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42
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PROGRESS IN ATOMIC MEDICINE
at Jeast four exponential components to the plasma Ca*’ disappearance
curve. The extrapolation of the slowest component to t. has been used
to calculate both exchangeable calcium pool and to estimate bone forma-
tion rate. A longer lived radioactive isotope of calcium, Ca** (ti, = 160
days}, is also available. but not as useful as Ca*’ because it can not be
used for external monitoring over bone and because it is difficult to
prepare for radio-assay.
Iron: In the normal person, approximately 75 per cent of the total
body iron is in circulating red cells. Smaller amounts are present in
erythropoietic cells in the marrow; in spleen, liver, and bone marrow as
storage iron, and even smaller quantities occur in other iron containing
compounds suchas catalase and transport iron. A measurement of total
body hemoglobin with carbon monoxide serves to set a lower limit to
body iron content. If the storage iron could be measured, then a good
approximation of total body iron could be obtained. The complex
models of iron metabolism 44.08.81 yield information regarding storage
iron but with considerable uncertainty. Gale et al.** have measured the
quantity of storage iron in the bone marrowwith Fe**.
.
Magnestum: Magnesium*, with a half-life of 21.3 hours, has been
cittastiatin
mln
used to measure exchangeable magnesium. The exchangeable magnesium
was less than one-fifth the total body magnesium.®
Plasma Proteins
A number of plasma proteins have been labelled with radioactive
iodine (1’*? and [’*) and their total body content and turnover
have been measured.”* While it is not difficult to label proteins with
radioactive iodine, considerable care is required to avoid denaturation.
The proteins studied include albumin.”’ 6.6 S gamma globulins,”* fibrinogen,” transferrin.” ceruloplasmin."’ and macroglobulin.’® Jodinated proteins have been used to measure plasma volume, catabolic rate and
total body content of the labelled protein. The last measurement requires
supplementary information or more elaborate analysis of the experimental data.
There are four methods for analyzing the data from iodine labelled
protein studies. These are: (1) extrapolation of the slowest component
of the plasma disappearance curve to the time of administration:°° (2)
measurement of the ratio of serum isotope content to whole bodyisotope
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content:”” (34 the equilibrium time method of Campbell et al. in which