Kallidin

Kallidin is a bioactive peptide that is a member of the kinin family of proteins. It is a decapeptide that is produced from kininogen by the action of the enzyme kallikrein. Kallidin is a potent vasodilator, meaning it can widen blood vessels and increase blood flow. It also has other effects, such as promoting inflammation and pain sensation.

Structure and Function

Kallidin is a decapeptide, meaning it is composed of ten amino acids. Its sequence is Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg. This sequence is identical to that of bradykinin, another member of the kinin family, except that kallidin has an additional lysine residue at the N-terminal end.

The function of kallidin is primarily as a vasodilator. It achieves this by binding to bradykinin receptors on the surface of cells in the blood vessels, which triggers a series of reactions that result in the relaxation of the smooth muscle cells in the vessel walls. This causes the vessels to widen, increasing blood flow.

Kallidin also has other effects. It can promote inflammation by increasing the permeability of blood vessels, allowing immune cells and other substances to enter tissues more easily. It can also stimulate pain sensation by acting on nerve cells.

Production and Regulation

Kallidin is produced from kininogen, a protein that is present in the blood. The conversion of kininogen to kallidin is catalyzed by the enzyme kallikrein. This reaction is part of the kallikrein-kinin system, a complex network of proteins that regulate blood pressure, inflammation, and other processes.

The production of kallidin is tightly regulated by the body. Factors that can increase its production include stress, injury, and certain diseases. Conversely, its production can be reduced by drugs that inhibit the action of kallikrein, such as ACE inhibitors.

Clinical Significance

Due to its effects on blood vessels and inflammation, kallidin has been implicated in a number of diseases. These include hypertension, heart disease, and certain types of cancer. It is also thought to play a role in the pain and swelling associated with conditions such as arthritis and gout.

Research is ongoing to develop drugs that can modulate the activity of kallidin for therapeutic purposes. These include drugs that can inhibit its production or block its effects, as well as drugs that can enhance its activity in cases where this might be beneficial.