Immunolocalization of alkaline phosphatase and surfactant-like particle proteins in rat duodenum during fat absorption

BACKGROUND & AIMS: In response to triacylglycerol feeding, rat duodenum secretes into the lumen and lamina propria phospholipid-rich membranes (surfactant-like particles) that are enriched with intestinal alkaline phosphatase. The purpose of this study was to determine whether the enzyme and particle proteins were coordinate in tissue distribution and in time. METHODS: Immunocytochemistry using specific polyclonal antisera against alkaline phosphatase and against the complex of particle proteins and its 40-kilodalton component was performed. RESULTS: Triacylglycerol feeding produced a peak between 3 and 5 hours in stain intensity for both antigens, intracellularly as well as in the paracellular space and lamina propria. In fasting animals, the microvillous membrane stained strongly for alkaline phosphatase; surfactant-like particle proteins were mainly localized to the lamina propria. Feeding Pluronic L-81 (BASF Wyandotte, Wyandotte, MI), a detergent that decreases transcellular triacylglycerol movement and surfactant-like particle secretion, produced a decrease in reactivity of both antigens in the paracellular space, lamina propria, and lumen and redistributed intracellular alkaline phosphatase and surfactant- like particle proteins from Golgi or cytosol to intracellular membranes, corresponding to the circumference of lipid droplets. CONCLUSIONS: These data support the hypothesis that some intestinal alkaline phosphatase is secreted from the cell associated with the surfactant-like particle and are consistent with a role for this particle in transepithelial transport of triacylglycerols in the enterocyte. (Gastroenterology 1996 Feb;110(2):478-88)