Pyruvate reverses fatty-acid-induced depression of ventricular function and calcium overload after hypothermia in guinea pig hearts

OBJECTIVE: High levels of free fatty acids have been shown to impair mechanical recovery and calcium homeostasis of isolated rat hearts following hypothermic perfusion. The objective of the present study was to investigate whether inhibition of fatty acid oxidation through activation of pyruvate dehydrogenase by millimolar concentrations of pyruvate could influence functional recovery and Ca2+ homeostasis after a hypothermic insult. METHODS: Ventricular function and myocardial calcium ([Ca]total) were measured in 3 different groups of Langendorff-perfused guinea pig hearts exposed to 40 min hypothermic (15 degrees C) perfusion, followed by 30 min rewarming at 37 degrees C. The hearts were perfused with either 11.1 mM glucose (G), glucose and 1.2 mM palmitate (GP), or glucose, palmitate and 5 mM pyruvate (GPP) as energy substrates. RESULTS: All groups showed marked elevations in [Ca]total during hypothermia (from 0.6-0.7 mumol.g dry wt-1 to 9.3-12.2 mumol.g dry wt-1 at 40 min hypothermia, P < 0.05), associated with a pronounced increase in left ventricular end-diastolic pressure (LVEDP from 0-2 to 50-60 mmHg). Following rewarming, GP-perfused hearts showed significantly lower recovery of mechanical function compared to both G- and GPP-perfused hearts (% recovery of left ventricular developed pressure: 27 +/- 8 vs. 62 +/- 3 and 62 +/- 8%, respectively, P < 0.05). The reduced mechanical recovery of GP-perfused hearts was associated with elevated [Ca]total. In separate experiments we found that addition of 1.2 mM palmitate reduced glucose oxidation ([14C]glucose) from 1.77 +/- 0.28 mumol.min-1.g dry wt-1 (G-perfused hearts) to 0.15 +/- 0.04 mumol.min-1.g dry wt-1 (GP-perfused hearts, P < 0.05), implying that fatty acids had become the major substrate for oxidative phosphorylation. Fatty acid oxidation was, however, less pronounced after further addition of 5 mM pyruvate. Thus, palmitate oxidation ([3H]palmitate) was more than 40% lower in GPP-perfused than in GP-perfused hearts (0.83 +/- 0.22 vs. 1.41 +/- 0.12 mumol.min-1.g dry wt-1, P < 0.05). CONCLUSIONS: The present results demonstrate impaired ventricular function and calcium homeostasis after hypothermia in guinea pig hearts perfused with fatty acids in addition to glucose, as compared to hearts perfused with glucose alone. Furthermore, we show that these unfavourable effects of fatty acids can be overcome by an exogenous supply of pyruvate.     

Deregulated production of interleukin-8 (IL-8) in autoimmune thyroid disease studied by newly developed IL-8 radioimmunoassay

Glucagon may regulate FFA metabolism in vivo. To test this hypothesis, six healthy male volunteers were infused with somatostatin, to inhibit endogenous hormone secretion, and insulin, glucagon, and GH to replace endogenous secretion of these hormones. In the hypoglucagonemia experiments, the glucagon infusion was omitted, and in the hyperglucagonemic experiments glucagon was infused at 1.3 ng/kg.min, to produce physiological hyperglucagonemia. In two sets of control experiments, glucagon was infused at 0.65 ng/kg.min, in order to maintain peripheral euglucagonemia, and the plasma glucose concentrations were clamped at the levels observed in either the hypo- or hyperglucagonemic experiments. Rates of FFA and glycerol (an index of lipolysis) appearance (Ra) were estimated with the isotope dilution method using [1-14C]palmitate and [2H5] glycerol. Plasma glucagon concentrations decreased during the hypoglucagonemic experiments (85 +/- 12 vs. 123 +/- 22 ng/L, P < 0.05) and increased during the hyperglucagonemic experiments (186 +/- 20 vs. 125 +/- 15 ng/L, P < 0.05), whereas other hormone concentrations remained the same. Hypoglucagonemia resulted in equivalent suppression of FFA Ra (3.7 +/- 0.2 vs. 5.9 vs. 0.3 mumol/kg.min, P < 0.01) and glycerol Ra (1.2 +/- 0.2 vs. 2.2 +/- 0.5 mumol/kg.min, P < 0.05). Similarly, hyperglucagonemia resulted in equivalent stimulation of FFA Ra (5.2 +/- 0.4 vs. 3.7 +/- 0.3 mumol/kg.min, P < 0.05) and glycerol Ra (1.5 +/- 0.3 vs. 1.1 +/- 0.1 mumol/kg.min, P < 0.05). These results indicate that glucagon has a physiological role in the regulation of FFA metabolism in vivo.     

Human gallbladder mucosal function: effects on intraluminal fluid and lipid composition in health and disease

OBJECTIVES: Fructose-1,6-diphosphate is a glycolytic intermediate that has been shown experimentally to cross the cell membrane and lead to increased glycolytic flux. Because glycolysis is an important energy source for myocardium during early reperfusion, we sought to determine the effects of fructose-1,6-diphosphate on recovery of postischemic contractile function. METHODS: Langendorff-perfused rabbit hearts were infused with fructose-1,6-diphosphate (5 and 10 mmol/L, n = 5 per group) in a nonischemic model. In a second group of hearts subjected to 35 minutes of ischemia at 37 degrees C followed by reperfusion (n = 6 per group), a 5 mmol/L concentration of fructose-1,6-diphosphate was infused during the first 30 minutes of reperfusion. We measured contractile function, glucose uptake, lactate production, and adenosine triphosphate and phosphocreatine levels by phosphorus 31-nuclear magnetic resonance spectroscopy. RESULTS: In the nonischemic hearts, fructose-1,6-diphosphate resulted in a dose-dependent increase in glucose uptake, adenosine triphosphate, phosphocreatine, and inorganic phosphate levels. During the infusion of fructose-1,6-diphosphate, developed pressure and extracellular calcium levels decreased. Developed pressure was restored to near control values by normalizing extracellular calcium. In the ischemia/reperfusion model, after 60 minutes of reperfusion the hearts that received fructose-1,6-diphosphate during the first 30 minutes of reperfusion had higher developed pressures (83 +/- 2 vs 70 +/- 4 mm Hg, p < 0.05), lower diastolic pressures (7 +/- 1 vs 12 +/- 2 mm Hg, p < 0.05), and higher phosphocreatine levels than control untreated hearts. Glucose uptake was also greater after ischemia in the hearts treated with fructose-1,6-diphosphate. CONCLUSIONS: We conclude that fructose-1,6-diphosphate, when given during early reperfusion, significantly improves recovery of both diastolic and systolic function in association with increased glucose uptake and higher phosphocreatine levels during reperfusion.     

Effect of MCI-154, a cardiotonic agent, on regional contractile function and myocardial oxygen consumption in the presence and absence of coronary artery stenosis in dogs

The effects of MCI-154 (6-[4-(4'-pyridyl)aminophenyl]-4,5-dihydro-3(2H)- pyridazinone hydrochloride.3H2O), a cardiotonic agent with calcium sensitizing actions, on regional contractile function and myocardial oxygen consumption (MVO2) were studied in the dog hearts with and without partial occlusion of the left anterior descending coronary artery and compared with those of dobutamine. Segment shortening by sonomicrometry, regional myocardial blood flow by microspheres and the oxygen content of coronary venous blood drawn from the ischemic left anterior descending coronary artery area were simultaneously measured. The ischemic zone segment shortening and left ventricular (LV) dP/dtmax were decreased after partial occlusion. The infusion of MCI-154 starting 20 min after ischemia improved the depressed segment shortening and LV dP/dtmax without increasing the ischemic zone MVO2 and regional myocardial blood flow. In the nonischemic hearts, MCI-154 did not increase MVO2 and coronary blood flow despite the augmentation of myocardial contractility. MCI-154 decreased LV end-diastolic pressure and systemic blood pressure. On the other hand, dobutamine failed to increase the ischemic zone segment shortening, but the drug increased MVO2, coronary blood flow and LV dP/dtmax in both ischemic and nonischemic hearts. These results indicate that MCI-154 alleviates the ischemic contractile failure without increasing myocardial oxygen demand. Thus, MCI-154 may be useful in the management of heart failure with reduced coronary reserve.     

Contribution of glycogen and exogenous glucose to glucose metabolism during ischemia in the hypertrophied rat heart

Although hypertrophied hearts have increased rates of glycolysis under aerobic conditions, it is controversial as to whether glucose metabolism during ischemia is altered in the hypertrophied heart. Because endogenous glycogen stores are a key source of glucose during ischemia, we developed a protocol to label the glycogen pool in hearts with either [3H]glucose or [14C]glucose, allowing for direct measurement of both glycogen and exogenous glucose metabolism during ischemia. Cardiac hypertrophy was produced in rats by banding the abdominal aorta for an 8-week period. Isolated hearts from aortic-banded and sham-operated rats were initially perfused under substrate-free conditions to decrease glycogen content to 40% of the initial pool size. Resynthesis and radiolabeling of the glycogen pool with [3H]glucose or [14C]glucose were accomplished in working hearts by perfusion for a 60-minute period with 11 mmol/L [3H]glucose or [14C]glucose, 0.5 mmol/L lactate, 1.2 mmol/L palmitate, and 100 mumol/mL insulin. Although glycolytic rates during the aerobic perfusion were significantly greater in hypertrophied hearts compared with control hearts, glycolytic rates from exogenous glucose were not different during low-flow ischemia. The contribution of glucose from glycogen was also not different in hypertrophied hearts compared with control hearts during ischemia (1314 +/- 665 versus 776 +/- 310 nmol.min-1.g dry wt-1, respectively). Glucose oxidation rates decreased during ischemia but were not different between the two groups. However, in both hypertrophied and control hearts, the ratio of glucose oxidation to glycolysis was greater for glucose originating from glycogen than from exogenous glucose. Our data demonstrate that glycogen is a significant source of glucose during low-flow ischemia, but the data do not differ between hypertrophied and control hearts.     

Responses of blood flow, oxygen consumption, and contractile function to inotropic stimulation in stunned canine myocardium

To examine the effects of inotropic stimulation on regional myocardial blood flow (MBF), oxidative metabolism, and contractile function in stunned myocardium, nine closed-chest dogs were studied 2 hours postreperfusion after a 25 minute occlusion of the left anterior descending coronary artery (LAD). MBF was determined with microspheres, and regional myocardial oxygen consumption (MVO2) was estimated from the rate constant k1 of the rapid clearance phase of [1-11C] acetate time activity curves, recorded with dynamic positron emission tomography. Myocardium at risk was determined from [13N] ammonia images obtained during occlusion. Wall motion, assessed by two-dimensional echocardiography, was impaired in postischemic myocardium in all dogs 2 hours after reperfusion. Dobutamine infusion increased the rate pressure product by 70% +/- 31% and significantly improved contractile function in the postischemic region in all dogs. In remote myocardium, MVO2 increased from 5.7 +/- 1.2 to 8.6 +/- 1.6 mumol/gm/min, and blood flow from 0.87 +/- 0.16 to 1.52 +/- 0.42 ml/gm/min in response to dobutamine. In reperfused myocardium, MVO2 increased from 3.1 +/- 0.7 to 7.4 +/- 1.5 mumol/gm/min, and blood flow from 0.51 +/- 0.12 to 1.2 +/- 0.4 ml/gm/min. Oxygen extraction increased significantly in reperfused myocardium relative to remote myocardium consistent with a flow-limited response to dobutamine stimulation. The improvement in contractile function failed to correlate significantly with relative increases in MBF or MVO2, suggesting that mechanical function is not as tightly coupled as MBF and MVO2 in postischemic myocardium during inotropic stimulation.     

Ischemia-reperfusion induced microvascular dysfunction in skeletal muscle: application of intravital video microscopy

Video microscopy of red cell flow in capillaries at the surface of skeletal muscle provided the opportunity to quantitate ischemia-reperfusion (I-R) induced microcirculatory changes, in vivo. Extensor Digitorum Longus (EDL) muscles of 22 male Wistar rats (300-400 g), anesthetized with sodium pentobarbital (Somnotol, 65 mg kg,-1 IP), were used to measure the number of perfused capillaries (CDper: mm-1) crossing lines drawn perpendicular to the muscle axis, and red blood cell velocity (VRBC: mm/s) within individual capillaries from controls (n = 6), and after 2 hr (n = 4), 3 hr (n = 4), and 4 hr (n = 5) of no-flow ischemia with the muscle temperature maintained at its normal value of 32 degrees C. Ischemia was induced by tightening a tourniquet placed around the limb above the EDL muscle. Measurements were made after 30, 60, and 90 min of reperfusion. To test the usefulness of this skeletal muscle model for evaluating proposed interventions in I-R, the effect of hypothermia (24 degrees C) on the microcirculation following 4 hr ischemia (n = 3) was measured. Edema formation was estimated from the wet/dry weight ratio of the ischemic and contralateral control EDL muscles. Capillary perfusion at the surface of the control muscles was remarkably stable over the 5 hr period studied, while significant changes occurred following the ischemic periods. Significantly lower CDper was measured 30 min following all periods of normothermic ischemia. However, unlike the 2 and 4 hr ischemic periods 3 hr normothermic ischemia resulted in a progressive decline in CDper throughout the reperfusion period. VRBC showed evidence of a hyperemic response following 2 hr normothermic ischemia (control: 0.12 mm/s +/- 0.19 compared to 0.26 mm/s +/- 0.03 following 90 min reperfusion; mean +/- sem). However, no such hyperemia was measured following either 3 or 4 hr normothermic ischemia (i.e., 3 hr control: 0.24 mm/s +/- 0.01 compared to 0.07 mm s +/- 0.003 following 90 min reperfusion). In fact, VRBC was essentially zero 90 min following 4 hr normothermic ischemia (0.01 mm/s +/- 0.01). However, when the muscle was allowed to cool to 24 degrees C during 4 hr ischemia no significant change in either VRBC or CDper was measured compared to pre-ischemic controls. Evidence of edema was found after 3 and 4 hr normothermic ischemia. This study establishes a skeletal muscle model of I-R, which may be useful in testing hypotheses regarding mechanisms of I-R injury, and effectiveness of proposed treatments of I-R.     

Relationship between fatty acid delivery and fatty acid oxidation during strenuous exercise

To evaluate the extent to which decreased plasma free fatty acid (FFA) concentration contributes to the relatively low rates of fat oxidation during high-intensity exercise, we studied FFA metabolism in six endurance-trained cyclists during 20-30 min of exercise [85% of maximal O2 uptake (VO2max)]. They were studied on two occasions: once during a control trial when plasma FFA concentration is normally low and again when plasma FFA concentration was maintained between 1 and 2 mM by intravenous infusion of lipid (Intralipid) and heparin. During the 20-30 min of exercise, fat and carbohydrate oxidation were measured by indirect calorimetry, and the rates of appearance (Ra) of plasma FFA and glucose were determined by the constant infusion of [6,6-2H2]glucose and [2H2]palmitate. Lipid-heparin infusion did not influence the Ra or rate of disappearance of glucose. During exercise in the control trial, Ra FFA failed to increase above resting levels (11.0 +/- 1.2 and 12.4 +/- 1.7 mumol.kg-1.min-1 for rest and exercise, respectively) and plasma FFA concentration dropped from a resting value of 0.53 +/- 0.08 to 0.29 +/- 0.02 mM. The restoration of plasma FFA concentration resulted in a 27% increase in total fat oxidation (26.7 +/- 2.6 vs. 34.0 +/- 4.4 mumol.kg-1.min-1, P < 0.05) with a concomitant reduction in carbohydrate oxidation, apparently due to a 15% (P < 0.05) reduction in muscle glycogen utilization. However, the elevation of plasma FFA concentration during exercise at 85% VO2max only partially restored fat oxidation compared with the levels observed during exercise at 65% VO2max. These findings indicate that fat oxidation is normally impaired during exercise at 85% VO2max because of the failure of FFA mobilization to increase above resting levels, but this explains only part of the decline in fat oxidation when exercise intensity is increased from 65 to 85% VO2max.     

Effect of exercise on left ventricular mechanical efficiency in conscious dogs

BACKGROUND: We studied the effect of exercise (7.2 to 8.0 km/h) on the efficiency of the conversion of metabolic energy to external work or stroke work (SW) by the left ventricle (LV). METHODS AND RESULTS: Energy use was calculated from LV myocardial oxygen consumption per beat (MVO2). LV volume was calculated from orthogonal dimensions and coronary flow measured with ultrasonic flow probes. The total mechanical energy of the LV was calculated as the pressure-volume area (PVA). At rest, the MVO2-PVA point fell on the MVO2-PVA relation determined by steady-state changes in arterial pressure produced by graded infusions of phenylephrine. Exercise increased the slope (Ees) of LV end-systolic pressure-volume (PV) relation by 29%. During exercise, the MVO2-PVA point shifted to the right only slightly above the control MVO2-PVA relation by 0.007 +/- 0.005 mL O2.beat-1.100 g LV-1. Despite the increase in ventricular contractility with exercise, the PVA/MVO2 ratio was unchanged because of the marked increase in PVA. During exercise, the transmission of total mechanical energy to external work (SW/PVA) increased from 65 +/- 5% to 72 +/- 4% (P < .01) as the ratio of the arterial end-systolic elastance to Ees decreased from 1.1 +/- 0.2 to 0.8 +/- 0.1 (P < .05). Thus, LV mechanical efficiency (SW/MVO2 = SW/PVA.PVA/MVO2) improved from 12.9 +/- 1.5% to 14.3 +/- 1.1% (P < .05) during exercise. CONCLUSIONS: Exercise increases the efficiency of conversion of metabolic energy to external work by the LV due to alteration in LV arterial coupling resulting in increased production of mechanical energy and enhanced transmission of mechanical energy to external work, which more than offsets any increased metabolic cost of the enhanced contractility.     

Transgenic A1 adenosine receptor overexpression increases myocardial resistance to ischemia

Activation of myocardial A1 adenosine receptors (A1AR) protects the heart from ischemic injury. In this study transgenic mice were created using the cardiac-specific alpha-myosin heavy chain promoter and rat A1AR cDNA. Heart membranes from two transgene positive lines displayed approximately 1,000-fold overexpression of A1AR (6,574 +/- 965 and 10,691 +/- 1,002 fmol per mg of protein vs. 8 +/- 5 fmol per mg of protein in control hearts). Compared with control hearts, transgenic Langendorff-perfused hearts had a significantly lower intrinsic heart rate (248 beats per min vs. 318 beats per min, P < 0. 05), lower developed tension (1.2 g vs. 1.6 g, P < 0.05), and similar coronary resistance. The difference in developed tension was eliminated by pacing. Injury of control hearts during global ischemia, indexed by time-to-ischemic contracture, was accelerated by blocking adenosine receptors with 50 microM 8-(p-sulfophenyl) theophylline but was unaffected by addition of 20 nM N6-cyclopentyladenosine, an A1AR agonist. Thus A1ARs in ischemic myocardium are presumably saturated by endogenous adenosine. Overexpressing myocardial A1ARs increased time-to-ischemic contracture and improved functional recovery during reperfusion. The data indicate that A1AR activation by endogenous adenosine affords protection during ischemia, but that the response is limited by A1AR number in murine myocardium. Overexpression of A1AR affords additional protection. These data support the concept that genetic manipulation of A1AR expression may improve myocardial tolerance to ischemia.     

Oxygen consumption for constant work is minimal at lowest working contractility in normal dog hearts

We tested whether minimal myocardial oxygen consumption (MVO2) for a given external work would exist in the middle of a normal contractility range as previously predicted theoretically. The left ventricle of the excised cross-circulated dog heart preparation was connected to a volume servo pump. Myocardial contractility in terms of ventricular end-systolic elastance (Emax) was gradually increased from control 8.9 +/- 3.4 (mean +/- SD) to 30.0 mmHg/(ml/100 g) by epinephrine and decreased to 1.8 mmHg/(ml/100 g) by propranolol while heart rate, end-systolic pressure and stroke work were kept constant. MVO2 was determined as the product of total coronary flow and coronary arteriovenous oxygen content difference in each contractile state. We plotted MVO2 values against E(max) values in each heart. The MVO2-E(max) relation for a constant cardiac work showed that MVO2 was minimal at the low end of the covered E(max) range. We conclude that minimal MVO2 for a given cardiac work is generally obtained at the lowest working contractility in normal dog hearts. This conclusion might pose some problems in the previous theoretical prediction as to the contractility that achieves the minimal MVO2 in a given external work.     

Novel approach for enhancing atrioventricular nodal conduction delay mediated by endogenous adenosine

The 2-amino-3-benzoylthiophene derivative PD 81,723 potentiates the A1 receptor-mediated negative dromotropic effect of exogenous adenosine and adenosine receptor agonists in guinea pig isolated perfused and in situ hearts. The objective of this study was to determine whether PD 81,723 could amplify the cardiac actions of endogenous adenosine. Two approaches known to increase the myocardial interstitial concentration of adenosine--hypoxia, which increases the production of adenosine and the inhibition of adenosine kinase, which decreases its metabolism--were used to test this hypothesis. In guinea pig hearts in situ, PD 81,723 (2 mg/kg i.v.) potentiated the atrioventricular (AV) nodal conduction delay caused by hypoxemia (PaO2, 14 to 19 mm Hg). In guinea pig isolated hearts, PD 81,723 (5 mumol/L) increased by twofold the stimulus-to-His bundle (S-H) interval prolongations induced by both a 5-minute period of hypoxia (25% O2/70% N2/5% CO2) and the administration of the adenosine kinase inhibitor iodotubercidin (40 to 70 nmol/L) but had no effect on coronary conductance. Hypoxia and hypoxia plus PD 81,723 (5 mumol/L) caused equivalent increases in the concentration of adenosine in epicardial transudate, from 0.13 +/- 0.15 to 0.48 +/- 0.1 and 0.45 +/- 0.4 mumol/L, respectively. Similar to the allosteric enhancer, the nucleoside uptake blocker draflazine (0.1 mumol/L) also increased by twofold the S-H interval prolongation caused by hypoxia. In contrast to the allosteric enhancer, draflazine increased the concentration of adenosine in epicardial transudate during hypoxia from 0.48 +/- 0.15 to 1.5 +/- 0.4 mumol/L. Draflazine also increased coronary conductance by approximately twofold in guinea pig normoxic constant-fold perfused hearts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dose-dependent effects of adenosine on interstitial fluid adenosine and postischemic function in the isolated rat heart

Exogenous adenosine produces numerous beneficial effects in ischemic myocardium, but pharmacological doses of adenosine are required to exert these effects. This is thought to be due to the rapid metabolism of adenosine by coronary endothelium, although there is no direct evidence supporting this hypothesis in the ischemic/reperfused heart. The purpose of this study was to determine the relationship between vascular and interstitial fluid (ISF) adenosine levels during adenosine-induced cardioprotection. Isolated perfused rat hearts were submitted to 30-min global normothermic ischemia and 30- min reperfusion. Left ventricular developed pressure (LVDP) was measured with a fluid-filled latex balloon, and ISF adenosine was estimated with cardiac microdialysis. Control hearts were compared with hearts treated with increasing doses of adenosine (1, 10 and 100 microM) for 10 min immediately preceding ischemia. Adenosine produced dose-dependent increases in coronary effluent adenosine levels, but only 10 and 100 microM adenosine increased dialysate adenosine concentrations. All adenosine doses increased coronary flow to the same extent, but only the two higher doses decreased spontaneous heart rate. Control and 1 microM adenosine-treated hearts recovered 60 +/- 3% and 46 +/- 7% of preischemic LVDP, respectively, whereas 10 and 100 microM adenosine improved recovery to 80 +/- 5% and 90 +/- 4% of preischemic LVDP, respectively, after 30-min reperfusion. Because ISF bathes the cardiac myocytes, these results are consistent with the hypothesis that adenosine protects the ischemic rat heart via the activation of cardiac myocyte adenosine receptors.     

Interaction of heart rate and hypothermia on global myocardial contraction of the isolated rabbit heart

We studied the effects of mild hypothermia on cardiac contractility in isolated rabbit hearts perfused with Krebs-Henseleit solution according to the technique of Langendorff. Isovolumetric left ventricular pressure (LVP) was measured with a fluid-filled balloon. Hearts were paced after induction of atrioventricular block. At low heart rates ( < 30 bpm) mild hypothermia (cooling to 30 degrees C) induced a 32% increase in LVp (146.5 +/- 10 mm Hg at 30 degrees C vs 110.7 +/- 13 mm Hg at 37 degrees C) but this positive inotropic response was progressively lost by increasing heart rate. At pacing rates > or = 90 bpm, lower systolic LVP, higher diastolic LVP, and lower positive and negative LV dP/dt were obtained in hypothermic (93 +/- 12 mm Hg, 55 +/- 18 mm Hg, 584 +/- 137 mm Hg/s, and 323 +/- 57 mm Hg/s at 210 bpm, respectively) compared to normothermic hearts (123 +/- 4 mm Hg, 10 +/- 4 mm Hg, 1705 +/- 145.5 mm Hg/s, and 1155 +/- 78 mm Hg/s at 210 bpm, respectively.) The duration of mechanical diastole was reduced or suppressed in these hearts. Exposure to the beta-adrenoreceptor agonist, isoproterenol, improved this diastolic dysfunction during hypothermia and pacing at high rates, suggesting that the sarcoplasmic reticulum Ca2+ uptake might be involved. Our data are also consistent with an increase in myofilament Ca2+ sensitivity that is opposed by isoproterenol during hypothermia.     

Effect of pinacidil on rat hearts undergoing hypothermic cardioplegia

We studied the effect of pinacidil, a potassium-channel opener, on the hemodynamic, biochemical, and ultrastructural changes in rat hearts undergoing hypothermic cardioplegia. Fifty-four male Wistar rats weighing 250 to 300 g were used. Isolated hearts were prepared for modified Langendorff circulation in the working mode using modified Krebs-Henseleit bicarbonate solution bubbled with a 95% O2 and 5% CO2 gas mixture. Eighty minutes of cardioplegia at 25 degrees C was followed by normothermic reperfusion for 30 minutes. Pinacidil, 5, 10, or 50 mumol/L added to the cardioplegic solution, did not affect heart rate, but is significantly improved the recovery of aortic flow as compared with controls (88.1% +/- 4.3 [5 mumol/L]; 83.2% +/- 8.5% [10 mumol/L]; 90.3% +/- 5.3% [50 mumol/L] compared with 55.6 +/- 4.3% [control]; p < 0.05). Administration of pinacidil during reperfusion did not further enhance the recovery of aortic flow. The dose-response curve of aortic flow to the pinacidil concentrations was flat from 5 to 50 mumol/L. However, preservation of myocardial adenosine triphosphate and calcium concentrations and mitochondrial morphology suggested that the optimal concentration of pinacidil cardioplegia is 10 mumol/L.     

Preconditioning of rat heart with monophosphoryl lipid A: a role for nitric oxide

Preconditioning with monophosphoryl lipid A (MLA) protects rabbit hearts from prolonged ischemic reperfusion injury by a mechanism involving inducible nitric oxide synthase (iNOS) activation. This study was undertaken to determine whether MLA also could precondition rat hearts in a similar manner. Rats were injected with two different doses of MLA (300 microg/kg or 450 microg/kg i.v.) or vehicle (control), and after 24 hr the animals were sacrificed for preparation of isolated perfused rat hearts. Hearts were then perfused by working mode, and then made ischemic for 30 min followed by 30 min of reperfusion. Another group of hearts were treated simultaneously with a nitric oxide (NO) blocker, L-nitro-arginine-methyl-ester (L-NAME) (10 mg/kg) and MLA (450 microg/kg). For arrhythmia studies, 12 hearts were used in each group (total, 48 hearts). Cardiac functions were examined in a separate group of 24 hearts (n = 6/group). MLA-treated hearts (either dose) were tolerant to ischemic reperfusion injury as evidenced by improved postischemic ventricular recovery [coronary flow (ml/min) 19.1 +/- 0.8 (300 microg/kg MLA), 22.6 +/- 1.0 (450 microg/kg MLA) vs. 15.9 +/- 0.7 (control); aortic flow (ml/min) 20.7 +/- 1.8 (300 microg/kg MLA), 25.8 +/- 1.4 (450 microg/kg MLA) vs. 11. 0 +/- 0.8 (control); left ventricular developed pressure (kPa) 13.3 +/- 0.6 (300 microg/kg MLA), 14.6 +/- 0.2 (450 microg/kg MLA) vs. 10. 3 +/- 0.7 (control)]. Incidences of ventricular fibrillation and ventricular tachycardia were decreased compared with the control group only in the 450 microg/kg dose of MLA-treated hearts (92% to 33%). Pretreatment of the hearts with L-NAME inhibited the preconditioning effect of MLA. To examine the induction of the iNOS expression, RNAs were extracted from the control and MLA-treated hearts (after 2, 4,6, 8, 12 and 24 hr of treatment) and Northern blot analyses were performed with a specific cDNA probe for iNOS. A single band of approximately 4.6 kb corresponding to iNOS mRNA was detected after 4 hr of MLA treatment, whereas the maximal iNOS expression was found between 6 and 8 hr of MLA treatment. The results of this study demonstrated that MLA induced the expression of iNOS and protected the myocardium from ischemic reperfusion injury which is blocked by an inhibitor of NO synthesis, which suggests a role of NO in MLA-mediated cardioprotection.     

Frequency-dependence of myocardial energetics in failing human myocardium as quantified by a new method for the measurement of oxygen consumption in muscle strip preparations

Diastolic dysfunction at high heart rates may be associated with increased myocardial energy consumption. Frequency-dependent changes of isometric force and oxygen consumption (MVO2) were investigated in strip preparations from endstage failing human hearts exhibiting various degrees of diastolic dysfunction. MVO2 was determined by a new method which was validated. When stimulation rate was increased from 40 to 200 min-1 (n=7), developed force decreased from 16.5+/-4.3 to 7.9+/-2.9 mN/mm2 (P<0.01), diastolic force increased from 15.9+/-3.2 to 22.0+/-3.0 mN/mm2 (P<0.01), and total MVO2 increased from 2.6+/-0.6 to 4.7+/-0.9 ml/min/100 g (P<0.025). Resting MVO2 and resting force were 1.8+/-0.4 ml/min/100 g and 15.9+/-3.0 mN/mm2, respectively. After addition of 30 mm 2,3-butanedione monoxime (BDM) to inhibit crossbridges, resting MVO2 and resting force decreased by 46% (P<0.05) and 15% (P<0.01), respectively, indicating the presence of active force generation in unstimulated failing human myocardium. In each muscle preparation, there was a significant correlation between force-time integral (FTI) and total MVO2 (r=0.96+/-0.01). The strength of these correlations did not vary with the contribution of diastolic FTI to total FTI. The ratio of activity related MVO2 to developed FTI, an inverse index of the economy of contraction, increased depending on the rise of diastolic FTI at higher stimulation rates. In conclusion, in failing human myocardium, diastolic force development is occurring at the same energy expenditure as systolic force generation. Therefore, in muscle preparations with disturbed diastolic function economy of contraction decreases with higher stimulation rates, depending on the rise of diastolic force.     

Ischemic preconditioning in the aged heart--myocardial protective effect as compared with the mature heart

It is now well established that pre-treatment with sublethal ischemia, followed by reperfusion, will delay myocardial necrosis during a later sustained ischemic episode, termed ischemic preconditioning (IPC); this has been confirmed experimentally and clinically. However, the effects for the senescent heart differ from those of the mature heart at both functional and cellular levels which have not yet been determined. Comparisons were made between aged (> 135 weeks, n = 18) and mature (15 approximately 20 weeks, n = 8) rabbit hearts which underwent 30 min. normothermic global ischemia with 120 min reperfusion in a buffer-perfused isolated, paced heart model, and the effects of IPC on post-ischemic functional recovery and infarct size were investigated. Ischemic preconditioned hearts (n = 6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. Global ischemic hearts (n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n = 6) were subjected to perfusion without ischemia. Post-ischemic functional recovery was better in the ischemic preconditioned hearts than in the global ischemic hearts in both aged and mature hearts. However, in the aged hearts, post-ischemic functional recovery was slightly reduced compared to that of the mature hearts, and only the coronary flow was well-preserved. In the mature hearts, myocardial infarction in the ischemic preconditioned hearts (14.9 +/- 1.3%) and in the control hearts (1.0 +/- 0.3%) was significantly decreased (p < 0.01) compared to that of the global ischemic hearts (32.9 +/- 5.1%). In the aged hearts, myocardial infarction in the ischemic preconditioned hearts (18.9 +/- 2.7%) and in the control hearts (1.1 +/- 0.6%) was significantly decreased (p < 0.001) compared to that of the global ischemic hearts (37.6 +/- 3.7%). The relationship between infarct size and post-ischemic functional recovery of left ventricularpeak developed pressure (LVDP) was linear and the correlation negative, with r = -0.934 (p < 0.001) and -0.875 (p < 0.001) for mature and aged hearts respectively. The data suggest that, in the senescent myocardium, the cellular pathways involved ischemic preconditioning responses that were post-ischemic, and that functional recovery was worse as compared to that of the mature myocardium. Furthermore, the effects of post-ischemic functional recovery became consistently weaker during the control period of 120 min. reperfusion after a prolonged ischemic insult in a buffer perfused isolated rabbit model. However, the effects of infarct size limitation were well-preserved in both senescent and mature myocardia.     

Dichotomy of ischemic preconditioning: improved postischemic contractile function despite intensification of ischemic contracture

BACKGROUND: Acceleration of ischemic contracture is conventionally accepted as a predictor of poor postischemic function. Hence, protective interventions such as cardioplegia delay ischemic contracture and improve postischemic contractile recovery. We compared the effect of ischemic preconditioning and cardioplegia (alone and in combination) on ischemic contracture and postischemic contractile recovery. METHODS AND RESULTS: Isolated rat hearts were aerobically perfused with blood for 20 minutes before being subjected to zero-flow normothermic global ischemia for 35 minutes and reperfusion for 40 minutes. Hearts were perfused at a constant pressure for 60 mm Hg and were paced at 360 beats per minute. Left ventricular developed pressure and ischemic contracture were assessed with an intraventricular balloon. Four groups (n=8 hearts per group) were studied: control hearts with 35 minutes of unprotected ischemia, hearts preconditioned with one cycle of 3 minutes of ischemia plus 3 minutes of reperfusion before 35 minutes of ischemia, hearts subjected to cardioplegia with St Thomas' solution infused for 1 minute before 35 minutes of ischemia, and hearts subjected to preconditioning plus cardioplegia before 35 minutes of ischemia. After 40 minutes of reperfusion, each intervention produced a similar improvement in postischemic left ventricular development pressure (expressed as a percentage of its preischemic value: preconditioning, 44 +/- 2%; cardioplegia, 53 +/- 3%; preconditioning plus cardioplegia, 54 +/- 4% and control, 26 +/- 6%, P<.05). However, preconditioning accelerated whereas cardioplegia delayed ischemic contracture; preconditioning plus cardioplegia gave an intermediate result. Thus, times to 75% contracture were as follows: control, 14.3 +/- 0.4 minutes; preconditioning, 6.2 +/- 0.3 minutes; cardioplegia 23.9 +/- 0.8 minutes; and preconditioning plus cardioplegia 15.4 +/- 2.4 minutes (P<.05 preconditioning and cardioplegia versus control). In additional experiments, using blood- and crystalloid-perfused hearts, we describe the relationship between the number of preconditioning cycles and ischemic contracture. CONCLUSIONS: Although preconditioning accelerates, cardioplegia delays, and preconditioning plus cardioplegia has little effect on ischemic contracture, each affords similar protection of postischemic contractile function. These results question the utility of ischemic contracture as a predictor of the protective efficacy of anti-ischemic interventions. They also suggest that preconditioning and cardioplegia may act through very different mechanisms.     

Medical and health impact of complex emergencies: implications for the International Society of Nephrology Disaster Relief Task Force

The aim of the present study was to measure whole body glucose uptake (M) and oxidation rate by euglycaemic hyperinsulinaemic clamp and indirect calorimetry in 7 morbidly obese subjects (BMI > 40 kg/m2) at three time points: before bilio-pancreatic diversion (BPD) surgery (Ob); 3 months after surgery POI; and after reaching stable body weight, at least 2 years after surgery POII. A group of 7 control subjects (C), matched groupwise for sex, age and BMI with POII patients, was also studied. The M value at POI was significantly higher than at Ob (49.12 +/- 8.57 vs 18.14 +/- 8.57 mumol.kg-1.min-1). No statistical difference was observed between the POII and C groups. Similarly, glucose oxidation rate was significantly increased at POI with respect to Ob (24.2 +/- 7.23 vs 9.42 +/- 3.91 mumol.kg-1.min-1) and was not significantly different between POII and C. Basal levels of non-esterified fatty acids (NEFA) decreased significantly both from Ob to POI and from POI to POII (1517.1 +/- 223.9 vs 1039.6 +/- 283.4 vs 616.0 +/- 77.6 mumol.1(-1). The same applied to basal plasma triglycerides (2.07 +/- 0.77 vs 1.36 +/- 0.49 vs 0.80 +/- 0.19 g.1(-1). Weight decreased mainly in the late postoperative period (POI to POII 124.28 +/- 11.22 to 69.71 +/- 11.78, 83% of total decrement), rather than in the early postoperative period (Ob to POI 135.25 +/- 14.99 to 124.28 +/- 11.22 kg, 17% of total decrement). We also report the clinical case of a young woman of normal weight, who underwent BPD for chylomicronaemia (secondary to familial lipoprotein lipase deficiency), whose M value, plasma insulin and blood glucose levels were normalized upon normalization of serum NEFA and triglyceride levels as determined by the therapeutic lipid malabsorption. In conclusion, in obese diabetic patients lipid malabsorption induced by BPD causes a definite enhancement of insulin sensitivity and glucose tolerance. This improvement in metabolism is noticeable before the surgery has major effects on body weight. These observations suggest that lowered plasma lipids, rather than weight loss per se, are the cause of the reversibility of insulin resistance.