Effects of solute-coupled transport on lymph flow and oncotic pressures in cat ileum

The effects of net volume absorption rate on steady-state lymphatic and capillary volume flows, lymphatic protein flux, and lymph oncotic pressure were analyzed in an isolated vascularly perfused cat ileum preparation. Solute-coupled fluid transport was stimulated by instilling either Tyrode solution, Tyrode + glucose, Tyrode + taurocholic acid (TC), Tyrode + TC + oleic acid, or Tyrode + aspartic acid, into the ileal lumen. Lymph flow increased in a sigmoidal fashion as net volume absorption rate increased. A linear relationship was observed between lymphatic protein flux and net volume absorption rate. The relative contributions of the intestinal capillary and lymphatic systems in removing absorbed volume from the mucosal interstitium was highly dependent on the rate of net volume absorption. Lymph oncotic pressure decreased progressively as net volume absorption rate increased with a maximal reduction in lymph oncotic pressure of 6.0-7.0 mmHg at the higher volume absorption rates. The results of this study indicate that 1) the rate of solute-coupled fluid transport greatly influences the rate of intestinal lympathic and capillary volume flows, lymphatic protein flux, and lymph oncotic pressure, 2) a reduction in tissue oncotic pressure may serve as the major driving force for vascular removal of absorved volume, and 3) the increase in capillary permeability to plasma proteins during fluid transport is related to the rate of volume absorption.