Evans blue permeation of intestinal mucosa in the rat

The azo dye Evans blue (EB; molecular weight, 960.83) is widely used as an indicator of increased capillary permeability. In the present study, however, rat gut absorption of EB was investigated after dye instillation 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 colon loop with a challenge period of 30, 60, or 120 min. After the rats had been killed the intestinal specimens were washed with 6 mM acetylcysteine dissolved in phosphate-buffered saline, which efficiently cleared the tissues of mucus, and thus of EB trapped in mucus. Only EB absorbed 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 colon. After instillation in the colon, but not in jejunum, EB could be detected in the blood. EB absorption from the jejunum remained unaffected by the addition of either ouabain (1 mM) or lidocaine (0.38 mM). Either 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 permeability differently in different parts of the gastrointestinal tract.(ABSTRACT TRUNCATED AT 250 WORDS)