Immunological control of drug absorption from the gastrointestinal tract: the mechanism whereby intestinal anaphylaxis interferes with the intestinal absorption of bromthymol blue in the rat.

Rats were immunized intraperitoneally with ovalbumin and the disappearance of bromthymol blue (BTB) from the intestinal lumen, its accumulation in the tissue, and its net absorption were examined by means of an in-situ recirculation technique during local anaphylaxis. The disappearance of BTB from the intestinal lumen and its net absorption were significantly reduced, but there was no significant effect on its accumulation in the tissue. The pH value of the luminal solution and the perfusate volume were not influenced by intraluminal challenge with the antigen in ovalbumin-immunized rats. In addition, no significant effect was observed on intestinal permeability to BTB in the in-vitro everted sac technique. The intestinal blood flow, measured by a hydrogen clearance method, was not reduced significantly by the intraluminal exposure to antigen. There was enhanced Evans Blue leakage and mucus release in the perfusate after intraluminal challenge with ovalbumin in ovalbumin-immunized rats, but not in non-immunized rats. A significant increase of BTB binding with macromolecular substances in the perfusate was observed during the local anaphylaxis. These findings suggest that the decreased absorption of BTB is due to the interaction with the macromolecular substances in the perfusate during local anaphylaxis.