Possible involvement of substance P immunoreactive nerves in the mediation of nicotine-induced contractile responses in isolated guinea pig bronchus.

Nicotine-induced contraction of the isolated guinea pig bronchial preparation was abolished by capsaicin and a substance P (SP) antagonist [( D-Arg1,D-Pro2,D-Trp7,9,Leu11]SP). Nicotine increased the release of immunoreactive SP from the preparations. The nicotine-evoked release of immunoreactive SP from the bronchial preparation was reduced by hexamethonium but not by tetrodotoxin. The results indicate that the responses to nicotine of the guinea pig bronchial preparation were mediated through the release of SP-like material(s), and that the nicotine-induced response may be produced through a process independent of the sodium action potential. In conclusion, the most likely site of action of nicotine in the isolated guinea pig bronchial preparation is the nicotinic receptor of SP immunoreactive nerves.