Specific motor effects of capsaicin on human jejunum.

Capsaicin (1 microM) produced a biphasic effect on the motility of longitudinal muscle strips from human jejunum e.g. an initial inhibitory effect on nerve-mediated contractions followed by a delayed increase in motility. Neither effect was observed upon a second application of the drug, indicating desensitization, a proposed marker of the action of capsaicin on sensory nerves. Both substance P and neurokinin A produced a contraction of isolated human jejunum, while calcitonin gene-related peptide had a small and inconsistent inhibitory effect.