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Cardiovascular System

3 out of 7

Bradykinin produces all except: (LQ) (AIPG 2008)

A Pain

B Vasoconstriciton

C Emigration of leucocytes

D Increases vascular Permeability

Ans. B Vasoconstriction

I. The kinin system generates vasoactive peptides from plasma proteins, called kininogens, by the action of specific proteases called kallikreins. Activation of the kinin system results in the release of the vasoactive nonapeptidebradykinin.

II. Bradykinin increases vascular permeability and causes contraction of smooth muscle, dilation of blood vessels, and pain when injected into the skin. These effects are similar to those of histamine.

III. It is triggered by the activation of Hageman factor (factor XII of the intrinsic clotting pathway; see later)upon contact with negatively charged surfaces, such as collagen and basement membranes.

IV. A fragment of factor XII (prekallikrein activator, or factor XIIa)is produced, and this converts plasma prekallikrein into an active proteolytic form, the enzyme kallikrein. The latter cleaves a plasma glycoprotein precursor, high-molecular-weight kininogen, to produce bradykinin.

V. Bradykinin is a powerful vasodilator which produces Local Vasodilatation, Emigration of leucocytes. It is also one of the pain producing substances.

VI. Bradykinin is also formed during active secretion in sweat glands, salivary glands and exocrine pancreas

VII. Bradykinin is degraded by

a. Kininase I-a carboxy peptidase that removes carboxy terminal Arg

b. Kininase II-removes Phe-Arg from carboxy terminal Kininase II is ACE (Angiotensin converting enzyme)that removes HIS leu from carboxyl terminal of angiotensin I.