Copyright © 2006, European Society of Cardiology
The endothelial glycocalyx affords compatibility of Starling's principle and high cardiac interstitial albumin levels
aClinic of Anesthesiology, Ludwig-Maximilians University Munich, Nussbaumstr. 20, D-80336 Munich, Germany
bInstitute of Anatomy, Ludwig-Maximilians University Munich, Pettenkoferstr. 11, D-80336 Munich, Germany
cInstitute of Physiology, Ludwig-Maximilians University Munich, Schillerstr. 44, D-80336 Munich, Germany
* Corresponding author. Nussbaumstrassse 20, D-80336 Munich, Germany. Tel.: +49 89 5160 2692; fax: +49 89 5160 4446. Email address: matthias.jacob{at}med.uni-muenchen.de
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 µl/min/g tissue). Supplementing perfusate with albumin caused a significant decrease, also vs. hydroxyethylstarch (1.04 vs. 2.67 µl/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.
Conclusion: 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.
KEYWORDS Capillaries; Capillary permeability; Coronary circulation; Microcirculation; Endothelial function
Time for primary review 35 days
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