Old mice live longer when given young ovaries. (Lease on Life).

Here's one more reason to be obsessed with reproduction. A new study with aging mice suggests that the reproductive system plays a role in determining how long animals live.

James Carey and his colleagues at the University of California, Davis transplanted ovaries from 2-month-old mice into mice whose ovaries had been removed a few weeks after birth. The procedure extended some of the animals' lives. It proved equivalent to enabling a 50-year-old woman to live to age 92 instead of 80, her current life expectancy, Carey explains.

"The gonads are communicating with the body to stay young for reproduction," he says.

In the June Aging Cell, Carey and his coworkers describe their experiments with five groups of female mice. One group retained its original ovaries. In four groups, the researchers removed the animals' ovaries when the mice were only 3 weeks old and thumbnail size. Of those mice, one group remained without ovaries. The researchers transplanted 2-month-old ovaries into the other groups when the animals reached 5, 8, or 11 months of age.

Carey compared the remaining life expectancies of each group when the mice were 11 months old, an age at which they're normally no longer capable of reproduction. The mouse group that had their original ovaries had about a month more to live than the group that had their ovaries removed and not replaced.

A mouse's age when it received its ovary transplant influenced its life expectancy. The mice that received new ovaries at 11 months of age benefited most, living 60 percent longer than those that had their ovaries removed but not replaced and 40 percent longer than those still with their original ovaries.

The mice that had received ovaries at 8 months had 24 percent longer to live than the mice with no ovaries did, and the group that received ovaries at 5 months lived about 7 percent longer.

"Clearly, there's some kind of cross talk between the reproductive organs and the soma [body] of the animal," says Leonard Guarente of the Massachusetts Institute of Technology, who investigates the genetic factors of longevity.

The ovary-transplant process kills many mouse egg cells. So, it's not clear whether the differences seen in the experiment result directly from the transplanted ovaries or indirectly from the reduction in eggs. In previous research, the nematode Caenorhabditis elegans lived 60 percent longer than normal if its germ cells--eggs or sperm--were destroyed, Cynthia Kenyon of the University of California, San Francisco reported in the Jan. 18, 2002 Science.

Kenyon cautions that the germ-cell connection to longevity she found in nematodes may not apply to mice. "When we understand both systems better," she says, "we can find out whether it's a coincidence or whether there's some evolutionarily conserved mechanism operating in the two animals."

In time, Carey speculates, the research could lead to life-prolonging interventions that exploit whatever signal helps keep the mice youthful.

"Reproduction is the cardinal function in life," Carey says. "It denies logic to believe that it isn't central to aging."