Water and ion metabolism in placenta. II. Water compartments and electrolytes in slices of rabbit placenta, at different periods of gestation, incubated at 0-1 degree C.

The movement and the distribution of water, sodium, potassium, chloride, magnesium and calcium have been studied in slices prepared from rabbit placentae at different periods of gestation, incubated in condition of depressed metabolism (0-1 degree C). In these conditions the tissue takes up water from the external medium up to a maximum of about 2.0 kg/kg d. wt., which represents 30 per cent of the initial H2O content of the fresh tissue. The extracellular compartment swells progressively and proportionally to the age of the placenta. The sodium and chloride content of the tissue increases while that of potassium decreases and their intracellular concentration reaches, after 120 min, that of the external medium. Magnesium does not show appreciable changes and calcium, too, despite its extreme variability, does not seem to undergo significant variations during the cold incubation. The results obtained show that placenta, like most of other mammalian cell systems, possesses specific metabolism-dependent mechanisms responsible for the maintenance of water distribution and ion gradients among the different tissue compartments. The characteristics and the regulation of these mechanisms are discussed in detail.