Antagonistic Effect Of ₂-adrenoceptor Agonist Bambuterol On Airway Inflammation Of Asthmatic Guinea Pigs And Its Mechanisms

Objective: To investigate the antagonistic effect of B2-adrenoceptor agonist bambuterol on airway inflammation of asthmatic guinea pigs and its possible mechanisms.Methods: An asthmatic model of guinea pigs was established by sensitizing with ovalbumin. Different doses of bambuterol were administered to guinea pigs by intragastric gavage(ig).(1) We used evans blue spectrophotometry for determination of pulmonary vascular permeability.(2) Eosinophils and lymphocytes in broncho-alveolar lavage fluid (BALF) were isolated by density gradient centrifugation. The number of eosinophils and lymphocytes was counted under light microscope. Cell apoptosis was determined by TdT-mediated dUTP nick end labeling(TUNEL).(3) The level of interleukin(IL)-10 and Eotaxin in BALF were measured by enzyme-linked immunoadsorbent assay(ELISA).(4) Pulmonary histopathologic change was observed by hematoxylin and eosin(HE) staining.(5) Protein expression of nuclear factor-kappa B(NF- k B) in lung tissues was inspected by immunohistochemistry.(6) Correlation between the number of lymphocytes in BALF and apoptosis index of lymphocytes, correlation between the level of Eotaxin and hypodense eosinophils(HEos) and normodense eosinophils(NEos), and correlation between NF- k B protein expression and apoptosis index of lymphocytes and the level of IL-10 were assessed by pearson correlative analysis.Results:(1) Comparing with model group, bambuterol at dose of 7.5, 15 and 30mg/kg decreased the pulmonary vascular permeability significantly.(2) The number of eosinophils and lymphocytes in BALF was higher and their apoptosis index was lower in model group than those in normal control. After treatment with bambuterol 15 and 30mg/kg, the number of eosinophils and lymphocytes was diminished and apoptosis index of lymphocytes was raised, but that of eosinophils had no change.(3) The level of Eotaxin was decreased and the level of IL-10 in BALF was increased remarkably after treatment with bambuterol 15 and 30mg/kg.(4) HE staining showed that lung tissues in model group had obvious histopathological signs of inflammation and bambuterol at dose of 15 and 30mg/kg attenuated inflammatory reactions in lung tissues.(5) Immunohistochemical staining revealed that the percentage of nuclear NF- k B positive cells in bambuterol treatment groups(15 and 30mg/kg) was lower significantly than that in model group.(6) These effects of bambuterol could be antagonized by pretreatment with propranolol.(7) There was a significantly negative correlation between the number of lymphocytes in BALF and apoptosis index of lymphocytes(r= -0.484, P<0.01); There was a significantly positive correlation between the level of Eotaxin and HEos and NEos( r=0.538, P<0.01; r=0.376, f<0.01); There was a significantly negative correlation between the activated NF- k B and apoptosis index of lymphocytes and the level of IL-10(r= -0.572, P<0.01; r= -0.458, P<0.01).Conclusions: B2-adrenoceptor agonist bambuterol could inhibit airway inflammation of asthmatic guinea pigs in some degree, and its mechanisms may be ascribed partly to:(1) Attenuating inflammatory exudation and edema by decreasing pulmonary vascular permeability.(2) Decreasing the number of eosinophils by inhibiting chemotaxis of Eotaxin.(3) Promoting apoptosis of lymphocytes and diminishing the number of lymphocytes by increasing the level of IL-10 and inhibiting the protein expression of NF- k B subsequently.