title: The endothelial glycocalyx affords compatibility of Starling's principle and high cardiac interstitial albumin levels.
abstract: OBJECTIVE
  To test the role of an oncotic pressure gradient across the endothelial glycocalyx with respect to extravasation of fluid and colloids and development of tissue edema in a whole organ setting.
  
  
  METHODS
  We measured filtration in the intact coronary system of isolated guinea pig hearts, comparing colloid-free perfusion and perfusion with 1.67% albumin or 2% hydroxyethylstarch (oncotic pressures 5.30 vs. 11.10 mm Hg, respectively). Heparinase was used to alter the endothelial glycocalyx.
  
  
  RESULTS
  Extremely high net organ hydraulic conductivity was obtained with colloid-free perfusion (9.14 microl/min/g tissue). Supplementing perfusate with albumin caused a significant decrease, also vs. hydroxyethylstarch (1.04 vs. 2.67 microl/min/g, p < 0.05). Albumin also lowered edema formation vs. the other perfusion modes (p < 0.05). Stripping the glycocalyx of heparan sulfate reduced the effect of colloids, especially that of albumin. The steady-state concentrations of hydroxyethylstarch and albumin in the mixed interstitial fluid leaving the intact coronary bed averaged about 95% of the intravascular level. Electron and light microscopy indicated that colloid extravasated mainly in the venular sections.
  
  
  CONCLUSIONS
  We propose a low-filtration model for the coronary system with different barrier properties in arteriolar/capillary and venular sections. Arteriolar/capillary: very little fluid and colloid extravasation due to the endothelial surface layer formed by the glycocalyx and albumin plus the endothelial strand barrier; venular: little net extravsation of fluid and colloids despite large pores, because of low hydrostatic and oncotic pressure differences between intra- and extravascular spaces. The latter sites provide physiological access of large solutes (colloids) to the tissue.
authors.affiliation: Clinic of Anesthesiology, Ludwig-Maximilians University Munich, Nussbaumstr. 20, D-80336 Munich, Germany. matthias.jacob@med.uni-muenchen.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Jacob
authors.forename: Dirk
authors.initials: D
authors.lastname: Bruegger
authors.forename: Markus
authors.initials: M
authors.lastname: Rehm
authors.forename: Mechthild
authors.initials: M
authors.lastname: Stoeckelhuber
authors.forename: Ulrich
authors.initials: U
authors.lastname: Welsch
authors.forename: Peter
authors.initials: P
authors.lastname: Conzen
authors.forename: Bernhard F
authors.initials: BF
authors.lastname: Becker
mesh_terms: D000418:Albumins / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002199:Capillary Permeability; D003327:Coronary Disease / Q000378:metabolism* / Q000473:pathology; D003331:Coronary Vessels / Q000648:ultrastructure; D004487:Edema / Q000378:metabolism* / Q000473:pathology; D004573:Electrolytes / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D045604:Extracellular Fluid / Q000378:metabolism*; D005122:Exudates and Transudates / Q000378:metabolism; D019276:Glycocalyx / Q000378:metabolism* / Q000648:ultrastructure; D006168:Guinea Pigs; D019763:Heparin Lyase; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D023421:Models, Animal; D010477:Perfusion; D011312:Pressure; D013213:Starch / Q000494:pharmacology; D014699:Venules
chemical_list: D000418:Albumins; D004573:Electrolytes; D013213:Starch; D019763:Heparin Lyase