[Nitric oxide (NO), vascular protection factor. Biology, physiological role and biochemistry of NO].

UNLABELLED

VASOMOTRICITY: The vascular endothelium plays a key role in vasomotricity by producing a number of factors which modulate smooth muscle relaxation and contraction. Nitric oxide (NO) has been found to be one of the most important relaxation factors. NO SYNTHESIS: Nitric oxide is synthesized from L-arginine by NO-synthetase whose activity is regulated by intracellular calcium concentration and modulated by pharmacological compounds such as acetylcholine, 5-hydroxytryptamine, bradykinin and ADP as well as the sheer forces produced by blood flow.

MODE OF ACTION

NO stimulates soluble guanylate cyclase in smooth muscles. Its action is mediated by increased intracellular cGMP which provokes smooth muscle relaxation. ACTIONS OF NO: The physiological role of NO produced by the vascular endothelium is quite complex and incompletely elucidated. NO helps maintain adequate blood supply to tissues by reacting rapidly to changes in pharmacological and mechanical stimuli. It opposes the direct vasoconstrictor effect of certain factors in the blood stream and its action on platelets and endogenous fibrinolysis helps prevent thrombus formation.