Myoendothelial contacts in the thoracic aorta of rat fetuses.

There is increasing documentation of the presence of endothelial-smooth muscle communication in both small and large arteries. We have found that morphological evidence of these contacts appears early in development. Intimate contacts between endothelial and muscle cells in the thoracic aorta of normal rat fetuses have been studied with transmission electron microscopy. These myoendothelial contacts were seen in the form of cytoplasmic projections passing through fenestrae in the elastic lamellae. Most of these cell processes seem to arise from the muscle cells and they usually have a club-shaped configuration. The specific nature of the cell-cell contact was predominantly via simple appositions with an intercellular space of 6-15 nm. Myoendothelial contacts are potential sites for electrical and metabolic communication between elements of the intima and media, ensuring that the vessel wall works as a unit. The demonstrated necessity of intact endothelium for smooth muscle cell response to load may depend on this type of contact.