Intestinal absorption of ester and ether glycerophospholipids in guinea pig. Role of a phospholipase A2 from brush border membrane

In vivo intestinal perfusion was used to follow the absorption of three different choline glycerophospholipids (CGP) in guinea pig. These included 1-[³H]palmitoyl-2-acyl-sn-glycero-3-phosphocholine (diacyl-GPC), 1-[³H]-O-hexadecyl-2-acyl-sn-glycero-3-phosphocholine (alkylacyl-GPC) and 1,2-di-O-hexadecyl-sn-glycero-3-phospho-[³H]-choline (dialkyl-GPC). About 80% of diacyl-GPC was absorbed within 4 hr, compared to 60% of alkylacyl-GPC and 30% of dialkyl-GPC. The radioactivity disappearing from the perfusion fluid was recovered in intestinal lipids, mostly triacylglycerol, free fatty acid and CGP from diacyl-GPC, CGP from alkylacyl-GPC and dialkyl-GPC. These results indicated that the nonhydrolyzable substrate dialkyl-GPC was much less absorbed, whereas diacyl-GPC, which released over 80% of [³H]palmitic acid in the perfusion fluid, displayed the highest absorption rate. The intermediate picture observed for alkylacyl-GPC suggested the possible involvement of a phospholipase A₂, which was detected in the entire intestinal tract. This enzyme was further found to concentrate in villus cells, where it is localized in the brush border membrane, as shown using two different subcellular fractionation procedures. These data suggest a possible role of this new enzyme in the digestion of alimentary phospholipids.