Alterations in cardiac beta-adrenoceptor responsiveness and adenylate cyclase system by congestive heart failure in dogs

Chronic beta-adrenoceptor blockade prevents the development of beta-adrenergic subsensitivity in experimental right-sided congestive heart failure in dogs

BACKGROUND

The reductions of myocardial beta-adrenergic receptor density and responsiveness to catecholamines in congestive heart failure are associated with excessive sympathetic stimulation. The purpose of this study was to determine whether the myocardial changes could be prevented by beta-receptor blockade.

METHODS AND RESULTS

We administered the oral beta-receptor blocking agent nadolol (40 mg/day) to dogs during an early stage of experimental right heart failure and to sham-operated dogs for 5 weeks. Animals receiving no nadolol were studied concurrently. Nadolol treatment did not prevent right ventricular hypertrophy or elevated concentrations of plasma norepinephrine that occurred in right heart failure, nor did it affect the decrease in myocardial norepinephrine content and norepinephrine uptake activity, suggesting that the hemodynamic stress imposed on the right ventricle of dogs with right heart failure was similar regardless of the presence or absence of beta-receptor blockade. Resting heart rate, right atrial pressure, aortic pressure, cardiac output, right ventricular dP/dt, and left ventricular dP/dt and dP/dt/P measured 5 days after discontinuation of nadolol did not differ significantly from those without nadolol treatment in either right heart failure or sham-operated animals. Sham-operated dogs also showed no changes in myocardial beta-receptor or adenylate cyclase activity after nadolol treatment. However, nadolol treatment prevented the reduction of myocardial beta-receptor density and attenuated the decrease in the cardiac beta-adrenergic sensitivity that occurred in right heart failure.

CONCLUSIONS

Excessive sympathetic stimulation may play an important role in the development of beta-receptor downregulation and beta-adrenergic subsensitivity in right heart failure.

Limb vascular responsiveness to beta-adrenergic receptor stimulation in patients with congestive heart failure

BACKGROUND

In patients with congestive heart failure, the chronotropic and inotropic responses to beta-adrenergic agonists are reduced. It is not known whether desensitization of peripheral beta-adrenoceptors accounts for impaired limb vasodilation in these patients. Accordingly, we studied 14 normal subjects and 13 age-matched patients with congestive heart failure.

METHODS AND RESULTS

To distinguish vasodilation mediated by beta-adrenoceptors and adenylate cyclase from that mediated by stimulation of guanylate cyclase, each subject received intrabrachial artery infusions of isoproterenol (1-100 ng/min) and sodium nitroprusside (0.3-10 micrograms/min), respectively. Forearm blood flow was determined by venous occlusion plethysmography. Maximal vasodilative potential, determined during reactive hyperemia, was reduced in the patients with congestive heart failure. The maximal forearm blood flow response to isoproterenol was comparable in patients with heart failure and in normal subjects (8.0 +/- 1.1 versus 9.2 +/- 1.2 ml/100 ml of tissue/min, respectively, p = NS). Furthermore, the dose-response relation to isoproterenol was similar in both groups. Likewise, the forearm vasodilative response to sodium nitroprusside was preserved in the heart failure group. Plasma concentration of norepinephrine was higher in the patients with heart failure (436 +/- 34 versus 201 +/- 74 pg/ml, p less than 0.01). When both groups were considered, there was no correlation between norepinephrine levels and the maximal forearm blood flow response to isoproterenol (r = 0.10, p = NS).

CONCLUSIONS

We conclude that beta-adrenoceptor desensitization does not occur in the limb vessels of patients with congestive heart failure.

Detrimental effects of beta-adrenergic stimulation on beta-adrenoceptors and microtubules in the heart

Increased plasma catecholamines - in particular, excessive beta-adrenoceptor activation in chronic heart failure - may easily desensitize the beta-adrenoceptors as well as the postreceptor signal transductions. Since these detrimental changes in the failing heart could be reversible, administration of low-dose beta-blocker, which minimizes the negative inotropic effects, may be effective in attenuating the harmful effects of sympathetic nerve activation. Beta-adrenoceptor stimulation may also produce microtubule disruptions of the cell either through direct action or through an increase in heart rate. Treatment with beta-blockers could attenuate Ca overload by slowing the heart rate and may be useful as a protection from the structural disintegration of the cell. Thus, to clarify the underlying mechanisms of beta-blocker therapy for chronic heart failure, we have to consider not only to the functional aspects but also to the structural changes of the cells.

Adverse effects on rat cardiac function ex vivo after repeated administration of the benzodiazepine partial inverse agonist, FG7142

1. The Langendorff preparation was used to investigate functional changes in rat heart one week after the last of a course of repeated injections of the benzodiazepine inverse agonist, FG7142 (20 mg kg-1 i.p; three times weekly for five weeks). 2. Under these conditions, FG7142 caused a statistically significant reduction in both cardiac basal tension and the inotropic effect of noradrenaline at doses giving 50 and 100% of the maximum response. 3. Basal heart rate, basal coronary perfusion pressure and the effects of noradrenaline ex vivo on these parameters were all unaffected by repeated administration of FG7142. 4. FG7142 had no intrinsic effects on cardiac function when administered in vitro. 5. We discuss mechanisms which could underlie the effects of FG7142 on cardiac tension ex vivo and consider the possibility that this action may be related to the anxiogenic or proconvulsant actions of this drug.

Neuroendocrine and beta-adrenoceptor response to chronic ethanol and aggression in rats

Male rats were administered either ethanol (6-8 g/kg/day) or dextrin-maltose, an isocaloric equivalent, for two weeks prior to a 24-hour resident-intruder test. After the first 20 minutes of the aggression test residents showed a greater increase in norepinephrine than intruders (216% vs. 97%), while intruders showed a greater increase in epinephrine (394% vs. 51%) and corticosterone (338% vs. 129%) than residents. Ethanol administration increased the initial epinephrine response of intruders almost two-fold compared to dextrin-maltose intruders. After 24 hours of aggression testing plasma norepinephrine was still elevated in residents (92%) and intruders (71%), however, only intruders continued to show an elevation in plasma corticosterone (98%) and epinephrine (107%). Using a cumulative dose-response technique, the dose of isoproterenol required to produce 50% of the maximal heart rate response (ED50) increased in intruders by 108% following aggression testing with ethanol intruders showing significantly smaller mean change. The increase in ED50 was related to drug type, behavior, and plasma corticosterone and epinephrine levels. Rats treated with ethanol had a greater beta-adrenoceptor density than control rats. However, no relationship was found between receptor density and the other measures in this study.

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.

Opiate receptor inhibition improves the blunted baroreflex function in conscious dogs with right-sided congestive heart failure

The endogenous opiate system is activated in congestive heart failure. because endogenous opioids are known to depress the baroreflex function, we conducted studies to determine whether the increased endogenous opioids play a role in causing the reduced baroreflex function that occurs in heart failure. Right-sided congestive heart failure was produced in 16 dogs by tricuspid avulsion and progressive pulmonary artery constriction. Seven sham-operated dogs were included for comparison. Baroreflex function was measured in the conscious dogs after pretreatment with either normal saline or an opiate-receptor antagonist by bolus administration of phenylephrine. The slope of the regression line relating systolic blood pressure to cardiac cycle (R-R) interval was taken as an index of baroreflex sensitivity. Plasma beta-endorphin was elevated in the dogs with heart failure (15.3 +/- 2.5 pmol/l) compared with the sham-operated dogs (4.2 +/- 0.4 pmol/l, p less than 0.001). The dogs with heart failure also exhibited a reduced baroreflex sensitivity (3.84 +/- 0.19 msec/mm Hg) after saline pretreatment when compared with the sham-operated dogs (10.86 +/- 1.20 msec/mm Hg, p less than 0.001). Administration of naloxone hydrochloride increased the baroreflex sensitivity of dogs with heart failure to 5.16 +/- 0.26 msec/mm Hg (p less than 0.01) but produced no significant effects in sham-operated dogs (11.36 +/- 1.42 msec/mm Hg). To further study the site of action for the effect of naloxone, we measured baroreflex sensitivity in the dogs with heart failure after pretreatment with naloxonazine, a selective mu-receptor antagonist, with ICI 154,129, a selective delta-receptor antagonist, or with naloxone methobromide, a quaternary analogue of naloxone that does not penetrate the blood-brain barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Opiate receptor antagonism in right-sided congestive heart failure. Naloxone exerts salutary hemodynamic effects through its action on the central nervous system

Opiate receptor inhibition causes adrenergic receptor-mediated increases in aortic pressure, cardiac output, and left ventricular contractile function in right heart failure. To study whether the effects of opiate receptor inhibition are mediated by means of an action on the central opiate system, we administered equimolar doses of naloxone hydrochloride and naloxone methobromide (MeBr) and normal saline to heart failure dogs. Chronic stable right heart failure was produced by progressive pulmonary artery constriction and tricuspid valve avulsion. Naloxone hydrochloride caused an increase in mean aortic pressure, cardiac output, left ventricular dP/dt and dP/dt/P, plasma catecholamines, and regional blood flows to the myocardium, quadriceps muscle, kidneys, and splanchnic beds. Plasma beta-endorphin and adrenocorticotropin also increased. In contrast, neither normal saline nor naloxone MeBr (which does not cross the blood-brain barrier) affected the systemic or regional hemodynamics or neurohormones. Naloxone hydrochloride was also administered to anesthetized heart failure dogs. Pentobarbital anesthesia removed cortical perception of nociceptive stimulation, reduced the increase in plasma epinephrine, and abolished vasodilation in skeletal muscle that occurred in conscious dogs after naloxone hydrochloride administration but had no major effects on responses of plasma norepinephrine, systemic hemodynamics, or other regional blood flows to opiate receptor inhibition. Naloxone hydrochloride had no effect in sham-operated dogs. The results indicate that the hemodynamic effects of naloxone are mediated by an action within the central nervous system. Furthermore, since pentobarbital anesthesia did not markedly alter the hemodynamic responses to naloxone hydrochloride, the acute salutary effects of opiate receptor inhibition probably are not caused by removal of the antinociceptive effect of endogenous opioids in heart failure.

Response of the beta-adrenergic system to maximal dynamic exercise in congestive heart failure secondary to idiopathic dilated cardiomyopathy

In congestive heart failure (CHF), prolonged exposure to high plasma catecholamine levels may reduce the responsiveness of the adrenergic system to physiologic stimuli. In healthy subjects, exercise is known to induce a rapid up-regulation of lymphocytic beta adrenoceptors. Lymphocytic beta-adrenoceptor density, lymphocytic basal and isoproterenol-stimulated cyclic adenosine monophosphate (cAMP) response, plasma catecholamine concentrations and plasma cAMP levels were studied during maximal ergometer exercise in 11 patients with CHF secondary to dilated cardiomyopathy and in 6 healthy control subjects. At rest, there was no difference in the lymphocytic beta-adrenoceptor levels between the patients and control subjects (48 +/- 3 vs 42 +/- 5 fmol/mg protein, respectively). However, the exercise-induced increase in lymphocytic beta adrenoceptors was attenuated in patients when compared with controls (26 +/- 6 fmol/mg protein [56%] vs 75 +/- 16 fmol/mg protein [204%], respectively, p less than 0.02). A subgroup of 4 patients with the lowest exercise capacity (peak oxygen uptake less than 12.5 ml/min/kg) had even more reduced up-regulation compared with the other 7 patients (13 +/- 1 fmol/mg protein [29%] vs 34 +/- 9 fmol/mg protein [71%], p less than 0.05). The lymphocytic cAMP response at rest and during exercise tended to be lower in patients compared with controls, but the differences did not reach statistical significance. The plasma levels of epinephrine and norepinephrine at rest were higher in patients compared with controls, but no difference was found in the exercise values. The plasma levels of cAMP correlated closely with plasma catecholamine levels at rest, but not during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term hemodynamic effects of vasopressin V1-receptor inhibition in chronic right-sided congestive heart failure

Arginine vasopressin is elevated in congestive heart failure. To determine the effect of arginine vasopressin upon systemic hemodynamics and regional blood flows, we administered the specific inhibitor of the vascular action of vasopressin [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),2-(O-methyl)-tyrosine]-arginine vasopressin [d(CH2)5Tyr(Me)AVP] to 15 dogs with chronic right-heart failure produced by tricuspid avulsion and progressive pulmonary artery constriction. The animals exhibited increased plasma arginine vasopressin and norepinephrine levels. Vasopressin inhibition increased cardiac output and left ventricular dP/dt and dP/dt/P, and it decreased total peripheral vascular resistance, whereas mean aortic pressure did not change significantly. Simultaneously, blood flow increased to skeletal muscle, kidneys, skin, and right and left ventricular myocardium. Plasma catecholamines also increased. Pretreatment with propranolol and prazosin abolished the increases in cardiac output and left ventricular function produced by vasopressin inhibition. Pretreatment also led to a decrease in mean aortic pressure after vasopressor inhibition. In contrast, administration of d(CH)2)5Tyr(Me)AVP to 11 sham-operated animals or administration of normal saline to nine sham-operated and eight heart-failure dogs was without effect either in the absence or in the presence of adrenergic receptor blockade. Thus, arginine vasopressin participates in the control of the circulation in right-sided congestive heart failure, with both a direct constrictor action on blood vessels and an indirect action by inhibition of the sympathetic nervous system.