PATHOLOGIC EFFECTS OF CHRONIC 
^°Sr INGESTION IN MINIATURE SWINE 
H. A. Ragan, P. L. Hackett, B. J. McClanahan and W. J. Clarke' 
Over 700 female miniature swine, extending through 
three generations, have been exposed to daily feedings 
of from 1 to 3100 fiCi ""Sr. In addition, there were 
200 untreated, female, littermate controls. Body bur- 
dens of ""Sr reached approximately 7.5 and 10 times 
the daily intake in the original and Fi-Fo generations, 
respectively, with the soft tissue radiation doses ^ 
1/1,000 that for bone. 
Although radiation osteitis was a common finding, 
only 7 pigs had evidence of 11 individual bone tumors, 
with >80% occurring in the skull. These tumors were 
classified morphologically as osteosarcomas (73%) or 
giant cell tumors (27%). 
The most consistent disorders associated with chronic 
""Sr feeding were eifects on the hematopoietic system. 
At levels >25 MCi/day (5,000-20,000 rads accumu- 
lated skeletal doses), there occurred a progressive de- 
crease in circulating leukocytes and platelets, and a pre- 
cipitous, terminal fall in erythrocytes, with many of 
these animals dying of hemorrhagic diatheses. A second 
syndrome, observed particularly in animals at the 125 
and 625 ^tCi/day levels, was a broad spectrum of mye- 
loproliferation ranging from myeloid metaplasia to 
frank blast cell leukemia. 
INTRODUCTION** 
In attempting to define the potential hazards 
of ^''Sr to man, there have been many animal 
studies performed over the past 30 years, utiliz- 
ing numerous animal models to evaluate the 
biologic damage. Interest in ^"Sr arose because 
of its relative abundance as a long-lived (28 
year radioactive half -life) radionuclide present 
in nuclear fallout. ^°Sr, by emission of an 0.54 
MeV beta particle, decays to ^°Y, which in turn 
emits a 2.27 MeV beta particle with a 64 hour 
radioactive half-life. Since strontium is metab- 
olized in a manner similar to calcium, it is de- 
posited primarily in, and excreted slowly from, 
the skeleton, thereby producing relatively high 
* Biology Department, Battelle, Pacific Northwest Laboratories 
Richland, Washington 99352. 
** This work supported under Contract AT (45-1) -1830 with the 
U. S. Atomic Energy Commission. 
radiation dose rates to osseous tissue and bone 
marrow. 
The majority of animal studies have utilized 
single or multiple injections of radioactive 
strontium in rodents or dogs. This mode of ad- 
ministration, as opposed to ingestion, results in 
uneven skeletal distribution, producing areas of 
high strontium concentrations and severe focal 
bone damage. Because of their small bone mass, 
rodents lose approximately 70 % of the ""Sr ra- 
diation energy from bone.^ This energy loss in 
man and miniature swine was found to be 
12 %i and 13%,^ respectively. 
To simulate the most probable route of ^°Sr 
entry and its distribution in man, our labora- 
tory initiated a study in 1958 using miniature 
swine exposed to ^^Sr by daily ingestion. This 
species was selected because it is an omnivore 
with a mature weight and bone mass similar to 
man, and an estimated life span in excess of 12 
years.^ This study, coupled with a similar expe- 
riment at the University of California at Davis 
using beagle dogs, was designed to supplement 
the rodent studies and provide the data neces- 
sary for extrapolation of the biohazards of ^•'Sr 
to man. 
MATERIALS AND METHODS 
The experimental design for this study has 
been previously reported in detail.* Briefly, the 
original generation female Pitman-Moore mini- 
ature swine were started on a daily ^<*Sr feed- 
ing regimen at 9 months of age and subse- 
quently bred to a control boar to produce the Fl 
generation, which in turn produced the F2 gen- 
eration. Thus, the Fl and F2 offspring were ex- 
posed to ''^'Sr in utero, from their dam's milk, 
and then by daily feeding. Weaning was accom- 
plished at 6 weeks of age, at which time the ani- 
mals were started on daily ^^Sr feeding at 1/4 
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