title: Albumin impacts the effects of tonicity on microvascular hydraulic permeability.
abstract: BACKGROUND
  An increase in tonicity shrinks endothelial cells. This cell shrinkage may open inter-endothelial gaps and allow more fluid to escape from the microvasculature. This increase in microvascular permeability is not supported by clinical studies suggesting that water is pulled into the vascular space, not lost into the interstitium. We hypothesized that albumin influences the change in trans-endothelial water movement caused by alterations in tonicity by a mechanism other than oncotic pressure.
  
  
  METHODS
  Hydraulic permeability (L(p)) was measured in rat mesenteric venules using the Landis micro-occlusion model. Measures of L(p) were obtained after successive perfusions with 1% albumin solution (BSA) of varying sodium chloride (NaCl) concentrations (85, 135, 185, and 235 mm) (n = 6). Additional venules were perfused with 7% NaCl followed by 7% NaCl + BSA and L(p) measured (n = 6). Units for L(p) are x10(-7) cm/sec(-1) cm/H(2)O(-1).
  
  
  RESULTS
  As the NaCl concentration in BSA increased from 85 mm to 235 mm, L(p) decreased from 1.93 +/- 0.41 to 0.97 +/- 0.11. Compared to results without albumin, BSA with 185 mm NaCl decreased L(p) from 3.93 +/- 0.08 to 1.25 +/- 0.18 (P = 0.04), and BSA with 235 mm NaCl decreased L(p) from 6.14 +/- 0.05 to 0.96 +/- 0.11 (P = 0.002). There was a three-fold decrease in L(p) when BSA was added to the 7% NaCl solution (P = 0.02).
  
  
  CONCLUSIONS
  Albumin attenuated the increase in L(p) that is associated with higher NaCl concentrations. Because this model controls for oncotic pressure, albumin may impact L(p) by a mechanism other than oncotic force. Albumin appears to stabilize the endothelial barrier during HS perfusion and prevents the loss of intravascular fluid. Appropriate albumin levels may play an important clinical role in modulating trans-endothelial fluid efflux during HS administration.
authors.affiliation: Department of Surgery, UCSF-East Bay, Alameda County Medical Center, Oakland, California 94602, USA. victorinog@surgery.ucsf.edu
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Victorino
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Chong
authors.forename: Brian
authors.initials: B
authors.lastname: Curran
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012462:Saline Solution, Hypertonic / Q000008:administration & dosage / Q000494:pharmacology*; D012710:Serum Albumin, Bovine / Q000737:chemistry / Q000494:pharmacology*; D013152:Splanchnic Circulation / Q000187:drug effects*; D014699:Venules / Q000378:metabolism*
chemical_list: D012462:Saline Solution, Hypertonic; D012710:Serum Albumin, Bovine