kininol: kinin n. one of a group of naturally occuring polypeptides that are powerful *vasodilators, 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.