A kinin is any of various structurally related polypeptides, such as

bradykinin Bradykinin (BK) (Greek brady-, slow; -kinin, kīn(eîn) to move) is a peptide that promotes inflammation. It causes arterioles to dilate (enlarge) via the release of prostacyclin, nitric oxide, and endothelium-derived hyperpolarizing factor an ...

and kallidin. They are members of the

autacoid Autacoids or "autocoids" are biological factors (molecules) which act like local hormones, have a brief duration, and act near their site of synthesis. The word ''autacoid'' comes from the Greek words "autos" (self) and "acos" (relief; i.e., drug) ...

family. Kinins are peptides that are cleaved from kininogens by the process of kallikreins. Kallikreins activate kinins when stimulated. It is a component of the kinin-kallikrein system. Their precursors are

kininogen Kininogens are precursor proteins for kinins, biologically active polypeptides involved in blood coagulation, vasodilation, smooth muscle contraction, inflammatory regulation, and the regulation of the cardiovascular and renal systems. Types o ...

s. Kininogens contain a 9-11 amino acid bradykinin sequence. In

botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...

, the

plant hormone Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...

s known as

cytokinin Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and lea ...

s were first called kinins, but the name was changed to avoid confusion.

Effects of Kinins

Kinin are short lived peptides that cause pain sensation, arteriolar dilation, increase vascular permeability and cause contractions in smooth muscle. Kinins transmit their effects through G protein- coupled receptors. Kinin act on axons to block nervous impulses, which leads to distal muscle relaxation. Kinin are also potent nerve stimulators. which is mostly responsible for the sense of pain (and sometimes itching). Kinin increase vascular permeability by acting on vascular endothelial cells to cause cell contraction. Concomitantly they induce local expression of adhesive molecules. Together they increase leukocytes adhesion and extravasation. Kinin are rapidly inactivated by the proteases locally generated during the above mentioned processes. They act locally to induce

vasodilation Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstrictio ...

and contraction of

smooth muscle Smooth muscle is an involuntary non- striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit ...

. Kinins function as mediators for inflammatory responses by triggering the immune system. They are also able to regulate cardiovascular and renal function through mediating the effects of ACE inhibitors. Reduced kinin activity can result in high blood pressure, sodium retention and the narrowing of blood vessels. Aspirin inhibits the activation of kallenogen by interfering with the formation of kallikrein

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

which is essential in the process of activation.

Where kinins are produced

Kinins are mostly produced at inflamed or injured tissue of the body and human body fluids. Kinin peptides (kallidin and bradykinin) are located in human blood and urine.

Kinin Receptors

There are two types of kinin receptors, B1 and B2. B1 receptors are G-protein coupled receptors that are induced by injured tissue. The quantity of B2 receptors in the human body, exceed B1 receptors.

History

Kinin was initially discovered by J.E. Abelous and E. Bardier in 1909 when performing experiments utilizing human body fluids. Human body fluids such as urine was injected into dogs and it was observed that the urine caused a reduction in blood pressure.

References

External links

The kinin-forming system at nic.sav.sk
Kinin–kallikrein system {{biochem-stub