Abstract
The early events of fatty acid absorption in the small intestine were ultracytochemically investigated by the PFP reaction, which stained unsaturated lipids. Five min after administration of the unsaturated long chain fatty acid, docosahexaenoic acid (C22:6), ordinary electron staining did not cause any morphological changes in the apical cytoplasm except for the electron dense droplets which appeared in the ER below the terminal web, but a PFP positive particulate or amorphous substance appeared in the microvilli, the terminal web and around the ER below the terminal web. It seemed to be formed by aggregation of small particles. Sometimes the particles appeared separately. The PFP positive substances did not seem to be enclosed by a membrane, and could be free fatty acid diffusing down to the ER. Fatty acid may penetrate the microvillus membranes in the form of a small particle, diffuse down the microvilli to the terminal web and be transformed to droplets by enzyme at the ER.
