AUTONOMIC INTERPLAY IN VIP‐INDUCED TRACHEAL SMOOTH MUSCLERELAXATION

1 VIP-induced inhibitory responses of the guinea-pig tracheal pouch, an in vivo preparation designed to demonstrate non-noradrenergic non-cholinergic innervation, where determined in chloralose-urethane anaesthetized animals under control conditions, or pretreated with atropine, propranolol, both atropine and propranolol or atropine-propranolol with indomethacin. 2 Of the five groups, the control group showed a significantly greater cumulative dose-response relaxation to VIP than did the treatment groups. 3 Among the treatment groups, the propranolol pretreated animals showed significantly greater relaxation than the remaining treatments. 4 The group that received atropine alone and the combination of atropine and propranolol showed the least relaxation to VIP. The relaxations in these two groups did not differ significantly. 5 The significantly greater relaxation of the pouch to VIP in the propranolol treated group suggested that the non-noradrenergic inhibitory mechanism for VIP is dependent upon the existing smooth muscle tone of the pouch. 6 Pretreatment of the guinea-pigs with indomethacin did not cause a significant change in the relaxation of the pouch due to VIP suggesting that VIP caused airway smooth muscle relaxation by a mechanism other than that of the release of bronchodilator prostaglandins.