forms and which were tumors whose cells were themselves subjected to the radiation
because the tumor was already present. Probably the former is true in some cases.
Aninal experiments to be described later are designed to explore this issup. The
observations on human tissue described above are reported in the following] publication.
Dobyns, B.M. and Robinsop,, Leon R. III:
with Nuclear Changes in
875-885, 1968.
Deoxyribonucleic Acid Content Asspciated
°~“{-Irradiated Human Thyroids. J. Clin. Endocrin}
& Metab. 23:
Our experimental results in animals suggest that there is a dose rv gk of 151r
which for a time after the radiation is given, neither completely destroys] the function
of the thyroid cell, nor interferes with the capacity of these cells to multiply and
pgresult in a larger gland. After a longer lapse of time and long after
Fhe dose of
I is dissipated, a defect develops in the ability of the radiated c
to divide,
although the capacity to build up DNA in preparation to division still exits. Clinical
observations in the human show that although the subtle danage may be aused to the
thyroid cell, it continues to survive and make thyroid hormone maintaining] the
individual in a euthyroid state. Superfic
y, it may appear that an ideal euthyroid
state is achieved in such a clinical subject. In fact, the euthyroid sta P may persist
for a good many years.
However, we now are seeing at 12, 15 and mre
years after
I
therapy in these human glands, which appeared to have adequate capacity to [manufacture
hormone, ultimately are failing and the individual begins to suffer from
hipo
reasonable assumption the aninal-experiments that the expected
replacement
This has become
from our long term study of these patients.
oidiss
It ib thus a
orma
of thyroid cells is not taking place and explains the ultimate failure of Fhe thyroid.
These observations and hypotheses have led our investigation of the capa
of
irradiated thyroid cells to replicate under a variety of conditions.
The Use of Tritiated
midine to
dy
the Mitotic Activity
in Irradiated
oids
The incorporation of tritiated thymidine into DNA in thyroid nuclei
whs first
Because the cells which are preparing for mitosis incorporate the
nidine avidly
Studied in this laboratory under this grant a little over nine years ago,
proved to be a very useful tool to study in another way the effects of
It has
radiation
just before they divide and because such cells bearing the label can be demonstrated by
radiocautography , this method was adapted to the study of mitosis in tayroif cells which
had been exposed to 13lr, The method for demonstrating DNA synthesis in the rat thyroid
was developed in the course of some experiments designed to test the effec of TSH on
cell division in weanling amd adult rats. One unit of TSH was injected infraperitomeally
into these two groups of rats; 16 hours later tritiated thymidine was givefi to each
animal by the same route. The animals were sacrificed 4 hows later and the thyroids
were quickly removed. They were placed in Carnoy's fixative for rapid fixption and
Microscopic sections prepared. After the sections had been deparafinized,| they were
dipped in photographic emulsion and stored in the dark for various periods]of time.
uently the film was developed and the sections beneath it stained.
2 occurrence
of labeled nuclei was then determined by noting the blackening in the emuilfion over each
of several thousand nuclei. It was observed in the weanling animals which]
had received
no TSH that 9% of 12% of thyroid nuclei were labeled. When TSH was given [Fo these
animals, the incidence rose to 14%. In the nonstimulated old animals the [incidence of