angiotensin

angiotensin /an·gio·ten·sin/ (-ten´sin) a decapeptide hormone (a. I) formed from the plasma glycoprotein angiotensinogen by renin secreted by the juxtaglomerular apparatus. It is in turn hydrolyzed by a peptidase in the lungs to form an octapeptide (a. II), which is a powerful vasopressor and stimulator of aldosterone secretion by the adrenal cortex. This is in turn hydrolyzed to form a heptapeptide (a. III), which has less vasopressor activity but more adrenal cortex–stimulating activity.

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an·gi·o·ten·sin (nj--tnsn)

n.

Any of a group of peptides with vasoconstrictive activity that function physiologically in controlling arterial pressure.

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angiotensin

[-ten′sin]

Etymology: Gk, angeion + L, tendere, to stretch

a polypeptide in the blood that causes vasoconstriction, increased blood pressure, and the release of aldosterone from the adrenal cortex. Angiotensin is formed by the action of renin on angiotensinogen, an alpha-2-glycoprotein that is produced in the liver and that constantly circulates in the blood. Renin, stimulated by juxtaglomerular cells in the kidney in response to decreased blood volume and serum sodium levels, acts as an enzyme in the conversion of angiotensinogen to angiotensin I, which is rapidly hydrolyzed to form the active compound, angiotensin II. The vasoconstrictive action of angiotensin II decreases the glomerular filtration rate, and the concomitant action of aldosterone promotes sodium retention, with the result that blood volume and sodium reabsorption increase. Plasma angiotensin II increases during the luteal phase of the menstrual cycle and is probably responsible for an elevated level of aldosterone during that period. Angiotensin is inactivated by peptidases, called angiotensinases, in plasma and tissues.

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angiotensin

a vasoconstrictive principle formed in the blood when renin is released from the juxtaglomerular apparatus in the kidney. The enzymatic action of renin cleaves a serum α₂-globulin, angiotensinogen, forming the decapeptide angiotensin I, which is relatively inactive. It in turn is acted upon by peptidases (converting enzymes), chiefly in the lungs, to form the octapeptide angiotensin II, a powerful vasopressor and a stimulator of aldosterone secretion by the adrenal cortex. By its vasopressor action, it raises blood pressure and diminishes fluid loss in the kidney by restricting blood flow. Angiotensin II is hydrolyzed in various tissues to form heptapeptide angiotensin III, which has less vasopressor activity but more effect on the adrenal cortex.

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angiotensin amide

an amide derivative of angiotensin II which is a powerful vasoconstrictor and vasopressor, and is used in the treatment of certain hypotensive states; usually administered by slow intravenous infusion, and sometimes intramuscularly or subcutaneously.

angiotensin-converting enzyme (ACE)

a peptidase which catalyzes the formation of angiotensin II from angiotensin I. See also ace.

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angiotensin

Any of a family of vasoconstricting peptides