Intestinal transudation, secretion, and lymph flow during volume expansion in the rat

The effect of volume expansion by intravenous infusion of saline on the rate of intestinal lymph flow (JL), serosal surface transudation (JT), and secretion (JS) from upper jejunum was determined. During saline infusion there was a large increase in JS and JT but a small increase in JL due to increased capillary filtration. About 20% of JL from the main intestinal lymph duct originated from the intestine and the rest from the mesenteric pedicle. JL (corrected for pedicle lymph flow), JT, and JS were estimated to account for 10, 30, and 60% of capillary filtrate from the intestine, respectively. Neither lymph nor secretion contained measurable protein, but transudation had a high protein concentration about half of that in the plasma. From these findings it is inferred that probably both JL and JS were derived from the capillary filtrate of mucosa and submucosa vascular beds and JT from that of muscular vascular bed and that capillaries and venules in the mucosa restricted the passage of protein molecules while those of the intestinal muscular tissue were highly permeable to protein.