Effect of hypertonic saline on microvascular permeability in the activated endothelium

Introduction. The effect of hypertonic saline (HTS) on microvascular permeability in microvessels with activated endothelial cells is unclear. We hypothesized that HTS and HTS with dextran would decrease hydraulic permeability after activation of the endothelium. Methods. Hydraulic permeability (L-p) was measured in rat mesenteric venules using the modified Landis micro-occlusion technique. The effects of 185 mM HTS and HTS plus 2% dextran (HSD) were tested in the activated endothelium by measuring LP at baseline, after perfusion with ATP, and again after HTS (n = 6) or HSD (n = 6). ATP (10 muM) activated endothelial cells and increased Lp 4-fold. Additional venules were used to test the effects of 135 mM NaCl (n = 6) and 235 mM (n = 6) NaCl after endothelial activation with ATP. Results. After endothelial activation with ATP, Lp values were 6.05 +/- 1.63. Subsequent perfusion with HTS decreased L-p to 2.05 +/- 0.52 (P = 0.01). In the HSD trails, Lp values after ATP were 6.17 +/- 1.38. Perfusion with HSD decreased LP to 1.65 +/- 0.30 (P = 0.001). After endothelial activation, 135 mM NaCl had no effect on L-p; however, 185 mM NaCl decreased L-p 3-fold and 235 mM NaCl decreased L-p 6-fold. Units for L-p are x10(-7) cm - s(-1) . cm-H2O-1. Conclusions. Both HTS and HSD decreased hydraulic permeability after endothelial activation. These findings suggest that HTS may decrease microvascular fluid loss during states of elevated microvascular leak. In addition to the ability of hypertonic solutions to withdraw intracellular water to increase plasma volume, these findings propose an endothelial barrier mechanism whereby HTS and HSD act to maintain intravascular volume. (C) 2003 Elsevier Inc. All rights reserved.