Endothelial glycocalyx as an additional barrier determining extravasation of 6% hydroxyethyl starch or 5% albumin solutions in the coronary vascular bed

Background: The impact on the endothelial glycocalyx for the extravasation of colloidal infusion solutions has not been investigated sufficiently. Methods: Isolated guinea pig hearts were perfused with Krebs-Henseleit buffer in a Langendorff mode. Solutions of 0.9% saline, 5% albumin (70 kd), or 6% hydroxyethyl starch (200 kd) were infused into the coronary system for 20 min at a rate of one third of the coronary flow, also during reperfusion after 15 min of ischemia, and after enzymatic digestion of the endothelial glycocalyx by heparinase. Net coronary fluid filtration was assessed directly by measuring the formation of transudate on the epicardial surface, and solute extravasation was assessed by measuring albumin and hydroxyethyl starch in the coronary effluent and transudate. Hearts were perfusion fixed to visualize the endothelial glycocalyx using transmission electron microscopy. Results: Only infusion of hydroxyethyl starch, not infusion of albumin, significantly decreased net coronary fluid filtration. Heparinase application without ischemia increased coronary leak by 25% but did not accelerate the passage of colloids. Ischemia alone did not alter permeability. However, there was a large (approximately + 200%), transient (approximately 4 min) increase in permeability for water, albumin, and hydroxyethyl starch after ischemia with heparinase application. Also, histamine (10(-6) M) only increased permeability after pretreatment of the hearts with heparinase. The thickness of the glycocalyx after colloid administration was 0.2-0.3 mum. No glycocalyx could be detected after application of heparinase. Conclusion: The endothelial glycocalyx acts as a competent barrier for water and colloids. Only after its destruction do changes in endothelial morphology (postischemic reperfusion or histamine application) become effective determinants of coronary extravasation.