Bromide transfer through mother's milk and its impact on the suckling rat.

Effects of a high bromide intake in lactating rats on the performance of the dams and on the prosperity of their young were studied. In the dams, two marked consequences undoubtedly caused by high bromide intake were observed: stagnation in the extent of diet and water consumption in the course of the lactation period, and a conspicuous drop in the production rate of mother's milk. A very high intake of bromide in the mothers in the course of the nursing period (about 220 mg Br-/d per dam) also caused a marked decrease in the body weight increments in their suckling young. Only about one-half of these young survived and their general condition was very poor. It is suggested that one of the possible reasons for the observed marked decrease in the production of mother's milk in dams with high bromide intake could be a decreased stimulation of the mammary glands as a consequence of reduced consumption of mother's milk by the suckling. Bromide ions ingested by the dams easily moved into the rat milk. Via mother's milk, bromide was transferred in a large extent to the suckling. The amount of bromide in mother's milk depended on the bromide concentration in the drinking water taken by the dams. With the addition of 5 g bromide per liter (providing the mean daily bromide dose of 220 mg), bromide ions replaced about 54% of the chloride in the milk. A rise in the concentration of both halogens caused also an increase in the concentration of sodium in mother's milk. The exact mechanism(s) of bromide interference with postnatal developmental processes in the young remain(s) unclear.

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

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.