The machinery of healthy vasoconstriction: an overview.

Tissue perfusion is acutely regulated by the changes in the vascular tone resulting in vasodilatation or vasoconstriction (there are also long-term changes in tissue perfusion, effectively accomplished by vascular remodeling). Even though vasodilatation predominates under physiological conditions, vasoconstriction represents an essential part of normal vascular physiology. The process of vasoconstriction is very complex, being influenced by many mediators, some of which are produced by the adjacent endothelial cells. The purpose of this review is to provide an overview of the machinery of vasoconstriction addressing the main components. First, the role of calcium is discussed including its intracellular and extracellular sources, its principal function in smooth muscle contraction machinery and mechanisms counteracting its effects. Subsequently, protein kinase C is included with its activation, effects and feedback. The role of RhoA/ROCK system is addressed in a similar way. The next section deals with the role of vascular endothelium-derived contracting factors and their effects on the adjacent smooth muscle cells. Finally, principal mechanisms of action of vasoconstrictive stimuli and myogenic tone are concisely discussed.