Mechanism of myocardial catecholamine depletion in cardiac hypertrophy and failure in rabbits

Differential pre- and postsynaptic effects of desipramine on cardiac sympathetic nerve terminals in RHF

Right heart failure (RHF) is characterized by chamber-specific reductions of myocardial norepinephrine (NE) reuptake, beta-receptor density, and profiles of cardiac sympathetic nerve ending neurotransmitters. To study the functional linkage between NE uptake and the pre- and postsynaptic changes, we administered desipramine (225 mg/day), a NE uptake inhibitor, to dogs with RHF produced by tricuspid avulsion and progressive pulmonary constriction or sham-operated dogs for 6 wk. Animals receiving no desipramine were studied as controls. We measured myocardial NE uptake activity using [(3)H]NE, beta-receptor density by [(125)I]iodocyanopindolol, inotropic responses to dobutamine, and noradrenergic terminal neurotransmitter profiles by glyoxylic acid-induced histofluorescence for catecholamines, and immunocytochemical staining for tyrosine hydroxylase and neuropeptide Y. Desipramine decreased myocardial NE uptake activity and had no effect on the resting hemodynamics in both RHF and sham animals but decreased myocardial beta-adrenoceptor density and beta-adrenergic inotropic responses in both ventricles of the RHF animals. However, desipramine treatment prevented the reduction of sympathetic neurotransmitter profiles in the failing heart. Our results indicate that NE uptake inhibition facilitates the reduction of myocardial beta-adrenoceptor density and beta-adrenergic subsensitivity in RHF, probably by increasing interstitial NE concentrations, but protects the cardiac noradrenergic nerve endings from damage, probably via blockade of NE-derived neurotoxic metabolites into the nerve endings.

Relationship between insulin resistance and cardiac sympathetic nervous function in essential hypertension

BACKGROUND

It has been suggested that hyperinsulinemia and insulin resistance participate in the pathogenesis of hypertension, in part by activating sympathetic activity.

OBJECTIVE

We aimed to examine the relationship between insulin resistance and cardiac sympathetic nervous function in patients with essential hypertension using 123I-metaiodobenzylguanidine (MIBG) cardiac scintigraphy.

METHODS AND RESULTS

Twenty-eight patients (18 men) with essential hypertension and 11 (seven men) control individuals with a mean age of 55.8+/-3.3 years were recruited. Patients with diabetes mellitus, congestive heart failure or coronary artery disease were excluded from this study. To evaluate insulin resistance, we used steady-state plasma glucose (SSPG; mg/dl) levels measured by the SSPG method. To evaluate cardiac sympathetic nervous function, we calculated the heart-to-mediastinum ratio from the delayed MIBG image (H:M-D) and the mean washout rate (WOR, %). There were significant differences (P<0.01) in SSPG, H:M-D and WOR between the essential hypertension and control individual groups (125 versus 103 mg/dl, 2.2 versus 2.4, and 32 versus 23%, respectively). Stepwise regression analysis showed that SSPG and plasma norepinephrine level are independent predictors for the cardiac sympathetic nervous function obtained from MIBG scintigraphy.

CONCLUSIONS

These findings indicate that insulin resistance is significantly related to activation of the cardiac sympathetic nervous function associated with left ventricular hypertrophy in patients with essential hypertension.

Cardiac noradrenergic nerve terminal abnormalities in dogs with experimental congestive heart failure

BACKGROUND

We have shown previously that norepinephrine (NE) uptake activity is reduced in the failing right ventricle of animals with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary constriction. However, it is unknown whether this defect in neuronal NE uptake is related to reduction of noradrenergic nerve terminals or whether these changes also occur in animals with left heart failure (LHF). It is also unknown whether increased NE release in heart failure contributes to the noradrenergic nerve abnormalities.

METHODS AND RESULTS

We measured myocardial NE content. NE uptake function, and noradrenergic nerve profiles in dogs with either RHF or LHF induced by rapid ventricular pacing. NE uptake activity was measured using [3H]NE, and noradrenergic nerve profiles were visualized by glyoxylic acid (SPG)-induced histofluorescence and tyrosine hydroxylase immunocytochemical staining. To study the effects of excess NE, we exposed normal dogs to 8 weeks of chronic NE infusion using subcutaneous osmotic minipumps. RHF and LHF animals exhibited reduced myocardial contractile function and congestive heart failure, as evidence by reduced cardiac output and elevated right atrial pressure. However, unlike that in LHF, left atrial pressure was not increased in RHF. The animals also showed an increase in plasma NE and a decrease in cardiac NE. In addition, SPG-induced histofluorescence correlated significantly with NE uptake activity (r = .712, P < .001) and tyrosine hydroxylase immunoreactive profiles (r = .569, P < .001) in the right ventricles of RHF dogs and in both ventricles of LHF dogs. The numbers of catecholaminergic profiles and tyrosine hydroxylase profiles significantly correlated with cardiac filling pressures. Chronic infusion of NE decreased heart rate in normal dogs but had no effect on either mean aortic pressure or left atrial pressure; like heart failure, it resulted in significant decreases in myocardial NE uptake activity and numbers of SPG-induced catecholaminergic histofluorescence and immunoreactive tyrosine hydroxylase profiles.

CONCLUSIONS

Myocardial NE uptake activity was reduced only in the failing ventricles with elevated filling pressure in RHF and LHF. These changes probably were caused by loss of noradrenergic nerve terminals in the failing ventricles, as evidenced by the reductions of catecholaminergic histofluorescence and tyrosine hydroxylase immunostained profiles. Furthermore, since similar reductions of myocardial NE uptake and noradrenergic nerve profiles could be produced by chronic NE infusion in normal dogs, elevated NE levels may play a role in the development of cardiac noradrenergic nerve abnormalities in congestive heart failure.

Altered myocardial acetylcholine and norepinephrine concentrations in right ventricular hypertrophy and failure

The progression of cardiac hypertrophy and failure is associated with marked changes in cardiac autonomic innervation, and there are sympathetic-parasympathetic interactions in the regulation of cardiac function. Although the indexes of sympathetic innervation have been found to be depressed with the development of heart failure, those of parasympathetic innervation have not yet been fully investigated. In order to better understand changes in markers of autonomic innervation associated with cardiac hypertrophy and failure, we measured the myocardial acetylcholine (ACh) store as a parasympathetic marker and the norepinephrine (NE) store as a sympathetic marker in pressure-overloaded right ventricular hypertrophy in rats. Two weeks after the injection of monocrotaline, significant right ventricular hypertrophy occurred. Three weeks after, severe right ventricular hypertrophy with no sign of heart failure occurred, and 4 weeks after, overt heart failure developed. In the right heart of monocrotaline rats, NE concentrations tended to increase at 1 week, returned to baseline at 2 weeks, decreased to one-half of the control values at 3 weeks, and then fell to 14% of the controls at 4 weeks. ACh concentrations in the right heart tended to increase at 1 week and exhibited a significant increase (136% and 129% of the controls in the right atrium and ventricle, respectively) at 2 weeks. As with NE, ACh concentrations in the right atrium and ventricle decreased to 76% and 54% of the controls at 3 weeks, and continued to decrease to 22% and 24% of the controls at 4 weeks after monocrotaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased adrenergic neuronal uptake activity in experimental right heart failure. A chamber-specific contributor to beta-adrenoceptor downregulation

The reduction of myocardial beta-adrenoceptor density in congestive heart failure has been thought to be caused by agonist-induced homologous desensitization. However, recent evidence suggests that excessive adrenergic stimulation may not produce myocardial beta-receptor downregulation unless there is an additional defect in the local norepinephrine (NE) uptake mechanism. To investigate the association between beta-adrenoceptor regulation and NE uptake activity, we carried out studies in 30 dogs with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary artery constriction and 23 sham-operated control dogs. We determined NE uptake activity by measuring accumulation of [3H]NE in tissue slices, NE uptake-1 carrier density by [3H]mazindol binding and beta-adrenoceptor density by [3H]dihydroalprenolol binding. Compared with sham-operated dogs, RHF dogs showed a 26% decrease in beta-adrenoceptor density, a 51% reduction in NE uptake activity, and a 57% decrease in NE uptake-1 carrier density in their right ventricles. In addition, right ventricle beta-receptor density correlated significantly with NE uptake activity and NE uptake-1 carrier density. In contrast, neither NE uptake activity nor beta-receptor density in the left ventricle and renal cortex was affected by RHF. Thus, the failing myocardium is associated with an organ- and chamber-specific subnormal neuronal NE uptake. This chamber-specific loss of NE uptake-1 carrier could effectively reduce local NE clearance, and represent a local factor that predisposes the failing ventricle to beta-adrenoceptor downregulation.

Effects of chronic progressive myocardial hypertrophy on indexes of cardiac autonomic innervation

The development of cardiac hypertrophy is associated with marked changes in cardiac autonomic innervation. Significant and sustained reductions of myocardial catecholamine stores and activities of tyrosine hydroxylase and dopamine beta-hydroxylase have been reported in models of acutely induced ventricular hypertrophy. Conversely, activity of choline acetyltransferase, a marker of parasympathetic nervous function, shows transient increases during the development of acute right ventricular hypertrophy. The potential physiological importance of these changes prompted us to examine a clinically more relevant model of slowly progressive ventricular hypertrophy. Application of a loose band around the pulmonary artery of weanling guinea pigs resulted in a growth-related progressive right ventricular pressure overload. Right ventricular weight-to-body-weight ratio was increased significantly and progressively at 9 and 18 weeks in banded animals (0.92 +/- 0.05 and 1.31 +/- 0.11 mg/g, respectively, p less than 0.01) compared with sham-operated controls (0.55 +/- 0.02 and 0.59 +/- 0.01 mg/g, respectively) but showed no further gain at 27 weeks (1.41 +/- 0.10 mg/g). Activities of tyrosine hydroxylase and dopamine beta-hydroxylase remained unchanged in all experiment groups, while right ventricular contents of norepinephrine in banded animals at 18 and 27 weeks exhibited sustained and progressive increases (2.45 +/- 0.11 and 3.40 +/- 0.19 micrograms/right ventricle, respectively) over controls (1.80 +/- 0.13 and 2.40 +/- 0.22 micrograms/right ventricle, respectively, p less than 0.01). The activity of choline acetyltransferase was markedly elevated in banded animals at 18 weeks (32.6 +/- 2.7 nmol/hr/right ventricle) but returned to baseline by 27 weeks (22.8 +/- 1.4 nmol/hr/right ventricle).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased number of beta-adrenergic receptors in the hypertrophied myocardium

Development of cardiac hypertrophy is associated with depletion of endogenous catecholamine stores and increased inotropic response to exogenous catecholamines. A biochemical basis for these changes is provided by the observation that the number of cardiac beta-adrenergic receptors - as reflected in specific [3H]dihydroalprenolol binding - is increased in hypertrophy without a change in the affinity of dihydroalprenolol for the binding sites or in the capacity of isoproterenol to displace dihydroalprenolol. This change in beta-receptor numbers may be an important adaptive mechanism for preserving the contractile performance of the hypertrophied myocardium.

Uptake of catecholamines by human cardiac muscle in vitro

Noradrenaline uptake was studied using heart muscle from 102 patients undergoing cardiac surgery. Slices of right atrium were incubated in Krebs-Henseleit solution containing 1.3 x 10(-7) M 3H-noradrenaline. Uptake was lower in failing heart muscle and was inhibited not only by increasing the noradrenaline concentration in the incubating medium but also by adding the drugs desmethylimipramine, amitryptyline, and ouabain.

Histochemically demonstrable monoamine oxidase activity in the adult human heart in various cardiac diseases

The present work was undertaken in order to study the role of monoamine oxidase (MAO) enzyme in the genesis of altered cardiac noradrenalin level in the human heart in various underlying pathologic conditions. The histochemical localization and the activity of MAO were studied in the right atrial appendage of man in ischemic heart disease, in valvular heart disease without or with congestive myocardial failure, and in hearts with an uncomplicated atrial septal defect. MAO was found to be localized mainly extraneuronally in the muscle cells, a little activity was detected in the connective tissue spaces, and nerves reacting positively were tentatively identified. There were no significant differences in MAO activity measured photometrically between the various heart disease groups. It seems that MAO activity measured photometrically between the various heart disease groups. It seems that MAO enzyme plays only a small or no role in the genesis of the latered noradrenalin level in the human heart observed in ischemic heart disease or congestive cardiac failure.