Tissue sources and blood flow limitations of osmotic water transport across the peritoneum

Despite the daily use of hypertonic solutions to remove fluid from patients throughout the world who are undergoing peritoneal dialysis, the tissue sources of this water flow are unknown. To study this phenomenon in specific tissues, small plastic chambers were affixed to parietal and visceral surfaces of the peritoneum and were filled with either an isotonic or hypertonic solution. The volume changes over 60 to 90 min were determined and divided by the chamber area to yield the volume flux. The hypertonic solution produced a positive flux into the chamber of 0.6 to 1.1 microl/min per cm2 in all tissues tested. In contrast, the isotonic solution resulted in a net loss or an insignificant change in the chamber volume. Additional experiments tested the influence of blood flow on the hypertonic water flux during periods of control, reduced (50 to 80%), or postmortem (no) blood flow, as determined by laser Doppler flowmetry. With the exception of the liver, small but insignificant changes in the flux into the chamber were observed during the period of reduced flow; all water fluxes were markedly depressed during the postmortem period. It is concluded that both parietal and visceral tissues are sources of osmotically induced water flow into the cavity. Except for the liver, marked blood flow reductions have small but insignificant effects on osmotic water transport.