Recovery Of Coronary Flow Research Articles

Effect of ACE Inhibitor Captopril and L-Arginine on the Metabolism and on Ischemia-Reperfusion Injury of the Isolated Rat Heart

We investigated the effects of in vivo treatment with the angiotensin-converting enzyme inhibitor (ACE-I) captopril and/or of in vitro administration of L-arginine on the metabolism and ischemia-reperfusion injury of the isolated perfused rat myocardium. Captopril (50 mg/l in drinking water, 4 weeks) raised the myocardial content of glycogen. After 25-min global ischemia, captopril treatment, compared with the controls, resulted in lower rates of lactate dehydrogenase release during reperfusion (8.58±1.12 vs. 13.39±1.88 U/heart/30 min, p<0.05), lower myocardial lactate contents (11.34±0.93 vs. 21.22±4.28 µmol/g d.w., p<0.05) and higher coronary flow recovery (by 25 %), and prevented the decrease of NO release into the perfusate during reperfusion. In control hearts L-arginine added to the perfusate (1 mmol/l) 10 min before ischemia had no effect on the parameters evaluated under our experimental conditions, presumably because of sufficient saturation of the myocardium with L-arginine. In the hearts of captopril-treated rats, L-arginine further increased NO production during reperfusion and the cGMP content before ischemia. Our results have shown that long-term captopril treatment increases the energy potential and has a beneficial effect on tolerance of the isolated heart to ischemia. L-arginine added into the perfusate potentiates the effect of captopril on the NO signaling pathway.

Gene therapy for myocardial protection: transfection of donor hearts with heat shock protein 70 gene protects cardiac function against ischemia-reperfusion injury.

Heat shock protein 70 (HSP70) gene transfection has been shown to enhance myocardial tolerance after normothermic ischemia-reperfusion. We investigated the effect of HSP70 gene transfection on mechanical and endothelial function in a protocol mimicking clinical heart preservation. Rat hearts were infused ex vivo with Hemagglutinating Virus of Japan-liposome complex containing HSP70 gene (HSP, n=8) or no gene (CON, n=8), and heterotopically transplanted into recipient rats. Four days after surgery, transfected hearts were perfused on a Langendorff apparatus for 45 minutes, arrested with St Thomas' No. 1 cardioplegia for 4 hours at 4 degrees C, and reperfused for 1 hour. Mechanical and endothelial function was studied before and after ischemia. Creatine kinase was measured in reperfusion effluent. Hearts underwent Western blotting and immunohistochemistry to confirm HSP70 overexpression. Postischemic recovery of mechanical function (% preischemic+/-SEM) was greater in HSP versus CON: Left ventricular developed pressure recovery was 76.7+/-3.9% versus 60. 5+/-3.1% (P:<0.05); dP/dtmax recovery was 79.4+/-4.9% versus 56. 2+/-3.2% (P:<0.05); dP/dtmin recovery was 74.8+/-4.6% versus 57. 3+/-3.6% (P:<0.05). Creatine kinase release was attenuated in HSP versus CON: 0.22+/-0.02 versus 0.32+/-0.04 IU/min/g wet wt. (P:<0. 05). Recovery of coronary flow was greater in HSP versus CON: 76. 5+/-3.8% versus 59.2+/-3.2% (P:<0.05). Recovery of coronary response to 5-hydroxytryptamine (5 x 10(-)(5) mol/L) was 55.6+/-4.7% versus 23. 9+/-3.2% (P:<0.05); recovery of coronary response to glyceryltrinitrate (15 mg/L) was not different between HSP and CON: 87.4+/-6.9% versus 84.3+/-5.8% (NS). In a clinically relevant donor heart preservation protocol, HSP70 gene transfection protects both mechanical and endothelial function.

Gene Therapy for Myocardial Protection

Background —Heat shock protein 70 (HSP70) gene transfection has been shown to enhance myocardial tolerance after normothermic ischemia-reperfusion. We investigated the effect of HSP70 gene transfection on mechanical and endothelial function in a protocol mimicking clinical heart preservation. Methods and Results —Rat hearts were infused ex vivo with Hemagglutinating Virus of Japan–liposome complex containing HSP70 gene (HSP, n=8) or no gene (CON, n=8), and heterotopically transplanted into recipient rats. Four days after surgery, transfected hearts were perfused on a Langendorff apparatus for 45 minutes, arrested with St Thomas’ No. 1 cardioplegia for 4 hours at 4°C, and reperfused for 1 hour. Mechanical and endothelial function was studied before and after ischemia. Creatine kinase was measured in reperfusion effluent. Hearts underwent Western blotting and immunohistochemistry to confirm HSP70 overexpression. Postischemic recovery of mechanical function (% preischemic±SEM) was greater in HSP versus CON: Left ventricular developed pressure recovery was 76.7±3.9% versus 60.5±3.1% ( P &lt;0.05); dP/dtmax recovery was 79.4±4.9% versus 56.2±3.2% ( P &lt;0.05); dP/dtmin recovery was 74.8±4.6% versus 57.3±3.6% ( P &lt;0.05). Creatine kinase release was attenuated in HSP versus CON: 0.22±0.02 versus 0.32±0.04 IU/min/g wet wt. ( P &lt;0.05). Recovery of coronary flow was greater in HSP versus CON: 76.5±3.8% versus 59.2±3.2% ( P &lt;0.05). Recovery of coronary response to 5-hydroxytryptamine (5×10 − 5 mol/L) was 55.6±4.7% versus 23.9±3.2% ( P &lt;0.05); recovery of coronary response to glyceryltrinitrate (15 mg/L) was not different between HSP and CON: 87.4±6.9% versus 84.3±5.8% (NS). Conclusions —In a clinically relevant donor heart preservation protocol, HSP70 gene transfection protects both mechanical and endothelial function.

Leukocyte-depleted reperfusion after long cardioplegic arrest attenuates ischemia-reperfusion injury of the coronary endothelium and myocardium in rabbit hearts.

Cardiopulmonary bypass activates leukocytes, which should injure the coronary endothelium and myocardium during reperfusion especially after long cardioplegic arrest with long cardiopulmonary bypass time. The present study was designed to determine the protective efficacy of leukocyte-depleted reperfusion in blood-perfused parabiotic isolated rabbit hearts as a surgically relevant model with long cardioplegic arrest. Each isolated rabbit heart, with a latex balloon inserted in the left ventricle, was parabiotically blood-perfused using a modified Langendorff column. The left ventricular developed pressure (DP), rate of pressure development (dP/dT), and coronary flow with a left ventricular end-diastolic pressure of 10 mmHg were measured before ischemia and after 15, 30, 45, and 60 min reperfusion after 4 h cardioplegic arrest kept at 20 degrees C (control, n=10). Leukocyte-depleted reperfusion was done in the test group (n=10). The endothelium of the coronary artery was observed by scanning electron microscopy (SEM) with percent injured area of endothelial cells measured to evaluate the extent of endothelial ischemia-reperfusion injury. The control hearts showed 53.3, 54.3, 48.4, and 39.0% recovery of DP compared to the pre-ischemia baseline data at 15, 30, 45, and 60 min after reperfusion began respectively. Leukocyte-depleted reperfusion enhanced the recovery of DP at 45 min (81.3%, P=0.0021) and 60 min (85.8%, P=0.0005) after reperfusion compared with that in the control group. The control hearts revealed 58.8%, 59.8%, 52.6%, and 43.4% recovery of dP/dT compared to the pre-ischemia baseline data at 15, 30, 45, and 60 min after reperfusion began, respectively. Leukocyte-depleted reperfusion also enhanced the recovery of dP/dT at 45 min (93.2%, P=0.0071) and 60 min (98.8%, P=0.0011) after reperfusion compared with that in the control group. There was also improvement of the recovery of coronary flow by leukocyte-depleted reperfusion (97.2%) compared with that in the control group (58.3%) after 60 min reperfusion (P=0.0121). Scanning electron microscopy showed that 69. 7% of coronary endothelial cells were morphologically injured in the control group. In contrast, leukocyte-depleted reperfusion prevented the extent of coronary endothelial damage with less injured area (0. 5%, P=0.0002). Leukocyte-depleted reperfusion improved functional recovery with reduced coronary endothelial injury after long cardioplegic arrest.

Ulinastatin attenuates reperfusion injury in the isolated blood-perfused rabbit heart

Background. Ventricular dysfunction after long cardioplegic arrest has been observed in cardiac operations. Urinary trypsin inhibitor, also called ulinastatin, may attenuate myocardial ischemia-reperfusion injury. The present study was designed to determine the protective efficacy of ulinastatin in blood-perfused parabiotic isolated rabbit hearts as a surgically relevant model with long (4-hour) cardioplegic arrest.Methods. Each isolated rabbit heart, with a latex balloon inserted in the left ventricle, was parabiotically blood-perfused using a modified Langendorff column. The left ventricular developed pressure, rate of pressure development, and coronary flow with a left ventricular end-diastolic pressure of 10 mmHg were measured before ischemia and 15, 30, 45, and 60 minutes after reperfusion began (control, n = 10). Ulinastatin (15,000 U/kg) was administered to the support animal just before reperfusion began (group U-1, n = 10) or at the beginning of the extracorporeal circulation and readministered before reperfusion (group U-2, n = 10). The endothelium of the coronary artery was observed by scanning electron microscopy to evaluate the extent of endothelial ischemia-reperfusion injury.Results. Ulinastatin enhanced the recovery of developed pressure in both the U-1 (p < 0.05) and U-2 (p < 0.01) groups compared with the control group. Although ulinastatin given just before reperfusion (group U-1) did not enhance the recovery of the rate of pressure development or the coronary flow compared with the control, earlier administration did improve the recovery of the rate of pressure development compared with the control (U-2, p < 0.05), and there was improvement of the recovery of coronary flow after 60 minutes of reperfusion (U-2, p < 0.05). Scanning electron microscopy showed that ulinastatin had ameliorated coronary endothelial damage.Conclusions. Ulinastatin improved functional recovery after long cardioplegic arrest and reduced coronary endothelial injury. Administration of ulinastatin at the beginning of cardiopulmonary bypass and just before reperfusion may be useful clinically in cases requiring prolonged aortic cross-clamping.

Protease-activated receptor-2 modulates myocardial ischemia-reperfusion injury in the rat heart.

Protease-activated receptor-2 (PAR-2) is a member of seven transmembrane domain G protein-coupled receptors activated by proteolytic cleavage whose better known member is the thrombin receptor. The pathophysiological role of PAR-2 remains poorly understood. Because PAR-2 is involved in inflammatory and injury response events, we investigated the role of PAR-2 in experimental myocardial ischemia-reperfusion injury. We show for the first time that PAR-2 activation protects against reperfusion-injury. After PAR-2-activating peptide (2AP) infusion, we found a significant recovery of myocardial function and decrease in oxidation at reflow. Indeed, the glutathione cycle (glutathione and oxidized glutathione) and lipid peroxidation analysis showed a reduced oxidative reperfusion-injury. Moreover, ischemic risk zone and creatine kinase release were decreased after PAR-2AP treatment. These events were coupled to elevation of PAR-2 and tumor necrosis factor alpha (TNFalpha) expression in both nuclear extracts and whole heart homogenates. The recovery of coronary flow was not reverted by L-nitroarginine methylester, indicating a NO-independent pathway for this effect. Genistein, a tyrosine kinase inhibitor, did not revert the PAR-2AP effect. During early reperfusion injury in vivo not only oxygen radicals are produced but also numerous proinflammatory mediators promoting neutrophil and monocyte targeting. In this context, we show that TNFalpha and PAR-2 are involved in signaling in pathophysiological conditions, such as myocardial ischemia-reperfusion. At the same time, because TNFalpha may exert pro-inflammatory actions and PAR-2 may constitute one of the first protective mechanisms that signals a primary inflammatory response, our data support the concept that this network may regulate body responses to tissue injury.

Effects of mibefradil and verapamil on ischemic-reperfusion in the hearts of guinea pigs with acute renal failure

Two parameters indicating the ischemic-reperfusion myocardial injury, coronary flow and lactate dehydrogenase (LDH) release rate, were evaluated in guinea pigs with gentamicine-induced acute renal failure (ARF) and compared with those of healthy animals. Isolated Langendorff's hearts were exposed to 50 min of zero-flow global ischemia and 60 min of reperfusion. The influences of calcium channel antagonists (of T- and L-type antagonist mibefradil and of L-type antagonist verapamil) in reperfusion solution were evaluated. Our results showed coronary dilatation and higher LDH release rate in ARF than in control hearts before ischemia. Recovery of coronary flow during reperfusion was better and LDH release rate lower in ARF vs. control hearts. Perfusion with mibefradil and verapamil did not additionally increase coronary flow, however 0.1 μM mibefradil and verapamil decreased LDH release rate during reperfusion in ARF hearts in comparison to control hearts. Our results showed some protective effects of 0.1 μM mibefradil and verapamil on LDH release rate during reperfusion, but not on coronary flow in guinea pigs hearts with ARF.

Increased temperature reduces the protective effect of University of Wisconsin solution in the heart

Background. The protective effect of University of Wisconsin solution (UW) for hypothermic storage of donor hearts has been demonstrated in the laboratory. However, clinical usage is associated with occasional primary graft failures. We postulated that this could be related to adverse effects of UW on the coronary vasculature during cardiac implantation and rewarming. We therefore assessed recovery of contractile function and coronary flow in rat hearts after cardioplegic arrest using UW compared with St. Thomas’ solution (ST) at 4°C or 25°C.Methods. Cardioplegia was induced in isolated rat hearts using either UW or ST at 4°C. Hearts were then maintained at 4°C or 25°C. In some hearts, UW at 4°C was used for inducing arrest followed by flushing with ST at 4°C and then rewarming to 25°C. After 40 minutes of arrest, recovery of function and coronary flow were measured. Nuclear track emulsion was used to assess microvascular competence.Results. Compared with ST–treated hearts, UW–treated hearts showed significant reduction in recovery of function at 25°C (76.2% ± 4.0% versus 25.0% ± 4.1%; p < 0.01) but not at 4°C (88.0% ± 1.6% versus 87.1% ± 2.6%). Recovery of coronary flow in the UW–treated hearts at 25°C was significantly lower than that in the ST–treated hearts at 25°C (71.7% ± 3.0% versus 94.5% ± 6.3%; p < 0.01). At 25°C, microvascular competence was reduced in the UW group compared with the ST group. At 25°C, flushing out UW with ST resulted in greater recovery of function compared with UW throughout (73.4% ± 7.1% versus 25.0% ± 4.1%; p < 0.01).Conclusions. University of Wisconsin solution provides effective donor heart protection under hypothermic conditions but can be deleterious at warmer temperatures.

Beneficial effects of ω-3 fatty acid treatment on the recovery of cardiac function after cold storage of Hyperlipidemic rats

Cardiac effects of ω-3 polyunsaturated fatty acids (PUFAs) were studied in female Wister rats fed a standard diet (control [C] diet) or a high-cholesterol (HC) diet. Subgroups of rats from these groups were treated with eicosapentaenoic acid-E (EPA) or docosahexaenoic acid-95E (DHA) for 5 weeks. Although plasma total cholesterol (TC) and triglyceride (TG) levels were higher in each group fed the HC diet versus each group fed the C diet, EPA administration with the HC diet (HC + EPA) significantly ( P < .05) reduced these levels. An isolated working-heart preparation was used to determine cardiac function. Cardiac output (CO) was lower in rats fed the HC diet and HC + DHA versus any of the groups fed the C diet ( P < .05). In addition, left ventricular (LV) maximum differentiation of pressure-time curve ( dp dt ) was lower in the rats fed the HC diet versus any of the C diet groups ( P < .05). After evaluation of cardiac function in each rat, the heart was stored in a histidine-tryptophanketoglutarate solution for 8 hours at 4°C. The heart was then reperfused, and recovery of cardiac function was evaluated. No significant differences were observed for post-preservative cardiac function within the C diet groups. However, within the HC diet groups, HC + EPA significantly ( P < .05) improved the recovery of cardiac function. In addition, HC + DHA also significantly ( P < .05) improved the recovery of coronary flow (CF) and LV dp dt . No significant differences were observed for plasma TC and TG concentrations in the C diet groups. EPA administration significantly decreased cardiac levels of palmitic, oleic, and linoleic acids in the HC diet groups. No significant differences were observed for cardiac levels of free fatty acids (FFAs) within the C diet groups. Cardiac EPA and DHA levels were significantly ( P < .05) elevated in EPA- or DHA-treated rats compared with the other diet-fed rats. Cardiac EPA levels were also elevated in DHA-treated rats compared with untreated rats ( P < .05). These results suggest that EPA attenuates coronary and myocardial preservation injuries through an increase in serum lipids and an accumulation of myocardial FFAs resulting from a HC diet.

Bradykinin-dependent cardioprotective effects of losartan against ischemia and reperfusion in rat hearts.

It is unclear whether losartan, an angiotensin II type 1 (AT1) receptor antagonist, protects the heart against acute ischemia-reperfusion injury. Therefore we evaluated cardiac protection conferred by pre- and postischemic treatment as well as by exclusive postischemic treatment with losartan. Furthermore, we sought to determine both the extent of this protection and its dependence on bradykinin in comparison with quinaprilat, a cardioprotective angiotensin-converting enzyme inhibitor. Cardiac protection was assessed as recovery of coronary flow, left ventricular developed pressure, phosphocreatine, and adenosine triphosphate (ATP) in isolated perfused rat hearts after 15 min of global ischemia and 30 min of postischemic reperfusion. We found that, in hearts pre- and postischemically treated with losartan (1 microM) or quinaprilat (0.1 microM), these variables all recovered significantly better than those in untreated control hearts. In hearts that were only postischemically treated with losartan, these variables also recovered significantly better than those in control hearts. In contrast, in hearts treated with the combination of the bradykinin B2 receptor antagonist Hoe 140 with quinaprilat or losartan, the recovery of the variables no longer differed from that in control hearts. In conclusion, losartan protects the heart against acute ischemia-reperfusion injury. This protection can be achieved by pre- and postischemic treatment as well as by exclusive postischemic treatment with losartan. Furthermore, the extent of this protection is equivalent to that conferred by quinaprilat and, unexpectedly, dependent on bradykinin.

Protective Effect of JTV519, A New 1,4-Benzothiazepine Derivative, on Prolonged Myocardial Preservation

JTV519 is know to protect cardiomyocytes from calcium overloading-induced damage. The aim of this study was to investigate the potential protective effect of JTV519 on myocardium subjected to prolonged ischemia and the underlying mechanism of such protection. The effect of JTV519 was also compared with that of diltiazem, a 1,5-benzothiazepine derivative. Isolated rat hearts were randomly divided into three groups. Control hearts were arrested with histidine-tryptophan-ketoglutarat (HTK) cardioplegic solution alone. In the JTV519 group of hearts, cardiac arrest was achieved with JTV519 (10(-3) mmol/L) in the HTK solution. Hearts in the diltiazem group were arrested with diltiazem (0.5 mmol/L) in the HTK solution. All the hearts were then subjected to 6-hour storage in HTK solution at 4 degrees C. After a 30-minute reperfusion, the left ventricular developed pressure in the JTV519 and diltiazem groups were improved significantly compared with the control group. There was a significantly lower left ventricular end-diastolic pressure level and higher recovery of coronary flow in the JTV519 group than in the control group. The postischemic intracellular calcium concentration was attenuated by adding JTV519 or diltiazem to HTK cardioplegia. As an adjunct to cardioplegia, JTV519 showed a significant protective effect on myocardium undergoing 6 hours of ischemia. The beneficial protective effects of JTV519 are correlated with its ability to inhibit the postischemic rise in intracellular calcium.

Inhibition of P-selectin attenuates neutrophil-mediated myocardial dysfunction in isolated rat heart

The expression of P-selectin on postischemic endothelium after reperfusion has been shown to trigger neutrophil attachment and the subsequent inflammatory responses. Extensive studies have demonstrated that P-selectin is involved in the progression of neutrophil-mediated myocardial infarction and no-reflow phenomenon. In the present study, we examined the effects of selectin inhibitors, sialyl Lewis X-oligosaccharide and anti-P-selectin monoclonal antibody, PB1.3 on neutrophil-dependent left ventricular dysfunction in isolated rat heart. The hearts were subjected to global ischemia for 20 min and then reperfused for 45 min with rat plasma in the presence of human neutrophils during the first 5 min of the reperfusion. Left ventricular developed pressure and other parameters of the left ventricular function deteriorated throughout the reperfusion period in a neutrophil-dependent manner. In contrast, the coronary flow was reduced early on (<15 min) but recovered to the level in the hearts reperfused with no neutrophils 45 min after the reperfusion. We examined the effects of selectin inhibitors under experimental conditions in which the hearts were perfused with 30 million neutrophils. The treatment with sialyl Lewis X-oligosaccharide at a dose of 0.3 mg/min resulted in amelioration of left ventricular developed pressure to 57.2±14%, compared to 26.1±4.3% in the saline-treated group ( P<0.05). Similarly, the treatment with mouse anti-human P-selectin monoclonal antibody (IgG1) PB1.3 at a dose of 0.6 mg/min resulted in the prominent recovery of left ventricular developed pressure after 45 min of reperfusion (59.9±9.3% vs. 26.1±4.3% in the saline-treated group, P<0.05). PB1.3 also attenuated the elevation of left ventricular end-diastolic pressure compared to that of the saline-treated group during the reperfusion period. Moreover, the treatment with PB1.3 ameliorated the recovery of coronary flow until 10 min after the reperfusion and the recovery of coronary flow 10 min after the reperfusion was 55.2±9.2%, as compared to 28.2±7.7% in saline-treated hearts ( P<0.05). To our knowledge, this is the first direct demonstration that the specific inhibition of P-selectin results in the inhibition of neutrophil-mediated left ventricular dysfunction or myocardial stunning.

Protection Against Ischamia-Reperfusion Induced Oxidative Stress by Vitamin E Treatment

The rat heart protection offered by vitamin E against oxidative stress after ischaemia-reperfusion was studied by using a new methodological approach. Functional recovery of hearts from ischaemia-reperfusion was correlated with a traditional index of oxidative stress such as lipid peroxidation and with antioxidant capacity and susceptibility to oxidants of the tissue evaluated by enhanced chemiluminescence techniques. Rats were treated with ten daily i.m. injections of 100 mg/kg body weight of vitamin E. The functional recovery during reperfusion (20 min, following 45 min ischaemia) of Langendorff preparations from control (vehicle-injected) and vitamin E treated rats was evaluated in terms of heart rate, left ventricular developed pressure (LVDP), double product (= heart rate.LVDP) and coronary flow recovery. Vitamin E treatment significantly improved functional recovery of heart rate, LVDP, double product and coronary flow. It also increased the level of vitamin E and reduced the levels of both malondialdehyde and hydroperoxides in the heart tissue at the end of the ischaemia-reperfusion protocol. In contrast, it did not affect the antioxidant capacity and the response of heart homogenates to in vitro oxidative stress measured after ischaemia-reperfusion. These results show a protective action of vitamin E treatment against lipid peroxidation and cardiac dysfunction associated with ischaemia-reperfusion. Although the precise mechanism of this protection is not evident, our model in part suggests a role of vitamin E other than as a free radical scavenger.

Influence of the Severity of Myocardial Ischemia on the Intensity of Ascorbyl Free Radical Release and on Postischemic Recovery during Reperfusion

Ascorbyl free radical (AFR), can be considered as an atoxic and endogenous indicator of oxidative stress. The purpose of our experiments was to investigate the influence of the severity and length of ischemia on the extent of AFR release during myocardial ischemia and reperfusion. For that purpose, isolated perfused rat hearts were submitted to a global ischemia, either total (residual flow 0%) or low flow (residual flow 5%), of 20 or 60 min length. Coronary effluents were collected at different times of experimentation and analyzed with Electron Spin Resonance (ESR) spectroscopy. AFR ESR doublet (g = 2.0054, a H = 0.188 MT) was not detected in coronary effluents collected during control perfusion periods. Nevertheless, during low-flow ischemia, a weak AFR release was noted. Moreover, a sudden and massive AFR liberation was observed at the time of reperfusion: this AFR release was weaker after low-flow ischemia than after total ischemia and was enhanced when the duration of ischemia increased from 20 min to 60 min. The large liberation of AFR noticed during global total ischemia was associated with a greater depression in myocardial contractile function and a lower recovery in coronary flow. In conclusion, our study demonstrates that AFR production at the time of reperfusion depends on the duration and strength of the ischemia, and is related to free radical injury. According to previously described ascorbate/AFR properties, we can conclude that AFR liberation in coronary effluents could represent a marker of oxidative stress during ischemia and/or reperfusion of hearts. This AFR release could be considered a sign of the severity of the ischemic episode, and could be related to the functional impairment during reperfusion.

Myocardial Protection of Contractile Function After Global Ischemia by Physiologic Estrogen Replacement in the Ovariectomized Rat

The role of physiologic estrogen levels (pg) on post-ischemic myocardial function was studied in the isolated working rat heart without (n=28, experiment No. 1) or with (n=15, experiment No. 2) preconditioning. For experiment No. 1, female ovariectomized rats were treated with placebo (n=19) or 17β-estradiol (E2,n=9; chronic E2), and 14 days later hearts were removed and perfused with modified Krebs–Henseleit bufferin vitro. In nine placebo-treated rats, E2 was administered at 20 min prior to ischemia (acute E2). The hearts were subjected to 15 min of global ischemia and 20 min of reflow. In experiment No. 2, ovariectomized rats were treated with placebo (n=8) or 17β-E2 (chronic E2,n=7). In this experiment, hearts were first preconditioned and then subjected to 20 min of sustained ischemia followed by 20 min of reflow. Global ischemia was produced by clamping the aorta and restricting left atrial flow so that coronary flow was reduced to zero; hemodynamics were continuously monitored throughout the study. Aortic flow, coronary flow, cardiac output, and dP/dtwere assessed at baseline, at the end of the ischemic period, and during reflow. The severity of ischemia was measured by post-ischemic release of lactate, lactate dehydrogenase, and creatine kinase and was similar among all groups in each study. In experiment No. 1, recovery of aortic flow, cardiac output, and dP/dtfollowing reperfusion, was significantly improved in rats treated with chronic E2 (P<0.05); acute E2 had no significant benefit. Post-ischemic recovery of coronary flow was not significantly affected. In experiment No. 2, chronic E2 treatment also significantly improved post-ischemic recovery of cardiac function in preconditioned hearts when compared with controls (P<0.05). In summary, E2 replacement in ovariectomized rats improves contractile function following global ischemia and reflow; cardioprotection by estrogen was observed over and above that conferred by ischemic preconditioning. Since the cardioprotective effect of E2 was independent of a significant improvement in coronary flow a direct effect of the hormone on the cardiac myocytes is postulated.

Chronic Alcohol Consumption Causes Accelerated Myocardial Preconditioning to Ischemia‐Reperfusion Injury

We have previously demonstrated that chronic alcohol consumption (8 to 10 weeks with ethanol as 36% of the caloric intake) does not exacerbate the effects of ischemia reperfusion injury on the heart. In those same studies, however, Gram-negative sepsis caused myocardial depression in both control and alcoholic rats, but also protected hearts from further damage due to ischemia-reperfusion. In the present study, we determined if preconditioning, a very short ischemia-reperfusion episode that protects the heart from more prolonged ischemia, would have similar effects on hearts from alcoholic and control rats with or without sepsis. Thus, rats were fed a liquid diet supplemented with ethanol or dextrin for 8 to 10 weeks. Some alcoholic and control rats were made septic with Escherichia coli injected into the subcutaneous space, whereas others received an injection of sterile saline. Isolated, isovolumically beating hearts were studied the following day. Hearts were made ischemic for 5 min, reperfused for 5 min, and then made ischemic for 35 min and reperfused for 25 min. Data from similar groups of hearts receiving only 35 min ischemia, and studied at the same time as the present groups, have been previously reported. The 5-min preconditioning episode was more effective in protecting hearts in the alcohol group than in the control group. Postischemic left ventricular developed pressure and +dP/dtmax were not significantly decreased from the preischemic values in the alcohol group, but were significantly decreased in the control group. The time to recovery of spontaneous contractions was decreased by preconditioning in the alcohol group but not in the control group, and the recovery of coronary flow was enhanced in the alcohol group, but not in the control group by pre-conditioning. Thus a single 5-min ischemic procedure was effective in protecting the heart from prolonged ischemia in the alcohol group, whereas it was not sufficient to elicit protection in the control group. Sepsis depressed preischemic function in both groups, but recovery from ischemia was complete.

Effects of Specific Sodium/Hydrogen Exchange Inhibitor During Cardioplegic Arrest

Background. The accumulation of intracellular sodium during myocardial ischemia couples an inappropriate calcium influx and depressed cardiac recovery during subsequent reperfusion. The effects of the selective sodium/hydrogen exchange inhibitor HOE 694 are evaluated during myocardial ischemia and reperfusion. Methods. Ten isolated rat hearts were subjected to a 2-minute infusion of St. Thomas’ cardioplegia ± 1 μmol/L HOE 694 followed by 50 minutes’ normothermic (37°C) global ischemia. Intracellular sodium accumulation was continuously measured using triple quantum filtered 23Na nuclear magnetic resonance spectroscopy without chemical shift reagents. Hemodynamic variables were assessed before and after ischemia. Results. The addition of 1 μmol/L HOE 694 to St. Thomas’ cardioplegic solution (n = 5) attenuated the accumulation of intracellular sodium after 50 minutes’ ischemia (160.5% ± 9.1% versus 203.4% ± 10.9% [mean ± standard error], HOE 694 versus control, respectively; p = 0.014) and after the initial reperfusion period (first 30 minutes) (288.7% ± 10.2% versus 335.9% ± 10.3%; p = 0.008). HOE 694–treated hearts showed significantly improved postischemic recovery of left ventricular developed pressure (53.5% ± 8.4% versus 26.4% ± 6.6%; p = 0.036) and rate–pressure product (40.2% ± 6.9% versus 13.2% ± 5%; p = 0.014). Postischemic recovery of coronary flow was not significantly different between the two groups (68.6% ± 5.9% versus 55.5% ± 4.6%, HOE 694 versus control, respectively; p = 0.11). Conclusions. The addition of 1 μmol/L HOE 694 to cardioplegic solution attenuates the increase of intracellular sodium during myocardial ischemia and early reperfusion. This is coupled with an improved recovery of contractile function, possibly as a result of decreased sodium and calcium overload of ischemic myocardium.

Inhibition of endogenous endothelin during cardioplegia improves low coronary reflow following prolonged hypothermic arrest

Endothelin-1 (ET) is a potent endogenous vasoconstrictor which has been shown to be increased following ischaemia and cardiopulmonary bypass. We tested the hypothesis that inhibition of ET synthesis during cardioplegic arrest using phosphoramidon (an ET converting enzyme inhibitor) or blockade of ET receptors using bosentan (a mixed ET(A)/ET(B) antagonist), might improve the postischaemic recovery of coronary flow. Using an isolated Langendorff perfused rat heart model we compared the addition of phosphoramidon or bosentan to St Thomas' Hospital No. cardioplegia vs. control (plain cardioplegia). We measured recovery of coronary flow following 4 h of cardioplegic arrest at 4 degrees C. In a second series of experiments using an isolated working rat heart model we measured the recovery of cardiac function following 4 h of cardioplegic arrest at 4 degrees C. Results are expressed as percentages of preischaemic values (+/- S.E.M). In the first series of experiments, addition of phosphoramidon to cardioplegia improved the postischaemic recovery of coronary flow after 30 min of reperfusion: control 81.3% (+/- 3.5); phosphoramidon 10(-6) M 86.2% (+/- 3.1); phosphoramidon 10(-5) M 95.0% (+/- 3.0) P = 0.03 vs. control. Likewise, addition of bosentan 10(-5) M improved coronary flow following 20 min of reperfusion: control 96.7% (+/- 4.0), and bosentan 109.6% (+/- 4.7) P = 0.04. The addition of phosphoramidon or bosentan had no effect on the postischaemic recovery of mechanical function following 30 min of reperfusion. Both inhibition of ET synthesis and ET receptor blockade during prolonged hypothermic arrest improves postischaemic coronary flow, but appears to have no effect on the recovery of cardiac mechanical function.

Impaired Cardioplegic Delivery and the Loss of Cardioprotection: a Role for Preconditioning

We have previously shown that, while ischemic preconditioning and cardioplegia afford similar protection against injury during ischemia and reperfusion, this protection is not additive. However, it is not known whether the same applies when the delivery of cardioplegia is suboptimal, such as may occur in the case of a coronary stenosis. To investigate the protective effect of cardioplegiavpreconditioning when the delivery of cardioplegia is impaired, isolated rat hearts were subjected to 40 min of global ischemia followed by 40 min of reperfusion. Seven groups of hearts (1 g wet wt) were studied (n=8/group): Group 1: controls with unprotected ischemia (no intervention); Group 2: in which only 0.2 ml of the St Thomas» cardioplegic solution was administered (2 min) prior to ischemia; group 3: in which the volume of cardioplegic solution was increased to 0.5 ml; Group 4: received 1.0 ml of cardioplegia; Group 5: received 2.0 ml of cardioplegia; Group 6: were subjected to ischemic preconditioning (3 min ischemia, 3 min reperfusion, 5 min ischemia, 5 min reperfusion) prior to ischemia; and Group 7: in which ischemic preconditioning and cardioplegia (1.0 ml) were used in combination. The mean postischemic recovery of left ventricular developed pressure (LVDP), expressed as a percentage of its pre-ischemic value, was 33±3% in the control group; this was significantly improved (P<0.05) in hearts receiving 2.0 ml of cardioplegia (59±5%), whereas volumes of 0.2, 0.5 or 1.0 ml of cardioplegia afforded no significant protection (recoveries of LVDP were 32±6%, 37±5% and 37±5%, respectively). Preconditioning alone and the combination of preconditioning plus 1.0 ml of cardioplegia afforded similar protection (57±3% and 58±3%;P<0.05vcontrols). At the end of reperfusion, left ventricular end-diastolic pressure (LVEDP) was substantially increased in control hearts (57±3 mmHg); it was decreased in the group receiving 2.0 ml of cardioplegic solution (40±5 mmHg;P<0.05vcontrol group), but not in the groups receiving 0.2, 0.5 or 1.0 ml of cardioplegic solution (59±4, 55±3 and 54±4 mmHg, respectively). Again, preconditioning alone or preconditioning plus 1.0 ml of cardioplegia afforded similar good protection (39±1 mmHg and 37±2 mmHg, respectively). A similar pattern was observed for the post-ischemic recovery of coronary flow. Under conditions where the delivery of cardioplegia is impaired (<2.0 ml/g myocardium) preconditioning alone or preconditioning in combination with cardioplegia is more protective that cardioplegia alone. These results may be of clinical interest because most patients undergoing surgery for ischemic heart disease suffer from severe coronary artery lesions that may prevent the delivery of sufficient cardioplegic solution to ensure maximum protection.

Dose-response studies with idrapril in the rat heart during acute myocardial ischaemia and reperfusion

We assessed the effects of idrapril, a novel angiotensin-converting enzyme inhibitor, and captopril in the isolated rat heart after ischaemia and reperfusion and measured angiotensin-converting enzyme activity in myocardial tissue. Hearts were perfused and subjected to global ischaemia and reperfusion. Idrapril (0.1, 1, 10, and 50 μg/ml), captopril (80 μg/ml) or vehicle were given before ischaemia and throughout reperfusion. Post-ischaemic recovery of coronary flow was significantly decreased with 50 μg/ml of idrapril (43 ± 9% compared to 64 ± 3% in controls) whereas heart rate was unaffected. Recovery of developed pressure and activity of cardiac angiotenδin-converting enzyme were significantly reduced by idrapril in a dose-dependent manner. This study suggests that protection or lack of protection by idrapril on recovery of contractile function seems to depend on the degree of inhibition of tissue angiotensin-converting enzyme activity in the setting of acute heart ischaemic insult. Our results suggest that while a certain degree of inhibition of angiotensin-converting enzyme in the heart is beneficial, marked tissue inhibition may be deleterious.