AbstractNeural control of the venous tone is provided by the adrenergic innervation. In some venous territories, a cholinergic innervation or a non-adrenergic non-cholinergic one were identified. Hormones are also involved in the control of venous tone. Catecholamines and angiotensin II are most important venoconstrictors. The relaxing action of estrogen and progesterone was also studied insome venous territories. Vasopressin, somatostatin, insulin, and thyroid hormones have actions in pathophysiologic states. Local control of venous tone includes: metabolic regulation; humoral control; ions and endothelium-dependent regulation through vasodilators and vasoconstrictors. Veins exhibit a less pronounced endotheliumdependent control and a different response profile to endogenous vasoactive substances than arteries. Other factors such as reactive oxygen species, cytokines, fibrinogen, thrombin, oxidized LDL (low density lipoprotein) and vasostatins also play role in venous regulation. Myogenic control of veins is less important than arterial one. Pharmacological agents can also modulate venous tone. Innervation, hormones, metabolic factors, ionic environment, humoral factors, endothelium-derived vasoactive factors, and even reactive oxygen species and cytokines act directly on venous smooth muscle and endothelial cells. In addition, to their vasoconstrictor or vasodilator actions, some of these factors may be involved in other important physiological (vascular hypertrophy, intimal hyperplasia, and venular permeability) and pathological mechanisms such as venous graft pathology or varicose veins.
Key words: Adrenergic innervation; Catecholamines; Endothelium derived vasoactive factor; Nitric oxide; Reactive oxygen species; LDL.