What is an important endpoint in animal research studies aiming to assess toxicity?

In animal research studies assessing toxicity, mortality rate serves as a crucial endpoint because it provides direct information about the lethal effects of a substance being tested. Monitoring the mortality rate helps researchers evaluate the overall safety and risk posed by the substance to the animals. A high mortality rate indicates significant toxicity, which can lead to the conclusion that a substance may be dangerous to other organisms, including humans.

While weight gain, extended lifespan, and behavior change can provide valuable insights into the effects of a substance, they are not as definitive in measuring toxicity as mortality rate. For instance, weight gain might indicate a positive response to a substance (in cases like nutritional testing) or, conversely, could reflect an unhealthy condition. Extended lifespan may not directly connect to toxicity assessments unless it reflects a detrimental impact of a tested substance. Similarly, behavior change is often subjective and can vary significantly among individuals and species, making it less reliable as a sole indicator of toxicity. Therefore, mortality rate is a key endpoint that directly measures the safety profile of substances in toxicity studies.