ACUTE RADIATION EFFECTS ON MAN
153
specimens by Kretchmar (1959) with the more precise but time-consuming
technique of column chromatography confirmed the results of Rubiniet al.
The source of the excess BAJBA excreted by the heavily irradiated is not
clear. It is possible that it originates from the breakdown of DNAderived
from destroyed cell nuclei, but it is equally possible that thymine-containing
molecules which were destined for DNA-synthesis are shunted into a catabolic pathway as a result of radiation-induced inhibition of DNA-synthesis.
This problem can be approached experimentally.
Whatever the mechanism
of increased BAIBA excretion after irradiation, however, it should be
realized that excess BAIBA excretionis far from being specific for radiation
injury. Increased urinary BAIBA output has been reported in bacterial
infections, in chronic leukaemia,in liver disease, and following surgery and
short periods of starvation. The last-mentioned finding may be pertinent
since irradiated patients may have severe nausea and vomiting producing a
short period of relative starvation. Some persons normally have a high
BAIBA excretion; this is an hereditary trait. A number of studies in
different laboratories and with differing techniques (reviewed by Killmann et
al., 1961 b) indicate that in a Caucasoid population, 10-1594 normally excrete
more than 400 uM of BAIBAper 24 hours. In other races this percentage
is even higher. The high BAIBA excretion in these so-called “normal high
excretors” appears to be constant with time.
From whathasbeensaidit will be obvious that data on BAIBA excretion
following acute exposure to ionizing radiation must be evaluated with
considerable caution. Low values during the first week after exposure
probably indicate that the exposure has becn low and that the prognosis is
good, but more data are needed. In contrast, elevated values do not
necessarily indicate heavy exposure, since high excretion may have many
causes Other than radiation injury.
In such cases pre-exposure determina-
tions would be of considerable help.
In summary, determinations of urinary BAIBA excretion are potentially
useful as a biological dosimeter of radiation.! Much experimental work
on the constancy and dose-dependence of BAIBA excretion is needed,
however, before the importance of this parameter can be appraised.
Mitotic Index
The bone marrow aplasia that is caused by radiation is due to cell
destruction and mitotic inhibition. The proliferative activity of a tissue is
often estimated by the mitotic index(I,,), i-e., the fraction of all cells which
are in mitosis at any time:
=
3
vs
mm
wi
out
tale
ri
1 During the meeting, Dr Hempeimann mentioned that BAIBA-excretion had been increased in the
fatally irradiated individual at Los Alamos, December 31, 1958, and Dr Andrews referred to studies by
Dr Kretchmar in Oak Ridge which showed a massive increase in BAIBA output in leukaemic patients after
therapeutic whole-body irradiation.