ACUTE RADIATION EFFECTS ON MAN
by Bond et al. (1961).
157
Shortly after exposure the number of DNA-
synthesizing cells decreased; it then rose to above normal, reaching a peak
around days 8-10, after whichit fell again and rose to a second peak above
normal around days 35-40 (Fig. 3). Similar studies were also made in
irradiated dogs; immediately after exposure there was a sharp drop in the
number of DNA-synthesizing cells, followed by an increase. This increase
was much more pronounced in dogs that had been partially shielded or had
received only unilateral irradiation than in dogs exposed to uniform radia-
tion. The function of these cells is not clear; the only thing we know about
them is that they synthesize DNA, which is a prerequisite for cell replica-
tion. This should be reason enough to study these cells further, since the
survival of patients suffering from radiation injury is dependent upon cell
regeneration.
A moredirect approachis to estimate the capacity of the remaining bone
marrow cells to synthesize DNA.
This can be done by determining the
percentageof a cell line that is labelled after in vitro incubation with ®=HTDR.
Fliedneret al. (unpublished observation) have recently used this technique to
study changes in rat bone marrow during the first few hours after exposure
to 500-1500 r. Both in the red cell and the white cell precursors aninitial
rise in labelling percentage was noted, rapidly followed by a marked decline
Studies over longer time intervals are clearly needed.
It would be reasonable
to expect that cell regeneration would be preceded by a return to the normal
labelling percentage, or even a rise above it. With a sufficient amount of
3HTDRof high specific activity and a fast film emulsion, such thymidine
uptake tests should be ready for evaluation after a few days’ exposure and
might thus becomeclinically useful if the above supposition should prove
to be correct.
The laboratory tests that have been discussed so far all require special
skills or equipment. In addition, all the studies described need to be
extended and substantiated before they can be considered of practical value
in prognosis. As yet the most useful laboratory procedure for evaluating
the status of irradiated individuals is serial blood counts. Blood counts
are indispensable in the clinical management of such cases and give some
idea of later developments at a relatively early stage. The magnitude of the
initial lymphocyte depression is an indication of the severity of exposure.
In dogs the rapidity of the decrease in total white count correlates well with
the lethality (Cronkite & Bond, 1960). A similar relationship exists in
man. Leucocyte counts around 500 per mm®* were found as early as one
day after the atomic bomb explosions in Japan in persons who were close
to the hypocentre (Le Roy, 1950). It will also be apparent from Fig. 4
that the white cell counts of the Yugoslav patients fell more rapidly and
more severely than those of the patients injured in the Y-12 accident who
received a smaller dose. Quantitative comparisons are difficult to make,
however, because the counts were made by different laboratories.