Prompted by these observations, an animal experiment using rats was esigned to
test this hypothesis. Thirty four female Sprague-Dawley Rats were divided into five
groups and given Remington Diet for three days to enhance the uptake of
+I.
Sased
on previous rat experiments, varying degrees of thyroid damage were produced by
giving these groups of nats 0, 10, 20, 50 and 100 uc of madioiodine by intraperitoneal
injection. The thyroids of these animals were subjected to in vivo countifhg at 2%
hours in order to determine the dose of radiation delivered to the thyroid.
Five weeks
were allowed to pass at which time all radioiodine disappeared from the
rats were then bred, and separately caged.
The number of offspring in each
oids.
litter
All
and the individual body weights of the individuals in each litter were recarded. When
the offspring reached approximately 100 days of age, they were given a trabe dose of
131] and 24 hours later were sacrificed. An effort was made to kill large mubers of
animals at the same time so that any variations in the type of observationB would be
kept to a minimm. Thyroids were meticulously dissected out, wej
on aj Roller
Smith torsion balance and then related to the body weight. The
I uptake in the
gland was measured.
each litter.
The original female rats were rebred following the
wenning of
Unfortunately, not all normal control rats conceived readily nor prodhced large
litters. However, when the radiated animals were arranged in order of micfo rd
uptake in the gland, there was in general
a diminishing rate of conceptic and size of
litters with heavier doses of radiation ond
only
so
faveeckofollatane Lalo
was only five weeks following
“°"I,
of time.
Most of
radiated
1 became preprent at the firet beeing which
The 34 animals produced 233 living
yong in the fir
mating, but in a total of 5 matings only a total of 447 were produced.
opt of the
animals conceived at the second mating at 22 weeks except animals in the
tho most heavil
radiated groups. Only 4 of the 12 in these 2 groups became pregnanc and 3{of these
litters were very small.
On numerous occasions rats appeared to be pregnant
following
breeding, but did not produce viable offspring. The incidence of stillbi
post partum deaths could not be determined because of suspected canabalism
Ss or early
All breeding animals were permitted to survive for 14 months and throagh
S litters.
At_the conclusion of the experiment, the breeding females were given a trafe dose of
I along with a small amount of tritiated thymidine before they wre
thyroids were dissected and weighed.
sacfificed.
The
When a destructive dose of 1S1I is given, thyroid function usually gradually
diminishes, depending on the size of the dose.
It is assumed therefore
that thyroid
function in these mother rats was better in those who received the smaller|doses and
that function should be better during the earlier matings. This appears t@ be the case
here although the numbers of animals in the experiment are small. At the gonclusion
of the experiments, the thyroids of the animls which received the
i doses of 131
were entirely replaced by white scar tissue. There was practically no
uptake in
these animals except in three that were found on gross dissection to le 4 smal)
surviving nodule of thyroid tissue in the area that had been the center of]the isthmus.
These 3 animals were the only ones of those in the higher dose range that gonceived
beyond the first ar seggnd litter. These animals had actually received 19]to 28 uc of
the original dose of
I in their glands. Animals which retained 7 to 15fuc similarly
had only two conceptions beyond the second breeding. Animals which receivdd 2. to
2.8 uc and 3.3 to 5.4 uc for the most part had rather full litters through|the secon
mating, but thereafter conceived poorly.