Acute respiratory distress syndrome (ARDS), characterized by acute hypoxic respiratory dysfunction or failure, is a manifestation of multiple organ failure in the lung, and the most common risk factor is sepsis. We previously showed that blocking α 2 -adrenoceptor (α 2 -AR) could attenuate lung injury induced by endotoxin in rats.α 2A -adrenoceptor (α 2A -AR), a subtype of α 2 -AR plays a key role in inflammatory diseases, but the mechanism remains unknown. Here, we explored the effect of BRL-44408 maleate (BRL), a specific α 2A -AR antagonist, on cecal ligation puncture (CLP)-induced ARDS in rats and the underlying mechanism. Preadministration of BRL-44408 maleate significantly alleviated CLP-induced histological injury, macrophage infiltration, inflammatory response, and wet/dry ratio in lung tissue. However, there was no statistical difference in survival rate between the CLP and CLP+BRL groups. Extracellular regulated protein kinase (ERK1/2), p38MAPK, and p65 were activated in the CLP group, and BRL-44408 maleate inhibited the activation of these signal molecules, c-Jun N-terminal kinase (JNK) and protein kinase A (PKA) showed no changes in activation between these two groups. BRL-44408 maleate decreased lipopolysaccharide (LPS)-induced expression of cytokines in NR8383 rat alveolar macrophages and reduced phosphorylation of ERK1/2, p38MAPK, and p65. JNK and PKA were not influenced by LPS. Together, these findings suggest that antagonism of α 2A -AR improves CLP-induced acute lung injury and involves the downregulation of ERK1/2, p38MAPK, and p65 pathway independent of the activation of JNK and PKA. K E Y W O R D S acute respiratory distress syndrome, BRL-44408 maleate, MAPK and NF-κB, protein kinase A, α 2A -AR 1 | INTRODUCTION Acute respiratory distress syndrome (ARDS), which is characterised by acute hypoxic respiratory dysfunction or failure with bilateral pulmonary infiltration, is a manifestation of multiple organ failure in the lung, often caused by various noncardiac reasons, either direct or indirect pulmonary injury, including severe pneumonia, aspiration of gastric contents, severe trauma, infection, shock, and sepsis (Williams et al., 2017). Because of the improvements in critical care practice, including lung-protective ventilation, timely resuscitation, and antimicrobial administration, restrictive transfusion strategies, the incidence of ARDS has a substantial decline (

Acute respiratory distress syndrome (ARDS) is a severe condition with high morbidity and mortality and few interventions. The role of sympathetic stress in the pathogenesis of ARDS has attracted recent research attention. Blockade of alpha-2- or alpha2A-adrenoceptor (α2A-AR) has been shown to attenuate lung injury induced by lipopolysaccharide in rats. However, the mechanism is unclear. We confirmed the role of α2A-AR in ARDS using knockout mice and alveolar macrophages following lipopolysaccharide stimulation to assess the underlying mechanisms. We found that α2A-AR deficiency decreased the permeability of the alveolar capillary barrier in ARDS mice and suppressed lung inflammation by reducing inflammatory cell infiltration and the production of TNF-α, IL-6, and CXCL2/MIP-2. Lipopolysaccharide stimulation decreased NF-κB activation in lung tissues of α2A-AR deficient mice and increased norepinephrine concentrations. In vitro, we found that norepinephrine inhibited the production of TNF-α, IL-6, and CXCL2/MIP-2 and promoted the secretion of IL-10 from lipopolysaccharide-stimulated murine alveolar macrophages. Blockade of α2A-AR by a specific antagonist further inhibited the production of TNF-α, IL-6, and IL-10. Furthermore, norepinephrine down-regulated NF-κB activation in stimulated alveolar macrophages. Altogether, these results suggest that α2A-AR deficiency ameliorates lung injury by increasing norepinephrine concentrations in lung tissues and inhibiting the activation of alveolar macrophages.