Constant Coronary Flow Research Articles

The evaluation of constant coronary artery flow versus constant coronary perfusion pressure during normothermic ex situ heart perfusion.

Evidence suggests that hearts that are perfused under ex-situ conditions lose normal coronary vasomotor tone and experience contractile failure over a few hours. We aimed to evaluate the effect of different coronary perfusion strategies during ex situ heart perfusion on cardiac function and coronary vascular tone. Porcine hearts (n=6 each group) were perfused in working mode for 6 hours with either constant aortic diastolic pressure (40 mmHg) or constant coronary flow rate (500 mL/min). Functional and metabolic parameters, cytokine profiles, cardiac and vascular injury, coronary artery function and oxidative stress were compared between groups. Constant coronary flow perfusion demonstrated better functional preservation and less edema formation (Cardiac index: flow control=8.33 vs pressure control=6.46 mL·min-1·g-1, p=0.016; edema formation: 7.92% vs 19.80%, p < 0.0001). Pro-inflammatory cytokines, platelet activation as well as endothelial activation were lower in the flow control group. Similarly, less cardiac and endothelial injury was observed in the constant coronary flow group. Evaluation of coronary artery function showed there was loss of coronary autoregulation in both groups. Oxidative stress was induced in the coronary arteries and was relatively lower in the flow control group. A strategy of controlled coronary flow during ex situ heart perfusion provides superior functional preservation and less edema formation, together with less myocardial damage, leukocyte, platelet, endothelial activation, and oxidative stress. There was loss of coronary autoregulation and decrease of coronary vascular resistance during ESHP irrespective of coronary flow control strategy. Inflammation and oxidative stress state in the coronary vasculature may play a role.

Reduced Flow during Ex-Situ Heart Perfusion Provides Superior Function Preservation and Less Edema Formation

PurposeEx-situ heart perfusion (ESHP) allows continuous functional and metabolic resuscitation of donor hearts before transplantation. Evidence indicates that hearts that are perfused under physiologic conditions lose the normal vasomotor tone and fail in a few hours. We aim to evaluate the reduced coronary flow during ex situ heart perfusion on cardiac function and coronary vascular resistance.MethodsPorcine hearts (n=6 each group) were perfused in working mode for 6 hours either by constant diastolic pressure perfusion (40 mmHg) or constant coronary blood flow rate perfusion (500mL/min). Cardiac functional parameters, coronary vascular resistance (CVR) and metabolism were monitored continuously. Myocardial injury parameter of cardiac troponin I and lipid peroxidation marker oxidized low-density lipoprotein were evaluated in the perfusate. These parameters were compared between groups at different time.ResultsCardiac function was better preserved in the flow control group at 5 hours (T5) of perfusion, indicated by higher stroke work and cardiac index (p<0.05, Figure AC). After perfusion the flow control group showed less edema than the pressure control group (p<0.001, Figure B). Both groups have a significant decrease of CVR, with relative higher in the flow control group (p<0.01, Figure D). cTnI was lower in the flow control group starting at T3, indicating less myocardial injury (p<0.05, Figure E). oxLDL increased in both groups, indicating lipid peroxidation formation; the level in the flow control group was significantly lower in comparison to the pressure control group (p<0.01, Figure F), suggesting less oxidative stress in this group.ConclusionReduced coronary flow during ex-situ heart perfusion decreased edema formation, showed less myocardial damage and oxidative stress which may contribute to better cardiac function preservation. The relative higher coronary vascular resistance induced by reduced coronary flow perfusion may help to maintain the cardiac function. Ex-situ heart perfusion (ESHP) allows continuous functional and metabolic resuscitation of donor hearts before transplantation. Evidence indicates that hearts that are perfused under physiologic conditions lose the normal vasomotor tone and fail in a few hours. We aim to evaluate the reduced coronary flow during ex situ heart perfusion on cardiac function and coronary vascular resistance. Porcine hearts (n=6 each group) were perfused in working mode for 6 hours either by constant diastolic pressure perfusion (40 mmHg) or constant coronary blood flow rate perfusion (500mL/min). Cardiac functional parameters, coronary vascular resistance (CVR) and metabolism were monitored continuously. Myocardial injury parameter of cardiac troponin I and lipid peroxidation marker oxidized low-density lipoprotein were evaluated in the perfusate. These parameters were compared between groups at different time. Cardiac function was better preserved in the flow control group at 5 hours (T5) of perfusion, indicated by higher stroke work and cardiac index (p<0.05, Figure AC). After perfusion the flow control group showed less edema than the pressure control group (p<0.001, Figure B). Both groups have a significant decrease of CVR, with relative higher in the flow control group (p<0.01, Figure D). cTnI was lower in the flow control group starting at T3, indicating less myocardial injury (p<0.05, Figure E). oxLDL increased in both groups, indicating lipid peroxidation formation; the level in the flow control group was significantly lower in comparison to the pressure control group (p<0.01, Figure F), suggesting less oxidative stress in this group. Reduced coronary flow during ex-situ heart perfusion decreased edema formation, showed less myocardial damage and oxidative stress which may contribute to better cardiac function preservation. The relative higher coronary vascular resistance induced by reduced coronary flow perfusion may help to maintain the cardiac function.

Relationship between myocardial oxygenation and blood pressure: Experimental validation using oxygenation-sensitive cardiovascular magnetic resonance.

BackgroundThe relationship between mean arterial pressure (MAP) and coronary blood flow is well described. There is autoregulation within a MAP range of 60 to 140 mmHg providing near constant coronary blood flow. Outside these limits flow becomes pressure-dependent. So far, response of myocardial oxygenation to changes in pressure and flow has been more difficult to assess. While established techniques mostly require invasive approaches, Oxygenation-Sensitive (OS) Cardiovascular Magnetic Resonance (CMR) is a technique that can non-invasively assess changes in myocardial tissue oxygenation. The purpose of this study was to follow myocardial oxygenation over a wide range of blood pressure variation within and outside known coronary autoregulatory limits using OS-CMR, and to relate these data to coronary hemodynamics.MethodsTen anaesthetized swine (German Large White) underwent left-sided thoracotomy and attachment of a perivascular flow probe to the proximal left anterior descending (LAD) coronary artery for continuous measurement of blood flow (QLAD). Thereafter, animals were transferred into a 3T MRI scanner. Mean arterial pressure (MAP) was varied in 10–15 mmHg steps by administering alpha1-receptor agents phenylephrine or urapidil. For each MAP level, OS-CMR images as well as arterial and coronary sinus blood gas samples were obtained simultaneously during brief periods of apnea. Relative changes (Δ) of coronary sinus oxygen saturation (ScsO2), oxygen delivery (DO2) and demand (MVO2), extraction ratio (O2ER) and excess (Ω) from respective reference levels at a MAP of 70 mmHg were determined and were compared to %change in OS-signal intensity (OS-SI) in simultaneously acquired OS-CMR images.ResultsQLAD response indicated autoregulation between MAP levels of 52 mmHg (lower limit) and127 mmHg (upper limit). OS-CMR revealed a global myocardial oxygenation deficit occurring below the lower autoregulation limit, with the nadir of OS-SI at -9.0%. With MAP values surpassing 70 mmHg, relative OS-SI increased to a maximum of +10.6%. Consistent with this, ΔScsO2, ΔDO2, ΔMVO2, ΔO2ER and ΔΩ responses indicated increasing mismatch of oxygenation balance outside the autoregulated zone. Changes in global OS-CMR were significantly correlated with all of these parameters (p≤0.02) except with ΔMVO2.ConclusionOS-CMR offers a novel and non-invasive route to evaluate the effects of blood pressure variations, as well as of cardiovascular drugs and interventions, on global and regional myocardial oxygenation, as demonstrated in a porcine model. OS-CMR identified mismatch of O2 supply and demand below the lower limit of coronary autoregulation. Vasopressor induced acute hypertension did not compromise myocardial oxygenation in healthy hearts despite increased cardiac workload and O2 demand. The clinical usefulness of OS-CMR remains to be established.

Staphylococcus aureus α-toxin and Escherichia coli hemolysin impair cardiac regional perfusion and contractile function by activating myocardial eicosanoid metabolism in isolated rat hearts

In sepsis, cardiac function is frequently depressed. Microcirculatory disturbances as evidenced in most organs may extend to the coronary circulation and may play a role in the occurrence of cardiac dysfunction. Staphylococcal alpha-toxin and Escherichia coli hemolysin (ECH), pore-forming exotoxins of clinically relevant bacteria, have recently been demonstrated to evoke cardiac dysfunction in isolated rat hearts by activating myocardial eicosanoid metabolism. alpha-Toxin activates synthesis of thromboxane (Tx) A2, ECH of cysteinyl-leukotrienes (Sibelius U, Grandel U, Buerke M, et al: Leukotriene-mediated coronary vasoconstriction and loss in myocardial contractility evoked by low doses of Escherichia coli hemolysin in perfused reat hearts. Crit Care Med 2003; 3:683-688, Sibelius U, Grandel U, Buerke M, et al: Staphylococcal alpha-toxin provokes coronary vasoconstriction and loss in myocardial contractility in perfused rat hearts-Role of Tx formation. Circulation 2000; 101:78-85). We now investigated whether cardiac dysfunction in response to alpha-toxin and ECH is caused by disturbances of regional cardiac perfusion. A prospective, experimental study. A research laboratory at a university hospital. Isolated hearts from male Wistar rats. Changes of regional perfusion were investigated by using colored microspheres in isolated rat hearts perfused with alpha-toxin or ECH either at constant coronary perfusion pressure or constant coronary flow rate. Significance of toxin-activated eicosanoid generation was evaluated by pharmacologic interventions. By eliciting eicosanoid formation, both toxins caused an increase in coronary vascular resistance and a loss in contractile function. In ECH-perfused hearts, reduction of regional perfusion predominantly occurred in subendocardial sections in either perfusion mode (coronary perfusion pressure or coronary flow rate). When synthesis of cysteinyl-leukotrienes was blocked by the 5-lipooxygenase inhibitor MK-886, disturbances of regional perfusion and the associated cardiac dysfunction were largely prevented. Coronary perfusion of alpha-toxin caused a decrease of regional perfusion that was more pronounced in subepicardial layers. Inhibiting the release of TxA2 by blocking the cyclooxygenase with indomethacin attenuated the perfusion abnormalities and the cardiodepression in response to alpha-toxin. Bacterial exotoxins of clinically relevant bacteria may impair cardiac function by eliciting distinct coronary perfusion abnormalities via release of vasoactive eicosanoids.

Reduced susceptibility to ischemia-induced arrhythmias in the preconditioned rat heart is independent of PI3-kinase/Akt

We examined the involvement of phosphatidylinositol 3-kinase (PI3K) and its effector protein kinase B (Akt) in cardioprotective effects of ischemic preconditioning (PC) with particular regards to its role in the protection against ischemia-induced arrhythmias in isolated perfused rat heart. PI3K/Akt inhibitor wortmannin (100 nM) was administered 15 min prior to 30-min regional (left anterior descending coronary artery occlusion) ischemia for the study of ischemic arrhythmias in the hearts perfused at constant coronary flow or prior to 30-min global ischemia followed by 2-h reperfusion for the infarct size (IS) determination (tetrazolium staining) in the hearts perfused at constant pressure. PC procedure (one cycle of ischemia/reperfusion, 5 min each) significantly reduced the total number of ventricular premature complexes (PVC) and severity of arrhythmias (arrhythmia score; AS) over the whole period of left anterior descending coronary artery occlusion in comparison with non-PC controls (PVC 166+/-40; AS 1.6+/-0.2 vs. 550+/-60 and 3.2+/-0.2; respectively; P<0.05). In a setting of global ischemia/reperfusion, PC decreased IS (in % of the left ventricle, LV) by 73 %. Pretreatment with wortmannin modified neither arrhythmogenesis nor IS in the non-PC hearts. Bracketing of PC with wortmannin did not abolish antiarrhythmic protection (PVC 92+/-25; AS 1.7+/-0.2; P<0.05 vs. non-PC hearts). On the other hand, wortmannin increased IS/LV in the PC hearts to 24+/-1.2 % as compared with 9 +/- 0.6 % in the untreated ones (P<0.05). In conclusion, PI3K/Akt inhibition did not affect reduced arrhythmogenesis during ischemia in the PC hearts indicating that in contrast to its positive role in the irreversible myocardial injury, PI3K/Akt activity is not required for protection induced by PC against ischemic arrhythmias in the rat heart.

Peptides Derived from the C2 Domain of Protein Kinase Cϵ (ϵPKC) Modulate ϵPKC Activity and Identify Potential Protein-Protein Interaction Surfaces

Peptides Derived from the C2 Domain of Protein Kinase Cϵ (ϵPKC) Modulate ϵPKC Activity and Identify Potential Protein-Protein Interaction Surfaces

Positive inotropic effects of carbon monoxide‐releasing molecules (CO‐RMs) in the isolated perfused rat heart

Carbon monoxide (CO) generated by the enzyme haeme oxygenase-1 (HO-1) during the breakdown of haeme is known to mediate a number of biological effects. Here, we investigated whether CO liberated from two water soluble carbon monoxide-releasing molecules (CO-RMs) exerts inotropic effects on the myocardium. Rat isolated hearts perfused either at constant flow or constant pressure were used to test the effect of CO-RMs. CORM-3, a fast CO releaser, produced a direct positive inotropic effect when cumulative doses (3, 10 and 30 microg min(-1)) or a single dose (5 microM) were infused at either constant coronary pressure (CCP) or constant coronary flow (CCF). The inotropic effect mediated by CORM-3 was abolished by blockade of soluble guanylate cyclase or Na(+)/H(+) exchanger, but not by inhibitors of L-type Ca(2+) channels and protein kinase C. CORM-3 also caused a slight reduction in heart rate but did not alter coronary flow. In contrast, the slow CO releaser CORM-A1 produced significant coronary vasodilatation when given at the highest concentration (30 mug min(-1)) but exerted no effect on myocardial contractility or heart rate. A rapid CO release from CORM-3 exerts a direct positive inotropic effect on rat isolated perfused hearts, whereas CO slowly released by CORM-A1 had no effect on myocardial contractility but caused significant coronary vasodilatation. Both cGMP and Na(+)/H(+) exchange appear to be involved in this effect but further work is needed to determine the relative contribution of each pathway in CO-mediated inotropic effect.

Activation of p38 Mitogen-Activated Protein Kinase Contributes to the Early Cardiodepressant Action of Tumor Necrosis Factor

The purpose of this study was to determine whether p38 mitogen-activated protein kinase (p38-MAPK) contributes to tumor necrosis factor-alpha (TNFalpha)-induced contractile depression. Tumor necrosis factor has both beneficial and detrimental consequences that may result from the activation of different downstream pathways. Tumor necrosis factor activates p38-MAPK, a stress-responsive kinase implicated in contractile depression and cardiac injury. In isolated hearts from mice lacking the p38-MAPK activator, MAPK kinase 3 (MKK3), perfused at constant coronary pressure or flow, we measured the left ventricular developed pressure (LVDP) and the relationship between end-diastolic volume and LVDP in the presence and absence of 10 ng/ml TNFalpha. Within 15 min at constant pressure, TNFalpha significantly reduced LVDP and coronary flow in outbred and mkk3(+/+) mice. This early negative inotropic effect was associated with a marked phosphorylation of both p38-MAPK and its indirect substrate, HSP27. In hearts lacking MKK3, TNFalpha failed to activate p38-MAPK or to cause significant contractile dysfunction. The actions of TNFalpha were similarly attenuated in MAPK-activated protein kinase 2 (MK2)-deficient hearts, which have a marked reduction in myocardial p38-MAPK protein content, and by the p38-MAPK catalytic site inhibitor SB203580 (1 micromol/l). Under conditions of constant coronary flow, the p38-MAPK activation and contractile depression induced by TNFalpha, though attenuated, remained sensitive to the absence of MKK3 or the presence of SB203580. The role of p38-MAPK in TNFalpha-induced contractile depression was confirmed in isolated murine cardiac myocytes exposed to SB203580 or lacking MKK3. Tumor necrosis factor activates p38-MAPK in the intact heart and in isolated cardiac myocytes through MKK3. This activation likely contributes to the early cardiodepressant action of TNFalpha.

Beneficial effects of amiodarone and dronedarone (SR 33589b), when applied during low-flow ischemia, on arrhythmia and functional parameters asssessed during reperfusion in isolated rat hearts.

The effects of short-term amiodarone and dronedarone treatments on action potential characteristics and arrhythmia (ventricular tachycardia ) induced by reperfusion after global low-flow ischemia were studied in rat hearts. The actions of amiodarone and SR on recovery of coronary flow and contractile function were also determined. Isolated hearts were stabilized for 40 min and were then submitted to 25-min global low-flow ischemia (constant coronary flow, 0.3 ml/min) followed by 30 min of reperfusion at constant pressure. Drugs were applied only during ischemia: consequently, action potential duration (APD) tended to widen. During reperfusion, APD tended to recover or shorten, and the more complete the recovery, the less the arrhythmia. Despite its ability to widen APD during ischemia, amiodarone facilitated APD recovery during reperfusion. Moreover, APD shortening and ventricular tachycardia suppression exhibit a bell-shaped concentration-response relation, implying that the drugs affect ventricular tachycardia by a class III-independent action. These results point to an anti-ischemic action supported by improvement in function and inhibition of reactive hyperemia.

Ca(2+)-sensitizing effect is involved in the positive inotropic effect of troglitazone.

1. Troglitazone, an insulin sensitizing agent, has a direct positive inotropic effect. However, the mechanism of this effect remains unclear. Thus, we examined the inotropic effect of troglitazone while focusing on intracellular Ca2+ handling. 2. Troglitazone significantly increased peak isovolumic left ventricular pressure (LVP(max)), peak rate of rise of LVP (dP/dt(max)), peak rate of fall of LVP (dP/dt(min)) in isolated rat hearts perfused at a constant coronary flow and heart rate. This inotropic effect of troglitazone was not inhibited by pretreatment with carbachol (muscarine receptor agonist), H89 (protein kinase A inhibitor), U73122 (phospholipase C inhibitor), H7 (protein kinase C inhibitor), verapamil (L-type Ca2+ channel antagonist), thapsigargin (Ca(2+)-adenosine triphosphatase inhibitor) or ryanodine (ryanodine receptor opener). 3. Radioimmunoassay showed that the cyclic adenosine monophosphate concentration in the left ventricle was not increased by troglitazone. 4. Whole-cell patch clamp analysis revealed that troglitazone had no effect on inward Ca2+ currents in cardiomyocytes. 5. In fura-2 loaded perfused rat hearts, troglitazone exerted its positive inotropic effect without increasing Ca2+ concentration. 6. These results suggest that neither the inward Ca2+ currents nor Ca2+ handling in the sarcoplasmic reticulum was involved in the inotropic effect of troglitazone. Furthermore, troglitazone exerted its positive inotropic effect without affecting the intracellular concentration of Ca2+. 7. In conclusion, the positive inotropic effect of troglitazone is mediated by a sensitization of Ca2+.

The temperature dependence of cardioplegic distribution in the canine heart

Background. Cold cardioplegic arrest can produce cooling contracture and suboptimal myocardial protection. This study examines whether cooling contracture is associated with maldistribution of cardioplegic solution, particularly subendocardial hypoperfusion, which may impair recovery. Methods. Canine hearts were arrested by antegrade cold and warm blood cardioplegia in random order. Cardioplegic distribution was measured using radiolabeled microspheres before and just after induction of each period of arrest. Results. With cold cardioplegia, perfusion of left ventricular subepicardial and midwall regions decreased. Subendocardial to subepicardial perfusion ratios increased significantly in the left ventricle as a whole, the anterior and posterior regions of the left ventricular free wall, and the interventricular septum. With warm arrest, transmural flow distribution was not significantly altered from preceding prearrest values. At constant coronary flow, coronary perfusion pressure was initially similar after induction of arrest at both temperatures, but it rose subsequently during warm cardioplegia. Conclusions. The data suggest that during normothermic arrest, vasomotor tone regulates cardioplegic distribution, and hyperkalemic vasoconstriction is of slow onset. In the absence of beating and with vasomotion inhibited by hypothermia, cardioplegic distribution during cold arrest appears to be primarily dependent on vascular anatomy. There was no evidence of subendocardial underperfusion during cooling contracture.

Hemodynamic basis for the acute cardiac effects of troglitazone in isolated perfused rat hearts.

Troglitazone is a thiazolidinedione used for the treatment of NIDDM and potentially for other insulin-resistant disease states. Troglitazone has recently been shown to increase cardiac output and stroke volume in human subjects. These actions are thought to be mediated by the reduction of peripheral resistance, but a potential direct effect on cardiac function has not been studied. Therefore, we investigated the direct cardiac hemodynamic effects of troglitazone in isolated perfused rat hearts. Five groups of hearts were studied. Hearts were tested under isovolumetric contraction with a constant coronary flow, and troglitazone (0.2, 0.5, and 1.0 micromol) was administered by bolus injection. Peak isovolumetric left ventricular pressure (LVPmax), peak rate of rise of LVP (dP/dt(max)), and peak rate of fall of LVP (dP/dt(min)) were significantly increased 1 min after troglitazone administration in a dose-dependent manner, while the heart rate (HR) and coronary perfusion pressure (CPP) were significantly decreased (P < 0.05). HR was then fixed by pacing and/or CPP was fixed with nitroprusside to eliminate any effect of the two variables on the action of troglitazone. With constant HR and/or constant CPP, the effect of troglitazone on LVPmax, dP/dt(max), and dP/dt(min) was still unchanged. In addition, the positive inotropic, positive lusitropic, and negative chronotropic actions of troglitazone were not influenced even when hearts were pretreated with prazosin, propranolol, or nifedipine. In conclusion, troglitazone has direct positive inotropic, positive lusitropic, negative chronotropic, and coronary artery dilating effects. The inotropic and chronotropic actions of troglitazone are not mediated via adrenergic receptors or calcium channels. These findings have important clinical implications for diabetic patients with congestive heart failure.

Effect of amiloride on age-dependent cardiac dysfunction after ischemia/reperfusion in the isolated, perfused rat heart.

This study was intended to compare the cardiac consequences of ischemia/reperfusion and amiloride treatment in immature (2-3 wk), juvenile (4-6 wk), and adult (3-5 mo) rats using an isolated, perfused heart model. Male immature, juvenile, and adult rats were anticoagulated and anesthetized. Hearts were harvested and coronary arteries were perfused on a Langendorff apparatus via retrograde perfusion of the aorta at a constant coronary flow (initially determined by perfusing the heart at 50 mm Hg perfusion pressure) with oxygenated Krebs-Henseleit-Bicarbonate (KHB) solution. Left ventricular peak systolic (LVPSP) and end diastolic (LVEDP) pressures were measured via a balloon-tipped catheter placed in the left ventricle through the mitral valve. Following a 20-30 min stabilization period, hearts underwent 30 min of normothermic ischemia and were then reperfused with Krebs-Henseleit-Bicarbonate alone for 30 min, or Krebs-Henseleit-Bicarbonate containing 500 microM amiloride for 5 min followed by Krebs-Henseleit-Bicarbonate alone for 25 min (n = 6/age group). Left ventricular generated pressure was calculated (left ventricular peak systolic-left ventricular end diastolic) and used as a measure of ventricular function. All hearts demonstrated a decrease in generated pressure, respectively, from preischemic levels at 15 and 30 min of reperfusion, although this decrease was significantly less for the immature hearts. Ischemia/reperfusion injury was attenuated by amiloride in adult and juvenile hearts, whereas ischemia/reperfusion injury was worsened by amiloride in immature hearts. Although immature hearts were relatively resistant to ischemia/reperfusion injury compared with adult and juvenile hearts, the presence of amiloride during reperfusion resulted in more severe ventricular dysfunction in immature hearts. These data suggest a differential age-dependent mechanism of sarcolemmal ion exchange in response to ischemia/reperfusion.

Inhibition of Angiotensin-converting Enzyme Increases the Nitric Oxide Levels in Canine Ischemic Myocardium

Since angiotensin-converting enzyme (ACE) produces angiotensin II in the heart, ACE inhibitors may prevent coronary vasoconstriction and increase coronary blood flow. On the other hand, since ACE inhibitors also inhibit kininase II which results in reduced degradation of bradykinin, ACE inhibitors may increase cardiac nitric oxide (NO) levels via stimulation of bradykinin receptors. This study was undertaken to test whether ACE inhibitors increase the cardiac NO levels and coronary blood flow in the ischemic myocardium. In 34 open-chest dogs, the left anterior descending coronary artery was perfused through an extracorporeal bypass tube from the left carotid artery. When either imidaprilat or cilazaprilat of 3μg/kg/min was infused into the bypass tube for 10 min after reduction of coronary blood flow due to partial occlusion of the bypass tube, coronary blood flow increased from 31±1 to either 45±5 or 43±4 ml/100 g/min despite no changes in coronary perfusion pressure (43±2 mmHg). During an infusion of either imidaprilat or cilazaprilat, bradykinin and the end-products of NO (nitrate+nitrite) concentrations of coronary venous blood were markedly increased, which were attenuated by either HOE-140 (an inhibitor of bradykinin receptors) or by Nω-nitro-L-arginine methyl ester (an inhibitor of NO synthase). We also observed increases in cardiac bradykinin and NO levels due to either imidaprilat or cilazaprilat in the low constant coronary blood flow condition. It is concluded that ACE inhibitors can increase cardiac NO levels via the accumulation of bradykinin in the ischemic myocardium.

Volatile anaesthetics reduce adhesion of blood platelets under low‐flow conditions in the coronary system of isolated guinea pig hearts

Inhibitory effects of volatile anaesthetics on platelet aggregation have been demonstrated in several studies. However, the influence of volatile anaesthetics on intracoronary platelet adhesion has not been elucidated so far. Isolated hearts of guinea pigs were perfused with buffer in the absence or presence of volatile anaesthetics (0.5 and 1 MAC) at constant coronary flow rates of 5 ml/min for 25 min, then 1 ml/min for 30 min and again 5 ml/min for 10 min. Before, during and after low-flow perfusion, a bolus of human platelets was applied into the coronary system. To simulate thrombogenic conditions, 0.3 U/ml human thrombin was infused during low-flow perfusion and reperfusion. The number of platelets sequestered to the endothelium was calculated from the difference between coronary in- and output of platelets. The myocardial production of lactate and consumption of pyruvate and coronary perfusion pressure were also determined. At a flow rate of 5 ml/min only about 3% of the applied platelets did not emerge from the coronary system, in any group. In contrast, 13.1 +/- 1.2% (mean +/- SEM) of infused platelets became adherent in low-flow perfusion in the control group without anaesthetic. The adherence was reduced with each 1 MAC isoflurane (to 6.2 +/- 1.2%), sevoflurane (to 4.4 +/- 0.9%) or halothane (to 3.2 +/- 1.5%) (each P < 0.05 vs. control). Volatile anaesthetic, 0.5 MAC, did not inhibit platelet adhesion to a statistically significant extent in any case. Perfusion pressure and metabolic parameters were not statistically different between the control and the hearts exposed to anaesthetics. Volatile anaesthetics in a concentration of 1 MAC can reduce the adhesion of platelets in the coronary system under reduced flow conditions. This action does not arise from vasodilation or inhibition of ischaemic stress.

Effects of magnesium sulphate on the cardiovascular system, coronary circulation and myocardial metabolism in anaesthetized dogs

We have studied the effects of i.v. bolus doses of magnesium sulphate (MgSO4) 60, 90 and 120 mg kg-1 on haemodynamic state, the coronary circulation and myocardial metabolism in nine dogs anaesthetized with pentobarbitone and fentanyl. MgSO4 produced dose-dependent decreases in arterial pressure, heart rate, left ventricular dP/dtmax and left ventricular minute work index (LVMWI) and an increase in the time constant of left ventricular isovolumic relaxation. Stroke volume increased, systemic vascular resistance decreased and cardiac output did not change significantly. MgSO4 produced decreases in coronary perfusion pressure, coronary vascular resistance and myocardial oxygen consumption (MVO2). Coronary sinus blood flow, lactate extraction ratio and the ratio of LVMWI to myocardial MVO2, that is an index of cardiac efficiency, did not change significantly. This study indicated that the depressant effect of MgSO4 on cardiac function was offset by lowering of peripheral vascular resistance, so that cardiac pump function remained effective, and the almost constant coronary sinus blood flow resulted from the decrease in coronary vascular resistance even at higher doses.

Perfusion-Independent Effect of Bradykinin and Fosinoprilate on Glucose Transport in Langendorff Rat Hearts

Angiotensin-converting enzyme (ACE) inhibitor-stimulated glucose metabolism and perfusion in muscle tissue seem to be, at least in part, mediated by kinins. However, the relative contribution of direct metabolic or secondary hemodynamically induced effects is unclear. It was the aim of this study to characterize the effects of ACE inhibition and bradykinin on glucose transport while changes in cardiocoronary function that might influence glucose transport were minimized. Hearts from Wistar rats were perfused by a Langendorff preparation and a set of functional parameters were simultaneously measured. Bradykinin (10−11M) and fosinoprilate (10−7M) were administered at concentrations that did not affect coronary flow. Insulin was employed as reference at half-maximal concentration. The nonmetabolizable glucose analog 3-O-[14C]methyl-d-glucose and the nontransportable tracer l-[3H]glucose were coperfused for the calculation of glucose transport. Using a 2-compartment mathematical model we found that the glucose transport rate, which was doubled with insulin, was increased almost 3-fold by either bradykinin or fosinoprilate. In the presence of the B2 bradykinin receptor antagonist HOE 140 (d-Arg[Hyp3,Thi5,d-Tic7,Oic8]-bradykinin; icatibant), the effect of both agents was completely abolished. Both agents also induced minor changes in contractility/relaxation parameters that again were completely neutralized with icatibant. A perfusion-independent but B2-kinin receptor-dependent stimulating effect on glucose transport by either bradykinin or fosinoprilate is concluded. This effect could, in analogy to insulin be due to increased glucose transporter translocation, increased endothelium-derived nitric oxide formation, or—despite constant coronary flow conditions—secondary to altered cardiac function.

Load-induced growth responses in isolated adult rat hearts. Role of the AT1 receptor.

Stimulation of the angiotensin II type 1 (AT1) receptor by angiotensin II appears to be mandatory for the acute load-induced hypertrophic response of cultured neonatal rat cardiocytes, but its role in the adult heart is controversial. We tested the hypothesis that AT1 receptor blockade will inhibit the acute induction of proto-oncogenes and protein synthesis by the elevation of systolic wall stress in isolated beating adult rat hearts. Using the established isovolumic perfused heart preparation under constant coronary flow, we found that an increment in left ventricular balloon volume generated an increase in systolic wall stress. The induction of left ventricular c-fos and c-myc mRNA (Northern blotting) was assessed in hearts subjected to increased systolic load without AT1 blockade (No AT1, n = 11) and with AT1 blockade (AT1, n = 11, losartan 40 mg.kg-1.d-1 x 5 days followed by 10(-5) mol/L infusion during perfusion). Flaccid hearts (no left ventricular balloon) served as controls (C, n = 9). The stimulation of new protein synthesis in response to increased systolic load was measured by incorporation of [3H]phenylalanine into cardiac proteins. Elevation of systolic load was associated with a twofold (P < .05) increase in c-fos and c-myc mRNA levels that was not blocked by losartan. The rate of [3H]phenylalanine incorporation into cardiac proteins was increased 2.7-fold (P < .01) in hearts subjected to increased systolic load compared with control hearts. However, AT1 receptor blockade with losartan did not prevent the stimulation of [3H]phenylalanine incorporation (881 +/- 97 versus 923 +/- 82 nmol.g protein-1.h-1, P = NS). In contrast with immature myocytes subjected to stretch, the acute growth responses induced by systolic pressure overload in adult rat hearts do not depend on AT1 receptor activation.

Beneficial Effects of a Nitric Oxide Donor on Recovery of Contractile Function Following Brief Hypoxia in Isolated Rat Heart

Brief myocardial hypoxia causes both systolic and diastolic dysfunction, the latter often persisting during re-oxygenation. The underlying mechanisms may involve cytosolic Ca2+overload as well as altered myofilament properties. Recent studies show that nitric oxide enhances myocardial relaxation via a cGMP-induced reduction in myofilament response to Ca2+. We studied the effects of pretreatment with a nitric oxide donor, sodium nitroprusside (0.1–1μm) on the response to 5 min hypoxia in isovolumic rat hearts perfused at constant coronary flow. Left ventricular relaxation was assessed by an exponential time constant of pressure fall. Sodium nitroprusside reduced the depression of peak left ventricular pressure and peak dP/dtduring hypoxia, and improved left ventricular relaxation both during hypoxia and re-oxygenation. Similar results were observed with a Ca2+antagonist, nicardipine (10 nm). However, adenosine (400 nm), which reduced coronary perfusion pressure to a similar extent as the other two drugs, failed to improve left ventricular function. Addition of sodium nitroprusside or nicardipine at re-oxygenation did not improve relaxation, but instead impaired recovery of peak left ventricular pressure. These results suggest that exogenous nitric oxide improves LV contractile function, in particular relaxation, during brief hypoxia–re-oxygenation independent of changes in coronary flow or coronary perfusion pressure. Its failure to be protective if administered only during re-oxygenation suggests that its action does not involve an anti-oxidant effect.

Synthetic 8-ornithine-vasopressin, a clinically used vasoconstrictor, causes cardiac effects mainly via changes in coronary flow.

8-ornithine-vasopressin (ornipressin, POR-8) is used as a potent peripheral vasoconstrictor mainly in combination with local anaesthetics. Because ornipressin causes vasoconstriction, any myocardial depressive effects could be caused indirectly by reduced myocardial perfusion secondary to coronary vasoconstriction, or directly by effects on myocardial tissue. On isolated guinea pig hearts, we compared direct effects of ornipressin by perfusion at constant flow with indirect effects by perfusion at constant pressure by Langendorff technique. Ornipressin concentrations tested were 0.05, 0.1, 0.25, 0.5 and 1.0 IU/L (1 International Unit (IU) ornipressin = 2.8 micrograms) Coronary flow decreased significantly (P < 0.001) in concentration-dependent manner with ornipressin at constant pressure while AV conduction time and percentage O2 extraction (%O2E) increased and heart rate (HR), systolic left ventricular pressure (LVP) and myocardial O2 consumption (MVO2) decreased. Coronary perfusion pressure increased significantly with increasing ornipressin at constant coronary flow while HR and AV time were unchanged and LVP decreased only at the higher concentrations. At an identical or slightly reduced HR LVP product (RPP), MVO2 increased up to 27 +/- 6% at 1.0 IU/L ornipressin during constant flow perfusion. An increase in %O2E coupled with a decrease in coronary flow at constant pressure is consistent with myocardial depression secondary to reduced tissue perfusion. These ornipressin-induced effects are not evident at constant coronary flow except for a small but direct myocardial depressant effect on LVP at higher concentrations. The increase of MVO2 at constant flow, despite equal or even reduced work, is described as Gregg's phenomenon and it is probably due to an increase in coronary perfusion pressure during coronary vasoconstriction. Even though extrapolation of our results in humans is questionable, the current indication for use of ornipressin as vasoconstrictor may need to be reconsidered, especially in patients with reduced coronary reserve.