Modulation of Airway Responsiveness to Acetylcholine by Nitric Oxide in a Rabbit Model

Abstract

Nitric oxide (NO) is an important mediator in the regulation of bronchial muscle tone and airway responsiveness. We investigated the influence of exogenous NO on airway responsiveness to acetylcholine aerosols (ACH) in normal and in hyperresponsive rabbits. White New Zealand rabbits were anesthetized, intubated, and breathed room air spontaneously. Responses of respiratory parameters in ACH challenge tests were measured. In group A the influence of NO on ACH infusion-induced airway constriction was measured. Airway responses to aerosols from 0.25 to 8.0% ACH solutions in saline were measured with 150 and 300 ppm NO inhalation (groups B and C) and compared with the same animals' responses without NO. Moreover, we examined the influence of NO synthase inhibition on airway responsiveness (group D) and the modulatory effect of NO in hyperresponsive animals (group E). 300 ppm NO inhalation significantly decreased the bronchoconstrictor response to intravenously administered ACH (group A). However, the baseline value of dynamic elastance (Edyn) was only marginally lower under the influence of 300 ppm NO. During inhalation of 150 or 300 ppm NO, responses to nebulized 2.0% and less ACH solutions remained nearly unaltered. Responses to aerosols of 4.0 and 8.0% diminished significantly (groups B and C). Following 40 min of aerosolized N-nitro-L-arginine-methyl ester (L-NAME) solution (a NO synthase inhibitor, 1.2 mM) inhalation, the response of Edyn to ACH increased significantly in group D. In group E, animals inhaled 500 mg/m3 ammonium persulfate (APS), an oxidant with various industrial applications, after the first ACH challenge test (0.2, 1.0, and 2.0% ACH). After 2 h of APS exposure, the ACH-induced broncho constriction was increased significantly in the challenge test. After another 2 h of APS inhalation, the airway responsiveness to ACH was tested under the influence of 300 ppm NO. NO significantly decreased the response to ACH to almost the same level as before APS exposure. The results indicate that responses to high ACH concentrations as well as an APS-induced increase in ACH responsiveness were effectively reduced by high concentrations of inhaled NO.

Inhaled Ammonium Persulphate Inhibits Non-Adrenergic, Non-Cholinergic Relaxations in the Guinea Pig Isolated Trachea

“…However, a cross-sectional study [24] did not show an increased risk of occupational asthma in a population of workers exposed to persulphate concentrations of about 1 mg/m 3 . Higher concentrations, up to 500 mg/m 3 , were used in animal studies [25]. Accidental exposure to uncontrolled high concentrations of irritant chemicals can lead to irritant-induced asthma, also known as reactive airways dysfunction syndrome [26].…”