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Department of Animal Science, University of British Columbia, Vancouver, B. C., Canada V6T2A2 * Section of Nutrition, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square, PA 19348
The kinetics of selenium metabolism in three nonpregnant ewes were studied by the intravenous injection of 75Se-sodium selenite and measurement of radioactivity responses in blood, tissues and excreta. Stable selenium measurements were also made to determine selenium intake, excretion in feces and urine, and mass of selenium in tissues. Immediately following tracer injection, there was a rapid disappearance of radioactivity from plasma reflecting the uptake of the element by the liver and blood cells. The decrease in plasma radioactivity ceased abruptly by 3045 min, and was followed by an increase to a peak by 34 h and a more gradual biphasic decline thereafter. A kinetic model of selenium metabolism in the whole animal was constructed employing the SAAM/CONSAM computer program. The multiphasic response of plasma radioactivity during a physiological steady state was explained on the basis of rapid hepatic uptake of selenium and its subsequent reappearance in the circulation in protein-bound form followed by further metabolism and excretion of the element. The model provides reference parameter values for 75Se-sodium selenite kinetics in selenium-replete, mature nonpregnant ewes for comparison with the kinetics in animals whose selenium status may be altered.
KEY WORDS: selenium kinetics metabolism sheep mathematical model SAAM/CONSAM
1 Supported by a strategic grant from the Natural Sciences and Engineering Research Council of Canada.
Manuscript received 7 March 1989. Revision accepted 9 March 1989.