E. A. Gusmano

Metabolism of Zinc-65 in Man

In view of the importance of zinc in many enzyme systems, and of the fact that zinc is an essential trace element in the human body, a study of the excretion, retention, and tissue distribution of Zn65 in man was performed. Zinc-65 is also a neutron-induced radionuclide and is, therefore, potentially an internal radiation hazard. The dose from Zn65 is a function of the y-particle distribution and turnover in the body. The tissue distribution and excretion of Zn65 have been investigated in animals (1, 2), and more recently these studies have been extended to man (3, 4). In the present investigation the blood levels, excretions, and tissue distribution of Zn65 in man were also related to the retention of Zn65 in the body as determined by the whole-body counting technique.

Formulation and testing of a compartmental model for calcium metabolism in man.

Movement of the tracer involves several concurrent processes and is much better represented by a multicompartmental model than by a single-compartment model. Several such multicompartmental models have been developed, with analog computers being used for the solution of the requisite differential equations (2-4). Although all these models consisted of four compartments, they differed somewhat in their structure. In view of the complexity of the model, the assumptions on mixing and pool homogeneity, and the approximate nature of the analog computer solution, none of these approaches could be said to be definitive. It appears that a reasonable

Comparative kinetics of Ca47 and Sr85 in man.

In studies of skeletal metabolism, the radionuclide Sr85 is frequently employed as a tracer for calcium on the basis that the chemical similarity of these two elements produces correspondingly similar metabolic responses. In certain processes, however, the two elements are handled discriminatively. For example, there is preferential absorption of calcium over strontium by the intestinal wall, and preferential elimination of Sr over Ca by the kidneys. Further, some evidence has been adduced which indicates that discrimination may also occur at the level of bone. Although this has not been established conclusively, crystallographic studies do indicate that Sr cannot easily substitute for Ca in the bone lattice because of the size of the Sr ion (1). The conditions under which Sr may be used as a tracer in order to characterize Ca metabolism in bone remains to be determined more precisely. Such a study necessitates a delineation of both the qualitative and the quantitative differences in the skeletal metabolism of Ca and Sr. The problem may be divided into two parts. The first situation is the short-term study (up to approximately 30 days) which is characterized by the rapid equilibration of Sr and Ca among blood, soft tissue, and bone, and by the subsequent rapid loss of Ca and Sr from bone which must follow the loss from the body. This study is the subject of the present paper. The second is the long-term study, which is characterized chiefly by the very slow loss of Ca and Sr from bone that occurs in remodeling as a result of resorption, and by slow exchange between bone and plasma. This long-term study is the subject of a separate paper (2). Measurements of whole-body retention of Sr85 and Ca47 were made with a wholebody gamma spectrometer. Simultaneous measurements of the tracers made on the excreta and on samples of plasma yielded data necessary for the determination of the skeletal accretion rate and exchange capacity. The kinetics of skeletal metabo-

Metabolism of scandium-46 in man☆

Abstract The metabolism, tissue distribution and biological turnover of radioactive chelated scandium were determined in man. When administered intravenously as the weak chelate Sc46 NTA (nitrilotriacetate), Sc46 disappeared very slowly from the vascular space; it was excreted principally via the intestine. When Sc46 was administered as the strong chelate of ethylene-diaminetetraacetic acid, EDTA, or of diethylenetriaminepentaacetic acid, DTPA, the plasma level of Sc46 decreased rapidly and urinary excretion was high, up to 82 percent of the dose being excreted in 24 hr. The concentration of Sc46 in various tissues determined 5,6 and 7 months after the administration of Sc46 NTA showed that uptake was highest in spleen. Evidence is presented which suggests that the high body retention of Sc46 NTA may be due to the formation of colloidal aggregates and to binding of scandium to proteins. The biological half-life of Sc46 NTA determined with the whole-body counter and computer analysis was 1300 days in one patient and 1557 days in another.

Kinetics of Strontium and Calcium Skeletal Metabolism in the Rat.

Conclusions The present study demonstrates that the absolute values for the computer derived parameters of skeletal metabolism obtained with Sr tracer data do not differ significantly from those obtained with Ca. Further, the whole-body turnover of bone-fixed Sr is not significantly different from that of Ca as measured by whole-body counting. The evidence here supports the common assumption that Sr is a reliable tracer of calcium in skeletal metabolism, at least over a 40-day period.

Evaluation of the parameters of strontium metabolism in the rat as a function of age.

A linear two-compartment open-ended model was used to describe the kinetics of strontium in the rat as a function of age. Strontium-85 was used as the tracer in the eight age groups (39 to 389 days...

ZINC-65 IN REACTOR WORKERS

Zinc-65, hitherto found in cyclotron workers and in other specialized populations, has now been detected in a group of reactor workers. While the highest levels detected are less than 0.2 percent of the maximum permissible concentration, the movement of this neutron-induced radionuclide is of interest, and the baseline information is important for future studies.

LONG-TERM Cs

In order to assess the radiation hazard of the fission product Cs/sup 137/, it is necessary to determine its long-term turnover rate in man. Results are reported from a longterm study of Cs/sup 137/ made on five patients. Measurements of whole-body retention were made with the Brookhaven whole-body counter. It has been found that the technique of radiochemical analysis of excreta is of limited sensitivity for determining whole-body retention at very long periods of time after isotope administration. In order to assay the radiation hazard, it is further necessary to estimate the retention over the normal life span of man on the basis of the data obtained. Thus a mathematical model must be developed from which long-term extrapolations can be made. Data analysis was carried out with the use of a computer in order to determine the parameters of the mathematical functions that best describe these data. (auth)

sup 137

Abstract An analytical method was developed, utilizing computer technics for the derivation of a model describing the kinetics of calcium in a patient with parathyroid insufficiency. The short-life of the Ca 47 tracer used permitted sequential studies of the same patient on both a normal and low calcium diet.

TURNOVER IN MAN AS MEASURED BY A WHOLE-BODY COUNTER

Summary Administration of Mg++ concurrently with radioactive strontium decreased significantly skeletal retention of the isotope. Mg++ administration had a small but significant lowering effect on the retention of radioactive strontium when administered after the isotope was well fixed in bone.