Effect of NaCl load administered to the fetus on the bidirectional movement of Cr-51-EDTA across rat placenta
Abstract
A hypothesis that, in the rat, fluid circulates across the placenta, with circulation being maintained by active transport of Na+ from mother to fetus, has been tested. Transfer of Cr-51-EDTA from mother to fetus and from fetus to mother has been measured and the respective unidirectional transfer constants, K-mf and K-fm, have been calculated.
Immediately before the transfer measurement, the fetuses were injected intravenously with 10 mu l of isotonic glucose (controls); with 30 or 300 mu l of isotonic saline; or with 10, 30, or 60 mu l of 9% NaCl. In controls, K-mf of Cr-51-EDTA was 2.0 +/- 0.6 mu l/min, and K-fm was 4.3 +/- 1.0 mu l/min.
Injecting the fetus with NaCl had no effect on K-mf, whereas the K-fm was increased significantly in a dose-dependent way. In other experiments, Cr-51-EDTA was injected into nephrectomized maternal animals, and the radioactivity of maternal and fetal plasma was followed for 30 h.
The time course of fetal plasma radioactivity supported the thesis that the transfer of Cr-51-EDTA across the rat placenta is highly asymmetrical.