A three-pore model of peritoneal transport.

The three-pore model of peritoneal transport treats the capillary membrane as a primary barrier determining the amount of solute that transports to the interstitium and the peritoneal cavity. According to the three-pore model, the principal peritoneal exchange route for water and water-soluble substances is a protein-restrictive pore pathway of radius 40-55 A, accounting for approximately 99% of the total exchange (pore) area and approximately 90% of the total peritoneal ultrafiltration (UF) coefficient (LpS). For their passage through the peritoneal membrane proteins are confined to so-called "large pores" of radius approximately 250 A, which are extremely few in number (0.01% of the total pore population) and more or less nonrestrictive with respect to protein transport. The third pathway of the three-pore model accounts for only about 2% of the total LpS and is permeable to water but impermeable to solutes, a so-called "water-only" (transcellular?) pathway. In contrast to the classical Pyle-Popovich (P&P) model, the three-pore model can predict with reasonable accuracy not only the transport of water and "small solutes" (molecular radius 2.3-15 A) and "intermediate-size" solutes (radius 15-36 A), but also the transport of albumin (radius 36 A) and larger molecules across the peritoneal membrane. The model operates with reflection coefficients(a) (sigma's) for small solutes < 0.1. These are approximately one order of magnitude lower than the sigma's in the P&P model. Furthermore, the peritoneal LpS is one order of magnitude higher than in the P&P model.(ABSTRACT TRUNCATED AT 250 WORDS)