Mechanisms of the fetomaternal transfer of Na+ across the dually perfused placenta of the rat.
In order to investigate mechanisms of fetal-maternal (F-M) transfer of Na+, clearance of 22Na+ and 51Cr-EDTA was measured simultaneously across the dually perfused placenta of the rat. In eight experiments clearance was measured successively in the F-M (Kfm) and in the maternal-fetal (M-F; Kmf) directions. Clearance of 22Na+ in the two directions was approximately equal (Kmf = 11.6 +/- 2.0 microliters/min; Kfm = 11.1 +/- 1.7 microliters/min: mean +/- s.d.) while Kfm of 51Cr-EDTA (4.4 +/- 0.7 microliters/min) was nearly double Kmf (2.4 +/- 0.8 microliters/min) for this tracer. Even greater asymmetry in the transfer of 51Cr-EDTA was found when measured across intact (non-perfused) placenta. It is suggested that this asymmetry is caused by volume flow in the F-M direction. In other experiments transfer was measured in the F-M direction only. Ouabain (0.1 mM) on the maternal side and reduced concentration of Na+ (25 mM) on the fetal side had no effect on the F-M transfer of the tracers. Reducing the temperature of the preparation by 5 degrees C significantly decreased transfer of 22Na+. The transfer of 22Na was inversely related to the concentration of K+ on the fetal side. These observations suggest that the F-M transfer of Na+ has three components: diffusion through paracellular routes; convective flow by filtration through wide placental pores, and transcellular transport by a mechanism which is uncertain at present.
Stulc
J
J
Department of Pharmacology, Second Faculty of Medicine, Charles University, Prague, Czech Republic.
Stulcová
B
B
Sibley
C P
CP
D000818:Animals; D002860:Chromium Radioisotopes; D003080:Cold Temperature; D005260:Female; D008431:Maternal-Fetal Exchange; D010042:Ouabain / Q000494:pharmacology; D010477:Perfusion; D010920:Placenta / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D012979:Sodium Radioisotopes
D002860:Chromium Radioisotopes; D012979:Sodium Radioisotopes; D010042:Ouabain; D012964:Sodium; D011188:Potassium