The Pathophysiology of Myocardial Ischemia and Perioperative Myocardial Infarction.

Ischemic heart disease, the leading cause of death worldwide, may result in devastating perioperative ischemia and infarction. The underlying pathophysiology, precipitating factors, and approach to prevention differ between patients presenting for noncardiac surgery, developing acute coronary syndrome versus stable angina. The first half of this article reviews the pathophysiology of acute coronary syndrome and stable angina. Acute coronary syndrome, otherwise known as Type 1 myocardial infarction, includes unstable angina, non-ST segment elevated myocardial infarction and ST segment elevated myocardial infarction. Acute coronary syndrome occurs as a result of vulnerable plaque rupture with subsequent varying degrees of thrombus formation, arterial spasm, and thus coronary occlusion. Stable angina, on the other hand, results from a myocardial oxygen delivery and demand mismatch in the setting of fixed coronary stenosis. After this discussion, the review article considers how both apply to perioperative myocardial infarctions and myocardial injury after noncardiac surgery. This article furthermore argues why myocardial oxygen delivery demand mismatch (Type 2) myocardial infarction is the most likely underlying pathophysiology responsible for perioperative myocardial infarctions. Being aware of this and knowledgeable about Type 2 infarctions may enable anesthetic providers to better predict the majority of triggers contributing to, and thus decreasing the incidence of, perioperative myocardial infarctions.

Myocardial susceptibility to ischaemia/reperfusion in obesity: a re-evaluation of the effects of age.

BACKGROUND: Reports on the effect of age and obesity on myocardial ischaemia/reperfusion (I/R) injury and ischaemic preconditioning are contradictory. The aim of this study was to re-evaluate the effects of age and diet-induced obesity (DIO) on myocardial I/R injury and preconditioning potential. METHODS: Four groups of Wistar male rats were used: age-matched controls (AMC) receiving standard rat chow for (i) 16 weeks and (ii) 16 months respectively; DIO rats receiving a sucrose-supplemented diet for (iii) 16 weeks and (iv) 16 months respectively. The ages of groups (i) and (iii) were 22 weeks ("young") and groups (ii) and (iv) 17 months ("middle-aged") at time of experimentation. Isolated perfused working hearts were subjected to 35 min regional ischaemia/1 h reperfusion. Endpoints were infarct size (tetrazolium staining) and functional recovery. Hearts were preconditioned by 3 × 5 min ischaemia/5 min reperfusion. Results were processed using GraphPad Prism statistical software. RESULTS: Age did not affect baseline heart function before induction of ischaemia and I/R damage as indicated by infarct size and similar values were obtained in hearts from both age groups. Age also had no effect on functional recovery of hearts during reperfusion after regional ischaemia in AMC rats, but cardiac output during reperfusion was better in hearts from middle-aged than young DIO rats. The diet reduced infarct size in hearts from young rats (% of area at risk: AMC: 32.4 ± 3.6; DIO: 20.7 ± 2.9, p < 0.05), with no differences in hearts from middle-aged rats (AMC: 24.6 ± 4.6; DIO: 28.3 ± 13.5, p = NS). Compared to their respective AMC, diet-induced obesity had no significant effect on functional recovery of hearts from both age groups after exposure to regional ischaemia. When exposed to the more severe stress of global ischaemia, the functional recovery potential of middle-aged DIO rats appeared to be impeded compared to hearts of young DIO rats, while age had no effect on the functional recovery of AMC hearts. Preconditioning reduced infarct size in hearts from young control rats and both middle-aged groups, but not from young DIO rats. Age had a significant effect on functional recovery in preconditioning: it was improved in hearts from young control and DIO rats, but depressed in both middle-aged groups. CONCLUSIONS: The data showed that middle-age and obesity had no effect on baseline myocardial function and did not increase susceptibility to I/R damage upon exposure to regional ischaemia. On the contrary, obesity reduced I/R damage in young rats. Preconditioned aging hearts showed a decreased infarct size, but a reduction in functional recovery.

The Impact of Chronic Glycogen Synthase Kinase-3 Inhibition on Remodeling of Normal and Pre-Diabetic Rat Hearts.

PURPOSE: There is an ongoing search for new drugs and drug targets to treat diseases like Alzheimer's disease, cancer and type 2 diabetes (T2D). Both obesity and T2D are characterized by the development of a cardiomyopathy associated with increased hypertension and compensatory left ventricular hypertrophy. Small, specific glycogen synthase kinase-3 (GSK-3) inhibitors were developed to replace lithium chloride for use in psychiatric disorders. In addition, they were advocated as treatment for T2D since GSK-3 inhibition improves blood glucose handling. However, GSK-3 is a regulator of hypertrophic signalling in the heart via phosphorylation of NFATc3 and ß-catenin respectively. In view of this, we hypothesized that chronic inhibition of GSK-3 will induce myocardial hypertrophy or exacerbate existing hypertrophy. METHODS: Rats with obesity-induced prediabetes were treated orally with GSK-3 inhibitor (CHIR118637 (CT20026)), 30 mg/kg/day for the last 8 weeks of a 20-week diet high in sugar content vs a control diet. Biometric and biochemical parameters were measured, echocardiography performed and localization and co-localization of NFATc3 and GATA4 determined in cardiomyocytes. RESULTS: Obesity initiated myocardial hypertrophy, evidenced by increased ventricular mass (1.158 ± 0.029 vs 0.983 ± 0.03 g) and enlarged cardiomyocytes (18.86 ± 2.25 vs 14.92 ± 0.50um(2)) in association with increased end-diastolic diameter (EDD = 8.48 ± 0.11 vs 8.15 ± 0.10 mm). GSK-3 inhibition (i) increased ventricular mass only in controls (1.075 ± 0.022 g) and (ii) EDD in both groups (controls: 8.63 ± 0.07; obese: 8.72 ± 0.15 mm) (iii) localized NFATc3 and GATA4 peri-nuclearly. CONCLUSION: Indications of onset of myocardial hypertrophy in both control and obese rats treated with a GSK-3 inhibitor were found. It remains speculation whether these changes were adaptive or maladaptive.

In vitro fermentation of nuts results in the formation of butyrate and c9,t11 conjugated linoleic acid as chemopreventive metabolites.

PURPOSE: The consumption of foods rich in dietary fiber and polyunsaturated fatty acids such as nuts can contribute to a healthy diet. Therefore, the formation of fermentation end-products which might exert chemopreventive effects regarding colon cancer was investigated after an in vitro simulated digestion and fermentation of nuts using human fecal microbiota. METHODS: Fermentation supernatants (FS) and pellets (FP) were obtained after an in vitro fermentation of hazelnuts, almonds, macadamia, pistachios and walnuts. Short-chain fatty acids (SCFA) and bile acids (BA) in FS as well as fatty acids in FP were analyzed via gas chromatography. Malondialdehyde (MDA) levels in FS were determined photometrically. RESULTS: Fermentation of nuts resulted in 1.9- to 2.8-fold higher concentrations of SCFA compared to the control and a shift of molar ratios toward butyrate production. In vitro fermentation resulted in the formation of vaccenic acid (C18:1t11, 32.1 ± 3.2 % FAME; fatty acid methyl ester) and conjugated linoleic acid (c9,t11 CLA, 2.4 ± 0.7 % FAME) exclusively in fermented walnut samples. Concentrations of secondary BA deoxycholic-/iso-deoxycholic acid (6.8-24.1-fold/4.9-10.9-fold, respectively) and levels of MDA (1.3-fold) were significantly reduced in fermented nut samples compared to the control. CONCLUSION: This is the first study that demonstrates the ability of the human fecal microbiota to convert polyunsaturated fatty acids from walnuts to c9,t11 CLA as a potential chemopreventive metabolite. In addition, the production of butyrate and reduction in potential carcinogens such as secondary BA and lipid peroxidation products might contribute to the protective effects of nuts regarding colon cancer development.

Sanguinarine non- versus re-circulation during isolated heart perfusion--a Jekyll and Hyde effect?

AIMS: In isolated rat heart perfusion experiments, drug administration occurs via retrograde perfusion. This can be done in the non-recirculating mode (coronary effluent is discarded), or recirculating mode (coronary effluent is collected and reused). It was recently observed in our lab while using sanguinarine, an MKP-1 inhibitor, that there were differences in outcomes depending on the mode of recirculation used. METHODS AND RESULTS: Hearts from control (C); diet-induced obese (DIO) Wistar rats and their age matched controls (AMC) were perfused on the rig. Hearts received buffer (control) , insulin, sanguinarine, insulin + sanguinarine combination or methanol (vehicle) for 15 mins pre- and 10 mins post-ischemia in either a non- or re-circulating manner. Hearts were subjected to 15 mins global ischemia and 30 mins reperfusion. Mechanical function was documented pre- and post-ischemia . When not-recirculated , sanguinarine alone and in combination with insulin in C, DIO and AMC groups, caused a significant decrease in functional recovery during reperfusion. However, when the coronary effluent was recirculated, hearts perfused with sanguinarine or sanguinarine + insulin exhibited a significant recovery in function when compared with their non-recirculation counterparts (p < 0.01). No differences were seen with either control, insulin nor vehicle hearts. CONCLUSION: Sanguinarine elicited a vast improvement in perfusion outcomes when recirculated compared to non-recirculation . Since this was seen during perfusion only when sanguinarine was present, it is possible that recirculating reperfusion of the drug caused profound changes in its composition. More investigation is needed into the mechanisms involved. Thus caution should be exercised by researchers when designing a perfusion protocol for drug research.

Temporal and spatial dispersion of human body temperature during deep hypothermia.

BACKGROUND: Clinical temperature management remains challenging. Choosing the right sensor location to determine the core body temperature is a particular matter of academic and clinical debate. This study aimed to investigate the relationship of measured temperatures at different sites during surgery in deep hypothermic patients. METHODS: In this prospective single-centre study, we studied 24 patients undergoing cardiothoracic surgery: 12 in normothermia, 3 in mild, and 9 in deep hypothermia. Temperature recordings of a non-invasive heat flux sensor at the forehead were compared with the arterial outlet temperature of a heart-lung machine, with the temperature on a conventional vesical bladder thermistor and, for patients undergoing deep hypothermia, with oesophageal temperature. RESULTS: Using a linear model for sensor comparison, the arterial outlet sensor showed a difference among the other sensor positions between -0.54 and -1.12°C. The 95% confidence interval ranged between 7.06 and 8.82°C for the upper limit and -8.14 and -10.62°C for the lower limit. Because of the hysteretic shape, the curves were divided into phases and fitted into a non-linear model according to time and placement of the sensors. During cooling and warming phases, a quadratic relationship could be observed among arterial, oesophageal, vesical, and cranial temperature recordings, with coefficients of determination ranging between 0.95 and 0.98 (standard errors of the estimate 0.69-1.12°C). CONCLUSION: We suggest that measured surrogate temperatures as indices of the cerebral temperature (e.g. vesical bladder temperature) should be interpreted with respect to the temporal and spatial dispersion during cooling and rewarming phases.

At the core of survival: autophagy delays the onset of both apoptotic and necrotic cell death in a model of ischemic cell injury.

Ischemic cell injury leads to cell death. Three main morphologies have been described: apoptosis, cell death with autophagy and necrosis. Their inherent dynamic nature, a point of no return (PONR) and molecular overlap have been stressed. The relationship between a defined cell death type and the severity of injury remains unclear. The functional role of autophagy and its effects on cell death onset is largely unknown. In this study we report a differential induction of cell death, which is dependent on the severity and duration of an ischemic insult. We show that mild ischemia leads to the induction of autophagy and apoptosis, while moderate or severe ischemia induces both apoptotic and necrotic cell death without increased autophagy. The autophagic response during mild injury was associated with an ATP surge. Real-time imaging and Fluorescence Resonance Energy Transfer (FRET) revealed that increased autophagy delays the PONR of both apoptosis and necrosis significantly. Blocking autophagy shifted PONR to an earlier point in time. Our results suggest that autophagic activity directly alters intracellular metabolic parameters, responsible for maintaining mitochondrial membrane potential and cellular membrane integrity. A similar treatment also improved functional recovery in the perfused rat heart. Taken together, we demonstrate a novel finding: autophagy is implicated only in mild injury and positions the PONR in cell death.

ANG II type I receptor antagonism improved nitric oxide production and enhanced eNOS and PKB/Akt expression in hearts from a rat model of insulin resistance.

Exogenous insulin therapy improves endothelial function in insulin resistant patients, indirectly indicating that nitric oxide synthase activity and NO production may be impaired. Insulin stimulates production of NO by activating a signaling pathway including insulin receptor substrate-1, phosphatidylinositol-3-kinase and protein kinase B (PKB/Akt). Angiotensin II type I (AT1) receptor-evoked oxidative stress is implicated in the inactivation of NO, impairing endothelium-dependent vasodilatation. Blocking the actions of Angiotensin II with an AT1 receptor antagonist (Losartan), has beneficial effects in patients with insulin resistance or type 2 diabetes mellitus. This study investigated whether elevated Angiotensin II influences myocardial insulin resistance, insulin signaling and NO production in a rat model of diet-induced obesity (DIO) by antagonizing the actions of the AT1 receptor with Losartan. Isolated, perfused hearts, Western blotting and flow-cytometric methods were utilized to determine myocardial function, expression and phosphorylation of key proteins and NO production, respectively. Results showed that hearts from DIO rats are insulin resistant (higher serine phosphorylation of IRS-1, lower insulin-stimulated phosphorylation of PKB/Akt and eNOS, lower NO production) and had poorer functional recovery and larger infarct development after ischaemia/reperfusion. Losartan improved the impaired functional recovery, and NO production and enhanced eNOS expression and phosphorylation and reduced infarct size in hearts from the DIO animals. Data obtained from Losartan treatment also revealed that Angiotensin II signaling modulates myocardial PKB/Akt expression. We conclude that Angiotensin II signaling exacerbates inhibition of NO production in insulin resistance and that this can be improved by AT1 antagonism.

Melatonin has profound effects on mitochondrial dynamics in myocardial ischaemia/reperfusion.

Research focus recently shifted to mitochondrial dynamics and the role of fusion and fission in cardioprotection. The aim of this study was to evaluate (i) the function and dynamics of mitochondria isolated from hearts exposed to ischaemia/reperfusion (I/R) (ii) the effects of melatonin, a powerful cardioprotectant, on mitochondrial dynamics in I/R. Isolated perfused rat hearts were stabilized for 30 min, subjected to 20 min global ischaemia, followed by 30 min reperfusion. Tissue was collected, mitochondria isolated for measurement of mitochondrial oxidative function and lysates from mitochondrial and cytosolic fractions prepared for western blotting. Melatonin (0.3 or 50 µM) was administered for 10 min immediately before the onset of ischaemia and for 10 min at the onset of reperfusion. Infarct size was assessed after 35 min regional ischaemia/60 min reperfusion using triphenyltetrazolium staining. The results show that reperfusion significantly reduced mitochondrial QO2 (states 3 and 4), with minor effects by melatonin. Cytosolic Beclin 1 and the LC3 II/I ratio were reduced by ischaemia and increased by reperfusion. Both ischaemia and reperfusion reduced mitochondrial PINK1 and Parkin levels, while reperfusion increased p62. An alternative mitophagy pathway mediated by Rab9 is activated during myocardial ischaemia/reperfusion. Ischaemia reduced and reperfusion increased cytosolic ULK1 expression, associated with redistribution of Rab9 and Drp1 between the cytosol and mitochondria. Melatonin significantly reduced mitochondrial p62 expression upon reperfusion. Throughout the protocol, melatonin significantly (i) increased cytosolic total (t) and phospho (p) ULK1, and Rab9 levels (ii) increased the cytosolic and reduced the mitochondrial pDrp1 levels and p/t Drp1 ratio, suggesting inhibition of mitochondrial fission. Fusion was affected to a lesser extent. Cardioprotection by melatonin is associated with substantial effects on mitophagy, the significance thereof remains to be established.

A role for the RISK pathway and K(ATP) channels in pre- and post-conditioning induced by levosimendan in the isolated guinea pig heart.

BACKGROUND AND PURPOSE: Myocardial reperfusion injury prevents optimal salvage of the ischaemic myocardium, and adjunct therapy that would significantly reduce reperfusion injury is still lacking. We investigated whether (1) the heart could be pre- and/or post-conditioned using levosimendan (levosimendan pre-conditioning (LPC) and levosimendan post-conditioning (LPostC)) and (2) the prosurvival kinases and/or the sarcolemmal or mitochondrial K(ATP) channels are involved. EXPERIMENTAL APPROACH: Isolated guinea pig hearts were treated with two 5 min cycles of levosimendan (0.1 microM) interspersed with vehicle perfusion, or two 5 min cycles of ischaemia/reperfusion, before coronary artery ligation (CAL) for 40 min at 36.5 degrees C. Hearts were treated with mitochondrial or sarcolemmal K(ATP) channel blockers before LPC or LPostC. For post-conditioning, hearts received three 30 s cycles of ischaemia/reperfusion or levosimendan/vehicle. Hearts were pretreated with levosimendan immediately before CAL (without washout). Cardiac function, infarct size and reperfusion injury salvage kinase activity was assessed. KEY RESULTS: LPC and LPostC halved the infarct size compared with controls (P<0.05). Treatment with K(ATP) channel blockers before LPC or LPostC reversed this decrease. Pretreating hearts with levosimendan increased activity of extracellular signal-regulated kinase (ERK) 42/44 on reperfusion and had the most marked infarct-lowering effect (P<0.05). CONCLUSIONS AND IMPLICATIONS: (1) Hearts could be pharmacologically pre- and post-conditioned with levosimendan; (2) levosimendan pretreatment is the most effective way to reduce infarct size, possibly by increasing ERK 42/44 activity; (3) benefits of LPC and LPostC were abolished by both K(ATP) channel blockers and (4) LPC may be useful before elective cardiac surgery, whereas LPostC may be used after acute coronary artery events.

CREB activation and ischaemic preconditioning.

PURPOSE: Previous studies from our laboratory showed that activation of p38 MAPK is one of the triggers of ischaemic preconditioning. The signalling events downstream of p38 MAPK and their links to the putative final effectors of preconditioning are not clear. The cAMP responsive element-binding protein (CREB) is also phosphorylated by exposure to short episodes of ischaemia/reperfusion, suggesting a triggering action. The aim of this study was to systematically investigate (1) the signalling pathways leading to CREB phosphorylation during an ischaemic or beta-adrenergic preconditioning protocol (2) changes in CREB phosphorylation during sustained ischaemia and their significance in ischaemia/reperfusion injury. METHODS: The isolated perfused working rat heart was preconditioned by 1 x 5 min global ischaemia or 3 x 5 min global ischaemia and freeze-clamped. Drugs to manipulate CREB activation were added 5 min before onset of ischaemia. Non-preconditioned and preconditioned hearts were subjected to 25 min global or 35 min regional ischaemia, followed by 30 min reperfusion. Infarct sizes were determined using tetrazolium staining. Phosphorylation of CREB was determined by Western blots. RESULTS: Exposure of hearts to 5 min global ischaemia followed by reperfusion, significantly increased CREB phosphorylation This is mediated by, amongst others, release of endogenous catecholamines and adenosine, as indicated by the use of receptor blockers. Events downstream of receptor stimulation were evaluated using inhibitors for PKA (H89), MSK-1 (H89, Ro318220), PKC (bisindolylmaleimide), p38 MAPK (SB203580) and ERK (PD98059). Activation of PKA, PKC, ERK and p38 MAPK is involved in preconditioning-induced CREB phosphorylation. Ischaemia-induced activation of iPLA(2) and cPLA(2) also contribute to CREB phosphorylation as indicated by the use of the inhibitors 4-bromo-enol-lactone (BEL) and AACOF(3,) respectively. Inhibition of CREB phosphorylation by either BEL or AACOF(3) during a preconditioning protocol partially attenuated cardioprotection. CREB phosphorylation was attenuated during sustained global ischaemia of both non-preconditioned and preconditioned hearts. CONCLUSIONS: These data suggest that CREB phosphorylation during an ischaemic preconditioning protocol may contribute to triggering preconditioning, while reduced phosphorylation during sustained ischaemia does not appear to be associated with cardioprotection.

Sarcolemmal phospholipid fatty acid composition and permeability.

In this study, the mechanism of ischaemia-induced increased sarcolemmal permeability, as manifested by release of intracellular enzymes, was investigated. The role of changes in the sarcolemmal phospholipid bilayer in this process was evaluated by experimental modulation of the phospholipid fatty acid composition. The isolated perfused rat heart subjected to low-flow hypoxia, was used as a model of global ischaemia. Glucose as well as saturated (palmitate) and unsaturated (linoleate) long-chain fatty acids were used as substrates. Hearts perfused with palmitate or linoleate (1.5 mM, fatty acid/albumin ratio, 3.4) showed a significantly higher rate of lactate dehydrogenase release in both control and ischaemic conditions than hearts perfused with glucose (10 mM). Lactate dehydrogenase release in the fatty acid-perfused hearts was associated with a significant increase in the percentage unsaturation of the sarcolemmal phospholipid fatty acids. Glucose-perfused hearts, on the other hand, showed only minor changes in the sarcolemmal phospholipid fatty acid composition. Attempts to correlate enzyme release directly with an increase in the percentage unsaturation of phospholipid fatty acids failed, since enzyme release was also stimulated in control fatty-acid-perfused hearts which (when compared with glucose) contained a higher percentage saturated phospholipid fatty acids. The results suggest that myocardial ischaemia, apart from changes in the sarcolemmal phospholipid fatty acid composition, also induces several other changes in sarcolemmal composition (e.g., cholesterol loss) which may affect is permeability for macromolecules.

Mitochondrial Ca2+ fluxes: role of free fatty acids, acyl-CoA and acylcarnitine.

It has been suggested that accumulation of lipid metabolites, such as fatty acids, fatty acyl-CoA and acylcarnitine, in the ischaemic myocardium, may be responsible for disturbances in mitochondrial Ca2+ fluxes. In view of the presence of an intracellular fatty acid binding protein, the question arose whether these intermediates affect mitochondrial Ca2+ uptake and release similarly in vivo. In this study the effects of linoleic acid, palmitic acid, palmitoyl-CoA and palmitoylcarnitine were studied on mitochondrial Ca2+ fluxes in the absence and presence of albumin, an avid binder of fatty acid derivatives. Albumin reversed the effects of the above compounds on mitochondrial Ca2+ uptake and release, suggesting that the presence of an intracellular fatty acid binding protein may protect the ischaemic myocardial cell against the deleterious effects of accumulated fatty acid derivatives.

Mitochondrial Ca2+ fluxes and levels during ischaemia and reperfusion: possible mechanisms.

It has been shown that myocardial ischaemia depresses the uptake and enhances the release of Ca2+ by mitochondria. Reperfusion of the ischaemic areas may result in a further deterioration of the above processes. Despite these marked changes in Ca2+ fluxes, reperfusion has been shown always to be associated with a marked increase in mitochondrial Ca2+ content. To explain the latter observation, it has been proposed that reperfusion promotes respiration-supported mitochondrial Ca2+ uptake in preference to ADP phosphorylation. To evaluate this hypothesis, the effect of exogenous ADP on mitochondrial respiration-linked Ca2+ uptake was investigated in control, ischaemic and ischaemic-reperfused hearts. The results show that ADP significantly depresses mitochondrial Ca2+ uptake in all three preparations, indicating that Ca2+ is not taken up preferentially to ADP phosphorylation in reperfused tissue. It is suggested that reperfusion-induced increased mitochondrial Ca2+ levels are probably not due to increased respiration-linked Ca2+ uptake, but rather to augmented conversion of ionized Ca2+ to calcium phosphate which does not participate in ionic fluxes.

Mitochondrial phospholipid composition and microviscosity in myocardial ischaemia.

Normothermic ischaemic arrest of the isolated perfused rat heart causes profound changes in mitochondrial ultrastructure. Since the mitochondrial membranes contain a high percentage of phospholipids, an evaluation of the effect of different periods of ischaemia on mitochondrial phospholipid content and fatty acid composition was made. The results showed that ischaemia had no effect on the content of the different phospholipid classes and no correlation was observed between ultrastructural changes and mitochondrial phospholipid content. However, the phospholipid fatty acid composition of several phospholipids showed marked changes. For example, with lysophosphatidylcholine a progressive increase in the percentage saturated fatty acids was observed with increasing periods of ischaemia, while a reduction occurred in lysophosphatidylethanolamine. To determine whether the ischaemia-induced changes in mitochondrial phospholipid fatty acid composition had an effect on the physical properties of the membrane, the microviscosity of mitochondrial preparations was studied, using the lipophilic probe, 1,6-diphenyl-1,3,5-hexatrine. Mitochondria isolated from ischaemic hearts showed a progressive increase in fluorescence polarization with longer periods of ischaemia, indicating an overall increase in microviscosity. This phenomenon may be responsible for the increased mitochondrial fragility which is characteristic of ischaemic damage.

Ischemic preconditioning and the beta-adrenergic signal transduction pathway.

BACKGROUND: Previous studies from our laboratory showed cyclic increases in tissue cAMP during a multiple-cycle preconditioning (PC) protocol, followed by attenuated cAMP accumulation during sustained ischemia. The aim of this study was to determine whether ischemia-induced activation of the beta-adrenergic signaling pathway could act as a trigger in eliciting protection. METHODS AND RESULTS: Isolated perfused rat hearts were preconditioned by 3x5 minutes of global ischemia, interspersed by 5 minutes of reperfusion. beta-Adrenergic responsivity was assessed by measurement of tissue cAMP generation after beta-adrenergic agonist administration at the end of the PC protocol. Tissue cAMP, adenylyl cyclase, and protein kinase A (PKA) activities and beta-adrenergic receptor characteristics were assessed at different times. The role of cAMP generation in eliciting PC was studied by investigation of functional recovery during reperfusion after 25 minutes of global ischemia after (1) cAMP increases in the trigger period were prevented with the beta-adrenergic blocker alprenolol 7.5x10(-5) mol/L and (2) increases in cAMP were elicited by administration of forskolin 10(-7) and 10(-6) mol/L or isoproterenol 10(-8), 10(-7), and 10(-6) mol/L. Intermittent ischemia resulted in reduced beta-adrenergic responsivity at the end of the protocol, although B(max) and K(d) values of the beta-adrenergic receptor population and adenylyl cyclase and PKA activities were increased. Abolishment of cyclic increases in cAMP before sustained ischemia attenuated myocardial protection against ischemia, whereas agonists elicited protection. No clear correlation between protection and beta-adrenergic desensitization was observed. CONCLUSIONS: Ischemia-induced activation of the beta-adrenergic signaling pathway during preconditioning should also be considered a trigger in eliciting preconditioning.

Normothermic ischaemic cardiac arrest of isolated working rat heart: effects of reserpine and propranolol on functional, metabolic and morphological recovery.

The ability to preserve myocardial structural and functional integrity during extended periods of total ischaemia has practical clinical significance. The role of endogenous catecholamines in the onset of irreversible damage in global ischaemia of the isolated rat heart was assessed by beta-blockade or catecholamine depletion. The effects of propranolol and reserpine pretreatment on myocardial ultrastructure, function and metabolism were studied during normothermic ischaemic arrest (NICA) and reperfusion of the isolated working rat heart. beta-Blockade as well as catecholamine depletion resulted in an increase in the percentage of totally ischaemic hearts which recovered mechanically upon reperfusion. In these studies mechanical recovery during reperfusion was associated with reversal of ultrastructural ischaemic alterations, but without an improvement in mitochondrial function. These findings support the concept that failure of mitochondria to recover functionally upon reperfusion is not the cause of either irreversible mechanical failure or ultrastructural damage of the ischaemic myocardium.

Radiation-induced damage of the Wistar rat heart: biochemistry and function.

A time sequence study was performed on Wistar rats to investigate the early effects of radiation on the mechanical function and energy metabolism of the heart. Two series of rats were exposed to 20 Gy electron irradiation to a field including the heart and approximately a third of the lungs. The hearts were excised at varying time intervals (8-180 days) post irradiation. In one series of hearts the mechanical function was measured using the isolated perfused working rat heart model. At the end of the perfusion the hearts were freeze-clamped for analysis of the high energy phosphate contents (ATP, ADP, AMP and creatine phosphate). In the second series, mitochondria were isolated and the oxidative phosphorylation function measured polarographically (substrate: glutamate). Maximal depression of mechanical function was observed at 60 days post irradiation. Thereafter the work performance of these hearts improved significantly, almost reaching control levels after 180 days. The mitochondrial oxidative phosphorylation function (as measured on the total mitochondrial population) was significantly depressed 30-120 days post irradiation. As in the case of the mechanical changes, the depression was transient and after 180 days post irradiation, values similar to those of controls were obtained. Myocardial high energy phosphates remained unaltered throughout the experiment.

Radiation-induced changes in the ultrastructure and mechanical function of the rat heart.

A time sequence study was performed to study the early effects of radiation on the ultrastructure of the rat heart. Wistar rats were exposed to 20 Gy electron irradiation to a field including the heart and a third of the lung. The hearts were excised at varying time intervals (1 h-180 days), and the ultrastructure of perfusion-fixed subepicardium and subendocardium studied. Changes were observed in both myocytes and interstitium at all time intervals. The most pronounced change observed in the myocyte was that of intercalated disc damage which reached a peak at 30 days post-irradiation. Mitochondrial damage, characterized by swelling and fenestration in areas of myofibrillar contracture, was focal and relatively scarce. Swelling of the capillary endothelial cells and collapse of the capillaries were marked up to 60 days. Of significance was the observation that the damage to both myocytes and interstitium receded after 60 days and the hearts exhibited an almost normal ultrastructure from 100 to 180 days post-irradiation. Mechanical function of these hearts followed a similar pattern: maximal depression was observed 60 days after irradiation. Thereafter the work performance of these hearts improved significantly, almost reaching control levels after 180 days.

Effect of oxygenated crystalloid cardioplegia on the functional and metabolic recovery of the isolated perfused rat heart.

The use of an oxygenated crystalloid cardioplegic solution to improve myocardial preservation during elective cardiac arrest was evaluated with the isolated perfused rat heart used as a model. Experiments were conducted at 4 degrees C and 20 degrees C. The oxygen tension of the nonoxygenated and oxygenated cardioplegic solutions averaged 117 and 440 mm Hg, respectively. At 4 degrees C, the adenosine triphosphate content of hearts subjected to 120 minutes of oxygenated cardioplegia was significantly higher than that of the nonoxygenated cardioplegia group. However, functional recovery during reperfusion was similar for both groups. At 20 degrees C, the myocardial adenosine triphosphate concentration decreased at a significantly faster rate during ischemia in the group receiving nonoxygenated cardioplegia compared with the oxygenated cardioplegia group. Hearts subjected to 180 minutes of ischemia with oxygenated cardioplegia had a normal ultrastructural appearance whereas hearts subjected to 120 minutes of nonoxygenated cardioplegia showed severe ischemic damage. Myocardial functional recovery in the group receiving oxygenated cardioplegia exceeded that of the group receiving nonoxygenated cardioplegia. The use of myocardial adenosine triphosphate concentration at the end of the ischemic period to predict subsequent cardiac output, peak systolic pressure, and total myocardial work showed significant positive correlations.