Rate of Exchange of Sodium and Potassium Between Amniotic Fluid and Maternal System. ∗

Abstract

Summary

The exchange rate of sodium to and from the amniotic fluid was determined by the simultaneous application of sodium-22 and sodium-24. This exchange rate, in opposite directions, was found to be 15 and 16 mEq. of sodium per hour, respectively. The transfer rate of hydrogen, sodium, and potassium from the amniotic fluid to the maternal system was determined by the simultaneous application of tracers for each of these elements. The disappearance constants for sodium and potassium were found to be nearly equal, indicating that the same percentage of these elements is exchanged per unit of time, while that for deuterium was found to be 5 times greater. The exchange rates were calculated as 31.9 moles of water, .014 mole of sodium, and .00041 mole of potassium per hour. It is concluded that the water and electrolytes of the amniotic fluid are in dynamic equilibrium with maternal plasma, each exchanging at its own characteristic rate.