American Journal of Clinical Nutrition, Vol 24, 77-90, Copyright © 1971 by The American Society for Clinical Nutrition, Inc.

Intestinal mucosal lacteal in transport of macromolecules and chylomicrons

¹ From the Gastrointestinal Research Laboratory, Veterans Administration Hospital, and Department of Medicine, George Washington University Medical Center, Washington, D.C.

The central lacteal of intestinal villi transports chylomicrons, macromolecules, and fluids. The normal structure of lacteals is reviewed here and briefly compared to the structure of intestinal mucosal capillaries. Pinocytotic vesicles of lacteal endothelium have been shown to occupy 15 % of cytoplasmic volume and to average 1,600 A in diameter. Apparent pinocytotic transport of macromolecules such as peroxidase, ferritin, and chylomicrons is easily demonstrated. When the intestinal mucosa is examined using great care to avoid trauma to tissues, the great majority of lacteal junctional complexes are too narrow to permit passage of macromolecules. Thus, by inference, it would appear that these substances gain entry into the lacteal by pinocytotic transport rather than by entry through endothelial cell junctions. Just as intestinal capillary fenestrae may represent both the small- and large-pore system postulated by physiologists, the lacteal pinocytotic vesicles appear to be the morphologic equivalent of the small- and large-pore system of lacteals. Lacteal junctions also represent the small-pore system.

Interestingly, the lacteal junctional complex remains tight in primary intestinal lymphangiectasia, a disease state in which intestinal lacteals are massively distended. This further suggests the major role of pinocytosis in lacteal endothelial transport of macromolecules. Open lacteal junctions in inflammatory disease states (such as Whipple's disease) may be the route by which some cells and even bacteria gain entry to the circulation.