EVANS BLUE PERMEATION OF INTESTINAL-MUCOSA IN THE RAT

The azo dye Evans blue (EB; molecular weight, 960.83) is widely used a s an indicator of increased capillary permeability. In the present stu dy, however, rat gut absorption of EB was investigated after dye insti llation in either the small or large intestine. During a brief period of ether anaesthesia, EB was injected either into jejunal loops with a challenge period of 30 or 60 min or into a proximal and a distal colo n loop with a challenge period of 30, 60, or 120 min. After the rats h ad been killed the intestinal specimens were washed with 6 mM acetylcy steine dissolved in phosphate-buffered saline, which efficiently clear ed the tissues of mucus, and thus of EB trapped in mucus. Only EB abso rbed by the gut wall remained to be estimated, and this absorption was found to be both dose- and time-dependent in the jejunum and the colo n. After instillation in the colon, but not in jejunum, EB could be de tected in the blood. EB absorption from the jejunum remained unaffecte d by the addition of either ouabain (1 mM) or lidocaine (0.38 mM). Eit her of these compounds inhibited EB uptake in the proximal part of the colon, while enhancing it in the distal part. Fluorescence microscopy showed penetration into the intestinal wall to be a prerequisite for EB to become fluorescent, and EB fluorescence increased with time. It is proposed that EB is transported over the mucosa by the paracellular route and that the amount of absorbed EB reflects epithelial permeabi lity differently in different parts of the gastrointestinal tract. The results suggest that active mechanisms also contribute to the EB upta ke in the large intestine. A particularly noteworthy finding was the e xistence of a functional heterogeneity between the proximal and distal colon.