Chloride and the generation of amniotic fluid in the early embryo

The concentrations of chloride in the amniotic fluid of the four and one‐half day chick embryo exceed those in the blood plasma and in the sero‐amniotic fluid. The electrical potential of the amniotic fluid is negative compared to the electrical potentials of the plasma and sero‐amniotic fluid. Nevertheless, the amniotic fluid volume continues to grow without a sensible diminution of its chloride concentration. There is evidence, therefore, of non diffusional influx of chloride into the amniotic fluid. Radioactive chloride injected into the blood stream of the embryo also indicates that chloride is transferred into the amniotic fluid partly by an active process. Similar experiments with sodium ion fail to unequivocally demonstrate the existence of a sodium pump. From these measurements the rate of transfer of chloride by a chloride pump and the rate of efflux of chloride under the influence of the electrochemical gradient were calculated. The calculated net influx of chloride agrees with the net influx calculated from the observed growth rate of the amniotic fluid, and the same is true for sodium. It is postulated that a metabolically driven transfer of chloride into the amniotic cavity is an early step in the generation of the amniotic fluid.