Influence of dexamethasone on acetylcholine and histamine response of smooth muscles of rat trachea and bronchi

Abstract

We searched dexamethasone influence on isolates of rat trachea and large bronchi under its short-term application. Dexamethasone 10^-7 —10^{- 5} g/ml did not change the exogenous acetylcholine-induced or histamineinduced smooth muscle basal tonus and contractility, but it decreased muscle responses to electric stimulation of nerve fibers and smooth muscle cells. The most response reduction (up to 76.0±4.7%) was noted under the stimulation of pre-ganglionar nerve fibers. The dexamethasone concentration of 10^-6 g/ml reduced the muscle responses caused by stimulation of the nerve fibers. The greatest changes were observed under the stimulation of the pre-ganglionar nerve fibers: 29.8±4.7% for 10^-5 g/ml of acetylcholine and 64.0±12.1% for 10^-6 g/ml of histamine. A gangliobloker entirely removed the dexamethasone effect under the acetylcholine-induced stimulation of the nerve fibers. It did not influence the dexamethasone effect under the histamine-induced stimulation of the pre-ganglionar nerve fibers and decreased the reactions caused by the stimulation of the post-ganglionar nerve fibers from 75.3±6.9% to 38.8±8.6%. Atropine wholly inhibited the dexamethasone influence on the drug under both types of the stimulation with acethylcholine or histamine application. We concluded that the elimination of bronchospasm resulted from the short-term application of dexamethasone is due not to its direct effect on the smooth muscle cells but to its interaction with the epithelial tracheobronchial receptors. This reaction is realised with different nervous ways under the exogenous acethycholine or histamine.