Interaction between SO2 and cold-induced bronchospasm in anesthetized rabbits

Abstract In anesthetized, paralyzed and artificially ventilated rabbits, reflex changes in lung resistance induced by cooling the inspired air from 38 to 15°C were studied before and after 45 min periods of SO 2 exposure at two different concentrations (0.5 or 5 ppm). Both concentrations of SO 2 induced significant increase in R l in intact animals (+ 16% and + 50%, respectively). The effect of ppm SO 2 persisted after vagotomy. The cold-induced bronchospasm was halved after exposure to 0.5 ppm SO 2 and was no longer significant after exposure to 5 ppm SO 2 . In both cases, l recovered to control values 40 min after the end of SO 2 exposure and then, the magnitude of cold-induced bronchospasm also recovered. The reflex bronchoconstrictor response to phenyldiguanide (PDG) i.v. disappeared after exposure to 5 ppm SO 2 . However, the bronchomotor response to histamine i.v., which involved both reflex and direct actions on airway smooth muscle, was not altered. These results show that (1) prolonged increase in R l measured after SO 2 exposure does not result from a vagal reflex; (2) the cold-induced bronchospasm, as well as the bronchomotor response to PDG, are reduced or suppressed during the period where the effect of SO 2 persisted. This suggests that 45 min exposure to SO 2 induces transient alterations in tracheobronchial wall, which reduce the accessibility to nervous receptors in the airways.