Mammals kinetic studies

The minimum value of /Jdf/v required for a reliable model depends on the quality of the determination of the data to be correlated. The smaller the experimental error in the data, the smaller the value of /Jdf/v required for dependable results. Experience indicates that in the case of chemical reactivity data /Jdf/v should be not less than 3. For bioactivity studies /Jdf/v depends heavily on the type of data for rate and equilibrium constants obtained from enzyme kinetics a value of not less than 3 is reasonable while for toxicity studies on mammals at least 7 is required. 

Fe, liver and kidney for cobalt nuclides, liver and prostate for Zn, skeletal muscle for Cs, and GI tract for Zr. The persistence of radionuclides in mammals varies with the chemical form, kinetics, species, and other variables. Thus, the time for 50% persistence of selected radionuclides in whole-animal studies ranges from 19 h to 14 days for 4 to 35 days for Cs 5 to 12h for the short-lived component of Co, 5 to 21 days for the long-lived component 25 to 593 days for Sr and 4 to 26 days for... 

Another radionuclide that has been commonly used in physiological studies of terrestrial animals is tritium. As stated in Section 8.2.1, water can be labeled as HTO and the compound used to study the water pool in plants. Somewhat similarly, total body water and water turnover in mammals can be studied. Longhurst et aL (1970) utilized HTO to compare water kinetics in winter and summer Columbian black-tailed deer (Odocoileus hemionus columbianus) and domestic sheet (Ovis aries). The animals were injected intravenously with 8 mCi HTO, and blood samples were collected periodically and examined for radioactivity with a liquid scintillation counting system. In a water-turnover study in mule deer (Odocoileus hemionus), Knox et aL (1969) also used HTO and observed that the biological half-life of HTO differed in animals maintained in a 0.9 X 1.5 m metabolism stall from that in the same animals maintained in a 4.6 X 5.8 m room. 

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