EFFECTS OF BETA(2)-RECEPTOR AGONISTS ON AIRWAY RESPONSIVENESS

Airway hyper-responsiveness is one of the characteristics of asthma. It may be distinguished by airway hyper-sensitivity and an increase of the maximal response plateau. Short-acting beta2-agonists have an acute protective effect on airway sensitivity, which is shorter in duration than the bronchodilating effect, without affecting the maximal response plateau. Long-term treatment has no beneficial effect on airway responsiveness. A diminishement of the protection against metacholine- and histamine-induced airway obstruction and a rebound increase of this after cessation of continuous treatment have been reported. Single doses of long-acting beta2-agonists give a prolonged protection against methacholine- and histamine-induced airway sensitivity of at least 12 hours. A small decrease in the maximal response plateau has been noted. Currently, there is little data on long-term treatment. One study has described the development of tolerance to the protecting effect on methacholine-induced airway sensitivity after 2 months treatment. However, a protection by 1.0 doubling dose remained and the bronchodilating effect was not influenced. So far, no rebound increase in airway sensitivity has been reported after cessation of continuous treatment.