Influence of the pH of cardioplegic solutions on intracellular pH, high-energy phosphates, and postarrest performance

Time Course of High-Energy Phosphate Depletion During Cold Storage of Human Heart Grafts Using the Celsior Solution

The aim of this study was to provide insight into high-energy phosphate compound concentration dynamics under realistic clinical cold-storage conditions using the Celsior solution in seven heart grafts discarded from transplantation. The hearts of seven local donors (three males, four females, age 37 ± 17 years, height 175 ± 5 cm, weight 75 ± 9 kg) initially considered for transplantation and eventually discarded were submitted to a Magnetic Resonance Spectroscopy observation in a clinical Magnetic Resonance Imaging scanner over at least 9 h. The grafts remained in their sterile container at 4°C during the entire examination. Hence, Phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi) and intracellular pH were recorded non-destructively at a 30-minute interval. With the ischemic time Ti, the concentration ratios decreased at PCr/ATP = 1.68-0.0028·Tis, Pi/ATP = 1.38 + 0.0029·Tis, and intracellular pH at 7.43-0.0012·Tis. ATP concentration remained stable for at least 9 h and did not decrease as long as phosphocreatine was detectable. Acidosis remained moderate. In addition to the standard parameters assessed at the time of retrieval, Magnetic Resonance Spectroscopy can provide an assesment of the metabolic status of heart grafts before transplantation. These results show how HEPC metabolites deplete during cold storage. Although many parameters determine graft quality during cold storage, the dynamics of HEPC and intracellular pH may be helpful in the development of strategies aiming at extending the ischemic time.

Comparison of lactated Ringer's solution and Plasma-Lyte A as a base solution for del Nido cardioplegia: a prospective randomized trial

OBJECTIVES

The use of del Nido cardioplegia has been increasing in popularity for adult cardiac surgery. However, the base solution, Plasma-Lyte A, is not always available in many countries. This prospective randomized controlled trial evaluated myocardial preservation and clinical outcomes when using lactated Ringer's solution (LRS) compared to Plasma-Lyte A as a base solution for del Nido cardioplegia.

METHODS

Adult patients undergoing first-time elective cardiac surgery for acquired heart disease, including isolated coronary artery bypass grafting, isolated valve surgery, combined valve surgery or concomitant coronary artery bypass grafting and valve surgery were randomized to receive either LRS (n = 100) or Plasma-Lyte A (n = 100).

RESULTS

There were no significant differences between the 2 groups in terms of age, comorbidities, Society of Thoracic Surgeons risk score and type of procedures. The primary outcome, postoperative troponin-T at 24 h, was similar in both groups (0.482 vs 0.524 ng/ml; P = 0.464). Other cardiac markers were also similar at all time points. The LRS group had a lower pH (7.228 vs 7.246; P = 0.005) and higher calcium levels (0.908 vs 0.358 mmol/l; P < 0.001) in the delivered cardioplegia, but there were no significant differences in clinical outcomes, such as ventricular fibrillation, left ventricular ejection fraction, inotrope/vasopressor requirement, intra-aortic balloon pump support, intensive care unit stay, hospital stay, atrial fibrillation, red cell transfusion and complications.

CONCLUSIONS

The results suggest that LRS can be used as an alternative to Plasma-Lyte A as the base solution for del Nido cardioplegia, with similar myocardial preservation and clinical outcomes.

CPA toxicity screening of cryoprotective solutions in rat hearts

In clinical practice, donor hearts are transported on ice prior to transplant and discarded if cold ischemia time exceeds ∼5 h. Methods to extend these preservation times are critically needed, and ideally, this storage time would extend indefinitely, enabling improved donor-to-patient matching, organ utilization, and immune tolerance induction protocols. Previously, we demonstrated successful vitrification and rewarming of whole rat hearts without ice formation by perfusion-loading a cryoprotective agent (CPA) solution prior to vitrification. However, these hearts did not recover any beating even in controls with CPA loading/unloading alone, which points to the chemical toxicity of the cryoprotective solution (VS55 in Euro-Collins carrier solution) as the likely culprit. To address this, we compared the toxicity of another established CPA cocktail (VEG) to VS55 using ex situ rat heart perfusion. The CPA exposure time was 150 min, and the normothermic assessment time was 60 min. Using Celsior as the carrier, we observed partial recovery of function (atria-only beating) for both VS55 and VEG. Upon further analysis, we found that the VEG CPA cocktail resulted in 50 % lower LDH release than VS55 (N = 4, p = 0.017), suggesting VEG has lower toxicity than VS55. Celsior was a better carrier solution than alternatives such as UW, as CPA + Celsior-treated hearts spent less time in cardiac arrest (N = 4, p = 0.029). While we showed substantial improvement in cardiac function after exposure to vitrifiable concentrations of CPA by improving both the CPA and carrier solution formulation, further improvements will be required before we achieve healthy cryopreserved organs for transplant.

Recovery from very long aortic cross-clamping in redo complex aortic surgery

A 68-year-old man had undergone ascending aortic replacement for acute type A aortic dissection. Three months later, he had a new aortic dissection with an ulcer-like projection located in the aortic arch with suspected graft infection. An emergent redo total aortic arch and root replacement was performed because of the coexistence of a fragile aortic root wall. The extensive redo procedure necessitated a very long aortic cross-clamping time (516 min). After 25 min of assisted circulation, he was easily weaned from the cardiopulmonary bypass. Finally, an omental flap was harvested to cover the graft. Postoperative ECG and CK-MB examinations showed no significant myocardial injury. He had no symptoms of heart failure and was discharged after a month of antibiotic therapy. One-year follow-up UCG study revealed no abnormal findings except for signs of pericardial adhesion.

Limitation of myocardial and endothelial injury of the rat heart graft after preservation with Centre de Résonance Magnétique Biologique et Médicale (CRMB) solution

Myocardial injury caused by prolonged storage compromises post-transplantation contractile performance and induces endothelial injury. The aim of this study was to compare a solution developed in our laboratory [Centre de Résonance Magnétique Biologique et Médicale (CRMBM) solution] with a widely used solution (Celsior, Genzyme, Saint Germain en Laye, France). Metabolic and contractile parameters as well as indexes of endothelial injury were measured in a heterotopic rat heart transplantation model with a 3-h ischaemia and a 1-h reperfusion. The two solutions were randomly used for cardioplegia and graft preservation in six experiments each. During reperfusion, developed pressure and rate pressure product were higher with CRMBM compared with Celsior (P = 0.0002 and P = 0.0135, respectively). Phosphocreatine and adenosine triphosphate (ATP) concentrations after reperfusion were significantly higher with CRMBM (P = 0.0069 and P = 0.0053, respectively). Endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) protein expression were decreased to the same extent after reperfusion compared with baseline with CRMBM (P = 0.0001 and P < 0.0001, respectively) and Celsior (P = 0.0007 and P < 0.0001, respectively). Total nitrate concentration (NOx) was significantly increased after reperfusion with CRMBM (P < 0.0001 versus baseline and P < 0.0001 versus Celsior). Na,K-ATPase activity was decreased in both groups versus baseline after reperfusion (P < 0.0001 for CRMBM and P < 0.0001 for Celsior). We showed limitation of both myocardial and endothelial damage with CRMBM compared with Celsior during heterotopic rat heart transplantation in vivo.

A single solution for multiple organ procurement and preservation

Two or three different solutions may be used to preserve thoracic and abdominal organs during a single procurement. The aim of this prospective, multi-center, noncomparative study was to evaluate the safety and efficacy of Celsior (study solution, solution S) as a flushing and cold storage solution for both thoracic and abdominal organs. Between August 1999 and July 2000, 72 consecutive multiple-organ procurements were performed using solution S as the sole solution for flushing out and cold-storing thoracic and abdominal grafts. Two hundred and sixty-four grafts were implanted into 245 recipients (131 kidneys, 9 kidney-pancreases, 69 livers, 34 hearts and 6 heart-lungs). The mean cold ischemia time was 21 h for kidneys (26%>24 h); 11 h 26 min for pancreases, 9 h 16 min for livers (23%>12 h), and 2 h 58 min for hearts and lungs. No cardiac failure or arrhythmia occurred on graft reperfusion. Fourteen percent of kidney recipients had delayed graft function. The mean serum creatinine level at 3 months was 123 +/- 41 micromol/l. All pancreas recipients were insulin-free at 3 months. Primary graft nonfunction occurred in one liver recipient. Complete hepatic artery thrombosis occurred in six liver recipients during the first month; four of these patients had a risk factor for thrombosis. All but three of the heart recipients were in sinus rhythm on day 1, and 65% were extubated on day 1. Inotropic drugs were necessary during the first 72 h in 25% of heart recipients. Twelve-month patient and graft survival rates were, respectively, 100% and 96% (kidney), 100% and 89% (pancreas), 88% and 83% (liver), 77.5% (heart) and 67% (heart-lung). These results suggest that Celsior, a ready-to-use solution, is safe and effective for multiple organ procurement and preservation.

Myocardial protection with oxygenated esmolol cardioplegia during prolonged normothermic ischemia in the rat

OBJECTIVE

We previously showed that arrest with multidose infusions of high-dose (1 mmol/L) esmolol (an ultra-short-acting beta-blocker) in oxygenated Krebs-Henseleit buffer (esmolol cardioplegia) provided complete myocardial protection after 40 minutes of normothermic (37 degrees C) global ischemia in isolated rat hearts. In this study we investigated the importance of oxygenation for protection with esmolol cardioplegia, compared it with that of St Thomas' Hospital cardioplegia, and determined the protective efficacy of multidose esmolol cardioplegia for extended ischemic durations.

METHODS

Isolated rat hearts (n = 6/group) were perfused in the Langendorff mode at constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer at 37 degrees C. The first part of the first study had four groups: (i) multidose (every 15 minutes) oxygenated (95% oxygen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (ii) multidose deoxygenated (95% nitrogen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (iii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia, and (iv) multidose deoxygenated esmolol cardioplegia during 60 minutes of global ischemia. The second part of the first study had three groups: (v) multidose St Thomas' Hospital solution during 60 minutes of global ischemia, (vi) multidose oxygenated St Thomas' Hospital solution during 60 minutes of global ischemia, and (vii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia. In the second study, hearts were randomly assigned to 60, 75, 90, or 120 minutes of global ischemia and at each ischemic duration were subjected to multidose oxygenated constant flow or constant pressure infusion of (i) Krebs-Henseleit buffer (constant flow), (ii) Krebs-Henseleit buffer (constant pressure), (iii) esmolol cardioplegia (constant flow), or (iv) esmolol cardioplegia (constant pressure). All hearts were reperfused for 60 minutes, and recovery of function was measured.

RESULTS

Multidose infusion of oxygenated esmolol cardioplegia completely protected the hearts (97% +/- 5%) after 60 minutes of 37 degrees C global ischemia. Deoxygenated esmolol cardioplegia was significantly less protective (45% +/- 8%). Oxygenation of St Thomas' Hospital solution did not alter its protective efficacy in this study (70% +/- 4% vs 69% +/- 7%). Infusion of esmolol cardioplegia at constant pressure provided complete protection for 60, 75, and 90 minutes (104% +/- 5%, 95% +/- 5%, and 95% +/- 3%, respectively), whereas protection with constant-flow esmolol cardioplegic infusion was significantly decreased at ischemic durations longer than 60 minutes. This decrease in efficacy of constant-flow esmolol cardioplegia was associated with increasing coronary perfusion pressure leading to myocardial injury.

CONCLUSIONS

Oxygenation of esmolol cardioplegia (Krebs-Henseleit buffer plus 1.0 mmol/L esmolol) was essential for optimal myocardial protection. Multidose infusion of oxygenated esmolol cardioplegia provided good myocardial protection during extended periods of normothermic ischemia. Esmolol cardioplegia may provide an efficacious alternative to hyperkalemia.

L-arginine during long-term ischemia: effects on cardiac function, energetic metabolism and endothelial damage

BACKGROUND

We have evaluated the addition of L-arginine, a precursor of nitric oxide, to a cardioplegic solution (named CRMBM) designed for long-term heart preservation.

METHODS

Isolated isovolumic-perfused rat hearts (n = 22) were arrested with the CRMBM solution either with (Arg) or without L-arginine (2 mmol/L) (Arg group, n = 12, vs control group n = 10), submitted to 8 hours of cold storage (4 degrees C) in the solution, and then reperfused for 60 minutes at 37 degrees C. In 11 hearts, we evaluated the quality of cardiac preservation with P-31 magnetic resonance spectroscopy and the measure of function and cellular integrity. Endothelium-dependent and independent vasodilatations were measured in 11 other hearts, using 5-hydroxytryptamine and papaverine to assess endothelial and smooth muscle function.

RESULTS

Adding L-arginine to the cardioplegic solution improved functional recovery during reflow, as shown by the rate pressure product (31% +/- 3% for control vs 47% +/- 3% for Arg, p = 0.003) together with higher coronary flow and diminished contracture. Purine release in coronary effluents during reperfusion was lower in the Arg group. During ischemia and reflow kinetics of intracellular pH and high-energy phosphates were similar in both groups. Coronary endothelium-dependent vasodilatation was similarly impaired in both groups, but smooth muscle was less altered with L-arginine.

CONCLUSIONS

As an additive to the CRMBM cardioplegic solution, L-arginine provides a protective effect for long-term heart preservation. Our data do not show coronary endothelial protection as the prominent mechanism.

Control of the inflammatory response in extended myocardial preservation of the donor heart

The damaging effects of inflammation after prolonged myocardial ischemia are typically manifest during the period of reperfusion. The imbalance between free radical generation and availability of natural free radical scavengers during postischemic reperfusion set the stage for free radical injury. Calcium overload may convert reversible ischemic damage to fatal myocyte contracture. Complement activation and neutrophil activation, adhesion, and diapedesis are central components of the damaging inflammatory response. Cytokines such as tumor necrosis factor and IL1 simulate IL8 synthesis which is also a potent chemoattractant for neutrophils. The endothelial contribution to ischemic-reperfusion injury results from an imbalance between the production of naturally occurring vasodilators, such as prostacycline and nitric oxide, and vasoconstrictor products, such as endothelin, thromboxane A2, and angiotensin 2. Knowledge of these basic mechanisms has stimulated the formulation of preservation solutions and strategies to ameliorate the inflammatory response during reperfusion.

Optimized cardiac graft preservation: a comparative experimental study using P-31 magnetic resonance spectroscopy and biochemical analyses

BACKGROUND

The University of Wisconsin (UW), St. Thomas (ST) and Broussais (B) solutions were compared to the CRMBM solution, that we developed for long term heart preservation.

METHODS

Isolated isovolumic rat hearts were arrested with each cardioplegic solution (n = 5) to 8 hearts in each group), submitted to 12 hours of cold storage (4 degrees C) in the same solution and then reperfused for 60 minutes at 37 degrees C. Function was measured during control and reflow. High energy phosphates and intracellular pH were monitored by P-31 magnetic resonance spectroscopy. Analyses were performed by biochemical assays and HPLC in coronary effluents (CK, Pi, lactate, purines) and in freeze-clamped hearts (amino acids, nucleotides, CK, LDH) at the end of reperfusion.

RESULTS

Functional recovery was significantly improved with the new cardioplegic solution (50+/-12% recovery for the rate pressure product at the end of reflow vs 8+/-3% with UW, 0% with B and with ST). This result was correlated with the best metabolic and cellular protection as assessed in particular by higher PCr levels during reflow (30+/-3% vs 10+/-3% with UW, 8+/-4% with B, and 7+/-1% with ST) as well as reduced creatine kinase leakage during reflow (110+/-15 IU/60 minute vs 270 +/- 57 IU/60 minute with UW, 323+/-36 IU/60 minute with Broussais solution and 237+/-18 IU/60 minute with ST).

CONCLUSION

This new solution is more effective in prolonged myocardial protection than the three most widely used solutions.

A specific inhibitor of heart cytosolic 5'-nucleotidase I attenuates hydrolysis of adenosine 5'-monophosphate in primary rat myocytes

ATP breakdown was triggered in primary rat myocytes in the presence of coformycin to force the catabolism of AMP through hydrolysis to adenosine. Selective inhibitors of the cytosolic 5'-nucleotidase I (c-N-I) from myocardium were used to measure the intracellular contribution of this enzyme to AMP hydrolysis under these conditions. The selective inhibitor 5-ethynyl-2',3'-dideoxyuridine inhibited the hydrolysis of AMP to adenosine in a concentration-dependent manner with an IC50 value of 20 microM. Maximal inhibition prevented 76% of the conversion of AMP to adenosine, indicating that under these conditions the majority of AMP hydrolysis in rat myocytes occurs through this enzyme. When ATP breakdown was triggered in the presence of thymidine 5'-phosphonate, a more potent inhibitor of the purified cytosolic 5'-nucleotidase, less inhibition of AMP hydrolysis occurred and only after prolonged preincubation of the myocytes with the inhibitor. These data demonstrate that the selective nucleoside inhibitors of c-N-I can effectively block the hydrolysis of AMP inside myocytes. Thus, these inhibitors may be useful tools in identifying the role of c-N-I during ATP catabolism in whole tissue and animal experiments.

Coronary endothelial dysfunction of isolated hearts subjected to prolonged cold storage: patterns and contributing factors

BACKGROUND

A key role of endothelial dysfunction in the pathogenesis of early low coronary flow of heart transplants and late cardiac allograft vasculopathy indicates the importance of optimal coronary endothelial preservation during cold heart storage. We designed this study to investigate the effect of prolonged cold storage on endothelial and smooth muscle function of proximal (epicardial) and distal (intramyocardial) coronary arteries.

METHODS

Four groups of isolated rat hearts were subjected to cold cardioplegic perfusion and immersed in storage medium at 4 degrees C. In groups 1, 2, and 3, hearts were perfused with and stored in Celsior solution for 10, 15, and 30 hours, respectively. In group 4, hearts were perfused with Plegisol and stored in saline for 15 hours. At the end of cold heart storage, arterial segments were taken from the proximal and distal parts of the left coronary artery and mounted on an isometric wire myograph for functional studies. In fifth group, proximal and distal segments of coronary artery isolated from fresh hearts were used as controls. At the end of control measurements, these vessels were used for storage in vitro at 4 degrees C for 15 hours in saline (group 5A) or Celsior (group 5B).

RESULTS

The endothelium-dependent relaxation to acetylcholine was reduced in distal coronary arteries in group 1, and in both proximal and distal coronary artery segments in groups 2, 3, 4, and 5A. Endothelial function was significantly more impaired in both proximal and distal coronary arteries in group 4, as compared with group 2. The impairment of relaxation to acetylcholine was more pronounced following cold storage of the heart than after a similarly long storage of the isolated vessels. The endothelium-independent relaxations to isoprenaline did not differ among all groups. The basal myogenic tone was increased in distal coronary arteries in group 1, and in both proximal and distal coronary arteries in groups 2, 3, 4, and 5A. The sensitivity to the vasoconstricting action of 5-hydroxytryptamine was increased in distal coronary arteries in group 2, and in both proximal and distal coronary arteries in groups 3, 4, and 5A.

CONCLUSIONS

Prolonged ischemic cold heart storage induces coronary endothelial dysfunction that is more pronounced in distal than in proximal arteries and is related to the duration of heart storage and the composition of storage medium.

The influence of temperature on metabolic and cellular protection of the heart during long-term ischemia: a study using P-31 magnetic resonance spectroscopy and biochemical analyses

We have compared the influence of two different cold temperatures (below 10 degreesC) for cardiac ischemia by measuring a large variety of hemodynamic and metabolic parameters during ischemia and reflow. Isolated isovolumic rat hearts were arrested with a preservation solution which was developed in our laboratory and then submitted to 5 h of cold storage (4 degreesC, group I; and 7.5 degreesC, group II) in the same solution. After an additional period of 50 min of ischemia at 15 degreesC with intermittent cardioplegic infusion, hearts were reperfused for 60 min at 37 degreesC. Function was assessed during the control period and reflow. High-energy phosphates and intracellular pH were followed by 31P magnetic resonance spectroscopy. Analyses of metabolites and enzymes were performed by biochemical assays and HPLC in coronary effluents and in freeze-clamped hearts to assess cellular integrity. The energetic pool was better preserved at 4 degreesC during ischemia (ATP at the end of 4 degreesC ischemia, 59 +/- 7% in group I vs 31 +/- 5% in group II, P < 0.01) and reflow (P < 0.05) but membrane protection was higher when increasing the temperature to 7.5 degreesC (reduction of creatine kinase leakage, 89 +/- 16 IU/min in group I vs 51 +/- 5 IU/min in group II, P < 0.05). As a result, functional recovery, represented by the rate pressure product, was higher in hearts preserved at 7.5 degreesC (52 +/- 6% recovery in group I vs 77 +/- 7% in group II at the end of reflow, P < 0.05). Altogether, cold storage at 7.5 degreesC provides a better protection than storage at 4 degreesC.

Myocardial ischemic injury and purine metabolism in patients undergoing coronary artery bypass

OBJECTIVES

High-energy phosphates and their catabolic products were determined in myocardium during coronary artery bypass surgery with blood cardioplegic reperfusion in order to evaluate the effects of aortic cross-clamping and reoxygenation on myocardial purine metabolism.

DESIGN AND METHODS

Transmural left ventricular biopsy specimens were taken with ITu-Cut biopsy needles, before aortic cross-clamping, before cross-clamp removal and after 30' of reperfusion; perchloric extracts of the material were analyzed for nucleotide content by capillary zone electrophoresis (CZE). The CZE procedure used separates the complete spectrum of purine metabolites in myocardial extracts obtained from 0.6-8.6 mg biopsy material.

RESULTS

The basal values of ATP/ADP ratio and energy charge were low, IMP content was high. After the ischemic period, ATP levels further decreased and IMP, nucleosides and bases accumulated. After reperfusion, nucleoside and base basal levels, but not energy charge, were restored to some extent.

CONCLUSIONS

The study arises the problem of myocardial preservation during heart surgery. In this investigation, capillary electrophoresis was an extremely adaptable technique for the evaluation of ischemic injury and could be useful in studying the effects of cardioplegic solutions.

Influence of the pH of cardioplegic solutions on cellular energy metabolism and hydrogen ion flux during neonatal hypothermic circulatory arrest and reperfusion: a dynamic 31P nuclear magnetic resonance study in a pig model

OBJECTIVES

The pH of cardioplegic solutions is postulated to affect myocardial protection during neonatal hypothermic circulatory arrest. Neither optimization of cardioplegic pH nor its influence on intracellular pH during hypothermic circulatory arrest has been previously studied in vivo. Thus we examined the effects of the pH of cardioplegic solutions on postischemic cardiac function in vivo, including two possible operative mechanisms: (1) reduction in adenosine triphosphate use and depletion of high-energy phosphate stores or (2) reduction of H+ flux during reperfusion, or both.

METHODS

Dynamic 31P spectroscopy was used to measure rates of adenosine triphosphate use, high-energy phosphate depletion, cytosolic acidification during hypothermic circulatory arrest, and phosphocreatine repletion and realkalinization during reperfusion. Neonatal pigs in three groups (n = 8 each)--group A, acidic cardioplegia (pH = 6.8); group B, basic cardioplegia (pH = 7.8); and group N, no cardioplegia--underwent hypothermia at 20 degrees C with 60 minutes of hypothermic cardioplegia followed by reperfusion.

RESULTS

Recoveries of peak elastance, stroke work, and diastolic stiffness were superior in group B. Indices of ischemic adenosine triphosphate use, initial phosphocreatine depletion rate, and tau, the exponential decay half-time, were not different among groups. Peak [H+] in group A (end-ischemia) was significantly elevated over that of group B. The realkalinization rate was reduced in group B compared with that in groups A (p = 0.015) and N (p = 0.035), with no difference between groups A and N (p = 0.3). Cytosolic realkalinization rate was markedly reduced and the half-time of [H+] decay was increased during reperfusion in group B.

CONCLUSIONS

Superior postischemic cardiac function in group B is not related to alterations in ischemic adenosine triphosphate use or high-energy store depletion, but may be due to slowing in H+ efflux during reperfusion, which should reduce Ca++ and Na+ influx.

Differing protection with aspartate and glutamate cardioplegia in the isolated rat heart

Aspartate and glutamate each have been shown to improve cardiac recovery after hypoxia or ischemia under normothermic conditions, but whether their effects are additive and to what extent they are modified by hypothermia has not been studied systematically. We set out to compare the individual and combined protective effects of aspartate and glutamate during cardioplegic arrest under normothermic and hypothermic conditions in the rat. Using isolated working rat hearts, functional and metabolic recovery was assessed after 0.5 hours of potassium arrest at 37 degrees C or 5 hours at 2 degrees C in control hearts (C) and in hearts in which 20 mmol/L glutamate (G), 20 mmol/L aspartate (A), or both (A + G) was added to the cardioplegic solution. Under normothermic conditions, percentage recovery of prearrest work (mean +/- standard error of the mean) was as follows: C = 31.7 +/- 2.8, G = 34.8 +/- 0.2, A = 49.6 +/- 2.8*, A + G = 53.7 +/- 2.3*. Under hypothermic conditions, the values were as follows: C = 40.4 +/- 4.0, G = 45.2 +/- 2.3, A = 59.4 +/- 1.8*, A + G = 54.1 +/- 1.2* (*p < 0.01 versus C and G). Recovery of postischemic high-energy phosphate content followed the same pattern: A = A + G > G or C. Measurement of postischemic myocardial content of amino acids showed that recovery of function and energy status correlated with maintenance of myocardial levels of aspartate (r = 0.9; p < 0.01) but not glutamate.(ABSTRACT TRUNCATED AT 250 WORDS)

Forty-hour preservation of the rabbit heart: optimal osmolarity, [Mg2+], and pH of a modified UW solution

The University of Wisconsin solution modified with 2,3-butanedione monoxime and calcium experimentally extends the limits of ischemic preservation of the heart. This study evaluates other characteristics of this modified solution that may further enhance preservation: osmolarity, Mg2+ concentration ([Mg2+]), and pH. Rabbit hearts were flushed with the modified University of Wisconsin solution and stored for 40 hours at 4 degrees C. Maximal left ventricular developed pressure (LVDP), left ventricular end-diastolic volume (LVEDV), maximum rate of increase of left ventricular pressure (dP/dt), heart rate, and coronary flow were measured during 60 minutes of isolated crystalloid reperfusion with an isovolumic left ventricular balloon at constant end-diastolic pressure. Creatine kinase release and myocardial adenine nucleotide content were measured at completion of reperfusion. Solution osmolarity was tested at 357, 327, 297, and 277 mOsm/L by reducing K+, Na+, and lactobionate concentrations. [Mg2+] was assessed at 5 and 16 mmol/L. Solution pH was studied at 7.0, 7.4, and 7.8. A control group of hearts was flushed and immediately reperfused to establish baseline function. Hearts stored in either hypertonic (357 mOsm/L) or hypotonic (277 mOsm/L) solutions functioned poorly, reaching 58% and 50% of control LVDP (p < 0.001), 49% (p < 0.01), and 58% (p = not significant) of LVEDV, 56% and 49% of +dP/dt (p < 0.001), respectively, and released substantially more creatine kinase (p < 0.001 versus control).(ABSTRACT TRUNCATED AT 250 WORDS)

New Na(+)-H+ exchange inhibitor HOE 694 improves postischemic function and high-energy phosphate resynthesis and reduces Ca2+ overload in isolated perfused rabbit heart

BACKGROUND

Experiments were carried out using the new Na(+)-H+ exchange inhibitor (3-methylsulfonyl-4-piperidinobenzoyl)guanidine methanesulfonate (HOE 694) to assess the role of Na(+)-H+ exchange in myocardial ischemic and reperfusion injury.

METHODS AND RESULTS

Three groups of rabbit hearts (n = 5 in each) were perfused with blood and were subjected to 45 minutes of global normothermic (37 degrees C) ischemia, followed by 1 hour of reperfusion. Group 1 was the control group (vehicle only); in group 2, HOE 694 (1 mumol/L) was administered before ischemia (pretreatment group); and in group 3, HOE 694 was given only during reperfusion to separate actions exerted during ischemia from those specifically obtained during reperfusion. End-diastolic pressure rise at 1 hour of reperfusion was reduced by administration of HOE 694 starting before ischemia (from 52.2 +/- 8.5 mm Hg in group 1 to 17.6 +/- 4.5 mm Hg in group 2, P < .01) or starting on reperfusion (28.8 +/- 5.4 mm Hg in group 3, P < .05 versus group 1). Left ventricular developed pressure (LVDP) and its derivative (dP/dt) recovered better in HOE 694-pretreated hearts (LVDP, 79 +/- 9.9 mm Hg in group 2 versus 24.8 +/- 10 mm Hg in group 1; dP/dt, 1580 +/- 198 mm Hg/s versus 340 +/- 221 mm Hg/s, P < .01). In hearts treated only on reperfusion, some improvement was observed, which, however, did not reach statistical significance. Coronary flow on reperfusion was higher in groups 2 and 3 compared with controls, and no "no-reflow" was observed. Two additional groups of hearts were perfused with phosphate-free Krebs-Henseleit solution to enable studies with 31P nuclear magnetic resonance (NMR). ATP was better preserved in HOE 694-pretreated (62 +/- 4.9% of preischemic value) than in control hearts (44 +/- 3.3%) at the end of 30 minutes of reperfusion, and phosphocreatine resynthesis was higher (109 +/- 3.7% versus 86 +/- 5.4%). HOE 694 did not affect the time course of intracellular acidosis during ischemia but suppressed a small alkaline overshoot occurring early in reperfusion (pH 6.96 +/- 0.02 in HOE 694-pretreated hearts versus 7.14 +/- 0.05 in control hearts). Electron microscopy with Ca2+ staining of the blood-perfused hearts showed that clumping of Ca2+ aggregates in mitochondria was prevented by HOE 694.

CONCLUSIONS

Postischemic dysfunction was associated with a rise in end-diastolic pressure. This rise was effectively blocked by HOE 694. The drug was most effective when hearts were treated before ischemia, although partial protection was observed when administration was started on reperfusion. The action of HOE 694 strengthens the idea that Na(+)-H+ exchange during both ischemia and reperfusion contributes to contractile dysfunction.

Age and protection of the ischemic myocardium: is alkaline cardioplegia appropriate?

Hypothermic alkaline pharmacologic cardioplegia used in pediatric cardiac surgery may be less than satisfactory despite its benefits in adults. We determined whether the pH (7.8) of standard St. Thomas' II cardioplegic solution contributes to inadequate protection of the ischemic immature heart and whether the effect is age-related. Modified hypothermic St. Thomas' II solution (pH range, 4.8 to 8.8) was compared with hypothermic bicarbonate buffer alone (pH 7.25) in protecting the ischemic immature (7 to 10 days old) and mature (12 months old) rabbit heart. Isolated hearts (n = 6 per group) were perfused with bicarbonate buffer, and aortic flow was measured before hypothermic (14 degrees C) ischemia (immature hearts: 4 hours; mature hearts: 3 hours). Hearts were reperfused, and enzyme leakage and recovery of function were measured. In the immature heart, a bell-shaped dose-response profile was observed for pH and recovery of aortic flow but not for postischemic creatine kinase leakage. Optimal recovery of aortic flow (98% +/- 3%) occurred at pH 6.8, which was greater than protection with hypothermia alone (82% +/- 4%; p < 0.05) and standard St. Thomas' II solution (72% +/- 2%; p < 0.05). In the mature heart, a bell-shaped dose-response curve existed for recovery of aortic flow and a U-shaped curve existed for creatine kinase leakage. Again, optimal recovery of aortic flow (84% +/- 5%), which was superior to that with standard St. Thomas' II solution (60% +/- 8%; p < 0.05), and minimal enzyme leakage also occurred at pH 6.8, as did the least enzyme leakage (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium ion transport in rat hearts during cold ischemic storage: 23Na and 31P NMR study

The success of heart transplantation is limited by the negative correlation between the length of the cold ischemic storage period and the quality of functional recovery. We use 23Na, 31P NMR spectroscopy, and hemodynamic parameters to describe temperature-dependent changes in sodium influx and the concentration of phosphorus high-energy compounds during different storage periods. Perfusion with Krebs-Henseleit solutions containing Dy(TTHA)3- permitted discrimination of intra- and extracellular sodium during cold ischemic storage. The 23Na NMR visibilities under the acquisition and processing parameters used in our experiments were 40 +/- 4% for the intracellular compartment and 97 +/- 11% for the extracellular compartment. At 4 degrees C, the intracellular Na+ accumulation exceeded that observed at 15 and 22 degrees C. The ATP and PCr depletion rates were much lower at 4 degrees C and the left ventricular contractility was higher after longer periods of storage, as the storage temperature decreased. The intracellular Na+ concentration cannot serve as a marker for the postischemic recovery probability. The relative activity of the Na/K ATPase pumps is not correlated with the preservation success. However, intracellular sodium ion accumulation is a major factor in the time lag of the reperfusion recovery.

Relation of myocardial protection to cardioplegic solution pH: modulation by calcium and magnesium

The relationship between myocardial preservation and cardioplegic solution pH was assessed in isolated, perfused rat hearts. A base solution without calcium or magnesium and the same solution containing 0.2 mmol/L ionized calcium or 16 mmol/L magnesium or both ions were studied at several values of pH between 6.8 and 8.7. Hearts were arrested at 8 degrees C by multidose infusions of these bicarbonate-buffered solutions bubbled with oxygen and a varying percentage of carbon dioxide to control pH. Diastolic tone (left ventricular balloon) and adenosine triphosphate (ATP) depletion during arrest both increased as the cardioplegic solution became more alkaline. Calcium increased these effects of pH. Magnesium weakened the effect of pH on diastolic tone, maintained ATP at all pH levels, and inhibited the effects of calcium on the relationships of pH to diastolic tone and ATP. When data from all solutions were considered together, ATP depletion was shown to be linearly related to diastolic tone. Calcium depressed functional recovery (left ventricular developed pressure during reperfusion expressed as a percentage of its prearrest value) at all pH levels. With the other solutions, recovery was similar and best within a broad and relatively alkaline pH range. With the solution containing calcium and magnesium, at pH levels of 8.28 +/- 0.02, 7.87 +/- 0.03, 7.58 +/- 0.02, 7.41 +/- 0.01, 7.06 +/- 0.02, and 6.80 +/- 0.01, recovery at 5 minutes of reperfusion was 101.4% +/- 3.7%, 102.9% +/- 2.8%, 107.3% +/- 3.7%, 102.8% +/- 2.9%, 91.8% +/- 3.6%, and 94.3% +/- 3.5%, respectively. This effect of alkalinity was short-lived. Extreme alkalinity of the base, acalcemic solution produced the calcium paradox, as reported previously. Good preservation of ATP by the most acid solutions did not predict good functional recovery. Magnesium increased the persistence of frequent extrasystoles during early reperfusion, but the effect was attenuated by calcium. The data support the inclusion of magnesium in cardioplegic solutions, particularly when they contain calcium, show that cardioplegic solution pH can have major effects on the arrested heart, and suggest that a relatively alkaline pH may modestly benefit functional recovery.

Beneficial actions of acidotic initial reperfusate in stunned myocardium of rat hearts

The effects of metabolic acidosis and alkalosis in the initial reperfusate on post-ischemic stunned myocardium were investigated in isolated rat hearts. Metabolic acidosis and alkalosis were produced by altering the doses of artificial buffer (Tris) in place of sodium bicarbonate. All hearts were subjected to global ischemia for 15 min at 37 degrees C. The initial reperfusate under study was given during the subsequent 10 min of reperfusion, just prior to release of the aortic clamp. After that, reperfusion using normal Krebs-Henseleit buffer solution was carried out for 40 min. The acidotic initial reperfusate (pH 6.8) resulted in better protection than the alkalotic initial reperfusate (pH 7.8), as demonstrated by 1) a higher recovery of aortic flow (80.6% +/- 3.8% vs 32.7% +/- 4.8%, p less than 0.01), 2) a smaller leakage of creatine kinase during the initial reperfusion phase (6.0 +/- 0.7 vs 14.6 +/- 2.1 IU/10 min/g dry weight, p less than 0.05) and during the post-ischemic Langendorff perfusion phase (8.8 +/- 1.7 vs 37.3 +/- 5.2 IU/10 min/g dry weight, p less than 0.05), and 3) a lower myocardial water content at the end of reperfusion (84.8% +/- 0.2% vs 85.7% +/- 0.3%, p less than 0.05). Not only Tris buffer system, but also HEPES buffer system indicated that acidotic initial reperfusate was effective to protect against myocardial injury. These results suggest that 1) the extracellular pH during initial reperfusion profoundly influences the reversible myocardial dysfunction (stunned myocardium), and 2) the acidotic initial reperfusate improves post-ischemic myocardial performance.

pH standardization for phosphorus-31 magnetic resonance heart spectroscopy at different temperatures

Intracellular pH typically is measured by NMR using the calibrated chemical shift of the inorganic phosphate peak in phosphorus-31 spectra. Heart spectroscopy experiments often require measurements of intracellular pH at temperatures from 5 to 37 degrees C. This paper provides NMR pH calibrations for this range of temperatures, a summary of calibration data reported to date, and a discussion of the factors influencing pH standardization.

Real-time continuous-flow spin trapping of hydroxyl free radical in the ischemic and post-ischemic myocardium

Real-time monitoring of spin-trapped oxygen-derived free radicals released by the isolated ischemic and reperfused rat heart has been achieved by ESR analysis of the coronary effluents using continuous flow detection and high-speed acquisition techniques. Two nitrone spin traps 5,5-dimethyl pyrroline 1-oxide (Me2PnO) and 3,3,5,5-tetramethyl pyrroline 1-oxide (MePnO) have been separately perfused at a concentration of 40 mM during a sequence of 50 min of low-flow ischemia (1 ml/min) followed by 30 min of global ischemia and subsequent reperfusion at the control flow rate (14 ml/min). ESR spectra were sequentially obtained in 5-min or 30-s blocks during low-flow ischemia and reperfusion, respectively. 1. The results show the formation of OH. free radicals in the ischemic and reperfused heart, as demonstrated by the observation of Me2PnO-OH (aN = aH = 14.9 G; g = 2.0053) and Me4PnO-OH (aN = 15.2 G, aH = 16.8 G; g = 2.0055) spin adducts. There is no evidence of significant biological carbon-centered or peroxyl free radicals spin-adduct formation in the coronary effluents or in lipid extracts analyzed after reflow. 2. The OH. generation began 15-20 min after the onset of ischemia and was moderate, peaking at 30-40 min. During reperfusion, an intense formation of OH. spin adducts was observed, with a maximum at 30-60 s and a further gradual decrease over the following 2 min. 3. Cumulative integrated values of the amount of spin adducts released during the ischemic period show a Me2PnO-OH level fourfold greater than that of Me4PnO-OH. It was 2.5 times greater during reflow, reflecting slower kinetics with the more stable Me4PnO. 4. The original ESR detection technique developed in this study allows accurate real-time quantitative monitoring of the oxygen-derived free radicals generated during myocardial injury. It might provide a quick and reliable new means for assessing the efficacy of free-radical inhibitors.

Association of myocardial glutamate and aspartate pool and functional recovery of postischemic heart

The effect of low flow ischemia and subsequent reperfusion with 5.5 mM glucose or 5 mM acetate on energy metabolism and catabolism of myocardial glutamate and aspartate was studied in isolated perfused guinea pig hearts. Reperfusion with acetate was followed by low recovery of the cardiac contractile function associated with a great rise in isovolumic end-diastolic pressure. It was combined with more profound losses of tissue adenine nucleotides and the total Cr compared to reperfusion with glucose. The total glutamate and aspartate pool decreased more than two-fold compared to the initial one regardless of substrate. However, glutamate content was reduced by 58 and 38% with acetate and glucose, respectively. The expenditure of both amino acids was caused by alanine formation stimulated by glycolysis/glycogenolysis. The remaining glutamate and aspartate pool in the reperfused hearts positively correlated with adenine nucleotides (r = 0.62), the total creatine (r = 0.65), and the recovery of contractile function (r = 0.64). The results suggest that the glutamate and aspartate pool may be of critical importance for postischemic functional and metabolic recovery of the heart.