Constrictor effect of cotton bract extract on isolated canine airways

Tissue bath techniques were used to examine the effects of cotton bract extract (CBE) on isolated canine airways. The CBE elicited strong contractions that were abolished by the 5-hydroxytryptamine (5-HT) antagonist, methysergide (3 x 10(-6) M), but were only slightly affected by atropine (5 x 10(-7) M) and pyrilamine (3 x 10(-6) M) Desensitization to repeated exposures to CBE was not observed, and maximal contractions were equal in force to those produced by supramaximal electrical stimulation (15 V, 25 Hz, 0.5 ms pulse duration). Responses to exogenous 5-HT were qualitatively and quantitatively similar to those produced by CBE. Partial purification of CBE by Amicon ultrafiltration yielded a bronchoactive fraction containing low molecular weight compounds (less than 500). Analysis of the 5-HT concentration in this fraction by high-pressure liquid chromatography, fluorescence, and column chromatography indicated that the amount of 5-HT present accounted for only 8 to 25% of the smooth-muscle-contracting activity of CBE. We conclude that cotton bracts contain a potent 5-HT receptor agonist that appears to be distinct from 5-HT.