Flows and pressures in lymphatic and blood vessels of intestine in water absorption

¹ Department of Physiology, University of Minnesota Medical School, Minneapolis, Minnesota

Under in vitro conditions the water transported across rat intestinal wall came out mainly from the lymphatic duct (85%). When mesenteric blood and lymphatic vessels were occluded a hydrostatic pressure developed from accumulation of the fluid absorbed. Lymphatic pressure was much higher than simultaneous venous pressure. With fat absorption the milky fluid flowed out from the lymphatic duct but there was no venous flow. These observations seem to suggest that initially water is mainly absorbed into the lymphatic system. Both venous and lymphatic pressures could be affected by changing the distention pressure in the lumen, but they were not simple reflections of the latter. At zero distention pressure both lymphatic and venous pressures were significantly higher than the former. Under conditions without water absorption such as O₂ lack, absence of glucose, presence of phlorhizin, or NaCN in the lavage fluid, no fluid was collected from the cannulas in the blood or lymphatic vessels and also no positive pressure could be recorded.