PSYC62H3 Chapter Notes -Lipid Bilayer, Dietary Supplement, Lipophobicity

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24 Apr 2012
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Chapter Three: Basic Principles of Pharmacology
The psychological effects of a drug at any particular time depend on many factors, including the
individual’s set and setting, the particular way the drug changes activities in the CNS, the route
of administration, the amount administered, the frequency, etc.
Drug originally referred to any substance used in chemistry or medicine; gradually restricted to
any agent used in medicine or any ingredient in medicine; today used as a synonym for a
narcotic agent or an illicit substance
In general, a drug is a chemical that affects one or more biological processes. However, not all
chemicals that affect biological processes are considered drugs. Substances that are commonly
used for nutritional purposes, such as salt, water, proteins, fats, carbohydrates, vitamins, and
minerals aren’t generally considered drugs, because they’re necessary for carrying out the
normal biological functions of the body. However, certain vitamins and minerals that might be
found in our diet, if isolated and used in certain quantities, might also be thought of as drugs
1994 Dietary Supplement Health and Education Act “dietary supplement” products may enter
the market untested, and the FDA can’t restrict the use of such supplements unless substantial
harm has been proved
o St john’s wort – very popular supplement herbal antidepressant documented
evidence for effectiveness; considerable evidence for its interacting with a variety of
medicines in adverse ways
These properties indicate that pharmacologically, one or more ingredients in St.
John’s wort would be considered a drug, but until there’s legislation to change
its status, the FDA can’t regulate it as a drug
Nicotine in the mid 1990s, governmental hearings were held to determine whether scientific
evidence supported assumptions that nicotine is a drug.
o If the FDA could prove that tobacco companies intended for cigarettes to provide
nicotine to satisfy an addiction, the FDA would have the right to regulate cigarettes
under the Federal Food, Drug, and Cosmetic Act, which considers a product to be a drug
if the vendor intends it to be one
o However, the US Supreme Court eventually ruled against allowing the FDA to regulate
tobacco products. This decision was made on the basis of political and legal
considerations and not on the basis of pharmacological principles
Similar issue alcohol prefer not to view it as a drug, but it’s not used for nutritional value, so
it should be considered a drug in that it affects the normal biological activities of the body
Chemicals originating or produced within an organism that are used to carry out the normal
biological functions in the body aren’t usually thought of as drugs – referred to as endogenous
substances
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We’ve isolated a variety of substances found to be important in the functions of the body, have
extracted or synthesized them, and have administered them in purified form to reverse
neurological deficits LDopa
From a pharmacological view, it seems most appropriate to define a drug as a non-food,
nonmechanical substance (usually a chemical substance) that exerts an effect upon a living
system
Basic Chemical Principles Related to Psychopharmacology
The water molecule H2O takes on a kind of V-shape, and there’s an uneven distribution of
charge: though electrically neutral overall, the oxygen end has a partial negative charge, while
the two hydrogen ends have partial positive charges. Because of this, we say that the water
molecule is polar
Water molecules are attracted to each other very powerfully. The partial positive charge of the
oxygen end of one molecule is attracted to the partial negative charge of the hydrogen end of
another by a type of bond known as a hydrogen bond. This bonding results in the fluid
characteristics of water; water tends to form beads or drops, in which the complex strings of
water molecules are bound together with mutual attraction.
Water is an excellent solvent for other substances that are polar or ionic
Table salt when immersed in water, the NaCl crystals dissociate into Na+ and Cl- ions that
easily dissolve in the water medium
Organic chemist’s view on the chemistry of life – a large component of living systems is in the
aqueous phase (ie. Water based). Hydrophilic molecules dissolve easily in the aqueous phase.
However, they’re also lipophobic.
In chemistry, organic refers to the chemistry of carbon-based substances
In living systems, the major constituents of the organic phase are hydrocarbons
o Fats or lipids high degree of hydrocarbon content
Eg. Cholesterol
Aqueous and organic phases don’t mix well
Adding salt to chicken soup most of the Na+ and Cl- ions would dissolve in the aqueous phase
(water) and few would dissolve in the fat
Gasoline very high hydrocarbon content; doesn’t mix well with water
Phospholipids are a type of diglyceride; they have a polar head and two fatty acid hydrocarbon
tails
The polar head, which has ionic charges and polar components, is attracted to water, while the
hydrocarbon tails are repelled by water, and attracted to each other as well as other
hydrocarbon chains
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Nerve cell membranes are composed of a phospholipid bilayer
o The polar heads point inward and outward toward the largely aqueous environments
inside and outside the cell, while the fatty acid tails from each layer point toward the
center of the membrane
o This lipid bilayer provides a barrier to the movement of any polar and charged
substances
Any drug that is highly lipid-soluble would easily be stored in adipose tissue
The cell membrane made up mostly of a lipid bilayer presents a barrier to the diffusion of
any substance too water-soluble (lipophobic), and not transported by proteins
o The stomach and intestines are lined with cells, and if a pill is introduced into the body,
this would be the first barrier to entry into systemic circulation
o BBB made up of tight junctions between the endothelial cells that compose the outer
lining of the blood vessels; can provide a significant resistance to the entry of drugs and
other substances into the brain, and subtle alterations in the chemical structure of drugs
can yield substantial differences in passage across the BBB
Ethanol relatively soluble in both water and lipid; one end of the molecule is a hydrocarbon,
while the other end has oxygen and hydrogen, and interacts easily with water
o Passes easily from the stomach into widespread circulation, easily dissolves in the blood,
and easily passes into the brain
o Metabolized by enzymes at a rate of 1 ounce/hour and the metabolites are also water
soluble are removed in the urine
Delta 9 THC properties contrasted with ethanol mostly hydrocarbon highly lipid-soluble
o Rapidly absorbed when smoked and easily passes through the BBB
o Not rapidly metabolized, and isn’t very water soluble, so it deposits itself in adipose
tissue for a very long time, perhaps several weeks
Morphine’s lower lipid solubility results in a slower onset of analgesia and less intensity, but a
longer duration of action than fentanyl
The effects of a particular drug on an organism depend heavily on the rate of accumulation and
the concentration of the drug at its sites of action and the duration of contact at those sites
These are a function not only of the amount of drug but also of its pharmacokinetics
Pharmacokinetics refers to the dynamic processes involved in the movement of drugs within
biological systems with respect to the drug’s absorption, distribution, binding or localization in
tissues, metabolic alterations, and the excretion from the body
In contrast, pharmacodynamics refers to the biochemical and physiological effects of drugs and
their mechanisms of action
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