From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Sat Aug 24 2002 - 15:29:28 MDT
On Sat, 24 Aug 2002, Joao Magalhaes wrote:
> The best explanation I know is hormesis. Hormesis is
> the name given to the stimulatory effects caused by low levels of
> potentially toxic agents. Basically, if you stress an organism -- with, for
> example, radiation -- it will stimulate its defences and it will thus be
> stronger afterwards.
I'm afraid I have to agree with Joao, and not with Anders in spite of the
nice mathematical model. [Quick everyone, mark Aug 24 2002 in your books
as a day Anders may have been wrong -- it may be another decade before we
see a similar event.]
Hormesis has a very reasonable basis in gene and protein expression.
One has a set of defenses against radiation, heat shock, toxins, etc.
The expression of these defense genes is activated by a set of "triggers".
But once activated, the mRNA gets transcribed and the proteins get translated
in order to provide the defense against the damaging agent. Presumably
these defenses have evolved some "anticipation" of future assaults.
E.g. continued radiation exposure when the Earth's magnetic field
flips, or continued UV exposure during the summer months, or continued
consumption of quasi-toxic foods (that are abundant in specific seasons).
So the defenses don't immediately turn-off when the triggers go away.
Normally having the defenses in place would be a good thing the next
time a trigger event occurs (e.g. UV exposure on the next sunny day).
The defenses provide better maintenance of your DNA and proteins
and thus extend longevity. We need a much better understanding
of the minimal trigger effects and the length of time the defenses
remain active. In that environment we could produce minimally
damaging triggers and reap the benefits of the activated defenses.
Some recent PubMed references:
Johnson TE, et al
Longevity genes in the nematode Caenorhabditis elegans also mediate increased resistance
to stress and prevent disease.
J Inherit Metab Dis. 2002 May;25(3):197-206.
http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12137228&dopt=Abstract
Cypser JR, Johnson TE.
Multiple stressors in Caenorhabditis elegans induce stress hormesis and extended longevity.
J Gerontol A Biol Sci Med Sci. 2002 Mar;57(3):B109-14.
http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11867647&dopt=Abstract
Robert
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