[Mechanisms of neutral red transport through the mucosa of the gastrointestinal tract].

The conditions of the passage of neutral red into the cavity of gastro--intestinal tract were investigated during the atropine blockade of the stomach secretory activity in the dogs with fundal, antral and duodenal fistulas. The neutral red begins to cross the gastric mucosa only after the PH of the perfusing solution has achieved 2.5 and for intestine--5.0. The intensity of the neutral red passage increases with further decrease of the perfusing solution pH. During perfusion of acid solutions through the stomach and particularly through the duodenum, retrodiffusion of H+ occurs into the mucosa. The excretion of neutral red into the cavity of gastro--intestinal tract seems to be a process of passive diffusion. The role of the H+ retrodiffusion in this process is discussed.