Functional role of beta2-adrenoceptors in the transplanted human heart

Acute electrophysiologic effects of inhaled salbutamol in humans

STUDY OBJECTIVES

Although inhaled beta2-agonists are in widespread use, several reports question their potential arrhythmogenic effects. The purpose of this study was to evaluate the cardiac electrophysiologic effects of a single, regular dose of an inhaled beta2-agonist in humans.

DESIGN

Prospective study.

SETTING

Tertiary referral center.

PATIENTS

Six patients with bronchial asthma and 12 patients with mild COPD.

INTERVENTIONS

All patients underwent an electrophysiologic study before and after the administration of salbutamol solution (5 mg in a single dose).

MEASUREMENTS AND RESULTS

Sinus cycle length, sinus node recovery time (SNRT), interval from the earliest reproducible rapid deflection of the atrial electrogram in the His bundle recording to the onset of the His deflection (AH), interval from the His deflection to the onset of ventricular depolarization (HV), Wenckebach cycle length (WCL), atrial effective refractory period (AERP), and ventricular effective refractory period (VERP) were evaluated just before and 30 min after the scheduled intervention. Salbutamol, a selective beta2-agonist, administered by nebulizer had significant electrophysiologic effects on the atrium, nodes, and ventricle. The AH length decreased from 86.1 +/- 19.5 ms at baseline to 78.8 +/- 18.4 ms (p < 0.001), and the WCL decreased from 354.4 +/- 44.2 to 336.6 +/- 41.7 ms (p = 0.001). Salbutamol significantly decreased the AERP and VERP too while leaving the HV unchanged. Additionally, inhaled salbutamol increased heart rate (from 75.5 +/- 12.8 beats/min at baseline to 93.1 +/- 16 beats/min, p < 0.001) and shortened the SNRT (from 1,073.5 +/- 178.7 to 925.2 +/- 204.9 ms, p = 0.001).

CONCLUSION

Inhaled salbutamol results in significant changes of cardiac electrophysiologic properties. Salbutamol enhances atrioventricular (AV) nodal conduction and decreases AV nodal, atrial, and ventricular refractoriness in addition to its positive chronotropic effects. These alterations could contribute to the generation of spontaneous arrhythmias.

Age-related differences in the response of blood stroke volume to stimulation of the sympathetic ganglion in rats with β-adrenoceptor blockade

Blood stroke volume in rats aging 21 and 56 days decreased during beta-adrenoceptor blockade with propranolol, but increased again by the 15th minute after treatment. Suprathreshold stimulation of the stellate ganglion decreased the stroke volume and increased the heart rate in control animals. Electrical stimulation after beta-adrenoceptor blockade was followed by a further decrease in stroke volume in young rats. In 100-day-old animals this parameter remained unchanged, while the cardiac output improved.

Effect of beta2-adrenergic receptor agonists on intercellular adhesion molecule (ICAM)-1, B7, and CD40 expression in mixed lymphocyte reaction

BACKGROUND

The plasma interleukin (IL)-18 level is elevated in acute rejection after organ transplantation. Although beta2-adrenergic receptor (AR) agonists suppress the rejection of organ and tissue transplants, little is known about their action mechanisms. We examined the effects of endogenous catecholamines and beta2-AR agonists on the expression of intercellular adhesion molecule (ICAM)-1, B7.1, B7.2, CD40, and CD40 ligand (CD40L) in human mixed lymphocyte reaction (MLR) and in an in vitro model of acute rejection in the presence or absence of IL-18.

METHODS

ICAM-1, B7.1 B7.2, CD40, and CD40L expression on monocytes was measured by flow cytometry, and the production of interferon (IFN)-gamma and IL-12 was determined by enzyme-linked immunosorbent assay. Lymphocytes proliferation in MLR was measured by [3H]-thymidine uptake. The relevant AR subtypes were characterized using subtype-selective agonists and antagonists.

RESULTS

beta2-AR agonists inhibited the expression of ICAM-1 and CD40 during MLR in the absence of IL-18. Among IL-18-induced expression of ICAM-1, B7.1, B7.2, CD40, and CD40L, beta2-AR agonists inhibited ICAM-1 and CD40 expression. beta2-AR agonists prevented the production of IFN-gamma and IL-12 in the presence of IL-18 but had no effect in the absence of IL-18. beta2-AR agonists inhibited lymphocyte proliferation in IL-18-treated MLR.

CONCLUSIONS

We found that beta2-AR agonists strongly inhibited the expression of ICAM-1 and CD40, irrespective of the presence or absence of IL-18, which is different from that of histamine and prostaglandin E2.

Terbutaline for chronotropic support in heart transplantation

OBJECTIVE

To report the use of oral terbutaline for chronotropic support in a patient who had undergone heart transplantation.

CASE SUMMARY

A 54-year-old white man received a heart transplant secondary to ischemic dilated cardiomyopathy. His clinical course was uncomplicated until postoperative day 10, when he became hemodynamically compromised despite inotropic therapy (BP 88/53 mm Hg, mean HR 80 beats/min) secondary to stage IIIa rejection. Although a continuous intravenous infusion of dobutamine was maintained, therapy with oral terbutaline 2.5 mg every 6 hours was initiated. Because the patient remained bradycardic on postoperative day 11 (HR 64 beats/min; mean 75), terbutaline was titrated to a dosage of 5 mg every 8 hours. Subsequently, an improvement in the hemodynamic profile (BP 140/78 mm Hg, mean HR 91 beats/min) was noted. Treatment with terbutaline was continued for 13 days and was well tolerated.

DISCUSSION

As of February 11, 2004, this is the first case, to our knowledge, to describe the use of oral terbutaline therapy for chronotropic support in the setting of acute rejection after heart transplantation. Terbutaline is a beta2-adrenergic agonist that may mediate its effects via direct beta2-receptor stimulation, baroreceptor-mediated increases in sympathetic tone, or via presynaptic beta2-stimulation. Although isoproterenol has been the mainstay of therapy for chronotropic support in this setting, its availability has been an issue in recent years. Terbutaline, therefore, may represent a useful alternative for chronotropic support in the setting of heart transplantation.

CONCLUSIONS

Terbutaline therapy did not appear to be associated with any significant adverse effects and warrants further application and study in this setting.

Cardiac effects of beta-adrenoceptor antagonists with intrinsic sympathomimetic activity in humans: beta1- and/or beta2-adrenoceptor mediated?

The aim of this study was to find out whether cardiac responses to the beta-adrenoceptor antagonists with intrinsic sympathomimetic activity (ISA) xamoterol and celiprolol are mediated by cardiac beta1- or beta2-adrenoceptors or both. For this purpose we assessed, in six healthy male volunteers, the effects of xamoterol (100 and 200 mg, p.o.) and celiprolol (200, 600, and 1,200 mg, p.o.) on blood pressure, heart rate, and heart rate-corrected duration of the electromechanical systole (QS2c, as a measure of inotropism). Xamoterol, in both doses, increased systolic blood pressure and heart rate, transiently decreased diastolic blood pressure, and shortened QS2c; all these effects were attenuated after pretreatment of the volunteers with the beta1-adrenoceptor antagonist bisoprolol. Celiprolol, in all three doses, increased heart rate, decreased diastolic blood pressure, and shortened QS2c but only marginally increased systolic blood pressure. Bisoprolol did not attenuate these celiprolol effects but rather enhanced celiprolol effects on systolic blood pressure and heart rate. In a further set of experiments, we studied cardiovascular effects of celiprolol in six healthy volunteers whose beta2-adrenoceptors had been desensitized by a 2-week treatment with 3x5 mg/day terbutaline. Under these conditions, celiprolol failed to increase heart rate or to shorten QS2c. We conclude that, under resting conditions, in healthy volunteers, beta-adrenoceptor antagonists with ISA can exert increases in heart rate and contractility that are mediated by either cardiac beta1-adrenoceptor (xamoterol) or cardiac beta2-adrenoceptor (celiprolol) stimulation. Thus in the human heart, the ISA of beta-adrenoceptor antagonists can be a beta1- or beta2-adrenoceptor agonistic component.