Evidence for the involvement of calcitonin gene-related peptide in the epithelium-dependent contraction of guinea-pig trachea in response to capsaicin

Capsaicin (10(-9) to 10(-5) M) contracted guinea-pig tracheal strips. Epithelium-containing tracheal strips developed a maximum active tension which was significantly higher than that observed in epithelium-free strips. Anti-CGRP (calcitonin gene-related peptide) serum blocked the epithelium-dependent potentiation of the capsaicin-induced contraction in the intact tracheal strips, without affecting the response of the epithelium-free strips. This result suggests the occurrence of an epithelium-dependent release of CGRP. This same serum markedly reduced the contraction induced by exogenous rat CGRP in both intact and epithelium-free tracheal strips. In epithelium-free tracheal strips, capsaicin-induced contraction was abolished by spantide (10(-6) and 10(-5) M), a substance P antagonist, but, in intact tracheal strips, spantide did not abolish the capsaicin-induced contraction, showing that both CGRP and substance P release are directly induced by capsaicin. Moreover, the contractile responses to rat CGRP of intact tracheal strips from guinea pig suggest that CGRP itself might be able to release a contracting factor from the airway epithelium. Therefore, CGRP originating from the airway epithelium may play a major role in the control of airway smooth muscle tone.