REN

REN, or renin, is produced by the proximal glomerular cells of the kidney. Renin is a protein hydrolyzing enzyme that mainly acts on angiotensinogen in plasma to produce inactive angiotensin I. Angiotensin I is further converted to active angiotensin II by angiotensin-converting enzyme, which causes vasoconstriction of small arteries and promotes the synthesis and secretion of aldosterone from the adrenal cortex, thus elevating blood pressure.
The renin-angiotensin system (RAS) plays an important role in the regulation of blood pressure, fluid and electrolyte homeostasis, and is essential for the maintenance of normal physiologic function. The release of renin is a critical determinant of plasma angiotensin concentration and has important implications for the bioactivity of angiotensin II and III.