Brown, M L

We used a noninvasive method to label the solid phase of contents in the unprepared human colon. 111In-labeled Amberlite pellets (0.5-1.8 mm diam) were placed in a gelatin capsule that was then coated with a pH-sensitive polymer (methacrylate). In vitro, the capsules disintegrated in simulated small bowel contents within 1-2 h; when ingested by healthy subjects, capsules released radiolabel in the distal ileum or proximal colon in 13 of 15 subjects. Transit of 111In-pellets through the unprepared colon could then be quantitated radioscintigraphically. Segmental transit was defined in the ascending (AC), transverse (TC), descending (DC), and rectosigmoid (RS) colon. Radioactivity was also quantitated in stools. At 12 h, radioactivity was most obvious in the AC (59 +/- 11%, mean +/- SE) and the TC (21 +/- 6%); at 24 h, counts were distributed equally between AC, TC, and stools (P greater than 0.05); by 48 h, 56 +/- 11% counts had been excreted, although 30 +/- 10% remained in the TC. At 24 and 48 h, the amount in DC or RS was lower (P less than 0.05) than in the TC or in stools. Emptying of the AC was characterized by an initial lag period, when no counts emptied into the TC, followed by a period of emptying that was approximately linear. Thus this simple approach is able to label contents in the healthy human colon. The ascending and transverse colon appear to be sites of storage of solid residue, whereas the left colon and rectosigmoid function mainly as conduits.

In five healthy male volunteers, we compared solid and liquid transit though the unprepared colon. 99mTc-diethylenetriaminepentaacetic acid in 10 ml saline was injected into the cecum through an orocecal tube at 1 ml/min immediately after a methacrylate-coated medication capsule was seen to deliver 111In-labeled Amberlite IR-120PLUS pellets (avg diam, 1.0 mm) into the cecum. Segmental transits through the ascending, transverse, descending, and rectosigmoid regions were determined using a dual gamma camera system and a variable region of interest program. There was no difference between solid [half time, 247 +/- 60 (SE) min] and liquid (312 +/- 88 min) emptying from the ascending colon. Colonic transit of solids and liquids was further compared by regional counts and stool outputs at 12 and 24 h. There were no significant differences between solids and liquids (P greater than 0.05). Our data suggest that transit through the unprepared human colon is not different for solids and small volumes of liquids, when these are delivered together to the ascending colon.

Our first aim was to compare 111In-labeled Amberlite IR-12OP resin pellets and 131I-labeled fiber in the assessment of gastric and small bowel transit and colonic filling in healthy humans. Both radiolabels were highly stable for 3 h in an in vitro stomach model and remained predominantly bound to solid phase of stools collected over 5 days [90.5 +/- 2.1 (SE)% for 131I and 87.4 +/- 1.4% for 111In). The lag phase of gastric emptying was shorter for 111In-pellets (30 +/- 11 min compared with 58 +/- 12 min for 131I-fiber, P less than 0.05). However, the slope of the postlag phase of gastric emptying and the half time of small bowel transit were not significantly different for 111In-pellets and 131I-fiber. Filling of the colon was characterized by bolus movements of the radiolabel (10-80% range, 26% mean) followed by plateaus (periods of no movement of isotope into colon lasting 15-120 min, range; 51 min, mean). Half of the bolus movements occurred within 1 h of the intake of a second meal. Thus 111In-labeled Amberlite pellets provide an excellent marker for the study of gastric and small bowel transit and colonic filling in humans. The ileum acts as a reservoir and transfers boluses of variable sizes into the colon, often soon after the intake of a subsequent meal.