title: Distribution of ionic sulfate, lithium, and bromide across the sheep placenta.
abstract: Salts of sulfate, lithium, and bromine were injected or infused intravenously into ewes in the last trimester of gestation. Ewes and fetuses had indwelling catheters; most fetuses were nephrectomized. Concentrations were measured in paired maternal and fetal samples over periods of 4--14 days. Maternal excretion of sulfate was too rapid to permit near equilibration of fetal and maternal plasma concentrations; the results, however, did not support the existence of a large potential difference across the exchange barrier. The concentrations of Li+ (given by continuous infusion) and 82Br- in maternal plasma did not change rapidly. The concentrations of these tracers in fetal plasma rose until they were nearly equal to the maternal plasma concentrations. Steady-state transplacental potentials, calculated by use of the Nernst equation, were 5.2 +/- 2.0 (SEM) mV (n = 26) for Li+ and -2.2 +/- 0.8 (SEM) mV (n = 10) for Br-. Nernst potentials calculated from previously measured maternal and fetal plasma concentrations of Na+, K+, Mg2+, and Cl- were +0.4, +3.6, +0.5, and -1.4 mV. We concluded that, of the total potential difference of about -50 mV (fetus negative) between the fetal lamb and the ewe, only a few mV are dropped across the placental exchange barrier.
mesh_terms: D000818:Animals; D001965:Bromides / Q000378:metabolism*; D004594:Electrophysiology; D005260:Female; D008094:Lithium / Q000378:metabolism*; D008431:Maternal-Fetal Exchange; D008433:Mathematics; D010920:Placenta / Q000378:metabolism / Q000502:physiology*; D011247:Pregnancy; D013431:Sulfates / Q000378:metabolism*
chemical_list: D001965:Bromides; D013431:Sulfates; D008094:Lithium