Cold-induced bronchospasm in normal and sensitized rabbits.

In anesthetized, paralyzed and artificially ventilated rabbits, changes in lung resistance induced by cooling the inspired air were studied under dry air conditions. Airway response to cold was measured in normal animals and in rabbits sensitized to bovine serum albumin. The magnitude of cold-induced bronchospasm was significantly greater in sensitized than in normal rabbits but the time course for recovery of control lung resistance during rewarming was the same in both groups and lasted longer than 4 min. Inhalation of a nebulized aerosol of sodium cromoglycate (SCG) markedly reduced cold-induced bronchospasm and shortened the recovery period, which then lasted only 20 to 30 sec. Vagotomy abolished the airway response to cold air in all cases and this was observed whether the vagus nerves were cut before or after SCG inhalation. SCG or vagotomy exerted the same effect on the response to cold air in normal or sensitized rabbits. Sensitized animals showed an hyperresponsiveness to histamine as well as to cold air. These results suggest that cold-induced bronchospasm results from a vagally mediated reflex whose effects are only enhanced and prolonged by a local release of humoral factors, linked to the reflex path. The increased response to cold air in the sensitized rabbits seems to correspond to non-specific hyperresponsiveness of bronchial smooth muscle rather than to an increased local release of inflammatory mediators.