kinin
1. One of a group of peptides, occurring in blood, that are involved in inflammation. Kinins are formed by the splitting of blood plasma globulins (kininogens) by the enzyme kallikrein at the site of inflammation. Kinins so far identified include bradykinin and kallidin. They cause local increases in the permeability of small blood vessels. Bradykinin is a potent stimulator of pain receptors in the skin.

2. See cytokinin.

kinin (ky-nin) n. one of a group of naturally occurring polypeptides that are powerful vasodilators, which lower blood pressure, and cause contraction of smooth muscle.