4XX4, 1BBS, 1BIL, 1BIM, 1HRN, 1RNE, 2BKS, 2BKT, 2FS4, 2G1N, 2G1O, 2G1R, 2G1S, 2G1Y, 2G20, 2G21, 2G22, 2G24, 2G26, 2G27, 2I4Q, 2IKO, 2IKU, 2IL2, 2REN, 2V0Z, 2V10, 2V11, 2V12, 2V13, 2V16, 2X0B, 3D91, 3G6Z, 3G70, 3G72, 3GW5, 3K1W, 3KM4, 3O9L, 3OAD, 3OAG, 3OOT, 3OQF, 3OQK, 3OWN, 3Q3T, 3Q4B, 3Q5H, 3SFC, 3VCM, 3VSW, 3VSX, 3VUC, 3VYD, 3VYE, 3VYF, 4AMT, 4GJ5, 4GJ6, 4GJ7, 4GJ8, 4GJ9, 4GJA, 4GJB, 4GJC, 4GJD, 4PYV, 4Q1N, 4RYC, 4RYG, 4RZ1, 4S1G, 4XX3597219701ENSG00000143839ENSMUSG00000070645P00797P06281NM_000537NM_031192NP_000528NP_112469Renin (etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin-angiotensin-aldosterone system (RAAS)—also known as the renin-angiotensin-aldosterone axis—that increases the volume of extracellular fluid (blood plasma, lymph, and interstitial fluid) and causes arterial vasoconstriction.

It acts on the smooth muscle and, therefore, raises the resistance posed by these arteries to the heart, and so for the same cardiac output, the blood pressure will rise.

Angiotensin II also acts on the adrenal glands and releases aldosterone, which stimulates the epithelial cells in the distal tubule and collecting ducts of the kidneys to increase re-absorption of sodium, exchanging with potassium to maintain electrochemical neutrality, and water, leading to raised blood volume and raised blood pressure.

The RAS also acts on the CNS to increase water intake by stimulating thirst, as well as conserving blood volume, by reducing urinary loss through the secretion of vasopressin from the posterior pituitary gland.

[10] Renin activates the renin–angiotensin system by using its endopeptidase activity to cleave the peptide bonds between leucine and valine residues in angiotensinogen,[11] produced by the liver, to yield angiotensin I, which is further converted into angiotensin II by ACE, the angiotensin–converting enzyme primarily within the capillaries of the lungs.

Renin is secreted from juxtaglomerular kidney cells, which sense changes in renal perfusion pressure, via stretch receptors in the vascular walls.

[13] The level of renin mRNA appears to be modulated by the binding of HADHB, HuR and CP1 to a regulatory region in the 3' UTR.

In current medical practice, the renin–angiotensin–aldosterone system's overactivity (and resultant hypertension) is more commonly reduced using either ACE inhibitors (such as ramipril and perindopril) or angiotensin II receptor blockers (ARBs, such as losartan, irbesartan or candesartan) rather than a direct oral renin inhibitor.

Renin was discovered, characterized, and named in 1898 by Robert Tigerstedt, Professor of Physiology, and his student, Per Bergman, at the Karolinska Institute in Stockholm.