Kinins


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Related to Kinins: Prostaglandins, Cytokines

Kinins

 

(1) Cytokinins, substances in plants and microorganisms, derivatives of 6-aminopurine. Many kinins are found in seeds and fruits; fewer are found in roots, stems, and leaves. For example, 1 g of a kinin called zeatin is obtained from every 70 kg of corn kernels (of milky ripeness). Kinins stimulate cell division, participate in the formation of roots and stems and in the differentiation of new organs, and help to prolong the life of cut leaves. Thus, the application of kinins to yellowed cut leaves causes them to turn green. These and other important functions of kinins are associated with their participation both in the formation of RNA, DNA, and protein and in the redistribution of metabolites in the plant; the application of kinins to one-half of a yellowed leaf intensifies the flow of metabolites from the other, untreated, half. One of the especially active kinins is kinetin, which has been isolated in yeasts.

K. E. OVCHAROV

(2) In animals, substances of a polypeptide nature with a broad spectrum of biological activity. Kinins relax the smooth musculature of the blood vessels, lower blood pressure, increase the permeability of the capillaries, produce sensations of pain, and contract or relax the smooth musculature of isolated organs.

Three kinins have been found in mammals and man: bradykinin, a linear nonapeptide (from nine amino acids); lysylbradykinin (or kallidin), a decapeptide (from ten amino acids); and methionyllysylbradykinin, an undecapeptide (from 11 amino acids). All kinins are formed in the blood plasma or in the intercellular spaces, splitting off (under the influence of kallikrein) from kininogen, an inactive proteinic precursor. A milliliter of human blood plasma normally contains 0–0.002 micrograms of kinins. Because of rapid enzymic inactivation in the blood and tissues (under the influence of kininase), kinins exert a predominantly local effect. The physiological role of kinins is associated with the regulation of local blood flow and capillary permeability.

T. S. PASKHINA

REFERENCE

Paskhina, T. S. “Biokhimicheskie osnovy patologii serdechno-sosudistoi sistemy.” In Molekuliarnye osnovy patologii. Moscow, 1966.
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13] These visceral reflexes are also evoked by chemicals such as kinin, histamine, prostaglandin, and serotonin, which stimulate the high threshold cardiopulmonary receptors to produce apnea, hypotension, and bradycardia.
Kinins act on B1 or B2 receptors to release conjointly endothelium-derived relaxing factor and prostacyclin from bovine aortic endothelial cells.
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Evidence of participation of B1 and B2 kinin receptors in formalin-induced nociceptive response in mouse.
Atkinson found that complement, kinins, prostaglandin, coagulation factors, histamine and serotonin are all normal in patients with SCLS (7).
Toxin inhalation increased airway kinins, and the response to inhaled toxin was enhanced after allergen challenge.
NEPs are abundant in kidney brush border membranes, cardiac myocytes, and endothelial cells and can degrade other circulating peptides, such as kinins, enkephalins, and neurotensins.
The local release of kinins that can occur during contraction of muscles with minimally reduced blood flow may be another alternate etiology of pain.
These factors are both intrinsic and extrinsic to the kidney, home of the intrinsic factors include an autoregulatory mechanism, intrarenal rennin-angiotensin mechanism, eicosanoids, and kinins.
In turn, these cells emit a range of immune system chemicals such as kinins.