When an antithyroid drug was added to the drinking water two monthsfafter a
small dose of I131 was given, there was a much greater rise in the incidence
of cells forming DNA than when such a stimulus was applied to non-radiated
controls. This propensity to over-respond with DNA formation on st4m
occurred even though there was no obvious microscopic change in the [cells
before the stimulus was applied.
‘This response occurred long after/the 1131
was gone, but while the gland as a whole still had a capacity to e«
under the antithyroid stimulus.
We had known from our earlier experiments that after giving a «
1131 which was insufficient to produce recognizable microscopic changes in
the thyroid, a latent effect was produced that later resulted in layge
abnormal nuclear forms when the st
us of thiouracil was applied.
had known from earlier experiments{3) that soon after an intermediate
(S=20 yc) dose of Y31 had been given, the thyroid could be induced to
hypertrophy, as does the normal gland when an antithyroid drug is agm
istered,
However, several months later and long efter all the 11231 fhad
disappeared from the gland, this ability of the gland to hypertrophy
gradually lost. It seemed in the more recent experiments that it was
those glands which still have a capacity to enlarge that develop
normal nuclear forms. It was these nuclear forms that had exceesivd DNA.
More attention in the manuscript has been placed on the rapid ¢
under the influence of iodine deficiency displayed a high degree of [D
syrthesis in preparation for cell division.
corrected, DNA synthesis promptly declined.
When the iodine deficis
The manuscript has beer
has been re-titled "DNA Synthesis in the Radiated and Stimulated
A Study of Nuclear Changes at the Time of Neoplasm Formation Following {151
Since we know that neoplasms sometimes develop in rat thyroids
ing small doses of 1131, and since the frequency of the occurrence
tumors is enhanced by giving thiouracil, it seemed appropriate to
tritiated thymidine technique to observe the behavior of thyroid nudlei as
tumors are beginning to develop.
We are interested here in the preparation for mitotic activity as
ky uptake of tritiated thymidine.
ested
After a brief period of iodine deficient diet to insure a high|uptake
of I131, » large series of approximately 100 rats were injected wit
either
5, 10, or 50 ue of r131,
Others received none.
of some of the rats was begun.
Following the rl3lland a
This series of rats were pubescent
weighed 120 to 140 grams when r131 was given.
Another large serieslof rats
which were somewhat younger and weighed from 8&0 to 100 grams were p
some months following the above series. Representatives of the varjous
groups were killed soon after 1131 was given to determine the a
of 1131 in the average gland.
Rats representing the various expe
groups were subdivided following I231 so that some received thiour