Renin

Renin is an enzyme that participates in the body's renin–angiotensin system (RAS) that mediates extracellular volume (i.e., that of the blood plasma, lymph and interstitial fluid), and arterial vasoconstriction. Thus, it regulates the body's mean arterial blood pressure.

Renin-angiotensin-aldosterone system

Function

Renin acts upon a protein circulating in the bloodstream called angiotensinogen, cleaving off a fragment called angiotensin I. Another enzyme called angiotensin converting enzyme (ACE) in the lungs subsequently converts angiotensin I into angiotensin II. Angiotensin II is a potent vasoconstrictive peptide that causes blood vessels to narrow, resulting in increased blood pressure. Angiotensin II also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone promotes sodium retention in the distal nephron, in the kidney, which also drives blood pressure up.

Regulation

Renin is secreted from juxtaglomerular kidney cells, which sense changes in renal perfusion pressure, via stretch receptors in the vascular walls. The macula densa senses changes in sodium delivery to the distal tubule, and responds to a drop in systemic blood pressure by releasing renin.

Clinical significance

An over-active RAS leads to hypertension. Thus, renin inhibitors, which inhibit the first and rate-limiting step of the RAS, can be used in the treatment of high blood pressure. An example of a renin inhibitor drug is aliskiren.

See also

• Renin inhibitor
• Renin–angiotensin system
• Hypertension

References

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