Orally Fed Digalactosyldiacylglycerol Is Degraded during Absorption in Intact and Lymphatic Duct Cannulated Rats

Membrane lipids of green plants digalactosyldiacylglycerol (DGalDG) and monogalactosyldiacylglycerol (MGalDG) are hydrolyzed in vitro by human duodenal contents, pancreatic juice and bile salt stimulated lipase and guinea pig and rat pancreatic lipase-related protein 2 to free fatty acids, di- and monogalactosylmonoacylglycerols and water soluble galactose-containing compounds. The fate of intermediate products is unknown. We have investigated the digestion and absorption of DGalDG in rats. [3H]- and [14C]-labeled DGalDG in galactolipid dispersions, and 200 g/L soybean triacylglycerol (TG) oil-galactolipid emulsions of different concentrations were fed orally to intact and lymphatic duct cannulated rats. Chyle, gastrointestinal tract, liver and plasma were analyzed for radioactivity in different lipid classes. Recovery of [3H] also was determined in feces. Comparison was made with an emulsion of [14C]dipalmitoyl-phosphatidylcholine ([14C]DPPC), soybean TG oil and soybean phosphatidylcholine (PC). Less than 2% of the radioactivity in chyle was found in DGalDG, >70% of the radioactivity in triacylglycerol (TG), and the remaining part in glycerophospholipids. In intact rats, <1.5% of radioactivity in liver and plasma was identified as DGalDG. In experiments where 120 mg galactolipid-phospholipid mixture or 120 mg PC were given in a soybean TG oil-emulsion, the absorption of galactolipid fatty acids was less complete than PC-fatty acids, as indicated by analysis of feces and intestinal contents. Galactolipids are not absorbed intact or as reacylated monoacyl compounds by rats.