Fig. 5.

Contraction force tracings of guinea pig tracheal rings with repeated exposure to capsaicin. A: contraction force tracing of tracheal ring receiving two successive exposures to 10 µM capsaicin. B: contraction force tracing of tracheal ring receiving vehicle followed by 10 µM capsaicin. A second exposure to capsaicin shows tachyphylaxis compared with the first, suggesting a “depletable” mechanism of contraction consistent with the activation of nonadrenergic, noncholinergic (NANC) nerves.