er
cor
xERO
c-K
L-j-K
eK tA (Lt An eB tK HAH Ot rh
t = time.
A sumnary of the calculations made to determine the normal range
of urinary radioiodine excretion at 15 days appears below.
* peak radioiodine content of the thyreid
Tt
psi
2X = physical decay constant for
J » rate constant for the uptake of radioiodine in the thyroid
K = rate constant for the release of iodine from the thyroid
ly * radioiodine content of urine
L « rate of turnover of extrathyroidal thyroxine
I
where
a * 0-60 LEKI,
dl,
ing expression shown below.
uptake of radioiodine was assumedto be exponential with a half-period of
increase of 4.5 hours, and 60% of the iodine released when extrathyroidal
thyroxine is degraded was assumed to be excreted in urine.
Rates of urinary radioiodine excretion were calculated from the result-
, thyroid only as thyroxine, and that the release of thyroxine and its subsequent degradation in the extrathyroidal hormonal espace can be adequately
described assuming first-order kinetics. Ranges for normal biological
half-life of iodine in the thyroid and normal turnoverrate of extrathyroidal
thyroxine were selected from the beat available data in the literature. The
the
tion for urinary radioiodine it was assumed that iodine is released from
Radioiodine appearing in urine, except for that during a relatively
ahort period following exposure, originates from the thyroid. In the calcula-
Yook €, Ng
CALCULATION OF URINARY RADIOIODINE EXCRETION
APPENDIC
diy,
study on the uptake and excretion of iodine in man which will be described
more fully in a UCRL report entitled, "The Dynamics of Iodine in Man."
The problem outlined above is a practical application of an analytical
On the basis of these calculations, the normal range of urinary radio-
0.16
0.21
7.2
13.6
17.15
17,15
3.7
3.7
iodine excretion at 15 days was estimated to be 0,05 to 0.2% of the
peak
thyroid content.
0.050
0.066
7.2
13.8
4.85
a
% of I,/day
4.85
day! x10 2
L
3.7
day * x 109
K
3.7
day
J
Urinary radioiodine excretion at 15 days.
i
OFFICIAL Uz ONLY
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pe SR
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