Intestinal microvascular exchange during lipid absorption.

The forces and membrane coefficients governing transcapillary and lymphatic fluid fluxes were measured in the cat jejunum before and during perfusion of the gut lumen with oleic acid (5 mM) solubilized with taurocholic acid (10 mM). Net transmucosal fluid flux, lymph flow, capillary pressure (Pc), blood flow, capillary filtration coefficient (Kf,c), and lymph and plasma oncotic pressures were measured under absorptive and nonabsorptive conditions. Interstitial fluid pressure was calculated for the two conditions from measured parameters. Stimulation of lipid absorption resulted in a fivefold increase in lymph flow, a threefold increase in Kf,c, a doubling of blood flow, a 2.5 mmHg increase in Pc, and a 1.0 mmHg reduction in interstitial (lymph) oncotic pressure. Lipid absorption was associated with a 3.6 mmHg increase in interstitial fluid pressure. During lipid absorption, approximately 35% of the absorbed fluid is removed from the mucosal interstitium by lymphatics while capillaries remove the remaining 65%. The results of this study indicate that the effects of lipid absorption on microvascular and lymphatic fluid dynamics are quantitatively different than those produced by glucose absorption. These differences can be largely explained by lipid absorption-induced increases in blood flow and microvascular permeability.