Chronic systemic administration of salmeterol to rats promotes pulmonary β₂‐adrenoceptor desensitization and down‐regulation of G_sα

Abstract

1 The aim of the present study was to examine the eects of chronic infusion of the long-acting agonist salmeterol on pulmonary b 2 -adrenoceptor function in Sprague-Dawley rats in vivo and to elucidate the molecular basis of any altered state. 2 Systemic administration of rats with salmeterol for 7 days compromised the ability of salmeterol and prostaglandin E 2 (PGE 2 ), given acutely by the intravenous route, to protect against AChinduced bronchoconstriction when compared to rats treated identically with vehicle. 3 b 1 -and b 2 -adrenoceptor density was signi®cantly reduced in lung membranes harvested from salmeterol-treated animals, which was associated with impaired salmeterol-and PGE 2 -induced cyclic AMP accumulation ex vivo. 4 Three variants of G sa that migrated as 42, 44 and 52 kDa peptides on SDS polyacrylamide gels were detected in lung membranes prepared from both groups of rats but the intensity of each isoform was markedly reduced in rats that received salmeterol. 5 The activity of cytosolic, but not membrane-associated, G-protein receptor-coupled kinase was elevated in the lung of salmeterol-treated rats when compared to vehicle-treated animals. 6 The ability of salmeterol, administered systemically, to protect the airways of untreated rats against ACh-induced bronchoconstriction was short-acting (t o *45 min), which contrasts with its long-acting nature when given to asthmatic subjects by inhalation. 7 These results indicate that chronic treatment of rats with salmeterol results in heterologous desensitization of pulmonary G s -coupled receptors. In light of previous data obtained in rats treated chronically with salbutamol, we propose that a primary mechanism responsible for this eect is a reduction in membrane-associated G sa . The short-acting nature of salmeterol, when administered systemically, and the reduction in b-adrenoceptor number may be due to metabolism to a biologically-active, short-acting and non-selective b-adrenoceptor agonist. British Journal of Pharmacology (2001) 132, 1261 ± 1270 Keywords: b 2 -adrenoceptor desensitization in vivo; salmeterol; down-regulation of G sa Abbreviations: FEF 25 ± 75 , forced expiratory¯ow at 25% and 75% of vital capacity; FEV 1 , forced expiratory volume in 1 s;

Beyond the dogma: novel 2-adrenoceptor signalling in the airways

“…a state of refractoriness that ensues following prolonged exposure or repeated application of an agonist [129,141]). Receptor desensitisation (as discussed below) can occur via a variety of processes, including uncoupling of the receptor from Gs, receptor internalisation [3,10,13], upregulation of cAMP PDE [154][155][156][157] and downregulation of Gs [158]. However, receptor desensitisation may not fully account for all of the effects of prolonged high-level dosing with b 2 -adrenoceptor agonists [9].…”

“…FINNEY and co-workers [158,267] have reported that long-term systemic treatment of rats with salbutamol and salmeterol blocks the ability of these agonists subsequently to protect against acetylcholine-induced bronchoconstriction. Moreover, the bronchoprotective effect of PGE 2 , which also acts through Gs-coupled prostanoid receptors of the PGE 2 receptor 4 subtype in rat airways [269], was similarly abolished, indicating that a state of heterologous desensitisation had been effected.…”

Respiratory syncytial virus induces insensitivity to β-adrenergic agonists in mouse lung epithelium in vivo

“…␤ 2 -AR can become desensitized as a result of prolonged exposure to exogenous ␤-agonists or high levels of endogenous catecholamines (9,32). We therefore examined the possibility that RSV infection might induce sufficient physiological stress to trigger activation of the adrenal medulla and thereby chronically elevate systemic endogenous catecholamine (norepinephrine and epinephrine) levels.…”

Effects of the β2-Agonist Clenbuterol on β1- and β2-Adrenoceptor mRNA Expressions of Rat Skeletal and Left Ventricle Muscles

“…Down-regulation is defined as a decline in the total number of receptors caused by prolonged exposures (16). On the one hand, β-AR binding to agonists is known to be desensitized because of the phosphorylation at the C-terminal tail of receptors by G-protein-coupling receptor kinase and / or at the third intracellular loop of receptors by cAMP-dependent protein kinase A (PKA) (16,17). The post processes, internalization -endosome formation -degradation or resensitization, depend on the magnitude, kinetics, and duration of stimulations (16).…”