In the rat, intestinal lymph carries a significant amount of ingested glucose into the bloodstream

Intestinal lymph flow in rats receiving an oral load of 3 mmoles of glucose was determined by measuring the amount of tritiated gavage water entering via the portal route [computed differential arterio-venous tritium water concentrations multiplied by portal blood flow) and measuring the total amount of tritium transferred from the intestinal lumen to the rest of the rat in a given time [from the blood tritium specific activity and the water space (795 ml.kg-1) of the rat]. The approximate figure obtained (79.8 ml.kg-1.h) was used for the evaluation of the amount of glucose (from 14C-labelled glucose in the gavage) transfer via intestinal lymph from the label present in the lymph and its flow. Lymph glucose concentration (c. 11 mM) and specific radioactivity were higher than those of blood. The amount of glucose actually taken up from the intestinal lumen was determined measuring the remaining label in the alimentary canal. The portal contribution to label distribution was measured as for tritium water transfer. Most glucose label passed through in the form of glucose, with much smaller proportions as CO2 and even smaller as lactate and other labelled compounds. The results suggest that the contribution of lymph circulation to dietary glucose incorporation into the bloodstream may be significant, amounting to values higher than 10% of the glucose actually incorporated.