-4A small trace dose of 1311 in addition to the tritiated thymidine fhas been
given to the animals four hours before sacrifice. Autoraciographs promptly
prepared from microscopic sections after the - ‘oval of the thyroid serbe to
identify any local areas in the gland where 1317 utilization ts differant fron
the rest of the gland.
Because the half life of 131t is much shorter than the
fi in tritiated thymidine, the 1311 disappears from the micrescopic sedtions
more rapidly and is sone after tvo or three months. lew cutcradiozraphp then
prepared from other microsecpic sections, adjacent to thcse used to dembnstrete
317 show only the location of the 311-thymidine.
Subsequent compariso
two autoradiographs from microscopic sections, which are almost identi
reveal two types Of information about the same cluster of cells which
both preperations.
We have several larve grours of rats whose thyroids have been i
with various doses cf 1312 which cause relatively little or no obvious
of thyroid tissue, these doses ranging from 0 to 40 microcuries of +31I
varying degrees of uptake depending on the experimental design.
Each
individually identified and its uptake determined for future refererce.
these animals were given an antithyroid drug chronically following tne
produce hyperplasia. Others are stimulated acutely only for a few days
sacrifice to see how much mitotic activity could be produced. Still ot
remained unstitulated, except for the intrinsic stizwlus which the
ani
received as a result of diminution in hormone output by its own radiat
The rats of this strein (Charles River strain, since 1947) very rarely
spontanecusly. These animals have been observed up to two years.
of the
abkpear in
Bestruction
with
ahi
wes
some: of
PS+I to
before
Although most animals in the current series have been sacrificerd
be described.
Even though neoplasms are induced by goitrezgens alone,
produced soone> and mere readily if relatively small amounts of 131I
given.
hafe first been
tt has been suspected that the age of the animal at the time 1311 Is given is
ixportant in the frequency end cpeed with which neoplasms are produced.] In previous
experiments with juvenile rats approaching sexual maturation, the ccecurfence of
necplases following 131] treatment and chronic administration of antith}roid
substances was fairly infreguent.
In fact, the yield of rats with necp
with
which to work was discouragingly low. A large series of weanling rets $5 to 85 gms
has ylelced a somewhat better occurence of neoplasms. These, Like previous animals,
were given Remingtcn diet to enhance the uptake and make hyperplasic thyroids. In
these. animals, the uptake of the dose was 25 to 40%.
We are now well aleng in still another series in which very young |
used by acquiring creenant females and injecting the litters with 1S1I
were reasonably sure of the healthy survivors (15 days; 39 to 40 gn; nojRemington
diet)
In this series, the uptake was about 10%.
Animals were sacrificéd
in
hours (to determine averace thyroid weights and to measure actual uptak@ to check
invivo counting), days, «ewexs and months up to almost two years. The
several hundred animals in these series ranged from 500 rads to 40,000
fac
a few considerably higher. These ranges have been explored in order tojfind the
level at which neoplasms wore most readily produced. Obvicusly doses
caused
too much destructicn left cells incapable of replacing themselves. 5S
other
lighter doses were too snall to cause any discernible untoward effects.] In thse
experiments the higher doses of about 20,000 rads o> more have produced|consicerable