To elucidate the importance of possible trapping of macromolecules in peritoneal tissue on the calculation of peritoneal lymphatic drainage, we compared the transport of inulin administered i.v. and i.p. in nine continuous ambulatory peritoneal dialysis (CAPD) patients on two separate days. In the intraperitoneal study inulin (5 g) was added to the dialysate and in the intravenous study inulin (5 g) was given i.v. 3 h before the test. No differences were found in the mass transfer area coefficients (MTC) of urea, creatinine, and glucose between the two tests. The MTC after inulin i.p. was 3.2 +/- 0.7 mL/min (mean +/- SD) and after inulin i.v. 1.8 +/- 0.5 (p less than 10(-5]. As the difference in transport kinetics between i.v. and i.p. administration is likely to be caused by lymphatic absorption, a mean lymphatic flow of 1.4 mL/min could be calculated. This value corresponds to the data obtained with macromolecules. Our results therefore favor the hypothesis that no local accumulation of macromolecules in the peritoneal tissues takes place and that their disappearance from the peritoneal cavity represents lymphatic absorption.

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