Scanning and Transmission Electron Microscopy of the Normal Rabbit Aortic Endothelium after Controlled Perfusion Fixation

Abstract

Light microscopy, scanning electron microscopy, and transmission electron microscopy were employed on the anterior wall of the rabbit thoracic aorta with the particular purpose to study endothelial marginal flaps and the structure of stomata under physiological conditions at 100 mm Hg. Intra-aortic pressure monitoring was performed during the whole period of perfusion (2 h), restricting pressure variations to a maximum of ± 5 mm Hg in order to preserve endothelial architecture. We found the endothelial surface uniformly smooth. Marginal flaps of the endothelial cells were mutually overlapping, often forming multiple layers. Underlying flaps might protrude to the lumen between neighbouring flaps as flat mushrooms. Flaps of adjacent cells might diverge for short distances to decover an underlying endothelial cell. Downstream flaps of the cells might be overlapped at their base by flaps of adjacent cells, the extremity of the flap thus appearing as a disc separated from the cell. The small discs and troughs thus formed are considered equivalent to the so-called stomata.

The Circumferential Length of the Internal Elastic Membrane Measured by Computer Digitizer Morphometry, and Its Relation to in vivo Aorta Diameter

“…We think they constitute a reserve layer of tissue which reduces the chance of injury to the endothe lial cells by excess tension during systolic distension. In a recent report, Garbarsch et al [1982] have drawn attention to mor phological peculiarities of endothelial cell junctions, which probably have significance in the cells ability to adapt to tension. The folds could well represent a further safetyvalve in order to protect endothelial cells against dangerous tension within the arteries.…”