Renin

Not to be confused with renin, also called chymosin, a digestive enzyme.

Renin (EC 3.4.23.15), also called angiotensinogenase, is a protein (enzyme) secreted by the juxtaglomerular cells of the kidney. It is usually secreted in cases of arterial hypotension and low blood volume. Renin also plays a role in the secretion of aldosterone, a hormone that helps control the body's water and salt balance.

Renin activates the renin-angiotensin-aldosterone system by catalyzing the hydrolysis of the angiotensinogen molecule (produced by the liver, fat, kidney, and CNS) producing angiotensin I. The break occurs at a specific leucine amino acid.

Discovery

Renin was discovered, described and named by Robert Tigerstedt, Professor of Physiology at the Karolinska Institutet in Stockholm, in 1898.

Biochemistry and Physiology

Structure

The primary structure of the renin precursor consists of 406 amino acids with a pre and a pro segment of 20 and 46 amino acids respectively. The mature form of renin contains 340 amino acids and has a mass of 37 kDa.

Discharge

The peptide is secreted by the kidney from specialized cells called granule cells of the juxtaglomerular apparatus in response to 3 main stimuli:

1. A decrease in blood pressure (which could be related to the decrease in volatile) which is detected by barorreceptors. This is the most directly related stimulus between pressure and renine
2. The decrease in the filtered fraction of sodium in the nephron. This flow is measured by the dense scale, also in the juxtaglomerular apparatus.
3. The activity the sympathetic nervous system, which allows to control blood pressure by acting through the B-adrenergic receptors (B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-₁)

Renin is secreted by at least two different cellular pathways: a constitutive pathway with prorenin secretion and a regulated pathway through mature renin secretion.

Renin-Angiotensin-Aldosterone Axis (RAA)

Renin-angiotensin system, showing the role of renin.

Mechanism of action of renin

The enzyme circulates in the blood and hydrolyzes angiotensinogen secreted by the liver, forming the peptide angiotensin I.

Angiotensin I (AI) pathway

Angiotensin I is hydrolyzed by an enzyme released from lung tissue, angiotensin-converting enzyme (ACE), which ultimately forms angiotensin II, a vasoactive peptide. Angiotensin II is a potent vasoconstrictor. It acts on the muscles increasing the resistance of the vessels. The heart, trying to compensate for this increase in its load, works more vigorously, causing an increase in blood pressure. ATII also acts at the level of the adrenal glands, increasing the release of aldosterone, which stimulates the cells of the distal convoluted tubule and the collecting duct, causing the kidney to reabsorb more sodium and water to the detriment of potassium, which causes an increase in blood volume It also produces an increase in the secretion of vasopressin, which increases the reabsorption of water at the distal level of the nephron, stimulating the Aquaporin channels. The normal concentration of renin in blood plasma is 1.98-24.6 ng/L.