Drug responses in antigen-induced contractions of tracheal strips of ovalbumin-sensitized guinea pigs

Guinea pig trachea strips were isolated after 21 d of ovalbumin-sensitization. Challenging the preparations with antigen induced a double-phase contractile response (DPCR) which consisted of a rapid contraction (RC) and a tonic contraction (TC). The effects of tetrodotoxin (TTX), atropine, hexamethonium, diphenhydramine and a substance P (SP) antagonist on the DPCR were observed. DPCR was insensitive to atropine or hexamethonium at 1 mumol/L. Diphenhydramine 2 mumol/L abolished RC, and inhibited TC by 48.0 +/- 5.6%. TTX 1 mumol/L and lidocaine 2 mumol/L almost completely abolished TC and reduced RC by 49.6 +/- 6.7% and 44.6 +/- 8.4%, respectively. The substance P antagonist, (D-Arg1, D-2,4-diCl2-Phe5, Asp6, D-Trp7,9, Nle11)-SP 10 mumol/L, inhibited RC by 49.9 +/- 6.1% and TC by 90.7 +/- 9.3%. The results suggest that SP sensory nerve fibers in respiratory tract play an important role in the pathogenesis of DPCR, especially in that of TC.