Tetrodotoxin-resistant non-cholinergic neurogenic contraction evoked by capsaicinoids and piperine on the guinea-pig trachea.

Contraction of the isolated tracheal strip to capsaicin was prevented by chronic denervation of the tissue. Tetrodotoxin, hyoscine and hexamethonium caused no inhibition of the response, suggesting that tetrodotoxin-resistant terminal portions of non-cholinergic nerves were activated in this way. There was a strong correlation between the pain-producing and tracheoconstrictor effects of piperine, pungent and non-pungent capsaicin congeners. Common site of action was evidenced by crossed tachyphylaxis. It is concluded that the capsaicin-sensitive sensory nerve endings have a dual sensory-efferent function. Excitation-secretion coupling in this system could operate without an axon reflex.