Moderate glucose deprivation preconditions myocardium against infarction

Glucose-free perfusion preconditions myocardium against the consequences of subsequent ischemia. We investigated whether mitochondrial ATP-sensitive potassium (mK (ATP)) channels are involved in preconditioning by glucose deprivation, and whether moderate glucose deprivation also preconditions myocardium. Isolated rat hearts underwent 30 min of no-flow ischemia followed by 1 h reperfusion. Controls were not further treated. Three groups were preconditioned by perfusion with 0, 40 or 80 mg/dl (0, 2.22, 4.44 mmol/l) glucose (correction of osmotic pressure by addition of urea) for 10 min followed by 10 min perfusion with normal buffer (150 mg/dl, or 8.33 mmol/l glucose) before the ischemia reperfusion protocol. In one group, 100 micromol/l of the mK (ATP) channel blocker 5-HD was added to the glucose-free perfusate. Two groups were treated with 5-HD or urea before ischemia without preconditioning. Left ventricular developed pressure and maximum ischemic contracture (82 +/- 21 mmHg) were similar in all groups. Mean left ventricular developed pressure was 100 +/- 16 mm Hg under baseline conditions, and poorly recovered to 8 +/- 11 mm Hg during reperfusion. Preconditioning with 0 and 40 mg/dl glucose containing buffer reduced infarct size from 41 +/- 10% (control) to 23 +/- 12% (p = 0.02) and 26 +/- 8% (p = 0.011). The 5-HD blocked preconditioning by glucose deprivation (38 +/- 9%, p = 0.04) while 80 mg/dl glucose, 5-HD and urea had no effect on infarct size (39 +/- 9%; 38 +/- 13%; 37 +/- 8%; p = 1.0 each). We conclude that transient severe glucose deprivation and moderate glucose deprivation preconditions the isolated rat heart. Preconditioning by complete glucose deprivation depends on the opening of mK (ATP) channels.

Haemodynamic changes during halothane, sevoflurane and desflurane anaesthesia in dogs before and after the induction of severe heart failure

BACKGROUND AND OBJECTIVE

The effects of desflurane and sevoflurane on the failing myocardium are still uncertain. We investigated the effects of different concentrations of sevoflurane, desflurane and halothane in dogs with pacing induced chronic heart failure.

METHODS

Global (left ventricular pressure, left ventricular dP/dt, Konigsbergtransducer) and regional myocardial function (systolic segment length shortening, ultrasonic crystals) were measured in chronically instrumented dogs with tachycardia induced severe congestive heart failure. Measurements were performed in healthy dogs and after induction of heart failure in the awake state and during anaesthesia with 0.75, 1.0, 1.25 and 1.75 minimum alveolar concentration (MAC) of halothane, sevoflurane or desflurane.

RESULTS

The anaesthetics reduced dP/dtmax in a dose-dependent manner in healthy dogs (dP/dtmax decreased to 43-53% of awake values at 1.75 MAC). Chronic rapid left ventricular pacing increased heart rate and left ventricular end-diastolic pressure and decreased mean arterial pressure, left ventricular systolic pressure and dP/dtmax. The reduction in contractility was similar in the failing myocardium (to 41-50% of awake values at 1.75 MAC). Segmental shortening was reduced during anaesthesia by 50-62% after pacing compared with 22-44% in normal hearts. While there were similar effects of the different anaesthetics on diastolic function in healthy dogs, after induction of heart failure a more pronounced increase of the time constant of isovolumic relaxation and a greater decrease of dP/dtmin was observed with sevoflurane than with desflurane, indicating a stronger depression of diastolic function.

CONCLUSIONS

While the negative inotropic effects of sevoflurane and desflurane were similar in normal and in the failing myocardium in vivo, desflurane led to a better preservation of diastolic function in the failing myocardium.

Cardioprotection by sevoflurane against reperfusion injury after cardioplegic arrest in the rat is independent of three types of cardioplegia

BACKGROUND

Sevoflurane protects the heart against reperfusion injury even after cardioplegic arrest. This protection may depend on the cardioplegic solution. Therefore, we investigated the effect of sevoflurane on myocardial reperfusion injury after cardioplegic arrest with University of Wisconsin solution (UW), Bretschneider's cardioplegia (HTK), and St Thomas' Hospital solution (STH).

METHODS

We used an isolated rat heart model where heart rate, ventricular volume, and perfusion pressure were constant. The hearts underwent 30 min of normothermic ischaemia followed by 60 min of reperfusion. Seven groups were studied (n = 9 each). Three groups received 7 degrees C cold cardioplegic solutions (UW, HTK, STH) during the first 2 min of ischaemia at a flow of 2 ml min-1. In three groups (UW + Sevo, HTK + Sevo, STH + Sevo), sevoflurane was additionally added to the perfusion medium (membrane oxygenator) at 3.8% (1.5 MAC) during the first 15 min of reperfusion after cardioplegic arrest. Nine hearts served as untreated control group (control). We measured left ventricular developed pressure (LVDP) and infarct size.

RESULTS

LVDP was similar in all groups during baseline (130 (SEM 2) mm Hg). HTK and STH improved recovery of LVDP during reperfusion from 5 (1) (control) to 67 (7) (HTK) and 52 (8) mm Hg (STH, both P < 0.05), while UW had no effect on myocardial function (7 (2) mm Hg). In the sevoflurane-treated groups, LVDP at the end of the experiments was not significantly different from the respective group without anaesthetic treatment (UW + Sevo 11 (2); HTK + Sevo 83 (8); STH + Sevo 64 (8) mm Hg; P = ns). Infarct size was reduced in the HTK and STH groups (HTK 20 (4); STH 17 (3)%; P < 0.05) compared with controls (39 (5)%; P < 0.05), but not in the UW group (52 (4)%). Compared with cardioplegia alone, sevoflurane treatment during reperfusion reduced infarct size (UW + Sevo 31 (4); HTK + Sevo 8 (1); STH + Sevo 4 (1)%; P < 0.05).

CONCLUSION

We conclude, that the protection against reperfusion injury offered by sevoflurane is independent of the three cardioplegic solutions used.

Xenon increases total body oxygen consumption during isoflurane anaesthesia in dogs

BACKGROUND

This study was designed to examine whether the coupling between oxygen consumption (VO2) and cardiac output (CO) is maintained during xenon anaesthesia.

METHODS

We studied the relationship between VO2 (indirect calorimetry) and CO (ultrasound flowmetry) by adding xenon to isoflurane anaesthesia in five chronically instrumented dogs. Different mixtures of xenon (70% and 50%) and isoflurane (0-1.4%) were compared with isoflurane alone (1.4% and 2.8%). In addition, the autonomic nervous system was blocked (using hexamethonium) to study its influence on VO2 and CO during xenon anaesthesia.

RESULTS

Mean (SEM) VO2 increased from 3.4 (0.1) ml kg(-1) min(-1) during 1.4% isoflurane to 3.7 (0.2) and 4.0 (0.1) ml kg(-1) min(-1) after addition of 70% and 50% xenon, respectively (P<0.05), whereas CO and arterial pressure remained essentially unchanged. In contrast, 2.8% isoflurane reduced both, VO2 [from 3.4 (0.1) to 3.1 (0.1) ml kg(-1) min(-1)] and CO [from 96 (5) to 70 (3) ml kg(-1) min(-1)] (P<0.05). VO2 and CO correlated closely during isoflurane anaesthesia alone and also in the presence of xenon (r2=0.94 and 0.97, respectively), but the regression lines relating CO to VO2 differed significantly between conditions, with the line in the presence of xenon showing a 0.3-0.6 ml kg(-1) min(-1) greater VO2 for any given CO. Following ganglionic blockade, 50% and 70% xenon elicited a similar increase in VO2, while CO and blood pressure were unchanged.

CONCLUSIONS

Metabolic regulation of blood flow is maintained during xenon anaesthesia, but cardiovascular stability is accompanied by increased VO2. The increase in VO2 is independent of the autonomic nervous system and is probably caused by direct stimulation of the cellular metabolic rate.

One MAC of sevoflurane provides protection against reperfusion injury in the rat heart in vivo

Volatile anaesthetics protect the heart against reperfusion injury. We investigated whether the cardioprotection induced by sevoflurane against myocardial reperfusion injury was concentration-dependent. Fifty-eight alpha-chloralose anaesthetized rats were subjected to 25 min of coronary artery occlusion followed by 90 min of reperfusion. Sevoflurane was administered for the first 15 min of reperfusion at concentrations corresponding to 0.75 (n=11), 1.0 (n=11), 1.5 (n=13), or 2.0 MAC (n=12). Eleven rats served as untreated controls. Left ventricular peak systolic pressure (LVPSP, tipmanometer) and cardiac output (CO, flowprobe) was measured. Infarct size (IS, triphenyltetrazolium staining) was determined as percentage of the area at risk. Baseline LVPSP was 131 (126-135) mm Hg (mean (95% confidence interval)) and CO 33 (31-36) ml min(-1), similar in all groups. During early reperfusion, sevoflurane reduced LVPSP in a concentration-dependent manner to 78 (67-89)% of baseline at 0.75 MAC (not significant vs controls 99 (86-112)%), 71 (62-80)% at 1 MAC (P<0.05), 66 (49-83)% at 1.5 MAC (P<0.05) and 56 (47-65)% at 2 MAC (P<0.05). CO remained constant. While 0.75 MAC of sevoflurane had no effect on IS (34 (27-41)% of the area at risk) compared with controls (38 (31-45)%, P=0.83), 1.0 MAC reduced IS markedly to 23 (17-30)% (P<0.05). Increasing the concentration to 1.5 MAC (23 (17-30)%) and 2 MAC (23 (13-32)%, both P<0.05 vs controls) had no additional protective effect. One MAC sevoflurane protected against myocardial reperfusion injury. Increasing the sevoflurane concentration above 1 MAC resulted in no further protection.

The effect of high-dose pentaerythritol tetranitrate on the development of nitrate tolerance in rabbits

Experimental studies with therapeutic doses of pentaerythritol tetranitrate (PETN) have shown unexpected actions such as a lack of nitrate tolerance and vasoprotective effects in atherosclerosis. We investigated the effect of a 3-week treatment with low- (6 mg kg(-1) day(-1), n=10) and high-dose (100 mg kg(-1) day(-1), n=10) oral PETN given twice daily on the development of nitrate tolerance in rabbits. We measured aortic relaxation in response to acetylcholine, S-nitroso-N-acetyl-D,L-penicillamine and PETN, constriction in response to phenylephrine and production of reactive oxygen species (ROS). Mean aortic pressure (AOPmean) and heart rate were measured after a single oral dose of PETN (50 mg kg(-1), n=6) and after increasing doses of pentaerythritol dinitrate (PEDN, n=5) and pentaerythritol mononitrate (PEMN, n=5) in anaesthetized rabbits. Oral PETN, even at high dosage, was not associated with nitrate tolerance. None of the aortic ring studies showed a difference in the responses to the vasodilators, while the vasoconstriction to phenylephrine was slightly reduced in both PETN groups. The production of vascular ROS was also not different. Oral PETN reduced AOPmean transiently (-19.3+/-4.4%, P<0.01 vs. controls) and i.v. administration of both PEMN and PEDN reduced AOPmean dose dependently (P<0.05, ANOVA). These results suggest that oral PETN elicits minor nitrate tolerance. This unique feature might be due to the slow onset of vasodilator activity of the predominantly active metabolites PEDN and PEMN and might contribute to the vasoprotective activity of PETN in atherosclerosis.

Thiopentone does not block ischemic preconditioning in the isolated rat heart

PURPOSE

Ischemic preconditioning protects the heart against subsequent prolonged ischemia by opening of adenosine triphosphate-sensitive potassium (K(ATP)) channels. Thiopentone blocks K(ATP) channels in isolated cells. Therefore, we investigated the effects of thiopentone on ischemic preconditioning.

METHODS

Isolated rat hearts (n=56) were subjected to 30 min of global no-flow ischemia, followed by 60 min of reperfusion. Thirteen hearts underwent the protocol without intervention (control, CON) and in 11 hearts (preconditioning, PC), ischemic preconditioning was elicited by two five-minute periods of ischemia. In three additional groups, hearts received 1 (Thio 1, n=11), 10 (Thio 10, n=11) or 100 microg x mL(-1) (Thio 100, n=10) thiopentone for five minutes before preconditioning. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial performance and cellular injury, respectively.

RESULTS

Recovery of LV developed pressure was improved by ischemic preconditioning (after 60 min of reperfusion, mean +/- SD: PC, 40 +/- 19% of baseline) compared with the control group (5 +/- 6%, P <0.01) and this improvement of myocardial function was not altered by administration of thiopentone (Thio 1, 37 +/- 15%; Thio 10, 36 +/- 16%; Thio 100, 38 +/- 16%, P=0.87-0.99 vs PC). Total CK release over 60 min of reperfusion was reduced by preconditioning (PC, 202 +/- 82 U x g(-1) dry weight) compared with controls (CON, 383 +/- 147 U x g(-1), P <0.01) and this reduction was not affected by thiopentone (Thio 1, 213 +/- 69 U x g(-1); Thio 10, 211 +/- 98 U x g(-1); Thio 100, 258 +/- 128 U x g(-1), P=0.62-1.0 vs PC).

CONCLUSION

These results indicate that thiopentone does not block the cardioprotective effects of ischemic preconditioning in an isolated rat heart preparation.

Lidocaine reduces ischaemic but not reperfusion injury in isolated rat heart

The local anaesthetic lidocaine protects the myocardium in ischaemia-reperfusion situations. It is not known if this is the consequence of an anti-ischaemic effect or an effect on reperfusion injury. Therefore, we investigated the effect of two concentrations of lidocaine on myocardial ischaemia-reperfusion injury and on reperfusion injury alone. We used an isolated rat heart model where heart rate, ventricular volume and coronary flow were kept constant. Hearts underwent 45 min of low-flow ischaemia followed by 90 min reperfusion. Two groups received lidocaine 1.7 or 17 microg ml(-1) starting 5 min before the onset of reperfusion. In two additional groups, lidocaine infusion started 5 min before low-flow ischaemia. In all groups, lidocaine administration was stopped after 15 min of reperfusion. One group served as an untreated control (n=11 in each group). Left ventricular developed pressure (LVDP) and total creatine kinase release (CKR) were measured. Lidocaine administration during ischaemia and reperfusion led to an improved recovery of LVDP during reperfusion (1.7 microg ml(-1), 54 (SEM 10) mm Hg; 17 microg ml(-1), 71 (9) mm Hg at 30 min of reperfusion; both significantly different from control (21 (4) mm Hg) (P<0.05)) and a reduced CKR (1.7 microg ml(-1), 79 (13) IU; 17 microg ml(-1), 52 (8) IU at 30 min of reperfusion; both significantly different from control (130 (8) IU (P<0.05)). Lidocaine given during early reperfusion only, affected neither LVDP during reperfusion (1.7 microg ml(-1), 19 (6) mm Hg (P=1.0); 17 microg ml(-1), 36 (8) mm Hg (P=0.46)) nor CKR (156 (21) IU (P=0.50) and 106 (14) IU (P=0.57)). We conclude that lidocaine protects the myocardium against ischaemic but not against reperfusion injury in the isolated rat heart.

Additive protective effects of late and early ischaemic preconditioning are mediated by the opening of KATP channels in vivo

We investigated whether a combination of ischaemic late preconditioning (LPC) and ischaemic early preconditioning (EPC) induces additive myocardial protection in vivo, and the role of ATP-sensitive K (KATP) channels in ischaemic LPC and in LPC + EPC. Sixty rabbits were divided into seven groups. Anaesthetized animals were subjected to 30 min of coronary artery occlusion and 120 min of reperfusion (I/R). Controls (CON, n = 9) were not preconditioned. LPC (n = 10) was induced in conscious rabbits by a 5-min period of myocardial ischaemia 24 h before I/R. The KATP channel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg) was given 10 min before I/R with (LPC + 5-HD, n = 9) or without LPC (5-HD, n = 8). EPC (n = 8) was induced by a 5-min period of myocardial ischaemia 10 min before I/R. Animals received LPC and EPC without (LPC + EPC, n = 8) or with 5-HD (LPC + EPC + 5-HD, n = 8). LPC reduced infarct size (IS, triphenyltetrazolium staining) from 57 +/- 11% (MW +/- SD, CON) of the area at risk to 31 +/- 19% (LPC, P = 0.004). 5-HD did not affect IS (5-HD: 60 +/- 12%, P = 0.002 versus LPC), but abolished the cardioprotective effects of LPC (LPC + 5-HD: 62 +/- 18%, P = 0.001 versus LPC). EPC reduced IS to 18 +/- 8%. Additional LPC led to a further reduction to 8 +/- 4% (LPC + EPC, n = 8; P = 0.005 versus EPC; P = 0.004 versus LPC). 5-HD abolished this additional cardioprotective effect of LPC + EPC (LPC + EPC + 5-HD, n = 8; 46 +/- 11%, P < or = 0.001 versus LPC + EPC). We conclude that the combination of ischaemic LPC and EPC induces additive cardioprotection. KATP channel opening mediates the cardioprotective effects of ischaemic LPC and LPC + EPC.

Ketamine, but not S(+)-ketamine, blocks ischemic preconditioning in rabbit hearts in vivo

BACKGROUND

Ketamine blocks KATP channels in isolated cells and abolishes the cardioprotective effect of ischemic preconditioning in vitro. The authors investigated the effects of ketamine and S(+)-ketamine on ischemic preconditioning in the rabbit heart in vivo.

METHODS

In 46 alpha-chloralose-anesthetized rabbits, left ventricular pressure (tip manometer), cardiac output (ultrasonic flow probe), and myocardial infarct size (triphenyltetrazolium staining) at the end of the experiment were measured. All rabbits were subjected to 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. The control group underwent the ischemia-reperfusion program without preconditioning. Ischemic preconditioning was elicited by 5-min coronary artery occlusion followed by 10 min of reperfusion before the 30 min period of myocardial ischemia (preconditioning group). To test whether ketamine or S(+)-ketamine blocks the preconditioning-induced cardioprotection, each (10 mg kg(-1)) was administered 5 min before the preconditioning ischemia. To test any effect of ketamine itself, ketamine was also administered without preconditioning at the corresponding time point.

RESULTS

Hemodynamic baseline values were not significantly different between groups [left ventricular pressure, 107 +/- 13 mmHg (mean +/- SD); cardiac output, 183 +/- 28 ml/min]. During coronary artery occlusion, left ventricular pressure was reduced to 83 +/- 14% of baseline and cardiac output to 84 +/- 19%. After 2 h of reperfusion, functional recovery was not significantly different among groups (left ventricular pressure, 77 +/- 19%; cardiac output, 86 +/- 18%). Infarct size was reduced from 45 +/- 16% of the area at risk in controls to 24 +/- 17% in the preconditioning group (P = 0.03). The administration of ketamine had no effect on infarct size in animals without preconditioning (48 +/- 18%), but abolished the cardioprotective effects of ischemic preconditioning (45 +/- 19%, P = 0.03). S(+)-ketamine did not affect ischemic preconditioning (25 +/- 11%, P = 1.0).

CONCLUSIONS

Ketamine, but not S(+)-ketamine blocks the cardioprotective effect of ischemic preconditioning in vivo.

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 microg/ml before preconditioning. Eight hearts received 20 microg/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 microg/ml) and 2 or 20 microg/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 microg/ml ketamine and 2 or 20 microg/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).

CONCLUSION

Ketamine can block the cardioprotective effects of ischemic preconditioning. This effect is caused by the R(-)-isomer.

Can isoflurane mimic ischaemic preconditioning in isolated rat heart?

Ischaemic preconditioning can protect the myocardium against ischaemic injury by opening of the adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel. Isoflurane is also thought to open this channel. The present investigation tested the hypothesis that pre-ischaemic treatment with isoflurane mimics ischaemic preconditioning (producing chemical preconditioning) and thereby protects the myocardium against ischaemic injury in an isolated rat heart model. Control hearts underwent 30 min of global no-flow ischaemia followed by 60 min of reperfusion. The hearts of the preconditioning group underwent two 5 min periods of no-flow ischaemia interspersed with 5 min of reperfusion before the sustained ischaemia. In three additional groups, hearts were subjected to 15 min of 1.5 minimal alveolar concentration (MAC) of isoflurane (ISO-1), 15 min 3 MAC (ISO-2) or 25 min 1.5 MAC (ISO-3) of isoflurane followed by 5 min washout before the global ischaemia. Left ventricular (LV) developed pressure and creatine kinase release were measured as variables of myocardial performance and cellular injury, respectively. Recovery of LV developed pressure was improved after ischaemic preconditioning [after 60 min reperfusion, mean 63 (SEM 6)% of baseline] compared with the control group [18 (4)% P<0.01] but not by isoflurane, independently of concentration or duration of administration [ISO-1, 17 (2)%, P=0.99 vs control; ISO-2, 12 (3)%, P=0.64; ISO-3, 4 (1)%, P=0.06]. Total creatine kinase release over 1 h of reperfusion was not significantly different between control [251 (36) U g(-1) dry weight] and all isoflurane groups [ISO-1, 346 (24) U g(-1), P=0.30; ISO-2, 313 (33) U g(-1), P=0.73; ISO-3, 407 (40) U g(-1), P=0.03]. These results indicate that pre-ischaemic administration of isoflurane does not cause anaesthetic-induced preconditioning in the isolated rat heart.

Spatial heterogeneity of energy turnover in the heart

Local myocardial blood flow varies substantially in spite of a rather homogeneous morphology. To further elucidate this paradox, the spatial heterogeneity of tricarboxylic acid cycle turnover (J(TCA), micromol min(-1) g(-1)) and coronary flow was assessed at a high spatial resolution (6x6x6 mm3) in the open chest dog. Local flow differed more than 2.5-fold between individual samples in each heart (n=7). Out of 1,500 myocardial samples, 1/10 received less than 60% and another 1/10 more than 138% of the normalized mean. In low- and high-flow samples, pyruvate uptake and metabolism were analyzed by 13C NMR spectroscopy. Following [3-13C]pyruvate infusion (2 mM, 12 min), glutamate [4-13C]/[3-13C] was significantly greater in low-flow (2.21+/-0.75, 40 samples) than in high-flow (1.64+/-0.49, 39 samples) areas. This suggests that there are major differences in J(TCA). Glutamate, citrate and lactate content positively correlated with flow. Anaplerotic pathways contributed a fraction similar to J(TCA) in low- and high-flow areas, as demonstrated by isotopomer analysis after 60 min of [3-13C]pyruvate application. Mathematical model analysis of NMR data and relevant pool sizes revealed that J(TCA) and thus myocardial oxygen consumption (MVO2) in high-flow areas exceed values in low-flow areas at least threefold. Thus low and high metabolic states normally coexist within the well perfused heart, suggesting that there is considerable spatial heterogeneity of cardiac energy generation and work.

Xenon administration during early reperfusion reduces infarct size after regional ischemia in the rabbit heart in vivo

The noble gas xenon can be used as an anesthetic gas with many of the properties of the ideal anesthetic. Other volatile anesthetics protect myocardial tissue against reperfusion injury. We investigated the effects of xenon on reperfusion injury after regional myocardial ischemia in the rabbit. Chloralose-anesthetized rabbits were instrumented for measurement of aortic pressure, left ventricular pressure, and cardiac output. Twenty-eight rabbits were subjected to 30 min of occlusion of a major coronary artery followed by 120 min of reperfusion. During the first 15 min of reperfusion, 14 rabbits inhaled 70% xenon/30% oxygen (Xenon), and 14 rabbits inhaled air containing 30% oxygen (Control). Infarct size was determined at the end of the reperfusion period by using triphenyltetrazolium chloride staining. Xenon reduced infarct size from 51%+/-3% of the area at risk in controls to 39%+/-5% (P<0.05). Infarct size in relation to the area at risk size was smaller in the xenon-treated animals, indicated by a reduced slope of the regression line relating infarct size to the area at risk size (Control: 0.70+/-0.08, r = 0.93; Xenon: 0.19+/-0.09, r = 0.49, P<0.001). In conclusion, inhaled xenon during early reperfusion reduced infarct size after regional ischemia in the rabbit heart in vivo.

Left stellate ganglion block has only small effects on left ventricular function in awake dogs before and after induction of heart failure

Left stellate ganglion block (LSGB) results in acute sympathetic denervation of the left ventricular (LV) posterobasal wall. We investigated the effects of LSGB in chronically instrumented awake dogs before and after the induction of pacing-induced congestive heart failure. Twelve dogs were instrumented for measurement of global hemodynamics [LV pressure (LVP)], its first derivative (dP/dt), cardiac output (CO), and regional myocardial function (systolic posterobasal segment length shortening, mean velocity [SLmv]). Before the induction of heart failure (n = 12), LSGB did not affect CO [3.2+/-1.4 (control, mean +/- SD) vs. 3.3+/-1.6 L/min (LSGB, P = 0.45)] and SLmv (11.1+/-4.0 vs. 10.8+/-4.0 mm/s, P = 0.16), but slightly reduced LVP (130+/-12 vs. 125+/-14 mm Hg, P = 0.04), dP/dt(max) (3614+/-755 vs. 3259+/-644 mm Hg/s, P = 0.003) and dP/dt(min) (-3153+/-663 vs. -2970+/-725 mm Hg/s, P = 0.03). During heart failure (n = 8), global hemodynamics [CO (2.8+/-1.2 vs. 2.7+/-1.2 L/min, P = 0.04), LVP (119+/-6 vs. 112+/-9 mm Hg, P = 0.01), dP/dt(max) (1945+/-520 vs. 1824+/-554 mm Hg/s, P = 0.03) and dP/dt(min) (-2402+/-678 vs. -2243+/-683 mm Hg/s, P = 0.04)], as well as regional myocardial function, were significantly different after LSGB [SLmv] (8.0+/-3.8 vs. 6.9+/-3.4 mm/s, P = 0.02)]. In conclusion, even during heart failure, the hemodynamic changes after LSGB are small, confirming its broad margin of safety.

Influence of the angiotensin II AT1 receptor antagonist irbesartan on ischemia/reperfusion injury in the dog heart

The aim of the present study was to investigate whether the non-peptide angiotensin II type 1 (AT1) receptor antagonist irbesartan (SR 47436, BMS 186295, 2-n-butyl-3 [2'-(1H-tetrazol-5-yl)-biphenyl-4-yl)methyl]-1,3-diaza-spiro [4,4]non-1-en-4-one) has myocardial protective effects during regional myocardial ischemia/reperfusion in vivo. Eighteen anesthetized open-chest dogs were instrumented for measurement of left ventricular and aortic pressure (tip manometer and pressure transducer, respectively), and coronary flow (ultrasonic flowprobes). Regional myocardial function was assessed by Doppler displacement transducers as systolic wall thickening (sWT) in the antero-apical and the postero-basal wall. The animals underwent 1 h of left anterior descending coronary artery (LAD) occlusion and subsequent reperfusion for 3 hours. Irbesartan (10 mg kg(-1), n = 9) or the vehicle (KOH, control, n = 9) was injected intravenously 30 min before LAD occlusion. Regional myocardial blood flow (RMBF) was measured after irbesartan injection and at 30 min LAD occlusion using colored microspheres. Infarct size was determined by triphenyltetrazolium chloride staining after 3 h of reperfusion. There was no recovery of sWT in the LAD perfused area in both groups at the end of the experiments (systolic bulging, -15.1+/-6.1% of baseline (irbesartan) vs. -12.3+/-3.0% (control), mean+/-SEM). Irbesartan led to an increase in RMBF in normal myocardium (2.47+/-0.40 vs. 1.35+/-0.28 ml min(-1) g(-1), p<0.05), and also to an increase in collateral blood flow to the ischemic area (0.27+/-0.04 vs. 0.17+/-0.02 ml min(-1) g(-1), P = <0.05). Infarct size (percent of area at risk) was 24.8+/-3.2 % in the treatment group compared with 26.9+/-4.8% in the control group (P = 0.72). These results indicate that a blockade of angiotensin II AT1 receptors with irbesartan before coronary artery occlusion led to an increase in RMBF, but did not result in a significant reduction of myocardial infarct size.

Effect of dantrolene in an in vivo and in vitro model of myocardial reperfusion injury

BACKGROUND

In skeletal muscle, dantrolene reduces free cytosolic calcium by inhibiting calcium release from the sarcoplasmic reticulum. A similar effect in ischemic-reperfused heart cells would protect myocardial tissue against reperfusion injury. We tested the hypothesis that dantrolene infusion during reperfusion protects the heart against reperfusion injury.

METHODS

Isovolumetric beating rat hearts were subjected to 30 min of ischemia followed by 60 min of reperfusion. Left ventricular (LV) developed pressure (LVDP) and creatine kinase release (CKR) were determined as indices of myocardial performance and cellular injury, respectively. In the treatment groups, dantrolene (25 (DAN25) or 100 (DAN100) micromol l(-1)) was infused during the first 15 min of reperfusion; control hearts received the respective concentration of the vehicle (mannitol (CON25, CON100), each group n=7). To investigate the effects of dantrolene on reperfusion injury in vivo, 18 chloralose-anesthetized rabbits were subjected to 30 min occlusion and 180 min reperfusion of a major coronary artery. LV pressure (LVP), cardiac output (CO), and infarct size were determined. During the last 5 min of ischemia, nine rabbits received 10 mg kg(-1) dantrolene intravenously (DAN). Another nine rabbits received the vehicle (dimethylsulfoxide) and served as controls (CON).

RESULTS

In isolated rat hearts, there was no recovery of LVDP in any group. Total CKR during 1 h of reperfusion was 845+/-76 (CON100) and 550+/-81 U g(-1) dry mass (DAN100, P<0.05). In rabbits in vivo, hemodynamic baseline values were similar between groups (CON vs. DAN: LVP, 99+/-6 (mean+/-SEM) vs. 91+/-6mm Hg, P=0.29; CO, 252+/-26 vs. 275+/-23 ml min(-1), P= 0.53). During coronary artery occlusion, LVP and CO were reduced in both groups (CON: LVP, 89+/-3%; CO, 90+/-5% of baseline values) and LVP did not recover to baseline values during reperfusion (51+/-5% (CON) vs. 67+/-7% (DAN) of baseline, P=0.10). Infarct size was 41+/-4% of the area at risk in controls and 37+/-6% in dantrolene treated hearts (P=0.59).

CONCLUSIONS

Dantrolene reduced CKR, indicating an attenuation of lethal cellular reperfusion injury in isolated rat hearts. However, in the rabbit in vivo, there was no effect on the extent of reperfusion injury after regional myocardial ischemia.

Effect of propofol on reperfusion injury after regional ischaemia in the isolated rat heart

Free oxygen radicals and intracellular calcium homeostasis play important roles in the development of myocardial reperfusion injury. Propofol is a radical scavenger with calcium channel blocking properties. We have investigated the effects of propofol on myocardial reperfusion injury. We used an isolated rat heart model where heart rate, ventricular volume and perfusion pressure were constant. The left anterior descending coronary artery (LAD) was occluded for 30 min and reperfused for 2 h. We studied an untreated control group, an Intralipid group (1 microliter ml-1) and a propofol group (Intralipid 1 microliter ml-1 and propofol 1 microgram ml-1) (n = 12 each). Drugs were infused for 20 min starting 5 min before reperfusion. We measured left ventricular developed pressure (LVDP), coronary flow and infarct size. LAD occlusion reduced mean LVDP from 129 (SEM 4) to 36 (3) mm Hg and mean coronary flow from 12.2 (0.3) to 5.2 (0.2) ml min-1. During reperfusion, LVDP recovered to 98 (4) mm Hg and coronary flow to 11.9 (0.4) ml min-1. Haemodynamic variables were similar in all groups. Propofol had no effect on infarct size compared with the Intralipid group (25.0 (3.7) vs 26.9 (3.3)% of the area at risk; P = 0.89). Infarct size in the Intralipid group tended to be smaller compared with the control group (34.8 (3.2)%; P = 0.19). We conclude that propofol, at a clinically relevant concentration, provided no protective effect against myocardial reperfusion injury in the rat heart in vitro.

Beneficial effects of sevoflurane and desflurane against myocardial reperfusion injury after cardioplegic arrest

PURPOSE

To determine whether sevoflurane or desflurane offer additional protective effects against myocardial reperfusion injury after protecting the heart against the ischemic injury by cardioplegic arrest.

METHODS

Isolated rat hearts in a Langendorff-preparation (n = 9) were arrested by infusion of HTK cardioplegic solution and subjected to 30 min global ischemia followed by 60 min reperfusion (controls). An additional 18 hearts were subjected to the same protocol, and sevoflurane (n = 9) or desflurane (n = 9) was added to the perfusion medium during the first 30 min of reperfusion in a concentration corresponding to 1.5 MAC in rats. Left ventricular (LV) developed pressure and creatine kinase (CK) release were determined as indices of myocardial performance and cellular injury, respectively.

RESULTS

The LV developed pressure recovered to 46+/-7% of baseline in controls. Functional recovery during reperfusion was improved by inhalational anesthetics to 67+/-3% (sevoflurane, P<0.05) and 61+/-5% of baseline (desflurane, P<0.05), respectively. Peak CK release during early reperfusion was reduced from 52+/-11 U x min(-1) x g(-1) in controls to 34+/-7 and 26+/-7 U x min(-1) x g(-1) in sevoflurane and desflurane treated hearts, respectively. The CK release during the first 30 min of reperfusion was reduced from 312+/-41 U x g(-1) in control hearts to 195+/-40 and 206+/-37 U x g(-1) in sevoflurane and desflurane treated hearts.

CONCLUSION

After ischemic protection by cardioplegia, sevoflurane and desflurane given during the early reperfusion period offer additional protection against myocardial reperfusion injury.

Effects of enflurane, isoflurane, sevoflurane and desflurane on reperfusion injury after regional myocardial ischaemia in the rabbit heart in vivo

It is known that volatile anaesthetics protect myocardial tissue against ischaemic and reperfusion injury in vitro. In this investigation, we have determined the effects of the inhalation anaesthetics, enflurane, isoflurane, sevoflurane and desflurane, administered only during early reperfusion, on myocardial reperfusion injury in vivo. Fifty chloralose-anaesthetized rabbits were subjected to 30 min of occlusion of a major coronary artery followed by 120 min of reperfusion. Left ventricular pressure (LVP, tip-manometer), cardiac output (CO, ultrasonic flow probe) and infarct size (triphenyltetrazolium staining) were determined. During the first 15 min of reperfusion, five groups of 10 rabbits each received 1 MAC of enflurane (enflurane group), isoflurane (isoflurane group), sevoflurane (sevoflurane group) or desflurane (desflurane group), and 10 rabbits served as untreated controls (control group). Haemodynamic baseline values were similar between groups (mean LVP 106 (SEM 2) mm Hg; CO 281(7) ml min-1). During coronary occlusion, LVP and CO were reduced to the same extent in all groups (LVP 89% of baseline; CO 89%). Administration of inhalation anaesthetics during early reperfusion further reduced both variables, but they recovered after discontinuation of the anaesthetics to values not different from control animals. Infarct size was reduced from 49 (5)% of the area at risk in the control group to 32 (3)% in the desflurane group (P = 0.021), and to 36 (2)% in the sevoflurane group (P = 0.097). In the enflurane group, infarct size was 39 (5)% (P = 0.272). Isoflurane had no effect on infarct size (48 (5)%, P = 1.000). The results show that desflurane and sevoflurane markedly reduced infarct size and therefore can protect myocardium against reperfusion injury in vivo. Enflurane had only a marginal effect and isoflurane offered no protection against reperfusion injury in vivo. These different effects suggest different protective mechanisms at the cellular level.

Effects of halothane, enflurane, isoflurane, sevoflurane and desflurane on myocardial reperfusion injury in the isolated rat heart

A specific action against myocardial reperfusion injury of the oxygen paradox type was recently characterized for halothane after anoxic perfusion in isolated rat hearts and isolated cardiomyocytes. In this study, we have characterized the protective effects of the clinically available inhalation anaesthetics during reperfusion after ischaemia. In isolated, isovolumically beating rat hearts perfused at a constant flow (10 ml min-1, PO2 80 kPa) and paced at 350 beat min-1, we determined left ventricular developed pressure (LVDP) and release of creatine kinase (CKR) as indices of myocardial performance and cellular injury, respectively. Seven control hearts underwent 30 min of no-flow ischaemia and 1 h of reperfusion. In the treatment groups, halothane, enflurane, isoflurane, sevoflurane or desflurane (each group n = 6) was added to the perfusion medium for the first 30 min of reperfusion at a concentration corresponding to 1.5 MAC in the rat. In the control group, cellular injury occurred at early reperfusion (peak CKR 283 (SEM 57) iu litre-1 at 10 min of reperfusion). Peak CKR to the coronary venous effluent was attenuated by all anaesthetics (halothane group 156 (45), enflurane group 134 (20), sevoflurane group 132 (20), desflurane group 159 (25) iu litre-1; each P < 0.05). Isoflurane did not differ from controls (303 (53) iu litre-1; P = 0.5). In the sevoflurane group, there was a delayed peak CKR after discontinuation of the anaesthetic at 30 min of reperfusion (260 (34) iu litre-1). Functional recovery was improved by all anaesthetics, but was seen much earlier with desflurane (LVDP 28 (3)% of baseline at 5 min reperfusion compared with halothane (6 (1)%), enflurane (11 (3)%), isoflurane (9 (6)%), sevoflurane (10 (2)%) and controls (3 (1)% of baseline)). At 30 min of reperfusion, recovery of LVDP was improved to a similar extent by all anaesthetics (halothane 30 (9)%, enflurane 36 (9)%, isoflurane 33 (5)%, sevoflurane 30 (5)%, desflurane 36 (4)% of baseline values) compared with controls (13 (5)%; each P < 0.05). All inhalation anaesthetics protected against myocardial reperfusion injury, but showed differences in attenuation of cellular injury and functional recovery. These differences may suggest different protective mechanisms.

Enflurane and isoflurane, but not halothane, protect against myocardial reperfusion injury after cardioplegic arrest with HTK solution in the isolated rat heart

To investigate the effects of halothane, enflurane, and isoflurane on myocardial reperfusion injury after ischemic protection by cardioplegic arrest, isolated perfused rat hearts were arrested by infusion of cold HTK cardioplegic solution containing 0.015 mmol/L Ca2+ and underwent 30 min of ischemia and a subsequent 60 min of reperfusion. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial function and cellular injury, respectively. In the treatment groups (each n = 9), anesthetics were given during the first 30 min of reperfusion in a concentration equivalent to 1.5 minimum alveolar anesthetic concentration of the rat. Nine hearts underwent the protocol without anesthetics (controls). Seven hearts underwent ischemia and reperfusion without cardioplegia and anesthetics. In a second series of experiments, halothane was tested after cardioplegic arrest with a modified HTK solution containing 0.15 mmol/L Ca2+ to investigate the influence of calcium content on protective actions against reperfusion injury by halothane. LV developed pressure recovered to 59%+/-5% of baseline in controls. In the experiments with HTK solution, isoflurane and enflurane further improved functional recovery to 84% of baseline (P < 0.05), whereas halothane-treated hearts showed a functional recovery similar to that of controls. CK release was significantly reduced during early reperfusion by isoflurane and enflurane, but not by halothane. After cardioplegic arrest with the Ca2+-adjusted HTK solution, halothane significantly reduced CK release but did not further improve myocardial function. Isoflurane and enflurane given during the early reperfusion period after ischemic protection by cardioplegia offer additional protection against myocardial reperfusion injury. The protective actions of halothane depended on the calcium content of the cardioplegic solution.

IMPLICATIONS

Enflurane and isoflurane administered in concentrations equivalent to 1.5 minimum alveolar anesthetic concentration in rats during early reperfusion offer additional protection against myocardial reperfusion injury even after prior cardioplegic protection. Protective effects of halothane solely against cellular injury were observed only when cardioplegia contained a higher calcium concentration.

Effect of acidotic blood reperfusion on reperfusion injury after coronary artery occlusion in the dog heart

A prolongation of the intracellular acidosis after myocardial ischemia can protect the myocardium against reperfusion injury. In isolated hearts, this was achieved by prolongation of the extracellular acidosis. The aim of this study was to investigate whether regional reperfusion with acidotic blood after coronary artery occlusion can reduce infarct size and improve myocardial function in vivo. Anesthetized open-chest dogs were instrumented for measurement of regional myocardial function, assessed by sonomicrometry as systolic wall thickening (sWT). Infarct size was determined by triphenyltetrazolium staining after 3 h of reperfusion. The left anterior descending coronary artery (LAD) was perfused through a bypass from the left carotid artery. The animals underwent 1 h of LAD occlusion and subsequent bypass-reperfusion with normal blood (control, n = 6) or blood equilibrated to pH = 6.8 by using 0.1 mM HCl during the first 30 min of reperfusion (HCl, n = 5). Regional collateral blood flow (RCBF) at 30-min occlusion was measured by using colored microspheres. There was no difference in recovery of sWT in the LAD-perfused area between the two groups at the end of the experiments [-2.8+/-1.2% (HCl) vs. -4.4+/-2.5% (control); mean +/- SEM; p = NS]. RCBF was comparable in both groups. Infarct size (percentage of area at risk) was reduced in the treatment group (12.8+/-2.8%) compared with the control group (26.2+/-4.8%; p < 0.05). These results indicate that reperfusion injury after coronary artery occlusion can be reduced by a prolonged local extracellular acidosis in vivo.

Effect of heart rate reduction by 4-(N-ethyl-N-phenyl-amino)-1,2-dimethyl-6-(methylamino)pyrimidinium chloride on infarct size in dog

Heart rate (HR) reduction may reduce the severity of myocardial ischemia. ZD7288 (4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino)pyrimidinium++ + chloride) is a novel bradycardic agent with a specific effect on the sinoatrial node without having any other direct effects on the heart. In the present study, the effect of ZD7288 on infarct size and regional myocardial function during regional myocardial ischemia and reperfusion was investigated. Seventeen anesthetized open chest dogs (control, n = 8, and ZD7288, n = 9) underwent 1 h of left anterior descendent artery (LAD) occlusion followed by 6 h of reperfusion. In one group, ZD7288 was given intravenously (0.7 mg/kg body weight) 45 min before LAD occlusion. Regional myocardial function was assessed by sonomicrometry as systolic wall thickening fraction (sWTF) in the anteroapical (interest region, IR) and the posterobasal wall (control region, CR). Ischemic regional myocardial blood flow (RMBF) was determined by colored microspheres and infarct size (IS) by triphenyltetrazolium staining. ZD7288 injection decreased HR from 104 +/- 5 to 74 +/- 3 bpm (mean +/- SEM, p < 0.001 vs control, vs baseline), but did not change sWTF. During reperfusion, sWTF of the IR was significantly greater in the ZD7288 group (26 +/- 12 vs -14 +/- 13%, 1 h reperfusion, p < 0.05), while sWTF of CR stayed equal (120 +/- 13 vs 111 +/- 16%, p = ns). IS was markedly reduced in the ZD7288 group (4.7 +/- 1.8 vs 18.0 +/- 5.2% of IR, p < 0.05). There was no difference in ischemic endocardial RMBF (ZD7288 11.0 +/- 4.3 vs control 12.3 +/- 6.5 ml/min/100 g, p = ns). ZD7288 reduces HR without having direct effects on regional myocardial function. This HR reduction leads to a smaller IS and to a better regional functional recovery.

Inotropic effects of glyceryl trinitrate and spontaneous NO donors in the dog heart

BACKGROUND

In vitro, NO has a biphasic effect on myocardial inotropy. To determine the inotropic effect of NO in vivo, we investigated the activity of glyceryl trinitrate (GTN) and the NO donors S-nitroso-N-acetyl-D,L-penicillamine (SNAP) and sodium-(2)-1-(N,N-diethyl-amino)-diazen-1-ium-1,2-diolat+ ++ (DEA/NO) in dogs.

METHODS AND RESULTS

Eight anesthetized open-chest dogs were instrumented for measurement of left ventricular and aortic pressures (tip manometers) and coronary flow (ultrasonic flow probes). Regional myocardial function was assessed by sonomicrometry as systolic wall thickening (sWT), mean systolic thickening velocity (Vs), and regional myocardial stroke work index (RSW). GTN, SNAP, and DEA/NO were infused into the left anterior descending coronary artery (LAD) to achieve defined coronary plasma concentrations of GTN, SNAP (both 10 to 100 micromol/L), and DEA/NO (2 to 20 micromol/L). All drugs increased LAD flow and myocardial contractile function in the LAD-dependent myocardium within the first 120 seconds. The greatest inotropic effect was noted after infusion of DEA/NO (20 micromol/L), which increased sWT by 9.7+/-3.1% from 28.5+/-2.2%, Vs by 10.3+/-3.4% from 9.1+/-1.1 mm/s, and RSW by 7.1+/-2.1% from 200.0+/-22.1 mm Hg x mm (P<.05). At the same time, systemic hemodynamics remained unchanged. Prevention of the flow response to GTN by external narrowing of the LAD did not influence the inotropic effect of GTN.

CONCLUSIONS

Organic nitrates and NO donors evoke a small but constant positive inotropic effect in vivo that is not caused by coronary vasodilation.

Halothane reduces reperfusion injury after regional ischaemia in the rabbit heart in vivo

In addition to having anti-ischaemic effects, halothane can protect isolated rat hearts and isolated cardiomyocytes against reperfusion injury of the "oxygen paradox" type. The aim of this study was to investigate if halothane can also protect against myocardial reperfusion injury in vivo. Twenty-two rabbits anaesthetized with alpha-chloralose underwent 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. Seven animals received 1 MAC of halothane for the first 15 min of reperfusion (halothane group), and eight animals served as untreated controls (controls group). In seven additional animals, the haemodynamic effects of halothane were antagonized by an i.v. infusion of noradrenaline (halothane-noradrenaline group). We measured cardiac output (CO) by an ultrasonic flow probe around the ascending aorta, left ventricular pressure (LVP) by a tip manometer and infarct size by triphenyltetrazolium staining. Baseline LVP was mean 92 (SEM 4) mm Hg and CO was 289 (16) ml min-1. During coronary occlusion, LVP was reduced to 86 (4)% of baseline and CO to 84 (4)% (similar in all groups). During halothane administration at reperfusion, LVP declined further to 55 (6)% of baseline and CO to 66 (9)% (P < 0.05 halothane group vs control group). Noradrenaline prevented the reduction in LVP (halothane-noradrenaline group 87 (5)% of baseline, control group 84 (6)% and reduction in CO (halothane-noradrenaline group 89 (5)%, control group 83 (6)%. Infarct size was 49 (6)% of the area at risk in controls and was reduced markedly by administration of halothane to 32 (3)% in the halothane group (P < 0.05) and to 30 (3)% in the halothane-noradrenaline group (P < 0.05). Treatment with halothane during the early reperfusion period after myocardial ischaemia protected the myocardium against infarction in vivo, independent of the haemodynamic effect of halothane.

[Effect of magnesium on infarct size after coronary occlusion. Animal experiment studies]

In addition to its antiarrhythmic and antithrombotic effects magnesium is said to have a beneficial effect in patients with acute myocardial infarction. Magnesium can protect myocardial tissue after coronary occlusion and reduces infarct size in experimental models of ischaemia and reperfusion, though the given doses of magnesium are relatively high and differ from clinically reachable serum concentrations. We tested 2 hypotheses in a dog model of ischaemia-reperfusion: 1. The protective effect may be due to a direct, local influence of magnesium on myocardial reperfusion injury. 2. Systemic magnesium treatment with low doses comparable to clinical study regiments may reduce myocardial infarct size. Anaesthetized open chest dogs underwent 1 h of left anterior descending artery occlusion followed by 6 h of reperfusion. 1. Ten animals received intracoronary magnesium aspartate (Mg i.c.) or vehicle infusion (control i.c.) for the first hour of reperfusion to increase regional Mg-concentration by 2 mmol/l. 2. Fourteen animals received intravenous infusion with magnesium potassium aspartate (Mg-K i.v.) or vehicle infusion (control i.v.), beginning 1 h before occlusion until the end of the 6 h reperfusion period. Regional magnesium concentration in the Mg i.c.-group increased to 2.7 +/- 1.00 mmol/l at 45 min of reperfusion. Intravenous infusion raised serum magnesium from 0.71 +/- 0.03 mmol/l to 1.29 +/- 0.14 mmol/l in the Mg-K i.v. group (5 min of reperfusion, p < 0.01 vs. baseline). Infarct size after 6 h reperfusion (TTC staining) was similar in both groups of intracoronary treatment (Mg i.c., 20.6 +/- 5.0; control, 24.4 +/- 8.7% of area at risk; p = n.s.) and intravenous treatment (Mg-K i.v. 18.1 +/- 14.8; control 14.1 +/- 12.2% of area at risk; p = n.s.). Neither regional nor systemic magnesium leads to a clinically relevant reduction of infarct size in the regional ischaemic-reperfused dog heart when it is given in clinically usable doses. The beneficial action of systemic Mg is probably not due to an early direct protective effect on ischaemic-reperfused myocardium but to its antiarrhythmic and antithrombotic effects. Possibly only to high doses of Mg applied under experimental conditions can reduce infarct size.

Effect of halothane on myocardial reoxygenation injury in the isolated rat heart

Several studies have reported a protective effect of halothane on myocardial injury in an ischaemia-reperfusion situation. It is unclear if the protection is a result of the haemodynamic effects of halothane or if halothane has a specific action on ischaemia or reperfusion pathomechanisms. To examine this question, we have used an isolated rat heart model where heart rate (300 beat min-1), ventricular volume and coronary flow are constant. Left ventricular developed pressure (LVDP) and release of creatine kinase (CK) were measured as variables of myocardial performance and cellular injury, respectively. Five control hearts were subjected to 35 min of low-flow (2 ml min-1) anoxic and substrate-free perfusion and were then perfused for 1 h with the oxygenated buffer. In the treatment groups, halothane 0.4 mmol litre-1 was added during the first 30 min of anoxic perfusion (n = 5) or during the first 30 min of reoxygenation (n = 5). In five additional hearts, the effect of halothane 0.4 mmol litre-1 was tested under normoxic conditions. Mean basal CK release was 0.29 (SEM 0.13) iu g-1 min-1 and LVDP was 105.5 (4.0) mm Hg. Under normoxic conditions, halothane reduced LVDP to 52.0 (2.6) mm Hg. In control hearts, the major cell injury occurred at the onset of reoxygenation (CK release increased to 149.1 (9.1) iu g-1 min-1) and functional recovery after 1 h of reoxygenation was poor (control LVDP, 14.2(2.)% of baseline). Halothane during anoxia attenuated myocardial injury only moderately (CK release 50.2(5.7) iu g-1 min-1) and LVDP recovered to 30.8(3.0)% (each P < 0.05 vs control). When halothane was administered at reoxygenation, CK release was reduced to 10.1 (0.9) iu g-1 min-1 and LVDP recovered to 69.4(4.9)% (each P < .05 vs control). We conclude that halothane not only attenuated ischaemic injury but had a specific protective action against reoxygenation injury.

Effect of inotropic stimulation on the synchrony of left ventricular wall motion in a dog model of myocardial stunning

BACKGROUND

Reperfusion after short coronary occlusion induces regional myocardial dysfunction ("stunning"), including asynchrony of left ventricular (LV) wall motion. Contractile function of stunned myocardium can be increased by inotropic stimulation, but whether this has an influence on wall motion asynchrony is unknown.

METHODS

In six anaesthetized dogs, the effect of inotropic stimulation on regional myocardial function, and LV asynchrony was tested after the induction of regional stunning (by 15 min of left circumflex artery side branch occlusion). Regional myocardial function was assessed as mean systolic wall thickening velocity (Vswt) by sonomicrometry in the stunned (posterobasal wall) and normal myocardium (anteroapical wall), and LV asynchrony by the phase difference (phi) of the first Fourier transform of the wall thickness signals.

RESULTS

In the stunned myocardium, Vswt decreased from 8.6 +/- 1.0 to 1.7 +/- 1.4 mm s-1 (mean +/- SEM), P < 0.01, and simultaneously phi increased from 10.8 +/- 3.6 to 85.7 +/- 14.3 degrees, P < 0.01. Intracoronary noradrenaline (NADR, 0.25 microgram) improved Vswt (8.3 +/- 1.4 mm s-1, P < 0.01) in the stunned region and changed phi to -38.1 +/- 18.0 degrees, P < 0.05. Systemic NADR (5 micrograms) also increased Vswt of the stunned region (to 3.8 +/- 2.1 mm s-1, P < 0.05), but left phi unchanged (82.9 +/- 19.8 degrees).

CONCLUSION

Regional function of stunned myocardium can be augmented by inotropic stimulation with noradrenaline, but this does not result in an improvement of LV wall motion asynchrony during systemic inotropic stimulation.

Unilateral changes of sympathetic tone to the heart impair left ventricular function

BACKGROUND

Different regions within the left ventricle are preferentially supplied by the left or right sympathetic system. In order to characterize different influences of left vs right sympathetic lateralization on LV function, haemodynamic effects of right and left stellate ganglion stimulations (RSGS and LSGS) as well as a right sympathetic block (RSB) were compared.

METHODS

Seven alpha-chloralose anaesthetized open chest dogs were instrumented for measurement of LV pressure (tip manometers) and regional LV wall thickness (WT, sonomicrometry) in the antero-apical wall (AW, innervated by right stellate ganglion) and postero-basal wall (PW, left stellate ganglion). Timing of regional myocadial wall motion was evaluated by the phase of the first Fourier transform of the WT signals, LV asynchrony by the phase difference (phi) between both regions, and LV diastolic function by the time constant of isovolumic relaxation (tau). Measurements were performed before and after RSB (5 ml of lidocaine 1%); in 6 dogs of this group, RSGS and LSGS (4 V, 0.2 ms, 20 Hz) were performed before RSB. In order to investigate a regional inotropic stimulation without systemic effect, 6 additional dogs received intracoronary noradrenaline injections (NIC, 0.25 microgram) into the left circumflex artery perfused myocardium.

RESULTS

LSGS and NIC led to an earlier PW-motion within the cardiac cycle (phase reduction by 40.0 +/- 15.0 degree (SEM) and 55.5 +/- 11.2 degrees) and RSGS induced an earlier AW-motion (by 33.7 +/- 15.2 degrees). After RSB, AW-motion was delayed (38.1 +/- 9.2 degrees). The consequence was an asynchronous wall motion pattern after all interventions (change in phi: LSGS-64.7 +/- 18.7 degrees, RSGS 41.1 +/- 15.7 degrees, NIC -74.5 +/- 17.4 degrees, RSB -52.6 +/- 14.6 degrees), and a prolonged relaxation (tau increase: RSGS 9.4 +/- 1.9, NIC 8.3 +/- 1.5, RSB 3.7 +/- 0.8 ms).

CONCLUSION

Unilateral increases as well as decreases of sympathetic tone to the heart result in an asynchronous wall motion pattern and an impaired LV relaxation.

Intracoronary magnesium is not protective against acute reperfusion injury in the regional ischaemic-reperfused dog heart

Intravenous magnesium lowers mortality in patients with suspected myocardial infarction. We tested the hypothesis that the protective effect may be due to a direct, local influence of magnesium on myocardial reperfusion injury in a dog model of ischaemia/reperfusion. Ten anaesthetized open chest dogs underwent 1 h of left anterior descending artery (LAD) occlusion and 6 h of reperfusion. The animals received intracoronary (i.c.) magnesium aspartate (Mg, n = 5) or vehicle infusion (n = 5) for the first hour of reperfusion. Mg infusion was adapted to actual LAD flow (ultrasonic flow probe) to increase regional plasma concentration by 4 mmol L-1. Regional myocardial function was measured as percent systolic wall thickening (sWTh, sonomicrometry). Intracoronary Mg increased LAD flow during application (at 15 min reperfusion; Mg, 194 +/- 44 (mean +/- SD); control, 116 +/- 41 mL min-1 100 g-1, P < 0.01). sWTh decreased during coronary occlusion from 14.3 +/- 7.1% to -4.7 +/- 2.7% in the control group and from 14.8 +/- 2.5% to -4.1 +/- 3.1% in the Mg group. Throughout the reperfusion period wall function remained depressed in both groups to a similar degree (control, -3.5 +/- 1.8%; Mg, -3.0 +/- 1.9% at 6 h reperfusion). Global haemodynamics were not different. Infarct size after 6 h reperfusion (TTC staining) was similar in both groups (Mg, 20.6 +/- 5.0; control, 24.4 +/- 8.7% of area at risk). Regional magnesium application (i.c.) to post-ischaemic reperfused myocardium had no influence on infarct size or post-ischaemic regional wall function in this model.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracoronary SIN-1C during reperfusion reduces infarct size in dog

Reperfusion of ischemic myocardium may aggravate the ischemic state of injury and thus augment infarct size (reperfusion injury). The aim of this study was to reduce infarct size by an intervention at the time of reperfusion that acts only on a reperfusion-specific pathomechanism. It was investigated whether SIN-1C, a metabolite of molsidomine, can protect against reperfusion injury in canine hearts in vivo. Ten anesthetized open chest dogs underwent 1 h of left anterior descendent artery (LAD) occlusion and were randomly assigned to receive either intracoronary SIN-1C or vehicle infusion as a placebo during the first hour of reperfusion. The infusion was adjusted to LAD flow to achieve a regional blood concentration of 5 x 10(-3) M. Infarct size was assessed by triphenyltetrazolium staining after 6 h of reperfusion. Left ventricular pressure (LVP) was similar in both groups (SIN-1C: 101 +/- 6, placebo: 89 +/- 6 mm Hg, mean +/- SEM, n = 5) at the beginning of the experiment and did not change significantly thereafter from baseline values in both groups. During SIN-1C infusion, the LAD flow was increased (SIN-1C: 195 +/- 38, control: 86 +/- 17 ml/min/100 g at 30 min of reperfusion, p < 0.05), while systemic hemodynamics remained unaltered. A reduction in infarct size (percent of area at risk) was seen in the SIN-1C group (11.4 +/- 2.8%) compared with the placebo group (24.4 +/- 3.9%, p < 0.05). Infusion of papaverin (5 x 10(-5) M) following an identical protocol caused a similar vasodilation as SIN-IC, but did not reduce infarct size in five additional dox experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Left stellate ganglion block impairs left ventricular function

Stellate ganglion block (SGB) is an established procedure for the diagnosis and treatment of chronic pain. SGB results in an acute sympathetic denervation of a part of the left ventricular (LV) wall innervated by the blocked ganglion, which may impair regional contractility. The resulting imbalance of myocardial contractility in different LV regions may affect LV function adversely by increasing LV asynchrony. Seven anesthetized open chest dogs were instrumented for measurement of aortic and LV pressure (tip manometers), cardiac output (CO, thermodilution), and regional LV wall thickness (WT, sonomicrometry) in the anteroapical (predominantly innervated by the right stellate ganglion) and posterobasal wall (left stellate ganglion). The contractility of both regions was assessed using the relationship between preload recruitable stroke work and end-diastolic WT relationship (MW). The timing of regional myocardial wall motion was evaluated by means of the phase of the first harmonic of the Fourier transform of the WT signals, LV asynchrony by the phase difference (PD) between both regions, and LV diastolic function by the time constant of isovolumic relaxation (tau). Measurements were performed before and after left SGB (LSGB). Mean arterial pressure was 105 +/- 25 (mean +/- SD) before and 97 +/- 10 mm Hg after LSGB (not significant). CO remained unchanged (3.09 +/- 1.03 vs 2.93 +/- 1.07 L/min). LSGB significantly reduced contractility in the posterobasal myocardium (MW -162 +/- 26 vs -80 +/- 7 mm Hg; P < 0.01), accompanied by a delay of regional wall motion within the cardiac cycle (phase 202 +/- 18 vs 223 +/- 17 degrees; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Regional contractile blockade at the onset of reperfusion reduces infarct size in the dog heart

An important mechanism of lethal myocardial reperfusion injury is the development of cellular hypercontracture at the onset of reperfusion. Hypercontracture can lead to cytolysis by mutual mechanical disruption of myocardial cells. 2,3-Butanedione monoxime (BDM) inhibits myofibrillar cross-bridge cycling and may therefore reduce infarct size in ischaemic reperfused myocardium. This study investigated whether a temporary presence of BDM protects against myocardial reperfusion injury in an intact-animal preparation. Anaesthetized open-chest dogs (n = 10) underwent 1 h of left anterior descendent artery (LAD) occlusion and received intracoronary BDM (25 mM, n = 5) or vehicle (n = 5) for 65 min starting with an anoxic local infusion 5 min before reperfusion. Infarct size was assessed by triphenyltetrazolium staining after 6 h reperfusion. The infusion of BDM was accompanied by a transient reduction of left ventricular systolic pressure from 84.3 +/- 11.2 mm Hg during occlusion to 66.4 +/- 9.9 mm Hg at 30 min reperfusion (mean +/- SD, P < 0.01 vs. control). LAD-flow and regional wall motion in the area at risk showed no difference between groups. Infarct size (% of area at risk) was reduced from 24.4 +/- 8.7 (control) to 6.6 +/- 2.0% (BDM) (P < 0.01). The results demonstrate that development of necrosis in reperfused myocardium can be greatly reduced by temporary presence of the contractile inhibitor BDM at the onset of reperfusion.

Adenosine A2-receptor activation at reperfusion reduces infarct size and improves myocardial wall function in dog heart

Reestablishment of blood supply to ischemic myocardium leads to biochemical and cellular changes which are believed to reduce the amount of potentially salvageable myocardium (reperfusion injury). In this situation, adenosine is known to have myocardial protective properties. Activation of adenosine A2-receptors may account for most of the beneficial effects of adenosine in reperfusion injury because A2-receptor activation mediates vasodilation, inhibits neutrophil adhesion to vascular endothelium and diminishes generation of free radicals by neutrophils, thus acting on some of the key mechanisms of reperfusion injury such as postischemic vascular dysfunction and neutrophil-mediated damage. Therefore, we investigated the effect of an intracoronary A2-agonist, CGS 21680, on regional postischemic myocardial function (measured as wall thickening) and infarct size [determined by triphenyltetrazolium chloride (TTC) staining]. Fourteen anesthetized open-chest dogs underwent 1-h left anterior descending artery (LAD) occlusion and 6-h reperfusion and were randomly assigned to receive intracoronary CGS 21680 or to serve as control. The drug was infused for 60 min starting 5 min before reperfusion with a concentration of 10(-7) M at a rate of 10 ml/min under anoxic conditions. The infusion was then continued for the first 55 min of reperfusion with 10(-6) M at a rate of 1 ml/min. Intracoronary infusion of CGS 21680 led to significant improvement in regional wall function in postischemic myocardium (p < 0.05 vs. control). Thickening fraction (percentage of baseline) increased from -13.1 +/- 13.7% (mean +/- SD) during occlusion to 15.3 +/- 29.8% at 30 min of reperfusion in the CGS 21680 treatment group and remained at this level throughout the reperfusion period.(ABSTRACT TRUNCATED AT 250 WORDS)

Afterload dependent prolongation of left ventricular relaxation: importance of asynchrony

OBJECTIVE

Acute increases in afterload and in left ventricular asynchrony both independently prolong left ventricular isovolumetric relaxation. The aim of the study was to investigate whether an increased left ventricular afterload augments left ventricular asynchrony, which in turn could mediate the afterload dependent prolongation of left ventricular isovolumetric relaxation.

METHODS

Seven chloralose anaesthetised open chest dogs were instrumented with a left ventricular pressure gauge and two pairs of ultrasonic wall thickness crystals in the antero-apical and postero-basal left ventricular wall. At a constant heart rate of 149(SEM 7) beats.min-1, left ventricular pressure was acutely increased by brief manual clamping of the descending (AOCD) and ascending AOCA) thoracic aorta. Left ventricular asynchrony was quantified by the phase difference of the first Fourier harmonic between postero-basal and antero-apical wall motion. Global left ventricular relaxation was measured as the time constant of isovolumetric pressure fall, tau. Regional myocardial relaxation was assessed as the mean rate to half end diastolic thinning.

RESULTS

AOCD increased left ventricular peak systolic pressure from 141.9(6.9) mm Hg to a maximum of 182.0(5.1) mm Hg and tau from 34.3(2.4) ms to 48.0(5.0) ms (p less than 0.05). Simultaneously, phase difference increased markedly during AOCD, from 12.7(3.5) degrees to 24.4(2.2) degrees (p less than 0.05). At matched left ventricular peak systolic pressures, AOCA increased tau from 33.4(2.5) ms to only 42.5(4.3) ms (p less than 0.05 v control and AOCD). Concomitantly, the increase in phase difference was smaller and statistically non-significant, at 13.7(2.9) degrees v 17.1(2.5) degrees. During 13 out of the 14 aortic clampings (7 AOCD, 6 AOCA), tau correlated linearly with phase difference [mean r = 0.74(0.03)]. In contrast to their effects on global left ventricular relaxation and asynchrony, neither AOCD nor AOCA influenced the rate to half end diastolic thinning.

CONCLUSIONS

(1) left ventricular asynchrony may increase during an acute augmentation of left ventricular afterload; (2) this increased left ventricular asynchrony possibly contributes to the afterload dependent prolongation of left ventricular isovolumetric relaxation rate.

Contribution of postsynaptic alpha 2-adrenoceptors to reflex sympathetic constriction of stenotic coronary vessels

Increases in the activity of efferent cardiac sympathetic nerves by 35 +/- 9% were induced by 60 s bilateral occlusion of the common carotid arteries (BCO) in anesthetized dogs. Under control conditions the reflex rise in sympathetic nerve activity enhanced left ventricular pressure (115 +/- 4 mm Hg) by 47% and regional myocardial oxygen consumption (9.7 +/- 1.1 ml/min.100 g) by 56%. Simultaneously, end-diastolic circumflex coronary resistance (0.99 +/- 0.11 mm Hg.min.100 g/ml) decreased by 16%. After exhaustion of coronary dilator reserve by production of a severe coronary stenosis, BCO enhanced left ventricular pressure (107 +/- 4 mm Hg) by 49%, oxygen consumption of the poststenotic area (7.6 +/- 0.8 ml/min.100 g) increased by 21%, and circumflex coronary resistance (0.54 +/- 0.05 mm Hg.min.100 g/ml) also increased by 19%. The reflex increase in coronary resistance during BCO was abolished after infusion of the alpha 2-adrenoceptor antagonist rauwolscine (0.2 mg/kg i.v.). Administration of rauwolscine, however, did not prevent the reflex increase of left ventricular pressure and regional myocardial oxygen consumption. Comparable increases in poststenotic coronary resistance during BCO were found in dogs which either received propranolol (2 mg/kg i.v.) or in which the reflex rise in mean aortic pressure was limited to 13 +/- 3 mm Hg. In both experimental groups, rauwolscine also effectively prevented the BCO-induced rise in coronary resistance. In contrast, the reflex increase of total peripheral resistance was not significantly reduced by rauwolscine, but was blunted after additional administration of the selective alpha 1-adrenoceptor antagonist prazosin (1.2 mg/kg i.v.). We conclude that: 1) Poststenotic coronary vasoconstriction occurs during shortlasting increases in efferent cardiac sympathetic discharge within the physiological range. 2) This increase in poststenotic coronary resistance is significantly reduced after administration of the alpha 2-adrenoceptor antagonist rauwolscine. 3) In contrast to poststenotic coronary resistance, functionally innervated alpha 2-adrenoceptors are of minimal importance for the reflex increase in total peripheral resistance.

Pain and myocardial ischemia: the role of sympathetic activation

In a first series, we tested whether the relative ischemia distal to a severe stenosis on the left circumflex coronary (CX) artery increases the activity of cardiac sympathetic (CS) nerves which, in turn, may result in a poststenotic vasoconstriction and an aggravation of ischemia. In 23 anesthetized, vagotomized dogs, an acute stenosis that reduced CX blood flow to 50% of control was produced and maintained for 20 min. The activity of postganglionic CS nerves increased by 23 +/- 4% within 20 min. In parallel, poststenotic coronary resistance increased from 0.48 +/- 0.03 (SEM) to 0.61 +/- 0.03 mm Hg.min.100 g/ml, resulting in a net lactate production after 15 min. The selective alpha 2-adrenoceptor antagonist rauwolscine (0.2 mg/kg i.v.; n = 6) and the calcium antagonist nifedipine (10 micrograms/kg i.v.; n = 6) prevented the progressive increase in poststenotic resistance and the net lactate production, but still permitted an increase in CS activity. Segmental anesthesia of CS nerves with epidural infiltration of procaine at segments C7-T6 (n = 6) prevented the sympathetic activation, the progressive increase in poststenotic resistance and the net lactate production. In six additional dogs with intact vagus nerves, CS activation and a concomitant increase in poststenotic resistance resulting in myocardial ischemia were also found. These data suggest a vicious cycle between poststenotic coronary vasoconstriction and CS activation, resulting in severe myocardial ischemia. In a second series, stimulation of high-threshold somatic afferents (= nociceptive stimulation: NCS) was used to cause reflex CS activation. The superficial peroneal nerve was electrically stimulated in 14 anesthetized, vagotomized dogs. With intact CX arteries, a 1 min stimulation resulted in a pronounced increase in CX blood flow and perfusion pressure. In contrast, NCS in the presence of a severe stenosis on the CX artery increased end-diastolic poststenotic coronary resistance by 96 +/- 15% due to a reflex activation of CS nerve fibers. This activation was markedly reduced after injection of fentanyl (27 micrograms/kg i.v.; n = 6). Injection of naloxone (60 micrograms/kg) restored the original effect. Systolic wall thickening (WT; sonomicrometry) in the CX artery-perfused myocardium was increased during NCS (10.9 +/- 3.9 (SD) vs. 13.6 +/- 5.0%) in additional five dogs with intact coronary arteries. In the presence of a stenosis on the CX artery, systolic WT was reduced to 7.0 +/- 2.5% and was further decreased to 4.6 +/- 2.3% during NCS. The additional deterioration of systolic regional function during NCS was prevented after i.v. injection of fentanyl, as was the increase in poststenotic coronary resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of a new alpha 2-adrenoceptor antagonist on poststenotic coronary resistance and myocardial function

The effect of the alpha 2-adrenoceptor antagonist 4-fluoro-2-(imidazoline-2-ylamino)-isoindoline maleate (BDF 8933) on poststenotic end-diastolic distal coronary resistance and poststenotic myocardial function (sonomicrometry) was investigated under control conditions and during cardiac sympathetic nerve stimulation (CSNS = electrical stimulation of the left ventrolateral cervical cardiac nerve). In 7 vagotomized, open-chest dogs end-diastolic distal coronary resistance was determined. This variable was essentially unchanged after administration of the agent. In additional 6 dogs regional myocardial function was measured as systolic wall thickening (SWT). CSNS increased SWT of the posterior circumflex-perfused myocardium from 12.7 +/- 4.6% to 21.9 +/- 8.4% (p less than 0.05) under control conditions. With a severe stenosis on the left circumflex coronary artery, SWT was reduced to 5.4 +/- 4.0% and further decreased to 2.1 +/- 5.1% (p less than 0.05) during CSNS. After i.v. injection of 150 micrograms/kg BDF 8933, poststenotic myocardial function at rest was 4.2 +/- 4.2%, and 5.6 +/- 3.6% during CSNS. Regarding to the systemic effects BDF 8933 significantly increased peak left ventricular pressure in all 13 dogs. Thus, the new alpha 2-adrenoceptor antagonist BDF 8933 at the chosen dosage prevents sympathetically induced myocardial ischemia, but increases left ventricular afterload resistance.

BRL 34915 ameliorates oxygen supply in ischemic myocardium by a simultaneous enhancement of coronary blood flow and a reduction of myocardial function

In the presence of stenotic coronary arteries, oxygen supply in the poststenotic myocardium is reduced. A counterbalancing poststenotic metabolic vasodilatation is attenuated up to 30% by an alpha 2-adrenoceptor-mediated vasoconstrictor tone. In six open-chest dogs, we determined whether cumulative intracoronary doses (1, 4, and 14 micrograms) BRL 34915, a vasodilator with additional dose-dependent cardiodepressant properties, could enhance coronary blood flow and simultaneously reduce myocardial function in poststenotic myocardium, thereby increasing oxygen supply and decreasing oxygen demand. BRL 34915 increased mean left circumflex coronary blood flow [ml/(min.100 g)] dose-dependently from 59 +/- 12.4 (mean +/- SEM) (no BRL) to 227 +/- 43.9 (14 micrograms BRL) (p less than 0.05) in intact coronary arteries and from 36 +/- 7.2 (no BRL) to 74 +/- 13.2 (14 micrograms BRL) (p less than 0.05) distal to a severe stenosis, respectively. In contrast, posterior systolic wall thickening (%), was significantly decreased only by 14 micrograms BRL from 9.7 +/- 1.82 (no BRL) to 7.8 +/- 2.07 (14 micrograms BRL) (p less than 0.05) when coronary arteries were intact and from 8.7 +/- 2.02 (no BRL) to 4.1 +/- 1.39 (14 micrograms BRL) (p less than 0.05) in poststenotic myocardium. We conclude that BRL 34915 can both enhance coronary blood flow in the poststenotic myocardium and decrease myocardial function simultaneously, potentially narrowing the gap between oxygen supply and demand.

Poststenotic ischaemic myocardial dysfunction induced by peripheral nociceptive stimulation

Sympathetic activation increases cardiac performance, and the increased myocardial oxygen demand is adequately met by an increase in coronary blood flow after metabolic coronary dilation under normal conditions. Distal to a severe coronary stenosis, however, activation of cardiac sympathetic nerves induces myocardial ischaemia by alpha 2-adrenergic coronary constriction. Activation of cardiac sympathetic nerves is one of the autonomous reactions associated with acute somatic pain. Therefore we investigated the effects of acute somatic pain on regional myocardial function distal to a severe coronary stenosis. In 5 anaesthetized, vagotomized dogs activation of cardiac sympathetic nerves was achieved by electrical stimulation of the nervus peronaeus superficialis. To analyse regional myocardial function, myocardial wall thickness was continuously measured by sonomicrometry in the circumflex-perfused posterior and in the anterior (control) myocardium. Under control conditions, nociceptive stimulation increased systolic wall thickening of the posterior myocardium from 10.9 +/- 3.9% to 13.6 +/- 5.0%. With a severe stenosis on the left circumflex coronary artery, systolic wall thickening was reduced to 7.0 +/- 2.5% and further decreased to 4.6 +/- 2.3% during nociceptive stimulation. Intravenous injection of 27 micrograms/kg fentanyl prevented the deterioration of poststenotic myocardial function during nociceptive stimulation.

CONCLUSION

Acute somatic pain can induce ischaemic myocardial dysfunction distal to a severe coronary stenosis by activation of cardiac sympathetic nerves. Fentanyl not only prevents the pain sensation but also poststenotic ischaemic myocardial dysfunction.

Augmentation of cardiac reflexes in the cat by the calcium antagonist verapamil

The effect of intravenous and intrapericardial administration of verapamil on cardiac reflexes was studied in chloralose-anesthetized cats. Cardiac reflexes were induced by either intrapericardial application of serotonin (80 micrograms/kg) and dimethylphenylpiperazinium iodide (DMPP) (20 micrograms/kg) or by occlusion of the ascending aorta for 30 s. Intrapericardial application of verapamil (3 and 6 micrograms/kg) did not change the epicardial chemoreflexes, whereas intravenous administration of verapamil in the normal clinical dose enhanced the cardiac reflexes induced by chemical or mechanical stimulation. These results indicate that verapamil does not act directly on the vagal afferent nerve fibers in the epicardium of the heart. We suggest that the augmentation of cardiac reflexes by verapamil might be caused by an action of verapamil on the sinoaortic baroreflex or baroreceptors.

Quinidine attenuates sympathetically induced poststenotic myocardial ischemia

Beside its antiarrhythmic properties, which in particular are used for the treatment of atrial fibrillation, quinidine is known to have alpha-adrenoceptor blocking properties. On the other hand, atrial fibrillation is reported to cause activation of the sympathetic nervous system which, in turn, reduces coronary blood flow when the coronary reserve is already compromised. Therefore, we tested the effect of quinidine (3 mg/kg i.v.) on the coronary vasculature during electrical stimulation of cardiac sympathetic nerves in the presence and absence of a stenosis on the left circumflex coronary artery. In 7 anesthetized dogs the end-diastolic distal coronary resistance during cardiac sympathetic nerve stimulation in the presence of a severe stenosis on the left circumflex coronary artery increased by 18% before, and decreased by 17% after administration of quinidine. We conclude that quinidine inhibits the vasoconstriction of poststenotic coronary arteries during cardiac sympathetic nerve stimulation and thus might prevent a poststenotic stress-induced myocardial ischemia.

Evidence against the adenosine-catecholamine antagonism in the canine heart in situ

Adenosine has been reported to attenuate the positive inotropic effects of catecholamines in isolated heart preparations of rodents. These results were not confirmed in anesthetized dogs during intracoronary infusion of isoprenaline. However, these experiments did not establish the effects of adenosine on the inotropic effects of endogenously released catecholamines. Therefore cardiac sympathetic nerve stimulation was performed in 5 anesthetized, vagotomized dogs. The left circumflex coronary artery was perfused at a constant pressure of 130 +/- 4 mmHg. The contractile function of the circumflex-perfused myocardium was analyzed by sonomicrometry. Cardiac sympathetic nerve stimulation at 1, 2, 5, 10 and 20 Hz increased systolic segment shortening in a frequency-dependent manner from 10.9 +/- 2.6 at control to 15.3 +/- 3.4% at 20 Hz. During intracoronary infusion of adenosine (50 micrograms/kg/min) cardiac sympathetic nerve stimulation still increased systolic segment shortening from 9.9 +/- 3.5 at control to 16.3 +/- 4.5% at 20 Hz. The lack of an adenosine-catecholamine antagonism in the present experiments was not due to the sequence of procedures, nor to the marked flow increase induced by adenosine, since systolic segment shortening at rest was reduced during adenosine infusion, and since during intracoronary infusion of papaverine and sodium nitroprusside similar results were obtained. The observation of an adenosine-catecholamine antagonism in rodents should be restricted to this species at present.

An easy and quick implantation procedure for the measurement of myocardial wall thickness using sonomicrometry

Ultrasonic techniques for the measurement of ventricular dimensions are widely used in acute and chronic experiments. Implantation of ultrasonic crystals is associated with reversible and irreversible myocardial damage which might limit the interpretation of the obtained results, in particular during acute experiments. We therefore developed a sonomicrometric device which can be easily and quickly implanted, and thus reduces the reversible myocardial damage induced by prolonged surgical implantation.