In the present study, we examined histochemically the tissue distribution of dextran sulfate sodium (DSS) in the acute phase of murine colitis induced by administering DSS in the drinking water. DSS was mainly observed in the Kupffer cells of the liver, in the macrophages of the mesenteric lymph node (MLN) and in the lamina propria of the large intestine after administration of DSS. We followed the time course of DSS distribution and found that DSS, which was considered as a large and negatively charged molecule that can not easily cross membranes, was distributed in the liver, the MLN, and the large intestine 1 day after the start of administration of DSS.—KEY WORDS: colitis, dextran sulfate sodium, distribution. J. Vet. Med. Sci. 61 (1): 67–70, 1999 such as the duodenum, jejunum, ileum, cecum, proximal colon, middle colon, and distal colon. The sections were stained with toluidine blue for the identification of sulfated polysaccharide by the metachromatic reaction at pH 2.5 [12], and haematoxylin and eosin (HE) for general examination. A microscopic examination of the colitis induced by DSS showed a loss of the crypt as the earliest histological feature which was followed by a separation of the crypt base from the muscularis mucosa. These changes developed in the middle and distal portion of the colon 2 to 3 days after the start of the administration of DSS. An inflammatory infiltration was not apparent, and the surface epithelial cells still remained morphologically intact at this time point. On day 5 after the start of the administration of DSS, the loss of the crypt had extended to the entire colon, and a moderate inflammatory infiltration consisting of macrophages, PMNs, and lymphocytes was observed in the lamina propria and submucosa. The crypts were replaced by various amounts of inflammatory cells, and focal erosion was present at these sites. On day 7 after the start of the administration of DSS, the erosion and inflammation in the mucosa become more extensive. Both the severity and the occurrence of erosion tended to be more frequent in the distal portion compared to the proximal portion of the colon. These morphological changes were similar to those seen in previous reports [1, 11].

The tissue distribution and time course changes of the metachromatic substances stained with toluidine blue after oral administration of DSS are summarized in Table 1. The metachromatic substance was recognized as a coarse-granule in the liver, the MLN, the spleen, the large intestine, the small intestine, and the kidney. The metachromatic substance was most prominent in the liver and MLN on day 7 after the start of the administration of DSS. In other tissues, the metachromatic reaction was not apparently except for metachromatic mast cells granules. In the liver, the metachromatic substances were present in the cytoplasm of sinusoidal Kupffer cells, but not in the mesenchymal cells (Fig. 1C). In the MLN, the metachromatic substance was seen in the macrophages of the subcapslar sinus (Fig.