Background Alpha 2A adrenergic receptor (AR) is a subtype of α2 AR belonging to G protein-coupled receptors,and exerts a variety of biological effects. Recent studies have demonstrated that the α2A AR activation was closely related with inflammatory reaction. The present study aimed to investigate the influence of α2A AR antagonist,yohimbine,on the severity of endotoxin-induced acute lung injury in rats.Methods A total of 72 male Sprague-Dawley rats were randomly divided into three groups:control group,lipopolysaccharide (LPS) group and LPS + yohimbine group. Rats were intratracheally administrated with normal saline or LPS (300 μg),and the rats in the LPS + yohimbine group were treated with additional yohimbine (2 mg/kg,i.p) soon after LPS administration. Six,24 and 48 hours after treatment,arterial blood gas analysis was carried out,and optical microscopy was performed to evaluate pathological changes in the lung,and lung injury score was assessed. The count of white blood cells in bronchoalveolar lavage fluid (BALF) was determined. The levels of norepinephrine,tumor necrosis factor (TNF)-α,interleukin (IL)-1β and IL-6 in BALF were measured with enzyme-linked immunosorbent assay.Immunocytochemistry was performed for the detection of α2AAR on inflammatory cells in BALF.Results When compared with the control group,the oxygenation index in the LPS group was significantly decreased,and white blood cell count,the lung histopathological scores,levels of norepinephrine and IL-6 as well as α2A AR expression on inflammatory cells in the BALF were dramatically increased at different time points,and the concentrations of TNF-α and IL-1β were also increased except at 48 hours after LPS administration. The oxygenation index decreased while white blood cell count in BALF and the lung histopathological scores were obviously increased in the LPS +yohimbine group. The level of norepinephrine in BALF was increased at each time interval in the LPS + yohimbine group,and so did the levels of TNF-α,IL-1β and IL-6 at 6 and 48 hours after LPS administration respectively. When compared with the LPS group,the oxygenation index,white blood cell count,the lung histopathological scores and the level of IL-6 in the LPS + yohimbine group were significantly improved at each time interval,and the concentrations of TNF-α and IL-1β were also lower at 24 hours of LPS administration (all P ＜0.05). Correlation analysis indicated the level of norepinephrine was related to the levels of TNF-α,IL-1β and IL-6 in the BALF and the lung histopathological scores (r=0.703,r=0.595,r=0.487 and r=0.688,respectively,P ＜0.001) and the intensity scores of immunoreactivity to α2A AR on inflammatory cells were also associated with the levels of TNF-α,IL-1β and IL-6 as well as the lung histopathologial scores (r=0.803,r=0.978,r=0.716 and r=0.808,respectively,P ＜0.001).Conclusions Yohimbine can inhibit TNF-α,IL-1β and IL-6 overproduction and relieve the severity of pulmonary inflammation induced by endotoxin,which is maybe mediated by blockade of α2A AR on inflammatory cells.