Kinin-kallikrein system

The kinin–kallikrein system or simply kinin system is a poorly understood hormonal system with limited available research. It consists of blood proteins that play a role in inflammation,blood pressure control, coagulation and pain. Its important mediators bradykinin and kallidin are vasodilators and act on many cell types.

The system was discovered in 1909 when researchers discovered that injection with urine (high in kinins) led to hypotension (low blood pressure). The researchers Emil Karl Frey, Heinrich Kraut and Eugen Werle discovered high-molecular weight kininogen in urine around 1930.

kinin [Gk] kīn(eîn) to move, set in motion. kallikrein [Gk ] kalli~ sweet and krein = kreos, flesh, named for the pancreatic extracts where it was first discovered

The system consists of a number of large proteins, some small polypeptides and a group of enzymes that activate and deactivate the compounds.

High-molecular weight kininogen (HMWK) and low-molecular weight kininogen (LMWK) are precursors of the polypeptides. They have no activity of themselves.

HMWK and LMWK are formed by alternative splicing of the same gene.

Inhibition of ACE with ACE inhibitors leads to decreased conversion of angiotensin I to angiotensin II (a vasoconstrictor) but also to an increase in bradykinin due to decreased degradation. This explains why some patients taking ACE inhibitors develop a dry cough, and some react with angioedema, a dangerous swelling of the head and neck region.

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