SECRETION AND DISTRIBUTION OF RAT INTESTINAL SURFACTANT-LIKE PARTICLES AFTER FAT FEEDING

Triacylglycerol feeding increases serum intestinal alkaline phosphatas e (IAP) activity and leads to the appearance of an alkaline phosphatas e-containing particle in the luminal washings over the apical surface of the rat enterocyte and in the blood (J. Clin. Invest. 84: 1355-1361 , 1989). To examine the coordinate appearance of these particles and t he enzyme and to follow their distribution in vivo after feeding, an e nzyme-linked immunoabsorbent assay (ELISA) was developed, using antise ra raised against the purified intact surfactant-like particle. Tissue compartments that were examined for phosphatase activity and particle content included isolated enterocytes, lamina propria, intestinal lum inal washings, and serum. Alkaline phosphatase activity peaked earlies t in the lamina propria (3 h), followed by the enterocyte and the lumi nal washings (5 h) and serum (7 h). Surfactant-like particle content p eaked in the enterocyte and lamina propria at 3 h, followed by the ser um (3-5 h) and the luminal washings (5 h). The buoyant density of the particle in the enterocyte (d = 1.08-1.09) and serum (d = 1.07-1.08) a fter fat feeding was similar to that of the isolated particle (d = 1.0 7-1.08). The density of particle proteins detected by ELISA in fasted serum was more diffuse and >1.10, consistent with partial degradation of the particle and/or its proteins. These data confirm that the parti cle and its bound IAP are secreted from the enterocyte after triacylgl ycerol feeding and that they appear in compartments adjacent to both t he basolateral (serum) and apical (luminal wash) surfaces of the enter ocyte. Moreover, the data show that the site of initial peak appearanc e of extracellular particle is the lamina propria, followed by peak co ncentration of the particle in both the serum and on the luminal surfa ce. The lamina propria may play a physiological role, perhaps as reser voir and/or as filter in the extracellular processing of the surfactan t-like particles.