Histochemical study of the amphibian digestive tract during normal and thyroxine‐induced metamorphosis. I. Alkaline phosphatase

Abstract

AbstractHistochemical patterns of alkaline phosphatase activity were demonstrated in specific regions of the digestive tube in a series of growing and metamorphosing larvae and frogs of Rana pipiens. In growing larvae activity in the mucosal epithelium was intense and sharply localized in the striated border of the duodenum posterior to the bile duct and of the mid‐small intestine. No activity was found in the epithelial lining of the esophagus, stomach (or its glands), duodenum anterior to the bile duct, end of small intestine, or large intestine. Connective tissue and blood vessels throughout the length of the digestive tract displayed moderate activity. As remodeling of the gut began in metamorphosing larvae, the high phosphatase activity in the striated border decreased sharply, but activity in the connective tissue of the entire digestive tract increased substantially. As metamorphosis neared completion and a new mucosal epithelium developed, activity became strong in the striated border throughout the small intestine, including the region anterior to the bile duct and the end‐small intestine. In adult well‐fed frogs activity remained in this location, although in unfed frogs kept in the cold it diminished in the striated border and became prominent in subepithelial blood vessels. Enzyme activity was not detected in connective tissue (excepting random blood vessels) in any region of the frog digestive tract. These histochemical observations represent an overview of the distribution of alkaline phosphatase activity along the length of the digestive tract during larval and adult stages of a single anuran species.