PSYC62H3 Chapter Notes - Chapter 7: Menopause, Weak Base, Respiratory Disease
Chapter 7: Nicotine and Caffeine
Nicotine: Key Psychoactive Ingredient in Tobacco
• Nicotiana tabacum produces greater amounts of nicotine than other Nicotiana species
• When tobacco is chewed/smoked, small nicotine-containing tobacco particles (tar) and
other chemicals enter the body
• Cigarettes = most commonly used tobacco product
o Most contain filter of cellulose acetate → reduces amount of tobacco tar inhaled
• Pipe smoking : inhaling smoke from a tobacco blend
o Smoke that has through a container of water
o Hookah
▪ Inhale tobacco smoke from a hose projecting from the top of the jar
• Tobacco use has serious health effects
o 3 primary causes of tobacco-related death each year:
▪ Cancer
▪ Pulmonary disease
▪ Cardiovascular disease
o African Americans have greater mortality rate from smoking, despite smoking
less than European Americans
o Secondhand smoke : smoke exhaled from a smoker or smoke released from a
burning tobacco product
o Thirdhand smoke: consists of remnants from tobacco smoking gathered on
material in smoker’s local environment after smoking has finished
▪ Cling to hair, clothes, walls, skin, etc
Discovery Of Tobacco
• Tobacco existed at least 2.5 million years ago
• Indigenous peoples in the Americas smoked tobacco as part of religious practices
• Religious practices remained primary use of tobacco until Europeans discovered it
during Colombus’s 1492 expedition
o Use of tobacco in Europe grew
o By 16th century → became a widely traded commodity
• By 1990’s
o Health risks were well characterized and widely publicized
Tobacco Use and Pharmacokinetic Properties
→ Tobacco Use and Nicotine Absorption
• Tobacco use consists of inhaling/chewing blends or other products
• Flue curing: venting heat through metal flue onto tobacco leaves
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o Reduces pH of smoke toward neutral (pH=7.0) by converting starches to sugars
→ makes smoke less harsh and irritating to inhale
• Absorption through lung and oral tissues
o Typical cigarette user consumes 13 cigs per day
o Cigar smokers absorb more nicotine than cigarette smokers
▪ Likely occurs from nicotine absorption through mucous membranes in the
mouth
o When smoking, tar adheres to tissues in the mouth, nose, throat, and if fully
inhaled, the lungs
▪ When exhaled → adheres to skin
▪ All tissue sites provide means of absorption
o Freebase form of nicotine is lipid soluble → allows for absorption through
mucous membranes in mouth
▪ Greatest amount of freebase nicotine that can be absorbed is 50% →
occurs at pH of 8.02
o pH levels for cigars favor greater nicotine absorption in the mouth
o Most tobacco products result in blood nicotine concentrations of 12-16
nanograms/mL
▪ Peak absorption for nicotine from cigarettes occurs after approx 7 min
o Smoker has ability to adjust amount of nicotine absorbed
▪ Vary number of inhalations
▪ Duration of an inhalation
▪ Completeness of inhalation
▪ Number of cigs smoked
→ Distribution and Biotransformation of Nicotine
• Nicotine readily passes through BBB
• In liver → CYP-2A6 enzymes metabolize 80-90% of nicotine
o Produces active metabolite → cotinine
o Genetic polymorphisms exhibit reduced CYP-2A6 activity levels
▪ Prevalent within Asian populations
▪ Nicotine levels remain higher in body because of reduced metabolism
▪ CYP-2A6*4, *7, and *9 polymorphisms exhibited reduced CYP-2A6
activity→ causing slower metabolism of nicotine to cotinine
o Indvs who exhibit homogenous mutant forms of these gene polymorphisms OR
heterogenous mutant forms that have combo of *4, *7, or *9 polymorphisms tend
to be light smokers and have lower risk of tobacco-related health effects
• African Americans exhibit slower metabolism of nicotine
→ Elimination of Nicotine
• Half-life of nicotine = 2 hours
• Chronic smokers have 30% faster elimination rate of nicotine than non smokers
o Suggests chronic tobacco use sensitizes pharmacokinetic processes for nicotine
• Half-life of for cotinine = ~17 hours
• Both nicotine and cotinine primarily excreted from body through urine
Nicotine and NS Functioning
• Nicotine = agonist for cholinergic nicotinic receptors
• Cotinine = weak agonist for nicotine receptors
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• When nicotinic receptor agonist binds to cholinergic nicotinic receptors, conformational
change takes place
o Opens channel for (+) charged ions → Ca2+, Na+, and K+
• Nicotinic receptors are ionotropic
o Alpha and beta subunits
• A short time after nicotine or another agonist activates nicotinic receptor → receptor
enters desensitized state
o Limits duration of action for nicotine’s acute pharmacological effects
o Channels close and receptors can;t be activated
o After period of time, desensitized state ends and receptors can again be
activated by an agonist
• Functional antagonism
o Agonists (nicotine) cause nicotinic-receptor channels to remain closed longer
than they are open → longer inactivated state than an activated state
o During chronic nicotinic administration, brain compensates for repeated closing
of nicotinic-receptor channels by upregulating nicotinic receptors
▪ Upregulation: increased production of proteins
• Both PNS and CNS have nicotinic receptors
o Peripherally
▪ Receptors located postsynaptically on neuromuscular junctions in
somatic NS → activation of receptors on muscle fibers causes muscles
to contract
▪ Receptors located in ganglia of autonomic system
• Activation of the receptors primarily increases sympathetic NS
activity
o Centrally
▪ Receptors found throughout
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Document Summary
Discovery of tobacco: tobacco existed at least 2. 5 million years ago. Tobacco use and nicotine absorption: tobacco use consists of inhaling/chewing blends or other products, flue curing: venting heat through metal flue onto tobacco leaves, reduces ph of smoke toward neutral (ph=7. 0) by converting starches to sugars. Distribution and biotransformation of nicotine: nicotine readily passes through bbb. Nicotine affects movement and cognitive functioning: behavioural effects differ b/w naive and chronic tobacco users, produces effects on motor stability especially noticeable in hands. In non-tobacco users hand tremor and reduce hand steadiness: studies show nicotine improves attention, especially when reorienting attention toward another stimulus, and improves information processing. In attention tasks nicotine improves info processing by shortening times to detect stimuli. In chronic smokers, nicotine produces feelings of vigor, arousal, and reduced fatigue: report effects as pleasant and produce a positive mood, mao inhibitors found in tobacco enhance nicotine-induced effects on nucleus accumbens dopamine levels.
