A kinin is any of various structurally related

peptides Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Dalton (unit), Da or more are called proteins. Chains of fewer t ...

, such as bradykinin and kallidin. They are members of the autacoid 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 kininogens. Kininogens contain a 9-11 amino acid bradykinin sequence. In

botany Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

, the

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

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 (biology), cell growth and cellular differentiation, differentiation, but also affect apical ...

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

Effects of kinins

Kinins are short-lived peptides that cause

pain Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...

sensation, arteriolar dilation, increase vascular permeability, and cause contractions in smooth muscle. Kinins transmit their effects through

G protein-coupled receptors G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large protein family, group of evoluti ...

. Kinins act on

axons An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pot ...

to block nerve impulses, which leads to distal muscle relaxation. They are also potent nerve stimulators which are mostly responsible for the pain sensation (and sometimes itching). Kinins increase vascular permeability by acting on vascular endothelial cells to cause cell contraction. Concomitantly, they induce local expression of adhesive molecules. Together they increase white blood cell adhesion and extravasation. Kinins are rapidly inactivated by the proteases generated locally during the aforementioned processes. They act locally to induce vasodilation and contraction of smooth muscle. Kinins function as mediators for inflammatory responses by triggering the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

. They are also able to regulate

cardiovascular In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart a ...

and renal (kidney) function by mediating the effects of ACE inhibitors. Reduced kinin activity can result in

high blood pressure Hypertension, also known as high blood pressure, is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms itself. It is, however, a major ri ...

, sodium retention, and the narrowing of blood vessels. Aspirin inhibits the activation of kallenogen by interfering with the formation of the kallikrein

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

, which is essential in the process of activation.

Where kinins are produced

Kinins are mostly produced at inflamed or injured tissues of the body and human

body fluids Body fluids, bodily fluids, or biofluids, sometimes body liquids, are liquids within the Body (biology), body of an organism. In lean healthy adult men, the total body water is about 60% (60–67%) of the total Human body weight, body weight; it ...

. Kinin peptides (kallidin and bradykinin) are located in human blood and

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

Kinin receptors

There are two types of kinin receptors: B1 and B2. Both are G-protein coupled receptors in which B2 are expressed in various tissues and B1 are induced from inflammation, tissue injuries, and stress. The human body contains more B2 receptors than B1 receptors. B1 and B2 receptors are essentially related as homologous genes. Both have the same cellular signaling pathways, although their patterns are different in intensity and duration; the B1 signaling pathway lasts longer than the B2 signaling pathway.

History

Kinin was initially discovered by J.E. Abelous and E. Bardier in 1909 while performing experiments where human body fluids, such as urine, were injected into dogs. The resulting observations state that the urine caused a reduction in blood pressure.

References

External links

The kinin-forming system at nic.sav.sk
{{Neuropeptides Kinin–kallikrein system 1900s neologisms