Regulation of electrolyte composition of fetal rat plasma

Abstract

Is fetal plasma a transudate of maternal plasma? Cl, Na, and K concentrations were measured in plasmas obtained by cardiac puncture of exposed rat fetuses while the maternal rat was under pentobarbital anesthesia. At rest, Cl had 0.95 x the maternal concentration, Na 1.00, and K 1.6x. When hypertonic NaCl was infused into a maternal vein, the Cl in the fetal plasma increased only half as much as in the maternal plasma, a steady differential being maintained at 1–3 hr. In contrast, Na increased alike in both plasmas. When electrolytes were depleted from the mother by intraperitoneal dialysis, both Na and Cl were lost proportionately. Sucrose solution added to the mother's blood diluted the electrolytes of her plasma but increased them in the fetal plasma by withdrawal of water. Analysis of the fetuses showed that water moved out from the fetuses while Na and Cl moved inward after NaCl was given to the mother; depletion of the mother led only to movement of Na and Cl from the fetus. Thus Cl and K are maintained in fetal plasma, when sampled in the above manner, at concentrations differing from those of maternal plasma; and circumstances were found in which these differences are exaggerated. Therefore fetal plasma is not a transudate.

The Transplacental Potential Difference in Guinea-Pigs

“…There seems to be no concentration gradients of ions across the placenta which could account for a transplacental potential difference higher than a few millivolts [Adolph and Hoy, 1963;Alexander et al, 1958;Christian son and Chester Jones, 1957;K aiser and Cummings, 1958;Phillips and Sundaram, 1966].…”

The ontogeny of the onset of drinking and plasma osmotic pressure regulation

“…Constable (1963) has shown that plasma volume, expressed as a percentage of body weight, decreases from birth to maturity in rats. Adolph and Hoy (1963) reported that in rat fetuses, sodium and potassium increase as a function of body weight. Jelinek (1961) found that for rats from 10 to 63 days of age, sodium and chloride increase as a function of age.…”

Some aspects of placental functionThis forms part of a thesis submitted to the University of London for the degree of Doctor of Philosophy.

“…In the same experiments, when a very large volume of water was introduced into the mother, the water content of the whole foetus did rise, when a maximal rate of ion extrusion is suggesting that there may be a threshold effect obtained, and at osmotic gradients higher than this level ions could flow into the foetus. Adolph and Hoy (1963) have also found the rat foetus very resistant to a gain in water content. Interest in the transport of carbohydrates is centred on the fact that the placentae of mammals may be separated into two categories with regard to the transfer of these materials.…”