kinin

One of a number of widely differing substances having pronounced and dramatic physiologic effects. Some ( e.g., kallidin and bradykinin) are polypeptides, formed in blood by proteolysis secondary to some pathological process, that stimulate visceral smooth muscle but relax vascular smooth muscle, thus producing vasodilation; others ( e.g., kinetin) are plant growth regulators. [G. kineo, to move, + -in]

- k. 9 SYN: bradykinin.

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ki·nin 'kī-nən n

1) any of various polypeptide hormones that are formed locally in the tissues and cause dilation of blood vessels and contraction of smooth muscle

2) CYTOKININ

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n.

one of a group of naturally occurring polypeptides that are powerful vasodilator, which lower blood pressure, and cause contraction of smooth muscle. The kinins bradykinin and kallidin are formed in the blood by the action of proteolytic enzymes (kallikreins) on certain plasma globulins (kininogens). Kinins are not normally present in the blood, but are formed under certain conditions; for example when tissue is damaged or when there are changes in the pH and temperature of the blood. They are thought to play a role in inflammatory response.

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ki·nin (kiґnin) [Gr. kinein to move] any of a group of vasoactive straight-chain polypeptides formed by kallikrein-catalyzed cleavage of kininogens; they cause vasodilation of most vessels but vasoconstriction of the pulmonary bed, and they also alter vascular permeability. Common examples are bradykinin and kallidin.