The exchange of protein between the plasma and the liver and intestinal lymph.

1. The exchange of T-1824 and I131-tagged albumin between the plasma, liver and intestinal lymph has been investigated in cats. Both disappeared from the plasma at similar rates for 8 hours after intravenous injection. 2. In intact, nembutalized cats after 8 hours about 70 per cent of the injected albumin remained in the circulation, whereas only 55 per cent remained in animals with the liver and thoracic lymph ducts cannulated. 3. The tagged albumin appeared first in the liver lymph and reached 90 per cent of the plasma levels in 3 to 4 hours; in the intestinal lymph it reached about 50 to 60 per cent of the plasma levels. 4. The specific activities of the plasma and liver lymph became identical after 3 to 4 hours, whereas equilibration of the plasma and intestinal lymph required 12 to 14 hours. 5. The size of the hepatic interstitial protein pool was calculated as 154 mg./100 g. of liver tissue, and the interstitial fluid as 3 per cent of the organ weight. 6. Following partial occlusion of the inferior vena cava above the liver there was an increase in liver lymph flow which accompanied the rise in portal venous pressure. An increase in portal venous pressure of about 10 to 12 cm. of H2O produced a ten-to twelvefold increase in the liver lymph flow and an equilibration of the plasma and liver lymph specific activities in about 1 hour. There were relatively small changesin the intestinal lymph flow. 7. Intravenous infusions of Ringer-Locke solution 100 ml./kg./5 hrs. produced large increases in intestinal lymph flow and reduced the equilibration time for the plasma and intestinal lymph specific activities to about 5 hours. There was a much smaller increase in liver lymph flow, and specific activity equilibration between plasma and liver lymph occurred after about 2 hours. 8. The significance of these results in the interpretation of capillary permeability and protein exchange dynamics is discussed.