Budesonide Prevents Cytokine-Induced Decrease of the Relaxant Responses to Formoterol and Terbutaline, but Not to Salmeterol, in Mouse Trachea

During asthma exacerbations, increased airway inflammation may impair the effects of beta(2)-adrenoceptor (beta(2)AR) agonists. It is unclear whether this impairment is prevented by inhaled glucocorticoids (GCs). We have investigated the relaxation of carbachol-contracted mouse tracheal segments to the beta(2)AR agonists formoterol, terbutaline, and salmeterol. The segments were pre-exposed for 4 days to the proinflammatory cytokines tumor necrosis factor alpha (100 ng/ml) and interleukin-1 beta (10 ng/ml) with or without the GC, budesonide (1 mu M). Formoterol and terbutaline induced greater maximal relaxation (R-max)than salmeterol. The cytokines decreased R-max of all beta(2)AR agonists, whereas budesonide had no effect. However, after concomitant treatment with cytokines and budesonide, the R-max values of formoterol and terbutaline were not impaired, whereas budesonide did not prevent the decrease in the R-max of salmeterol. A similar pattern was observed for cAMP production by the agonists. In tracheal smooth muscle, beta(2)AR mRNA was not affected by the cytokines but increased with budesonide. However, the cytokines markedly increased cyclooxygenase (COX)-2 mRNA expression, which may lead to heterologous desensitization of beta(2)AR. It is noteworthy that the cytokine-induced increase of COX-2 was blocked by concomitant budesonide suggesting that heterologous desensitization of beta(2)AR by the cytokines may be prevented by budesonide treatment. Budesonide prevented cytokine-induced impairment of the tracheal relaxation and beta(2)AR/cAMP signaling for formoterol but not for salmeterol. This suggests that differences exist between formoterol and salmeterol in beta(2)AR coupling/activation and/or signal transduction upstream of cAMP. These results imply that maximal bronchodilator effects of formoterol, but not of salmeterol, are maintained by budesonide treatment during periods with increased inflammation, such as asthma exacerbations

Postnatal changes in β-adrenoceptors in the lung and the effect of hypoxia induced pulmonary hypertension of the newborn

1. β-adrenoceptor activation leads to pulmonary vasodilatation. The increase in circulating catecholamines at birth may assist the postnatal fall in vascular resistance by their activation. To study β(1)- and β(2)-adrenoceptors during postnatal adaptation, we used [(125)I]-iodocyanopindolol (ICYP) binding to lung membranes and sections to quantify and locate the binding sites in piglets from birth to 14 days of age and compared them with those in adult pigs. In addition, pulmonary hypertension was induced in newborn piglets by hypobaric hypoxia. 2. In lung membranes the equilibrium dissociation constant (K(d)) did not change with age for total β-adrenoceptors or for β(2)-adrenoceptors, but there was a significant increase in maximum binding sites (B(max)) between birth and 3 days of age. On tissue sections, B(max) increased between 3 days and adulthood with no change in K(d). 3. Binding sites of β(1)- and β(2)-adrenoceptors were localized to the bronchial epithelium, to endothelium of extra- and intra-pulmonary arteries and to lung parenchyma. Total β-adrenoceptor density increased with age at all locations (P<0.05 – 0.01). At birth intrapulmonary arteries showed no binding, β(2)-adrenoceptors appeared on day 1 and increased up to 14 days of age. β(1)-adrenoceptors appeared by 3 days of age and increased with age. 4. Hypobaric hypoxia from birth led to attenuation in the normal postnatal increase in receptor number, but hypoxia from 3 – 6 days did not decrease receptor density. 5. The normal postnatal increase in β-adrenoceptors suggests a potential for catecholamine induced dilatation in the lung during adaptation which is attenuated in pulmonary hypertension

Glucocorticoids reverse IL-1β-induced impairment of β-adrenoceptor-mediated relaxation and up-regulation of G-protein-coupled receptor kinases

1. The aim of the present study was to examine the effects of glucocorticoid dexamethasone on airway responsiveness to albuterol after intratracheal instillation of saline or IL-1β in Brown-Norway rats in vivo and to elucidate the molecular mechanism of this effect. 2. IL-1β caused a significant reduction in albuterol-mediated relaxation to protect against MCh-induced bronchoconstriction. Dexamethasone attenuated the IL-1β-induced impaired relaxation while alone had no effect when compared to rats treated identically with saline. 3. The density of β(2)-adrenoceptors was significantly reduced in lung membranes harvested from IL-1β-treated rats, which was associated with impaired isoproterenol- and forskolin-stimulated cyclic AMP accumulation and adenylyl cyclase (AC) activity ex vivo. Dexamethasone did not prevent IL-1β-induced down-regulation of β(2)-adrenoceptors but completely blocked IL-1β-induced impairment of cyclic AMP accumulation and AC activity stimulated by isoproterenol and forskolin. 4. The inhibitory G-protein subtypes, G(iα1), G(iα2) and G(iα3), were detected in lung membranes prepared from all groups of rats but the intensity of G(iα1) and G(iα2) was markedly increased in IL-1β-treated rats, which were not prevented by dexamethasone. 5. The activity of cytosolic GRK and the expression of GRK2 and GRK5 were elevated in the lung of IL-1β-treated rats, which were completely abolished by dexamethasone. 6. These results indicate that treatment of rats with IL-1β results in desensitization of pulmonary β(2)-adrenoceptors. In light of data obtained in this study, we propose that both the decrease in AC activity and the increase in GRK activity, which are reversed by dexamethasone, may underlie β(2)-adrenoceptor desensitization