FLUID EXCHANGES ACROSS THE PARIETAL PERITONEAL AND PLEURAL MESOTHELIA

In 31 anesthetized rabbits, after removal of superficial tissues. glas s micropipettes filled with 0.5 M NaCl solution and connected to an el ectrohydraulic servo-null system were used to measure extraperitoneal interstitial fluid pressure (Pi,per) and peritoneal liquid pressure (P liq,per) at various heights. Linear regressions relating pressure to r ecording height (H) were Pi,per = 1.07 - 0.27H and Pliq,per = 0.9 - 0. 64H, respectively. Protein concentration (C(p); g/dl) and colloid osmo tic pressure (PI; cmH2O) of plasma and of peritoneal and pleural liqui ds were 5.48 +/- 0.38 and 24.61 +/- 3.23, 3.07 +/- 0.5 and 13.29 +/- 1 .87, and 1.76 +/- 0.42 and 8.45 +/- 2, respectively. The equation rela ting PI to C(p) was PI = 4.64C(p) + 0.0027C(p)2. Tissue fluid samples were collected with saline-soaked wicks implanted in vivo or dry wicks inserted postmortem in extraperitoneal and extrapleural interstitial spaces. After 60 and 15 min, respectively. wicks were withdrawn and ce ntrifuged; wick fluid was analyzed in colloid osmometer for small samp les. Average extraperitoneal and extrapleural PI values were 14.2 +/- 2.49 and 11.94 +/- 1.52 cmH2O, corresponding to C(p) of 3.07 and 2.57 g/dl, respectively. The average net pressure gradient, assuming reflec tion coefficient and hydraulic conductivity (Negrini et al. J. Appl. P hysiol. 69: 625-630, 1990; 71: 2543-2547, 1991), was 1.18 and 0.98 cmH 2O for parietal peritoneal and pleural mesothelia, respectively, favor ing filtration from the extraserosal interstitia into the serosal cavi ties. Total parietal peritoneal filtration was 1.49 ml . kg-1 . h-1, a pproximately 15-fold higher than that for pleural mesothelium.