**2. Endothelium molecular biology, vascular tonicity and its regulation**

Vascular tonicity is regulated by multiple molecules, proteins, hormones, and peptides secreted or with action mechanisms on the ECs such as an atrial natriuretic peptide, eicosanoids, adrenal steroids, sodium, and water excretion, and reno-medullary endothelial systems [3].

Examples of several endothelium-derived hyperpolarizing factors are NO and prostacyclin, whereas endothelin-1 (ET-1), angiotensin II, thromboxane A2 and reactive oxygen species (ROS), relaxing factors [4].
