Development of the gastrointestinal mucosal barrier: changes in phospholipid head groups and fatty acid composition of intestinal microvillus membranes from newborn and adult rats.

Phospholipids in microvillus membrane (MVM) prepared from the proximal small intestine of newborn (less than 24 h of age) and adult rats were characterized to determine if differences in composition existed. Our hypothesis is that developmental differences in composition of the MVM may account for mucosal barrier differences to microorganisms and antigens during the perinatal period. Lipid analysis showed that both cholesterol and total phospholipids, per mg of membrane protein, were much higher in the newborn MVM than the adult, but the molar ratio of these two lipid classes remained unchanged. Increased phosphatidylcholine and decreased phosphatidylinositol levels were found in the newborn MVM compared to the adult. In addition, the major difference in fatty acid composition of total lipid extracts and three major membrane phospholipids, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol appeared to be an increased ratio of palmitate (16:0) to stearate (18:0) and of oleate (18:1) to linoleate (18:2) in the newborn. These data suggest that changes in the proportion of phospholipid polar head groups and fatty acyl groups as well as changes in the amount of total phospholipids and cholesterol exist in the newborn MVM. These observations are consistent with differences in MVM fluidity previously noted and may help explain the increased uptake of antigens and other mucosal barrier defects in the newborn intestine.