Role of the intraluminal contents and the continuity of intrinsic neurons in intracolonic capsaicin-induced contraction and defecation in dogs

Abstract

We, herein, examined the role of the intraluminal contents and continuity of colonic intrinsic neurons in intracolonic capsaicin-induced enhancement of colonic motility and defecation. Five beagle dogs were equipped with three strain gauge force transducers throughout the colon. The colonic contractile activity in response to intracolonic capsaicin was studied in intact dogs, dogs after colonic cleansing and dogs with transection/re-anastomosis (T/R) between the proximal and middle colon. The effects of intravenous yohimbine, a α2 adrenergic antagonist, on the colonic motility and defecation were also studied in the same models. In intact dogs, capsaicin (10mg) and yohimbine (2mg/kg) immediately induced contractions throughout the colon, with defecation occurring in all experiments. In dogs after colonic cleansing and T/R, the capsaicin (10mg)-induced enhancement of colonic motility was decreased in the middle and distal colon, and capsaicin-induced defecation was observed in 0-20% of experiments (p<0.05 compared to intact dogs). The effect of yohimbine (2mg/kg) in inducing colonic contractions was unaltered after colonic cleansing and T/R; in contrast, yohimbine-induced defecation was not observed after colonic cleansing, but was unchanged after T/R. The continuity of the colonic intrinsic nerves as well as the intraluminal contents appear to play an important role in the colonic motor response to intracolonic capsaicin.