Min Of Normothermic Global Ischemia Research Articles

Comparisons of ESR and HPLC methods for the detection of OH . radicals in ischemic/reperfused hearts : A relationship between the genesis of free radicals and reperfusion arrhythmias

In this study we compared two methods, electron spin resonance (ESR) spectroscopy and high performance liquid chromatography (HPLC), which are currently used to detect directly hydroxyl radical (OH .) formation in the ischemic and reperfused heart. Isolated buffer-perfused rat hearts were subjected to 30 min of normothermic global ischemia followed by 30 min of reperfusion. 5,5-Dimethyl-pyrroline- N-oxide (DMPO) was used as a spin-trap agent to detect OH . radicals by ESR and HPLC. In additional HPLC studies, salicylic acid was infused into the heart for the detection of OH . radicals. In all studies, the effects of Superoxide dismutase (SOD) and catalase (CAT) on the OH . generation were examined. The results of our studies indicate that, irrespective of the method, OH . was always detected when an ischemic heart was reperfused and showed ventricular fibrillation. The OH . concentration increased dramatically between 60 and 90 sec of reperfusion, peaked between 180 and 210 sec, and then progressively decreased. In all cases, both SOD and CAT were able to reduce the formation of OH . radicals, with SOD being relatively more effective. Our results indicate that OH . was produced only in the fibrillating hearts that peaked between 180 and 210sec (1.64 ± 0.09 nmol/ mL measured by ESR), but not in the non-fibrillating hearts. Although SOD or CAT reduced the OH . formation, they had no effects on the incidence of reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT). However, when SOD (5 × 10 4 IU/L) was coadministered with CAT (5 × 10 4 IU±L), the incidence of reperfusion-induced VF (total) and VT was reduced from their control value of 92 and 100 to 33 (P < 0.05) and 50% (P < 0.05), respectively. The results of this study indicate that the HPLC method, as well as ESR, can be used to detect OH . formation in ischemic/ reperfused hearts. Because of the convenience, reproduribility and greater sensitivity, the HPLC technique may be more suitable for OH . detection. Our results further suggest the potential therapeutic value of the combination therapy of SOD and CAT for the reduction of reperfusion-induced VF and VT.

Recovery of Function and Adenosine Triphosphate Metabolism Following Myocardial Ischemia Induced in the Presence of Volatile Anesthetics

Using a normothermic isolated working rabbit heart model, experiments were performed to determine whether exposure to halothane or isoflurane prior to ischemia improved postischemic recovery of myocardial function and the preservation of myocardial high energy phosphates. After 30 min of Langendorff perfusion, hearts were perfused for 30 min in the working mode. Three groups were studied: 1) the blank undergoing no pretreatment during an additional 15 min of working mode; 2) hearts exposed to 1.5% halothane; and 3) hearts exposed to 2.3% isoflurane during the additional 15 min of working mode. Subsequently, all hearts underwent 15 min of global normothermic ischemia, followed by 5 min of Langendorff reperfusion and 15 min of working heart mode using a perfusate devoid of volatile anesthetic. Adenosine triphosphate (ATP) and catabolites were determined after 15 min exposure to volatile anesthetics or blank, after 15 min global ischemia and at the end of the recovery phase. Myocardial function was determined after 30 min of working mode, after exposure to volatile anesthetics, and at the end of the recovery phase. In nonischemic hearts, 15-min treatment with 1.5% halothane or 2.3% isoflurane resulted in a significant decrease in positive LVdP/dt, from 1858 +/- 286 to 1316 +/- 180 mm Hg.s-1 and from 1888 +/- 304 to 1541 +/- 226 mm Hg.s-1, respectively. Coronary flow was increased significantly after isoflurane but not after halothane.(ABSTRACT TRUNCATED AT 250 WORDS)

Malondialdehyde production and ascorbate decrease are associated to the reperfusion of the isolated postischemic rat heart

Isolated Langendorff-perfused rat hearts after 20 min of normoxic perfusion in the presence of 2.5 mM Ca ++ and 11 mM glucose were subjected to 30 min of global normothermic ischemia followed by 30 min of normoxic reperfusion with the starting buffer. At the end of each perfusion condition, hearts were freeze-clamped and deproteinized by 0.6 M HClO 4. Two-hundred μL of the neutralized tissue extracts were analyzed by a recently developed high-performance liquid chromatography (HPLC) method for the simultaneous determination of malondialdehyde (MDA), ascorbic acid, and adenine nucleotides. By means of this analytical technique, it was possible to demonstrate that MDA is undetectable in control hearts. In contrast, 30 min of ischemia induced a modest production of MDA (0.012 μmol/g dw), while a large amount of MDA (0.103 μmol/g dw) was observed in reperfused hearts. Values referring to ascorbic acid showed that the concentration of this antioxidant progressively decreased from 1.190 (control hearts) to 0.837 (ischemic hearts) and to 0.595 μmol/g dw (reperfused hearts). The overall conclusions of this study are that reperfusion induces an oxidative stress to the isolated myocardium, a decrease of ascorbate, and an increase of lipid peroxidation. Therefore, by means of proper analytical method, MDA may represent a valid biochemical parameter to demonstrate the relationship between myocardial reperfusion and a detectable tissue damage.

Reperfusion-induced arrhythmias and myocardial ion shifts: a pharmacologic interaction between pinacidil and cicletanine in isolated rat hearts.

Pinacidil is a member of the new antihypertensive drug family possessing an action that involves an increased potassium efflux in vascular and cardiac muscle. We investigated the contribution of opening of ATP-sensitive potassium channel to the development of reperfusion-induced arrhythmias and myocardial ion shifts, particularly that of Na+, K+, Ca2+, and Mg2+ in isolated rat hearts. After 30 min of normothermic global ischemia, pinacidil with 1 to 60 mumol/l failed to reduce the incidence of reperfusion-induced arrhythmias, even on the postischemic/reperfused myocardium in a subset of hearts unresponsive to reperfusion-induced arrhythmias (the duration of ischemia was reduced to 25 min), pinacidil treatment was associated with a greater incidence of reperfusion-induced arrhythmias (100%) as compared to the control value (50%). These proarrhythmic effects of pinacidil were also reflected in a maldistribution of myocardial ion contents both in nonischemic and ischemic/reperfused hearts. Cicletanine, a furopyridine antihypertensive agent that has no effect on coronary resistance, reduced the incidence of reperfusion arrhythmias, and its antiarrhythmic effect was antagonized by pinacidil. The same observation was made in relation to myocardial ion content, e.g., pinacidil-induced K+ loss and Ca2+ gain were antagonized by cicletanine, both in nonischemic and ischemic/reperfused hearts. It is hypothesized that the increased tendency to develop reperfusion-induced ventricular fibrillation is associated with the pinacidil-induced K+ efflux. The present study does not attempt to address the question of specific ionic currents; however, it has been suggested that proarrhythmic and antiarrhythmic effects of pinacidil and cicletanine, respectively, may relate to same receptor sites in which the latter may reflect a specific blockade of the outward K+ ion current via ATP-sensitive K+ channels. If this is so, the use of K+ channel openers as antihypertensive agents may be of particular concern in that population of postinfarction patients who are known to be at high risk of sudden coronary death.

Existence and participation of xanthine oxidase in reperfusion injury of ischemic rabbit myocardium

Using a highly specific assay that minimizes enzyme inactivation in vitro, we found that rabbit myocardial tissue contained low levels of xanthine oxidase (XO) and xanthine dehydrogenase (XD) activity that were effectively inhibited by pretreatment of hearts with allopurinol. In parallel, allopurinol treatment also improved ventricular developed pressure, peak systolic pressure, and coronary flow in isolated hearts subjected to 30 min of normothermic global ischemia and 30 min of reperfusion. Although function was protected by allopurinol treatment, creatine kinase (CK) release was not altered by allopurinol. Inhibition of myocardial XO with allopurinol did not increase myocardial ATP or phosphocreatine. In addition, allopurinol did not scavenge superoxide anion or hydrogen peroxide in vitro. The results support the possibility that relatively low amounts of XO activity, similar to levels reported in human myocardium, may contribute to cardiac ischemia-reperfusion injury.

Role of phospholipases A2 and C in myocardial ischemic reperfusion injury

We investigated the role of phospholipase A2 (PLA2) and phospholipase C (PLC) in myocardial phosholipid degradation and cellular injury during reperfusion of ischemic myocardium. For this purpose, isolated rat hearts were perfused with isotopic arachidonic acid to label its membrane phospholipids. Hearts preperfused with antiphospholipase A2 (anti-PLA2) retained a significantly higher amount of radiolabel in phosphatidylcholine and phosphatidylinositol and a corresponding lower amount of radiolabel in lysophosphatidylcholine and nonesterified fatty acids (P less than 0.05) after 30 min of reperfusion following 30 min of normothermic global ischemia compared with hearts preperfused with nonimmune immunoglobulin G. In similar experiments, antiphospholipase C (anti-PLC)-treated hearts were associated with significantly (P less than 0.05) higher radiolabel in all phospholipids and lower radiolabel in diacyglycerol compared with nonimmune immunoglobulin G-treated hearts. Measurement of phospholipase activity in subcellular organelles of these hearts showed decreased PLA2 activity in cytosol, mitochondria, and microsomes of anti-PLA2-treated hearts and decreased PLC activity of microsomes in anti-PLC-treated hearts. Furthermore, both the antiphospholipases attenuated the release of creatine kinase and lactate dehydrogenase into perfusate and increased contractility as well as coronary flow in the reperfused hearts. Results of this study suggest that both PLA2 and PLC are involved in the degradation of phospholipids and cellular injury that occur during reperfusion of ischemic myocardium.

Sarcoplasmic reticulum function in the “stunned” myocardium

Transient ischemia does not induce myocardial necrosis but may be associated with prolonged contractile dysfunction (“stunned” myocardium). It has been suggested that alteration of the excitation-contraction coupling system (sarcoplasmic reticulum) could be responsible for this phenomenon. We tested this hypothesis by characterizing sarcoplasmic reticulum (SR) function in an isolated rat heart model of “stunned” myocardium (hearts reperfused after 10 min of normothermic global ischemia). At the end of the ischemic period oxalatesupported Ca-uptake was depressed either in the whole homogenate or in isolated SR (to 47% and 22% of control values, respectively). During reperfusion Ca-uptake of the whole heart homogenate recovered almost completely whereas slight but significant depression persisted in isolated SR (48 ± 2 vs 67 ± 4 nmol/min × mg, P < 0.01). In the presence of ruthenium red or ryanodine, two inhibitors of SR Ca-release channels, Ca-uptake was stimulated. Both in the whole heart homogenate and in isolated SR, such stimulation was remarkably smaller after reperfusion than in control conditions ( P < 0.001) suggesting reduced conductivity state of the SR Ca-release channels. Ca-stimulated, magnesium-dependent ATPase activity was remarkably reduced during ischemia and postischemic reperfusion induced only incomplete recovery (93 ± 18 vs 169 ± 14 nmol ATP/min × mg protein, P < 0.05). We conclude that complex modifications of SR function occur in the “stunned” myocardium and could contribute to the contractile impairment found in this condition.

Mechanism of membrane phospholipid degradation in ischemic-reperfused rat hearts

We investigated the mechanism of membrane phospholipid degradation during reperfusion of ischemic myocardium using isolated and perfused rat hearts. Thirty min of myocardial reperfusion after 30 min of normothermic global ischemia resulted in a significant decrease of phosphatidylcholine (PC) content associated with a small but significant increase in lysophosphatidylcholine (LPC) content. Myocardial ischemia for up to 60 min caused no significant loss of any of the major phospholipids. Isotopic incorporation of [14C]arachidonic acid (AA) as well as [3H]-glycerol into PC was significantly attenuated in the ischemic-reperfused heart compared with the normally perfused heart, suggesting that both reacylation and de novo pathways for PC synthesis were inactivated during reperfusion. In the heart prelabeled with [14C]AA, the radiolabeled PC was decreased significantly during reperfusion, associated with a small but significant increase in [14C]AA accumulation. The decreases of PC content and incorporation of [14C]AA into PC, as well as the increases of LPC content and the [14C]AA during reperfusion, were prevented by reperfusion with low Ca2+ (50 microM) buffer or by pretreatment with trifluoperazine (10 microM) or mepacrine (50 microM), but not with verapamil (1 microM). The inhibition of loss of PC was associated with significant diminution of creatine kinase release from the reperfused hearts. The present study indicates that the net loss of membrane phospholipids, especially with respect to PC during reperfusion, may result from 1) inhibition of reacylation of AA, 2) inhibition of de novo synthesis, and 3) stimulation of phospholipase activity. These results are consistent with an influx of Ca2+, although other interpretations are also possible.

Changes in Na +, K +, Cl −, Ca 2+, lactic acid, inorganic phosphate and nucleosides in reperfusates after 10 min of normothermic global ischemia in isolated working rabbit hearts : H. Van Belle, F. Goossens. Department of Biochemistry, Janssen Research Foundation, B-2340 Beerse, Belgium

Changes in Na +, K +, Cl −, Ca 2+, lactic acid, inorganic phosphate and nucleosides in reperfusates after 10 min of normothermic global ischemia in isolated working rabbit hearts : H. Van Belle, F. Goossens. Department of Biochemistry, Janssen Research Foundation, B-2340 Beerse, Belgium

Sex differences in the tolerance of immature rat myocardium to global ischemia.

Currently there is considerable interest in the metabolism of the immature myocardium and in particular the mechanisms underlying its greater tolerance to ischemia than that of the adult heart. In order to investigate whether this tolerance is sex-related, we compared the recovery of function in isolated hearts from male and female neonatal rats (three to five days old) following 60 min of normothermic global ischemia and 30 min of reperfusion (n = 8 per group). The female hearts exhibited significantly better (p less than 0.05) recovery of rate (81 +/- 5% vs. 65 +/- 5%) and the rate-pressure product (73 +/- 9% vs. 37 +/- 8%), and a tendency towards better recovery of contractile function (left ventricular developed pressure, 89 +/- 9% vs. 59 +/- 12%; dP/dt, 84 +/- 12% vs. 54 +/- 13%). This evidence for greater resistance of female hearts to ischemic injury was supported by a delayed onset of contracture (mean time to onset, 29.4 +/- 2.7 min vs. 24.9 +/- 2.6 min). The loss in left ventricular compliance during ischemia and reperfusion was also smaller in the female hearts (increase in left ventricular end diastolic pressure, 6.5 +/- 1.2 mm Hg vs. 13.6 +/- 3.8 mm Hg). These results suggest that there may be sex-related differences in the tolerance of immature hearts to ischemia, a factor which should be taken into account in the design and interpretation of experimental studies.

Recombinant superoxide dismutase reduces oxygen free radical concentrations in reperfused myocardium.

It has been proposed that oxygen free radicals mediate damage that occurs during postischemic reperfusion. Recombinant human superoxide dismutase (r-h-SOD) has been shown to be effective at reducing reperfusion injury, but it is not known if this infused enzyme actually reduces oxygen free radical concentrations in the myocardial tissue. Electron paramagnetic resonance spectroscopy was used to directly measure the effect of r-h-SOD on free radical concentrations in the postischemic heart. Hearts were freeze clamped at 77 degrees K after 10 min of normothermic global ischemia followed by 10 s of reflow with control perfusate (n = 7) or perfusate containing 60,000 U r-h-SOD (n = 7). The spectra of these hearts exhibited three different signals: signal A isotropic, g = 2.004, identical to the carbon-centered ubiquinone free radical; signal B anisotropic with axial symmetry, g parallel = 2.033, g perpendicular = 2.005, identical to the oxygen-centered alkyl peroxyl free radical; and the signal C an isotropic triplet, g parallel = 2.000, an = 24 G, similar to a nitrogen-centered free radical such as a peroxyl amine. With r-h-SOD administration the concentration of the oxygen free radical, signal B, was reduced 49% from 6.8 +/- 0.3 microM to 3.5 +/- 0.3 microM (P less than 0.01) and the concentration of the nitrogen free radical, signal C, was reduced 38% from 3.4 +/- 0.3 to 2.1 +/- 0.3 microM (P less than 0.01). The concentration of the carbon-centered free radical, signal A, however, was increased 51% from 3.3 +/- 0.2 to 5.0 +/- 0.2 microM (P less than 0.01). Identical reperfusion with peroxide-inactivated r-h-SOD did not alter the concentrations of free radicals indicating that the specific enzymatic activity of r-h-SOD is required to decrease the concentrations of reactive oxygen free radicals. Additional measurements performed varying the duration of reflow demonstrate a burst of oxygen free radical generation peaking at 10 s of reperfusion. r-h-SOD entirely abolished this burst. These studies demonstrate that superoxide-derived free radicals are generated during postischemic reperfusion and suggest that the beneficial effect of r-h-SOD is due to its specific enzymatic scavenging of superoxide free radicals.

Direct measurement of free radical generation following reperfusion of ischemic myocardium.

Electron paramagnetic resonance spectroscopy was used to directly measure free radical generation in perfused rabbit hearts. Hearts were freeze-clamped at 77 degrees K during control perfusion, after 10 min of normothermic global ischemia (no coronary flow), or following post-ischemic reperfusion with oxygenated perfusate. The spectra of these hearts exhibited three different signals with different power saturation and temperature stability: signal A was isotropic with g = 2.004; signal B was anisotropic with axial symmetry with g parallel = 2.033 and g perpendicular = 2.005; signal C was an isotropic triplet with g = 2.000 and hyperfine splitting an = 24 G (1 G = 0.1 mT). The g values, linewidth, power saturation, and temperature stability of signal A are identical to those of a carbon-centered semiquinone, whereas those of signal B are similar to alkyl peroxyl or superoxide oxygen-centered free radicals; signal C is most likely a nitrogen-centered free radical. In the control heart samples signal A predominated, whereas in ischemic hearts signal A decreased in intensity, and signals B and C became more intense; with reperfusion all three signals markedly increased. Free radical concentrations derived from the intensities of the B and C signals peaked 10 sec after initiation of reflow. At this time the oxygen-centered free radical concentration derived from the intensity of signal B was increased over six times the concentration measured in control hearts and over two times the concentration measured in ischemic hearts. Hypoxic reperfusion did not increase any of the free radical signals over the levels observed during ischemia. These experiments directly demonstrate that reactive oxygen-centered free radicals are generated in hearts during ischemia and that a burst of oxygen radical generation occurs within moments of reperfusion.

Conjugated dienes in ischemic and reperfused myocardium: an in vivo chemical signature of oxygen free radical mediated injury

Free radical reactions have been suggested to be important events in the mechanism of myocardial injury during ischemia and reperfusion. Most of the in vivo evidence implicating free radical mediated events in the etiology of myocardial injury has been based on intervention studies which document the efficacy of oxygen free radical scavengers in improving function or tissue salvage. We have assayed free fatty acid oxidation products (hydroxy conjugated dienes) derived from myocardial phospholipid as chemical markers of oxidative injury. Biopsies, harvested from canine myocardium subjected to cardiopulmonary bypass with no aortic crossclamp (control), from pre-ischemic, end ischemic (at the end of 45 min of global normothermic ischemia induced by aortic crossclamp) and at 5, 10, 15, 30 and 60 mins of reperfusion were analyzed for hydroxy conjugated dienes using HPLC with structural confirmation by GC-MS. All biopsies were taken from non-necrotic myocardium as indicated by gross tetrazolium staining of myocardial cross sections. Trace levels of hydroxy conjugated dienes could be detected in the preischemic biopsies or control biopsies harvested from hearts subjected to cardiopulmonary bypass with no ischemia. At the end of 45 min ischemia, however, a significant increase in 18:2 and 20:4 hydroxy isomers was detected and confirmed by GC-MS (P less than 0.05 vs. control). After 5 mins of reperfusion a further significant increase in hydroxy conjugated dienes was noted with 18:2, 20:4 and 22:6 isomers being identified (P less than 0.01 vs. end ischemia). By 30 min of reperfusion the concentration of phospholipid oxidation products had returned to pre-ischemic levels. This study presents the first chemically rigorous in vivo evidence for the formation of products of phospholipid oxidation (hydroxy conjugated dienes) during myocardial ischemia and reperfusion and supports the concept of oxygen free radical mediated lipid peroxidation. This study emphasizes the formation of phospholipid oxidation products during ischemia and particularly during the early phase of reperfusion and illustrates the transient nature of these products in myocardial phospholipid.

Sarcoplasmic reticulum dysfunction: phospholipid alterations induced by lysosomal phospholipase C.

Previous work has demonstrated that myocardial ischemia results in a breakdown of the excitation-contraction coupling system of cardiac muscle associated with lysosomal activation. It has been hypothesized that lysosomal activation during the course of myocardial ischemia is mediated by the production of oxygen free radicals. We have tested the hypothesis that myocardial ischemia results in the activation of lysosomal phospholipase C and disruption of calcium transport in sarcoplasmic reticulum (SR) mediated by oxygen free radicals. Three groups of dogs were studied: sham-operated controls (n = 6); normothermic global ischemia of 30-min duration (n = 6); and 30 min of normothermic global ischemia pretreated with intracoronary superoxide dismutase (SOD, 10 micrograms/ml) plus catalase (25 micrograms/ml). In vitro, isolated SR demonstrated a significant depression of calcium uptake rates and Ca2+-stimulated, Mg2+-dependent ATPase activity at both pH 7.0 and 6.4 with the depression at pH 6.4 greater than 7.0. This depression of SR function was significantly inhibited in hearts pretreated with SOD plus catalase. In sham-operated controls, acid-induced dysfunction was associated with substantial loss of phospholipid phosphorus and major changes in phospholipid composition. SR contained an extremely active, ion-independent sphingomyelinase-phospholipase C (SM-PLC) that had maximal activity at pH 4.5-5.0. This SM-PLC was activated when control SR was incubated at acid pH and the specific activity of SM-PLC was decreased 50% in SR isolated from normothermic global ischemia. Activity remained at control levels in hearts pretreated with SOD plus catalase.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of short term normothermic global ischemia and acidosis on cardiac myofibrillar Ca 2+−Mg 2+ ATPase activity

There is now good evidence to indicate the onset of myocardial ischemia is accompanied by a decline in intracellular pH which parallels the decrease in tension development. The component of the excitation--contraction coupling system which is responsible for the loss in tension development has not been determined although the contractile proteins are a likely candidate since the calcium sensitivity of tension development and of myofibrillar ATPase are both inhibited by a decrease in pH. However, these studies have utilized normal tissues and the effects of pH compounded with ischemia have not been determined. It is plausible to suggest that there may occur ischemic damage to the excitation--contraction coupling system which would depress function in a manner distinct from that incurred by acidosis. Toya-Oka and Ross have demonstrated a loss in regulatory proteins during regional ischemia, suggesting an effect of ischemia independent of pH. We recently demonstrated, in sarcoplasmic reticulum isolated from ischemic myocardium, a defect in function which could not be accounted for solely on the decrease in pH. It was, therefore, the purpose of this study to determine the effects of decreasing pH on cardiac myofibrillar ATPase activity isolated from hearts which had been subjected to short-term, global normothermic ischemia. This design permits us to answer the following questions: Is there a decrease in myofibrillar ATPase activity in the canine heart following 30 min of normothermic global ischemia? Does acidosis play a contributory role in any observed depression of myofibrillar ATPase activity during ischemia? and Does the ischemic process, independent of acidosis, produce a further depression of myofibrillar ATPase activity?

Effects of bepridil on regional and global myocardial ischemia/reperfusion-induced injury.

The effectiveness of the calcium entry blocker bepridil in protecting the myocardium from ischemic injury, was assessed in a canine model of regional ischemia and in a feline model of global ischemia. Bepridil administration (5 mg/kg or 15 mg/kg/24 h intravenously) did not reduce ultimate infarct size as assessed in anesthetized, open-chest dogs subjected to 90 min of occlusion of the left circumflex coronary artery and 24 h of reperfusion. Bepridil (5 mg/kg administered intravenously to a blood donor cat) did not provide any protection of the isolated blood-perfused cat heart from 90 min of normothermic global ischemia and 60 min of reperfusion. Treatment of the perfused cat heart with bepridil did not prevent tissue accumulation of calcium or loss of tissue potassium and ATP. Bepridil, however, significantly reduced reperfusion tachyarrhythmias in the dog model for assessing ultimate infarct size and prevented reperfusion-induced ventricular fibrillation of the cat isolated heart. These results indicate that the calcium entry blocker, bepridil, as assessed in the models employed, does not protect the myocardium from ischemic reperfusion injury. However, it does prevent reperfusion-induced tachyarrhythmias and ventricular fibrillation.

Treatment of Postischemic Reperfusion Cardiac Injury with a Perfluorochemical Solution

We assessed the effects of a perfluorochemical solution on reperfusion injury in a globally ischemic heart model. An isolated rabbit heart, retrogradely perfused at a constant flow rate, served as our experimental model. After initial perfusion with whole blood, hearts were exposed to 30 min of normothermic global ischemia. Reperfusion was then begun with either whole blood or a 20% perfluorochemical solution (FC-43). After 120 min of reperfusion, a markedly greater recovery of contractile function was observed in the perfluorochemical-reperfused hearts (85 +/- 5% of baseline developed pressure) compared with blood-reperfused hearts (57 +/- 3% of baseline developed pressure). This recovery of function was accomplished with only 1 h of perfluorochemical reperfusion and was not lost on returning to blood perfusion. The improved recovery of function could not be attributed to the chemical composition, oxygen-carrying capacity, pH, or temperature of the perfluorochemical perfusate. Neither could the beneficial effects of perfluorochemical be related to differences in left ventricular resting pressure. We speculate that, because of marked differences in coronary resistance during reperfusion with perfluorochemical solution and blood, improved recovery of cardiac function is related to the superior rheological properties of perfluorochemicals.

Enhanced cardiac efficiency with dobutamine after global ischemia

Dopamine and dobutamine are used in low output states following cardiopulmonary bypass but the consequences of increased inotropic activity on myocardium recovering from ischemia is unknown. Dogs on cardiopulmonary bypass were subjected to 20 min of normothermic global ischemia followed by 20 min of reperfusion. Dopamine or dobutamine (both at 10 μg/kg/min) or normal saline infusion was begun and 10 min later the dogs weaned from cardiopulmonary bypass while the infusions continued. Serial measurements were made of regional myocardial and systemic blood flow (15 μm radiolabeled spheres), myocardial oxygen consumption, creatine phosphate, and ATP levels. On bypass mean aortic pressure was decreased and heart rate, oxygen consumption, and left ventricular blood flow were increased by both catecholamine infusions ( P < 0.01), but neither drug lowered ATP or creatine phosphate levels. Renal blood flow was decreased in dobutamine-treated dogs ( P < 0.01). Off bypass, heart rate and mean aortic pressure were similar in all groups. While both drugs increased left ventricular blood flow to a similar extent ( P < 0.01), dopamine treatment raised cardiac output by only 30% ( P < 0.05) and dobutamine treatment increased cardiac output by 85% ( P < 0.01). In addition, myocardial oxygen consumption was increased in dopamine-treated dogs ( P < 0.05) while values in dobutamine animals were similar to controls. Therefore, dobutamine seems advantageous to dopamine following bypass because it increases cardiac output (by increasing stroke volume) but does not increase myocardial oxygen consumption. Both drugs are potentially detrimental on bypass because they greatly increase heart rate and oxygen consumption and, in addition, dobutamine causes an unexplained fall in renal blood flow.

Isovolumic relaxation as a critical determinant of postischemic ventricular function

The importance of ventricular relaxation was studied in a canine right-heart bypass model employing three different modes of cardioplegia. Although both contractility and relaxation indices were depressed in all animals after 60 min of normothermic global ischemia, changes in overall left ventricular function correlated only with max neg dP/dt/P and with T, the exponential of the isovolumic phase of ventricular relaxation ( r = 0.78). There was no significant correlation between postischemic left ventricular function and max dP/dt/P. We conclude that relaxation indices are a sensitive index of deterioration of left ventricular function after ischemia, and impaired relaxation may be the rate-limiting step in recovery of left ventricular performance after ischemia.