Effects of angiotensin peptides on cholinergic neurotransmission in rabbit tracheal smooth muscle

To determine the effects of angiotensins I, II, and III (A I, A II, and A III) on airway smooth muscle functions, we studied isolated tracheal segments from rabbits under isometric conditions in vitro. Addition of A II and A III but not A I potentiated the contractile response to electrical field stimulation (EFS) at 5 Hz in a dose-dependent fashion. The frequency-response curves for EFS were displaced to the left by A II and A III, whereas the contractile responses to exogenous acetylcholine remained unchanged. Angiotensin-induced potentiation of the response to EFS was further increased in the presence of physostigmine. These results suggest that A II and A III may prejunctionally potentiate the vagally-mediated contraction of airway smooth muscle.