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Nicotine

Nicotine


Nicotine, C10H14N2, is a highly toxic, pale yellow alkaloid produced in tobacco plants in response to leaf damage. Nicotine is synthesized in the roots of tobacco plants in response to hormones released by damaged tissue, and it is then carried to the leaves, where it is stored in concentrations of between 2 percent and 8 percent by weight. Nicotine is used commercially as an insecticide (it is one of the few poisons to which insects have not become resistant). Tobacco smoke contains nicotine, believed to be the active (and addictive) ingredient.

Mayan peoples of South America used tobacco for recreational and ceremonial, as well as medicinal, purposes. Mayan sculptures depict high-ranking persons smoking cigars and priests blowing tobacco smoke over human sacrifices. By the time of the arrival of Christopher Columbus in the New World, tobacco use had spread throughout both North America and South America. Early accounts by European explorers describe Native Americans carrying glowing sticks from which they inhaled, and many pipes are found among Native American artifacts. Tobacco was often chewed by Native Americans; the juice was dropped into eyes to improve night vision and applied to skin as an agent having antiseptic properties.

The men who accompanied Columbus encountered many users of tobacco, but early European explorers showed little interest in the plant until they acquired an awareness that it might be used to treat diseases. Europeans at first forbade tobacco use, but tobacco gradually gained a reputation among court physicians as a medicine. For many Europeans, tobacco was suddenly a valuable New World commodity.

Nicotine is the active ingredient of tobacco. Nicotine is soluble in water and in nonpolar solvents. It can be absorbed by the body from smoke that has been taken into the lungs, or through the skin. It rapidly crosses the blood-brain barrier, appearing in brain tissue minutes after its absorption into capillaries lining the alveoli of the lungs. The presence of nicotine in the body stimulates nicotinic-cholinergic receptors of the nervous system, resulting in increased attention span, increased heart rate and blood pressure, and increases in the concentrations of some hormones. Habitual users have a feeling of well-being after intake of nicotine, ascribed to the increased concentrations of dopamine in the brain. The increased metabolic rate that is associated with nicotine use may be what is in back of the common belief that it is easier to lose weight when using nicotine.

Nicotinic-cholinergic receptors that are part of the autonomic nervous system may be stimulated at low concentrations of nicotine, but blocked at higher concentrations. The repeated use of nicotine-containing products (which includes chewing tobacco, chewing nicotine-containing gum, or the use of therapeutic patches that release nicotine for skin absorption) promotes the formation of (new) nicotinic-cholinergic receptors. The tolerance and eventual addiction that go along with repeated use may result in increased craving for nicotine.

Many environmentally hazardous substances, such as asbestos and radon, are much more hazardous when they become mixed with cigarette smoke, probably because the particulate matter in smoke in the atmosphere may adsorb these dangerous substances and carry them into the alveoli of lungs. Many cancers may be caused by substances or materials associated with nicotine use, such as tobacco smoke or the tobacco plant itself (as in chewing tobacco). Nicotine itself, although not known to cause cancer directly, causes proliferation of both healthy and neoplastic cells, and may further the development of cancer by stimulating angiogenesis (the growth of new blood vessels) and thus providing cancerous tissues with increased blood supplies. The effect of nicotine on cell growth is especially strong in tissue environments having low concentrations of carbon dioxide, for example, in damaged lungs; thus, the effect would be greater in persons whose breathing was already impaired. Nicotine's stimulation of cell growth may account for the observation that atherosclerotic plaques (which are intracellular accumulations of lipids ) grow more rapidly in the presence of this alkaloid substance. This effect may actually become the basis of medical treatments intended to improve blood flow to tissues damaged by atherosclerosis.

Single exposure to nicotine in quantities as small as 50 mg (0.0018 oz) may result in vomiting and seizures; the average cigarette yields about 3 mg(0.00011 oz). As nicotine can be absorbed through skin, accidental exposures in persons working with nicotine-containing pesticide preparations may be fatal. Extracts of chewing tobacco are effective insecticides; commercial insecticide products contain much higher amounts of nicotine than products intended for human consumption.

see also Dopamine; Radon; Toxicity.

Dan M. Sullivan

Bibliography

Brautbar, N. (1995). "Direct Effects of Nicotine on the Brain: Evidence for Chemical Addiction." Archives of Environmental Health (July 1):263.

Nicotine and Tobacco Research. Various issues.

Internet Resources

"A Brief History of Tobacco." Available from <http://www.cnn.com/US/9705/tobacco/history/index/html>.

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"Nicotine." Chemistry: Foundations and Applications. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

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nicotine

nicotine is a simple alkaloid produced by the tobacco plant. The history of chewing and smoking tobacco, and of taking snuff, is of great antiquity. All the acute effects of the tobacco habit are dependent on nicotine, which has complex actions, both on the central nervous system and in the rest of the body. Nicotine acts on certain cell membrane receptors, which were therefore given the name nicotinic receptors. Nicotine was found to mimic the actions of the neurotransmitter acetylcholine at these sites: at the neuromuscular junctions in skeletal (voluntary) muscle; at the synapses in the relay stations (the ganglia) of the autonomic nervous system; and in various parts of the brain and spinal cord. In many situations nicotine first activates the nicotinic receptors and then by its continued presence desensitizes them. Normally, at these nicotinic synapses, the transmitter (acetylcholine) is rapidly destroyed by the enzyme cholinesterase, so its action is evanescent; this is not the case with nicotine.

Nicotinic receptors are proteins which span the cell membrane (e.g. of a muscle cell or neuron) and when activated by acetylcholine or by nicotine undergo a conformational change that creates ion channels in the membrane. These channels allow the passage of sodium ions inwards and potassium ions outwards through the membrane, leading to excitation of the cell.

Increased levels of nicotine can be measured in the blood up to one hour after a cigarette. Nicotine-taking, in whatever form, is for self gratification and reward, requiring reinforcement at intervals. If nicotine is withdrawn, irritability and failure to concentrate is the result. The actions of nicotine are caused by effects in the brain. Repeated intake of nicotine leads to increased numbers of nicotinic receptors in the brain, which might be expected to reduce the need for nicotine rather than increase it. But it seems likely that many of the receptors are in a desensitized form and that the number of functional receptors is reduced, so that the addict requires increasing and repeated doses to maintain the effect. The claims that nicotine increases concentration, learning ability, and retention of learned information are well founded — numbers of performance tests have confirmed this. Nicotine produces a sense of alertness, but nevertheless of calm. This seems to be due to inhibition of reflex nerve loops in the spinal cord, with the effect of causing muscular relaxation.

The above actions all take place in the central nervous system. The effects of nicotine in the rest of the body are due to actions on the ganglia of the autonomic nervous system, predominantly on the sympathetic ganglia. Mimicking the effects of physiological sympathetic stimulation, they include increases in heart rate, cardiac output, and blood pressure, and reduction in gut motility and digestive functions. Because the adrenal medulla is a modified sympathetic ganglion — with secretion normally stimulated by acetylcholine — adrenaline and noradrenaline are released by the action of nicotine; these are likely to be responsible for most of the cardiovascular effects. Nicotine also releases antidiuretic hormone from the posterior pituitary gland, hence reducing the formation of urine.

Nicotine is not used therapeutically, except for nicotine patches and chewing gum, which are used to help smokers give up the habit. They do not have the dangers associated with constituents of tobacco smoke.

For some time nicotine enjoyed popularity as an insecticide. However, in its concentrated form it is highly poisonous, and it can be absorbed through the skin, so is no longer used for spraying on plants. Lobeline, another plant alkaloid from Lobelia species, has very similar actions to nicotine.

Alan W. Cuthbert


See also acetylcholine; autonomic nervous system; neurotransmitters; membrane receptors; smoking.

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"nicotine." The Oxford Companion to the Body. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

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"nicotine." The Oxford Companion to the Body. . Retrieved August 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/nicotine

nicotine

nicotine, C10H14N2, poisonous, pale yellow, oily liquid alkaloid with a pungent odor and an acrid taste. It turns brown on exposure to air. Nicotine, a naturally occurring constituent of tobacco, is the active ingredient in tobacco smoke. The amount of nicotine in tobacco leaves ranges from approximately 2% to 7%. In concentrated form, it is used as an insecticide.

Nicotine, which mimics the affects of acetylcholine, acts primarily on the autonomic nervous system. In a dose of less than 50 mg, it can cause respiratory failure and general paralysis. Smaller toxic doses can cause heart palpitations, lowered blood pressure, nausea, and dizziness. A person who smokes inhales approximately 3 mg from one cigarette. This amount increases the heart rate, constricts the blood vessels, and acts on the central nervous system, imparting a feeling of alertness and well-being. Although not considered carcinogenic, nicotine probably contributes to the increased incidence of heart disease seen in smokers and may enhance the growth of tumors caused by carcinogens.

People who use tobacco products develop a physiological addiction to nicotine. Research has shown that nicotine increases the flow of the neurotransmitter dopamine in the brain, creating pleasurable feelings and a craving to keep in the bloodstream levels of nicotine that will maintain these feelings. Lack of nicotine causes withdrawal symptoms (heart rate and blood pressure changes, sleeping problems, brain wave disturbances, and anxiety) in smokers.

Nicotine-containing chewing gums and skin patches that administer nicotine to people who are trying to cease smoking have been developed. Although the rate of absorption is slower with these methods than with smoking—smoking delivers nicotine to the brain within six seconds—and although nicotine obtained in this way does not provide the same pleasurable results as smoking, the gums and patches do help relieve some of the symptoms of withdrawal. Combining the use of patches or gum with continued smoking can result in nicotine overdose and toxicity, causing nausea, palpitations, and headache. Nicotine nasal sprays and inhalers more closely mimic the delivery and intensity of nicotine obtained by smoking. Some researchers have suggested, however, that prolonged use of nicotine replacement, especially inhalers, beyond the few months recommended to break the cigarette habit could damage cells lining the blood vessels and lungs. It is not clear if the use of nicotine replacement therapy is effective in enabling smokers to quit permanently.

See also smoking.

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nicotine

nic·o·tine / ˈnikəˌtēn/ • n. a toxic colorless or yellowish oily liquid, C10H14N2, that is the chief active constituent of tobacco. It acts as a stimulant in small doses, but in larger amounts blocks the action of autonomic nerve and skeletal muscle cells.

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nicotine

nicotine (nik-ŏ-teen) n. a poisonous alkaloid derived from tobacco, responsible for the dependence of regular smokers on cigarettes. In small doses nicotine has a stimulating effect on the autonomic nervous system. Large doses cause paralysis of the autonomic ganglia.

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nicotine

nicotine Poisonous alkaloid obtained from the leaves of tobacco, used in agriculture as a pesticide and in veterinary medicine to kill external parasites. Nicotine is the principal addictive agent in smoking tobacco. See also cigarette

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nicotine

nicotine XIX. — F., f. modL. nicotiāna tobacco-plant, f. name of Jacques Nicot, French ambassador at Lisbon, by whom tobacco was first introduced into France in 1560; see -INE5.

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nicotine

nicotine A colourless poisonous alkaloid present in tobacco. It is used as an insecticide.

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nicotine

nicotine •diamantine • dentine • Benedictine •Christine, pristine, Sistine •Springsteen • tontine • protein •Justine • libertine • mangosteen •brigantine • Augustine • nicotine •galantine • guillotine • carotene •quarantine • astatine • travertine •brilliantine • ethene • polythene •hypersthene • olivine • Slovene •go-between • fanzine •benzene, benzine •bombazine • organzine

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