Stereospecific Effect of Bupivacaine Isomers on Atrioventricular Conduction in the Isolated Perfused Guinea Pig Heart

Background: The local anesthetic bupivacaine is an equal mixture of two optically active isomers known to exert different cardiotoxic profiles in vivo. Enantiomer-specific forms of bupivacaine may have differential effects on cardiovascular function, specifically on cardiac electrophysiology. The authors' aim was to determine if there were any direct functional differences in the cardiac effects of bupivacaine isomers. The isolated heart was used to avoid possible indirect cardiac effects of bupivacaine, such as autonomic nervous and hormonal influences, as well as preload and afterload factors.

Methods: The hearts of 12 ketamine-anesthetized guinea pigs were perfused with Krebs-Ringer's solution (97% oxygen, 3% carbon dioxide) at constant perfusion pressure using the Langendorff technique. Atrial and ventricular bipolar electrodes were placed to measure heart rate (HR) and atrioventricular (AV) conduction time. Left ventricular pressure (LVP), coronary flow, and inflow and outflow oxygen tensions were also measured. Oxygen delivery, oxygen consumption (MVO2), and percentage of oxygen extraction were calculated. Each heart was perfused with increasing randomized concentrations (0.5, 1, 5, 10 micro Meter) of both isomers and the racemate of bupivacaine.

Results: Racemic and isomeric bupivacaine equally and dose dependently decreased cardiac function. At 10 micro Meter bupivacaine these changes were HR, -17 +/- 2%; LVP, -50 +/- 3%; coronary flow, -20 +/- 40%; and MVO2, -46 +/- 40%. The (+) isomer significantly prolonged AV conduction compared with the racemate and the (-) isomer at all concentrations. At 10 micro Meter, AV time was 54 +/- 6% longer with the (+) isomer and 30 +/- 4% longer with the (+/-) racemate than with the (-) isomer. The greater delay in AV time with the (+) than the racemate or (-) isomer led to a second-degree AV dissociation in 10 of 12 of hearts treated with (+) bupivacaine.     

Effects of Volatile Anesthetics on Atrial and AV Nodal Electrophysiological Properties in Guinea Pig Isolated Perfused Heart

Background: Knowledge of the anesthetic effects on atrial and atrioventricular (AV) nodal electrophysiologic properties is fundamental to understand the modulatory role of anesthetics on the pathogenesis of supraventricular tachycardias, and to individualize the perioperative management of patients with supraventricular tachycardias or AV nodal conduction disturbances. Therefore the authors studied the effects of three commonly used volatile anesthetics on the electrophysiologic properties of the atrium and AV node.

Methods: The concentration-dependent electrophysiologic effects of halothane, isoflurane, and desflurane (0 - 2 minimum alveolar concentration [MAC]) were studied in guinea pig Langendorff-perfused hearts fit with instruments to simultaneously measure atrial and AV nodal conduction times and atrial monophasic action potential duration. Atrial and AV nodal effective refractory periods were measured simultaneously using a computer-assisted premature stimulation protocol. The concentrations of anesthetics in the gas phase were monitor by an infrared gas analyzer.

Results: Volatile anesthetics caused markedly different concentration-dependent effects on atrial conduction, repolarization, and refractoriness, and on AV nodal function. At equianesthetic concentrations, halothane depressed atrial conduction the most, whereas desflurane caused the greatest shortening of atrial monophasic action potential duration. Halothane had no significant effect on atrial refractoriness, whereas at 2 MAC desflurane significantly shortened and isoflurane significantly prolonged atrial effective refractory periods by 18.1 +/- 13.5% and 13.2 +/- 14.7%, respectively. On an equi-MAC basis, the rank order of potency for the anesthetics to prolong AV nodal conduction time and AV nodal ERP was halothane > desflurane > isoflurane.     

Experimental Model of Isolated Lung Perfusion in Rats: First Brazilian Experience Using the IL-2 Isolated Perfused Rat or Guinea Pig Lung System

Introduction

Lung transplantation has become the mainstay therapy for patients with end-stage lung disease refractory to medical management. However, the number of patients listed for lung transplantation largely exceeds available donors. The study of lung preservation requires accurate, cost-effective small animal models. We have described a model of ex vivo rat lung perfusion using a commercially available system.

Methods

Male Wistar rats weighing 250 g-300 g were anesthetized with intraperitoneal sodium thiopental (50 mg/kg body weight). The surgical technique included heart-lung block extraction, assembly, and preparation for perfusion and data collection. We used an IL-2 Isolated Perfused Rat or Guinea Pig Lung System (Harvard Apparatus, Holliston, Mass, United States; Hugo Sachs Elektronik, Alemanha).

Results

Preliminary results included hemodynamic and pulmonary mechanics data gathered in the experiments.

Conclusion

The isolated rat lung perfusion system is a reliable method to assess lung preservation.     

Effects of Ketamine and Its Isomers on Ischemic Preconditioning in the Isolated Rat Heart

Background: Ischemic preconditioning protects the heart against subsequent ischemia. Opening of the adenosine triphosphate-sensitive potassium (KATP) channel is a key mechanism of preconditioning. Ketamine blocks KATP channels of isolated cardiomyocytes. The authors investigated the effects of ketamine and its stereoisomers on preconditioning.

Methods: Isolated rat hearts (n = 80) underwent 30 min of no-flow ischemia and 60 min of reperfusion. Two groups with eight hearts each underwent the protocol without intervention (control-1 and control-2), and, in eight hearts, preconditioning was elicited by two 5-min periods of ischemia before the 30 min ischemia. In the six treatment groups (each n = 8), ketamine, R (-)- or S (+)-ketamine were administered at concentrations of 2 or 20 [mu]g/ml before preconditioning. Eight hearts received 20 [mu]g/ml R (-)-ketamine before ischemia. Left ventricular (LV) developed pressure and creatine kinase (CK) release during reperfusion were determined as variables of ventricular function and cellular injury.

Results: Baseline LV developed pressure was similar in all groups: 104 +/- 28 mmHg (mean +/- SD). Controls showed a poor recovery of LV developed pressure (17 +/- 8% of baseline) and a high CK release (70 +/- 17 IU/g). Ischemic preconditioning improved recovery of LV developed pressure (46 +/- 14%) and reduced CK release (47 +/- 17 IU/g, both P < 0.05 vs. control-1). Ketamine (2 [mu]g/ml) and 2 or 20 [mu]g/ml S (+)-ketamine had no influence on recovery of LV developed pressure compared with preconditioning (47 +/- 18, 43 +/- 8, 49 +/- 36%) and CK release (39 +/- 8, 30 +/- 14, 41 +/- 25 IU/g). After administration of 20 [mu]g/ml ketamine and 2 or 20 [mu]g/ml R (-)-ketamine, the protective effects of preconditioning were abolished (LV developed pressure-recovery, 16 +/- 14, 22 +/- 21, 18 +/- 11%; CK release, 67 +/- 11, 80 +/- 21, 82 +/- 41 IU/g; each P < 0.05 vs. preconditioning). Preischemic treatment with R (-)-ketamine had no effect on CK release (74 +/- 8 vs. 69 +/- 9 IU/g in control-2, P = 0.6) and functional recovery (LV developed pressure 12 +/- 4 vs. 9 +/- 2 mmHg in control-2, P = 0.5).     

Comparative Cardiac Effects of Terlipressin, Vasopressin, and Norepinephrine on an Isolated Perfused Rabbit Heart

Background: Terlipressin, a synthetic analog of arginine-vasopressin (AVP), has been proposed as an effective vasopressive therapy in catecholamine-resistant vasodilatory shock. Although beneficial effects of terlipressin on systemic arterial pressure have been clearly demonstrated, its intrinsic effects on coronary circulation and myocardial performances remain unknown.

Methods: The authors compared the coronary and myocardial effects of terlipressin (1-100 nm, n = 10), AVP (10-1000 pm, n = 10), and norepinephrine (1-100 nm, n = 10) on an erythrocyte-perfused isolated rabbit heart. The cardiac effects of terlipressin were also assessed in erythrocyte-perfused hearts in which the myocardial oxygen delivery was maintained constant and buffer-perfused hearts. Finally, the cardiac effects of terlipressin and AVP were studied in hearts pretreated by [d(CH2)5Tyr(Me)]AVP (0.1 [mu]m), a selective V1a receptor antagonist.

Results: Norepinephrine induced a biphasic coronary effect associated with a concentration-dependent increase in myocardial performances. AVP and terlipressin significantly decreased coronary blood flow and impaired myocardial performances from 30 pm and 30 nm, respectively (P < 0.05). The cardiac side-effects of terlipressin were confirmed in buffer-perfused hearts but the maintenance of a constant myocardial oxygen delivery constant abolished its effects on myocardial performances. The cardiac effects induced by terlipressin and AVP were nearly completely abolished on hearts pretreated by [d(CH2)5Tyr(Me)]AVP.     

Autoregulation of Coronary Blood Flow in the Isolated Beating Pig Heart

The isolated beating pig heart model is an accessible platform to investigate the coronary circulation in its truly morphological and physiological state, whereas its use is beneficial from a time, cost, and ethical perspective. However, whether the coronary autoregulation is still intact is not known. Here, we study the autoregulation of coronary blood flow in the working isolated pig heart in response to brief occlusions of the coronary artery, to step‐wise changes in left ventricular loading conditions and contractile states, and to pharmacologic vasodilating stimuli. Six slaughterhouse pig hearts (473 ± 40 g) were isolated, prepared, and connected to an external circulatory system. Through coronary reperfusion and controlled cardiac loading, physiological cardiac performance was achieved. After release of a coronary occlusion, coronary blood flow rose rapidly to an equal (maximum) level as the flow during control beats, independent of the duration of occlusion. Moreover, a linear relation was found between coronary blood flow and coronary driving pressure for a wide variation of preload, afterload, and contractility. In addition, intracoronary administration of papaverine did not yield a transient increase in blood flow indicating the presence of maximum coronary hyperemia. Together, this indicates that the coronary circulation in the isolated beating pig heart is in a permanent state of maximum hyperemia. This makes the model excellently suitable for testing and validating cardiovascular devices (i.e., heart valves, stent grafts, and ventricular assist devices) under well‐controlled circumstances, whereas it decreases the necessity of sacrificing large mammalians for performing classical animal experiments.     

The Combined Effects of Antihypertensive Drugs and Anaesthetics (Halothane and Ketamine) on the Isolated Heart

The effects of three concentrations of halothane or ketamine were investigated on isolated rabbit hearts, which were perfused with hydralazine, clonidine, propranolol or methyldopa. In hearts not subjected to the influence of an anaesthetic, clonidine was the only drug stimulating myocardial function. In those perfused with halothane or ketamine alone, both anaesthetics exerted a negative chronotropic and inotropic action in a dose-related manner. Ketamine markedly increased the coronary flow. Clonidine distinctly reduced the myocardial depression caused by halothane or ketamine. Hydralazine had no marked effects with either of these anaesthetics, except that it sensitized the hearts to the arrhythmic action of a high concentration of halothane. Propranolol, when combined with halothane, aggravated myocardial depression and decreased coronary flow. With ketamine, propranolol caused no other harmful interactions, apart from inhibiting the increase in coronary flow caused by this anaesthetic. Methyldopa intensified the myocardial depression induced by halothane, but tended to diminish that caused by ketamine. The results suggest that clonidine has a stimulatory cardiac action when combined with either of these anaesthetics. Disadvantageous interactions may exist between methyldopa or propranolol and halothane.     

Volatile Anesthetics Do Not Alter Bradykinin-induced Release of Nitric Oxide or L-Citrulline in Crystalloid Perfused Guinea Pig Hearts

Background: Nitric oxide (NO) and L-citrulline (L-cit) are released by endothelial NO synthase (eNOS) to induce vasodilation via guanylyl cyclase and cyclic guanosine monophosphate (cGMP). Volatile anesthetics directly reduce vascular muscle tone, but their effects on the eNOS cGMP pathway is controversial. The aim of this study was to examine the effects of anesthetics on bradykinin-induced increases in flow, NO, and L-cit in isolated hearts.

Methods: Guinea pig hearts were isolated, perfused at 55 mmHg with a crystalloid or erythrocyte perfusate at 37 [degree sign]C, and heart rate, left ventricular pressure, coronary flow (CF), effluent pH, and oxygen tension were monitored. Effluent [NO] was measured by a Clark-type electrode (sensitivity >or= 1 nM = 3 pA) with a selectively permeable membrane. Effluent [L-cit] was measured by chromatography. Before, during, and after exposure to halothane, isoflurane, or sevoflurane, hearts were infused with as much as 100 nM bradykinin to induce increases in CF and effluent release of NO and L-cit.

Results: In crystalloid-perfused hearts, 10 nM bradykinin produced maximal concentration-dependent increases in CF (87 +/- 2%), [NO] (24 +/- 4 nM), NO release (128 +/- 18 pmol [middle dot] g [middle dot]-1 min [middle dot]-1), and [L-cit] (58 +/- 8 nM). Isoflurane slightly increased CF but not NO. Anesthetics did not alter the bradykinin-induced CF, NO slope relationship, or change [L-cit]. In erythrocyte-perfused hearts, isoflurane also did not alter the bradykinin-induced increase in CF and decrease in percentage of oxygen extracted.     

Ionic Basis of the Differential Effects of Intravenous Anesthetics on Erythromycin-induced Prolongation of Ventricular Repolarization in the Guinea Pig Heart

Background: Dysrhythmias and death occur in patients with acquired long QT syndrome (LQTS). Little information exists regarding interactions between anesthetics and drugs that prolong ventricular repolarization. Therefore the effects of three commonly used intravenous anesthetics on ventricular repolarization were investigated in the setting of drug-induced, long QT syndrome.

Methods: The effects of increasing concentrations (0, 10, 25, and 50 micro Meter) of propofol, ketamine, and thiopental on ventricular repolarization were evaluated by measuring the monophasic action potential duration at 90% repolarization (MAPD90) in guinea pig Langendorff-perfused hearts in the absence or presence of erythromycin (100 micro Meter). If an anesthetic enhanced erythromycin-induced prolongation of MAPD90, its effects on the delayed rectifier (IK) and inward rectifier (IKl) potassium currents were measured using the whole-cell patch-clamp technique.

Results: At clinically relevant concentrations, only thiopental significantly modulated erythromycin's effect on MAPD90. Thiopental at 10, 25, and 50 micro Meterr prolonged MAPD90 from a control of 163 +/- 6 ms by 18 +/- 4, 30 +/- 3, and 31 +/- 4 ms, respectively. In a separate group, erythromycin prolonged MAPD90 from 155 +/- 2 ms to 171 +/- 2 ms (n = 21, P < 0.001). In the presence of erythromycin, thiopental at 10, 25, and 50 micro Meter caused significantly greater prolongation from a control of 171 +/- 2 ms by 39 +/- 2, 58 +/- 3, and 72 +/- 6 ms, respectively. Whole-cell patch-clamp experiments indicated that thiopental inhibited IK and IKl.     

Ionic Mechanisms Mediating the Differential Effects of Methohexital and Thiopental on Action Potential Duration in Guinea Pig and Rabbit Isolated Ventricular Myocytes

Background: Commonly used barbiturate anesthetics may significantly influence cardiac electrophysiologic characteristics. The authors evaluated thiopental (a thiobarbiturate) and methohexital (an oxybarbiturate), two compounds with similar physicochemical properties but different structures, to determine whether they have distinct effects on the major ionic currents that determine action potential duration (APD) in ventricular myocytes.

Methods: The effects of thiopental and methohexital (50 [micro sign]M) on APD at 50% (APD50) and 90% (APD90) repolarization were studied in guinea pig and rabbit single ventricular myocytes using the patch-clamp technique in a whole-cell configuration. The ionic mechanisms underlying the APD changes were evaluated by measuring the anesthetics' effects on the L-type calcium inward current, the inward rectifier potassium current, and the delayed rectifier potassium current in guinea pig cells and on the transient outward potassium current in rabbit cells.

Results: Thiopental and methohexital caused opposite effects on APD. Whereas thiopental prolonged APD50 and APD90 in guinea pig and rabbit ventricular myocytes, methohexital shortened them. Thiopental markedly depressed both the inward and outward components of the inward rectifier potassium current, whereas methohexital caused minimal inhibition of the inward component and no change in the outward component. The delayed rectifier potassium current was inhibited by thiopental but significantly potentiated by methohexital. Neither thiopental nor methohexital significantly affected the transient outward potassium current or the L-type calcium inward current.     

氯胺酮对离体SD大鼠乳头肌收缩性能的影响

观察氯胺酮不同浓度在不同时间对离体Ｓｐｒａｇｕｅ－Ｄａｗｌｅｙ大鼠乳头肌收缩性能的影响。方法：１０条乳头肌分别给予氯胺酮１０、２０、３０、４０μｇ／ｍｌ，观察等长张力峰值，张力上升最大速度、     

Absence of Stereospecific Effects of Bupivacaine Isomers on Heart Mitochondrial Bioenergetics

Background: Highly lipophilic local anesthetics interfere with mitochondrial energy metabolism. These metabolic effects could, in part, explain some toxic effects of local anesthetics, such as bupivacaine-induced myocardial depression. The purpose of this study was to compare the optically pure isomers of bupivacaine on heart mitochondrial bioenergetics.

Methods: Both bupivacaine enantiomers were tested on rat heart isolated mitochondria. Oxygen consumption, adenosine triphosphate synthesis, and enzymatic activities of the four complexes of the respiratory chain were measured.

Results: No significant differences were found between R(+)- and S (-)-bupivacaine on mitochondrial oxidative phosphorylation with a similar dose-dependent decrease in adenosine triphosphate synthesis. Complex I (nicotinamide adenine dinucleotide ubiquinone reductase) was the enzymatic complex of the respiratory chain most sensitive to the bupivacaine isomers. Half-inhibitory concentrations for R (+)- and S (-)-bupivacaine were not statistically different (3.3 +/- 0.4 mm and 2.8 +/- 0.6 mm, respectively).     

Sevoflurane and Isoflurane Protect the Reperfused Guinea Pig Heart by Reducing Postischemic Adhesion of Polymorphonuclear Neutrophils

Background: Polymorphonuclear neutrophils (PMNs) contribute to reperfusion injury. Because volatile anesthetics can reduce PMN adhesion in the reperfused, nonworking heart, the authors analyzed whether this action of volatile anesthetics affects cardiac performance after ischemia and reperfusion and further clarified the underlying mechanism.

Methods: Isolated guinea pig hearts perfused with crystalloid buffer and performing pressure-volume work were used. Hearts were subjected to 15 min global ischemia and 20 min reperfusion. In the intervention groups an intracoronary bolus of 3 x 106 PMNs was applied in the second min of reperfusion, either in the absence or presence of 0.5 or 1 minimum alveolar concentration sevoflurane or isoflurane. The number of sequestered PMNs was calculated from the difference between coronary input and output (coronary effluent) of PMNs. Performance of external heart work, determined pre- and postischemically, served as criterion for recovery of myocardial function. Additionally, the expression of the integrin CD11b on the cell surface of PMN was measured before and after coronary passage.

Results: Injection of PMN in the reperfusion phase, but not under nonischemic conditions, reduced recovery of external heart work significantly (from 55 +/- 7% to 19 +/- 11%). Addition of sevoflurane or isoflurane in concentrations of 0.5 and 1 minimum alveolar concentration to the perfusate reduced postischemic PMN adhesion from 36 +/- 8% to basal values (20 +/- 7%) and prevented decline of cardiac function. CD11b expression on PMNs increased significantly during postischemic coronary passage under control conditions. Again, both anesthetics in both concentrations inhibited that activation.     

Heart Donation After Cardiac Death: Preliminary Study on an Isolated,Perfused Swine Heart After 20 Minutes of Normothermic Ischemia

BackgroundWe measured the functional and metabolic status of hearts submitted to normothermic ischemia before preservation through the use of an ex vivo pig heart model to assess the feasibility of donation after cardiac death (DCD) in heart transplantation.MethodsTen pigs were separated into 2 groups: control (n = 6, brain-dead group) and DCD (n = 4, heart donation after cardiac death). In the control group, hearts were excised 20 minutes after the brachiocephalic trunk cross-clamping and were immediately reperfused. In DCD, hearts were excised 20 minutes after exsanguination and asphyxia, stored in the Centre de Résonance Magnétique Biologique et Médicale (CRMBM) solution for 2 hours, and then were reperfused. Cardioplegic arrest was induced with the use of 1 L of CRMBM solution (4°C) and the heart was reperfused for 60 minutes through the use of an ex vivo perfusion system in Langendorff mode with normothermic autologous blood. During reperfusion, functional parameters were analyzed. Biochemical assays were performed in myocardial effluents and freeze-clamped hearts.ResultsNo electromechanical activity was found in DCD compared with control. Creatine kinase (CK) was higher at 2 minutes of reperfusion in DCD versus control (P = .005). Adenosine triphosphate was lower in DCD versus control (P = .0019). Malondialdehyde, an oxidative stress index, was present only in DCD. The nitric oxide (NO) pathway was impaired in DCD versus control, with lower eNOS expression (P < .0001) and total nitrate concentration content (P = .04).ConclusionsWe reported no cardiac functional and metabolic recovery in the DCD group after normothermic ischemia and reperfusion, which indicates that a single immersion of the cardiac graft during storage does not provide an optimal protection. New strategies in heart preservation are necessary for recruiting heart donation after cardiac death.     

Xenon Does Not Alter Cardiac Function or Major Cation Currents in Isolated Guinea Pig Hearts or Myocytes

Background: The noble gas xenon (Xe) has been used as an inhalational anesthetic agent in clinical trials with little or no physiologic side effects. Like nitrous oxide, Xe is believed to exert minimal unwanted cardiovascular effects, and like nitrous oxide, the vapor concentration to achieve 1 minimum alveolar concentration (MAC) for Xe in humans is high, i.e., 70-80%. In the current study, concentrations of up to 80% Xe were examined for possible myocardial effects in isolated, erythrocyte-perfused guinea pig hearts and for possible effects on altering major cation currents in isolated guinea pig cardiomyocytes.

Methods: Isolated guinea pigs hearts were perfused at 70 mmHg via the Langendorff technique initially with a salt solution at 37[degrees]C. Hearts were then perfused with fresh filtered (40-[mu]m pore) and washed canine erythrocytes diluted in the salt solution equilibrated with 20% O2 in nitrogen (control), with 20% O2, 40% Xe, and 40% N2, (0.5 MAC), or with 20% O2 and 80% Xe (1 MAC), respectively. Hearts were perfused with 80% Xe for 15 min, and bradykinin was injected into the blood perfusate to test endothelium-dependent vasodilatory responses. Using the whole-cell patch-clamp technique, 80% Xe was tested for effects on the cardiac ion currents, the Na+, the L-type Ca2+, and the inward-rectifier K+ channel, in guinea pig myocytes suffused with a salt solution equilibrated with the same combinations of Xe, oxygen, and nitrogen as above.

Results: In isolated hearts, heart rate, atrioventricular conduction time, left ventricular pressure, coronary flow, oxygen extraction, oxygen consumption, cardiac efficiency, and flow responses to bradykinin were not significantly (repeated measures analysis of variance, P > 0.05) altered by 40% or 80% Xe compared with controls. In isolated cardiomyocytes, the amplitudes of the Na+, the L-type Ca2+, and the inward-rectifier K+ channel over a range of voltages also were not altered by 80% Xe compared with controls.