Even at the most basic molecular level sex matters---and it's not just about hormones. Did you know that muscle stem cells from female mice regenerate new muscle faster than cells from male mice? And cells from male and female mice respond to stress differently. Yet most researchers who use basic cell cultures in their work do not even identify the sex of the cells they use.
We already know that this lack of sex identification can have serious consequences when we study new therapeutics. Most adverse drug effects reported occur in female humans! Since most basic drug studies start with cell cultures, shouldn't we be comparing the two sets of cells at the start of the "experiment" before it reaches humans??? It certainly would be cheaper and may prevent serious consequences once the drug is used in humans!
At first, it is easy to blame hormones for the differences but researchers have found that hormones may not always be the culprit. The way a cell metabolizes its food (energy) may be different by sex and other biologic functions could be affected by sex. A recent commentary by Elizabeth Pollitzer explores this issue and makes a plea for researchers to include the sex in their publications on all studies--cellular, animal and human.