摘要:

Ischemia and reperfusion of the lower torso lead to leukotriene- and neutrophil (PMN)-dependent lung injury characterized by lung PMN sequestration, increased permeability, and noncardiogenic edema. It is thought that PMNs require adhesion to endothelium to alter barrier function. This study tests the role of CD 18, the PMN adherence receptor, in mediating lung permeabilily after lower torso ischemia and reperfusion. Anesthetized rabbits (n=9) underwent 3 hours of bilateral hind limb ischemia. Ten minutes after the release of the tourniquets, plasma leukotriene B4levels increased to 395±85 pglml, higher than 129±35 pg/ml in controls (n=9,p<0.01). At this time there was a reduction in circulating white blood cells (×103), 3.56±0.49/mm3relative to 6.07±0.61/mm3in controls (p<0.01). PMNs were sequestered in the hind limbs, indicated by increased myeloperoxidase activity of 1.06±0.19 units/g compared with 0.56±0.09 units/g in controls (p<0.05). Four hours after tourniquet release, PMNs were sequestered in the lungs, 52±4 PMNs per 10 high-power fields, a value higher than 31.5±3 PMNs per 10 high-power fields in controls; bronchoalveolar lavage fluid protein content increased to 554±90 μg/ml relative to 277±46 μg/ml in controls; and there was lung edema, measured by increased wet weight-to-dry weight ratios of 5.19±0.10, higher than 4.29±0.21 in controls (allp<0.01). The wet/dry ratios of the heart, liver, and kidney were unchanged. Pretreatment of other rabbits (n=8) with a purified anti-CD 18 monoclonal antibody (R 15.7, 1 mg/kg) 10 minutes before tourniquet release did not affect the rise in leukotriene B4but was effective in preventing leukopenia (7.29±1.05/mm3,p<0.01) and sequestration of PMNs in the hind limbs (myeloperoxidase activity, 0.46±0.12 units/g,p<0.05). Further, the anti-CD 18 monoclonal antibody prevented lung sequestration of PMNs (34±3 PMNs per 10 high-power fields,p<0.01) and reduced permeability, shown by a fall in bronchoalveolar lavage fluid protein to 324±41 μg/ml and a fall in wet/dry weight ratio to 4.61±0.10 (bothp<0.05). These data suggest that CD 18 is important in PMN-dependent lung injury after remote ischemia.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Verapamil has beneficial effects on ischemic myocardium, including reduction in electrophysiological derangements, prevention of intracellular K+loss, and preservation of high-energy phosphates, but the mechanisms underlying these actions are not clear. Recent studies have demonstrated a role of ATP-regulated K+(KATP) current in action potential shortening and K+loss during ischemia and metabolic inhibition. Therefore, we studied the effects of verapamil on KATPcurrent in feline ventricular myocytes to test the hypothesis that the drug prevents ischemic electrophysiological disturbances by affecting the KATPchannel. Membrane potentials and currents were recorded using standard patch-clamp techniques. During 15-minute superfusion with 1 mM CN−, action potential duration measured at 90% repolarization was reduced from 259±12 to 98±15 msec (62% reduction) in the absence of verapamil and from 266±11 to 183±16 msec (31% reduction) in the presence of 2 μM verapamil (p<0.01). In inside-out membrane patches, the KATPcurrent, activated in the absence of ATP, was significantly suppressed by intracellular application of 2 μM verapamil, but the single-channel conductance was not changed. Verapamil did not change the mean open and closed times of the channel within bursts (e.g., the mean open time was 1.92±0.18 and 1.82±0.21 msec in the absence and presence of 2 μM verapamil, respectively), but it shortened the mean lifetime of bursts from 41.1±3.5 to 24.9±2.8 msec (p<0.01) and prolonged the closed time between bursts from 39.4±4.6 to 78.5±5.1 msec (p<0.01). As a result, the open-state probability of the channel was significantly reduced from 0.31±0.04 to 0.03±0.01 (p<0.01). We suggest that these effects of verapamil on the KATPchannel in isolated ventricular myocytes provide, in part, an explanation for its amelioration of electrophysiological disturbances and K+loss during ischemia.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

To elucidate the pathophysiological role of the hydroxyl radical (OH) during the postischemic reperfusion of the heart, we measured the OH product in the coronary effluent from isolated perfused rat heart during a 30-minute reperfusion period after various ischemic intervals of 5, 10, 15, 20, 30, and 60 minutes. Salicylic acid was used as the probe for OH, and its derivative, 2,5-dihydroxybenzoic acid (2,5-DHBA), was quantified using high-performance liquid chromatography with ultraviolet detection. 2,5-DHBA was negligible in the effluent from nonischemic hearts, but a significant amount was detected from the hearts rendered ischemic for 10 minutes or longer. The peak of 2,5-DHBA was seen within 90 seconds after the onset of reperfusion in every group. The accumulated amount of 2,5-DHBA was maximal in the group with 15-minute ischemia (6.73± 1.04 nmol/g wet heart wt after 30 minutes of reperfusion); it decreased as the ischemic time was prolonged and was 2.38±0.84 nmol/g wet wt after 30 minutes of reperfusion in the group with 60-minute ischemia. In the model of 15-minute ischemia/30-minute reperfusion, there was no correlation between the accumulated amount of 2,5-DHBA and functional recovery (±dP/dt, heart rate, and coronary flow), lactate dehydrogenase release, and morphological damage. Although treatment with 0.5 mM deferoxamine, an iron chelator, significantly decreased 2,5-DHBA (from 6.73±1.04 to 2.29±0.80 nmol/g wet wt after 30 minutes of reperfusion,p<0.01), it failed to reduce the postischemic myocardial injury in the group with 15-minute ischemia. The results suggest that OH production is influenced by the preceding ischemic interval and that OH does not exert an immediate direct effect on postischemic damage during early reperfusion in the isolated perfused rat heart, although a possibility remains that the small portion of OH trapped by salicylic acid may not be intimately associated with myocardial injury.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

This study characterizes the sequential alterations of, and relations between, multiple electrolytes in cytoplasm, mitochondria, and whole cells during hypoxia and on reoxygenation in isolated neonatal rat ventricular myocytes. Subcellular electrolyte content and distribution were measured by electron probe x-ray microanalysis, membrane phospholipid degradation by tritiated arachidonic acid release, and cell morphology by electron microscopy. At 1–2 hours of hypoxia, the myocyte population showed a loss of cytoplasmic potassium, magnesium, and chlorine without alteration of cytoplasmic sodium or calcium. Mitochondria showed increased potassium with unchanged magnesium content. There was no morphological evidence of cell injury or tritiated arachidonic acid release. At 3–5 hours of hypoxia, the myocyte population showed a further loss of cytoplasmic potassium and magnesium and an increase in cytoplasmic sodium, chlorine, and calcium. At a single-cell level, the increase in cytoplasmic sodium preceded the increase in cytoplasmic calcium. Mitochondria showed increased sodium and chlorine and decreased magnesium before increased calcium content; potassium loss was manifest only at 5 hours of hypoxia. At 3–5 hours of hypoxia, there was also tritiated arachidonic acid release and morphological evidence of cell injury. Reoxygenation for 1 hour after 5 hours of hypoxia partially reversed the mean alterations of all electrolytes, except calcium, in the cytoplasm of the myocyte population, whereas analysis was required at a single-cell level to show a partial reversal in calcium levels in cytoplasm of reoxygenated cells. Reoxygenation for 1 hour after 5 hours of hypoxia partially reversed the mean alterations of all electrolytes, including calcium, in the mitochondria of the myocyte population. Recovery of potassium in the cytoplasm correlated with reduction of mitochondrial calcium content on reoxygenation and best predicted recovery of cellular homeostasis of sodium, chlorine, magnesium, and calcium. This study demonstrates that in this experimental model of hypoxia 1) initial losses of cytoplasmic potassium and magnesium occur in the absence of cell injury; 2) increases of sodium, chlorine, and calcium occur in association with cell injury, with sodium increasing before calcium; 3) membrane phospholipid degradation and electrolyte derangement, including increased calcium, may contribute to reversible and irreversible phases of cell injury; 4) analysis of calcium at a subcompartmental level and at a single-cell level is required to correlate reduction of calcium on reoxygenation with recovery of cell homeostasis; 5) reduction of calcium content in mitochondria may predict recovery of cell homeostasis; and 6) recovery of potassium on reoxygenation best predicts recovery of cell membrane function and cell homeostasis.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We tested the hypothesis that transmural differences in coronary microvascular pressures may be greater in the setting of hypertension and left ventricular hypertrophy. Epicardial and endocardial microvascular pressures were measured in isolated lidocaine-arrested hearts during adenosine vasodilation. In both normotensive (n=19) and hypertensive (one clip, one kidney,n=10) dogs, microvascular pressures in endocardial arterioles at 60, 70, 80, 90, and 100 mm Hg of left main coronary perfusion pressures were lower than in epicardial arterioles (p<0.05 at all perfusion pressures). The pressures in epicardial arterioles as a percentage of the left main coronary perfusion pressure were similar in normotensive versus hypertensive hearts at all perfusion pressures. In contrast, the pressures in endocardium at 90 and 100 mm Hg of perfusion pressure were significantly (p<0.05) lower in dogs with hypertension and hypertrophy than in the controls (41±4 versus 50±2 and 40±4 versus 50±3 mm Hg at 90 and 100 mm Hg of perfusion pressure, respectively). Thus, there is a greater transmural resistance to microvascular perfusion in hearts with myocardial hypertrophy secondary to hypertension. This is likely due to differences in the vascular anatomy, secondary to hypertension and hypertrophy, and may contribute to vulnerabilities in subendocardial ischemia encountered in this condition.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Abnormalities of myocardial gap junction-mediated cell coupling have been implicated in cardiac arrhythmogenesis. The potential role of gap junctional dysfunction in the generation of reperfusion-induced arrhythmias is uncertain. The purpose of this study was to measure the effects of myocardial ischemia and reperfusion on gap junctional conductance (gj) between isolated ventricular myocytes. By using a new experimental model, myocyte pairs were isolated from Langendorif-perfused rabbit hearts 1) after 30 minutes of global normothermic ischemia followed by 30 minutes of reperfusion, 2) after 75 minutes of control perfusion, or 3) immediately after removal of the heart. Myocytes and myocyte pairs were studied using whole-cell recording techniques. Action potential characteristics of cells in all three groups were normal. Despite similar mean gjin all three groups (0.88±0.27,1.15±0.18, and 1.24±0.25 μS, respectively;p> 0.05), the postischemic group was more widely distributed and had a significantly greater proportion of poorly communicating cell pairs than either control group (gj<25% of mean in eight of 15 myocyte pairs versus zero of 15 and one of 13, respectively;p<0.02). Thus, postischemic myocyte pairs represent a heterogeneous population of electrically coupled cells in which individual deficits in coupling are masked by a normal mean value. In the reperfused intact heart, local disturbances of cell coupling, similarly undetected by gross measures of conduction, could disrupt myocardial conduction and activation on a microscopic scale and thus enhance arrhythmogenicity.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Studies were designed to investigate the mechanisms underlying the augmentation by angiotensin I converting enzyme (ACE) inhibitors of the endothelium-dependent relaxations evoked by bradykinin. Isometric tension, tissue levels of cGMP, and transmembrane potential were measured in isolated canine coronary arteries as indications of the respective contribution of nitric oxide and endothelium-derived hyperpolarizing factor. In rings of coronary artery with endothelium, relaxations to bradykinin were potentiated by the ACE inhibitors cilazaprilat and perindoprilat.NG-Nitro-l-arginine (NLA), a nitric oxide synthase inhibitor, impaired relaxations to bradykinin. But the presence of ACE inhibitors partially restored this activity. Bradykinin stimulated the production of cGMP, and this was enhanced significantly by ACE inhibitors, indicating an augmented release of nitric oxide. NLA abolished the increase induced by bradykinin irrespective of the presence of ACE inhibitors. Electrophysiological studies revealed that bradykinin elicited an endothelium-dependent hyperpolarization of vascular smooth muscle that was insensitive to NLA and potentiated by ACE inhibitors. The bradykinin-induced hyperpolarization and NLA-resistant relaxations were transient and impaired by potassium depolarization. Thus, production of endothelium-derived hyperpolarizing factor may account for the NLA-resistant relaxations of canine coronary arteries. The relaxations induced by bradykinin were unaffected by the B, kinin receptor antagonist des-Arg9,[Leu8]-bradykinin either in the absence or in the presence of NLA but were antagonized by the B2kinin receptor antagonist d-Arg[Hyp3,d-Phe7]-bradykinin. Molecular exclusion chromatography of125I-labeled [Tyr8]-bradykinin and its degradation products demonstrated that the breakdown of the kinin by isolated coronary arteries was prevented in the presence of perindoprilat. The experiments suggest that the potentiating effect of ACE inhibitors on relaxations evoked by bradykinin involves the protection of bradykinin from breakdown by ACE, which results in greater production of endothelium-derived nitric oxide and hyperpolarizing factor, via stimulation of endothelial B2kinin receptors.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

To characterize the interaction between mechanical and fluid transport properties in hypertension, we measured in vivo elastic material constants and hydraulic conductivity in intact segments of carotid arteries in normal and spontaneously hypertensive rats (SHR). With the use of a finite element model, the arterial wall was modeled as a large-deformation, two-phase (solid/fluid) medium, which accounts for the existence and motion of the tissue fluid. Measurements of internal diameter and transmural pressures were obtained during continuous increases in pressure from 0 to 200 mm Hg. Strain and stress components were calculated based on a pseudostrain exponential energy density function. To measure the hydraulic conductivity, segments of the carotid artery were isolated, filled with a 4% oxygenated albumin-Tyrode's solution, and connected to a capillary tube. The movement of the meniscus of the capillary tube represented the fluid filtration across the artery. To study the influence of transmural pressure on hydraulic conductivity, measurement of fluid filtration across the arterial wall was obtained at transmural pressures of 50 and 100 mm Hg. The material constants in the SHR (n=9) were higher (p<0.05 for all variables) than in normal rats (n=10):c=1,343±96 versus 1,158±65 mm Hg,b1= 1.84±0.24 versus 1.22±0.22,b2=0.769±0.114 versus 0.616±0.11,b3=0.017±0.005 versus 0.0065±0.002,b4=0.206±0.04 versus 0.083±0.03,b5=0.0594±0.007 versus 0.0217±0.006, andb6=0.22±0.09 versus 0.123±0.02, respectively. The hydraulic conductivity of the total wall, calculated from the filtration data, was lower (p<0.05) at both 50 and 100 mm Hg in the SHR (n=6) compared with normal rats (n=7): 1.12±0.31×10−8and 0.72±0.23×10−8versus 1.95±0.53×10−8and 1.35±0.47×10−8cm/(sec mm Hg), respectively. The intergroup comparisons between 50 and 100 mm Hg in both SHR and normal rats were also different (p<0.05). The finite element model was used to predict tissue fluid pressure distribution, tissue fluid velocity distribution, and total Cauchy stress gradients developed in the arterial wall during fluid pressurization in both species. From these results, we conclude that 1) it is not adequate to treat the arterial wall as a single-phase, incompressible material because fluid moves across the boundaries of the arterial wall, resulting in a change in tissue volume; therefore, the incompressibility assumption is not valid; 2) hydraulic conductivity is dependent on pressure and may be a function of altered wall strain; 3) measurements of material constants and hydraulic conductivity can define differences in the physical properties of the arterial wall between SHR and normal rats; and 4) finite element models based on large-deformation, materially nonlinear, two-phase theory accurately reproduced the nonlinear stiffening response and the creep response under constant transmural pressure, which was observed experimentally in both species.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Atrial distension, which stimulates atrial natriuretic peptide secretion by atrial myocytes, also stretches nonmuscle cells. In a noncontracting in vitro preparation of combined right and left atria we demonstrated by electron microscopy that, at 37°C, transition from zero pressure to a physiological distending pressure of 5.1 mm Hg rapidly rendered atrial endocardial endothelium permeable to the macromolecular probes horseradish peroxidase (HRP;Mr, ≈40,000) and wheat germ agglutinin-HRP (Mr, ≈70,000); each probe was introduced at the atrial cavitary endocardial surface. Stretch-dependent permeabilization was also demonstrable in spontaneously contracting atria, was reversed by removing the distending pressure, and was unaffected by varying external Ca2+concentration from 0.2 to 1.4 mM or by experimental perturbations that markedly decrease ANP secretory rates. Although transendocardial HRP and wheat germ agglutinin-HRP passage required stretch, native ferritin (Mr, ≈500,000) could traverse unstretched endocardium. Probes were detected in noncoated endocardial vesicles and intercellular junctions between endocardial cells, but the relative contributions of vesicular transcytosis and paracellular diffusion could not be determined. Although HRP entered plasmalemmal caveolae of myocytes in stretched atria, myocytes did not internalize HRP by fluid-phase endocytosis. Distending pressure also caused apparent flow reversal in thebesian blood vessels, with retrograde transfer of HRP across the endocardium into the myocardium. HRP and ferritin presented at the external surface of the epicardium (visceral pericardium) were endocytosed by mesothelial cells, entered junctions between mesothelial cells, and readily crossed the epicardium of both stretched and unstretched preparations.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Chronic supraventricular tachycardia (SVT) causes left ventricular (LV) dilatation and dysfunction. Changes in myocyte function and structure may be important factors in the development of SVT cardiomyopathy. Accordingly, LV function and isolated myocyte structure and function were examined in six pigs with pacing-induced SVT cardiomyopathy (3 weeks at 240 beats per minute) and six control pigs. LV function was examined by simultaneous echocardiography and catheterization, and isolated myocyte function was studied using computer-assisted video microscopy. Indexes of isolated myocyte contractile performance were examined in the unloaded, unattached state (31 control and 24 SVT cells) and after attachment to a basement membrane substrate (65 control and 45 SVT cells). LV fractional shortening and peak +dP/dt significantly decreased in SVT cells compared with control cells (12±2% versus 28±2%, and 842±61 versus 1,216±119 mm Hg/sec, respectively;p<0.05). Isolated myocyte percent shortening and normalized peak velocity of shortening of SVT myocytes adherent to a basement membrane were significantly lower than attached control myocytes (1.2±0.2% versus 4.3±0.3%, and 15±2 versus 37±5% resting cell length/sec, respectively;p<0.05). Similarly, in the unattached state, the extent and velocity of shortening of SVT myocytes were reduced by over 50% from control values. Contractile properties of attached and unattached cardiocytes were also examined in the presence of 2–8 mM extracellular Ca2+. For both attached and unattached SVT myocytes, responsiveness to increases in extracellular Ca2+were significantly blunted from control values. Ultrastructural examination of SVT myocytes revealed that the percent volume of myofibrils within isolated myocytes was reduced from control values (46±7% versus 65±2%,p<0.05). In summary, SVT cardiomyopathy is probably due to a primary defect in isolated myocyte contractile performance. The reduced contractile function of SVT cardiomyopathic myocytes was associated with abnormalities in cytoarchitecture and Ca2+responsiveness.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID