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


METHODS
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.


RESULTS
In intact dogs, capsaicin (10 mg) and yohimbine (2 mg/kg) immediately induced contractions throughout the colon, with defecation occurring in all experiments. In dogs after colonic cleansing and T/R, the capsaicin (10 mg)-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 (2 mg/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.


CONCLUSIONS
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.
Department of Surgery, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai, 980-8574, Japan.
Daisuke
D
Kikuchi
Chikashi
C
Shibata
Hirofumi
H
Imoto
Soutoku
S
Someya
Tomohiro
T
Miyachi
Koh
K
Miura
Takeshi
T
Naitoh
Michiaki
M
Unno
D058669:Adrenergic alpha-2 Receptor Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D003106:Colon / Q000294:innervation*; D003672:Defecation / Q000187:drug effects*; D004285:Dogs; D005766:Gastrointestinal Contents; D005769:Gastrointestinal Motility / Q000187:drug effects*; D009474:Neurons / Q000502:physiology*; D015016:Yohimbine / Q000008:administration & dosage / Q000494:pharmacology
D058669:Adrenergic alpha-2 Receptor Antagonists; D015016:Yohimbine; D002211:Capsaicin