Vascular biology of angiotensin and the impact of physical activity

摘要

The renin-angiotensin system (RAS) is important for regulating blood pressure and extracellular fluid. The concept of the RAS has recently evolved from a classical systemic endocrine system to an appreciation of local RASs functioning in a paracrine manner, including in the vascular wall. Angiotensin II (AII), the main effector of the RAS, is a potent vasoconstrictor formed by the action of angiotensin-converting enzyme (ACE). ACE is multifunctional and also destroys the endogenous vasodilator bradykinin. A recently discovered novel ACE2 enzyme is responsible for forming a vasodilatory compound, angiotensin 1-7, from AII. Thus, the actions of ACE and ACE2 are antagonistic. Tissue actions of AII are mediated by specific receptors, AT1 and AT2, with AT1 mediating the classical actions. AT1-stimulated vasoconstricton occurs via phospholipase-D-mediated second messenger generation directly, and indirectly via the coupling of AT1 to the prooxidant enzyme NADPH oxidase. Since the vascular NADPH oxidase is a major source of vascular reactive oxygen species generation and is responsible for the breakdown of the vasodilator nitric oxide (NO), there is another potential link between RAS and regulation of vasodilatory pathways. AT2 signaling is antagonistic to AT1 signaling, and results in bradykinin and NO formation. Chronic AII signaling induces vascular dysfunction, whereas pharmacological management of the RAS can not only control blood pressure, but also correct endothelial dysfunction in hypertensives. Exercise training can also improve endothelial function in hypertensives, raising the question of whether there is a potential role for RAS in mediating the vascular effects of exercise training. Recent studies have demonstrated reductions in the expression of NADPH oxidase components in the vascular wall in response to exercise training, thus tempering one of the main cellular effectors of AII, and this is associated with reduced vascular ROS production and enhanced NO bioavailability. Importantly, it has now been demonstrated in human arteries that exercise training also tempers vascular AT1 receptor expression and AII-induced vasoconstriction, while enhancing endothelium-dependent dilation. The signals responsible for these chronic adaptations are not clearly understood, and may include changes in RAS components prompted by acute exercise. ACE genotype may have an effect on physical activity levels and on the cardiovascular responses to exercise training, and the II genotype (compared with ID and DD) is associated with the largest endothelium-dependent dilations in athletes compared with those in sedentary individuals. Thus, the tissue location of the RAS, the complement of ACE/ACE2, the receptor expression of AT1/AT2, and the ACE genotype are all variables that could impact the vascular responses to exercise training, but the responses of most of these variables to regular exercise training and the mechanisms responsible have not been systematically studied.%Le système rénine-angiotensine (RAS) joue un rôle important dans la régulation de la pression sanguine et du volume de liquide extracellulaire. Traditionnellement considéré comme partie intégrante du système endocrinien, le concept du RAS a évolué de telle sorte qu'on lui reconnaît maintenant une fonction paracrine à action locale comme on l'observe dans les parois des vaisseaux sanguins. L'angiotensine II (AII), l'effecteur propre du RAS constitue un puissant vasoconstricteur obtenu par l'action de l'enzyme de conversion de l'angiotensine (ACE). L'ACE a plusieurs fonctions dont celle de détruire la bradykinine, une substance endogène vasodilatatrice. L'ACE2, une enzyme récemment identifiée, catalyse à partir de l'AII la formation de l'angiotensine 1-7 à action vasodilatatrice. Ainsi donc, les actions de l'ACE et de l'ACE2 sont antagonistes. Les actions tissulaires de l'AII sont médiées par des récepteurs spécifiques, AT1 et AT2, le premier exerçant son action classique. La vasoconstriction issue des AT1 dépend de l'action d'un deuxième messager, la phospholipase D, en ce qui concerne la voie directe et du couplage de AT1 à la NADPH oxydase, une enzyme pro-oxydante, en ce qui concerne la voie indirecte.