TPEN, a transition metal chelator, improves myocardial protection during prolonged ischemia.

In view of the hypothesis that free radicals induced damage during ischemia and reperfusion is mediated by transition metals, we investigated the effect of the potent metal chelator TPEN (N,N,N'N'-tetrakis(-)[2-pyridylmethyl]-ethylenediamine) on cardiac function after prolonged myocardial ischemia. Isolated working rat hearts were subjected to 12 hours of cold ischemic arrest followed by reperfusion for 1 hour. The study was carried out on five groups (nine hearts in each): (1) St. Thomas' Hospital cardioplegic solution; (2) St. Thomas' Hospital cardioplegic solution with 7.5 mumol/L TPEN; (3) protection conditions as in group 2, but with TPEN administration during preischemic and reperfusion periods; (4) University of Wisconsin solution; and (5) the same conditions as in group 4 with TPEN administration during the preischemic and reperfusion periods. Significant enhancement of hemodynamic recovery was observed in the presence of TPEN throughout the experiment. The recovery of cardiac output was 24% +/- 4% in group 3, as compared to 12% +/- 4% in group 1 (p < 0.01). The postischemic left ventricular pressure recovery was 57% +/- 4% in group 3, as compared to 18% +/- 7% in group 1 (p < 0.005). The hearts in group 5 recovered, reaching 29% +/- 2% of the preischemic cardiac output and at 65% +/- 2% of the left ventricular pressure recovery (p < 0.05 versus group 3). Lactate dehydrogenase was released throughout the reperfusion. TPEN addition to groups 2 and 3 did not significantly reduce lactate dehydrogenase release; however, TPEN in University of Wisconsin solution and throughout the experiment significantly decreased lactate dehydrogenase release.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preservation with 8-bromo-cyclic GMP improves pulmonary function after prolonged ischemia

Background. Cyclic guanosine monophosphate (cGMP) is a potent second messenger for the nitric oxide pathway in the pulmonary vasculature. Increased cytosolic cGMP levels elicit pulmonary vasodilatation resulting in decreased pulmonary vascular resistance and maximized pulmonary function after ischemia-reperfusion injury. We hypothesized that the addition of a membrane-permeable cGMP analogue (8-bromo-cGMP) to a Euro-Collins (EC) preservation solution would ameliorate pulmonary reperfusion injury better than prostaglandin E₁ injection alone after prolonged hypothermic ischemia.Methods. All lungs from New Zealand White rabbits (weight, 3 to 3.5 kg) were harvested en bloc, flushed with EC solution, and reperfused with whole blood for 30 minutes. Group 1 lungs (immediate control) were immediately reperfused. Group 2 lungs (control) were stored inflated at 4°C for 18 hours before reperfusion. Groups 3 and 4 lungs were flushed with EC solution containing 200 μmol/L 8-bromo-cGMP and stored at 4°C for 18 and 30 hours, respectively. Fresh, nonrecirculated venous blood was used to determine single-pass pulmonary venous–arterial oxygen gradients at 10-minute intervals. Assays for cGMP, cyclic adenosine monophosphate, nitric oxide synthase activity, and myeloperoxidase were performed on all lung tissue samples. Wet to dry weight ratios were determined after 2 weeks of passive desiccation.Results. Oxygenation (venous-arterial oxygen gradient), pulmonary artery pressure, pulmonary vascular resistance, and edema formation were significantly improved in groups 3 and 4 (addition of 8-bromo-cGMP to EC plus 18 or 30 hours of hypothermic ischemia). Hypothermic storage (groups 2, 3, and 4) decreased both nitric oxide synthase activity and myeloperoxidase levels compared with immediate reperfusion (group 1).Conclusions. These results suggest that the addition of a membrane-permeable cGMP analogue to an EC pulmonary flush solution improves pulmonary function after prolonged storage compared with EC and prostaglandin (E₁) preservation alone. The finding of myeloperoxidase reduced levels after hypothermic storage and subsequent reperfusion may suggest a more important role for pulmonary hemodynamic control in mitigating pulmonary reperfusion injury.     

Hepatic ischemia models for determining the effects of ATP-MgCl2 treatment

Although ATP-MgCl2 treatment after global hepatic ischemia has been shown to improve cell function, a recent report has failed to confirm this in a model of regional hepatic ischemia. To determine the reason for this, rats were anesthetized and blood vessels to the left and median lobes of the liver were occluded. After 90 min of ischemia, the ligature around those vessels was removed. In Model 1, blood flow to the right lobes of the liver was then occluded whereas in Model 2, flow to those lobes was left intact. In both models the rats received intravenously 1.0 ml of saline or ATP-MgCl2 (12.5 mumole each) after ischemia. One hour after reflow, hepatic blood flow in the right and/or left lobe was measured following which mitochondria from the respective lobes were isolated and their function measured. The results indicated that although ATP-MgCl2 infusion following hepatic ischemia significantly improved hepatic blood flow and mitochondrial function in Model 1 (in which the right lobes were ligated following release of the occlusion to the left and median lobes), it failed to do so in Model 2 (in which the right lobes were not occluded after release of the occlusion to the left and median lobes). These results emphasize the importance of the rapid restoration of blood flow following hepatic ischemia. In the presence of shunts such as occur in Model 2, it is unlikely that any therapeutic agent would be effective.     

Effects of left heart bypass on cardiac performance following myocardial ischemia.

A series of nine dogs underwent 20 minutes of myocardial ischemia by cross clamping the aorta while total cardiopulmonary bypass. The four dogs that did not have subsequent left bypass all showed a deterioration of ventricular function curve 30 minutes after restarting the heart beat when compared to their own preischemic values. The five animals which were supported for 30 minutes in left heart after bypass all showed essentially unchanged cardiac function after bypass. This study suggests that an improvement of myocardial performance after ischemic damage can be achieved with left heart bypass.     

Expression of BCL-2 in liver grafts after adenoviral transfer improves survival following prolonged ischemia and reperfusion in rat liver transplantation

Apoptosis represents a crucial mechanism of ischemia-reperfusion injury after liver transplantation. Bcl-2 may inhibit apoptosis. This study investigates the effect on ischemia/reperfusion injury and survival after rat liver transplantation of adenoviral bcl-2 transfer into donor livers. METHODS: A nonreplicative adenovirus, expressing bcl-2 under control of a tetracyclin-inducible promoter (adv TetOn bcl-2) was used to treat male Lewis rats in combination with a second adenovirus transferring the TetOn repressor protein under control of a cytomegalovirus promoter (advCMVRep). Virus induction was achieved by addition of doxycyclin to the drinking water. Controls were pretreated with a control adenovirus (advCMV GFP) or with doxycycline. Liver transplantations were performed after 16-hour graft storage. Bcl-2 expression was evaluated by Western blot and immunohistology. Survival was monitored for 7 days, and tissue specimens were collected at 24 hours and 7 days post reperfusion. RESULTS: After pretreatment with advTetOn bcl-2/adv CMVRep, intrahepatic bcl-2 expression was evident at 24 hours and 7 days but was absent among controls. Bcl-2 expression was detected in hepatocytes and, to a high degree, in sinusoidal lining cells. TUNEL-positive sinusoidal lining cells were strikingly reduced after bcl-2 transfer (0.1 +/- 0.3 cells/hpf, mean +/- SD) compared to control virus (4.8 +/- 2.3) or doxycyclin-treated grafts (1.3 +/- 0.2); P < .05. After bcl-2 treatment, survival after transplantation was 100%, whereas it was 50% in both control groups (P = .035). CONCLUSION: The study shows the feasibility of transient, doxycyclin-controlled adenoviral gene transfer in a transplantation model. Bcl-2 expression increased survival after ischemia/reperfusion in rat liver transplantation, potentially through protection of sinusoidal lining cells.     

Isoflurane improves the tolerance to pacing-induced myocardial ischemia

Fourteen patients with normal, global, left ventricular function scheduled for elective myocardial revascularization were studied at rest and during atrial pacing before and during isoflurane anesthesia (0.5% end-tidal) plus 50% nitrous oxide. Rapid atrial pacing was performed in a stepwise fashion until the onset of angina pectoris in the awake patients. The same step increase in pacing rate was applied in the anesthetized patients. Compared with prepacing baseline values, isoflurane significantly decreased systemic blood pressure, coronary perfusion pressure, the rate-pressure product, and cardiac index. No patient had ST-segment depression while awake or during isoflurane anesthesia before pacing was started. Prepacing left and right ventricular filling pressures and wave forms were normal, both while awake and during isoflurane anesthesia. The mean pacing rate at which first signs of myocardial ischemia appeared (V5 ST-segment depression greater than or equal to 0.1 mV, increase in pulmonary capillary wedge pressure (PCWP) to greater than or equal to 15 mmHg, and prominent PCWP v-waves greater than or equal to 20 mmHg) was significantly higher during isoflurane anesthesia than in the awake patients (128 +/- 4 vs. 115 +/- 5 beats/min). With the exception of one patient, the individual pacing rates inducing first signs of ischemia in the awake patients were below the anginal threshold. None of the patients had a reduced ischemic threshold during anesthesia. Eleven anesthetized patients tolerated a higher pacing rate until initial signs of ischemia appeared. In four of these patients, the pacing rate required to induce first signs of ischemia was above the heart rate at which chest pain had been induced while they were awake. At a peak atrial pacing rate of 129 +/- 5 beats/min, which had induced angina pectoris in the awake patients, the increase in PCWP was significantly smaller during pacing with isoflurane than during control pacing. Prominent PCWP v-waves (greater than or equal to 20 mmHg) appeared in 12 of the 14 patients during initial pacing to angina and in eight patients paced during isoflurane anesthesia. In six of these eight patients, the abnormal v-waves were less prominent than those observed during control pacing. Ischemic ST-segment changes developed in 13 of 14 patients during initial pacing and in nine patients during pacing with isoflurane. Mean V5 ST-segment depression during the two pacing periods was significantly different, averaging 0.19 and 0.11 mV, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)     

Histopathology of muscle flap microcirculation following prolonged ischemia

The purpose of this study was to evaluate histological changes occurring in the microcirculation of a muscle flap following prolonged ischemia and to correlate them with the flow hemodynamics. The cremaster muscle flap model was used for direct in vivo studies of the microcirculation. In 45 rats, vascular clamps were applied to the iliac and femoral vessels following flap isolation. Flaps were subjected to various periods of ischemia, ranging from 4 to 6 hours, and 2 hr of reperfusion. In vivo observations of the microcirculation and vessel diameter measurements were taken at 1 hour intervals for an 8 hr period. With prolonged ischemia, return of circulation to the flap was delayed and no flow was observed following 6 hr of ischemia. Morphologic changes at 6 hr revealed red cell and platelet thrombi formation within the capillaries, marked dilatation of postcapillary venules, endothelial swelling in the capillaries, and microhemorrhage formation around the venules. © 1995 Wiley-Liss, Inc.     

Intravenous transplantation of mesenchymal stem cells improves cardiac performance after acute myocardial ischemia in female rats

Mesenchymal stem cells (MSCs) are potential sources of cells for tissue repairing. However, little information is available regarding the therapeutic potency of intravenously transplanted MSCs for myocardial ischemia (MI). In the present study, MSCs were isolated from bone marrow of male rats and expanded in vitro. Three hours after ligation of left anterior descending artery, the transplanted group received an infusion of MSCs through the tail vein. At the same time, a coronary-ligated control group was injected with culture medium. Homing of MSCs to the heart was assessed by expression of the Y chromosome sry gene using fluorescent in situ hybridization (FISH). At 1 week or 8 weeks after transplantation, sry positive cells were present in cardiac tissue in the transplanted group, but not in the hearts of control group. Cardiomyocytes, smooth muscle cells, and endothelial cells that bore sry gene were identified in transplanted group at 8 weeks after transplantation. Ultrastructural observation revealed that a large number of capillary and some immature myocytes were found to survive in the ischemia region. MSCs transplantation also decreased LVEDP pressure and -dP/dt, but increased LVSP and +dP/dt. The cardiac infarct size was significantly smaller in transplanted group than in control group. Our data suggest that intravenously transplanted MSCs improve cardiac performance and promote the regeneration of blood vessels and cardiomyocytes.     

Comparative analysis of the performance of various crystalloid cardioplegic solutions on myocardial protection after prolonged cold ischemia

Introduction

The quality and effectiveness of myocardial protection are fundamental problems to expand the use of and consequently good outcomes of donated hearts for transplantation.

Objective

The purpose of this investigation was to compare the cardioprotective effects of Krebs-Henseleit, Bretschneider-HTK, St Thomas, and Celsior solutions using a modified nonrecirculating Langendorff column model of isolated perfused rat heart during prolonged cold storage.

Materials and Methods

After removal 36 rat hearts underwent isolated perfusion into a Langendorff apparatus using Krebs-Henseleit solution for a 15-minute period of recovery; we excluded organs that did not maintain an aortic pressure above 100 m Hg. Subsequently, we equally distributed the hearts into four groups according to the cardioprotection solution; group 1, Krebs-Henseleit (control); group II, Bretschneider-HTK; group III, St Thomas; and group IV, Celsior. Each heart received the specific cardioplegic solution at 10°C for 2-hour storage at 20°C, before a 15 minutes perfusion with Krebs-Henseleit solution for recovery and stabilization. After 60 additional minutes of perfusion, every 5 minutes we determined heart rate (HR), coronary flow (CF), left ventricular systolic pressure (LVSP), and positive and negative peak of the first derivative of left ventricular pressure (+dP/dt and −dP/dt, respectively).

Results

Comparative analysis by Turkey's test showed the following performances among the groups at 60 minutes of reperfusion: HR: II = IV > III > I; CF: II = IV > I = III; LVSP: IV > I = II = III; +dP/dt: IV > I = II = III; and −dP/dt: IV = II > I = II.

Conclusion

Cardioprotective solutions generally used in clinical practice are not able to avoid hemodynamic alterations in hearts exposed to prolonged ischemia. Celsior solution showed better performance than Bretschneider-HTK, St Thomas, and Krebs-Henseleit.     

Improved myocardial protection by aprotinin pretreatment in prolonged global ischemia

Protective effect of aprotinin pretreatment was assessed by functional, biochemical and morphological preservation in four hour global ischemia followed by one hour reperfusion in dogs. Cardioplegia was induced by intermittent infusion of cold Mg-lidocaine solution. Aprotinin 10,000 KIU/kg was given in low dose group (8 dogs), and 20,000 KIU/kg in high dose group (6 dogs); one half was given before ischemia and another half during ischemia. Betamethasone, coenzyme Q and nifedipine were also given equally in both groups before ischemia. Results were as follows: 1. Four (50%) of low dose group and all of high dose group were successfully taken off CPB and survived for one hour reperfusion. 2. High dose group showed significantly higher blood pressure and LVSWI than low dose group after one hour reperfusion (p less than 0.05). 3. Serum N-acetyl-beta-D-glucosaminidase and mitochondrial aspartate aminotransferase showed the significantly lower activity in high dose group than in low dose group after one hour reperfusion (p less than 0.05). There was no significant difference in the activities of serum beta-glucuronidase and MB-creatine kinase. 4. Myocardial tissues, excised after one hour reperfusion, contained significantly higher creatine phosphate in high dose group than in low dose group (p less than 0.05). There was no significant difference in the contents of adenosine triphosphate, calcium and water. 5. Severely injured mitochondrion were significantly lesser in high dose group than in low dose group. All lysosomes showed mild swelling or enlargement, but those membranous structures were well-preserved in both groups. In conclusion, aprotinin pretreatment might be effective in myocardial protection against prolonged global ischemia, by inhibiting the "leak out" of lysosomal enzymes.     

Direct inhibition of the sodium/hydrogen exchanger after prolonged regional ischemia improves contractility on reperfusion independent of myocardial viability

BACKGROUND: A mechanism for myocardial dysfunction after ischemia and reperfusion is Na(+)/H(+) exchanger activation. Although past in vivo models of limited ischemia and reperfusion intervals demonstrate that Na(+)/H(+) exchanger inhibition confers myocardial protection when administered at the onset of ischemia, the effect of Na(+)/H(+) exchanger inhibition on myocardial function after prolonged ischemia and reperfusion remains unknown. This investigation tested the hypothesis that Na(+)/H(+) exchanger inhibition instituted at reperfusion and after prolonged coronary occlusion in pigs would influence myocardial contractility independent of myocardial viability. METHODS: A coronary snare and sonomicrometry crystals were placed in pigs (n = 21, 32 kg). Coronary occlusion was instituted for 120 minutes followed by reperfusion for 180 minutes. At 105 minutes of ischemia, pigs were randomized to ischemia and reperfusion only (saline solution, n = 11) or Na(+)/H(+) exchanger inhibition (HOE-642, 3 mg/kg intravenously, n = 10). Myocardial injury was determined by tissue staining and measurement of plasma myocyte-specific enzymes. Myocardial contractility was determined by calculation of the regional end-systolic pressure-dimension relation (millimeters of mercury per centimeter) and by assessment of interregional shortening. RESULTS: Infarct size was not different between groups (39% +/- 6%, P =.26). Moreover, at 180 minutes of reperfusion, plasma troponin-I and creatine kinase MB values had increased to identical levels in the ischemia and reperfusion-only and Na(+)/H(+) exchanger inhibition groups (300 +/- 35 and 50 +/- 6 ng/mL, respectively). At 90 minutes of ischemia, regional end-systolic pressure-dimension relation decreased from baseline (5.7 +/- 0.5 versus 2.7 +/- 0.3, P <.05) in the area at risk. By 30 minutes of reperfusion, regional end-systolic pressure-dimension relation decreased further in the ischemia and reperfusion-only group (1.6 +/- 0.2, P <.05), but improved with Na(+)/H(+) exchanger inhibition (4.4 +/- 0.7, P <.05). CONCLUSIONS: Na(+)/H(+) exchanger inhibition instituted at reperfusion improved contractility independent of myocardial viability as assessed by absolute infarct size and myocyte-specific enzyme release. Thus, modulation of Na(+)/H(+) exchanger activity in the setting of prolonged ischemia and reperfusion may hold therapeutic potential.     

Superior myocardial preservation with modified UW solution after prolonged ischemia in the rat heart

Cardiac transplantation remains constrained by poor graft tolerance of prolonged cold ischemia. University of Wisconsin solution has remarkably extended ischemic preservation in pancreas, kidney, and liver transplantation. To assess its efficacy in cardiac preservation, modified University of Wisconsin solution flush and storage were tested against St. Thomas' cardioplegia flush and normal saline solution storage after six hours of ischemia at 0 degrees C in 46 isolated rat hearts. After ischemia, groups were compared before and after reperfusion. After ischemia but before reperfusion, University of Wisconsin solution hearts had significantly less tissue water (3.8%), superior tissue sodium, potassium, calcium, and magnesium profiles, and elevated adenosine and inosine levels, and tended toward better histological preservation. After reperfusion, University of Wisconsin solution more effectively preserved left ventricular compliance (75% versus 35% of baseline), developed pressure (71% versus 45% of baseline), histological integrity, and tissue potassium and calcium profiles than St. Thomas' solution. The University of Wisconsin solution provided superior preservation of systolic and diastolic ventricular function, tissue histology, tissue water, and tissue electrolytes than did St. Thomas' cardioplegia and normal saline solution storage in this experimental model, and might result in improved graft tolerance of ischemia in clinical cardiac transplantation.     

外源性三磷酸腺苷-氯化镁预处理对大鼠供肝热缺血损伤的保护作用

目的 观察三磷酸腺苷-氯化镁(ATP-MgCl2)预处理对无心跳大鼠供肝热缺血损伤的保护作用.方法 根据ATP-MgCl2预处理与否及供肝获取前经历的供体心脏停搏时间(即热缺血时间)30min或45min,将实验动物分为4组,即非预处理的30min(N-30min)组和45min(N-45min)组,以及ATP-MgCl2预处理的30min(tN-30min)组和45min(tN-45min)组行原位肝移植,观察存活状况,取材行光学显微镜及电子显微镜检查,移植术后1、3、7d 采集血样检测肝功能.结果 N-30min组和N-45min组的1周存活率分别为50.0%和16.7%,而tN-30min组和tN-45min组的1周存活率分别为83.3%和66.7%,预处理组移植肝脏的病理及肝功能明显好于非预处理组.结论 ATP-MgCl2预处理能够减轻供肝的热缺血损伤,改善肝功能,减轻病理损害,提高大鼠肝移植的存活率.     

The breakdown of fractal heart rate dynamics predicts prolonged postoperative myocardial ischemia

Patients with myocardial ischemia after noncardiac surgery have a three- to ninefold increased risk of adverse cardiac events. In this study we tested the hypothesis that altered preoperative heart rate variability (HRV) predicts postoperative prolonged myocardial ischemia (>10 min) in elderly surgical patients. Thirty-two patients, age 60 yr or older, admitted to hospital for surgical repair of a traumatic hip fracture with preoperative night and daytime Holter recordings were included. Holter monitoring was initiated at arrival at hospital and continued until the third postoperative morning. Conventional HRV measures along with analysis of short-term fractal scaling exponent (alpha(1)) of RR intervals were assessed for night (from 2 AM to 5 AM) and day (7 AM to 12 AM) periods in each patient. Preoperative alpha(1) was significantly lower (i.e., increased randomness in HRV) during the nighttime compared with daytime (mean +/- SEM; 0.92 +/- 0.08 versus 1.03 +/- 0.06; P = 0.002) in patients with postoperative myocardial ischemia. Patients without ischemia had no such difference. In stepwise multivariate logistic regression analysis, increased preoperative night-day difference of alpha(1) was the only independent predictor of postoperative prolonged ischemia. The odds ratio for an increase of 0.16 U in night-day difference of alpha(1) (corresponding to interquartile range) was 7.7 (95% confidence interval, 1.9-51.4; P = 0.0018). Breakdown of fractal-like heart rate dynamics is predictive for postoperative prolonged myocardial ischemia in elderly patients having emergency surgery for traumatic hip fracture. IMPLICATIONS: Night and daytime Holter recordings before surgical repair of traumatic hip fracture were analyzed with linear and nonlinear heart rate variability methods. Preoperatively increased randomness in heart rate variability was predictive for postoperative, silent prolonged myocardial ischemia. Prolonged myocardial ischemia increases the risk for adverse cardiac events.     

Metabolic intervention to affect myocardial recovery following ischemia.

Myocardial recovery during reperfusion following ischemia is critical to patient survival in a broad spectrum of clinical settings. Myocardial functional recovery following ischemia correlates well with recovery of myocardial adenosine triphosphate (ATP). Adenosine triphosphate recovery is uniformly incomplete during reperfusion following moderate ischemic injury and is therefore subject to manipulation by metabolic intervention. By definition ATP recovery is limited either by (1) energy availability and application in the phosphorylation of adenosine monophosphate (AMP) to ATP or (2) availability of AMP for this conversion. Experimental data suggest that substrate energy and the mechanisms required for its application in the creation of high energy phosphate bonds (AMP conversion to ATP) are more than adequate during reperfusion following moderate ischemic injury. Adenosine monophosphate availability, however, is inadequate following ischemia due to loss of diffusable adenine nucleotide purine metabolites. These purine precursors are necessary to fuel adenine nucleotide salvage pathways. Metabolic interventions that enhance AMP recovery rather than those that improve substrate energy availability during reperfusion are therefore recommended. The mechanisms of various metabolic interventions are discussed in this framework along with the rationale for or against their clinical application.