Aquaporin-1 Expression and Ultrafiltration of the Peritoneal Membrane

Peritoneal dialysis in adults involves diffusion and osmosis through a peritoneal membrane, measuring 1 m2, that is highly vascularized (flow rate, 100 to 150 ml per minute) and has a total available capillary surface area of approximately 2 m2.1 For decades, glucose has been used as the prototypical crystalloid osmotic agent to drive water removal in peritoneal dialysis.2 Glucose is a small osmotic agent (molecular weight, 180 g per mole) that is prone to crystallization but easily diffuses across semipermeable membranes; hence, it is known as a crystalloid substance. In contrast, colloid and noncrystalline substances are retained by membranes because . . .