Increased dopamine in the failing hamster heart: transvesicular transport of dopamine limits the rate of norepinephrine synthesis

Sympathetic nerve function--assessment by radioisotope dilution analysis

Radioisotope dilution measurements of norepinephrine spillover (rate of entry of the transmitter into plasma) provide more accurate assessments of sympathoneural transmitter release than allowed by measurements of plasma catecholamine concentrations alone. Measurements of total body norepinephrine spillover, as an index of global sympathetic outflow, allow effects on plasma clearance to be distinguished from effects on release of catecholamines into plasma, while spillovers from specific tissues enable examination of regionalized sympathetic responses. However, spillovers of norepinephrine represent only a fraction of the transmitter that escapes neuronal and extraneuronal uptake after release by nerves. Numerous factors may influence this fraction and measures spillovers independently of transmitter release by nerves. Modified radioisotope dilution methods for assessment of rate processes operating within and between intracellular and extracellular compartments have further improved our understanding of the relationships of norepinephrine release, uptake, spillover, turnover, and metabolism. This article reviews the breadth of information about sympathetic nerve function attainable using catecholamine radioisotope dilution analyses against a backdrop of the relative advantages and methodological limitations associated with the methodology.

Beneficial effects of metoprolol on myocardial sympathetic function: Evidence from a randomized, placebo-controlled study in patients with congestive heart failure

BACKGROUND

We sought to investigate whether beta-blockers exert a presynaptic effect in the myocardium as measured by 123I-metaiodobenzylguanidine.

METHODS

The study comprised 59 patients with congestive heart failure, New York Heart Association class II or III, and left ventricular ejection fraction <35%. After an open label titration phase, patients were randomized to their maximal tolerable dose of metoprolol or placebo. Myocardial MIBG uptake was measured before the titration phase and after 6 months of treatment. Other parameters were maximal oxygen consumption, 6-minute walking test, plasma neurohormones, and echocardiographic parameters.

RESULTS

We found a 21.9% increase in mean myocardial MIBG uptake after 6 months of treatment with metoprolol. In contrast, MIBG uptake decreased by 7.8% in the placebo group (P = 0.03 compared with metoprolol). Left ventricular end-diastolic diameter decreased from 74 +/- 11 mm to 67 +/- 10 mm (P <.05, within-group comparison) and LVEF increased from 25.3% +/- 7.4% to 32.6% +/- 9.6% (P <.05, within-group comparison) in the metoprolol group. Placebo-treated patients showed no significant changes. Comparison of changes in left ventricular end-diastolic diameter and LVEF between metoprolol and placebo did not reach statistical significance (P = 0.2).

CONCLUSIONS

This randomized, placebo-controlled study demonstrates that metoprolol has a presynaptic effect as measured by myocardial MIBG scintigraphy in both ischemic and nonischemic cardiomyopathy.

Relationship between cardiac 123I-metaiodobenzylguanidine imaging and the transcardiac gradient of neurohumoral factors in patients with dilated cardiomyopathy

Cardiac sympathetic nervous function is altered in congestive heart failure (CHF) and the uptake and washout rate of cardiac 123I-metaiodobenzylguanidine (MIBG) are useful markers for evaluating the severity of it. To assess what parameters predict decreased uptake or increased washout rate of MIBG, the concentrations of neurohumoral factor in both the aorta (Ao) and coronary sinus (CS) were measured, as well as hemodynamic parameters by catheterization, in patients with dilated cardiomyopathy (DCM). MIBG imaging was performed within 1 week of cardiac catheterization. Regarding MIBG parameters, the correlation with the transcardiac gradient of norepinephrine (NE), brain natriuretic peptide (BNP) and hemodynamics was investigated. Stepwise multivariate regression analysis was used to determine which variables closely correlated with cardiac MIBG parameters. There was a significant increase in the NE level between the Ao (446 pg/ml) and the CS (727 pg/ml). According to stepwise multivariate regression analysis, the heart/mediastinum (H/M) ratio independently correlated with the transcardiac gradient of BNP (r=-0.480, p<0.01), and the washout rate independently correlated with the transcardiac gradient of NE (r=0.481, p<0.01). These findings indicate that the H/M ratio may reflect the transcardiac gradient of BNP, which implies the degree of left ventricular dysfunction and/or damage and the washout rate may reflect altered cardiac sympathetic nerve terminal in DCM patients with CHF, suggesting that both the H/M ratio and washout rate provide important information about the failing ventricle.

Autonomic nervous system activity imbalance in cardiomyopathic hamster

There is strong evidence that autonomic imbalance plays an important role in progression of heart failure. Analysis of heart rate variability (HRV) has achieved substantial acceptance as a noninvasive method for the assessment of autonomic tone. The purpose of this investigation was to study HRV in an experimental model of heart failure using cardiomyopathic (BIO TO.2) hamsters. Animals showed an autonomic imbalance of cardiac control that seems due to attenuation of parasympathetic activity and an enhanced sympathetic tone. The reduction of parasympathetic activity in BIO TO.2 hamsters is suggested by (a) the reduction of the high-frequency (HF) spectrum, and (b) the lack of atropine to generate a response. The increased sympathetic activity is indicated by (a) the decreased time-domain indexes, (b) the increased LF/HF ratio of the power spectrum, and (c) the alteration of HRV indexes induced by propranolol. These results support the notion that in heart failure, there is a similar autonomic imbalance in both human and hamster and suggest that the cardiomyopathic hamster is a suitable experimental model for studying the involvement of the autonomic nervous system in the progression of heart failure.

Differential recruitment of alpha 1- and beta-adrenoceptors in inotropic control of atrial child myocardium by endogenous noradrenaline

Noradrenaline release, graded by frequency variation of field stimulation (0.1-2 Hz), in atrial myocardial specimens (n=45) from children (n=21) with congenital heart defects, was used to examine the inotropic responses of graded, receptor-selective, endogenous stimulation. Muscle trabeculae subjected to autonomic blockage by timolol, prazosin and atropine showed a slight positive force-frequency relationship (staircase phenomenon). Blockage by atropine/prazosin (i.e. beta-adrenoceptor stimulation) or atropine/timolol (i.e. alpha1-adrenoceptor stimulation) both resulted in positive inotropic effects. A group of specimens opposed by atropine and primarily subjected to frequency variation, secondly was returned to 1 Hz. Stabilization was followed by sequential reversal by beta-blocker (timolol), alpha 1-adrenoceptor stimulation by exogenous noradrenaline, reversal by alpha 1-blocker (prazosin), and finally supramaximal beta-adrenoceptor stimulation (isoprenaline). The maximal levels of inotropic responses mediated by exogenous alpha 1- and beta-adrenoceptor stimulation was estimated. Analysis of the contraction-relaxation cycles revealed that alpha1- and beta-adrenoceptors were recruited differentially. The alpha1-adrenoceptor mediated, endogenous inotropic effect at 1 Hz was close to the level obtained by exogenous noradrenaline stimulation. In contrast, less than 70% of the beta-adrenoceptor mediated, exogenous inotropic effect was expressed by endogenous noradrenaline at the same stimulating frequency, thus indicating that the alpha1-adrenoceptors may be located closer to the adrenergic nerve terminals than the beta-adrenoceptors. There may be a heterogeneous relationship within the same heart as to the relative distance between the nerve terminals and the adrenoceptors. Spatial localization of adrenergic receptors relative to adrenergic nerve terminals adds another aspect to adrenergic regulation. The alpha1-adrenoceptor pathway may play an important role, especially in low-intensity sympathetic inotropic myocardial control, whereas the beta-adrenoceptor pathway adds important effects to the high-intensity sympathetic regulation. Sympathetic activity may thus tonically stimulate the alpha1-adrenoceptor pathway, without necessarily stimulating the beta-adrenoceptor pathway to the same extent.

Catecholamine concentration in rat liver after high level transection of the spinal cord

The high level transection of the spinal cord (C-7) provokes a sustained increase of rat liver catecholamines: biphasic increase in norepinephrine level 1 hour and 24 hour after the operation and 7-fold increase of dopamine content 4 hour after the chordotomy. In contrast to cervical transection, sham operation causes only an initial catecholamine increase, the maximum being at the first hour after the surgery. Our experimental data indicate a possible participation of cervical spinal pathways in regulation of liver catecholamine content. It is also shown that bilateral adrenalectomy augments liver norepinephrine concentration in spinal rats as compared to the non-adrenalectomized ones. The results presented here indicate that cervical chordotomy affects the functioning of the sympatho-adrenal system, thus provoking specific changes in liver catecholamine content. The potential effect of such changes on a liver metabolic system (tyrosine aminotransferase induction) is discussed.

Monoamine- and histamine-synthesizing enzymes and neurotransmitters within neurons of adult human cardiac ganglia

BACKGROUND

Cardiac ganglia were originally thought to contain only cholinergic neurons relaying parasympathetic information from preganglionic brain stem neurons to the heart. Accumulating evidence, however, suggests that cardiac ganglia contain a heterogeneous population of neurons that synthesize or respond to several different neurotransmitters and neuropeptides. Reports regarding monoamine and histamine synthesis and neurotransmission within cardiac ganglia, however, present conflicting information or are limited in number. Furthermore, very few studies have examined the neurochemistry of adult human cardiac ganglia. The purpose of this study was, therefore, to determine whether monoamine- and histamine-synthesizing enzymes and neurotransmitters exist within neurons of adult human cardiac ganglia.

METHODS AND RESULTS

Human heart tissue containing cardiac ganglia was obtained during autopsies of patients without cardiovascular pathology. Avidin-biotin complex immunohistochemistry was used to demonstrate tyrosine hydroxylase, L-dopa decarboxylase, dopamine beta-hydroxylase, phenylethanolamine-N-methyltransferase, tryptophan hydroxylase, and histidine decarboxylase immunoreactivity within neurons of cardiac ganglia. Dopamine, norepinephrine, serotonin, and histamine immunoreactivity was also found in ganglionic neurons. Omission or preadsorption of primary antibodies from the antisera and subsequent incubation with cardiac ganglia abolished specific staining in all cases examined.

CONCLUSIONS

Our results suggest that neurons within cardiac ganglia contain enzymes involved in the synthesis of monoamines and histamine and that they contain dopamine, norepinephrine, serotonin, and histamine immunoreactivity. Our findings suggest a putative role for monoamine and histamine neurotransmission within adult human cardiac ganglia. Additional, functional evidence will be necessary to evaluate what the physiological role of monoamines and histamine may be in neural control of the adult human heart.

The sympathetic nervous system in chronic heart failure

The sympathetic nervous system plays a pivotal role in the natural history of chronic heart failure (CHF). There is early activation of cardiac adrenergic drive, which is followed by an increasing magnitude of generalized sympathetic activation, with worsening heart failure. The adverse consequences predominate over the short-term compensatory effects and are mediated through downregulation of beta-receptor function and harmful biological effects on the cardiomyocyte. beta-blockers exert a beneficial effect on the natural history of CHF by attenuating the negative biological effects, restoring homogeneity of contractile/relaxant mechanisms, and reducing the risk of myocardial ischemia and arrhythmias. After pioneering work conducted over 20 years ago, numerous studies have shown the beneficial effects of beta-blockade on left ventricular function, and survival, morbidity, and mortality rates in CHF. Large-scale trials are underway to determine the overall benefits of beta-blockade in heart failure.

Myocardial sympathetic denervation prevents chamber-specific alteration of beta-adrenergic transmembrane signaling in rabbits with heart failure

OBJECTIVES

The purpose of this study was to assess the effect of myocardial sympathetic denervation on the chamber-specific alteration of beta-adrenergic signaling in left ventricular failure in rabbits.

BACKGROUND

Local abnormalities in sympathetic nerve terminals, including the neuronal reuptake of norepinephrine, are thought to be responsible for the chamber-specific regulation of beta-adrenergic signaling in heart failure.

METHODS

Sixteen rabbits were given 6-hydroxydopamine, 25 mg/kg body weight intravenously on days 1 and 2 and 50 mg/kg intravenously on days 7 and 8. Another 16 rabbits received vehicle. Aortic regurgitation was induced in eight of the 6-hydroxydopamine-treated and eight of the vehicle-treated rabbits on day 14. Another eight of the 6-hydroxydopamine-treated and eight of the vehicle-treated rabbits underwent a sham operation. The hearts were excised for biochemical analysis on day 21.

RESULTS

Hemodynamic characteristics on day 21 showed left ventricular failure in both the aortic regurgitation groups. The plasma norepinephrine concentration on day 21 was higher in both the aortic regurgitation groups than in the sham groups. The beta-adrenoceptor densities and isoproterenol plus 5'-guanylylimidodiphosphate-, 5'-guanylylimidodiphosphate- and sodium fluoride-stimulated adenylyl cyclase activities were decreased only in the failing left ventricle of the vehicle-pretreated aortic regurgitation group, but in both ventricles of the 6-hydroxydopamine-pretreated aortic regurgitation group. The basal and forskolin-stimulated adenylyl cyclase activities were similar in both the aortic regurgitation groups and in the sham groups.

CONCLUSIONS

Sympathetic denervation prevented chamber-specific alterations in beta-adrenergic signaling in acute left ventricular failure. Local loss of sympathetic nerve endings, and especially the defective neuronal norepinephrine reuptake, are likely to be responsible for the chamber-specific alteration of the beta-adrenoceptor-G protein-adenylyl cyclase system in heart failure in rabbits.

Cardiac sympathetic nerve function in congestive heart failure

BACKGROUND

Increased availability of norepinephrine (NE) for activation of cardiac adrenoceptors (increased cardiac adrenergic drive) and depletion of myocardial NE stores may contribute to the pathophysiology and progression of congestive heart failure. This study used a comprehensive neurochemical approach to examine the mechanisms responsible for these abnormalities.

METHODS AND RESULTS

Subjects with and without congestive heart failure received intravenous infusions of [(3)H]NE. Cardiac spillover, reuptake, vesicular-axoplasmic exchange, and tissue stores of NE were assessed from arterial and coronary venous plasma concentrations of endogenous and [(3)H]-labeled NE and dihydroxyphenylglycol. Tyrosine hydroxylase activity was assessed from plasma dopa, and NE turnover was assessed from measurements of NE metabolites. NE release and reuptake were both increased in the failing heart; however, the efficiency of NE reuptake was reduced such that cardiac spillover of NE was increased disproportionately more than neuronal release of NE. Cardiac NE stores were 47% lower and the rate of vesicular leakage of NE was 42% lower in the failing than in the normal heart. Cardiac spillover of dopa and NE turnover were increased similarly in congestive heart failure.

CONCLUSIONS

Increased neuronal release of NE and decreased efficiency of NE reuptake both contribute to increased cardiac adrenergic drive in congestive heart failure. Decreased vesicular leakage of NE, secondary to decreased myocardial stores of NE, limits the increase in cardiac NE turnover in CHF. Decreased NE store size in the failing heart appears to result not from insufficient tyrosine hydroxylation but from chronically increased NE turnover and reduced efficiency of NE reuptake and storage.

Abnormalities of cardiac sympathetic function in pacing-induced heart failure as assessed by [123I]metaiodobenzylguanidine scintigraphy

BACKGROUND

Increased activity of the sympathetic nervous system contributes significantly to the pathophysiology of heart failure. However, cardiac efferent sympathetic function has not been well characterized in this disorder. In this study, we evaluated cardiac sympathetic innervation using [123I]metaiodobenzylguanidine (MIBG) and compared this with left ventricular (LV) tissue norepinephrine concentration and myocardial perfusion, assessed by 201Tl, in a canine model of heart failure.

METHODS AND RESULTS

Planar and tomographic cardiac imaging was performed for MIBG and 201Tl in 23 dogs: 8 normal dogs (group 1) and 15 dogs with heart failure induced by right ventricular pacing at 250 beats per minute either continuously for 3 weeks (group 2) or intermittently for 7 weeks (group 3). Plasma and LV tissue norepinephrine concentrations were also measured. Scintigraphic studies in group 2 demonstrated reduced cardiac MIBG activity at heart failure (0.17 +/- 0.04 versus 0.29 +/- 0.05 counts per megabecquerel per pixel at baseline, mean +/- SD; P = .0001), whereas thallium activity was unchanged from baseline. This reduction in cardiac MIBG activity with heart failure was associated with increased intraimage variability in the distribution of MIBG activity (21 +/- 8% versus 13 +/- 7% at baseline, mean +/- SD; P = .0001). The MIBG heart-to-lung ratio was calculated for all groups to control for the inhibitory effect that plasma norepinephrine has on the neuronal uptake of MIBG. There was a positive correlation between LV tissue norepinephrine and the MIBG heart-to-lung ratio (r = .67; P < .001; n = 22), for which the group 2 heart failure animals had the lowest values. No relation existed between plasma norepinephrine concentration and the MIBG heart-to-lung ratio. In addition, regional LV tissue norepinephrine concentration and MIBG activity were both lowest at the apex in normal (group 1) and heart failure (group 2) dogs. The MIBG heart-to-lung ratio also correlated inversely with cardiac filling pressure (r = -.59; P < .05) and heart rate (r = -.65; P < .01) and positively with cardiac output (r = .53; P < .05).

CONCLUSIONS

Heart failure is associated with severe cardiac adrenergic dysfunction manifested by reduced MIBG activity and increased heterogeneity in the LV distribution of MIBG. Furthermore, MIBG scintigraphy is a simple noninvasive method for assessing global and regional LV tissue norepinephrine levels.

Beta-blockers in heart failure: promising or proved?

Despite recent improvements in the management of congestive heart failure, the prognosis of many patients with this condition remains poor. The level of neurohormonal activation appears to be predictive of survival, and clinical studies indicate that inhibition of overactivated neurohormonal systems may be beneficial. Activation of the renin-angiotensin-aldosterone system is well documented in heart failure, and angiotensin-converting enzyme inhibition now has an established role in treatment based on evidence of hemodynamic, symptomatic and mortality benefit. Sympathetic nervous system activation also occurs as a compensatory mechanism in heart failure but with long-term deleterious effects. Increasing evidence suggests that beta-adrenergic blockade can produce hemodynamic and symptomatic improvement in heart failure of idiopathic or ischemic etiology. Trials of beta-adrenergic blocking agents in patients after myocardial infarction suggest a beneficial effect on mortality, even among those with heart failure. However, there remains uncertainty as to how generalizable are the results from the postinfarction trials, particularly in the current therapeutic environment with routine angiotensin-converting enzyme inhibitor therapy. Appropriately powered randomized, controlled trials are required to determine precisely the balance of benefit and risk resulting from long-term beta-blocker therapy in patients with heart failure of ischemic and other etiology.

Myocardial carnitine metabolism in congestive heart failure induced by incessant tachycardia

Persistent tachycardia induces congestive heart failure (CHF), but the mechanism(s) of progressive ventricular dysfunction is (are) unclear. This study was designed to define possible metabolic causes of myocardial dysfunction in rapid ventricular pacing induced CHF. Twelve adult mongrel dogs were paced to 250 beats/min for 19 days. Plasma carnitine, norepinephrine and renin were measured at 0, 1, 2, and 3 weeks. Myocardial high energy phosphates, carnitine, glycogen, glucose, non-collagenous protein and collagen were measured at 19 days. Cardiac output, arterial pressure and pulmonary wedge pressure, measured at baseline and with CHF, showed a decrease in cardiac output and increase in pulmonary wedge pressure. Neurohumoral activation was evident by progressively increasing plasma norepinephrine and renin activity and depletion of myocardial norepinephrine. Plasma free carnitine rose significantly from 12.6 +/- 2.0 control to 28.3 +/- 3.8 nmol/ml at 19 days (p < 0.001), whereas myocardial total carnitine was lower in paced than in control dogs (6.0 +/- 1.9 vs. 14.1 +/- 3.5 nmol/mg non-collagenous protein, p < 0.001). Myocardial ATP ATP and ADP were unchanged, while AMP decreased 22%, and creatine phosphate decreased 30% compared to control animals. Myocardial glucose was normal but glycogen was decreased 54% (p < 0.005). The low myocardial carnitine and elevated plasma carnitine in pacing induced CHF suggests altered carnitine transport or membrane integrity.

Sympathetic dysfunction in heart failure

CHF is a common, complex and life-threatening clinical syndrome. It is widely accepted that enhanced peripheral vascular tone plays a major role in the pathophysiology of CHF. Increased activity of the sympathetic nervous system is one of the most important factors responsible for the increased afterload in CHF. This increase in sympathetic activity occurs early in the course of development of CHF. Efferent sympathetic activity is distributed in a non-uniform way in CHF, with significant increases to the heart and kidney but normal activity to some other organs such as the lung. Increased renal sympathetic activity contributes significantly to altered neural haemodynamics, sodium and water retention, and modulation of the actions of other vasoactive hormones. The regional alteration in sympathetic activity may be largely responsible for the changes in resting regional blood flow to different organs in CHF and the maldistribution of blood flow that occurs during the stress of exercise. Disordered function of cardiovascular reflexes is observed in CHF and may contribute to disordered sympathetic function. In CHF there are significant interactions between the sympathetic nervous system and other humoral systems such as the renin-angiotensin system, AVP, ANP, endothelin and renal DA. The various drugs used in the treatment of CHF have different effects on sympathetic activity: digitalis and ACE inhibitors tend to suppress activity while diuretics may have the opposite effect. Following cardiac transplantation, there is a prompt return of sympathetic function towards normal, although the heart may remain significantly denervated for a long time, with gradual reinnervation. Cyclosporin therapy tends to increase sympathetic activity and this may contribute to post-transplant hypertension.

Dihydroxyphenylalanine and dopamine are released from portal vein together with noradrenaline and dihydroxyphenylglycol during nerve stimulation

The overflows of 3,4-dihydroxyphenylalanine, dopamine, noradrenaline, and 3,4-dihydroxyphenylglycol in canine portal vein superfused in vitro were studied before, during, and after depolarization of sympathetic nerve endings. The four compounds were separated from superfusate and from tissue on Sep-Pak C-18 cartridges and quantified by HPLC with electrochemical detection. Physiological and biochemical methods were used to show that the compound released was most probably 3,4-dihydroxyphenylalanine; the identity of the other endogenous compounds has been established previously. Release of 3,4-dihydroxyphenylalanine was calcium and frequency dependent, inhibited by a-m-L-p-tyrosine (an inhibitor of tyrosine hydroxylase) and augmented by 3-hydroxybenzylhydrazine (an inhibitor of aromatic amino acid decarboxylase). The overflows of dopamine, noradrenaline, and 3,4-dihydroxyphenylglycol from the vein were calcium and frequency dependent. It was estimated that under control conditions, approximately 80% of the total 3,4-dihydroxyphenylalanine that was synthesized was directed to catecholamine biosynthesis, approximately 8% overflowed from the vein, and approximately 14% remained unchanged within the tissue. It is concluded that 3,4-dihydroxyphenylalanine and dopamine are released together with noradrenaline and 3,4-dihydroxyphenylglycol from portal vein upon nerve depolarization.

Beta-adrenergic neuroeffector abnormalities in the failing human heart are produced by local rather than systemic mechanisms

In order to investigate the general cause of beta-adrenergic receptor neuroeffector abnormalities in the failing human heart, we measured ventricular myocardial adrenergic receptors, adrenergic neurotransmitters, and beta-adrenergic receptor-effector responses in nonfailing and failing hearts taken from nonfailing organ donors, subjects with endstage biventricular failure due to idiopathic dilated cardiomyopathy (IDC), and subjects with primary pulmonary hypertension (PPH) who exhibited isolated right ventricular failure. Relative to nonfailing PPH left ventricles, failing PPH right ventricles exhibited (a) markedly decreased beta 1-adrenergic receptor density, (b) marked depletion of tissue norepinephrine and neuropeptide Y, (c) decreased adenylate cyclase stimulation in response to the beta agonists isoproterenol and zinterol, and (d) decreased adenylate cyclase stimulation in response to Gpp(NH)p and forskolin. These abnormalities were directionally similar to, but generally more pronounced than, corresponding findings in failing IDC right ventricles, whereas values for these parameters in nonfailing left ventricles of PPH subjects were similar to values in the nonfailing left ventricles of organ donors. Additionally, relative to paired nonfailing PPH left ventricles and nonfailing right ventricles from organ donors, failing right ventricles from PPH subjects exhibited decreased adenylate cyclase stimulation by MnCl2. These data indicate that: (a) Adrenergic neuroeffector abnormalities present in the failing human heart are due to local mechanisms; systemic processes do not produce beta-adrenergic neuroeffector abnormalities. (b) Pressure-overloaded failing right ventricles of PPH subjects exhibit decreased activity of the catalytic subunit of adenylate cyclase, an abnormality not previously described in the failing human heart.

Myocardial catecholamine and neuropeptide Y depletion in failing ventricles of patients with idiopathic dilated cardiomyopathy. Correlation with beta-adrenergic receptor downregulation

BACKGROUND

Myocardial adrenergic neurotransmitters and beta-adrenergic receptor levels were measured in left and right ventricular myocardial specimens obtained from 30 patients with biventricular failure resulting from idiopathic dilated cardiomyopathy.

METHODS AND RESULTS

Nonfailing myocardium obtained from 12 organ donors provided control data. Norepinephrine, dopamine, and neuropeptide Y concentrations were significantly decreased in failing compared with nonfailing control hearts. The mean ratio of dopamine to norepinephrine and of dopamine to neuropeptide Y in failing hearts was also significantly decreased compared with nonfailing control hearts. Compared with nonfailing control hearts, Bmax and beta 1-receptor density were significantly decreased in failing hearts and there were weak but significantly positive correlations of Bmax and beta 1-adrenergic receptors with norepinephrine, dopamine, and neuropeptide Y.

CONCLUSIONS

Norepinephrine and its cotransmitter neuropeptide Y are depleted in failing human ventricular myocardium. Decreased norepinephrine stores correlate weakly with beta 1-adrenergic receptor downregulation consistent with the hypothesis that norepinephrine depletion occurs in response to increased adrenergic drive. Decreased dopamine relative to norepinephrine implies that an abnormality of dopamine conversion to norepinephrine is not present in failing human heart.

Peripheral dopamine in pathophysiology of hypertension. Interaction with aging and lifestyle

Dopamine, an ancestral catecholamine, is physiologically natriuretic and vasodilating, thus essentially protecting against hypertension. Its actions are overshadowed by the opposite effects of its main biological partner, norepinephrine, and this is accentuated with aging. Clinical observations combined with molecular biology approaches to catecholamine-synthesizing and catecholamine-metabolizing enzymes and receptors permit the identification of some inborn defects. Subtle changes in the dopamine-norepinephrine balance may account for the enhanced peripheral noradrenergic activity seen in the setting of decreased dopaminergic activity in advanced age. These changes may contribute to the diminished ability of the aged kidney to excrete a salt load, as well as to the finding that systolic blood pressure increases with age in populations with a high, but not in those with a low, intake of salt. The attainment of advanced age in Western societies with adverse lifestyle changes (mental rather than physical stress, excess salt intake, overeating, sedentarism) appears to facilitate the development of hypertension. The adaptation to all the preceding lifestyle changes necessitates an increased dopamine generation, which may initially compensate to maintain appropriate natriuresis and vasodilation since many patients with initial borderline essential hypertension express their sympathetic hyperfunction, in addition to increased norepinephrine release, by excessive dopamine release. However, the progression of hypertension is accompanied by a peripheral dopaminergic deficiency and diminished ability to excrete salt. This may represent an eventual inadequacy of a phylogenetically redundant system resulting in decreased natriuresis and vasodilation and may account for the responsiveness of established chronic hypertension to salt restriction, diuretics, and dopaminomimetic medication.

Cardiac levels of norepinephrine, dopamine, serotonin and histamine in Chagas' disease

Extraction and measurement of biogenic amines (norepinephrine, dopamine, serotonin and histamine) were carried out on human ventricular myocardium obtained from autopsies of individuals divided in the three following groups: chronic Chagas' heart disease (with congestive heart failure: 16 cases, and with sudden and unexpected death: 13 cases); hypertensive heart disease (12 cases); and control patients (with no heart disease: 12 cases). The myocardial samples were obtained from the free walls of left and right ventricles and from the apex. A significant depletion of norepinephrine was detected in those with congestive failure. A poorly elevated level of dopamine was also seen in right ventricular and apical myocardium from those with failure. Left ventricular and apical concentration of serotonin were significantly elevated in the presence of hypertensive heart disease. The most important findings were obtained with histamine, which is increased in both groups of Chagasic patients. We believe that the approach here reported may provide useful informations on the pathogenetic mechanisms, thus far poorly understood, of chronic Chagas' heart disease.

Medical management of chronic heart failure: inotropic, vasodilator, or inodilator drugs?

On the basis of pathophysiologic mechanisms, the medical therapy of today for chronic heart failure is reviewed. The advantages and disadvantages of the vasodilator drugs and the inotropic drugs are presented. Finally, the therapeutic value of the inodilator drugs, which combine the central myocardial effects of positive inotropic agents with those of peripheral vasodilators, is discussed. In particular, the orally available dopaminergic agents, such as ibopamine, which interact with beta-receptors in the heart (mediating a positive inotropic effect) as well as with dopaminergic receptors in the peripheral vessels (mediating a systemic vasodilator effect) and in the kidneys (potentiating the natriuretic effect of diuresis), seem to be an advancement in the modern medical therapy of chronic heart failure. Data are shown during long-term treatment with ibopamine, in which the sustained clinical benefit in heart failure was not diminished, despite a decrease of the adrenergic receptors in blood cells. Dopamine plasma concentration was permanently normalized during long-term treatment. The discrepancy between clinical improvement and the measured adrenergic downregulation may be due to the interference of the inodilator with neurohormonal systems at multiple sites and is probably independent of receptor activation. It is suggested that the biosynthesis of noradrenaline is improved by increasing intracellular dopamine transport.

Vesicular and ganglionic norepinephrine in the rat: progressive increase with age

This study analyzed dopamine (DA) and norepinephrine (NE) in the synaptic vesicles and cytoplasm of brains of rats of 2 months and 14 months. The data revealed a clear NE increase in the synaptic vesicles of the 14-month-old rats, contrasting with NE in the cytoplasmic fraction of the rat brain, which remained unchanged with age. Synaptic vesicles from different regions of rat brain, including those from the striatum, consistently exhibited higher NE than DA concentrations, suggesting that they are predominantly noradrenergic. In the brain, DA concentrations in vesicular and cytoplasmic fractions did not vary with age, whereas in the superior cervical ganglia DA and NE concentrations increased in the older rats. L-3,4-Dihydroxyphenylalanine administration significantly increased DA without affecting NE in the ganglia of rats of all ages. In the brain, such a treatment significantly raised DA only in the synaptic vesicles of the older rats, suggesting an increased facilitation of DA transport into the synaptic vesicles with age, which may account for the higher vesicular NE in the older rats.

Vesicular accumulation of dopamine following L-DOPA administration

In this study, the accumulations of dopamine (DA) and norepinephrine (NE) were measured in the brain tissues and in the synaptic vesicle fractions prepared from whole brain of control rats and rats injected with L-DOPA. In the normal rat brain, a 3-fold increase in DA following L-DOPA administration was followed by a small, but not significant increase in vesicular DA, indicating a restricted vesicular uptake of exogenous DA. At the same time, NE in the vesicular fraction and in the whole brain tissue did not change, suggesting a possible link between DA vesicular uptake of DA and brain NE. However, in rats pretreated with alpha-methyl-p-tyrosine, which significantly (P less than 0.05) reduced DA and NE levels in brain tissues and in the synaptic vesicles, L-DOPA administration led to a significant increase in vesicular DA (P less than 0.05), suggesting that catecholamine depletion may result in greater vesicular uptake of cytoplasmic DA. The increase in vesicular DA was accompanied by increases in tissue and vesicular NE, underscoring again the existence of a link between vesicular uptake of DA and brain NE following L-DOPA administration. The results also demonstrated a large increase in 3,4-dihydroxyphenylacetic acid (DOPAC) following L-DOPA, in the brain tissues but not in the synaptic vesicle, indicating that monoamine oxidase activity is confined to the cytoplasm.

Modification of vesicular dopamine and norepinephrine by monoamine oxidase inhibitors

The possible effects of inhibitors of the two forms of monoamine oxidase (types A and B) on dopamine (DA) and norepinephrine (NE) accumulation and metabolism in the cytoplasmic and microsomal (vesicular) fractions of the rat brain have been examined. It was found that, while L-DOPA treatment raised only cytoplasmic DA without affecting vesicular DA and NE, clorgyline and pargyline treatments caused significant increases in DA and NE concentrations in both cytoplasmic and vesicular fractions. The DA increase in the synaptic vesicles (200-600%) was much more pronounced than that (150%) in the cytoplasm. In contrast, deprenyl treatment increased vesicular DA only slightly without any effect on either vesicular or cytoplasmic NE. L-DOPA administration to rats pretreated with clorgyline and pargyline, but not with deprenyl, further increased cytoplasmic and vesicular DA and NE concentrations. However, excessive increases in vesicular DA lowered vesicular NE. Reserpine drastically reduced vesicular and cytoplasmic DA and NE, and L-DOPA administration to the reserpine-treated rats caused a DA increase only in the cytoplasmic fraction without affecting vesicular DA or NE. The effect of reserpine was abolished by pargyline treatment, which suggests that pargyline may interact with the reserpine-sensitive vesicular uptake. There was a significant correlation between vesicular DA and NE increase.

Sustained hemodynamic improvement during long-term therapy with levodopa in heart failure: role of plasma catecholamines

Long-term therapy with oral sympathomimetic amines in patients with heart failure has been limited by the eventual development of diminished pharmacologic efficacy. However, a previous investigation in five subjects with heart failure suggested that long-term ingestion of levodopa, which is decarboxylated endogenously to dopamine, produces a sustained improvement in cardiac function. In the present study, levodopa was administered orally (1.5 to 2.0 g) to 14 patients with heart failure while hemodynamic responses and plasma catecholamines were monitored. Initially, an increase in cardiac index and stroke volume index was accompanied by a decline in systemic vascular resistance, mean pulmonary capillary wedge pressure and mean right atrial pressure. Heart rate and mean arterial pressure were unchanged. Plasma concentrations of dopamine rose substantially after drug ingestion and correlated significantly with changes in cardiac index (r = 0.73, p less than 0.05). After 12 weeks of treatment with levodopa, the changes in cardiac index, stroke volume index, systemic vascular resistance and plasma dopamine levels persisted (n = 12 patients). Moreover, a significant decrease occurred in the heart rate at rest. Although there was an initial tendency for plasma norepinephrine concentrations to increase, a return to control levels was documented after long-term treatment. Thus, tolerance to the hemodynamic actions of levodopa did not develop during long-term administration of the drug. The hemodynamic responses observed can be ascribed to the activation of beta 1-adrenoceptors and dopamine1 receptors by dopamine generated from levodopa. The dopamine2 activity of dopamine does not appear to be responsible for the improvement in cardiac performance produced by levodopa.

Catecholamine, dopamine-beta-hydroxylase and atrial natriuretic factor content in separate heart chambers of cardiomyopathic hamsters

Since previous investigations have suggested a relationship between atrial natriuretic factor (ANF) and dopamine-beta-hydroxylation, cardiomyopathic hamsters were studied for atrial and ventricular catecholamine (CA) and dopamine-beta-hydroxylase (D beta H) content as correlates to a parallel finding of markedly decreased atrial but increased ventricular ANF concentrations in these animals. It was noted that, with progressive cardiomyopathy, the reduced tissue norepinephrine (NE) content paralleled the declining D beta H activity in the atria. In the ventricles, however, the progressively-decreasing NE content was associated with an increase of D beta H. These data indicate that the NE depletion is mediated by different mechanisms in the ventricles and atria. They do not support a simple relationship between NE depletion and tissue D beta H activity or between the latter and tissue ANF concentrations.

Heterogeneous myocardial catecholamine concentrations in patients with congestive heart failure

Left ventricular catecholamine and plasma norepinephrine levels were assayed in 39 patients undergoing cardiac transplantation to test the hypothesis that in congestive heart failure (CHF) the normally high concentration of myocardial norepinephrine is depleted while dopamine is increased because dopamine conversion to norepinephrine is the rate-limiting step in norepinephrine synthesis. Plasma norepinephrine was elevated in all patients (average 741 +/- 472 micrograms/ml), but myocardial norepinephrine was variable, ranging from 79 to 2,127 ng/g (average 512 +/- 392). Myocardial dopamine also varied considerably (range 0 to 713 ng/g, average 143 +/- 150). Nineteen patients had the expected pattern of low cardiac norepinephrine and elevated dopamine levels. However, myocardial catecholamine levels were normal (high norepinephrine, low dopamine) in 7 patients; both norepinephrine and dopamine were low in 6 patients; and norepinephrine levels were preserved but dopamine high in 7 patients. Cardiac norepinephrine level correlated only weakly with peripheral vascular resistance (r = 0.39, p less than 0.05), and examination of multiple other variables failed to reveal likely causes of the differences in cardiac norepinephrine and dopamine between patients. Thus, myocardial norepinephrine is not uniformly reduced in patients with severe CHF, and further attempts to delineate the factors regulating myocardial catecholamine concentration and adrenergic function in such patients are needed.

An active pathway for serotonin synthesis by renal proximal tubules

Serotonin (5HT) has significant effects on renal metabolism and glomerular function and is a potent renal vasoconstrictor. In this study we describe and localize a highly active biosynthetic pathway for serotonin in the kidney. Rat kidneys were dissected into cortical and medullary fractions; in some experiments the cortex was also separated into subfractions enriched with glomeruli or proximal tubules. Serotonin and tryptophan hydroxylase (TyOH) were measured by radioenzymatic techniques. (table; see text) Renal denervation did not alter tryptophan hydroxylase activity. In kidneys from human cadaveric donors, cortical tryptophan hydroxylase (4.13 +/- 0.68 nM/30 min/g) exceeded that in the medulla (1.96 +/- 0.86 nM/30 min/g). Aromatic L-amino acid decarboxylase, the remaining enzyme for serotonin synthesis, is present in both rat renal cortex and medulla; however, we found 15-fold greater decarboxylase activity in proximal tubular (2070 nM/30 min/g) as compared to glomerular (131 nM/30 min/g) subfractions. We were able to demonstrate that under physiological conditions, free urine serotonin reflects actual biosynthesis by the kidney. Thus, although serotonin stores retained by the kidney appear small and relatively localized to the medulla, the enzymatic activity for the synthesis of serotonin in the kidney is comparable to that in the brain, with the complete pathway localized to renal cortical proximal tubules. These data suggest that further studies of renal serotonin metabolism may contribute to our understanding of renal function in health and disease.

Renal hypertensive hypertrophy in the rat: a substrate for arrhythmogenicity

We investigated the ability of ouabain to produce lethal arrhythmias in rats with myocardial hypertrophy resulting from chronic renal hypertension. A gradual pressure overload was produced in female Wistar rats by left renal artery stenosis (two kidney, one clip, Goldblatt hypertension). Hypertension (systolic blood pressure greater than 150 mm Hg) developed within three weeks after clipping of the left renal artery and blood pressure continued to increase for the next five weeks. At ten weeks after the onset of hypertension animals were anesthetized with sodium pentobarbital (40 mg/kg) and artificially ventilated with room air while ECG was continually monitored and recorded. Continuous infusion of ouabain was maintained (0.7 mg/kg/min) through the inferior vena cava. Body weight and heart rate of control animals (C) was not significantly different from hypertensive (H) values, while systolic blood pressure in animals hypertensive for ten weeks was considerably greater (187 +/- 8.4 mm Hg) than their age-matched normotensive counterparts (123 +/- 6.0 mm Hg). Heart weight in hypertensive animals was elevated by 69% +/- 2.5 by time of study. Serological evaluation of both groups of animals revealed no significant differences in electrolytes and blood gases while significant differences were noted in glucose, BUN and creatinine. The average time to the first premature ventricular contraction was significantly shorter in H animals (3.5 +/- 0.2 min) when compared to C rats (6.0 +/- 0.2 min). The average time to ventricular tachycardia, ventricular fibrillation and death were also significantly shorter in H rats when compared to C animals (7.5 +/- 0.6 vs. 13.5 +/- 0.3; 13.5 +/- 0.5 vs. 21.0 +/- 0.5; 15.6 +/- 0.4 vs. 24.0 +/- 0.6 min). Thus, the hypertensive hypertrophied myocardium displays an increased propensity for lethal cardiac arrhythmias due to ouabain.

Endogenous catecholamine levels in chronic heart failure. Relation to the severity of hemodynamic abnormalities

Plasma free epinephrine, norepinephrine, and dopamine concentrations were determined in 48, 63, and 45 patients, respectively, with overt congestive heart failure, and compared with those in 26 patients with stable angina but without heart failure. Systemic hemodynamic values were determined to assess the severity of heart failure. Arterial epinephrine levels were not different between patients with heart failure (73 +/- 92 pg/ml) and patients without heart failure (55 +/- 73 pg/ml). In patients with congestive heart failure, norepinephrine (665 +/- 510 pg/ml, mean +/- SD) and dopamine (407 +/- 405 pg/ml) levels were significantly higher than in patients with stable angina without heart failure (norepinephrine 184 +/- 136 pg/ml, p less than 0.001, and dopamine 197 +/- 259 pg/ml, p less than 0.02). However, in patients with congestive heart failure, the plasma norepinephrine levels did not correlate with cardiac index (r = 0.21, p = NS), pulmonary capillary wedge pressure (r = 0.11, p = NS), mean arterial pressure (r = 0.11, p = NS), or systemic vascular resistance (r = 0.18, p = NS). Similarly, there was no correlation between dopamine levels and the hemodynamic abnormalities in patients with congestive heart failure. These findings suggest that although endogenous norepinephrine and dopamine levels are frequently elevated in patients with heart failure, reflecting enhanced sympathetic activity, catecholamine levels do not reflect the severity of heart failure.

Neurohumoral mechanisms involved in congestive heart failure

Congestive heart failure (CHF) promotes an array of biologic changes that are largely designed to compensate for reduced flow. These include activation of the sympathetic nervous system and the renin-angiotensin system, as well as the release of arginine vasopressin. The ultimate expression of these compensatory mechanisms is heightened vascular tone, increased sodium and water retention and antidiuresis. The peripheral circulation is normally under the fine control of circulating and neuronally released moieties, which can directly or indirectly alter vascular tone. Angiotensin II appears to be a key element in this regard because of its multiple biologic activities. Direct arteriolar vasoconstriction, facilitation of norepinephrine release and stimulation of aldosterone are some of the activities that are likely to be of major importance in the syndrome of CHF. Therefore, it is not surprising that converting enzyme inhibitors have a growing role as treatment. Other pharmacologic agents that can reduce sympathetic tone by acting on presynaptic receptors are being developed. Selective dilation of certain vascular beds may be possible with agents designed to interact with vascular dopaminergic receptors. The mechanisms whereby circulating epinephrine and norepinephrine modulate norepinephrine release and vascular tone are beginning to be understood and likely involve presynaptic, postsynaptic and nonsynaptic vascular receptors. A better appreciation of the mechanisms involved in the fine control of the peripheral circulation should allow for more selective and more imaginative pharmacologic therapy for CHF.

Elevated left ventricular myocardial dopamine in preterminal idiopathic dilated cardiomyopathy

The adrenergic nervous system is chronically activated in patients with congestive heart failure (CHF). One consequence of this is depletion of the normally high levels of myocardial norepinephrine. In this study, myocardial norepinephrine and dopamine concentrations from the left ventricular walls of 3 patients undergoing cardiac transplantation for severe refractory CHF are reported. The dopamine/norepinephrine ratios were high in all 3 patients (29, 58 and 26%). This finding supports data from animal studies suggesting a change in the rate-limiting step for myocardial norepinephrine synthesis in CHF. Conversion of tyrosine to dopa by tyrosine hydroxylase is replaced as the rate-limiting step by inability to hydroxylate dopamine to norepinephrine. Thus, dopamine accumulates while norepinephrine is depleted.

Plasma norepinephrine concentration and plasma dopamine-beta-hydroxylase activity in patients with congestive heart failure

The relationship between plasma norepinephrine (NE), epinephrine (E) and dopamine-beta-hydroxylase activity (DBH) was studied in 90 cardiac patients (New York Heart Association [NYHA] classes I-IV), 85 healthy control subjects and 18 competitive skiers. The cardiac patients in NYHA classes III and IV had significantly higher NE (p less than 0.001) and lower DBH (p less than 0.001) levels than the controls, whereas the skiers had significantly lower NE (p less than 0.001) and higher DBH (p less than 0.05) levels than the controls. Seven cardiac patients in whom successful cardiac surgery was performed had decreased NE (p less than 0.001) and increased DBH (p less than 0.02), as well as significantly improved NYHA cardiac status (p less than 0.001). These findings demonstrate an inverse relationship between NE and DBH in a population of athletes, normal subjects and cardiac patients; the same inverse relationship holds for these patients when sequential studies are done after a change in cardiac status.