Researchers at the National Institute on Aging in Baltimore have tacked one of the key questions in their field: Do reproductive organs age in the same way as other body organs? The question is especially important since more women in developed countries are postponing childbirth until later in life.

The researchers found that aging does lead to large changes in the gene activity in the ovaries of mice, but only limited changes in testes, according to the study published in BMC Biology. Indeed, the study showed that ovaries age in a much different way from testes. Some of the aging effects were reversed when the mice were put on a lifespan-extending calorie-restricted diet, but the changes in somatic organs were widespread, while gonad-specific genes were only slightly impacted.

The researchers suggest that changes in ovaries could be influenced by the way the tissue composition of ovaries changes as females age and ovulation ceases.

The researchers also found that calorie restriction in females reduced the expression of genes involved in metabolism and follicle growth, which seems to be in line with the consensus belief that calorie restriction causes a reduction in energy for reproduction and an increase in general body maintenance and repair. However, male mice on the same diet did not appear to sacrifice reproductive function, suggesting an evolutionary difference between males and females when confronting a food shortage.

"This poses an interesting question," the researchers write. "Is an additional explanation required to account for the difference between males and females in terms of evolutionary basis of aging? For example, it is conceivable that under (calorie restriction) conditions a need to shut down reproductive function is much greater in females than in males, because the lives of both mother and fetus are at a risk in pregnant females? Some theories of aging may need to be reexamined in the light of new data reported in this paper."