PHYSIOLOGICAL ROLES OF NITRIC-OXIDE

Vasomotricity: The vascular endothelium plays a key role in vasomotric ity by producting a number of factors which modulate smooth muscle rel axation 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 regulat ed by intracellular calcium concentration and modulated by pharmacolog ical compounds such as acetycholine, 5-hydroxy-tryptamine, bradykinin and ADP as well as the sheer forces produced by blood Row. Mode of act ion: NO stimulates soluble guanylate cyclase in smooth muscles. its ac tion is mediated by increased intracellular cGMP which provokes smooth muscle relaxation. Actions of NO: The physiological role of NO produc ed by the vascular endothelium is quite complex and incompletely eluci dated. NO helps maintain adequate blood supply to tissues by reacting rapidily to changes in pharmacological and mechanical stimuli. It oppo ses the direct vasoconstrictor effect of certain factors in the blood stream and its action on platelets and endogenous fibrinolysis helps p revent thrombus formation. (C) 1998, Masson, Paris.