Kinanins

Kinanins are a family of secreted signaling molecules that play a role in various physiological processes, including inflammation, pain perception, and smooth muscle contraction. They are peptides that belong to the kinin-kallikrein system, a complex cascade involved in blood pressure regulation and hemostasis. The main kinin peptides are bradykinin and kallidin. Bradykinin is formed from high molecular weight kininogen by the action of kallikreins. Kallidin, also known as lysyl-bradykinin, is formed from low molecular weight kininogen by tissue kallikreins.

These peptides exert their effects by binding to specific G protein-coupled receptors, primarily B1 and B2 receptors. The B2 receptor is constitutively expressed and is responsible for most of the physiological actions of kininins, such as vasodilation and increased vascular permeability. The B1 receptor is typically induced during inflammatory conditions and is involved in amplifying inflammatory responses and pain. The kinin-kallikrein system is tightly regulated by enzymes like kininases, which degrade kininins, thus controlling their activity and duration of action. Dysregulation of this system has been implicated in various diseases, including hypertension and inflammatory disorders.