Renin-angiotensin system (RAS) or renin-angiotensin-aldosteronesystem (RAAS) is an important body fluid regulating system in the human body. RAS exists in both the circulatory system as well as other tissues such as vascular wall, heart, central, kidney and adrenal gland. They work together to participate in the regulation of the target organ. Under normal circumstances, it has an imprint role the normal development of the cardiovascular system as well as the maintenance of the cardiovascular homeostasis, electrolyte and body fluid balance, and blood pressure regulation.

The traditional principle is that the renin in the circulatory system is mainly from the kidney, being a kind of acidic protease synthesized and secreted by the renal proximal cells. It enters into the blood circulation through the renal vein to initiate the RAS chain reaction. When renal blood flow decreases due to various kinds of reasons, renin secretion starts to increase; when the plasma Na+ concentration decreases, the renin secretion also increases. In recent years, with the extensive application of molecular biology techniques, scholars such as Dzau et al have found that there are gene expression of both renin and angiotensin in various organs and tissues such as myocardium, vascular smooth muscle, skeletal muscle, brain, kidney and gonad. And these tissues are rich in angiotensin converting enzyme (ACE) and angiotensin Ⅱ receptor, thus confirming that in addition to systemic RAS, there is still relatively independent local RAS existing in cardiovascular organs and tissues. They can directly participate into the regulation of cardiovascular activity through paracrine and (or) autocrine. There is growing evidence that this local RAS plays a more direct and important physiological and pathological role in the regulation of cardiovascular activity than circulating RAS.