Docosahexaenoic acid (DHA) accretion in the placenta but not the fetus is matched by plasma unesterified DHA uptake rates in pregnant Long Evans rats

Maternal delivery of docosahexaenoic acid (DHA, 22:6n-3) to the developing fetus via the placenta is required for fetal neurodevelopment, and is the only mechanism by which DHA can be accreted in the fetus. The aim of the current study was to utilize a balance model of DHA accretion combined with kinetic measures of serum unesterified DHA uptake to better understand the mechanism by which maternal DHA is delivered to the fetus via the placenta. Female rats maintained on a 2% α-linolenic acid diet free of DHA for 56 days were mated, and for balance analysis, sacrificed at 18 days of pregnancy, and fetus, placenta and maternal carcass fatty acid concentration were determined. For tissue DHA uptake, pregnant dams (14-18 days) were infused for 5 min with radiolabeled 14C-DHA and kinetic modeling was used to determine fetal and placental serum unesterified DHA uptake rates. DHA accretion rates in the fetus were determined to be 38 ± 2 nmol/d/g, 859 ± 100 nmol/d/litter and 74 ± 3 nmol/d/pup, which are all higher (P < 0.05) than the fetal serum unesterified DHA uptake rates of 16 ± 6 nmol/d/g, 239 ± 145 nmol/d/litter and 14 ± 8 nmol/d/pup. No differences (p > 0.05) in placental DHA accretion rates versus serum unesterified DHA uptake rates were observed as values varied only 6-35% between studies. No differences in placental accretion and uptake rates suggests that serum unesterified DHA is a significant pool for the maternal-placental transfer of DHA, and lower fetal DHA uptake compared to accretion supports remodeling of placental DHA for delivery to the fetus.