Placental transfer of aspartate and its metabolites in the primate

Abstract

The placental transfer of aspartate was tested in pregnant monkeys infused maternally with sodium aspartate. In five animals infused at 100 mg/kg/hr, maternal plasma aspartate levels increased from 0.36 ± 0.19 to 80.2 ± 11.5 μmole/dl (mean ± SD). However, fetal plasma aspartate levels increased only slightly from 0.42 ± 0.31 to 0.98 ± 0.24 μmole/dl ( p = 0.02). Erythrocyte aspartate levels were unchanged in both fetal and maternal circulation. In two animals infused at 200 mg/kg/hr, maternal plasma aspartate levels increased from 0.28 and 0.31 μmole/dl to values of 141 and 237 μmole/dl, respectively. This increase produced a significant ( p = 0.001) increase in fetal plasma aspartate levels from 0.53 and 0.67 to 3.3 and 4.5 μmole/dl, respectively. Maternal plasma aspartate levels in two animals infused at 400 mg/kg/hr increased from 0.5 and 0.7 μmole/dl to 400 and 750 μmole/dl, respectively, at the end of the infusion. Fetal plasma aspartate levels increased from 0.21 and 0.25 μmole/dl to 60 and 92 μmole/dl, respectively. Maternal aspartate infusion at each level increased maternal, but not fetal, plasma taurine levels. The increase in maternal taurine levels was not in proportion to the dose of aspartate infused. Aspartate metabolites, glucose, and lactate were readily transferred across the placenta. The data indicate that aspartate, like glutamate but unlike most amino acids, is not concentrated toward the fetal circulation in the pregnant primate, and suggest that a barrier to aspartate transfer exists unless maternal plasma levels are grossly elevated.