Basic mechanisms controlling lymph transport in the mesenteric lymphatic net

Abstract

This minireview summarizes an oral presentation given at the National Institute of Diabetes and Digestive and Kidney Diseases National Institutes of Health workshop "Lymphatics in the Digestive System: Physiology, Health, and Disease" in Bethesda, Maryland on November 3-4, 2009. The concepts of extrinsic and intrinsic pumps, as well as intrinsic and extrinsic flows, are discussed in relation to the lymph transport in mesenteric lymphatic vessels. Age-related alterations in the structure and regulatory mechanisms of lymph flow in mesenteric lymphatic vessels may provide the basis for their diminished ability to work during the periods of increased functional loads in them. The recent development of modern experimental tools provides the opportunity to extend the knowledge on lymph transport function of lymphatic vessels that is absolutely necessary to maintain fluid and macromolecular homeostasis and to provide a transportation route for lipids adsorbed in gut and to immune cells.

Figure 1

Age-induced alterations in muscle cell density in rat mesenteric lymphatic vessels. Lymphatic wall in 9-month-old (Top: max lymphatic diameter ~130 µm) and 24-month-old (Bottom: max lymphatic diameter ~120 µm) Fisher-344 rats. Live isolated rat mesenteric lymphatic vessels underwent 30 min loading by CellTracker™ Green CMFDA (Invitrogen Corp. Carlsbad, CA). The segments were observed at 50× magnification, using a Leica AOBS SP2 Confocal-Multiphoton Microscope System (Leica Microsystems Heidelberg Gmbh, Mannheim, Germany). Confocal images were acquired at 0.3-µm intervals via 489 nm of peak excitation wavelength and 508 nm peak emission wavelength in order to completely image the entire lymphatic vessel. Three-dimensional projections were generated from a series of images using confocal images processing software, provided by microscope manufacturer. Transmural pressure is ~7 cm H₂O.