Dialysate to blood transport of macromolecules during peritoneal dialysis

Asymmetrical transport of macromolecules between plasma and the peritoneal cavity results primarily from unidirectional lymphatic removal from the peritoneal cavity. Recent work suggests, however, that macromolecular transport across the peritoneal-plasma barrier via the capillary wall (i.e., the peritoneal membrane) may also be asymmetrical. We determined the diffusive and convective transport properties for creatinine, p-aminohippurate, and neutral dextran (13-40 A) across the peritoneal membrane in the dialysate to blood direction during peritoneal dialysis using isotonic and hypotonic solutions in awake New Zealand White rabbits. Values of the diffusive permeability-area product that were calculated during the isotonic exchange were similar to, yet somewhat smaller than, those previously determined in the blood to dialysate direction for all test solutes. Solute reflection coefficients that were calculated during the hypotonic exchange were variable, yet the resulting mean solute reflection coefficient values for all the test solutes were similar to those previously determined in the blood to dialysate direction. We conclude that asymmetrical peritoneal transport of macromolecules with radii less than 40 A is not due to asymmetrical transport across the peritoneal membrane.