Amino acid uptakes in normal and small-for-date placentas, with special reference to activity of transport ATPase in placental slices and isolated trophoblastic membrane.

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Abstract
In both normal and SFD [small-for-date] human placentas, uptakes of amino acids were about 2-3 times as great for neutral amino acid serine as for basic amino acid lysine. In the SFD placenta, amino acid uptake became significantly slower than in the normal after 30 min of incubation. After 90 min, uptake was lower than the normal by some 32% for serine and 42% for lysine. Serine uptake began to be interrupted by addition of 10-3 M ouabain at 30 min and showed about 31% decrease at 90 min, revealing an amino acid uptake pattern similar to that of the SFD placenta. But lysine uptake was not noticeably affected by ouabain. As for release of intracellular amino acids into the incubation medium, no differences were observed between serine and lysine or between the normal and SFD placenta. Activity of transport ATPase of the isolated trophoblastic membrane was lower in SFD than in the normal placenta. The low f/m [fetal (maternal)] ratio of amino acids in SFD pregnancy accounts for a decreased placental transport of amino acids corresponding with depression in the activity of its major promotor-membrane-bound transport ATPase.