Animal Experimentation Issues

Birth Defects Research: Why Animal Experiments Are Not the Answer

Inherent Problems with Animal Research

"Karnofsky's Law" is frequently cited by those who work in the area of birth defects. This "law" states that any substance can harm fetal development if given in the right dose to the right species at the right time. This calls into question the validity of animal tests and makes the interpretation of results from animal tests very difficult.

There are many sources of error in using animal tests to predict human causes for birth defects. Rats and rabbits are most commonly used, not because they are so similar to humans, but because they are easy to handle and their use has generated an enormous, although not necessarily correct, amount of data.

• Species differences can have enormous effects on results:
  
  • There are genetic differences among species of animals which can affect susceptibility.
  • Different species develop in utero at different rates and along different schedules, therefore, because chemicals appear to exert their affect on the fetus at different stages of development, these differences can affect the interpretation of animal data.
  • Humans have a longer period of fetal development, thus may be more sensitive to birth defect-causing agents than other species.
  • Differences in the placenta between species may affect the results of animal tests.
• The route of administration of a potential birth defect-causing agent to the animal may not be the most common route of human exposure. For instance, animals may be given nicotine intravenously, whereas human exposure is through inhaling cigarette smoke.
• The animals may not be given the chemical at the same time schedule as typical human exposure. For instance, animals are usually given the substance once a day whereas humans might be exposed to the agent several times per day or continually. These differences can affect the results of the tests.
• One of the doses usually chosen in animal tests is that which produces some illness in the mother, however, this may not be applicable to the human situation where the same maternal effect may not be observed.
• Stress imposed by animal handling, food or water deprivation, and restraint, which are routine in all labs, may have adverse effects on pregnancy and cause birth defects and other problems.
• Animal studies are too insensitive to detect many subtle problems such as learning or behavioral problems.

Using animals to test substances for their potential to produce birth defects is too costly to be practical. These animal tests cost about $60,000 per chemical. Considering the tens of thousands of chemicals in widespread use (many of them untested) and the addition of about 1,000 new chemicals per year, conducting animal tests for all of them is simply not practical.

Animals are also used for physiology experiments in newborns such as tests for heart or lung function. However, because animals are physiologically different than humans in many respects, the results of these animal physiology experiments are often not applicable to humans.

Human Population Studies Versus Animal Experimentation

In contrast to animal experiments, studies of human populations have consistently provided crucial information:

• Virtually all known developmental hazards were identified and/or characterized through studies of human populations.
• Human population studies were responsible for identifying, among other things, the thalidomide disaster, fetal rubella syndrome, fetal alcohol syndrome, the association of folic acid with spinal cord abnormalities, and the effects of lead and methyl mercury on development.
• One of the most popular reference sources among genetic counselors is Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk by Briggs, Freeman, and Yaffe. This book presents no animal data, but rather relies solely on human data.

In Vitro Studies Versus Animal Experimentation

Scientists are turning to cell culture and test-tube (in vitro) studies because of all the inherent problems and inaccuracies with animal testing:

• Cell culture and test-tube studies offer many advantages including the fact that they are less expensive, faster, and more reproducible than animal tests. They also offer the hope for discovering the mechanisms whereby substances can cause birth defects.
• Some in vitro tests for the causes of birth defects have been successful in determining the relative "toxicity" of related chemicals.
• However, none of the in vitro tests are sufficiently developed to identify human birth defects with ease. More resources need to be devoted to this area.

Conclusion

Reliance on faulty information obtained from animal tests puts human health in jeopardy as well as causing needless pain and suffering for animals. In addition, the progress of science is slowed as money that could be better spent on clinical studies and the development of more reliable in vitro studies is wasted on animal tests.

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