Angiotensin II (Ang II), the main effector of the renin-angiotensin system, exerts its vasoconstrictory and trophic actions on smooth muscle cells via AT1 receptors. However, Ang II does not act only on smooth muscle cells, as Ang II receptors are also present in endothelial cells. 2. The receptor type on these cells differs depending on the origin of the endothelium and the species. The rat endothelial receptors are mostly of the AT1 type, but AT2 receptors have also been found. The pharmacological characteristics of the AT1 receptors on endothelial cells are similar to those of other cell types. 3. Ang II stimulates phospholipase C and phospholipase A2 activation via the AT1 receptor in endothelial cells. Ang II also stimulates the tyrosine phosphorylation of several proteins in these cells. 4. Some studies suggest that the AT1 receptor mediates the release of vasodilator molecules by endothelial cells and could modulate Ang II effect on smooth muscle cells. Ang II may also inhibit endothelial cell growth via the AT2 receptor. Finally, endothelial Ang II receptors may be implicated in the regulation of fibrinolysis.
