SITES OF WATER EXCHANGE BETWEEN THE MATERNAL SYSTEM AND THE AMNIOTIC FLUID OF RABBITS1

Abstract

It is well established that there is rapid ex- change of water between the maternal circulation and the amniotic fluid in the guinea pig and the human (1-4). It has been suggested that amni- otic fluid may be formed, partly or entirely, by the amnion (5), by the fetal kidney (6, 7), by the fetal lung (8, 9) and in the buccal and nasal cavi- ties (10). It has been implied that the calculated rates of exchange of water represent real volumes of water crossing the barriers and that the sites of formation and of removal of amniotic fluid are not necessarily the same (7). Some of these sug- gestions and concepts would lead to the hypothesis that water entered the amniotic fluid by way of the placenta and the fetus and left by way of some other route, possibly across the fetal mem- branes; the system as a whole would then be a series one for water with "feed-back" from the amniotic fluid to the maternal system. Mainte- nance of the relative constancy of volume of the amniotic fluid would be the result of a steady state rather than of equilibrium with respect to water between amniotic and maternal fluids.3