Selective uptake of intraluminal dextran sulfate sodium and senna by macrophages in the cecal mucosa of the guinea pig.

The involvement of macrophages in the passage of intraluminal substances into the lamina propria was examined in the large intestine of the guinea pig. Dextran sulfate sodium (DSS) and senna, which, experimentally, induce ulcerative colitis and melanosis coli, respectively, were chosen for examination, since these substances are visible under the microscope without any special treatment. DSS (MW 50,000) and senna were orally administered to guinea pigs. In tissue sections of the intestine, the presence of DSS was demonstrated by toluidine blue staining, while senna was visible under the light microscope as brown pigment. In the large intestine of guinea pigs, macrophages were most numerous in the cecum, decreasing in number towards the rectum. Metachromatic reaction due to DSS was first recognized in the epithelium of the cecum, and was subsequently incorporated by macrophages. The presence of DSS, either in the epithelium or in macrophages, was not recognized in the small intestine or the distal colon. Senna pigmentation was also limited to the cecum and proximal colon, in which pigmented macrophages aggregated in the lamina propria. The two different substances administered orally were taken up in the cecum, and partly also in the proximal colon; the substances passed through the epithelium and were incorporated by macrophages. This finding suggests the existence of a weak point in the intestinal barrier in this particular portion of the intestine.