Abstract-Recently it has been demonstrated that catecholamines are produced and used by macrophages and mediate immune response. The aim of this study is to verify whether endothelial cells (ECs), which are of myeloid origin, can produce catecholamines. We demonstrated that genes coding for tyrosine hydroxylase, Dopa decarboxylase, dopamine  hydroxylase (DH), and phenylethanolamine-N-methyl transferase, enzymes involved in the synthesis of catecholamines, are all expressed in basal conditions in bovine aorta ECs, and their expression is enhanced in response to hypoxia. Moreover, hypoxia enhances catecholamine release. To evaluate the signal transduction pathway that regulates catecholamine synthesis in ECs, we overexpressed in bovine aorta ECs either protein kinase A (PKA) or the transcription factor cAMP response element binding, because PKA/cAMP response element binding activation induces tyrosine hydroxylase transcription and activity in response to stress. Both cAMP response element binding and PKA overexpression enhance DH and phenylethanolamine-N-methyl transferase gene expression and catecholamine release, whereas H89, inhibitor of PKA, exerts the opposite effect, evidencing the role of PKA/cAMP response element binding transduction pathway in the regulation of catecholamine release in bovine aorta ECs. We then evaluated by immunohistochemistry the expression of tyrosine hydroxylase, Dopa decarboxylase, DH, and phenylethanolamine-N-methyl transferase in femoral arteries from hindlimbs of C57Bl/6 mice 3 days after removal of the common femoral artery to induce chronic ischemia. Ischemia evokes tyrosine hydroxylase, Dopa decarboxylase, DH, and phenylethanolamine-N-methyl transferase expression in the endothelium. Finally, the pharmacological inhibition of catecholamine release by fusaric acid, an inhibitor of DH, reduces the ability of ECs to form network-like structures on Matrigel matrix. In conclusion, our study demonstrates for the first time that ECs are able to synthesize and release catecholamines in response to ischemia. Key Words: catecholamines Ⅲ ischemia Ⅲ endothelium Ⅲ angiogenesis E ndothelial cells (ECs) cover the interior surface of blood vessels throughout the entire circulatory system, and they are involved in many aspects of vascular biology.1-4 Indeed, angiogenesis is a phenomenon intimately associated with EC migration and proliferation during embryonic development.
5Similarly, ECs play major roles in immune and inflammatory reactions by regulating lymphocyte and leukocyte migration into tissues by means of direct interaction with ECs.6 Moreover, ECs have an important role in the regulation of the vascular tone by releasing vasoactive agents controlling smooth muscle cell proliferation and contractility.Indeed, ECs are known to release both vasodilators (NO) and vasoconstrictors (thromboxane, platelet-derived growth factor, and endothelin 1) in response to local and circulating stimuli. [7][8][9][10][11][12][13][14] To this purpose, the endothelium is regulated in a fine way by a s...