Re: Dr. Raabe's Work

["Otto G. Raabe" <ograabe@ucdavis.edu>]

November 11, 1997
Davis, CA

Concerning the news report, here is the Abstract of the paper that I
presented on this subject at the San Antonio meeting of the Health Physics
Society. The key to understanding this study is that it involved the acute
irradiation of developing sperm at high dose rate at the critical time when
the spermatogonia are most sensitive to radiation exposure. We do not know
whether the effect that we observed is detrimental.

HEALTH PHYSICS IMPLICATIONS OF STUDIES OF BRIEF IRRADIATION OF REPRODUCTIVE
CELLS UTILIZING THE MOUSE CHIMERA ASSAY.*  O.G. Raabe,1 T. Straume2 and
L.M. Wiley1
(1Institute of Toxicology and Environmental Health, University of
California, Davis, CA 95616;
2Lawrence Livermore National Laboratory, Livermore, CA 94550)

In previous studies the mouse chimera assay has shown sensitive responses
to irradiation by both male and female reproductive germ cells. Chimeras
are made with 4-cell preimplantation embryos and cultured for 30 hours to
about 2 to 3 cell cycles. Cultured chimeras are dissociated to count the
cells from each partner embryo and these cell numbers are expressed as a
"proliferation ratio" (PR, number of cells from the affected embryo divided
by the total number of cells in the chimera). A PR=0.5 occurs when both
embryos exhibit similar proliferation rates, while a PR significantly less
than 0.5 indicates a proliferation disadvantage for affected embryo cells.
Significant decreases in PR have been observed for paternal F0 irradiation
with 137Cs gamma rays at particular times prior to F1 conception for acute
absorbed doses from 0.01 Gy to 1 Gy. Similar results have been observed for
maternal F0 irradiation for acute 137Cs gamma ray doses of about 0.1 Gy and
for brief irradiation with injected tritiated thymidine for an absorbed
dose of 0.2 Gy, indicating a cell nucleus target. Recent studies have found
significant decreases in PR for F2 embryos obtained from F1 males that were
conceived 6 to 7 weeks after paternal F0 irradiation with an acute dose of
1 Gy of 137Cs gaama rays showing heritable mutations. These results may be
relevant to the finding in Great Britain of increased incidence of leukemia
and non-Hodgkin's lymphoma in children of fathers employed at the
Sellafield nuclear reprocessing plant. That no increased leukemia in
offspring has been found for the Japanese atomic bomb survivors may be
explained by the need to consider only irradiation during the sensitive
part of spermatogenesis. Germ cell irradiation during critical periods
prior to conception may require special radiation safety considerations.

*(This work was supported by USPHS NIH Grant R01 ES06516, L.M. Wiley, P.I.)


		*****************************************************
		Prof. Otto G. Raabe, Ph.D., CHP
                [President, Health Physics Society, 1997-1998]
		Institute of Toxicology & Environmental Health (ITEH)
		     (Street address: Old Davis Road)
		University of California, Davis, CA 95616
		Phone: 530-752-7754     FAX: 530-758-6140
		E-Mail: ograabe@ucdavis.edu
		******************************************************