The Distribution of Radioactive Potassium in the Uterus of Pregnant Rats and Guinea-pigs

Recent experiments on placental exchange and transfer have made use of the introduction of tracer quantities of a radioactive substance into the maternal circulation to examine its distribution in maternal and foetal tissues and fluids. Such experiments have been performed in different species at varying stages of gestation, using radioactive sodium (Flexner & Roberts, 1939; Flexner & Pohl, 1941; Flexner & Gellhorn, 1942; for other references see Reynolds, 1949, and Marshall, 1952), iron (Vosburgh & Flexner, 1950), and phosphorus (Nielson, 1941; Naeslund, 1951) as tracer substances. The distribution of injected radioactive potassium ions in the tissue of the body has been examined by a number of investigators (see D'Silva & Neil, 1951; Walker & Wilde, 1952; and Ginsburgh, 1952, for references). It has been found that some cells (e.g. those of liver and kidney) readily exchange their potassium with that of the plasma, whereas others (e.g. red cells and skeletal muscle) exchange their potassium slowly.