Effect of Cigarette Smoke Exposure In Vivo on Bronchial Smooth Muscle Contractility In Vitro in Rats

Abstract

Cigarette smoking is a risk factor for the development of airway hyperresponsiveness and chronic obstructive pulmonary disease. Little is known concerning the effect of cigarette smoking on the contractility of airway smooth muscle. The current study was performed to determine the responsiveness of bronchial smooth muscles isolated from rats that were subacutely exposed to mainstream cigarette smoke in vivo. Male Wistar rats were exposed to diluted mainstream cigarette smoke for 2 h/d every day for 2 wk. Twenty-four hours after the last cigarette smoke exposure, a marked airway inflammation (i.e., increases in numbers of neutrophils, lymphocytes, and macrophages in bronchoalveolar lavage fluid and peribronchial tissues) was observed. In these subacutely cigarette smoke-exposed animals, the responsiveness of isolated intact (nonpermeabilized) bronchial smooth muscle to acetylcholine, but not to high K+ -depolarization, was significantly augmented when compared with the air-exposed control group. In alpha-toxin-permeabilized bronchial smooth muscle strips, the acetylcholine-induced Ca2+ sensitization of contraction was significantly augmented in rats exposed to cigarette smoke, although the contraction induced by Ca2+ was control level. Immunoblot analyses revealed an increased expression of RhoA protein in the bronchial smooth muscle of rats that were exposed to cigarette smoke. Taken together, these findings suggest that the augmented agonist-induced, RhoA-mediated Ca2+ sensitization may be responsible for the enhanced bronchial smooth muscle contraction induced by cigarette smoking, which has relevance to airway hyperresponsiveness in patients with chronic obstructive pulmonary disease.

Glucocorticoids Ameliorate Antigen-Induced Bronchial Smooth Muscle Hyperresponsiveness by Inhibiting Upregulation of RhoA in Rats

“…The expressions of RhoA protein and mRNA were assessed in the main and intrapulmonary bronchial smooth muscles without epithelia and lung parenchyma (7,11,12,30). As reported previously, the expression of RhoA protein in bronchial smooth muscle of the repeatedly antigen-challenged rats was markedly and significantly increased as compared with that of the sensitized control group ( Fig.…”

“…The airways were carefully cleaned of adhering connective tissues, blood vessels and lung parenchyma under a stereomicroscopy. The epithelium was removed as much as possible by gently rubbing with keen-edged tweezers: histological examinations revealed that almost all the cells other than bronchial smooth muscle cells and cartilages were removed by this process (7,11,12,30). The resultant bronchial tissues were defined as "bronchial smooth muscles" in this manuscript.…”

“…To determine the change in bronchial smooth muscle contractility, the isometric contraction of the circular smooth muscle of the main bronchus, defined as bronchial smooth muscle, was measured as described previously (7,11,12,30). In brief, 24 h after the last antigen challenge, the rats were sacrificed by exsanguinations from abdominal aorta under chloral hydrate (400 mg / kg, i.p.)…”

“…Protein samples of bronchial tissues were prepared as previously described (7,11,12,30). In brief, the airway tissues below the main bronchi to lungs were removed and immediately soaked in ice-cold, oxygenated KrebsHenseleit solution.…”

Airway hyperresponsiveness in asthma: lessons fromin vitromodel systems and animal models: Fig. 1—

“…Furthermore, active allergic sensitisation of guinea pigs without subsequent allergen exposure is already sufficient to increase RhoA expression and enhance its contribution to contraction ex vivo and airway responsiveness in vivo [183]. Remarkably, similar observations were made using passively sensitised guinea pig airway preparations [184], and recent data indicate that the same is true for cigarette-smoke-induced hyperresponsiveness of rat bronchial smooth muscle [185]. In vivo experiments using a guinea pig model of asthma have further indicated that increased Rho kinase activity contributes to the allergeninduced AHR following both the early and late asthmatic reaction, which is effectively reversed by inhalation of Y-27632 [186].…”