Lymph protein concentration in initial and collecting lymphatics of the rat.

Lymph samples were obtained from villus initial and mesenteric prenodal collecting lymphatics of the anesthetized rat using standard micropuncture techniques. The protein concentrations of the lymph samples were determined using a fluorometric microassay. These procedures were performed on preparations either superfused with a modified Krebs solution or covered with paraffin oil. The protein-concentrating ability of the intestinal lymphatics was evaluated to test the osmotic theory of lymph formation. The mean initial lymph protein concentration in superfused preparations was 2.08 g/dl (SE = 0.20). The lymph protein concentration in collecting vessels in superfused preparations was 2.20 g/dl (SE = 0.19). The protein concentration from initial lymphatics in oil-covered preparation was 2.48 g/dl (SE = 0.17). The lymph protein concentration in collecting vessels in oil-covered preparations was 2.32 g/dl (SE = 0.15). The difference between initial and collecting lymph protein concentration found was an order of magnitude lower than that predicted by the osmotic theory. These results cast serious doubts on the effectiveness of the osmotic mechanism of lymph formation as it is presently defined.