Fetomaternal Potassium Relations in the Fetal Rat on the Twentieth Day of Gestation

Abstract

Extract when pentobarbital was employed as the anesthetic agent (I I). It isTime-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. SpeculationPotassium 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.The rapid increase of cell mass in the developing conceptus would be expected to create a critical demand for potassium in the fetus as a result of high intracellular concentrations of this solute. Because of the importance of the extracellular fluids as the immediate source of the solutes available to cells, there have been many studies of potassium concentrations in the plasma of maternal and fetal animals carried out during the past 20 years. Many of the studies have been performed on the rat where there has been considerable disagreement on the appropriate fetal values. Whereas maternal concentrations have ranged from 4.6 to 5.4 mEq/liter (averaging 4.9 mEq/liter), fetal values in these same studies have ranged from 4.3 to 9.0 mEq/liter (see Table I). Since almost all of the studies have been performed on pregnant rats at similar stages of gestation, and on the same or related strains, it is likely that methodologic differences between studies have been responsible for the differences.It has been demonstrated that ion concentrations in fctal plasma are relatively dependent upon the state of fetal oxygenation (3, 13). Episodes of fetal hypoxia lead to the extracellular accumulation of molecules normally found in high concentration within cells. This was shown to rapidly elevate the total osmotic pressure of fetal plasma as well as to increase its potassium concentration. I n the rat, it has been shown that events which are likely to induce fetal hypoxia, such as killing of the dam. ligation of uterine arteries, or umbilical cord section, lead to significant increases in the potassium concentrations found (10). Potassium concentrations in the plasma of the fetal rat will increase as a function of the time elapsing between removal of fetuses from the uterus and plasma sampling (2). It has also been demonstrated that maternal ether anesthesia resulted in higher fetal concentrations ...

The control of potassium concentration in the cerebrospinal fluid and brain interstitial fluid of developing rats.

“…This value is slightly lower but close to those obtained for adult rats in other studies, which mostly range from 4 to 5 mM-K+ (e.g. Amtorp & S0rensen, 1974;Fantel, 1975; 12.…”

“…-i (Ferguson & Woodbury, 1969;Amtorp, & Sorensen, 1974;Johanson et al 1976) and for fetuses (Fantel, 1975) where recorded values range from 3 to 9 mm, the majority being greater than 5 mm. It is possible that these differences can be attributed to the techniques used, since all previous studies have measured [K+] in centrifuged blood samples using flame photometry.…”

“…C. JONES AND R. F. KEEP Saunders, 1972), monkey (Bito & Myers, 1970) and rat (Ferguson & Woodbury, 1969;Amtorp & S0rensen, 1974;Fantel, 1975;Johanson, Reed & Woodbury, 1976). In young rats, however, there is considerable variation in the values obtained for both CSF and plasma [K+].…”

Fetomaternal Potassium Relations in the Rat on the Twentieth Day of Gestation. II. Effects of Maternal Hypokalemia

“…The procedure for sampling of plasma has also been described in detail (7). It involved taking blood samples from the umbilical artery or vein of individual fetuses by micropuncture of the desired vessel.…”

“…The methodology employed for the measurement of transplacental potentials was adapted from Mellor (11) and has been described in detail (7). Fetuses were sampled serially and potentials were measured between the maternal peritoneal fluid and the fetal amniotic fluid or the fetal peritoneal fluid.…”