THE ROLE OF THE MONKEY FETUS IN THE EXCHANGE OF THE WATER AND SODIUM OF THE AMNIOTIC FLUID*

Abstract

The total exchange rates for H2O and Na of the amniotic fluid were determined under the assumption of a closed 2-compartment system. For pregnant rhesus monkeys at term, an average of 8.4 mols of H2O and 4.7 meq of Na were found to exchange/hour. This is 3 times greater than the exchange rate (per kg) for the human; the ratio of transfer rates is identical for the 2 species. Under the assumption of a closed 3-compartment system (mother, fetus and amniotic fluid) time-activity curves for mother, fetus and amniotic fluid could be used for the calculation of transfer rates if the amniotic fluid was used as the primary compartment. About 1000 ml of water is exchanged between fetus and mother; 50 ml/hour between fetus and amniotic fluid and the direct exchange between mother and amniotic fluid amounts to 5-20 ml/hour. The primate fetus transmits at least 75% of the water leaving the amniotic fluid. For labeled water the assumed kinetic model represents the pregnant organism reasonably well but for Na the model is not applicable. Only a rough estimate of the sodium exchange rates could be made.