The renin-angiotensin-aldosterone (RAAS) system plays an important role in regulating blood volume, arterial pressure, cardiac and vascular function, and may contribute to the pathogenesis of atherosclerosis.
It stimulates an increase in nitric oxide synthase mRNA, protein expression, and nitric oxide production in pulmonary vessels. This system is found in various vertebrates, from elasmobranchs to mammals.
Angiotensins consist of at least three polypeptide hormones: angiotensin I (Ang I), angiotensin II (Ang II), and angiotensin III (Ang III).
Ang I is a decapeptide generated by the cleavage of angiotensinogen, a protein secreted from the liver, by renin.
Ang I is converted to Ang II by the angiotensin converting enzyme (ACE) or kininase II, a dipeptidyl-carboxypeptidase. Ang II is a potent vasopressor regulating blood pressure, the conservation of total blood volume and salt homeostasis. It controls the release of antidiuretic hormone (ADH) and aldosterone.
Ang II is the precursor of Ang III, which in turn stimulates aldosterone release from the adrenal glands.
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