EMBARGOED FOR RELEASE UNTIL OCTOBER 9, 2006
Contact:
Christine Guilfoy
Office: (301) 634-7253
cguilfoy@the-aps.org
Everybody Dance! (The
Energy You Use Won’t Shorten Your Life)
virginia Beach,
Va (October 9, 2006) – The theory that animals die when they’ve
expended their lifetime allotment of energy may be reaching the end of its
own life, according to a study presented at The American Physiological
Society conference, Comparative Physiology 2006. However, the
longitudinal study leaves open a newer form of the theory -- that
antioxidants help prolong life by limiting the damage that oxidative stress
can cause to cells.
“These findings join a growing body of evidence
suggesting that lifetime energy expenditure per se does not underlie
senescence,” wrote Lobke Vaanholt, Serge Daan, Theodore Garland Jr. and G.
Henk Visser in a summary of the study presented at Comparative Physiology
2006: Integrating Diversity. Vaanholt, Daan and Visser are from the
University of Groningen, The Netherlands. Garland is from the University of
California at Riverside. The conference takes place Oct. 8-11 in Virginia
Beach, Virginia.
A bit of background: One early theory, the rate of
living theory, held that every organism has a set amount of energy to
expend. Once the animal expended that number of calories, the grim reaper
was on the doorstep. Over the years, the theory has become much more
sophisticated, but metabolic rate and aging have remained linked, Vaanholt
explained.
Decades ago, physiologists discovered that during
metabolism, oxygen (O2) can split into single oxygen atoms, known
as free radicals. These rogue oxygen atoms can remain on their own or
combine with hydrogen atoms to form reactive oxygen species (ROS), which
wreak havoc with enzymes and proteins and adversely affect cell function.
The faster the metabolism, the more ROS produced, the modern theory goes.
Energy expenditure not the
key
In this study the researchers divided the mice into
three groups of 100 mice each. Two groups were “runner” mice, that is, mice
that loved to run on the running wheels placed in their cages. One group of
runner mice had access to running wheels, but the second group of runner
mice did not. The third group consisted of regular laboratory mice that had
a running wheel.
Vaanholt’s team followed 60 mice from each of the three
groups throughout their natural lives, nearly three years. They measured
wheel running activity and took periodic measurements of body mass.
They found:
-
Runner mice that had access to a wheel expended 25% more
energy over the course of their lives compared to both the runner group
that did not have a wheel and the regular mice
-
Both groups of mice bred for running, one group with the
wheel and one without, lived about 90 days less than the regular mice
-
The regular (non-runner) mice lived longest, 826 days,
compared to the runners with a wheel, 735 days and runners without a
wheel, 725 days
The rate of living theory would have predicted that the
running group that expended more energy would die earlier than the two
groups that did not, Vaanholt said. This was not the case. There was no
difference in life span between the two runner groups, even though one
expended more energy.
In addition, the rate of living theory would have
predicted that the runner mice without the wheel and the normal mice would
live approximately the same life span because there was no difference in
energy expenditure between the two. This was not the case. The runner mice
without the wheel died sooner.
“The shorter life span cannot, therefore, be explained
by a difference in metabolism,” Vaanholt concluded. “There must be something
else going on that causes these animals to age and die.”
More activity = higher
metabolism = more antioxidants?
A second portion of the experiment involved the
remaining 40 mice in each of the three groups. The researchers periodically
used mice from these three groups to determine energy expenditure, body
composition and the antioxidant enzyme levels and protein synthesis in the
heart and liver tissues. The researchers selected mice, at two months, 10
months, 18 months and 26 months for this analysis.
Since the group of runner mice that expended more
energy lived as long as the runner group that was less active, the
researchers tested whether there was a difference in antioxidant production
between the two groups. Since metabolic rate rises with activity level and
oxidative stress rises with metabolic rate, perhaps the runner mice that
expended more energy also produced more antioxidants, the body’s defense
against oxidative stress, Vaanholt said.
However, the study found no difference in antioxidant
levels among the groups, at least in the heart and the liver, regardless of
energy expenditure. “We would have expected additional antioxidants among
the group of mice that expended 25% more energy, but that was not the case,”
Vaanholt said.
“We can conclude that the presence of a running wheel
resulted in increased daily energy expenditure without a change in lifespan
or in antioxidant enzyme activity in the heart and liver,” Vaanholt
explained.
Further research must examine whether tissues in other
areas of the body generated additional antioxidants to help cope with the
increased oxidative stress brought on with increased activity and metabolic
rate, she said. In addition, future studies may examine whether other
mechanisms are at work, including whether activity level is connected to DNA
repair rates.
* * *
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