ABSTRACT

[Jim Muckerheide <jmuckerheide@delphi.com>]

If anyone gets this paper, please comment/review, and send a copy (electronic
if possible). 
Send an email and I can let you know whether we've already gotten it. Review
anyway.

J Appl Toxicol 2000 Mar-Apr;20(2):103-12 

 Hormesis: an adaptive expectation with emphasis on ionizing radiation. 

 Parsons PA 
 School of Genetics and Human Variation, La Trobe University, Bundoora,
Victoria 3083, Australia.

 Non-linear fitness gradients with maxima between extremes are expected for
any environmental variable to which free-living populations are exposed. For
exceedingly toxic agents, including ionizing radiation, such deviations from
linearity are close to zero exposure and are conventionally called hormesis.
Accordingly, hormesis is an extreme version of the non-linear fitness
gradients for general environmental stresses such as temperature fluctuations,
for which maximum fitness occurs at the moderate temperature fluctuations to
which free-living populations are most commonly exposed. Some metabolic
reserves should occur under moderate temperature stresses because of the need
for pre-adaptation enabling survival during exposure to occasional periods of
more extreme stress, especially at species borders where selection for stress
resistance is likely to be most intense. Because heat shock proteins are
induced by all stresses, adaptation to extreme temperatures should translate
into adaptation to other stresses. Consequently, metabolic reserves from
adaptation to extreme temperatures in the past should translate into
protection from correlated abiotic stresses, especially in human populations
where modern cultural processes are now ameliorating exposure to extreme
stresses. Ambient and man-made radiations of non-catastrophic dimensions
should therefore lead to stress-derived radiation hormesis. Other stresses
can, in principle, be incorporated into this model. Accordingly, evolutionary
and ecological considerations suggest two components of hormesis in relation
to ionizing radiation: background radiation hormesis based upon the background
exposure to which all organisms on earth are subjected; and stress-derived
radiation hormesis. Exposure under stress-derived radiation hormesis is
considerably larger than under background radiation hormesis, so significant
deleterious effects from non-catastrophic radiation normally may be impossible
to detect. Suggestions are provided for testing such postulated deviations
from the commonly assumed linear no-threshold (LNT) hypothesis for the
biological consequences of exposure to radiation. Copyright 2000 John Wiley &
Sons, Ltd.

Thanks.

Regards, Jim
muckerheide@mediaone.net
Radiation, Science, and Health
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