Background: Substance P is present in bronchial nerve fibres, The physiolog
ical actions of substance P are mediated via tachykinin NK1 receptors, Immu
nochemical studies have demonstrated tachykinin NK1 receptors in the rat ai
rway epithelium, Objective: To elucidate how epithelial tachykinin NK1 rece
ptors affect smooth muscle response to substance P. Methods: Contractile re
sponse of isolated rat bronchial trunk with or without epithelium was recor
ded. Results: In intact segments precontracted by 5-hydroxytryptamine, rela
xation was induced by substance P and the nitric oxide donor, sodium nitrop
russide, Removal of the epithelium abolished relaxation induced by substanc
e P but did not affect relaxation induced by sodium nitroprusside. The cycl
o-oxygenase inhibitor, indomethacin, but not the nitric oxide synthase inhi
bitor, L-N-G-monomethylarginine, reduced the relaxation in response to subs
tance P, Conclusions: Epithelial tachykinin NK1 receptors mediate substance
-P-induced relaxation of rat bronchial smooth muscle via release of prostan
oids but not nitric oxide.