Uneven distribution of sialic acids on the luminal surface of aortic endothelium.

Lectins which bind sialic acid (aprotinin, wheat germ) were used to measure sialic acid density on the luminal surface of aortic endothelium of rabbit. The bound fluorescein-labelled lectin was released from the sialic acids by the competing ligand N-acetyl-D-glucosamine and measured fluorimetrically. The specificity of the technique was shown by an 80% decrease of bound fluorescence after neuraminidase treatment of the endothelium. Endothelial sialic acid density was the same in the thoracic and abdominal parts of the aorta but significantly less in the arch. Around the orifices of the branches of the intercostal arteries, less surface fluorescence was observed. Ultrastructural studies have shown much less staining of the surface membranes with peroxidase-conjugated wheat germ lectin at these places than elsewhere. These areas, where less sialic acid density was found, coincide with the sites where the atherosclerotic process is known to develop.