renin re·nin (rē'nĭn, rěn'ĭn)
A protein-digesting enzyme that is released by the kidneys and that catalyzes the hydrolysis of angiotensinogen to angiotensin I. Also called angiotensinogenase.
enzyme secreted by the kidney (and also, possibly, by the placenta) that breaks down protein and produces a rise in blood pressure. In the blood, renin acts on a fraction of the plasma proteins and releases angiotensin I. Angiotensin II is formed by the action of converting enzyme, which splits off two amino acids from the 10-amino-acid chain of angiotensin I. The resultant octapeptide (previously called hypertensin, or angiotonin) constricts arterioles, causing a rise in both systolic and diastolic blood pressure. It is one of the most active vasoconstrictors known; on a weight basis it is about six times as potent as norepinephrine. It also increases the secretion of cortisol and aldosterone by a direct action on the adrenal cortex.
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