The in vivo staining of the lining of mouse forestomach by porphyrins and other fluorescent substances.

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1. It was observed that the forestomach in rats and mice became red fluorescent when these animals were maintained on a diet of chlorophyll-containing "Fox Chow". 2. Little or no red fluorescence was observed in the forestomach when mice were fed "Dog Chow", white bread, or peeled boiled potatoes. 3. The materials that gave rise to red fluorescence of the forestomach originated from two main sources: a. the chlorophyll porphyrin derivatives (chiefly phylloerythrin) resulting from the degradation of chlorophyll in the food, and b. the porphyrins in the red fluorescent Harderian gland secretions that passed to the stomach via the naso-lacrimal duct, nasopharynx and esophagus. 4. The porphyrins from these sources or porphyrins artificially added to the diet had a tendency to accumulate in the mucus of the forestomach, but not in the mucus of the glandular stomach. Methylcholanthrene, when fed with "Dog Chow", was also observed to accumulate in the forestomach mucus. Other fluorescent substances, when added to the diet, do not stain the mucus of the gastro-intestinal tract so selectively. 5. A pH difference (or double gradient) resulting from the secretion of acid in the glandular (middle) part of the stomach was found to be responsible for this differential diffusion of porphyrin into the mucus of the two parts of the stomach. The effect was thought to be related to the pH solubility curves of the porphyrins and/or to the fact that gastric mucus at its isoelectric point (pH 3) becomes permeable to some substances. When the pH of the alimentary contents was within the range of minimum water solubility of a given porphyrin, the rate of diffusion of the porphyrin into the mucus was greatest.