In 2014, The National Institutes of Health (NIH) made a bold statement: essentially, future studies of animals and cells would have to take place in both sexes, or risk losing funding. This move has not been without criticism, time and cost being the two issues most often raised. However, there are some worries that sex differences in preclinical data may not matter as much as predicted.
Why Make The Change?
Historically, preclinical testing has been performed only in male animals. However, diseases have both different rates and symptoms in males in females. In humans, women and men have different heart attack symptoms, and as a result, women die from heart attacks more often. This is due in part to differences in anatomy. Males have larger right ventricles, hypothesized to lead to more detectable symptoms. Furthermore, there is some debate as to whether or not hormones play a role in some disease states. Studying animals, cells, and tissues from only one sex does not take into account these anatomical and physiological differences.
While this sounds like a good idea on paper, some researchers have voiced complaints. These complaints are usually related to resources. Being required to include both sexes automatically doubles a sample size. On a more practical level, there is also an issue of animal estrous cycles. Although it is possible to test animals with synchronized estrous cycles, this is an additional, time-consuming step. As a result, animals may be going through different phases of the estrous cycle, complicating measures.
Will It Make A Difference?
Several preclinical studies have already discovered relevant sex differences. Knowing that there is a sex-related biological component to certain diseases can improve both diagnosis and therapeutics. There are also benefits to knowing that there are no differences between sexes; for example, a drug that works the same in both sexes. Studying both males and females is proving to be worth additional time and effort.
Editor: Summer Lee