Evan's blue dye blocks capsaicin-induced cough and bronchospasm in the guinea pig.

The influence of Evan's blue dye on capsaicin-induced bronchoconstrictor and cough responses was investigated in the guinea pig. Evan's blue (30 mg kg-1 i.v.) pretreatment shifted the bronchoconstrictor dose-response to capsaicin (0.3-100 micrograms kg-1 i.v.) to the right by 10-fold, but had no effect on the bronchospasm elicited by neurokinin A (0.3-10 micrograms kg-1 i.v.). Evan's blue (0.3-30 mg kg-1 s.c.) also inhibited capsaicin-induced cough in a dose-dependent manner. Evan's blue blocked capsaicin responses by the intravenous, subcutaneous, or inhaled routes of administration. We conclude bronchoconstrictor responses and cough in vivo.