From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Tue Mar 26 2002 - 08:44:13 MST
On Mon, 25 Mar 2002, spike66new wrote:
> But all else being equal and assuming weight is not an issue, would not
> a lower metabolism lead to a longer life?
At first glance yes. Less free radical damage should result in less
DNA damage. But it turns out there may be some quite explicit control
of the redox levels within cells so external tinkering with the metabolic
rate may be offset by internal compensations. (Less free radical damage
may lead to less production of enzymes to deal with free radical damage
resulting in a similar steady state level of free radical damage.)
> How does that work? Is cell reproduction rate proportional to metabolism?
Not particularly. Eukaryotic cells generally reproduce at a maximal
division rate of once every 24 hours. In practice none of the cells
in your body reproduce that fast. I think stomach cells may turn over
every 3 days or so. Cellular reproduction can be slowed by internal
checkpoints that detect excessive DNA damage, which could in turn
be due to free radical levels. But if tolerance level is relatively
fixed as I outline above, then the only way you are going to change
it is by going in and tinkering with the program in a significant way.
All of the above not withstanding, one of the general mechanisms that
is thought to lead to lifespan extension through caloric restriction
is a reduction in metabolism, exhibiting itself as a slightly decreased
body tempterature, leading to lower free radical production and
increased longevity. But the details of this are still largely
unknown.
Robert
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