Animals in Research: The Importance of Animals
in the Science of Toxicology
Necessity of Animal Research
Research
involving laboratory animals is important to people and to our quality
of life. In the past century, most inhabitants of this planet have experienced
an unprecedented rise in living standards, life expectancy and personal opportunity,
in large part due to the many ways chemicals have been put to work for us.
For example, drugs whose effects range from curing previously fatal bacterial
infections, reducing the impact of AIDS, minimizing heart disease, decreasing
age-related wrinkles, to reducing hair loss are widely available today. The
many benefits of the diverse uses of our natural resources are an outcome
of careful scientific research and of using chemicals in an appropriate
and safe manner. Toxicologists, the scientists who help determine the limits
for
safe use of materials, use modern technological research methods, including
tests on animals, to protect human and animal health and the environment.
What is toxicology?
Toxicology is the study of how chemical substances interact with living systems
and affect normal processes, and the use of this information to predict safe
exposure levels. Toxicological research and testing helps us to live safely
and to derive benefit from natural and synthetic substances while avoiding
harm. Toxicologists are involved in the evaluation of household products,
medicines and the effects of incidental and occupational exposure to natural
and manufactured substances. Toxicology also helps us develop the best treatments
in the event that accidental overexposure does occur.
What is safe?
Toxicologists know that no substance is risk-free. One fundamental tenet of
the science of toxicology is that all chemicals can cause harm at some level
of exposure, summed up in the phrase "the dose makes the poison."
This means that exposure to a specific small amount of any substance will
have no detectable impact on normal biological processes and is considered
safe. Some doses actually have beneficial effects, as we all know from use
of medicines. But increasing exposure to most substances will, at some point,
cause harmful effects. Substances are considered toxic at that level. For
example, digitalis is a plant product that has been used with great benefit
to treat heart irregularities, but too large a dose will cause death. Oxygen
provides another example of how increasing the dose can turn a safe compound
into a toxic one. Oxygen is essential to life and part of the air we breathe,
but when given at high concentrations it can cause lung and eye damage in
infants.
Sometimes the possible negative effects of a substance are outweighed by
the positive benefits at that dose. Dogs are treated with heartworm medication
because the risk of death from heartworms is much greater than the risk of
toxicity of the medication. Similarly, chemotherapeutic agents are used to
destroy cancerous cells even though they may damage healthy cells in the process.
Prior to the use of new substances, toxicologists and policy makers are
responsible for determining the range of exposure that is safe and the level
of exposure that may be harmful to human health or to the environment. The
effect of the level of exposure is also important when toxicologists assess
the risk caused by a substance already present in the environment. The benefits
of using a new substance, or the costs of removing an environmental contaminant,
are viewed relative to the perception of what is safe.
How do toxicologists determine which exposures may harm?
Toxicologists conduct basic research, using both whole animals and in vitro
methods, to learn how various chemicals and dosages interact with living systems.
Basic research is necessary to understand mechanisms that maintain living
organisms and to determine baselines for physiological processes.
For many chemicals that enhance the quality of our lives, the mechanism
that produces the beneficial effect is the same mechanism that makes the chemical
toxic. For example, aspirin reduces pain and fever by reducing the activity
of enzymes in the body that normally increase production of compounds associated
with pain and distress. However, acute toxicity can occur when the aspirin
dose is so high that inhibition of similar enzymes in the heart interferes
with normal function. Animal studies help determine the ratio between the
beneficial dose and the toxic dose of medications.
Toxicologists determine which levels of a substance cause harm by conducting
safety studies which progress from the test tube to animal studies and, in
some cases, to human trials. Safety testing is needed to identify the crossover
points between no impact, beneficial effects and harmful effects. For example,
alcohol, when ingested, is taken directly into the bloodstream and blood levels
rise in direct proportion to consumption. Many people enjoy the feeling produced
by one alcoholic beverage and may consider that a beneficial effect. However,
one drink, such as 12 ounces of beer, will impact motor skills and judgment.
Two such drinks in a short interval result in a blood alcohol content of .08%
in a 120-pound woman. Persons with levels above 0.08% ethanol in the bloodstream
are considered too impaired to drive an automobile in many states. Further
increases (above 0.4%) can lead to loss of consciousness and death.
Vitamins also illustrate the variation in effect depending upon the dose.
Vitamins are essential elements that are not manufactured by the body and
must be furnished from the outside, typically in the diet. In general, either
vitamin deficiency or vitamins in excess can affect health and even cause
birth defects. Birth defects such as spinal bifida are less likely to occur
if the mother has a daily vitamin A intake of 5000 IU in advance of the pregnancy.
However, women using one prescription treatment for acne that involves high
doses (50,000 IU) of a form of this vitamin (isotretinoin) must take precautions
to avoid pregnancy due to the risk of birth defects.
Safety evaluations establish a margin of safety to compensate for differences
in response among individuals. For example, women in general are affected
more by the same dose of alcohol than men are, not only because of smaller
body size but also because alcohol is processed at different rates by men
and women. Persons of differing ethnic heritages also metabolize ethanol at
different rates.
Toxicologists use in vitro methods and animal models that have been
accepted by the scientific community and recognized by regulatory bodies so
that people who use and are exposed to a variety of chemicals can enjoy the
benefits with a minimum of risk. Similarly, use of accepted tests protects
other organisms, including pets and farm animals, as well as the environment.
[Necessity of Animal Research]
[Reliability of Animal Data]
[Commitment
to ResponsibleTreatment] [Advancing Valid Alternatives]
[Position Statement]
[Guiding
Principles] [Further Information] [Selected
References]
[Public Policy Statement] [Download
Printable Brochure]
Research
involving laboratory animals is necessary to ensure and enhance human and
animal health and protection of the environment.
SOT Animals in Research Public Policy
Statement
|
