Abstract
Extract: Time-corrected measurements of transplacental and transamniotic potentials were made in the fetal rat on the 20th day of gestation. These averaged 14.3 mV and 18.4 mV, respectively. The measured maternal potassium concentration in plasma of 4.8 mEq/liter and these potential measurements were used in the Nernst equation to predict the fetal concentrations in plasma. The concentration in amniotic fluid was predicted, using the potentials and either the fetal or maternal plasma concentration. The predicted concentrations in fetal plasma and amniotic fluid were 2.8 and 2.5 mEq/liter, respectively. The sampling time-corrected potassium concentration in fetal plasma was 2.9 mEq/liter and the mean in amniotic fluid was 4.6 mEq/liter. The observed concentration in amniotic fluid is significantly higher than the predicted level.
Speculation: Potassium is passively distributed between maternal and fetal plasma according to electrochemical gradients. By contrast, there is active transfer of this ion into the amniotic fluid, probably from the fetal plasma across the kidney.
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Fantel, A. Fetomaternal Potassium Relations in the Fetal Rat on the Twentieth Day of Gestation. Pediatr Res 9, 527–530 (1975). https://doi.org/10.1203/00006450-197506000-00003
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DOI: https://doi.org/10.1203/00006450-197506000-00003
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