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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.
(named after the French diplomat J. Nicot, who in 1560 was the first to introduce tobacco into France), 1-methyl-2 (3-pyridyl)-pyrrolidine, a volatile, colorless liquid alkaloid with a characteristic odor; boiling point, 247°C. Nicotine, a strong base, is readily soluble in water and organic solvents. It turns cinnammon-brown on exposure to air. It has the following structural formula:
Nicotine is present as salts of acetic, citric, and malic acids, constituting about 2 percent of the weight of Nicotiana tabacum leaves and about 8 percent of the weight of N. rustica leaves; it is also found in other plants.
Nicotine is sublimated during the smoking of tobacco. It penetrates with the smoke into the respiratory tract and, after being absorbed, acts on the ganglia of the autonomic nervous system and on the cholinergic structures of the central and peripheral nervous systems. The action of nicotine is two-phase: excitatory in low doses and inhibitory and causing paralysis of the nervous system, respiratory standstill, and cardiac arrest in large doses. Nicotine is one of the most toxic alkaloids; a few drops amounting to 100–200 mg—the quantity contained in 200 g of tobacco—may cause death when injected into man. Nicotine is quickly absorbed by the mucous membranes but is also quickly excreted and neutralized. However, the repeated absorption of low doses during smoking causes habituation, addiction, and chronic intoxication. Acute poisoning is accompanied by nausea, vomiting, diarrhea, intensified salivation, and, at times, convulsions and disturbances of hearing and vision. Medical treatment of acute nicotine poisoning is aimed at maintaining respiration, since paralysis of the respiratory center results in death.
Nicotine has long been used in pharmacological and physiological experiments. It has no therapeutic value. It is used in the form of a 40-percent aqueous solution of nicotine sulfate, in the form of a water extract from tobacco, and in the form of other preparations as an insecticide to control crop pests.