Re: Radiation - net benefit or detriment?

["Bjorn Cedervall" <bcradsafers@hotmail.com>]

>There is an article (probably Mutation Research and for a mammal - cannot 
>remember which - maybe humans) where the number of point mutations in 
>somatic cells are shown as a function of age.
---
Several people asked me about the underlying reference. It was easy to find 
via Medline (see the abstract below). Please observe that there are several 
steps involved - induction -> repair processes -> final result (for instance 
chromosomal aberrations).

Bjorn Cedervall    bcradsafers@hotmail.com
------------------------------------------
"Measurement of spontaneous and X-irradiation-induced 
6-thioguanine-resistant human blood lymphocytes using a T-cell cloning 
technique.

Vijayalaxmi, Evans HJ, Mutat Res. 1984 Jan;125(1):87-94.

Lymphocytes separated from human peripheral blood were cultured in vitro, in 
the presence of 6-thioguanine (TG), to select and clone rare TG-resistant 
(TGr) cells present in the circulation in vivo. The incidence of such TGr 
cells ranged from 0.83 X 10(-5) to 2.53 X 10(-5) (mean 1.48 X 10(-5) ) in 
healthy individuals aged between 19 and 79 years; did not differ between 
males and females; but increased significantly with age at a rate of 2.4 
cells/10(7) lymphocytes/year.

Exposure of lymphocytes (G0) in vitro to X-ray doses of up to 200 rad 
resulted in a dose-dependent increase in TGr cell frequencies. The rates of 
increase were approximately in proportion to the square of the dose and 
these rates were closely similar to those obtained in cultured skin 
fibroblasts and suggest that the bulk of these mutations are a consequence 
of chromosome structural aberrations. The cloned TGr cells are considered to 
be HPRT- mutants and the mutation frequencies in lymphocytes determined 
using this cloning technique were compared with the variant frequencies 
obtained in earlier experiments utilising an autoradiographic technique to 
detect azaguanine-resistant (AGr) variant cells. Mutation frequencies with 
the cloning technique were 10-20-fold lower than variant frequencies with 
the autoradiographic method.

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