Heterogeneity of local myocardial flow and oxidative metabolism

In mammalian hearts, local myocardial flow (LMF) varies between 20 and 200% of the mean. It is not clear whether oxidative metabolism has a similar degree of heterogeneity. Therefore, we investigated the relation between LMF and local oxidative metabolism in isolated rabbit hearts. Buffer oxygenation with (18)O(2) resulted in labeled myocardial oxidation water (H(2)(18)O). In four hearts, myocardial oxygen consumption (MVO(2)) was calculated from the H(2)(18)O production and compared with that calculated according to Fick. In eight additional hearts, LMF was measured using microspheres. Coronary venous H(2)(18)O kinetics and local H(2)(18)O residues were determined and analyzed by mathematical modeling. MVO(2) recovery from H(2)(18)O was >93% compared with that according to Fick. LMF ranged from 1.91 to 11.24 ml. min(-1). g(-1), and local H(2)(18)O residue ranged from 0.41 to 1.04 micromol/g. Both variables correlated (r = 0.62, n = 64, P < 0.001). Measurements in nine hearts were fitted by modeling using capillary permeability-surface area products (PS(c)) from 2 to 10 ml. min(-1). g(-1). With flow-proportional PS(c), a 3.33-fold difference in LMF was associated with a 6.45-fold difference in local MVO(2). Both LMF and local oxidative metabolism are spatially heterogeneous, and they correlate to one another.     

Tempol reduces infarct size in rodent models of regional myocardial ischemia and reperfusion.

Reactive oxygen species (ROS) contribute to ischemia-reperfusion injury of the heart. This study investigates the effects of tempol, a membrane-permeable radical scavenger on (i) the infarct size caused by regional myocardial ischemia and reperfusion of the heart in vivo (rat, rabbit) and in vitro (rat), and (ii) the cell injury caused by hydrogen peroxide (H2O2) in rat cardiac myoblasts (H9c2 cells). In the anesthetized rat, tempol reduced the infarct size caused by regional myocardial ischemia (25 min) and reperfusion (2 h) from 60 +/- 3% (control, n = 8) to 24 +/- 5% (n = 6, p < .05). In the anesthetized rabbit, tempol also attenuated the infarct size caused by myocardial ischemia (45 min) and reperfusion (2 h) from 59 +/- 3% (control, n = 6) to 39 +/- 5% (n = 5, p < .05). Regional ischemia (35 min) and reperfusion (2 h) of the isolated, buffer-perfused heart of the rat resulted in an infarct size of 54 +/- 4% (control n = 7). Reperfusion of hearts with buffer containing tempol (n = 6) caused a 37% reduction in infarct size (n = 6, p < .05). Pretreatment of rat cardiac myoblasts with tempol attenuated the impairment in mitochondrial respiration caused by H2O2 (1 mM for 4 h). Thus, the membrane-permeable radical scavenger tempol reduces myocardial infarct size in rodents.     

Age-related resistance to skeletal muscle fatigue is preserved during ischemia.

During voluntary contractions, the skeletal muscle of healthy older adults often fatigues less than that of young adults, a result that has been explained by relatively greater reliance on muscle oxidative metabolism in the elderly. Our aim was to investigate whether this age-related fatigue resistance was eliminated when oxidative metabolism was minimized via ischemia induced by cuff (220 mmHg). We hypothesized that 1) older men (n = 12) would fatigue less than young men (n = 12) during free-flow (FF) contractions; 2) both groups would fatigue similarly during ischemia; and 3) reperfusion would reestablish the fatigue resistance of the old. Subjects performed 6 min of intermittent, maximal voluntary isometric contractions of the ankle dorsiflexors under FF and ischemia-reperfusion (IR) conditions. Ischemia was maintained for the first 3 min of contractions, followed by rapid cuff deflation and reperfusion for 3 additional minutes of contractions. Central activation, peripheral activation, and muscle contractile properties were measured at 3 and 6 min of contractions. Older men fatigued less than young men during FF (P 相似文献   

O2 delivery and redox state are determinants of compartment-specific reactive O2 species in myocardial reperfusion

Reperfusion of the ischemic myocardium leads to a burst of reactive O(2) species (ROS), which is a primary determinant of postischemic myocardial dysfunction. We tested the hypothesis that early O(2) delivery and the cellular redox state modulate the initial myocardial ROS production at reperfusion. Isolated buffer-perfused rat hearts were loaded with the fluorophores dihydrofluorescein or Amplex red to detect intracellular and extracellular ROS formation using surface fluorometry at the left ventricular wall. Hearts were made globally ischemic for 20 min and then reperfused with either 95% or 20% O(2)-saturated perfusate. The same protocol was repeated in hearts loaded with dihydrofluorescein and perfused with either 20 or 5 mM glucose-buffered solution to determine relative changes in NADH and FAD. Myocardial O(2) delivery during the first 5 min of reperfusion was 84.7 +/- 4.2 ml O(2)/min with 20% O(2)-saturated buffer and 354.4 +/- 22.8 ml O(2)/min with 95% O(2) (n = 8/group, P < 0.001). The fluorescein signal (intracellular ROS) was significantly increased in hearts reperfused with 95% O(2) compared with 20% O(2). However, the resorufin signal (extracellular ROS) was significantly increased with 20% O(2) compared with 95% O(2) during reperfusion. Perfusion of hearts with 20 mM glucose reduced the (.)NADH during ischemia (P < 0.001) and the (.)ROS at reperfusion (P < 0.001) compared with 5.5 mM-perfused glucose hearts. In conclusion, initial O(2) delivery to the ischemic myocardium modulates a compartment-specific ROS response at reperfusion such that high O(2) delivery promotes intracellular ROS and low O(2) delivery promotes extracellular ROS. The redox state that develops during ischemia appears to be an important precursor for reperfusion ROS production.     

Platelets activated by transient coronary occlusion exacerbate ischemia-reperfusion injury in rat hearts

Platelets (Plt) accumulate in reperfused myocardium but their effect on myocardial necrosis has not been established. We tested the hypothesis that the effect of Plt depends on their activation status. Pig Plt were obtained before 48 min of coronary occlusion (pre-CO-Plt), 10 min after reperfusion (R-Plt), or after a 60-min sham operation (sham-Plt). Plt were infused into isolated rat hearts (n = 124) and subsequently submitted to 60 min of ischemia and 60 min of reperfusion. P-selectin expression was higher (P = 0.02) in R-Plt than in pre-CO-Plt or sham-Plt. Lactate dehydrogenase (LDH) release during reperfusion was similar in hearts receiving pre-CO-Plt, sham-Plt, or no Plt, but R-Plt increased LDH release by 60% (P = 0.004). Activation of pre-CO-Plt with thrombin increased P-selectin expression and LDH release (P < 0.001), and these results were unaffected by tirofiban. There was a close correlation between P-selectin expression and LDH release (r = 0.84; P < 0.001), and myocardial Plt accumulation (r = 0.85; P < 0.001). We conclude that the deleterious effect of Plt on reperfused myocardium depends on their activation status as represented by P-selectin expression, which is enhanced by ischemia-reperfusion.     

Ischemic preconditioning enhances scavenging activity of reactive oxygen species and diminishes transmural difference of infarct size

Reactive oxygen species (ROS) enhance myocardial ischemia-reperfusion (I/R) injury. Ischemic preconditioning (PC) provides potent cardioprotective effects in I/R. However, it has not been elucidated whether PC diminishes ROS stress in I/R and whether PC protects the myocardium from ROS stress transmurally and homogeneously. Isolated rabbit hearts perfused with Krebs-Henseleit buffer underwent 30 min of ischemia and 60 min of reperfusion. Hemodynamic changes and myocardial damage extent were analyzed in four groups. The control group underwent I/R alone. The H2O2 group underwent I/R with H2O2 infusion (50 microM) in the first minute of reperfusion to enhance oxidative stress. The PC and H2O2+PC groups underwent 5 min of PC before control and H2O2 protocols, respectively. Extracted myocardial DNA was analyzed for 8-hydroxydeoxyguanosine (8-OHdG), an indicator of oxidative DNA damage, with the use of the HPLC-electrochemical detection method. Glutathione peroxidase (GPX) activity and the reduced form of GSH were measured by spectrophotometric assays. The myocardial infarct size was significantly reduced in the PC group (19 +/- 2%) compared with the control group (37 +/- 4%; P < 0.05), particularly in the subendocardium. H2O2 transmurally increased the infarct size by 59 +/- 4% (P < 0.05), which was significantly diminished in the H2O2+PC group (31 +/- 4%; P < 0.01). The GSH levels, but not GPX activity, were well preserved transmurally in protocols with PC. The 8-OHdG levels were significantly decreased in PC and were significantly enhanced in H2O2 (P < 0.01). These changes in oxidative DNA damage were effectively diminished by PC. In conclusion, PC enhanced the scavenging activity of GSH against ROS transmurally, reduced myocardial damage, particularly in the subendocardium, and diminished the transmural difference in myocardial infarct size.     

A polymerized bovine hemoglobin oxygen carrier preserves regional myocardial function and reduces infarct size after acute myocardial ischemia

The purpose of this study was to test if HBOC-201, a hemoglobin-based oxygen-carrying solution, can decrease infarct size (or Inf) during acute, severe myocardial ischemia and reperfusion. To test the impact of HBOC-201 on infarct size, ischemia was produced in 18 dogs by coronary stenosis to achieve 80-95% flow reduction for 195 min along with pacing 10% above the spontaneous heart rate, followed by 180 min of reperfusion. Animals were randomized to intravenous infusion of HBOC-201 (1 g/kg) (n=6), normal saline (NS) (n=6), or phenylephrine (Phe) (n=6, as a control for the increased blood pressure seen with HBOC-201), given 15 min after the start of ischemia. Amount of infarct was quantified as the ratio between area at risk (AAR) and Inf after Evans blue and 2,3,5-triphenyltetrazolium chloride staining. Hearts were divided into five layers from base (layer A) to apex (layer E) and photographed for digital image analysis of AAR and Inf. Regional myocardial function (RMF) was also measured after 60 min of ischemia and 15 min of reperfusion. Inf/AAR was significantly reduced after HBOC-201 therapy (4.4+/-2.2%) vs. NS (26.0+/-3.6%) and Phe (25.7+/-4.1%) (both, P<0.05). RMF after reperfusion was restored to 92% of baseline with HBOC-201 compared with 11% of baseline after NS (P<0.05) and 49% after Phe (P=not significant). HBOC-201 administration after induction of severe myocardial ischemia by acute coronary stenosis reduces infarct size and improves myocardial viability.     

Hypoxic reperfusion of the ischemic heart and oxygen radical generation

Postischemic myocardial contractile dysfunction is in part mediated by the burst of reactive oxygen species (ROS), which occurs with the reintroduction of oxygen. We hypothesized that tissue oxygen tension modulates this ROS burst at reperfusion. After 20 min of global ischemia, isolated rat hearts were reperfused with temperature-controlled (37.4 degrees C) Krebs-Henseleit buffer saturated with one of three different O2 concentrations (95, 20, or 2%) for the first 5 min of reperfusion and then changed to 95% O2. Additional hearts were loaded with 1) allopurinol (1 mM), a xanthine oxidase inhibitor, 2) diphenyleneiodonium (DPI; 1 microM), an NAD(P)H oxidase inhibitor, or 3) Tiron (10 mM), a superoxide scavenger, and were then reperfused with either 95 or 2% O2 for the first 5 min. ROS production and tissue oxygen tension were quantitated using electron paramagnetic resonance spectroscopy. Tissue oxygen tension was significantly higher in the 95% O2 group. However, the largest radical burst occurred in the 2% O2 reperfusion group (P < 0.001). Recovery of left ventricular (LV) contractile function and aconitase activity during reperfusion were inversely related to the burst of radical production and were significantly higher in hearts initially reperfused with 95% O2 (P < 0.001). Allopurinol, DPI, and Tiron reduced the burst of radical formation in the 2% O2 reperfusion groups (P < 0.05). Hypoxic reperfusion generates an increased ROS burst originating from multiple pathways. Recovery of LV function during reperfusion is inversely related to this oxygen radical burst, highlighting the importance of myocardial oxygen tension during initial reperfusion.     

Glutathione disulfide as an index of oxidative stress during postischemic reperfusion in isolated rat hearts

The objectives of this study were to determine 1) whether reactive oxygen species generated upon postischemic reperfusion lead to oxidative stress in rat hearts, and 2) whether an exogenous prooxidant present in the early phase of reperfusion causes additional injury. Isolated buffer-perfused rat hearts were subjected to 30 min of hypothermic no-flow ischemia followed by 30 min of reperfusion. Increased myocardial content of glutathione disulfide (GSSG) and increased active transport of GSSG were used as indices of oxidative stress. To impose a prooxidant load, cumene hydroperoxide (20 M) was administered during the first 10 min of reperfusion to a separate group of postischemic hearts. Reperfusion after 30 min of hypothermic ischemia resulted in a recovery of myocardial ATP from 28% at end-ischemia to 50–60%, a release of 5% of total myocardial LDH, and an almost complete recovery of both coronary flow rate and left ventricular developed pressure. After 5 and 30 min of reperfusion, neither myocardial content of GSSG nor active transport of GSSG were increased. These indices were increased, however, if cumene hydroperoxide was administered during early reperfusion. After stopping the administration of cumene hydroperoxide, myocardial GSSG content returned to control values and GSH content increased, indicating an unimpaired glutathione reductase reaction. Despite the induction of oxidative stress, reperfusion with cumene hydroperoxide did not cause additional metabolic, structural, or functional injury when compared to reperfusion without cumene hydroperoxide. We conclude that reactive oxygen species generated upon postischemic reperfusion did not lead to oxidative stress in isolated rat hearts. Moreover, even a superimposed prooxidant load during early reperfusion did not cause additional injury.     

Relation between energy metabolism,glycolysis, noradrenaline release and duration of ischemia

We studied the effect of 12–36 min of global ischemia followed by 36 min of reperfusion in Langendorff perfused rabbit hearts (n = 26). Metabolism was determined in terms of peak and total release of purines (adenosine, inosine, hypoxanthine), lactate and noradrenaline during reperfusion; and myocardial content of nucleotides (ATP, ADP, AMP), glycogen and noradrenaline at the end of reperfusion. An inverse relationship (r = –0.79) existed between duration of ischemia and developed pressure post-ischemia. Early during reperfusion, after 12 min of ischemia, the purine concentration (peak release) increased 100x (p < 0.01), that of lactate and noradrenaline lOx (p < 0.05) . Total purine release rose with progression of the ischemic period (30x after 36 min of ischemia; p < 0.01), concomitant with a reduction in nucleotide content. Lactate release was independent from the duration of ischemia, although glycogen had declined by 30% (p < 0.01) after 36 min of ischemia. The acid insoluble glycogen fraction, which presumably contains proglycogen, increased substantially during short-term ischemia. Peak noradrenaline increased 100x and 200x (p < 0.05) after 24 and 36 min of ischemia, respectively. Total noradrenaline release due to various periods of ischemia mirrored its peak release. Function recovery was inversely related to total purine and noradrenaline efflux (both r =–0.81); it correlated with tissue nucleotide content (r = 0.84). In conclusion, larger amounts of noradrenaline are released only after a substantial drop in myocardial ATP. During severe ischemia ATP consumption more than limited ATP production by anaerobic glycolysis, is a key factor affecting recovery on subsequent reperfusion. In contrast to lactate efflux, purine and noradrenaline release are useful markers of ischemic and reperfusion damage.     

Ischemic defects in the electron transport chain increase the production of reactive oxygen species from isolated rat heart mitochondria

Cardiac ischemia decreases complex III activity, cytochrome c content, and respiration through cytochrome oxidase in subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The reversible blockade of electron transport with amobarbital during ischemia protects mitochondrial respiration and decreases myocardial injury during reperfusion. These findings support that mitochondrial damage occurs during ischemia and contributes to myocardial injury during reperfusion. The current study addressed whether ischemic damage to the electron transport chain (ETC) increased the net production of reactive oxygen species (ROS) from mitochondria. SSM and IFM were isolated from 6-mo-old Fisher 344 rat hearts following 25 min global ischemia or following 40 min of perfusion alone as controls. H(2)O(2) release from SSM and IFM was measured using the amplex red assay. With glutamate as a complex I substrate, the net production of H(2)O(2) was increased by 178 +/- 14% and 179 +/- 17% in SSM and IFM (n = 9), respectively, following ischemia compared with controls (n = 8). With succinate as substrate in the presence of rotenone, H(2)O(2) increased by 272 +/- 22% and 171 +/- 21% in SSM and IFM, respectively, after ischemia. Inhibitors of electron transport were used to assess maximal ROS production. Inhibition of complex I with rotenone increased H(2)O(2) production by 179 +/- 24% and 155 +/- 14% in SSM and IFM, respectively, following ischemia. Ischemia also increased the antimycin A-stimulated production of H(2)O(2) from complex III. Thus ischemic damage to the ETC increased both the capacity and the net production of H(2)O(2) from complex I and complex III and sets the stage for an increase in ROS production during reperfusion as a mechanism of cardiac injury.     

TNF-alpha antibodies are as effective as ischemic preconditioning in reducing infarct size in rabbits

Pretreatment with tumor necrosis factor-alpha (TNF-alpha) antibodies abolishes myocardial infarct size reduction by late ischemic preconditioning (IP). Whether or not TNF-alpha is also important for myocardial infarct size reduction by classic IP is unknown. Anesthetized rabbits were untreated (group 1, n = 7), classically preconditioned by 5 min left coronary artery occlusion/10 min reperfusion (group 2, n = 6), or pretreated with TNF-alpha antibodies without (group 3, n = 6) or with IP (group 4, n = 6) before undergoing 30 min of occlusion and 180 min of reperfusion. Infarct size in group 1 was 44 +/- 11 (means +/- SD)% of the area at risk. With a comparable area at risk, infarct size was reduced to 13 +/- 7%, 23 +/- 8%, and 19 +/- 12% (all P < 0.05) in groups 2, 3, and 4, respectively. The circulating TNF-alpha concentration was increased during ischemia in group 1 from 752 +/- 403 to 1,542 +/- 482 U/ml (P < 0.05) but remained unchanged in all other groups. Circulating TNF-alpha concentration during ischemia and infarct size correlated in all groups (r = 0.76). IP, TNF-alpha antibodies, and the combined approach reduced infarct size to a comparable extent. Therefore, the question of whether or not TNF-alpha is causally involved in the infarct size reduction by IP in rabbits could not be answered.     

Myocardial fatty acid oxidation during ischemia and reperfusion

Inhibition of fatty acid oxidation is an early event in myocardial ischemia that most likely contributes to tissue injury by the accumulation of potentially toxic intermediates such as acylCoA and acylcarnitine. After reperfusion both myocardial oxygen consumption and fatty acid oxidation may rapidly recover to preischemic levels, even when contractile function remains depressed. The mechanisms underlying the apparent dissociation between contractile function and oxidative metabolism early during reperfusion are still controversial. In isolated rat hearts subjected to 60 min of no-flow ischemia myocardial oxygen consumption and oxidation of palmitate were lowered during reperfusion by 3 mM of NiCl₂ and by 6 µM of ruthenium red. The results provide indirect evidence for the hypothesis that intracellular calcium transport may be involved in the mechanisms responsible for the high oxidative metabolic rate early after reperfusion     

Myeloperoxidase enhances nitric oxide catabolism during myocardial ischemia and reperfusion

Impaired microvascular function during myocardial ischemia and reperfusion is associated with recruitment of polymorphonuclear neutrophils (PMN) and has been attributed to decreased bioavailability of nitric oxide (NO). Whereas myeloperoxidase (MPO), a highly abundant, PMN-derived heme protein facilitates oxidative NO consumption and impairs vascular function in animal models of acute inflammation, its capacity to function in this regard during human myocardial ischemia and reperfusion remains unknown. Plasma samples from 30 consecutive patients (61 +/- 14 years, 80% male) presenting with acute myocardial infarction were collected 9 +/- 4 h after vessel recanalization and compared to plasma from healthy control subjects (n = 12). Plasma levels of MPO were higher in patients than in control subjects (1.4 +/- 0.9 vs 0.3 +/- 0.2 ng/mg protein, respectively, p < 0.0001). The addition of hydrogen peroxide to patient plasma resulted in accelerated rates of NO consumption compared to control subjects (0.53 +/- 0.25 vs 0.068 +/- 0.039 nM/s/mg protein, respectively, p < 0.0001). Myocardial tissue from patients with the same pathology revealed intense recruitment of MPO-positive PMN localized along infarct-related vessels as well as diffuse endothelial distribution of non-PMN-associated MPO immunoreactivity. Endothelium-dependent microvascular function, as assessed by an acetylcholine-dependent increase in forearm blood flow in 75 patients with symptomatic coronary artery disease, inversely correlated with MPO plasma levels (r = -0.75, p < 0.005). Plasma from patients undergoing myocardial reperfusion contained increased levels of MPO, which catalytically consumed NO in the presence of H(2)O(2). Given the correlation between intravascular MPO levels and forearm vasomotor function in patients with coronary artery disease, MPO appears to be an important modulator of vasomotor function in inflammatory vascular disease and a potential therapeutic target for treatment.     

Exercise training impacts the myocardial metabolism of older individuals in a gender-specific manner

Aging is associated with decreases in aerobic capacity, cardiac function, and insulin sensitivity as well as alterations in myocardial substrate metabolism. Endurance exercise training (EET) improves cardiac function in a gender-specific manner, and EET has been shown to improve whole body glucose tolerance, but its effects on myocardial metabolism are unclear. Accordingly, we studied the effect of EET on myocardial substrate metabolism in older men and women. Twelve healthy older individuals (age: 60-75 yr; 6 men and 6 women) underwent PET with [(15)O]water, [(11)C]acetate, [(11)C]glucose, and [(11)C]palmitate for the assessment of myocardial blood flow (MBF), myocardial O(2) consumption (MVo(2)), myocardial glucose utilization (MGU), and myocardial fatty acid utilization (MFAU), respectively, at rest and during dobutamine infusion (10 microg.kg(-1).min(-1)). Measurements were repeated after 11 mo of EET. Maximal O(2) uptake (Vo(2max)) increased (P = 0.005) after EET. MBF was unaffected by training, as was resting MVo(2); however, posttraining dobutamine MVo(2) was significantly higher (P = 0.05), as was MGU (P < 0.04). Although overall dobutamine MFAU was unchanged, posttraining dobutamine MFAU increased in women (P = 0.01) but decreased in men (P = 0.03). Thus, EET in older individuals improves the catecholamine response of myocardial glucose metabolism. Moreover, gender differences exist in the myocardial fatty acid metabolic response to training. These findings suggest a role for altered myocardial substrate metabolism in modulating the cardiovascular benefits of EET in older individuals.     

The effect of superoxide dismutase in the myocardium during reperfusion in the dog.

The aim of the study was to investigate the pathological role of free radicals during myocardial reperfusion. Low (0.5 mg/kg body weight) and high doses (5 mg/kg) of superoxide dismutase (SOD) were infused into the left atrium of mongrel dogs for 4 min starting 29 min after ligation and 1 min before reperfusion of the left anterior descending coronary artery (LAD). Arterial blood pressure, heart rate, electrocardiogram, and the regional contractile force of the left ventricle were monitored throughout the ligation (30 min) and reperfusion periods (20 min). Concentrations of creatine kinase (CK) and malondialdehyde (MDA) in the coronary sinus blood were determined before (0 min) and during ligation (15 and 25 min) and during reperfusion of the LAD (2, 7, and 20 min). In other groups of dogs, the effect of the two doses of SOD on epicardial blood flow was investigated during ligation and reperfusion by the measurement of epicardial temperature using a thermocardiograph. Experimental subjects were mongrel dogs of either sex (n = 25), weight 10-35 kg. Compared to controls (mean +/- SEM, 43.1 +/- 1.2; n = 7), the number of ventricular extrasystoles during the first 5 min of reperfusion was significantly (p < .001) decreased in dogs treated with the high dose (15.01 +/- 2.14; n = 5), but not in those receiving the low dose of the drug (34.6 +/- 5.66; n = 5). The concentrations of CK increased gradually until the end of reperfusion without differences among the different groups. Plasma MDA was the highest in control dogs 7 min after reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

The intermediary metabolite pyruvate attenuates stunning and reduces infarct size in in vivo porcine myocardium

The intermediary metabolite pyruvate has been shown to exert significant beneficial effects in in vitro models of myocardial oxidative stress and ischemia-reperfusion injury. However, there have been few reports of the ability of pyruvate to attenuate myocardial stunning or reduce infarct size in vivo. This study tested whether supraphysiological levels of pyruvate protect against reversible and irreversible in vivo myocardial ischemia-reperfusion injury. Anesthetized, open-chest pigs (n = 7/group) underwent 15 min of left anterior descending coronary artery (LAD) occlusion and 3 h of reperfusion to induce stunning. Load-insensitive contractility measurements of regional preload recruitable stroke work (PRSW) and PRSW area (PRSWA) were generated. Vehicle or pyruvate (100 mg/kg i.v. bolus + 10 mg x kg(-1) x min(-1) intra-atrial infusion) was administered during ischemia and for the first hour of reperfusion. In infarct studies, pigs (n = 6/group) underwent 1 h of LAD ischemia and 3 h of reperfusion. Group I pigs received vehicle or pyruvate for 30 min before and throughout ischemia. In group II, the infusion was extended through 1 h of reperfusion. In the stunning protocol, pyruvate significantly improved the recovery of PRSWA at 1 h (50 +/- 4% vs. 23 +/- 3% in controls) and 3 h (69 +/- 5% vs. 39 +/- 3% in controls) reperfusion. Control pigs exhibited infarct sizes of 66 +/- 1% of the area at risk. The pyruvate I protocol was associated with an infarct size of 49 +/- 3% (P < 0.05), whereas the pyruvate II protocol was associated with an infarct size of 30 +/- 2% (P < 0.05 vs. control and pyruvate I). These findings suggest that pyruvate attenuates stunning and decreases myocardial infarction in vivo in part by reduction of reperfusion injury. Metabolic interventions such as pyruvate should be considered when designing the optimal therapeutic strategies for limiting myocardial ischemia-reperfusion injury.     

Protective effect of lung inflation in reperfusion-induced lung microvascular injury

We used the isolated-perfused rat lung model to study the influence of pulmonary ventilation and surfactant instillation on the development of postreperfusion lung microvascular injury. We hypothesized that the state of lung inflation during ischemia contributes to the development of the injury during reperfusion. Pulmonary microvascular injury was assessed by continuously monitoring the wet lung weight and measuring the vessel wall (125)I-labeled albumin ((125)I-albumin) permeability-surface area product (PS). Sprague-Dawley rats (n = 24) were divided into one control group and five experimental groups (n = 4 rats per group). Control lungs were continuously ventilated with 20% O(2) and perfused for 120 min. All lung preparations were ventilated with 20% O(2) before the ischemia period and during the reperfusion period. The various groups differed only in the ventilatory gas mixtures used during the flow cessation: group I, ventilated with 20% O(2); group II, ventilated with 100% N(2); group III, lungs remained collapsed and unventilated; group IV, same as group III but pretreated with surfactant (4 ml/kg) instilled into the airway; and group V, same as group III but saline (4 ml/kg) was instilled into the airway. Control lungs remained isogravimetric with baseline (125)I-albumin PS value of 4.9 +/- 0.3 x 10(-3) ml x min(-1) x g wet lung wt(-1). Lung wet weight in group III increased by 1.45 +/- 0.35 g and albumin PS increased to 17.7 +/- 2.3 x 10(-3), indicating development of vascular injury during the reperfusion period. Lung wet weight and albumin PS did not increase in groups I and II, indicating that ventilation by either 20% O(2) or 100% N(2) prevented vascular injury. Pretreatment of collapsed lungs with surfactant before cessation of flow also prevented the vascular injury, whereas pretreatment with saline vehicle had no effect. These results indicate that the state of lung inflation during ischemia (irrespective of gas mixture used) and supplementation of surfactant prevent reperfusion-induced lung microvascular injury.     

Regional myocardial blood flow and glucose utilization during fasting and physiological hyperinsulinemia in humans

We investigated the effect of insulin on total and regional myocardial blood flow (MBF) and glucose uptake (MGU) in healthy subjects (50 +/- 5 yr) by means of positron emission tomography (PET) with oxygen-15-labeled water (H(2)(15)O) and fluorine-18 labeled fluorodeoxyglucose ((18)FDG) before and during physiological hyperinsulinemia (40 mU.min(-1).m(-2)). Twelve male subjects were included in the study. During hyperinsulinemia, MBF increased from 0.91 +/- 0.28 to 1.01 +/- 0.31 ml.min(-1).g(-1) (n = 7 patients, P = 0.05; n = 112 regions, P < 0.005). Intersubject variability ranged from -3.0 to +41%. MGU increased from 0.11 +/- 0.08 (n = 5) to 0.56 +/- 0.08 micromol.min(-1).g(-1) (P < 0.0001, n = 7). MBF and insulin-mediated MGU were higher in the septum and anterior and lateral wall along short-axis regions of the heart. During hyperinsulinemia, MBF was also higher in the apex and midventricle compared with the base. MBF and MGU were positively correlated before (r = 0.66, P < 0.0001) and during hyperinsulinemia (r = 0.24, P < 0.05). These results provide evidence that insulin stimulates MBF in normal human hearts and appears to involve mainly those regions of the heart where insulin-mediated MGU is higher. Furthermore, regional distribution of insulin-stimulated MBF and MGU does not appear to be uniform across the left ventricular wall of healthy subjects.