Dual-tracer assessment of coupling between cardiac sympathetic neuronal function and downregulation of beta-receptors during development of hypertensive heart failure of rats

Chronic ethanol increases calcium/calmodulin-dependent protein kinaseIIδ gene expression and decreases monoamine oxidase amount in rat heart muscles: Rescue effect of Zingiber officinale (ginger) extract

OBJECTIVE

Association between chronic alcohol intake and cardiac abnormality is well known; however, the precise underlying molecular mediators involved in ethanol-induced heart abnormalities remain elusive. This study investigated the effect of chronic ethanol exposure on calcium/calmodulin-dependent protein kinase IIδ (CaMKIIδ) gene expression and monoamine oxidase (MAO) levels and histological changes in rat heart. It was also planned to find out whether Zingiber officinale (ginger) extract mitigated the abnormalities induced by ethanol in rat heart.

METHODS

Male wistar rats were divided into three groups of eight animals each: control, ethanol, and ginger extract treated-ethanol (GETE) groups.

RESULTS

After 6 weeks of treatment, the results revealed a significant increase in CaMKIIδtotal and isoforms δ2 and δ3 of CaMKIIδ gene expression as well as a significant decrease in the MAO levels in the ethanol group compared to that in the control group. Moreover, compared to the control group, the ethanol group showed histological changes, such as fibrosis, heart muscle cells proliferation, myocyte hypertrophy, vacuolization, and focal lymphocytic infiltration. Consumption of ginger extract along with ethanol ameliorated CaMKIIδtotal. In addition, compared to the ethanol group, isoforms gene expression changed and increased the reduced MAO levels and mitigated heart structural changes.

CONCLUSION

These findings indicate that ethanol-induced heart abnormalities may, in part, be associated with Ca2+ homeostasis changes mediated by overexpression of CaMKIIδ gene and the decrease of MAO levels and that these effects can be alleviated by using ginger extract as an antioxidant and anti-inflammatory agent.

Monoamine oxidase B prompts mitochondrial and cardiac dysfunction in pressure overloaded hearts

AIMS

Monoamine oxidases (MAOs) are mitochondrial flavoenzymes responsible for neurotransmitter and biogenic amines catabolism. MAO-A contributes to heart failure progression via enhanced norepinephrine catabolism and oxidative stress. The potential pathogenetic role of the isoenzyme MAO-B in cardiac diseases is currently unknown. Moreover, it is has not been determined yet whether MAO activation can directly affect mitochondrial function.

RESULTS

In wild type mice, pressure overload induced by transverse aortic constriction (TAC) resulted in enhanced dopamine catabolism, left ventricular (LV) remodeling, and dysfunction. Conversely, mice lacking MAO-B (MAO-B(-/-)) subjected to TAC maintained concentric hypertrophy accompanied by extracellular signal regulated kinase (ERK)1/2 activation, and preserved LV function, both at early (3 weeks) and late stages (9 weeks). Enhanced MAO activation triggered oxidative stress, and dropped mitochondrial membrane potential in the presence of ATP synthase inhibitor oligomycin both in neonatal and adult cardiomyocytes. The MAO-B inhibitor pargyline completely offset this change, suggesting that MAO activation induces a latent mitochondrial dysfunction, causing these organelles to hydrolyze ATP. Moreover, MAO-dependent aldehyde formation due to inhibition of aldehyde dehydrogenase 2 activity also contributed to alter mitochondrial bioenergetics.

INNOVATION

Our study unravels a novel role for MAO-B in the pathogenesis of heart failure, showing that both MAO-driven reactive oxygen species production and impaired aldehyde metabolism affect mitochondrial function.

CONCLUSION

Under conditions of chronic hemodynamic stress, enhanced MAO-B activity is a major determinant of cardiac structural and functional disarrangement. Both increased oxidative stress and the accumulation of aldehyde intermediates are likely liable for these adverse morphological and mechanical changes by directly targeting mitochondria.

Monoamine oxidases as sources of oxidants in the heart

Oxidative stress can be generated at several sites within the mitochondria. Among these, monoamine oxidase (MAO) has been described as a prominent source. MAOs are mitochondrial flavoenzymes responsible for the oxidative deamination of catecholamines, serotonin and biogenic amines, and during this process they generate H2O2 and aldehyde intermediates. The role of MAO in cardiovascular pathophysiology has only recently gathered some attention since it has been demonstrated that both H2O2 and aldehydes may target mitochondrial function and consequently affect function and viability of the myocardium. In the present review, we will discuss the role of MAO in catecholamine and serotonin clearance and cycling in relation to cardiac structure and function. The relevant contribution of each MAO isoform (MAO-A or -B) will be discussed in relation to mitochondrial dysfunction and myocardial injury. Finally, we will examine both beneficial effects of their pharmacological or genetic inhibition along with potential adverse effects observed at baseline in MAO knockout mice, as well as the deleterious effects following their over-expression specifically at cardiomyocyte level. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

The role of renin angiotensin system intervention in stage B heart failure

This article outlines the link between the renin angiotensin aldosterone system (RAAS) and various forms of cardiomyopathy, and also reviews the understanding of the effectiveness of RAAS intervention in this phase of ventricular dysfunction. The authors focus their discussion predominantly on patients who have had previous myocardial infarction or those who have left ventricular hypertrophy and also briefly discuss the role of RAAS activation and intervention in patients with alcoholic cardiomyopathy.

Transient hypercapnic stress causes exaggerated and prolonged elevation of cardiac and renal interstitial norepinephrine levels in conscious hypertensive rats

The responses of sympathetic nerve activity to transient stress can be exaggerated in salt-sensitive (SS), hypertensive subjects. Cardiac and renal interstitial norepinephrine (iNE) levels during and after transient hypercapnia were investigated in conscious SS rats. Dahl SS and salt-resistant (SR) 6-wk-old rats were fed a high-salt diet, and at 12 wk iNE levels in the heart and kidney were determined using microdialysis with probes inserted in the left ventricular (LV) wall and kidney. A telemetry system determined blood pressure and heart rate (HR) in separate animals. After recovery from the operation, data were collected before, during, and after exposure to normoxic 10% CO2 for 25 min under unanesthetized conditions. The plasma NE concentrations at baseline did not differ between the two strains. Both cardiac and renal iNE levels were much higher in SS rats than in SR rats at baseline as well as during hypercapnic stress. After stress, the markedly increased iNE levels of SS rats were prolonged in the LV as well as in the kidney. During hypercapnic stress, HR decreased in both SS and SR rats, while sudden increases in HR immediately after the withdrawal from stress were followed by its slower reduction in SS rats compared with SR rats. In conclusion, transient hypercapnic stress causes exaggerated and prolonged elevation of iNE levels in the heart as well as in kidneys of SS animals.

Fluvastatin attenuates diabetes-induced cardiac sympathetic neuropathy in association with a decrease in oxidative stress

BACKGROUND

Increased oxidative stress might contribute to diabetic (DM) neuropathy, so the effects of long-term treatment with fluvastatin (FL) on myocardial oxidative stress and cardiac sympathetic neural function were investigated in diabetic rats.

METHODS AND RESULTS

FL (10 mg . kg(-1) . day(-1), DM-FL) or vehicle (DM-VE) was orally administered for 2 weeks to streptozotocin-induced DM rats. Cardiac oxidative stress was determined by myocardial 8-iso-prostaglandin F(2alpha) (PGF(2alpha)) and NADPH oxidase subunit p22(phox) mRNA expression. Sympathetic neural function was quantified by autoradiography using (131)I- and (125)I-metaiodobenzylguanidine (MIBG). FL did not affect plasma glucose levels but remarkably decreased PGF(2alpha) levels compared with DM-VE rats (13.8+/-9.2 vs 175.0+/-93.9 ng/g tissue), although PGF(2alpha) levels were below the detection limit in non-DM rats. FL significantly reduced myocardial p22(phox) mRNA expression. Cardiac (131)I-MIBG uptake was lower in DM-VE rats than in non-DM rats, but the decrease was attenuated in DM-FL rats (1.31+/-0.08, 1.88+/-0.22, and 1.58+/-0.18 %kg dose/g, respectively, P<0.01). Cardiac MIBG clearance was not affected by the induction of DM or by FL, indicating that the reduced MIBG uptake in DM rats might result from impaired neural function.

CONCLUSIONS

FL ameliorates cardiac sympathetic neural dysfunction in DM rats in association with attenuation of increased myocardial oxidative stress.

Brief Episode of Myocardial Ischemia Before Prolonged Ischemia Attenuates Cardiac Sympathetic Nerve Injury

BACKGROUND

The aim of this study was to investigate the effects of brief ischemia before prolonged ischemia on cardiac sympathetic neural function. Brief ischemia inhibits the sympathetic neural release of norepinephrine (NE) during subsequent sustained ischemia. However, whether it can attenuate the neural function after sustained ischemia remains unknown.

METHODS AND RESULTS

Sympathetic neural function was assessed using 123I-metaiodobenzylguanidine (MIBG) in patients who with (Group I) or without angina (Group II) within 3 days prior to acute myocardial infarction. In the rat experiment, cardiac interstitial NE (iNE) with or without pretreatment of 5-min coronary ligation was determined during a 30-min occlusion. Differences between MIBG and Thallium-201 for the total defect score were significantly greater in Group II than in Group I (6.1 +/- 4.0 vs 0.4 +/- 4.4). Levels of iNE were less in rats with a 5-min pretreatment (7.3 +/- 2.3 vs 18.6 +/- 5.9 x 10(3) pg/ml, p < 0.01) and MIBG uptake of ischemic region was greater (0.061 +/- 0.029 vs 0.031 +/- 0.011 %kg dose/g, p < 0.05) compared with rats without the pretreatment.

CONCLUSION

A brief episode of ischemia attenuates the sympathetic neural injury caused by subsequent prolonged ischemia and this protective effect is associated with attenuation of NE release during the prolonged ischemia.

Ischemia-Induced Norepinephrine Release, but not Norepinephrine-Derived Free Radicals, Contributes to Myocardial Ischemia - Reperfusion Injury

BACKGROUND

Norepinephrine (NE)-derived free radicals may contribute to myocyte injury after ischemia -reperfusion, so the influence of sympathetic denervation on myocardial ischemia - reperfusion injury was investigated in the present study.

METHODS AND RESULTS

Cardiac sympathetic denervation was produced in Wistar rats by a solution of 10% phenol 1 week before ischemia. Atenolol (0.5 mg/kg) was intravenously administered 10 min before the coronary occlusion. The left coronary artery was occluded for 30 min and thereafter reperfused. Cardiac interstitial fluid was collected by a microdialysis probe and free radicals in dialysate were determined by electron paramagnetic resonance (EPR) spin trapping, using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap. The ratio of infarct size to the ischemic area at risk (I/R) was decreased in both the phenol and atenolol groups compared with control (28.5+/-11.3, 31.8+/-10.7 vs 50.6+/-14.7%, p<0.05). During the coronary occlusion, concentrations of interstitial NE increased markedly in the control and atenolol groups, but was unchanged in the phenol group. EPR signal intensity (relative value to internal standard) was maximal at 1 h after reperfusion and was similar in the phenol and control groups (0.32+/-0.15 vs 0.45+/-0.19).

CONCLUSIONS

Cardiac denervation protected myocyte against ischemia-reperfusion injury through decreasing direct NE toxicity, but not through decreasing NE-derived free radicals.

Cardiac neurotransmission SPECT imaging

The sympathetic nervous system has great influence on cardiovascular physiology. Cardiac neurotransmission single photon emission computed tomography (SPECT) imaging allows in vivo noninvasive assessment of presynaptic reuptake and storage of neurotransmitters, which offers characterization of the cardiac neuronal function in different diseases of the heart and other altered metabolic or functional conditions. Therefore assessment of the integrity of cardiac sympathetic innervation may help in the diagnosis of these disorders, as well as in prognostication, and will result in better therapy and outcome. At present, the most widely available SPECT tracer by which to assess cardiac neurotransmission is metaiodobenzylguanidine labeled with iodine 123. This article focuses on reviewing the characteristics of cardiac SPECT imaging with I-123 metaiodobenzylguanidine and its role in the assessment of pathophysiologic changes during relevant clinical conditions.

Saturated glucose uptake capacity and impaired fatty acid oxidation in hypertensive hearts before development of heart failure

Abnormalities in energy metabolism may play an important role in the development of hypertensive heart failure. However, the transition from compensated hypertrophy to heart failure is not fully understood in terms of energy metabolism. In Dahl salt-sensitive (DS) and salt-resistant (DR) rats, myocardial fatty acid and glucose uptake values were determined using (131)I- or (125)I-labeled 9-methylpentadecanoic acid ((131)I- or (125)I-9MPA), and [(14)C]deoxyglucose ([(14)C]DG), fatty acid beta-oxidation was identified using thin-layer chromatography, and insulin-stimulated glucose-uptake was observed using a euglycemic hyperinsulinemic glucose clamp. Six-week-old rats were fed a diet that contained 8% NaCl, which resulted in development of compensated hypertrophy in DS rats at 12 wk of age and ultimately led to heart failure by 18 wk of age. Uptake of [(14)C]DG increased markedly with age in the DS rats, whereas (131)I-9MPA uptake was marginally but significantly increased only in animals aged 12 wk. The ratio of (125)I-9MPA beta-oxidation metabolites to total uptake in the DS rats was significantly lower (P < 0.05) at 12 (37%) and 18 (34%) wk compared with at 6 (45%) wk. Insulin increased [(14)C]DG uptake more than twofold in the DS rats at 6 wk, although this increase was markedly attenuated at 12 and 18 wk (11 and 8%, respectively). Our data suggest that in a hypertrophied heart before heart failure, fatty acid oxidation is impaired and the capacity to increase glucose uptake during insulin stimulation is markedly reduced. These changes in both glucose and fatty acid metabolism that occur in association with myocardial hypertrophy may have a pathogenic role in the subsequent development of heart failure.

Supersensitive response to isoproterenol in patients with marked global reduction of cardiac metaiodobenzylguanidine uptake

It is unknown whether the non-transplanted, denervated human heart is supersensitive to beta-adrenergic agonist in terms of inotropism and chronotropism. In the present study, 36 patients with normal left ventricular (LV) wall motion were divided into 3 groups according to the cardiac metaiodobenzylguanidine (MIBG) scintigrams: group I with normal MIBG uptake, group II with regionally reduced MIBG uptake, and group III with globally reduced MIBG uptake (heart-to-mediastinum ratio <1.6). Before isoproterenol (IP) infusion, heart rate (HR), blood pressure (BP) and echocardiographic indices were similar among the groups. There was a trend toward a greater increase in HR with IP (0.01 microg x kg (-1) x min(-1)) in group III (27+/-18 beats/min) than in groups I (20+/-8) and II (17+/-8) despite the lack of a significant difference in BP reduction by IP. During IP infusion, increases in posterior wall motion amplitude and LV fractional shortening were significantly greater in group III (4.5+/-1.8 mm and 16.4+/-5.4%, respectively) than in groups I (1.5+/-2.5 mm and 8.7+/-6.4%) and II (2.6+/-1.7 mm and 8.9+/-7.9%). The present results suggest that the sympathetically denervated human heart is supersensitive to IP and the exaggerated responses may be caused, at least in part, by a postsynaptic mechanism.

Long-term treatment with low-dose, but not high-dose, guanethidine improves ventricular function and survival of rats with heart failure after myocardial infarction

OBJECTIVES

We sought to evaluate the effects of various doses of guanethidine, a sympathoinhibitory drug, on ventricular function and survival in chronic heart failure (CHF) after myocardial infarction (MI) in rats.

BACKGROUND

Direct inhibition of sympathetic outflow by a sympathoinhibitory drug might be an effective approach to therapy of CHF. However, recent clinical trials suggest that excessive suppression of sympathetic activity has an adverse effect on outcome. It remains unclear whether the beneficial effects of the sympathoinhibitory drug would be modified by its dosage.

METHODS

Three doses of guanethidine (low-dose [LG], 1 mg/kg/day; medium-dose, 3 mg/kg/day; high-dose, 10 mg/kg/day) were administered via an osmotic mini-pump for 4 weeks. Hemodynamics, left ventricular (LV) diameters, plasma and myocardial norepinephrine (NE) levels, and survival were determined for four weeks after MI.

RESULTS

As compared with MI rats receiving vehicle, LG suppressed LV dilation (9.2 +/- 0.9 mm vs. 11.0 +/- 0.8 mm, p < 0.05) and improved LV fractional shortening (25.0 +/- 4.5% vs. 16.4 +/- 4.7%, p < 0.05) in association with a reduction of plasma NE levels (520 +/- 250 pg/ml vs. 1,000 +/- 570 pg/ml, p < 0.05), but not with a significant reduction of noninfarcted myocardial NE levels (154 +/- 71 ng/g vs. 207 +/- 71 ng/g). Low-dose guanethidine reduced 24-h (6%) and 28-day mortality (6%), as compared with untreated MI rats (36% and 52%, respectively). High-dose guanethidine also reduced 24-h mortality (12%) but increased 28-day mortality (91%), in association with a depletion of myocardial NE. Medium-dose guanethidine had no beneficial effects on LV hemodynamics or long-term survival.

CONCLUSIONS

These results indicate that the dosage of the sympathoinhibitory drug might be quite important for the treatment of CHF.

Expression of V-1, a novel catecholamine biosynthesis regulatory protein, is enhanced by hypertension in atrial myocytes of Dahl salt-sensitive rats

V-1 positively controls catecholamine synthetic gene transcription to promote catecholamine production in PC12D cells. In this study, immunohistochemical analysis revealed that in Wistar rats, V-1 immunoreactivity was localized not only in sympathetic axons but also in the cytoplasm of cardiomyocytes, and that the immunoreactivity in atrial myocytes was more intense than that in ventricular myocytes. Western blot analysis also showed that V-1 expression level in the atrium was higher than that in the ventricle of Wistar rat hearts. When Dahl salt-sensitive (DS) rats were fed an 8% NaCl diet after the age of 6 weeks, blood pressure was raised 230mm Hg at 18 weeks. V-1 expression was shown to be increased in the atrial myocytes of these DS rats, but not in the sympathetic axons, when assayed by immunohistochemistry. These results suggest that in normotensive rats, V-1 is preferentially expressed in the cytoplasm of cardiomyocytes in the atrium rather than in the ventricle. It is also suggested that V-1 expression is increased by hypertension in DS rat atrium.

Effects of the angiotensin-converting enzyme inhibitor enalapril on sympathetic neuronal function and beta-adrenergic desensitization in heart failure after myocardial infarction in rats

One of the beneficial effects of angiotensin-converting enzyme (ACE) inhibitors in the treatment of heart failure may derive from sympathoinhibition and the prevention of beta-adrenergic desensitization. However, the roles of these properties in the overall effects of ACE inhibitor are not clear. We studied the effects of chronic enalapril treatment (20 mg/L in drinking water for 12 weeks) on left ventricular (LV) function, cardiac norepinephrine (NE), sympathetic neuronal function assessed by 131I-metaiodobenzylguanidine (MIBG), beta-receptors, and isometric contraction of papillary muscle in rats with myocardial infarction (MI) induced by coronary artery ligation. Decreased LV function in the MI rats was associated with reduced cardiac NE content and MIBG uptake, and severely blunted responses of non-infarcted papillary muscle to isoproterenol, forskolin, and calcium. Enalapril attenuated LV remodeling in association with a reduction of the ventricular loading condition and restored baseline developed tension of non-infarcted papillary muscle to the level of sham-operated rats. However, enalapril did not improve cardiac NE content, MIBG uptake, or inotropic responsiveness to beta-agonists. These results suggest that the major effect of the ACE inhibitor enalapril in the treatment of heart failure is not due to sympathoinhibition or restoration of beta-adrenergic pathway in this model of heart failure.

Norepinephrine transporter (NET) is expressed in cardiac sympathetic ganglia of adult rat

The sympathetic nervous system plays a cardinal role in regulating cardiac function through releasing the neurotransmitter norepinephrine (NE). In comparison with central nervous system, the molecular mechanism of NE uptake in myocardium is not clear. In present study, we proved that in rat the CNS type of NE transporter (NET) was also expressed in middle cervical-stellate ganglion complex (MC-SG complex) which is considered to control the activity of heart, but not expressed in myocardium. The results also showed that NET expression level in right ganglion was significantly higher than in the left, rendering the greater capacity of NE uptake in right ventricle, a fact which may contribute to the maintenance of right ventricular function under pathologic state.

The role of neuronal and extraneuronal plasma membrane transporters in the inactivation of peripheral catecholamines

Catecholamines are translocated across plasma membranes by transporters that belong to two large families with mainly neuronal or extraneuronal locations. In mammals, neuronal uptake of catecholamines involves the dopamine transporter (DAT) at dopaminergic neurons and the norepinephrine transporter (NET) at noradrenergic neurons. Extraneuronal uptake of catecholamines is mediated by organic cation transporters (OCTs), including the classic corticosterone-sensitive extraneuronal monoamine transporter. Catecholamine transporters function as part of uptake and metabolizing systems primarily responsible for inactivation of transmitter released by neurons. Additionally, the neuronal catecholamine transporters, recycle catecholamines for rerelease, thereby reducing requirements for transmitter synthesis. In a broader sense, catecholamine transporters function as part of integrated systems where catecholamine synthesis, release, uptake, and metabolism are regulated in a coordinated fashion in response to the demands placed on the system. Location is also important to function. Neuronal transporters are essential for rapid termination of the signal in neuronal-effector organ transmission, whereas non-neuronal transporters are more important for limiting the spread of the signal and for clearance of catecholamines from the bloodstream. Besides their presynaptic locations, NET and DAT are also present at several extraneuronal locations, including syncytiotrophoblasts of the placenta and endothelial cells of the lung (NET), stomach and pancreas (DAT). The extraneuronal monoamine transporter shows a broad tissue distribution, whereas the other two non-neuronal catecholamine transporters (OCT1 and OCT2) are mainly localized to the liver, kidney, and intestine. Altered function of peripheral catecholamine transporters may be involved in disturbances of the autonomic nervous system, such as occurs in congestive heart failure and hypernoradrenergic hypertension. Peripheral catecholamine transporters provide important targets for clinical imaging of sympathetic nerves and diagnostic localization and treatment of neuroendocrine tumors, such as neuroblastomas and pheochromocytomas.

Beta-adrenergic receptors and calcium cycling proteins in non-failing, hypertrophied and failing human hearts: transition from hypertrophy to failure

Left ventricular hypertrophy may lead to heart failure. The transition between hypertrophy and heart failure is, however, incompletely understood. On the cellular level, human heart failure is characterized by alterations in Ca(2+)-cycling proteins and beta-adrenergic receptor density, but the hypertrophied human heart remains largely under studied. In this investigation, 21 donor hearts which could not be used for transplantation were studied. Ten of these hearts came from organ donors with documented left ventricular hypertrophy and normal cardiac function. Eleven of the hearts were non-failing, obtained from individuals with no evidence of cardiac disease. Nine failing hearts from transplant recipients were also studied. beta-adrenergic receptor density was determined by radioligand binding. mRNA for atrial natriuretic factor, calsequestrin, sarcoplasmic reticulum Ca(2+)-ATPase, and phospholamban was measured by Northern blot. Actin, calsequestrin, sarcoplasmic reticulum Ca(2+)-ATPase, and phospholamban proteins were quantified by Western blot. In both hypertrophied and failing ventricles, mRNA for atrial natriuretic factor was expressed, as compared to no expression in non-failing hearts. In failing hearts, beta -adrenergic receptor density and both mRNA and protein levels of the Ca(2+)-ATPase were significantly decreased v non-failing hearts. By comparison, hypertrophied hearts showed a reduction in mRNA expression for both the Ca(2+)-ATPase and phospholamban with no change in the corresponding protein levels, and no change in beta-receptors. These data suggest that the previously demonstrated reduction in beta-adrenergic receptors and Ca(2+)-cycling proteins in the failing human heart may be features of the decompensated state, but are not found in human hearts with left ventricular hypertrophy and preserved systolic function.

Heterogeneous cardiac sympathetic innervation in heart failure after myocardial infarction of rats

We examined cardiac neuronal function and beta-receptor with a dual-tracer method of [(131)I]meta-iodobenzylguanidine (MIBG) and [(125)I]iodocyanopindolol (ICYP) in rat heart failure after myocardial infarction (MI). In rats with MI, left ventricular (LV) systolic function decreased, and LV dimension and right ventricular (RV) mass increased gradually. MIBG accumulations of the noninfarcted LV (remote region) and RV decreased by 15% at 1 wk compared with sham-operated rats, and these accumulations were restored by 71% and 56%, respectively, at 24 wk compared with age-matched sham rats despite sustained depletion of myocardial norepinephrine contents in these regions. ICYP accumulation of the remote region and of the RV did not decrease at any stages. Myocardial MIBG distribution was heterogeneous at 1 wk when it was lower in the peri-infarcted region than in the remote region, associated with reduced ICYP accumulation in the peri-infarcted region. The heterogeneous distribution of both isotopes disappeared at 12 wk. Thus cardiac sympathetic neuronal alteration was coupled with downregulation of beta-receptors in rat heart failure after MI. The abnormal adrenergic signaling occurred heterogeneously in terms of ventricular distribution and time course after MI.