Water and ion metabolism in placenta. I. water and ion content of rabbit placenta in different periods of gestation.

Total tissue water of rabbit plancenta decreases by 18% between the 9th day and the end of gestation. In the same period intracellular water decreases by 40% and the extracellular compartment swells. Total tissue sodium and chloride content increase by 34% and 27% respectively from the 16th to the 33rd day while potassium decreases by 30%. The intracellular concentration of these ions does not vary greatly during gestation. Moreover the total tissue magnesium content decreases by about 23% at the end of gestation while its intracellular concentration does not show marked changes. Calcium content of rabbit placenta substantially increases during gestation and intracellular calcium shows a fivefold increase from the 16th to the 33rd day of gestation. The results are discussed in terms of relation between water and ion content and placental tissue growth and aging.