The Importance of Animals in Research
‘Research involving laboratory animals is necessary to ensure and enhance human and animal health and protection of the environment.’
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.
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