Biological half-lives of bromide and sodium in the rat are connected and dependent on the physiological state

Abstract

The parallel course of the excretion rates of sodium and bromide ions was demonstrated in adult male rats administered simultaneously with ²⁴Na-sodium chloride and ⁸²Br-bromide. These excretion rates were inversely proportional to the magnitude of sodium intake in the animals. The biological half-life of bromide, as a substitute for sodium or chloride, was investigated with the aid of the radionuclide ⁸²Br in animals situated in very different physiological states (i.e., in lactating and nonlactating female rats as well as in young rats of varying ages [2,4,6, and 10 wk of age]). The ⁸²Br radioactivity retained in mothers and in whole litters was measured in vivo at appropriate time intervals (up to 240 h) after the application of ⁸²Br-bromide to the mothers. The time-course of the changes in the ⁸²Br radioactivity of the young was calculated as the difference between the rate of ⁸²Br intake in the mother's milk and the ⁸²Br excretion through the kidneys into the urine. The rate of ⁸²Br excretion through the kidneys of the dam could be calculated also. Nonweaned young rats (12 d) had the highest half-life (269 h) and lactating dams had the lowest (44 h). The determined values demonstrated that nonweaned young apparently conserve sodium, because of its relatively low concentration in mother's milk, whereas lactating dams, because of their large food intake, waste sodium.