Quantitation of the relationship between aortic endothelial intercellular cleft morphology and permeability to albumin.

The aortic endothelial intercellular cleft (AEC) is a determinant of permeability to macromolecules. This study compared the surface density and frequency of AEC profile types between areas of rat aorta that were permeable/impermeable to albumin-bound Evans Blue dye (EBD). Five adult male Wistar rats were given saturating i.v. doses of EBD and 30 min later were perfusion, fixed and their aortae excised. Samples of impermeable (White) and permeable (Blue) areas were prepared for EM. Sections were coded randomly and all AEC profiles observed were assigned to 4 different morphological classes. Ten to 15 micrographs per sectioned sample, per area, per rat were taken to determine the surface density of AEC's relative to the endothelial cell layer. The frequency distribution of AEC profile types from Blue areas was significantly (P less than 0.01) different from that of the White areas. The Blue regions had relatively more AEC profiles of a less complex structure than did the White areas. The majority of cleft profiles in the Blue areas were of the simple 'overlap' type, whereas the commonest in the White areas were the 'mortise' type. The mean surface density of the AEC's in Blue areas was 0.066 +/- 0.002 micron-1, which was significantly (P less than 0.05) less than in White areas (0.11 +/- 0.002 micron-1). These findings confirm earlier qualitative observations and indicate that AEC's in areas permeable to macromolecules, such as albumin, are less complex in structure and of lower surface area than those in areas relatively impermeable to such macromolecules.