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

Airway hyper-responsiveness is one of the characteristics of asthma. I t may be distinguished by airway hyper-sensitivity and an increase of the maximal response plateau. Short-acting beta2-agonists have an acut e protective effect on airway sensitivity, which is shorter in duratio n than the bronchodilating effect, without affecting the maximal respo nse plateau. Long-term treatment has no beneficial effect on airway re sponsiveness. A diminishement of the protection against metacholine- a nd histamine-induced airway obstruction and a rebound increase of this after cessation of continuous treatment have been reported. Single do ses 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 ha s described the development of tolerance to the protecting effect on m ethacholine-induced airway sensitivity after 2 months treatment. Howev er, a protection by 1.0 doubling dose remained and the bronchodilating effect was not influenced. So far, no rebound increase in airway sens itivity has been reported after cessation of continuous treatment.