FOCAL AND REGIONAL VARIATIONS IN THE COMPOSITION OF THE GLYCOCALYX OFLARGE VESSEL ENDOTHELIUM

The glycocalyx of the endothelium of the systemic arteries and vena ca va of the rabbit was visualised by in situ perfusion fixation with glu taraldehyde containing Alcian blue. The thickness of the layer ranged from 45 +/- 1 nm in the coronary artery to 81 +/- 2 nm in the carotid. The glycocalyx was 20 +/- 1.5 nm thicker on the downstream side of in tercostal ostia than on the upstream side. Changes in the staining pat tern with increasing concentrations of MgCl2 indicated that carboxyl g roups made the major contribution to the surface charge, though sulpha te groups were also present, particularly in the aortic arch and carot id artery. Segments of the thoracic aorta and carotid artery were also stained in vitro with fluorescence labelled wheat germ agglutinin, an d fluorescence intensity in histological sections was quantified using a video microscope equipped with a microcomputer-based image analysis system. The fluorescence intensity in the carotid was 1.65 +/- 0.15 t imes that in the aorta. Pretreatment with neuraminidase reduced fluore scence intensity by 60 +/- 4% in the carotid and 53 +/- 2% on the upst ream side of intercostal ostia, but only by 37 +/- 3% on the downstrea m side. Chondroitinase and heparanase both reduced binding and when us ed together their effect was additive, reducing fluorescence by 27 +/- 3, 51 +/- 4, and 32 +/- 3% at the three sites, respectively. Though t he interpretation of the lectin binding experiments is complicated by a number of factors, these results support previous reports that sialy l groups are abundant in the endothelial glycocalyx. Glycosaminoglycan s are also present, however, in significant amounts.