Na+/H+ exchange inhibition with cariporide prevents alterations of coronary endothelial function in streptozotocin-induced diabetes

Hyperglycemia encountered during diabetes triggers abnormalities of vascular function associated with cell acidosis and calcium overload. The purpose of this study was to determine, whether Na⁺/H⁺ exchanger (NHE-1) inhibition by cariporide protects coronary cells against the deleterious effect of hyperglycemia in the rat. In vivo hyperglycemia was triggered by streptozotocin injection. One week after, the glycemia was checked and the control and diabetic animals were treated or not with cariporide (2.5 mg/kg/day) for two weeks. Glycemia was again estimated and the hearts were perfused according to the Langendorff mode at forced flow. The left ventricle developed pressure (LVDP) and heart rate (HR) were determined with a latex balloon inserted into the left ventricle. Coronary pressure was artificially increased to 130 mmHg by infusing a thromboxane A₂ analogue (U46619). This allowed the evaluation of endothelium-dependent (EDD) and endothelium-independent (EID) dilatation through bolus injections of carbamoylcholin and sodium nitroprusside, respectively. Releases of lactate and pyruvate in the coronary effluents were also determined. Diabetes did not modified LVDP, but reduced HR (−15%). This was associated with a marked decrease in EDD (−56%) and EID (−30%), while the cytosolic redox potential (estimated as the lactate/pyruvate ratio) was reduced. NHE-1 inhibition restored EDD and the lactate/pyruvate ratio without improving EID and HR. The present findings indicate that NHE-1 exchanger inhibition by cariporide protects the coronary endothelium against the deleterious effects of hyperglycemia.     

Infarct-induced chronic heart failure increases bidirectional protein movement across the alveolocapillary barrier

Chronic heart failure (CHF) is associated with adaptive structural changes at the alveolocapillary barrier that may be associated with altered protein permeability. Bidirectional protein movement across the barrier was studied in anesthetized rats with infarct-induced CHF by following (125)I-labeled albumin ((125)I-albumin) flux into the alveoli and the leakage of surfactant protein (SP)-B from the alveoli into the circulation. Three groups were studied: controls [0% left ventricular (LV) infarction], moderate infarct (25-45% LV infarction), and large infarct (>46% LV infarction). Wet and dry lung weights increased in the large infarct group (both P < 0.001), consistent with increased lung water and solid lung tissue. (125)I-albumin flux increased across the endothelial (P < 0.001) and epithelial (P < 0.01) components of the alveolocapillary barrier in the large infarct group. Plasma SP-B increased 23% with moderate infarcts (P < 0.05) and 97% with large infarcts (P < 0.001), independent of alveolar levels. Lavage fluid immune cells (P < 0.01) and myeloperoxidase activity (P < 0.05) increased in the large infarct group, consistent with inflammation. Bidirectional protein movement across the alveolocapillary barrier is increased in CHF, and alveolar inflammation may contribute to this pathophysiological defect.     

Induction of heat shock protein 72 in the failing heart is attenuated after an exposure to heat shock

Induction of heat shock protein (Hsp) 72 in the right ventricular muscle of the rat with heart failure following acute myocardial infarction (AMI) was examined. AMI was induced by the left coronary artery ligation (CAL). The animals at the 8th, but not 2nd, week after CAL revealed a decrease in cardiac output index (COI), suggesting that heart failure had developed by 8 weeks after CAL. Increases in the right ventricular developed pressure and the ratios of right ventricle/body weight and lung/body weight at the 2nd and 8th weeks showed the development of the right ventricular hypertrophy. After measurement of hemodynamic parameters, the hearts isolated from animals at the 2nd and 8th weeks after CAL (2w- and 8w-CAL hearts, respectively) were perfused and subjected to heat shock (at 42 degrees C, for 15 min) followed by 6-h perfusion. At the end of perfusion, Hsp72 content in the left ventricle without infarct area (viable LV) and the right ventricle (RV) was determined by the Western immunoblotting method. The production of myocardial Hsp72 in the viable LV and RV of the 2w-CAL heart increased after an exposure to heat shock. In contrast, induction of Hsp72 in the viable LV and RV of the 8w-CAL heart was blunted. The results suggest that the development of heart failure following AMI may result in a decrease in the ability for Hsp72 induction not only in the viable LV but also in the RV, leading to contractile dysfunction of the heart.     

MicroRNA-19a attenuates hypoxia-induced cardiomyocyte apoptosis by downregulating NHE-1 expression and decreasing calcium overload

miR-19a has been shown to be involved in coronary microvascular obstruction injury; however, the underlying molecular mechanisms remain unknown. In our study, we tried to explore the role of miR-19a in cardiomyocyte apoptosis and calcium overload in vivo and in vitro induced by hypoxia. We established the acute myocardial infarction (AMI) rat model by ligating the left anterior descending artery. The expression of miR-19a in the infarct zone of AMI rats and myocardial tissue in the same position in sham rats was analyzed using RT-qPCR while Na⁽⁺⁾/H⁽⁺⁾ exchanger 1 (NHE-1) was detected by Western blotting. We also observed the effects of overexpressing miR-19a or administering an NHE-1 inhibitor (cariporide) on hypoxia-induced (HI) calcium overload and apoptosis in primary cardiomyocytes. In addition, dual-luciferase reporter assays were conducted to investigate the potential target of miR-19a on NHE-1. Decreased miR-19a expression, as well as increased apoptosis and NHE-1 expression, were observed in the AMI model. Furthermore, after hypoxia stimulation, miR-19a was gradually reduced as time increased in primary cardiomyocytes. Overexpressing miR-19a using mimics ameliorated the increase in NHE-1 in hypoxic cardiomyocytes and thereby reduced the HI cell calcium overload and cell apoptosis rate from 12.32% to 9.5% (P < .01). In addition, the dual-luciferase reporter gene assay results verified that NHE-1 was the direct target of miR-19a. Our findings suggest that miR-19a activation can attenuate HI cardiomyocyte apoptosis by downregulating NHE-1 expression and decreasing calcium overload.     

Effective protection by NHE-1 inhibition in ischemic and reperfused heart under preconditioning blockade

We compared the protective effects of ischemic preconditioning (IPC) and the Na(+)/H(+) exchanger-1 (NHE-1) inhibitor cariporide in isolated rat hearts subjected to global ischemia (45 or 90 min) and 30-min reperfusion and determined the protective effects of cariporide under IPC blockade with the mitochondrial ATP-sensitive K(+) channel blocker 5-hydroxydecanoate (5-HD). With 45-min ischemia, both IPC and cariporide equally increased maximum recovery of left ventricular developed pressure twofold (P < 0.05), although recovery was significantly greater with cariporide for the first 15 min of reperfusion. 5-HD almost completely blocked the protective effects of IPC on recovery but had no influence on the salutary effects of cariporide. With 90-min ischemic control, recovery was only 3% of preischemia and was unaffected by IPC, although cariporide increased recovery to approximately 30% (P < 0.05). This was associated with a 37% preservation of viable cardiac cells, whereas no structurally intact cells were found in either IPC or control hearts. Our study shows that NHE-1 inhibition is a more effective cardioprotective strategy than IPC in this model, possibly because of enhanced myocyte salvage, and because protection by NHE-1 inhibition is completely unaffected by IPC blockade with 5-HD.     

Targeted deletion of MMP-2 attenuates early LV rupture and late remodeling after experimental myocardial infarction

Matrix metalloproteinase-2 (MMP-2) is prominently overexpressed both after myocardial infarction (MI) and in heart failure. However, its pathophysiological significance in these conditions is still unclear. We thus examined the effects of targeted deletion of MMP-2 on post-MI left ventricular (LV) remodeling and failure. Anterior MI was produced in 10- to 12-wk-old male MMP-2 knockout (KO) and sibling wild-type (WT) mice by ligating the left coronary artery. By day 28, MI resulted in a significant increase in mortality in association with LV cavity dilatation and dysfunction. The MMP-2 KO mice had a significantly better survival rate than WT mice (56% vs. 85%, P < 0.05), despite a comparable infarct size (50 +/- 3% vs. 51 +/- 3%, P = not significant), heart rate, and arterial blood pressure. The KO mice had a significantly lower incidence of LV rupture (10% vs. 39%, P < 0.05), which occurred within 7 days of MI. The KO mice exerted less LV cavity dilatation and improved fractional shortening after MI by echocardiography. The LV zymographic MMP-2 level significantly increased in WT mice after coronary artery ligation; however, this was completely prevented in KO mice. In contrast, the increase in the LV zymographic MMP-9 level after MI was similar between KO and WT mice. MMP-2 activation is therefore considered to contribute to an early cardiac rupture as well as late LV remodeling after MI. The inhibition of MMP-2 activation may therefore be a potentially useful therapeutic strategy to manage post-MI hearts.     

Preserved ventricular contractility in infarcted mouse heart overexpressing beta(2)-adrenergic receptors

Effects of cardiac specific overexpression of beta(2)-adrenergic receptors (beta(2)-AR) on the development of heart failure (HF) were studied in wild-type (WT) and transgenic (TG) mice following myocardial infarction (MI) by coronary artery occlusion. Animals were studied by echocardiography at weeks 7 to 8 and by catheterization at week 9 after surgery. Post-infarct mortality, due to HF or cardiac rupture, was not different among WT mice, and there was no difference in infarct size (IS). Compared with the sham-operated group (all P < 0.01), WT mice with moderate (<36%) and large (>36%) IS developed lung congestion, cardiac hypertrophy, left ventricular (LV) dilatation, elevated LV end-diastolic pressure (LVEDP), and suppressed maximal rate of increase of LV pressure (LV dP/dt(max)) and fractional shortening (FS). Whereas changes in organ weights and echo parameters were similar to those in infarcted WT groups, TG mice had significantly higher levels of LV contractility in both moderate (dP/dt(max) 4,862 +/- 133 vs. 3,694 +/- 191 mmHg/s) and large IS groups (dP/dt(max) 4,556 +/- 252 vs. 3,145 +/- 312 mmHg/s, both P < 0.01). Incidence of pleural effusion (36% vs. 85%, P < 0.05) and LVEDP levels (6 +/- 0.3 vs. 9 +/- 0.8 mmHg, P < 0.05) were also lower in TG than in WT mice with large IS. Thus beta(2)-AR overexpression preserved LV contractility following MI without adverse consequence.     

Decrease of myocardial infarct size with desferrioxamine: possible role of oxygen free radicals in its ameliorative effect

The ability of an iron chelator, desferrioxamine, to inhibit the infarct size in in vivo rat heart was assessed. Anaesthetised rats were subjected to coronary artery ligation (CAL) for 72 hr and infarct size was measured macroscopically using TTC staining. Systolic blood pressure and ECG were monitored. Desferrioxamine (10 mg/kg and 20 mg/kg i.v.) administered half an hour after CAL markedly reduced the infarct size. However, drug treatment did not alter the systolic blood pressure of animals. In addition, desferrioxamine in vitro and in vivo demonstrated an inhibition of rat PMN-evoked and luminol-enhanced chemiluminiscence. The capacity of desferrioxamine to impair the generation or to scavenge directly oxygen free radicals may be responsible for its beneficial effect on myocardial infarct size in rats.     

Exercise training preserves coronary flow and reduces infarct size after ischemia-reperfusion in rat heart.

The effect of endurance training on the resistance of the heart to left ventricular (LV) functional deficit and infarction after a transient regional ischemia and subsequent reperfusion was examined. Female Sprague-Dawley rats were randomly assigned to an endurance exercise training (Tr) group or a sedentary (Sed) control group. After 20 wk of training, hearts were excised, perfused, and instrumented for assessment of LV mechanical function, and the left anterior descending coronary artery was occluded to induce a transient regional ischemia (1 h) that was followed by 2 h of reperfusion. Throughout much of the regional ischemia-reperfusion protocol, coronary flow rates, diastolic function, and LV developed pressure were better preserved in hearts from Tr animals. During the regional ischemia, coronary flow to myocardium outside the ischemic zone at risk (ZAR) was maintained in Tr hearts, whereas it progressively fell in Sed hearts. On release of the coronary artery ligature, flow to the ZAR was greater in Tr than in Sed hearts. Infarct size, expressed as a percentage of the ischemic ZAR, was significantly smaller in hearts from Tr rats (24 +/- 3 vs. 32 +/- 2% of ZAR, P < 0.05). Mn- and CuZn-SOD protein expression were higher in the LV myocardium of Tr animals (P < 0.05 for both isoforms). Our data indicate that long-term exercise training leads to infarct sparing and better maintenance of coronary flow and mechanical function after ischemia-reperfusion.     

Na(+)/H(+) exchange subtype 1 inhibition reduces endothelial dysfunction in vessels from stunned myocardium

Myocardial ischemia and reperfusion cause myocyte and vascular dysfunction, frequently termed "stunning." We hypothesized that inhibiting the Na(+)/H(+) exchanger subtype 1 isoform (NHE(1)) during ischemia and reperfusion limits myocardial and coronary microvascular stunning. Anesthetized rats completed 2 x 10-min coronary artery occlusions separated by 5-min of reperfusion, followed by 15 or 60 min of reperfusion. Vehicle (saline) or the NHE(1) inhibitor cariporide (HOE-642) was administered 15 min before ischemia and was continued throughout each protocol. After reperfusion, hearts were excised, and the reactivity of resistance arteries (internal diameter, approximately 120 microm) was assessed. The first derivative of left ventricular (LV) pressure, LV developed pressure, and LV systolic wall thickening were depressed (P < 0.05) similarly in vehicle- and cariporide-treated rats during ischemia and after 15 or 60 min of reperfusion compared with sham-operated animals that were not exposed to ischemia (i.e., controls). In vessels obtained after 15 min of reperfusion, the maximal response to acetylcholine-induced relaxation (10(-8)-10(-4) M) was blunted (P < 0.05) in vessels from vehicle- (approximately 35%) and cariporide-treated rats (approximately 55%) compared with controls (approximately 85%). However, the percent relaxation to acetylcholine was greater (P < 0.05) in cariporide-treated rats compared with vehicle-treated rats. Maximal contractile responses to endothelin-1 (10(-11)-10(-7) M) were increased (P < 0.05) similarly in vehicle- and cariporide-treated rats compared with controls. Relaxation to sodium nitroprusside (10(-4) M) was not different among groups. Results were similar in vessels obtained from animals after 60 min of reperfusion. These findings suggest that NHE(1) inhibition before coronary occlusion lessens ischemia-induced microvascular dysfunction for 15-60 min after reperfusion but does not alter myocardial contractile function in the area at risk.     

Induction of myocardial infarcts of a predictable size and location by branch pattern probability-assisted coronary ligation in C57BL/6 mice

The ability to create experimental myocardial infarctions of reproducible size and location is tantamount to progress in multiple facets of ischemic heart disease research. Branches of the mouse left main descending coronary artery penetrate the myocardium close to their origin and require "blind" ligation. Our objective was to develop a technique for ligation of nonvisible coronary artery branches to permit the reliable creation of infarcts of uniformly small size and location. From latex castings of the left coronary artery of C57BL/6J mice (n = 53), we calculated the highest probability for the location of branch points of two of three left ventricular (LV) branches distal to the origin of the left main descending artery. On the basis of these anatomic probabilities, we blindly ligated two areas that were likely to be locations of these nonvisible LV branches. We were successful in producing two types of small transmural myocardial infarctions (16.04 +/- 3.64 and 4.68 +/- 1.47% of the LV) in 57% of attempts. Thus our branch pattern probability-assisted method permits routine creation of small infarcts of uniform size in the mouse.     

An ovine model of postinfarction dilated cardiomyopathy in animals with highly variable coronary anatomy

Studies on cardiac regeneration require large mammalian models of dilated cardiomyopathy (DCM) after acute myocardial infarction (AMI), and pig and sheep models are increasingly used in this field of preclinical research. Given the large interindividual variability in ovine left anterior descending artery (LAD) anatomy, protocols based on the coronary arteries to be ligated often lead to significant variation in infarct sizes and hence to heterogeneous results, ranging from no ventricular remodeling to acute, lethal left ventricular (LV) failure. We designed an ovine model of postinfarction DCM based on estimated infarct size rather than on a predetermined menu of coronary artery ligatures. In seven adult sheep we induced an anterolateral AMI of approximately 25% of the LV mass by ligating the branches of the LAD that, by visual inspection, would lead to such an infarct size. In 10 to 12 weeks, LV end-diastolic volume more than doubled and LV end-systolic volume almost tripled. LV ejection fraction decreased dramatically, as did LV percent fractional shortening and LV percent wall thickening. Infarct size (planimetry) was approximately 25% of the LV endocardial surface. We conclude that in sheep, an anterolateral AMI of approximately 25% of the LV mass--regardless of the coronary branches ligated to attain that infarct size--results in a model of postinfarction DCM that may prove useful in preclinical research on myocardial regeneration.     

A novel model of cryoinjury-induced myocardial infarction in the mouse: a comparison with coronary artery ligation

Mouse myocardial infarction (MI) models are frequently used research tools. The most commonly applied model is coronary artery ligation. However, coronary ligation often gives rise to apical aneurysmatic infarcts of variable size. Other infarct models include cryoinfarction, which produces reproducible infarcts of the anterior wall. Thus far, this model has not been extensively described in mice. Therefore, we developed a murine cryoinfarction model and compared it with coronary ligation. Studies were performed under isoflurane anesthesia with a follow-up of 4 and 8 wk. Cryoinfarction was induced using a 2- or 3-mm cryoprobe. Two-dimensional guided M-mode echocardiography was used to assess fractional shortening and left ventricular (LV) dimensions at baseline and end point. At end point, hemodynamics were assessed using a 1.4-Fr Millar catheter. Pressure-diameter relations were constructed by combining echocardiography and hemodynamic data. Histological and morphometric analyses of infarct and remote areas were performed. At 4 wk, 3-mm cryoinfarction resulted in decreased LV fractional shortening as well as decreased global LV contractility and relaxation, which was comparable with coronary ligation. No adverse remodeling was observed at this time point, in contrast with the ligation model. However, progressive LV remodeling occured between 4 and 8 wk after cryoinfarction with a further decline in hemodynamic parameters and LV pump function. Histologically, cryoinfarction resulted in highly reproducible, transmural, cone-shaped infarcts with reperfusion at the macrovascular level. These results indicate that the cryoinfarction model represents the anterior myocardial infarct with modest adverse remodeling and may thus be representative for infarcts encountered in clinical practice.     

Myocardial Connective Tissue Growth Factor (CCN2/CTGF) Attenuates Left Ventricular Remodeling after Myocardial Infarction

Aims

Myocardial CCN2/CTGF is induced in heart failure of various etiologies. However, its role in the pathophysiology of left ventricular (LV) remodeling after myocardial infarction (MI) remains unresolved. The current study explores the role of CTGF in infarct healing and LV remodeling in an animal model and in patients admitted for acute ST-elevation MI.

Methods and Results

Transgenic mice with cardiac-restricted overexpression of CTGF (Tg-CTGF) and non-transgenic littermate controls (NLC) were subjected to permanent ligation of the left anterior descending coronary artery. Despite similar infarct size (area of infarction relative to area at risk) 24 hours after ligation of the coronary artery in Tg-CTGF and NLC mice, Tg-CTGF mice disclosed smaller area of scar tissue, smaller increase of cardiac hypertrophy, and less LV dilatation and deterioration of LV function 4 weeks after MI. Tg-CTGF mice also revealed substantially reduced mortality after MI. Remote/peri-infarct tissue of Tg-CTGF mice contained reduced numbers of leucocytes, macrophages, and cells undergoing apoptosis as compared with NLC mice. In a cohort of patients with acute ST-elevation MI (n = 42) admitted to hospital for percutaneous coronary intervention (PCI) serum-CTGF levels (s-CTGF) were monitored and related to infarct size and LV function assessed by cardiac MRI. Increase in s-CTGF levels after MI was associated with reduced infarct size and improved LV ejection fraction one year after MI, as well as attenuated levels of CRP and GDF-15.

Conclusion

Increased myocardial CTGF activities after MI are associated with attenuation of LV remodeling and improved LV function mediated by attenuation of inflammatory responses and inhibition of apoptosis.     

Na(+)/H(+) exchange inhibition attenuates hypertrophy and heart failure in 1-wk postinfarction rat myocardium

Na(+)/H(+) exchange (NHE) represents a major mechanism for intracellular pH regulation, particularly in the ischemic myocardium. NHE has also been shown to be important in the regulation of cell proliferation and growth. We examined whether inhibition of NHE results in an attenuation of early postinfarction myocyte remodeling responses in the rat. Male Sprague-Dawley rats were randomized to receive either a control diet or an identical diet supplemented with the NHE inhibitor cariporide. After 1 wk, animals were anesthetized, subjected to ligation of the left main coronary artery, and maintained for an additional week, after which time they were anesthetized and intraventricular pressures were obtained. Hearts were removed, and myocytes were isolated to obtain cell dimensions and determine the response to isoproterenol. Body, heart, and lung weights were obtained. Coronary artery ligation in control animals resulted in a significant elevation in left ventricular end-diastolic pressure, as well as increased heart weight- and lung weight-to-body weight ratios, both of which were abrogated by cariporide. Cell length and area significantly increased by 14 and 19.2%, respectively, whereas cell width increased by 4.1% (P > 0.05). These cells exhibited a significant hyporesponsiveness to the positive inotropic responses to isoproterenol at the lower drug concentrations (3 and 10 nM). A <1% dimensional change occurred in myocytes from cariporide-fed animals, and the hyporesponse to isoproterenol was reversed. Cariporide had no effect on infarct size or blood pressure. These studies suggest that the early adaptive hypertrophic response of surviving myocytes is dependent on NHE activity. As such, it is attractive to suggest that NHE inhibition could be an effective therapeutic strategy for prevention of postinfarction remodeling, independent of infarct size or afterload reduction.     

Beta-adrenoceptor and adenylate cyclase function in the infarct model of rat heart failure.

In order to determine the possible etiology for diminished inotropic responsiveness to catecholamines in the infarction model of chronic congestive heart failure in rats, we studied beta-adrenoceptor number and site-specific stimulated adenylate cyclase activity in noninfarcted left ventricular tissue of rats at 3 months after ligation of the left coronary artery. Rats were divided into sham, small infarct, and large infarct groups according to infarct size. The large infarct groups showed increased right ventricle to body weight ratio (0.93 +/- 0.07 mg/g for the large infarcts vs 0.52 +/- 0.02 and 0.54 +/- 0.02 mg/g for the shams and small infarcts, respectively). Beta-Adrenoceptor number among the groups was similar (shams, 27 +/- 1 fmol/mg; small infarcts, 26 +/- 1 fmol/mg; and large infarcts, 29 +/- 1 fmol/mg), as was Kd (20 +/- 1 pmol, 18 +/- 2 pmol, and 18 +/- 2 pmol, respectively). Site-specific stimulation of adenylate cyclase using isoproterenol, Gpp(NH)p, forskolin, and MnCl2 revealed no significant differences among the groups. We conclude that this system is not responsible for the altered inotropic responsiveness to catecholamines seen in this model.     

Difference in the relation between infarct and occluded bed in pentobarbital-anesthetized and conscious dogs

The relationship between myocardial infarct size (IS) and occluded bed size (OBS) in pentobarbital-anesthetized (A, n = 16) and conscious (C, n = 20) dog models were compared. IS and OBS (postmortem coronary arteriography) were measured by computerized planimetry of weighed left ventricular (LV) rings 7 days after permanent left anterior descending (LAD, n = 19) or circumflex (LC, n = 17) coronary artery occlusion. For both A and C groups, IS was directly related to OBS (p less than 0.001) and no infarcts developed for small occluded beds. For either LAD or LC subgroups, infarcts were larger in A than C dogs (49 +/- 18 vs. 30 +/- 19% OBS, p less than 0.025), with greater slope of the linear regression between IS and OBS (p less than 0.001) and less epicardial sparing on topographic mapping (p less than 0.05). Although postocclusion mean arterial and left atrial pressures were similar in A and C groups, heart rates were greater in the A dogs, both pre- (125 vs. 88 beats/min, p less than 0.001) and post-occlusion (151 vs. 108 beats/min, p less than 0.001). Endocardial flows (radioactive microspheres) in infarct centers and margins were less in A than C dogs. Also, endocardial/epicardial (endo/epi) flow ratios in all regions were less in A than C dogs, both pre- and post-occlusion. Increasing heart rate in 10 other C dogs with LAD occlusion to that of the A group (151 beats/min) by right ventricular pacing resulted in larger infarcts with greater slope of the linear regression and less endo/epi flow ratios, as in the A group.(ABSTRACT TRUNCATED AT 250 WORDS)     

P2X receptor-mediated muscle pressor reflex in myocardial infarction

A previous report from this laboratory demonstrated that the ATP-sensitive P2X receptor-mediated muscle pressor reflex was augmented in rats with heart failure (HF). The purpose of this study was to better understand the underlying mechanisms for this greater response in HF rats. We examined 1) responsiveness of the P2X receptor to alpha,beta-methylene ATP (alpha,beta-me-ATP), a P2X receptor agonist, in control and HF rats induced by myocardial infarction (MI); 2) the relationship between P2X-induced blood pressure response and left ventricular (LV) function; and 3) the expression of P2X receptors in the dorsal root ganglion (DRG) of control rats and rats with HF. Eight to 14 wk after coronary artery ligation, the severity of the MI was determined by echocardiography. In the first group of the experiment, alpha,beta-me-ATP (0.0625, 0.125, 0.25, and 0.5 mM) was injected into the arterial blood supply of the hindlimb muscles to evoke a pressor response in 17 decerebrated rats (6 controls, 6 small MIs with infarcts of the LV between 10 and 35%, and 5 large MIs with infarcts >35%). The P2X agonist increased blood pressure, and the effect was significantly accentuated in large MI rats compared with small MI rats and control rats. A significant correlation was observed between alpha,beta-me-ATP-evoked pressor response and the LV fractional shortening, an index of LV function. In the second group of the experiment, immunocytochemistry was used to examine the immunoreactivity of P2X receptor in the DRG neurons of small diameter fibers in six healthy control rats, five small MI, and five large MI rats. The percentage of P2X immunostaining-positive neurons in the DRG was markedly greater in large MI rats (52% vs. 29% in controls and 34% in small MIs, P < 0.05). In conclusion, our findings demonstrate that 1) muscle afferent-mediated pressor response of P2X activation was exaggerated in MI animals, and the responsiveness was related to the degree of LV dysfunction; and 2) augmented reflex response was associated with upregulated P2X receptors in the DRG neurons of thin fiber afferent nerves following MI. The data suggest that P2X-mediated responsiveness in the processing of muscle afferent signals may have important implications for understanding cardiovascular responses to exercise in HF.     

Echocardiographic parameters discriminating myocardial infarction with pulmonary congestion from myocardial infarction without congestion in the mouse.

Our aim was to establish parameters describing systolic and diastolic function in mice after myocardial infarction (MI) that distinguish MI with pulmonary congestion from MI without congestion. Echocardiography, left ventricular (LV) catheterization, and infarct size measurements were performed on days 3, 5, 7, and 14 after ligation of the left coronary artery in C57BL/6 mice. Sham-operated mice were used as controls (Sham). MI mice with lung weight normalized to tibial length >125% of the average in the corresponding Sham group were considered to have pulmonary congestion (MIchf). MI mice with a smaller increase were called MI nonfailing (MInf). An infarct >40% of total LV circumference measured in two-dimensional long axis distinguished MIchf from MInf on both an average and an individual basis. Mean maximum rate of rise of LV pressure, LV fractional shortening, and posterior wall shortening velocity were significantly lower in MIchf compared with Sham at all time points and to MInf at 7 days. The diastolic parameters mitral flow deceleration velocity, LV end-diastolic pressure, and maximum rate of decline in LV pressure (LVdP/dtmin) discriminated the MIchf groups from Sham at all time points. Mitral flow deceleration velocity and LVdP/dtmin separated MIchf from MInf at 7 days. In addition to distinguishing all the groups on an average basis, left atrial diameter distinguished all MIchf animals from Sham and MInf. In conclusion, significantly increased left atrial diameter and infarct size >40% of total LV circumference may serve as major criteria for heart failure with pulmonary congestion after MI in mice.     

Na(+)/H(+) exchange inhibition-induced cardioprotection in dogs: effects on neutrophils versus cardiomyocytes

Numerous studies have examined the effect of Na(+)/H(+) exchanger (NHE) inhibition on the myocardium; however, the effect of NHE-1 inhibition on neutrophil function has not been adequately examined. An in vivo canine model of myocardial ischemia-reperfusion injury in which 60 min of left anterior descending coronary artery occlusion followed by 3 h of reperfusion was used to examine the effect of NHE-1 inhibition on infarct size (IS) and neutrophil function. BIIB-513, a selective inhibitor of NHE-1, was infused before ischemia. IS was expressed as a percentage of area at risk (IS/AAR). NHE-1 inhibition significantly reduced IS/AAR and reduced neutrophil accumulation in the ischemic myocardium. NHE-1 inhibition attenuated both phorbol 12-myristate 13-acetate- and platelet-activating factor-induced neutrophil respiratory burst but not CD18 upregulation. Furthermore, NHE-1 inhibition directly protected cardiomyocytes against metabolic inhibition-induced lactate dehydrogenase release and hypercontracture. This study provides evidence that the cardioprotection induced by NHE-1 inhibition is likely due to specific protection of cardiomyocytes and attenuation of neutrophil activity.