PRELIMINARY DATA ON CHROMOSOME ABERRATIONS 
IN SWINE AND HUMAN LEUKOCYTES WITH A BRIEF REVIEW 
OF FACTORS AFFECTING THEIR OBSERVED FREQUENCY 
F. P. Hungate and B. J. McClanahan* 
Preliminary results from a study of relative sensi- 
tivities of porcine and human leukocyte chromosomes 
to X-rays suggest that aberration frequencies are 
slightly greater in human cells. Data are also reported 
for '"Sr-'"'Y irradiation of swine leukocytes, but com- 
parable results of tests with human cells are not yet 
available. 
Radiation dose and dose rate, quality of radiation as 
measured by linear energy transfer, and the modifying 
factors, oxygen and virus, are briefly discussed for their 
j general role in modifying the frequency of aberrations 
observed following radiation exposure. 
INTRODUCTION** 
This paper discusses the effects on the cell's 
information system which are important in 
altering survival of somatic cells, i.e., effects on 
the chromosomes. To introduce this topic we will 
describe some preliminary results from a chro- 
mosome breakage study in progress in our 
laboratory. 
In an ongoing study of effects on miniature 
swine of daily ingestion of ^''Sr, a study to be 
described in more detail later in this session by 
Dr. Ragan, we have consistently failed to ob- 
serve chromosome aberrations in frequencies 
appreciably above those observed in unirradi- 
ated controls, even with cummulative doses cal- 
culated to be in excess of 10-20 K rads. This 
raised the question of the sensitivity of swine 
chromosomes which this study is attempting to 
j answer in terms of the relative sensitivity of 
swine and human chromosomes. 
METHODS 
To compare the relative radiosensitivities of 
swine and human chromosomes, peripheral 
* Battelle, Pacific Northwest Laboratories, Richland, Washington 
I 99352. 
I ** This work was performed under the United States Atomic 
Energy Commission Contract AT (45-1) -1830. 
blood samples were obtained from unexposed 
control animals and from a female human vol- 
unteer. Leukocyte cultures were exposed to 
X-rays or to radiations from ^°Sr-^°Y. 
Samples of heparinized whole blood, ob- 
tained under sterile conditions from female Pit- 
man Moore swine and a female human volun- 
teer, were allowed to sediment in the collection 
syringe at room temperature for approximately 
one hour. One milliliter of the plasma was 
placed in sterile plastic culture bottles and ir- 
radiated. Following irradiation, 1 ml of fetal 
calf serum and 5 ml of NCTC109 (Difco) con- 
taining 300 units/ml penicillin-G, 0.3 mg/ml 
streptomycin and phytohemagglutinin-M (Difco) 
were added. The cell culture was then incubated 
at 37° C for 45 hours at which time 0.01 mg 
colchicine was added to arrest mitosis in the 
metaphase stage, and four hours later the cells 
were prepared for observation essentially as de- 
scribed by Moorhead et al.^ The slides were 
quickly blaze dried and stained with 2 % Giemsa 
in phosphate buffer, pH 6.8. Suitable meta- 
phases were photographed under oil immersion. 
A 250 kVp X-ray unit operated at 15 ma and 
with 1 mm copper + 1 mm aluminum filtration 
was used as the radiation source. Air doses 
were determined using Victoreen dosimeters 
and confirmed with LiF thermoluminescent 
dosimeters. The 1 ml plasma volume irradiated 
was contained in a 30 ml plastic culture flask. 
The doses used were 50, 100 and 200 R delivered 
at a constant rate of 11 R/min. 
Beta irradiations were accomplished by mix- 
ing four millicuries of carrier free foSr-^'^Y 
(6.7 mCi/ml 0.01 N HCl) with 100 ml of the 
culture medium previously described and add- 
ing appropriate amounts of this solution to cell 
suspensions containing 1 ml of test plasma and 
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