OSMOTIC BARRIER OF THE PARIETAL PERITONEUM

Fluid movement into the peritoneal cavity results after instillation o f a hypertonic solution. Some investigators have assumed that the peri toneum is a significant barrier to small solutes and have predicted th at fluid would be drawn by an osmotic gradient into the cavity from th e tissue surrounding the peritoneal cavity, resulting in tissue hydros tatic pressures well below atmospheric pressure. Contrary to this, we have previously shown that protein and fluid cross the peritoneum and enter the tissue at the same rate during either isotonic or hypertonic dialysis. To investigate the nature of the osmotic barrier of the per itoneum, the hydrostatic pressure profiles were measured in the abdomi nal wall of the rat during conditions of either isotonicity or hyperto nicity in the peritoneal cavity and constant intraperitoneal hydrostat ic pressure (P-ip). Measurements were made with a micropipette mounted on a micromanipulator and connected to a servo-null pressure measurem ent system. No interstitial pressures below atmospheric pressure were observed with either type of solution in the peritoneal cavity. For th e three P-ip values tested, there were few significant differences bet ween the corresponding pressure profiles of isotonic or hypertonic sol utions. It is concluded that the parietal peritoneum is not a function al barrier to small solutes, which are often used to raise the osmolal ity of intraperitoneal solutions. This finding also implies that the t issue interstitium underlying the parietal peritoneum is not the sourc e of water flow into the cavity, which is observed during hypertonic d ialysis.