The Effect of Tonicity and Hypertonic Solutions on Microvascular Permeability

Abstract

Background. The effect of hypertonic saline (HS) on microvascular permeability is unclear. We hypothesized that varying degrees of tonicity and HS solutions alter microvascular fluid flux across the endothelium. Methods. Hydraulic permeability ( L p) is a measure of water flow across the endothelial barrier. L p was measured in cannulated rat mesenteric venules using the modified Landis micro-occlusion technique. The effect of tonicity was tested by measuring L p after successive perfusions with Ringers' solutions of varying sodium chloride (NaCl) concentrations (85, 135, 185, and 235 mM) ( n = 6). Additional venules were perfused with control Ringers' ([NaCl] = 135 mM) and measures of L p were obtained after subsequent perfusions with 7% NaCl followed by 7% NaCl with 6% dextran ( n = 6). Results. Tonicity had a significant dose-dependent effect on L p ( P < 0.0001). Perfusion with 7% NaCl significantly increased L p ( P < 0.0001). The addition of 6% dextran to 7% NaCl significantly decreased L p compared with perfusion with 7% NaCl alone ( P = 0.002). Conclusions. We conclude that (1) tonicity influences microvascular permeability, (2) HS increases microvascular permeability, and (3) the addition of dextran to HS greatly attenuates this response. These findings suggest an important role for tonicity and a possible deleterious effect of HS in modulating microvascular permeability as well as the benefit of dextran with HS for maintaining intravascular volume.