摘要:

BackgroundWe have observed persistent desensitization to exogenous norepinephrine after balloon injury. We postulated that this desensitization may be due to a local increase in the release of neuronal norepinephrine.Methods and ResultsNew Zealand White rabbits underwent left iliac artery angioplasty; 4 weeks later, both iliac arteries were harvested. Maximal response to exogenous norepinephrine was reduced in injured compared with noninjured vessels (12.3±1.0 g versus 10.3±1.5 g; n=7,P= .056). By contrast, response to electrical stimulation (to induce neuronal norepinephrine release) was significantly greater in injured tissues (36±7% versus 14±3%; values expressed as percent of maximal contraction to exogenous norepinephrine;P= .025). Direct measurement of tissue norepinephrine revealed a threefold increase 4 weeks after injury (1236±410 versus 466±97 pg/mg; injured versus noninjured). To determine if desensitization to exogenous norepinephrine was due to a persistent increase in neuronal norepinephrine release, the experiments were repeated after chemical sympatholysis using 6-hydroxydopamine (6-OHDA) (65 mg/kg). To determine if activation of vascular angiotensin II contributed to facilitation of adrenergic neurotransmission, other animals received ramipril (RAM; 1 mg/kg per day). Both treatments were initiated 7 days before angioplasty. In the 6-OHDA group there was no evidence of desensitization, judged by maximal response to exogenous norepinephrine (7.5±0.6 versus 7.5±0.8, noninjured versus injured). Similar results were obtained in RAM animals (9.9±0.8 versus 9.6±1.2, noninjured versus injured).ConclusionsThis is the first study to demonstrate enhanced adrenergic neurotransmission after balloon injury. The facilitation of adrenergic neurotransmission may be due to increased local concentrations of angiotensin II and is associated with desensitization to exogenous norepinephrine.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundThe development of molecular strategies for the treatment of restenosis has been hindered by low efficiencies of in vivo arterial transfection. Expression of intracellular marker proteins is generally evident in <1% of vascular smooth muscle cells after in vivo arterial transfection. Efforts to improve the efficiency of in vivo gene transfer have been further impeded by the use of transgenes encoding for intracellular marker proteins, necessitating tissue removal and limiting survey for expression to one point in time.Methods and ResultsTo study gene expression on a serial basis in vivo and determine the relation between a secreted gene product and transfection efficiency after in vivo arterial gene transfer, a method for performing and serially monitoring gene expression in vivo was developed using the central artery of the rabbit ear. Liposome-mediated transfection of plasmid DNA containing the gene for human growth hormone (hGH) was successfully performed in 18 of 23 arteries. Serum hGH levels measured 5 days after transfection ranged from 0.1 to 3.8 ng/mL (mean, 0.97 ng/mL); in contrast, serum drawn from the control arteries demonstrated no evidence of hGH proene duction. Serial measurement of hGH from transfected arteries demonstrated maximum hGH secretion 5 days after transfection and no detectable hormone after 20 days. Despite these levels of secreted gene product documented in vivo, immunohistochemical staining of sections taken from the rabbit ear artery at necropsy disclosed only rare cells in which there was evidence of successful transfection.ConclusionsThese experiments demonstrate a useful method of performing serial in vivo analyses of gene expression after vascular transfection and that anatomic analyses of transfection efficiency may underestimate the potential magnitude of expression in the case of a secreted gene product. These findings have implications for the clinical application of somatic gene therapy because low-efficiency transfection with a gene encoding for a secreted protein may achieve therapeutic effects not realized by transfection with genes encoding for proteins that remain intracellular.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundAcute myocardial ischemia is accompanied by an increase in glucose uptake and metabolism, which appears to be important in protecting myocardial cells from irreversible ischemic injury. Because insulin augments myocardial glucose uptake by inducing the translocation of glucose transporters from an intracellular compartment to the plasma membrane, we hypothesized that acute ischemia would trigger a similar translocation.Methods and ResultsWe used a subcellular fractionation method to separate intracellular membranes and plasma membranes from control, ischemic, and hypoxic Langendorff-isolated perfused rat hearts and determined the expression of the major myocardial glucose transporter, GLUT4, in these separated membrane fractions. We found that translocation of GLUT4 molecules occurred in ischemic, hypoxic, and insulintreated hearts and in hearts that underwent ischemia plus insulin treatment. The percentages of GLUT4 molecules present on the plasma membrane in the different conditions were as follows: control. 18.0±2.8%; ischemia, 41.3±9.4%; hypoxia, 31.1±2.9%; insulin, 61.1±2.6%; and ischemia plus insulin, 66.8±5.7%. Among the statistically significant differences in these values were the difference between control and ischemia and the difference between ischemia alone and insulin plus ischemia.ConclusionsIschemia causes substantial translocation of GLUT4 molecules to the plasma membrane of cardiac myocytes. A combination of insulin plus ischemia stimulates an even greater degree of GLUT4 translocation. GLUT4 translocation is likely to mediate at least part of the increased glucose uptake of ischemic myocardium and may be a mechanism for the cardioprotective effect of insulin during acute myocardial ischemia.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundLeft ventricular hypertrophy is a generalized adaptation to increased afterload, but the growth factors mediating this response have not been identified. To explore whether the hypertrophic response was associated with changes in local insulin-like growth factor-I (IGF-I) gene regulation, we examined the induction of the cardiac IGF-I gene in three models of systolic hypertension and resultant hypertrophy.Methods and ResultsThe model systems were suprarenal aortic constriction, uninephrectomized spontaneously hypertensive rats (SHR), and uninephrectomized, deoxycorticosterone- treated, saline-fed rats (DOCA salt). Systolic blood pressure reached hypertensive levels at 3 to 4 weeks in all three systems. A differential increase in ventricular weight to body weight (hypertrophy) occurred at 3 weeks in the SHR and aortic constriction models and at 4 weeks in the DOCA salt model. Ventricular IGF-I mRNA was detected by solution hybridization/RNase protection assay. IGF-I mRNA levels increased in all three systems coincident with the onset of hypertension and the development of ventricular hypertrophy. Maximum induction was 10-fold over control at 5 weeks in the aortic constriction model, 8-fold at 3 weeks in the SHR, and 6-fold at 6 weeks in the DOCA salt model. IGF-I mRNA levels returned to control values by the end of the experimental period despite continued hypertension and hypertrophy in all three systems. In contrast, ventricular c-mycmRNA content increased twofold to threefold at 1 week and returned to control levels by 2 weeks. Ventricular IGF-I receptor mRNA levels were unchanged over the time course studied. The increased ventricular IGF-I mRNA content was reflected in an increased ventricular IGF-I protein content, as determined both by radioimmunoassay and immunofluorescence histochemistry.ConclusionsWe conclude that (1) hypertension induces significant increases in cardiac IGF-I mRNA and protein that occur coordinately with its onset and early in the development of hypertrophy, (2) IGF-I mRNA levels normalize as the hypertrophic response is established, (3) in comparison to IGF-I, both c-mycand IGF-I receptor genes are differentially controlled in experimental hypertension. These findings suggest that IGF-I may participate in initiating ventricular hypertrophy in response to altered loading conditions. The consistency of these findings in models of high-, moderate-, and low-renin hypertension suggests that they occur independently of the systemic renin-angiotensin endocrine axis.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundThe relation between left ventricular (LV) oxygen consumption (MVo2) and pressure-volume area (PVA) developed in isolated hearts provides a powerful method to understand cardiac energetics. We investigated application of this relation to the intact circulation, determining its response to steady-state and transient load alterations and enhanced contractility in conscious animals.Methods and ResultsEight dogs were instrumented to measure LV pressure (micromanometer), LV volume (three sonomicrometers), and left circumflex and anterior descending coronary artery flows (ultrasonic flowmeter). Data were acquired after recovery from the surgery with the animals awake and unsedated. After administration of hexamethonium and atropine, steady-state loading conditions were changed with phenylephrine or nitroprusside in four to five steps before and during the infusion of dobutamine (6 to 10 μg−1−1kg.−1min). MVo2and PVA obtained under steady-state conditions were linearly correlated both before and during dobutamine. The MVo2-PVA relation obtained on a beat-to-beat basis during transient caval occlusion was less linear and not coincident with the steady-state relation. Dobutamine shifted the steadystate MVo2-PVA relation upward in all hearts, increasing the MVo2 axis intercept of the MVo2-PVA relation (P< .01). This intercept correlated with ventricular contractility assessed by the slope (Ees) of the LV end-systolic pressure-volume relation determined by caval occlusion (r= .76,P< .05). The slope of the MVo2-PVA relation increased with dobutamine in seven of eight animals, with the inverse of the slope (representing contractile efficiency) being 31±6% during control and 24±6% after dobutamine (P= .06).ConclusionsMVo2and PVA are linearly related during steady-state alterations in loading conditions in conscious dogs not on a beat-by-beat basis during transient caval occlusion. Increase in contractility by dobutamine produces an upward shift of the MVo2-PVA relation.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundIt is generally accepted that the adrenergic nervous system provides inotropic support for the failing heart. However, the magnitude of this support has never been studied extensively. The present study was performed to test the hypothesis that the adrenergic nervous system is capable of maintaining indexes of pump and contractile function in the normal range despite significant innate myocardial depression.Methods and ResultsWe used our model of experimental canine mitral regurgitation, which produces left ventricular dysfunction after 3 months of volume overload. We studied indexes of contractile function on and off β-blockade at baseline and again on and off β-blockade 3 months after chronic mitral regurgitation had induced significant contractile dysfunction. At baseline, acute β-blockade caused insignificant reductions in the mass-corrected slope of the endejection stress-volume relation (EESVR), the end-systolic stiffness constant, and the ejection fraction-end-systolic stress and the mean velocity of circumferential fiber shortening (VCF)-end-systolic stress relations. After 3 months of chronic mitral regurgitation, all indexes of contractile function were normal in the unblocked state except for the VCF-stress relation, which was mildly reduced. However, after acute β-blockade after 3 months of chronic mitral regurgitation, the EESVR fell to 303±27 versus 443±24 during acute P-blockade before mitral regurgitation was created (P< .05), and the end-systolic stiffness constant was reduced to 2.54±0.15 versus 3.27±0.11 (P< .05). Only after,β-blockade was the ejection fraction-stress relation significantly reduced for dogs with chronic mitral regurgitation. The VCF-stress relation became markedly more abnormal. The viscosity-velocity relation of myocytes isolated from the ventricles of the dogs with mitral regurgitation confirmed that substantial innate contractile depression was present.ConclusionsAfter 3 months of chronic mitral regurgitation, the adrenergic nervous system was able to maintain most indexes of contractile function in the normal range despite significant depression in innate contractile function. Thus, in the absence of β-blockade, significant innate contractile depression may be obscured by adrenergic support.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundValve areas derived by the Gorlin formula have been observed to vary with transvalvular volume flow rate. Continuity equation valve areas calculated from Doppler- echo data have become a widely used alternate index of stenosis severity, but it is unclear whether continuity equation valve areas also vary with volume flow rate. This study was designed to investigate the effects of changing transvalvular volume flow rate on aortic valve areas calculated using both the Gorlin formula and the continuity equation in a model of chronic valvular aortic stenosis.Methods and ResultsUsing a canine model of chronic valvular aortic stenosis in which anatomy and hemodynamics are similar to those of degenerative aortic stenosis, each subject (n=8) underwent three studies at 2-week intervals. In each study, transvalvular volume flow rates were altered with saline or dobutamine infusion (mean, 10.3±5.1 flow rates per study). Simultaneous measurements were made of hemodynamics using micromanometer-tipped catheters, of ascending aortic instantaneous volume flow rate using a transit-time flowmeter, and of left ventricular outflow and aortic jet velocity curves using Doppler echocardiography. Valve areas were calculated from the invasive data by the Gorlin equation and from the Doppler-echo data by the continuity equation. In the 24 studies, mean transit-time transvalvular volume flow rate ranged from 80±33 to 153±49 mL/min (P< .0001). Comparing minimum to maximum mean volume flow rates, the Gorlin valve area changed from 0.54±0.22 cm2to 0.68±0.21 cm2 (P< .0001), and the continuity equation valve area changed from 0.57±0.18 cm2 to 0.70±0.20 cm2 (P< .0001). A strong linear relation was observed between Gorlin valve area and mean transit-time volume flow rate for each study (median,r= .88), but the slope of this relation varied between studies. The Doppler-echo continuity equation valve area had a weaker linear relation with transit-time volume flow rate for each study (median,r= .51).ConclusionsIn this model of chronic valvular aortic stenosis, both Gorlin and continuity equation valve areas were flow-dependent indices of stenosis severity and demonstrated linear relations with transvalvular volume flow rate. The changes in calculated valve area that occur with changes in transvalvular volume flow should be considered when measures of valve area are used to assess the hemodynamic severity of valvular aortic stenosis.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundThe effects of chronic exercise training on myocardial contractility and β-adrenergic signal transduction in hearts with left ventricular dysfunction have not been determined.Methods and ResultsFourteen-week-old cardiomyopathic BIO 53.58 and normal F1B Syrian hamsters underwent 10 weeks of treadmill training and were compared with 24-weekold BIO 53.58 and F1B untrained controls. Left ventricular isovolumic maximum positive dP/dt and peak developed pressure were significantly lower in BIO 53.58 than in F1B controls. Exercise training improved left ventricular contractile indices in BIO 53.58 but not F1B hamsters. The left ventricular β-adrenergic receptor number (Bmax) was similar in BIO 53.58 and F1B controls. Basal adenylate cyclase activity (ACA) and ACAs stimulated by isoproterenol, 5′-guanylylimidodiphosphate (GppNHp), sodium fluoride, and forskolin were significantly lower in BIO 53.58 than in F1B controls. The functional activity of stimulatory guanine nucleotide-binding protein (Gs), as determined by reconstitution with S49 lymphoma cyc−cell membranes, was significantly lower in BIO 53.58 controls. After 10 weeks of exercise training, Bmaxand basal and isoproterenol-stimulated ACAs were unchanged in either BIO 53.58 or F1B hamsters compared with controls. However, in F1B hamsters, training decreased ACAs stimulated by GppNHp, sodium fluoride, and forskolin, with a reduced functional activity of GsIn contrast, these ACAs increased significantly in association with an enhanced G, activity in cardiomyopathic BIO 53.58 hamsters after training.ConclusionsChronic exercise training does not change receptor-mediated β-adrenergic responsiveness in either F1B or BIO 53.58 hamsters. However, exercise training reduces Gsactivity in normal F1B hamsters and improves the functional abnormality of Gsin cardiomyopathic BIO 53.58 hamsters. This improvement may potentially contribute to augmented left ventricular contractility in BIO 53.58 after training.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundTumor necrosis factor-α (TNF-α) has been reported to have an antiviral effect in vitro; however, its in vivo effect remains to be clarified.Methods and ResultsTo investigate the role of TNF-α in viral myocarditis using a murine model induced by encephalomyocarditis virus (EMCV), we evaluated (1) plasma TNF-α levels by enzyme-linked immunosorbent assay (ELISA), (2) the effect of recombinant human TNF-α for its possible antiviral effect in vivo, and (3) the effect of anti-murine TNF-α monoclonal antibody (mAb) in vivo. Four-week-old DBA/2 mice were inoculated intraperitoneally with EMCV (day 0). Mice were injected intravenously daily with 1,μg of TNF-α or 2×103units of anti–TNF-α mAb starting on day -1, day 0, or day 1 until day 2 (TNF-α study) or day 4 (anti-TNF-α mAb study). A portion of the mice were killed on day 5 (protocol 1); their hearts were removed, and plaque assays were performed to demonstrate the myocardial virus content. The remaining mice were killed on day 14 (protocol 2); myocardial lesions were examined histopathologically in terms of severity, and their survival rates were determined. Plasma TNF-α concentration was elevated in the blood of infected mice compared with uninfected mice 3, 5, and 7 days after virus inoculation. The myocardial virus content was higher in the TNF-α–treated group than in the control group. Histopathological analysis revealed that myocardial necrosis and cellular infiltration were more prominent in the TNF-α group than in the control group. The anti-TNF-α mAb improved survival and myocardial lesions when its treatment was started 1 day before virus inoculation. However, it showed no therapeutic effect when administered simultaneously with the inoculation or on day 1.ConclusionsTNF-α may play an important role in the very early stage of the immune response, and anti-TNF-α mAb may prevent the early pathway of acute viral myocarditis.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundPremature stimulation is used to characterize the reentrant circuit during ventricular tachycardia (VT) in patients. The goal of this study was to compare the effects of premature stimulation on functional and anatomic reentrant VT.Methods and ResultsIn 18 Langendorff-perfused rabbit hearts, thin layers of anisotropic left ventricular subepicardium were created by a cryoprocedure. In 8 hearts, rapid pacing induced reentry around a line of functional conduction block; in 10 hearts, reentry occurred around a fixed epicardial obstacle created by a cryoprobe. The cycle lengths (CL) of functional and anatomic VT were 110±10 and 167±17 milliseconds, respectively. During anatomic VT, the excitable gap measured 43% of the CL and premature stimuli could always reset VT (44±12 milliseconds). During early premature beats, conduction of the orthodromic wave was slightly depressed, but anatomic VT was never terminated. Reset curves at different sites in the ventricle revealed three different response types, both determined by and characterizing the spatial and temporal relation between pacing and recording sites. Premature stimulation during functional VT revealed a local excitable gap at the pacing site measuring 27% of the cycle length of VT. However, in only 3 of 8 hearts, premature stimuli could reset functional VT by 8%. In 5 VTs, advancement of the paced activation was fully compensated by prolongation of the return cycle, and VT was not reset. Due to slow conduction both toward and inside the circuit, the paced orthodromic wave lost its prematurity already within a distance of 6 to 10 mm from the pacing site.ConclusionsBoth during anatomic and functional reentry, an excitable gap is present in the reentrant circuit. Three different response curves reveal the localization of the pacing and recording sites in the circuit. Anatomic VT can always be reset by premature stimuli, whereas in 5 of 8 hearts, functional VT could not be reset. In the other 3 hearts, VT could only be reset for less than 7% to 11% of the VT interval. Therefore, it seems very unlikely that clinical VT based on functional reentry can be reset.

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID