INTERRELATIONSHIP BETWEEN ALPHA-ADRENERGIC AND BETA-ADRENERGIC AGONISTS AND HISTAMINE IN CANINE AIRWAYS

[摘要] To determine the interrelationship between adrenergic receptors in airway smooth muscle and histamine-induced airway constriction, the responses of 26 parasympathectomized dogs to selective and mixed .alpha.- and .beta.-adrenergic stimulation were studied in situ by an isometric tracheal smooth-muscle preparation. Intra-arterial (IA) phenylephrine (PE) caused dose-related tracheal contraction beginning at 10-8 mol; maximal active tension was 9.47 .+-. 2.2 gm F/cm (mean .+-. SD) at 10-5 mol. Pretreatment with propranolol augmented tracheal contraction to PE (maximum 35.5 .+-. 3.2 gm f/cm). The contractile response to PE was blocked with a dose of phentolamine (200 .mu.g/kg IA), which did not alter the response to acetylcholine. Isoproterenol (ISO) caused dose-related tracheal relaxation beginning at 4.2 .times. 10-11 mol (maximum 43.2 .+-. 19.6 gm F/cm). Norepinephrine (NE) also caused tracheal relaxation beginning at 1.2 .times. 10-6 mol, which was less than relaxation caused by ISO. Prestimulation with histamine did not augment the contractile response to PE but reduced maximal tracheal relaxation to NE. Selective .alpha.-adrenergic stimulation apparently causes tracheal contraction. Nonselective stimulation results in tracheal relaxation, even with a weak .beta.-agonist such as NE. Histamine does not augment .alpha.-adrenergic contraction but causes physiologic antagonism of .beta.-adrenergic relaxation of tracheal muscle.