Adenosine-enhanced ischemic preconditioning provides enhanced postischemic recovery and limitation of infarct size in the rabbit heart

Conditioning-induced cardioprotection: Aging as a confounding factor

The aging process induces a plethora of changes in the body including alterations in hormonal regulation and metabolism in various organs including the heart. Aging is associated with marked increase in the vulnerability of the heart to ischemia-reperfusion injury. Furthermore, it significantly hampers the development of adaptive response to various forms of conditioning stimuli (pre/post/remote conditioning). Aging significantly impairs the activation of signaling pathways that mediate preconditioning-induced cardioprotection. It possibly impairs the uptake and release of adenosine, decreases the number of adenosine transporter sites and down-regulates the transcription of adenosine receptors in the myocardium to attenuate adenosine-mediated cardioprotection. Furthermore, aging decreases the expression of peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α) and subsequent transcription of catalase enzyme which subsequently increases the oxidative stress and decreases the responsiveness to preconditioning stimuli in the senescent diabetic hearts. In addition, in the aged rat hearts, the conditioning stimulus fails to phosphorylate Akt kinase that is required for mediating cardioprotective signaling in the heart. Moreover, aging increases the concentration of Na⁺ and K⁺, connexin expression and caveolin abundance in the myocardium and increases the susceptibility to ischemia-reperfusion injury. In addition, aging also reduces the responsiveness to conditioning stimuli possibly due to reduced kinase signaling and reduced STAT-3 phosphorylation. However, aging is associated with an increase in MKP-1 phosphorylation, which dephosphorylates (deactivates) mitogen activated protein kinase that is involved in cardioprotective signaling. The present review describes aging as one of the major confounding factors in attenuating remote ischemic preconditioning-induced cardioprotection along with the possible mechanisms.

Hyperkalemic cardioplegia for adult and pediatric surgery: end of an era?

Despite surgical proficiency and innovation driving low mortality rates in cardiac surgery, the disease severity, comorbidity rate, and operative procedural difficulty have increased. Today's cardiac surgery patient is older, has a "sicker" heart and often presents with multiple comorbidities; a scenario that was relatively rare 20 years ago. The global challenge has been to find new ways to make surgery safer for the patient and more predictable for the surgeon. A confounding factor that may influence clinical outcome is high K(+) cardioplegia. For over 40 years, potassium depolarization has been linked to transmembrane ionic imbalances, arrhythmias and conduction disturbances, vasoconstriction, coronary spasm, contractile stunning, and low output syndrome. Other than inducing rapid electrochemical arrest, high K(+) cardioplegia offers little or no inherent protection to adult or pediatric patients. This review provides a brief history of high K(+) cardioplegia, five areas of increasing concern with prolonged membrane K(+) depolarization, and the basic science and clinical data underpinning a new normokalemic, "polarizing" cardioplegia comprising adenosine and lidocaine (AL) with magnesium (Mg(2+)) (ALM™). We argue that improved cardioprotection, better outcomes, faster recoveries and lower healthcare costs are achievable and, despite the early predictions from the stent industry and cardiology, the "cath lab" may not be the place where the new wave of high-risk morbid patients are best served.

On-pump inhibition of es-ENT1 nucleoside transporter and adenosine deaminase during aortic crossclamping entraps intracellular adenosine and protects against reperfusion injury: role of adenosine A1 receptor

OBJECTIVE

The inhibition of adenosine deaminase with erythro-9 (2-hydroxy-3-nonyl)-adenine (EHNA) and the es-ENT1 transporter with p-nitro-benzylthioinosine (NBMPR), entraps myocardial intracellular adenosine during on-pump warm aortic crossclamping, leading to a complete recovery of cardiac function and adenosine triphosphate (ATP) during reperfusion. The differential role of entrapped intracellular and circulating adenosine in EHNA/NBMPR-mediated protection is unknown. Selective (8-cyclopentyl-1,3-dipropyl-xanthine) or nonselective [8-(p-sulfophenyl)theophyline] A1 receptor antagonists were used to block adenosine A1-receptor contribution in EHNA/NBMPR-mediated cardiac recovery.

METHODS

Anesthetized dogs (n = 45), instrumented to measure heart performance using sonomicrometry, were subjected to 30 minutes of warm aortic crossclamping and 60 minutes of reperfusion. Three boluses of the vehicle (series A) or 100 μM EHNA and 25 μM NBMPR (series B) were infused into the pump at baseline, before ischemia and before reperfusion. 8-Cyclopentyl-1,3-dipropyl-xanthine (10 μM) or 8-(p-sulfophenyl)theophyline (100 μM) was intra-aortically infused immediately after aortic crossclamping distal to the clamp in series A and series B. The ATP pool and nicotinamide adenine dinucleotide was determined using high-performance liquid chromatography.

RESULTS

Ischemia depleted ATP in all groups by 50%. The adenosine/inosine ratios were more than 10-fold greater in series B than in series A (P < .001). ATP and function recovered in the EHNA/NBMPR-treated group (P < .05 vs control group). 8-Cyclopentyl-1,3-dipropyl-xanthine and 8-(p-sulfophenyl)theophyline partially reduced cardiac function in series A and B to the same degree but did not abolish the EHNA/NBMPR-mediated protection in series B.

CONCLUSIONS

In addition to the cardioprotection mediated by activation of the adenosine receptors by extracellular adenosine, EHNA/NBMPR entrapment of intracellular adenosine provided a significant component of myocardial protection despite adenosine A1 receptor blockade.

Matching coronary blood flow to myocardial oxygen consumption

At rest the myocardium extracts approximately 75% of the oxygen delivered by coronary blood flow. Thus there is little extraction reserve when myocardial oxygen consumption is augmented severalfold during exercise. There are local metabolic feedback and sympathetic feedforward control mechanisms that match coronary blood flow to myocardial oxygen consumption. Despite intensive research the local feedback control mechanism remains unknown. Physiological local metabolic control is not due to adenosine, ATP-dependent K(+) channels, nitric oxide, prostaglandins, or inhibition of endothelin. Adenosine and ATP-dependent K(+) channels are involved in pathophysiological ischemic or hypoxic coronary dilation and myocardial protection during ischemia. Sympathetic beta-adrenoceptor-mediated feedforward arteriolar vasodilation contributes approximately 25% of the increase in coronary blood flow during exercise. Sympathetic alpha-adrenoceptor-mediated vasoconstriction in medium and large coronary arteries during exercise helps maintain blood flow to the vulnerable subendocardium when cardiac contractility, heart rate, and myocardial oxygen consumption are high. In conclusion, several potential mediators of local metabolic control of the coronary circulation have been evaluated without success. More research is needed.

Mitochondrial ATP-sensitive potassium channels in surgical cardioprotection

ATP-sensitive potassium channels allow for the coupling of membrane potential to cellular metabolic status. Two K(ATP) channel subtypes coexist in the myocardium with one subtype located in the sarcolemma membrane and the other in the inner membrane of the mitochondria. The ATP-sensitive potassium channels can be pharmacologically modulated by a family of structurally diverse agents of varied potency and selectivity, collectively known as potassium channel openers and blockers. Sufficient evidence exists to indicate that the ATP-sensitive potassium channels and in particular the mitochondrial ATP-sensitive potassium channels play an important role both as a trigger and an effector in surgical cardioprotection. In this review, the biochemistry and specificity of the ATP-sensitive potassium channels is examined in relation to surgical cardioprotection.

Adenosine in myocardial protection in on-pump and off-pump cardiac surgery

Adenosine is most well known for its potent vasodilation of the vasculature. However, it also promotes glycolysis, and activates potassium-sensitive adenosine triphosphate (K(ATP)) channels. Adenosine also strongly inhibits neutrophil function such as superoxide anion production, protease release, and adherence to coronary endothelial cells. Hence adenosine attenuates ischemic injury as well as neutrophil-mediated reperfusion injury. Adenosine has also been implicated in the cardioprotective phenomenon of ischemic preconditioning. Accordingly experimental evidence shows that adenosine reduces postischemic injury when administered before ischemia and at the onset of reperfusion. Clinical studies in cardiology and cardiac surgery show cardioprotective trends with adenosine treatment but the effects are not as dramatic as those reported by experimental studies.

Long-term treatment with nipradilol, a nitric oxide-releasing beta-adrenergic blocker, enhances postischemic recovery and limits infarct size

BACKGROUND

This study examines whether the chronic administration of nipradilol, a nitric oxide-releasing beta-adrenergic blocker, decreases ischemia-reperfusion injury.

METHODS

Rats were treated with nipradilol (10 mg/kg per day orally) or a vehicle alone for 4 weeks. Isolated rat hearts were assigned to one of five groups (each n = 6): global ischemia groups treated with the vehicle or with nipradilol were subjected to 20 minutes of ischemia; ischemic preconditioning groups treated with the vehicle or with nipradilol were subjected to 3 minutes of ischemic preconditioning; and the L-arginine group treated with the vehicle received 1 mmol/L of L-arginine before global ischemia. Hemodynamic variables and coronary flow were recorded continuously. Nitrites and nitrates levels were measured 60 minutes after reperfusion, and the infarct size was determined. In another series (each n = 6), lipid peroxidation was investigated.

RESULTS

In the nipradilol group, significant preservation of the left ventricular pressure and coronary flow, as well as the level of nitrates and nitrites, was observed, compared with the global ischemia group. The infarct size was also significantly reduced in the ischemic preconditioning (23.5%+/-5.47%), L-arginine (25.6%+/-5.59%), and especially the nipradilol (10.7%+/-1.65%) groups. However, in the nipradilol plus ischemic preconditioning group, the protective effects were eliminated. Lipid peroxidation after nipradilol treatment was significantly reduced before and after global ischemia, compared with the global ischemia group.

CONCLUSIONS

The chronic administration of nipradilol improves postischemic functional recovery and infarct size, partly by preventing the formation of lipid peroxides. These cardioprotective effects were, however, abolished by ischemic preconditioning.

Effects of NHE-1 inhibition on cardioprotection and impact on protection by K/Mg cardioplegia

BACKGROUND

Cardiac sodium hydrogen exchanger isoform-1 (NHE-1) activity during ischemia/reperfusion contributes to myocardial injury. The effects of NHE-1 inhibition during ischemia or reperfusion and on the protection afforded by K/Mg cardioplegia was unknown.

METHODS

Rabbit hearts were used for Langendorff perfusion. Control hearts were perfused for 180 minutes. Global ischemia (GI) hearts received 30 minutes normothermic global ischemia and 120 minutes reperfusion. K/Mg hearts received cardioplegia 5 minutes before ischemia. Separate groups of GI and K/Mg hearts received the NHE-1 inhibitor, HOE-642, before ischemia (HOE-642-I), at the immediate start of reperfusion (HOE-642-R), or both before ischemia and at the immediate start of reperfusion (HOE-642-IR).

RESULTS

Left ventricular peak developed pressure was significantly increased in HOE-I, HOE-R, and HOE-IR throughout reperfusion (p < 0.05 versus GI). Infarct size was significantly decreased (p < 0.05 versus GI) in all groups, but was significantly increased in HOE-R as compared with HOE-IR (p < 0.05). NHE-1 inhibition with K/Mg cardioplegia significantly decreased left ventricular peak developed pressure after 90 minutes of reperfusion (p < 0.05 versus K/Mg), with no significant effect on infarct size.

CONCLUSIONS

NHE-1 inhibition used alone provides cardioprotection with optimal effects being observed with HOE-IR. NHE-1 inhibition with K/Mg cardioplegia decreases postischemic functional recovery during late reperfusion.

Adenosine-enhanced ischemic preconditioning modulates necrosis and apoptosis: effects of stunning and ischemia-reperfusion

BACKGROUND

Adenosine-enhanced ischemic preconditioning extends the protection of ischemic preconditioning by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery.

METHODS

The effects of adenosine-enhanced ischemic preconditioning on necrosis and apoptosis were investigated in the sheep heart using models of stunning (15 minutes regional ischemia, 120 minutes reperfusion) and ischemia-reperfusion (30 and 60 minutes regional ischemia, 120 minutes reperfusion). Ischemic preconditioned hearts received 5 minutes regional ischemia, 5 minutes reperfusion before ischemia. Adenosine-enhanced ischemic preconditioned hearts received a 10 mmol/L adenosine bolus (10 mL) through the left atrium coincident with ischemic preconditioning. Adenosine hearts received a 10 mmol/L bolus (10 mL) of adenosine. Regional ischemic hearts received no pretreatment.

RESULTS

Minimal apoptosis (< 45 per 3,000 myocytes) was observed in the stunning models but was significantly increased with ischemia-reperfusion in regional ischemic hearts after 30 minutes (p < 0.05 versus ischemic preconditioning, adenosine, or adenosine-enhanced ischemic preconditioning) and in adenosine and ischemic preconditioned hearts after 60 minutes ischemia (p < 0.05 versus adenosine-enhanced ischemic preconditioning). DNA laddering was apparent after 60 minutes ischemia in regional ischemia, adenosine, and ischemic preconditioning but not in adenosine-enhanced ischemic preconditioned hearts.

CONCLUSIONS

Adenosine-enhanced ischemic preconditioning significantly ameliorates necrosis and apoptosis in the regional ischemic blood-perfused heart.

L-Arginine given after ischaemic preconditioning can enhance cardioprotection in isolated rat hearts

OBJECTIVE

Ischaemic or pharmacological preconditioning with L-arginine has been reported to be insufficient for optimal cardioprotection. The ability of nitric oxide (NO) to enhance ischaemic preconditioning was assessed, and the role of L-arginine-induced ischaemic preconditioning in myocardial protection was determined.

METHODS

Isolated rat hearts were prepared and divided into six groups: control hearts (control, n=6) were perfused without global ischaemia at 37 degrees C for 160 min; global ischaemia hearts (GI, n=6) were subjected to ischaemia for 20 min and reperfusion for 120 min; ischaemic preconditioned hearts (IP, n=6) received 2 min of zero-flow global ischaemia followed by 5 min reperfusion, before 20 min of global ischaemia; L-arginine hearts (ARG, n=6) received 1 mmol/l L-arginine for 5 min, before 20 min of global ischaemia; ischaemic preconditioning plus nitro-L-arginine methyl ester hearts (IP+L-NAME, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 3 mmol/l L-NAME in Krebs-Henseleit buffer, before 20 min of global ischaemia; and ischaemic preconditioning plus L-arginine hearts (IP+ARG, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 1 mmol/l L-arginine in Krebs-Henseleit buffer. Haemodynamic parameters and coronary flow were recorded continuously. Nitrites and nitrates (NOx) were measured 5 and 60 min after reperfusion, and infarct size was also determined.

RESULTS

In the IP+ARG group, significant amelioration and preservation of left ventricular peak developed pressure and coronary flow was observed compared with the GI, IP, ARG and IP+L-NAME groups. Infarct size in the IP+ARG group was reduced significantly compared with that in the GI, IP, ARG and IP+L-NAME groups. Significant preservation of NOx was observed during reperfusion in the IP+ARG group compared with the GI group.

CONCLUSIONS

Inhibition of NO synthase with L-NAME had little impact on ischaemic preconditioning, suggesting that endogenous NO is not a major mediator of ischaemic preconditioning. Nevertheless, enhancement of the effects of ischaemic preconditioning can be achieved with L-arginine, a precursor of NO, improving post-ischaemic functional recovery and infarct size in the isolated rat heart.

Opening of mitochondrial ATP-sensitive potassium channels enhances cardioplegic protection

BACKGROUND

Mitochondrial and sarcolemmal ATP-sensitive potassium channels have been implicated in cardioprotection; however, the role of these channels in magnesium-supplemented potassium (K/Mg) cardioplegia during ischemia or reperfusion is unknown.

METHODS

Rabbit hearts (n = 76) were used for Langendorff perfusion. Sham hearts were perfused for 180 minutes. Global ischemia hearts received 30 minutes of global ischemia and 120 minutes of reperfusion. K/Mg hearts received cardioplegia before ischemia. The role of ATP-sensitive potassium channels in K/Mg cardioprotection during ischemia and reperfusion was investigated, separately using the selective mitochondrial ATP sensitive potassium and channel blocker, 5-hydroxydecanoate, and the selective sarcolemmal ATP-sensitive potassium channel blocker HMR1883. Separate studies were performed using the selective mitochondrial ATP-sensitive potassium channel opener, diazoxide, and the nonselective ATP-sensitive potassium channel opener pinacidil.

RESULTS

Infarct size was 1.9%+/-0.4% in sham, 3.7%+/-0.5% in K/Mg, and 27.8%+/-2.4% in global ischemia hearts (p < 0.05 versus K/Mg). Left ventricular peak-developed pressure (percent of equilibrium) at the end of 120 minutes of reperfusion was 91%+/-6% in sham, 92% +/-2% in K/Mg, and 47%+/-6% in global ischemia (p < 0.05 versus K/Mg). Blockade of sarcolemmal ATP-sensitive potassium channels in K/Mg hearts had no effect on infarct size or left ventricular peak-developed pressure. However, blockade of mitochondrial ATP-sensitive potassium channels before ischemia significantly increased infarct size to 23%+/-2% in K/Mg hearts (p < 0.05 versus K/Mg; no statistical significance [NS] as compared to global ischemia) and significantly decreased left ventricular peak-developed pressure to 69%+/-4% (p < 0.05 versus K/Mg). Diazoxide when added to K/Mg cardioplegia significantly decreased infarct size to 1.5%+/-0.4% (p < 0.05 versus K/Mg).

CONCLUSIONS

The cardioprotection afforded by K/Mg cardioplegia is modulated by mitochondrial ATP-sensitive potassium channels. Diazoxide when added to K/Mg cardioplegia significantly reduces infarct size, suggesting that the opening of mitochondrial ATP-sensitive potassium channels with K/Mg cardioplegic protection would allow for enhanced myocardial protection in cardiac operations.

Adenosine-enhanced ischemic preconditioning: adenosine receptor involvement during ischemia and reperfusion

Adenosine-enhanced ischemic preconditioning (APC) extends the cardioprotection of ischemic preconditioning (IPC) by both significantly decreasing myocardial infarct size and significantly enhancing postischemic functional recovery. In this study, the role of adenosine receptors during ischemia-reperfusion was determined. Rabbit hearts (n = 92) were used for Langendorff perfusion. Control hearts were perfused for 180 min, global ischemia hearts received 30-min ischemia and 120-min reperfusion, and IPC hearts received 5-min ischemia and 5-min reperfusion before ischemia. APC hearts received a bolus injection of adenosine coincident with IPC. Adenosine receptor (A(1), A(2), and A(3)) antagonists were used with APC before ischemia and/or during reperfusion. GR-69019X (A(1)/A(3)) and MRS-1191/MRS-1220 (A(3)) significantly increased infarct size in APC hearts when administered before ischemia and significantly decreased functional recovery when administered during both ischemia and reperfusion (P < 0.05 vs. APC). DPCPX (A(1)) administered either before ischemia and/or during reperfusion had no effect on APC cardioprotection. APC-enhanced infarct size reduction is modulated by adenosine receptors primarily during ischemia, whereas APC-enhanced postischemic functional recovery is modulated by adenosine receptors during both ischemia and reperfusion.

Differential role of sarcolemmal and mitochondrial K(ATP) channels in adenosine-enhanced ischemic preconditioning

Adenosine-enhanced ischemic preconditioning (APC) extends the protection afforded by ischemic preconditioning (IPC) by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery. The purpose of this study was to determine whether APC is modulated by ATP-sensitive potassium (K(ATP)) channels and to determine whether this modulation occurs before ischemia or during reperfusion. The role of K(ATP) channels before ischemia (I), during reperfusion (R), or during ischemia and reperfusion (IR) was investigated using the nonspecific K(ATP) blocker glibenclamide (Glb), the mitochondrial (mito) K(ATP) channel blocker 5-hydroxydecanoate (5-HD), and the sarcolemmal (sarc) K(ATP) channel blocker HMR-1883 (HMR). Infarct size was significantly increased (P < 0.05) in APC hearts with Glb-I, Glb-R, and 5-HD-I treatment and partially with 5-HD-R. Glb-I and Glb-R treatment significantly decreased APC functional recovery (P < 0.05 vs. APC), whereas 5-HD-I and 5-HD-R had no effect on APC functional recovery. HMR-IR significantly decreased postischemic functional recovery (P < 0.05 vs. APC) but had no effect on infarct size. These data indicate that APC infarct size reduction is modulated by mitoK(ATP) channels primarily during ischemia and suggest that functional recovery is modulated by sarcK(ATP) channels during ischemia and reperfusion.

Preconditioning the Brain and Heart: Implications for Cardiac Surgery

Despite many recent advances in emboli detection, aortic imaging, myocardial preservation, and perfusion equipment, ischemic injury to the heart and brain remains a serious complications after cardiac surgery. Hypoperfusion (particularly in the heart) and microem boli (particularly in the brain) during cardiopulmonary bypass constitute the etiology of ischemia. Although hypothermia has traditionally been the mainstay for systemic protection from transient ischemia, there has been a general trend to accept warmer heart and core temperatures during bypass, which increases the poten tial for ischemic injury to various organs. This article discusses recent advances in the understanding of myocardial and brain preconditioning and their poten tial role to provide additional protection during cardiac surgery.

Phentolamine prevents the adverse effects of adenosine on glycolysis and mechanical function in isolated working rat hearts subjected to antecedent ischemia

Adenosine inhibits glycolysis from exogenous glucose, reduces proton production and enhances post-ischemic left ventricular minute work (LV work) following ischemia in isolated working rat hearts perfused with glucose and fatty acids. In hearts partially depleted of glycogen by antecedent ischemic stress (AIS)--two cycles of ischemia (10 min) and reperfusion (5 min)--adenosine stimulates rather than inhibits glycolysis, increases proton production and worsens recovery of post-ischemic LV work. We determined if the switch in adenosine effect on glycolysis and recovery of LV work following ischemia in hearts subject to AIS was due to the reduction in glycogen content per se or because of alpha-adrenoceptor stimulation. One series of hearts underwent a 35-min period of substrate-free Langendorff perfusion (substrate-free glycogen depletion; SFGD) and a second series of hearts was subjected to AIS. Both series of hearts had a similar glycogen content (approximately 70 micromol/g dry wt) prior to drug treatment. In SFGD hearts perfused aerobically, adenosine (500 microM) inhibited glycolysis from exogenous glucose and reduced proton production. In SFGD hearts reperfused after prolonged ischemia, adenosine exerted similar effects on glucose metabolism and enhanced recovery of post-ischemic LV work (87.2 +/- 2.2% of preischemic values) relative to untreated hearts (25.9 +/- 13.3% of preischemic values). In AIS hearts perfused aerobically or subject to ischemia and reperfusion, phentolamine (1 microM) given in combination with adenosine, prevented adenosine-induced stimulation of glycolysis from exogenous glucose and reduced calculated proton production from glucose. Recoveries of post-ischemic LV work in AIS hearts for untreated, adenosine, phentolamine and adenosine/phentolamine groups were 34.4 +/- 11.4%, 8.6 +/- 3.9%, 16.3 +/- 13.5% and 73.2 +/- 13.1% respectively, of preischemic values. Glycogen depletion in the absence of ischemia does not switch the effect of adenosine from inhibition to stimulation of glycolysis or alter the cardioprotective properties of adenosine in hearts subject to ischemia and reperfusion. The detrimental switch in the metabolic and cardioprotective effects of adenosine, in hearts subject to AIS, can be prevented by phentolamine, an alpha-adrenoceptor antagonist. These data support the concept that modulation of glucose metabolism is an important factor in the mechanical functional recovery of the post-ischemic heart.

Alternatives for myocardial protection: adenosine-enhanced ischemic preconditioning

Intrinsic to the development of new myoprotective protocols for use in cardiac surgery are the requirements of new protocols to be equal to or better than conventional cardioplegia in providing for enhanced post-ischemic functional recovery and decreased myocardial infarct size. Our data suggest that adenosine-enhanced ischemic preconditioning, in which a bolus injection of adenosine to the myocardium is used coincident with ischemic preconditioning, meets these requirements, providing equal cardioprotection as that of cold blood cardioplegia, significantly decreasing myocardial infarct size and significantly enhancing post-ischemic myocardial functional recovery in both the isolated perfused rabbit heart and in the in situ blood-perfused sheep heart. These results further suggest that adenosine-enhanced ischemic preconditioning may provide an effective, alternative myocardial protective protocol to reduce the morbidity and mortality in cardiac surgery.

Adenosine-enhanced ischemic preconditioning provides myocardial protection equal to that of cold blood cardioplegia

BACKGROUND

We recently described a novel myoprotective protocol-adenosine-enhanced ischemic preconditioning (APC)-that extends the protection of ischemic preconditioning (IPC) by both reducing myocardial infarct size and enhancing postischemic functional recovery in the isolated perfused heart. In the present report the efficacy of APC in the blood-perfused heart was investigated and compared with that of cold blood cardioplegia (CBC).

METHODS

Cardiopulmonary bypass was instituted in 21 sheep hearts. The APC hearts (n = 6) received a bolus injection of adenosine through the aortic root at the immediate start of IPC (5 minutes of zero-flow global ischemia, followed by 5 minutes of reperfusion) before 30 minutes of global ischemia and 120 minutes of reperfusion. Nine other hearts received CBC. A control group (n = 6) received IPC only.

RESULTS

Infarct size was significantly decreased (p<0.01) in the APC (3.0%+/-0.8%) and CBC (2.6%+/-0.2%) hearts compared with the IPC hearts (16.3%+/-1.6%). The preload recruitable stroke work relation, mean arterial pressure, and the time constant of pressure decay (tau) were significantly preserved (p<0.05) in APC and CBC hearts compared with IPC hearts. No significant differences were observed between APC and CBC hearts.

CONCLUSIONS

Use of APC is as effective as CBC in significantly decreasing infarct size and enhancing post-ischemic functional recovery.

Adenosine-enhanced ischemic preconditioning provides enhanced cardioprotection in the aged heart

BACKGROUND

Recently we have reported a novel myo-protective protocol "adenosine-enhanced ischemic preconditioning" (APC), which extends and amends the protection afforded by ischemic preconditioning (IPC) by both reducing myocardial infarct size and enhancing postischemic functional recovery in the mature rabbit heart. However, the efficacy of APC in the senescent myocardium was unknown.

METHODS

The efficacy of APC was investigated in senescent rabbit hearts and compared with magnesium-supplemented potassium cardioplegia (K/Mg) and IPC. Global ischemia (GI) hearts were subjected to 30 minutes of global ischemia and 120 minutes of reperfusion. Ischemic preconditioning hearts received 5 minutes of global ischemia and 5 minutes of reperfusion before global ischemia. Magnesium-supplemented potassium cardioplegia hearts received cardioplegia just before global ischemia. Adenosine-enhanced ischemic preconditioning hearts received a bolus injection of adenosine in concert with IPC. To separate the effects of adenosine from that of APC, a control group (ADO) received a bolus injection of adenosine 10 minutes before global ischemia.

RESULTS

Infarct size was significantly decreased to 18.9%+/-2.7% with IPC (p<0.05 versus GI); 17.0%+/-1.0% with ADO (p<0.05 versus GI); 7.7%+/-1.3% with K/Mg (p<0.05 versus GI, IPC, and ADO); and 2.1%+/-0.6% with APC (p<0.05 versus GI, IPC, ADO, and K/Mg; not significant versus control). Only APC and K/Mg significantly enhanced postischemic functional recovery (not significant versus control).

CONCLUSIONS

Adenosine-enhanced ischemic preconditioning provides similar protection to K/Mg cardioplegia, significantly enhancing postischemic functional recovery and decreasing infarct size in the senescent myocardium.