Circulating plasma concentrations of atrial natriuretic peptide and catecholamines in response to maximal exercise in normal and asthmatic subjects

The Impact of Catecholamines on Defibrillation Threshold in Patients with Implanted Cardioverter Defibrillators

OBJECTIVES

To determine the effect of physiologic catecholamine concentrations on the defibrillation threshold (DFT) in patients with implanted cardioverter defibrillators.

BACKGROUND

DFT is the minimum energy delivered by an implanted cardioverter defibrillator that successfully converts ventricular fibrillation. DFT testing is performed under conscious sedation. Since activities of daily living enhance sympathetic tone substantially over these nadir levels, it is important to explore the impact of catecholamines on DFT.

METHODS

In this double-blind study, we determined DFT by the step-down method. Patients (n = 50) were stratified by beta-blocker use and then randomized to a 7-minute infusion of epinephrine, norepinephrine, or placebo. After study infusion, DFT testing was repeated. Changes in DFT with different study medications were compared. Subgroup analyses of the effects of catecholamines on DFT, based on beta-blocker use, were also performed.

RESULTS

Norepinephrine reduced DFT from baseline measurements by 22.6% (P = 0.008). Neither epinephrine nor placebo impacted DFT (P = 0.999, P = 0.317, respectively). In the subgroup analyses, DFT was reduced with norepinephrine regardless of beta-blocker use, while epinephrine reduced DFT among those receiving beta-blockers. No change in DFT was observed in either of the placebo subgroups.

CONCLUSIONS

Elevation of plasma norepinephrine concentrations reduces the DFT, while elevations in epinephrine had no effect. Norepinephrine seems to reduce DFT regardless of beta-blocker therapy but epinephrine's effects are beta-blocker dependent.

Guanylyl cyclases, nitric oxide, natriuretic peptides, and airway smooth muscle function

Airway smooth muscle (ASM) plays an important role in asthma pathophysiology through its contractile and proliferative functions. The cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) are second messengers capable of mediating the effects of a variety of drugs and hormones. There is a large body of evidence to support the hypothesis that cAMP is a mediator of the ASM's relaxant effects of drugs, such as beta2-adrenoceptor agonists, in human airways. Although most attention has been paid to this second messenger and the signal transduction pathways it activates, recent evidence suggests that cGMP is also an important second messenger in ASM with important relaxant and antiproliferative effects. Here, we review the regulation and function of cGMP in ASM and discuss the implications for asthma pathophysiology and therapeutics. Recent studies suggest that activators of soluble and particulate guanylyl cyclases, such as nitric oxide donors and natriuretic peptides, have both relaxant and antiproliferative effects that are mediated through cGMP-dependent and cGMP-independent pathways. Abnormalities in these pathways may contribute to asthma pathophysiology, and therapeutic manipulation may complement the effects of beta2-adrenoceptor agonists.

Plasma atrial natriuretic peptide during spontaneous bronchoconstriction in asthmatics

The aim of this work was to establish the role of endogeneous ANP during a spontaneous asthma attack. Forced expiratory lung volume in 1 s (FEV1), cardiovascular parameters, and plasma ANP, cAMP, and cGMP were measured for 60 min before and 10 min after treatment with a bronchodilator in 10 asthmatics. The results show that in the presence of moderate bronchoconstriction, FEV1 was 54 +/- 3% (+/-SE); ANP levels initially were slightly elevated at 47 +/- 10 pg/ml and decreased to 26 +/- 3 pg/ml (p < 0.05) over 60 min, with no change in FEV1. Following salbutamol inhalation, FEV1 increased to 77 +/- 4% with no change in ANP. We conclude that endogenous ANP does not act as a bronchodilator in asthmatics with moderate bronchospasm.

Effect of atrial natriuretic peptide given by intravenous infusion on bronchoconstriction induced by ultrasonically nebulized distilled water (fog)

Atrial natriuretic peptide (ANP) is secreted by cardiac atria and lung tissue; it has a bronchodilator action in normal subjects and patients with asthma and has been shown to protect against histamine-induced bronchoconstriction in patients with asthma. Bronchoconstriction caused by inhalation of ultrasonically nebulized distilled water (fog), in contrast to histamine-induced bronchoconstriction, has features in common with exercise-induced asthma but can be given more easily in a dose-response fashion. The present study aimed to determine the effect of elevated plasma ANP concentrations on the bronchoconstrictor response to inhalation of fog. Eight patients with atopic asthma were studied, mean baseline FEV1 3.00 1, equivalent to 89% (range 76-103%) predicted. The provocation dose of fog producing a 25% fall in FEV1 (PD25) was determined for each subject. On 4 study days, subjects received an intravenous infusion of placebo or ANP at a rate of 1.25, 3.0, or 10.0 pmol/kg/min in randomized, double-blind manner for 30 min to allow steady-state plasma concentrations to be achieved; the PD25 fog was then administered and FEV1 recorded over 30 min. Mean (SEM) baseline plasma ANP concentration was 19.3 (4.1) pg/ml and increased to 39.4 (6.6), 106.4 (11.1), and 445.9 (105.4) with the three rates of ANP infusion. The highest rate of infusion increased prechallenge FEV1 by 8.7 (2.4)% (p less than 0.01), but the lower rates of infusion had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)