1982 Volume 31 Issue 6 Pages 343-349
Effect of noradrenaline on cholinergic neurotransmission was studied using isolated tracheal stripchain preparation of guinea-pig. Electrical stimulation (1-30 Hz, 0.5msec, 40 pulses and supramaximal voltage) produced a frequency-dependent contraction of the tracheal muscle pretreated with guanethidine (10μM) and indomethacin (2μM). The elicited contraction seems to have been mediated by cholinergic nerve stimulation, since the response was abolished by tetrodotoxin (0.2μM) and atropine (0.2μM). The electrically-induced contractions were inhibited by noradrenaline (0.1-3μM), in a dose-dependent manner. The inhibitory effet of naradrenaline was unaffected by propranolol (2μM) or prazosin (3μM) treatment, but completely reversed by phentolamine (1μM) or yohimbine (2μM). Noradrenalne (3μM) also inhibited contractions of the tracheal muscle induced by exogenously applied acetylcholine (0.1-3μM), which was completely antagonized by propranolol (2μM). These results suggest that noradrenaline inhibits cholinergic neurotransmission in guinea-pig tracheal muscle principally via presynaptic α_2-adrenoceptors and to a very limited degree, via postsynaptic β-adrenoceptors.
