RESUMO
PURPOSE: Mucins are the principal glycoproteins in mucus and have been implicated in the limitation of intestinal drug absorption; however, the contribution of these molecules to intestinal drug absorption remains unclear. In this study, the relationship between the effect of the mucus layer on intestinal drug permeation and mucin distribution in different parts of the rat gastrointestinal tract was evaluated. METHODS: The intestinal permeability of various lipophilic drugs in rat small intestine was evaluated using the in vitro sac method. The expression profiles of mucin mRNA and proteins were evaluated by quantitative real-time RT-PCR and western blotting, respectively. RESULTS: The intestinal permeability of griseofulvin and antipyrine was enhanced by dithiothreitol (DTT) treatment in the proximal small intestine, such as duodenum and jejunum, but not in the distal regions. The mRNA expression analysis of rat mucin genes revealed that the intestinal expression of Muc5ac was considerably higher in the duodenum, whereas that of Muc1, Muc2, and Muc3A was gradually increased toward the lower intestine. In addition, Muc5ac protein was detected only in the luminal fluids from the proximal small intestine after DTT treatment. CONCLUSIONS: Mucus limits the intestinal permeation of lipophilic drugs in the rat proximal small intestine, in which Muc5ac may be involved.