F. W. LENGEMANN
urinary I was increased.
These new levels
were maintained during the entire course of
perchlorate administration and attest to the
rapidity and completeness of action of this
level of perchlorate. Due to a loss of samples,
it is uncertain how quickly the plasma Ilevel
rose. The rapid inerease in urinary I, however, suggests that the plasma I" may have
risen much more rapidly than depicted in the
graph.
From the graph (Figure 1) it is apparent
on the last day of the control pertod and again
on the last day of a period of intravenous thy-
roxine administration and the blood I’* ¢on-
centrations were followed. Each experiment
was started about 2 hr after the morning milk-
ing. As seen from Figure 3, the Ilevels of
crease until some time after the start of perehlorate dosing.
Figure 2 is a plot of the data obtained for
one of the four cows given L-thyroxine (Table
a
T
T
=
T
PERCENT GAILY DOSE PER LITER
[ CONTROL
aF
al
'
|
SMG L-THYRGXINE) [OMG L-THYAOXINE)
CONTROL
Doe
oMILK
="
DAYS
1
2
=i
wads
i
o CONTROL
rex
apt
o PLASMA
M/P RATIO
ee
a
—_-
a
te
o L—THYROXINE
L,=
_—lo 2
Deemed
te
=
dig &
1
This animal was somewhat atypical, be-
cause the milk I’ varied widely and showed
a downward trend during the control period.
Data are presented, however, because they show
that administration of t-thyroxine reduced the
milk Ilevels and that upon stopping the
thyroxine a rapid return of the radioiodine
concentrations to that of the start of the experiment was noted. In agreement with the
results of the other cows, it took about two
days for the effect of thyroxine to become apparent. Increasing the amount of L-thyroxine
from 5 to 10 mg resulted in only a slight
further decrease in milk radioiodine. Twenty
nilligrams of thyroxine per day had no greater
effect than 10 mg in another of these cows;
moreover, at this high level the cow stopped
eating and showed a marked drop in milk production. Figure 2 also shows that L-thyroxine
reduced the milk/plasma I™ ratio. This ratio
returned to near control levels when thyroxine
dosing stopped.
In another experiment I’” was injected into
one quarter of the mammary gland of a cow
i
40
r
Fie. 2, Effect of daily injections of L-thyroxine
upon the milk and plasma radioiodine concentrations.
1}.
PERCENT PER LITER
that thyroid Idid not show a noticeable de-
80
i
120
it
j
200
MINUTES
Fie. 3. Blood Ievels of I’ as a function of
time after injection of I’ into the mammary
gland of a cow.
blood rose more steeply and to greater heights
during the control phase of the experiment than
during the period when the cow was receiving
5 mg of thyroxine per day. Since thyroxine
administration would tend to reduce thyroid
I™ uptake, the lower blood values during the
thyroxine-period
are indicative
of
a
lesser
transfer of iodine from the mammary gland
back to the body.
DISCUSSION
At the outset it is important to restate that
the radioiodine was given to these cows in
twice-daily oral doses. In this way the levels
of radioiodine in the various tissues tended to
approach a steady state condition and any
differences between milk and plasma were real
and not artifacts due to time differences in
production of milk or eollection of samples.
It has been demonstrated in this paper that
KCI1O, Nal, and .-thyroxine can produce
marked decreases in the transfer of radioiodine
from plasma to milk. Garner et al. (3) have
[4 ]