in young adult and middle-aged rats, but not in aged rats. APC decreased intracellular Na and intracellular Ca accumulation during ischemia in young adult and middle-aged hearts. APC improved adenosine triphosphate recovery in young rats but not in aged rats. Creatine kinase and infarct sizes were significantly reduced and left ventricular developed pressure was improved with APC in the young adult and middle-aged groups but not the aged group. CONCLUSIONS: The benefits of APC are significantly reduced with advanced age in an isolated rat heart model.     

钙预适应在心肌内源性保护机制中的应用

目的 观察钙离子变化对心肌保护作用的影响。方法 将５６只雄性ＳＤ大鼠随机分为７组,Ａ：缺血对照（ＩＣ）组;Ｂ：短暂无镍复钙灌流（ＣＰＣ）组,Ｃ：短暂缺血复灌（ＩＰＣ）组,Ｄ：短暂无钙复钙灌流十维拉帕米（ＣＰＣ＋Ｖｅｒａ）组,Ｅ：短暂缺血复灌十维拉帕米（ＩＰＣ＋Ｖｅｒａ）组;Ｆ：钙通道激动剂（Ｂａｙ Ｋ８６４４）组;Ｇ：Ｌ－型钙通道阻滞剂〖维拉帕米（ｖｅｒａｐａｍｉｌ）〗组。实验中观察缺血前及再灌后     

Reduced Efficacy of Volatile Anesthetic Preconditioning with Advanced Age in Isolated Rat Myocardium

Background: Ischemic preconditioning and anesthetic preconditioning (APC) are reported to decrease myocardial infarct size during ischemia-reperfusion injury. However, the beneficial effects of ischemic preconditioning have been shown to decrease with advancing age. Although the mechanisms of ischemic preconditioning and APC are thought to be similar, it is not known whether the beneficial effects of APC are also reduced in the aged myocardium.

Methods: Male Fischer 344 rats of three age groups (2-4, 10-12, and 20-24 months) were used. Hearts were Langendorff perfused. Six hearts in each age group were pretreated with 10 min of sevoflurane and a 5-min washout before 25 min of ischemia and 60 min of reperfusion. Six control hearts in each age group received no treatment before ischemia. Nuclear magnetic resonance was used to measure intracellular Na, intracellular Ca, and intracellular pH, respectively. Left ventricular developed pressure, creatine kinase, and infarct size were measured.

Results: Ischemia decreases intracellular pH and increases intracellular Na and intracellular Ca in all age groups. APC blunts the pH decreases in young adult and middle-aged rats, but not in aged rats. APC decreased intracellular Na and intracellular Ca accumulation during ischemia in young adult and middle-aged hearts. APC improved adenosine triphosphate recovery in young rats but not in aged rats. Creatine kinase and infarct sizes were significantly reduced and left ventricular developed pressure was improved with APC in the young adult and middle-aged groups but not the aged group.