1-napthol beta-D-glucuronide formed intraluminally in rat small intestine mucosa and absorbed into the colon

UDP-glucuronosyltransferase expressed in the rat intestinal epithelial cell s is important as the first barrier against chemicals. The distribution of 1-naphthol and its glucuronide formed in rat intestine was estimated by usi ng everted intestine. Roughly 60% of the 1-naphthol added to the mucosal fl uid was absorbed into the mucosa of the small intestine and colon within 30 min. Approximately 66% of the 1-naphthol absorbed in the proximal intestin e was secreted intraluminally as a glucuronide, and a minimal 9% was transp orted into the serosal fluid as a glucuronide. In the distal intestine, sim ilar to 34% was secreted intraluminally and 30% was transported into the se rosal fluid as a glucuronide. The greatest amount of the glucuronide (37% o f the absorbed 1-naphthol) was transported into the serosal fluid, whereas a minimal 7% was secreted intraluminally in the colon. In marked contrast, the colon was found to transport 1-naphthol-glucuronide from,the mucosal fl uid into the serosal fluid at an approximately 8-fold higher rate than that of the small intestine. These results suggest that, in the small intestine , phenolic xenobiotics are mostly glucuronidated and secreted intraluminall y and that the resulting glucuronide is absorbed and transported into the s erosal side of the colon.