Effects of maternal sodium depletion on the composition of ovine fetal fluids.

Effects of maternal sodium depletion on the composition of ovine fetal fluids were studied. Maternal Na depletion was achieved by 48-h drainage of parotid saliva. There was a significant decrease in both maternal and fetal plasma Na concentration, indicating that both mother and fetus had experienced the Na-depletion stimulus. There was a significant increase in maternal blood aldosterone but the change in fetal blood aldosterone was not significant. In animals where there was an increase in fetal blood aldosterone the increase could be accounted for by transfer of aldosterone across the placenta from the mother. There was a significant decrease in fetal urinary Na concentration and Na excretion and the urinary Na/K ratio fell in seven out of eight studies. These observations are consistent with the hypothesis that fetal Na depletion sensitizes the fetal kidney to the action of circulating aldosterone as in the adult.