Re: mice v. elephants

["DAVE GILMORE" <DGILMORE@navajo.astate.edu>]

Here's an illustration with numbers:  Suppose a tissue can remove 99.9
percent of the molecular lesions it experiences and that 10 mrad causes
1000 lesions.  At 10 mrad there are 1000 lesions, but 999 are repaired,
leaving only 1 lesion that might go on to produce cancer.  At 20 mrad there
are 2000 lesions, but 1998 are repaired, leaving 2 lesions that might
produce cancer.  And so on.  If only 1996 are repaired at 2 mrad (leaving 4
lesions that might produce cancer), then I can see a basis for nonlinearity.

I'm not a _radio_biologist, but here's another consideration: enzyme 
induction.  The exposure to 10 mrad may activate the cellular stress 
response which increases the numbers of repair enzymes.  A subsequent 
exposure to 10 or 20 mrad would then result in more efficient repair 
and less damage.  This would be the basis for the hormesis effect: a 
cellular response to low level damage.  Makes modeling even worse I 
imagine.

David F. Gilmore
Assistant Professor of Environmental Biology    0  0 
P.O. Box 599, Dept. of Biological Sciences       __    "have a day" 
Arkansas State University 
State University, AR 72467
dgilmore@navajo.astate.edu
ph  501-972-3082    fax 501-972-2638