The Change Of Cyclic Nucleotides Phosphodiesterase Activity In The Lung Tissue From The Experimental Rat Model Of Asthma

Introduction: Asthma is a complex inflammatory disease characterized by variable airflow obstruction, airway hyperresponsiveness and airway inflammation. IL-4 plays a pivotal role in the pathogenesis of this disease, including its role in B cell-class switching to IgE production, as a growth factor for mast cells and its ability to promote the migration and aggregation of eosinophil and basophil. Accumulating evidences show that prior systemic infection with Bacillus Calmette Guerin(BCG) can inhibit antigen-specific IgE responses and airway reactivity and BCG-infected mice exhibit elevated IFN- Y production and decreased IL-4 production. Cyclic nucleotide phosphodiesterase(PDE) is a large and diverse family of enzymes with hydrolyzing activity of cyclic AMP and cyclic GMP, ubiquitous second messengers that regulate countless biologic processes. It has been proved that phosphodiesterase activity in mononuclear leukocytes of patients with atopic disease such as atopic dermatitis was elevated and the total cAMP PDE activity was increased in monocytes taken from mild asymptomatic asthmatics compared to healthy subjects. Some studies in vitro suggested that IL-4 stimulated PDE activity, which provided apossible mechanism of immune and inflammatory regulation. Objective The object of this study was: (1) To compare pulmonary function of and phosphodiesterase(PDE) activity and IL-4 level in the lung tissue from repeatedly ovalbumin (OA) challenged sensitized sprague dawley (SD) rats with the normal subjects. (2) To observe the effects of antiasthmatic drugs such as aminophylline and dexamethasone and BCG immunization prior to sensitization on PDE activity and IL-4 level in the lung tissue from the asthmatic rats. (3) To explore regulation mechanism of PDE activity by IL-4 level in the rat lung model of asthma. Methods SD rats weighing about 150g were sensitized with ovalbumin and Bordetella pertussiss killed organisms 2 weeks ago and were challenged repeatedly by OA for 7 days. Dynamic lung compliance and pulmonary resistance of pulmonary function were determined using a single chamber whole body plethysmograph. PDE reaction was performed in the assay buffer PBS which contained 10 u 1 lung tissue homogenate of the rats and substrate cGMP and cAMP concentration were 1 u mol ?L"1. The cGMP-PDE and cAMP-PDE activity was determined by HPLC measurement of the substrate level of cGMP and cAMP. IL-4 level in the lung tissues was determined by ELISA. The protein concentration was determined by the Bradford colorimetric method with Coomassie blue as the reagent and using bovine serum albumin as a standard. The data were expressed as * ?s. A statistical analysis was performed using one-way ANOVA or nonparametric test. Results 1. Effect of aminophylline, dexamethasone, and BCG immunization on pulmonaryfunction of repeatedly OA challenged sensitized rats:Dynamic lung compliance of repeatedly OA challenged sensitized rats was significantly lower than the control rats while the pulmonary resistance wassignificantly higher (PO.05). Aminophylline (2 mg/kg) and dexamethasone (0.5 mg/kg) treated OA challenged sensitized rats had significantly higher dynamic lung compliance and lower pulmonary resistance than the OA challenged sensitized rats (n=8 , PO.05). Pulmonary resistance of aminophylline (10 mg/kg) and dexamethasone (0.1 mg/kg) treated OA challenged rats was significantly decreased (n=8, P<0.05) while dynamic lung compliance changes were not statistically significant. Dynamic lung compliance and pulmonary resistance of BCG control rats did not change significantly compared with control rats while BCG immunization increased dynamic lung compliance and decreased pulmonary resistance of OA challenged sensitized rats significantly ( n=7, PO.05).2. Effect of aminophylline, dexamethasone, and BCG immunization on cGMP-PDE and cAMP-PDE activity in lungs of repeatedly OA challenged sensitized rats:The cGMP-PDE and cAMP-PDE activity in lungs of repeatedly OA challenged sensitized rats were significantl...