[A new non-invasive method for measurement of airway responsiveness in sedated rats]

Sprague-Dawley rats sedated with intraperitoneal injection of diazepam (7.5 mg/kg) were placed in a plethysmograph to measure the changes in spontaneous respiration. Inhalation of methacholine (MCh) or acetylcholine (ACh) aerosol did not alter the volume of breathing, but increased respiratory frequency (RF) to the same extent in a concentration-dependent manner. On the other hand, the tachypnea effect of MCh lasted 11 min, and that of ACh only 3 min. Urethane anesthesia inhibited spontaneous respiration and the response to MCh. Atropine, salbutamol and aminophylline inhibited MCh-induced tachypnea. In sensitized rats, the response to MCh was potentiated 6 h after inhalation of ovalbumin aerosol. The results indicate that sedation with diazepam and inhalation of MCh aerosol used in this report are suitable for measuring airway responsiveness in terms of degree of increase of respiratory frequency.