Inhibitory effect of anti-allergic drugs on cholinergic and non-cholinergic neurotransmissions of guinea pig bronchial muscle in vitro.

To determine whether anti-allergic drugs can inhibit autonomic neurotransmission of airway smooth muscle, we studied the effect of sodium cromoglycate (SCG, Intal) and related anti-allergic drugs on electrically induced neurogenic contractions of isolated guinea pig bronchial muscle. Electrical field stimulation (8 Hz, 0.5 msec, 30 V) evoked a biphasic contraction of bronchial muscle, consisting of an initial phasic component followed by a sustained one which was mediated by cholinergic and non-cholinergic nerve stimulations, respectively. Sodium cromoglycate, tranilast, ketotifen, and azelastine at concentrations higher than 10(-6) M caused a concentration-dependent inhibition in the height of the non-cholinergically mediated contractions. The cholinergically mediated contractions were also inhibited by tranilast, ketotifen, and azelastine but not by SCG. Submaximal contractions of bronchial muscle evoked by exogenous substance P (2 X 10(-7) M) were less potently inhibited by these drugs than those by exogenous acetylcholine (2 X 10(-6) M). These results indicate that in isolated guinea pig bronchial muscle, anti-allergic drugs may inhibit non-cholinergic neurotransmission mainly by prejunctional reduction of the transmitter release and partly by postjunctional depression of the response.