Intracolonic Administration of the TRPA1 Agonist Allyl Isothiocyanate Stimulates Colonic Motility and Defecation in Conscious Dogs

Background The aim of the present study was to investigate the effects of the intracolonic transient receptor potential (TRP) A1 agonist allyl isothiocyanate (AITC) on colonic motility and defecation. Methods The effects of AITC administered into the proximal colonic lumen on colonic motility and defecation were studied in neurally intact dogs equipped with strain-gauge force transducers on the colon, with or without various antagonists. Effects of intracolonic AITC were also studied in dogs with either transection/re-anastomosis (T/R) between the proximal and middle colon and complete extrinsic denervation of an ileocolonic segment. Results AITC increased colonic motility and induced giant migrating contractions (GMCs) with defecations in 75 % of experiments in neurally intact dogs. These effects were inhibited by atropine, hexamethonium, ondansetron, and HC-030031 but unaltered by capsazepine. In dogs with T/R, the increase in colonic motility was inhibited in the middle-distal colon. In dogs with extrinsic denervation, the increase in colonic motility in the distal colon was decreased. Conclusions Intracolonic AITC stimulates colonic motility and defecation via cholinergic, serotonergic, and TRPA1 pathways. Continuity of colonic enteric neurons plays an essential role in the intracolonic AITC-induced colonic motor response, while extrinsic nerves are important in occurrence and propagation of GMCs.