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The physiological role of nitric oxide


Key words Nitric oxide Abstract bioactive molecules nitric oxide (nitric oxide, NO) from the beginning that its important physiological functions increasingly being recognized is what is know that the strongest contraction of vascular relaxing factor and the factor, its role is extremely broad, it may be used as medium, messenger or regulator of cell functions and participate in many physiological and pathological body processes, and with the occurrence of some diseases. This paper introduces the biosynthesis of NO in the cardiovascular system , central nervous system, gastrointestinal tract, the role of the immune response, NO-mediated synaptic transmission reversibly, NO-mediated role of excitatory amino acids. Chinese papers League finishing. Key words nitric oxide; physiological Furchgott [1] Source found in endothelial relaxing factor (EDRP) in 1987 by Palmer et al [2] by using chemiluminescence method confirmed that the nature of NO. NO not only on the cardiovascular system, central nervous system and digestive system regulation, and both in vivo role of multiple systems, it also involved in numerous in vivo physiological and pathological processes, is a novel neuronal messenger [3], played the role of neurotransmitters, excitatory amino acid mediated synaptic transmission and reversible, endogenous or exogenous excess production and release of NO directly cause nerve toxicity. 1 NO biosynthesis vivo vascular endothelial cells, nerve cells, macrophages, neutrophils, hepatocytes and other cells can produce NO, but vascular endothelial cells produce NO under physiological conditions is the most important cells. L-arginine (l-arginine, L-Arg) is the precursor of NO formation, L-Arg in a intramolecular guanidine nitrogen atoms are oxidized to produce NO and citrulline , catalyzed the reaction of the enzyme is nitric oxide synthase (NOS), a number of L-Arg analogues can be used as a competitive inhibitor of NOS to reduce the generation of NO [4]. Vivo as a set of NOS isoenzymes, according to the Ca2 +-dependent NOS difference, divided into native NOS (cNOS) and inducible NOS (iNOS) two categories, which do not rely Ca2 +. cNOS physical presence for the NOS form a series of cerebral blood flow and other physiological processes in vivo regulatory role from the messenger; iNOS is involved in autoimmune responses and cause pathological damage. 2 NO physiological role 2.1 NO on the cardiovascular system in vascular endothelial cells under physiological conditions can produce endothelium derived relaxing factor and endothelium derived shrinkage factor, regulating vasomotor, vascular endothelial cells produce NO, passing rapidly through the cell membrane to the vascular smooth muscle cells, smooth muscle relaxation, arterial vasodilation, thereby regulating blood pressure and blood flow distribution. This vasodilatation can be NOS inhibitor L-monomethyl arginine (L-NMMA) blocked. Endogenous NO regulation of vascular endothelial growth, trigger vasoactive substances, promote blood vessel growth and regeneration. NO produced by endothelial cells in physiological and pathological conditions have maintained the integrity of the role of vascular endothelial cells. Experiments show that, NO as a strong vasodilator of brain involved in the regulation of cerebrovascular basic tension [5], cerebral vascular endothelial cells release NO can increase vascular smooth muscle cells in the guanylate cyclase activity guanosine cyclic monophosphate causes elevated levels, so that the vascular relaxation; the contrary, such as the application of NOS inhibitors to experimental animals, found that guanosine cyclic monophosphate content decreased cerebral artery contraction. NO also by inhibiting platelet and leukocyte aggregation in order to protect the brain vascular endothelium. NO can also prevent the basic content of cerebral arteries to norepinephrine and 5 - hydroxytryptamine-induced contraction and other substances [6]. Based on the above principle, in ischemic brain injury in the early stage, NO on the edge with cerebral ischemia, cerebral collateral circulation and cerebral microcirculation in the open and restore blood flow has a positive role in promoting. 2.2 NO on the central nervous system (CNS) role in the CNS, NO promotion of neurotransmitter release in synaptic reversible process, in vision, pain and smell the smell distinction in terms of regulating blood-brain barrier permeability, high-level brain functions involved in activities such as learning and memory function . NO can amplify the calcium signal in nerve cells, so that weak, easily overlooked signal amplification, which leads to cell physiological changes significantly. High concentrations of the cytotoxic effect of NO may aggravate ischemic brain damage [7]. Found that cerebral ischemia increases the local excitatory amino acids, activated N-methyl-D-aspartate (NMDA) receptor, Ca2 + influx. Excessive production of NO can lead to nerve cell death, and property in the primary cortex by the NMDA-mediated neurotoxicity plays a major role . Application of NOS inhibitor on cerebral ischemia in a significant protective effect, and to protect the embryo cortex, hippocampus and tail - putamen from the toxicity of glutamate neurotoxicity, and the NOS inhibitor L-anti-drug role can be arginine reversed. Thus believe that, NOS inhibitors and NMDA antagonists protect against nerve injury, it is developing its medical value. 2.3 NO effect on the gastrointestinal tract Experiments show that under physiological conditions, NO can cause gastrointestinal smooth muscle and sphincter relaxation, excess NO is a disincentive to regulate stomach bowel movement. NO has been reported as a gastrointestinal non-adrenergic non-cholinergic (NANC) nerves of the transmitter, causing the dog duodenal longitudinal muscle relaxation. Stimulation of canine ileocecal sphincter dominant NANC nerves release NO, dilation effect. In the human gastrointestinal tract smooth muscle in vitro experiments, exogenous NO on the role of the circular smooth muscle relaxation is similar to electrical stimulation of NANC nerve responses, in the light, NO as a neurotransmitter in the NANC nerves and mammals widely distributed within the digestive tract, the normal movement of the gastrointestinal tract plays an important regulatory role. At the same time, NO on parietal cells, chief cells, mucous cells and gastrointestinal epithelial cells, regulating gastric acid , pepsinogen, mucus, HCO-3 and other gastrointestinal secretion. 2.4 NO role in the immune response NO can inhibit platelet aggregation and adhesion, reducing the aggregation of white blood cells, preventing the formation of thrombus; can inhibit lymphocyte proliferation, inhibition of mast cell inhibited the activity of oxidation products of macrophages; in chronic infection and inflammation, activated macrophages and leukocytes produce NO, in killing bacteria, viruses, parasites,[link widoczny dla zalogowanych], fungi, tumor cells, and in other series immune process, excess NO can induce mutations and tumors.