ACUTE EXPERIMENTAL DISTAL COLITIS ALTERS COLONIC TRANSIT IN RATS

Data from humans with active distal colitis suggest that the proximal colon exhibits increased contractile activity and delayed transit, whe reas the distal colon shows decreased contractile activity and rapid t ransit. The present study used the acetic acid rat model of experiment al colitis to determine the effect of distal colitis on total and regi onal colonic transit in vivo and on the in vitro contractility of circ ular smooth muscle from the proximal and distal colon. Distal colitis was induced in rats by intracolonic administration of 4% acetic acid; sham control rats received saline enemas. Control and colitic rats wer e studied 2 days postenemas. Total colon transit was determined by cal culating the geometric center of distribution of a radiolabeled marker (Cr-51) instilled into the proximal colon. Regional transit was asses sed by expressing the radioactivity in the cecum, proximal and distal colon, and excreted stool as a percent of total radioactivity. Muscle strips from the proximal and distal colon were stimulated with 100 mu M acetylcholine (ACh) and 60 mM KCI and the tension was expressed as k ilograms per square centimeter. Distal colitis was characterized by de creased total colon transit, increased retention of marker in the cecu m and proximal colon, and decreased retention of marker in the distal colon. In vitro contractility studies revealed that distal colitis inc reased proximal colon circular smooth muscle contractility and decreas ed distal colon circular smooth muscle contractility to both ACh and p otassium. Distal colitis is associated with regional differences in co lonic circular smooth muscle contractility, which may contribute to de layed transit in the proximal colon and rapid transit in the distal co lon. (C) 1997 Academic Press.