Esterification of vitamin A by the human placenta involves villous mesenchymal fibroblasts

Vitamin A (retinol) and its active derivatives (retinoic acids) are essenti al for growth and development of the mammalian fetus. Maternally derived re tinol must pass the placenta to reach the developing fetus. Despite its app arent importance, little is known concerning placental transfer and metabol ism of retinol, and particularly of placental production and storage of ret inyl esters, To elucidate this metabolic pathway, we incubated, in the pres ence of retinol, 1) human full-term placental explants and 2) primary cultu res of major cells types contributing to placental function: trophoblasts a nd villous mesenchymal fibroblasts. We used HPLC to determine the types and concentrations of retinyl eaters produced by these explants and cells. Abo ut 14% of total cellular retinol in placental explants was esterified. The most abundant esters were myristate and palmitate. Primary cell cultures sh owed that fibroblasts efficiently produced retinyl esters, but trophoblasts did not. In both types of experiments, no retinyl esters were detected in the culture medium, suggesting that retinyl eaters were produced for storag e purpose. These results suggest that villous mesenchymal fibroblasts are p rimary sites of retinol esterification and storage in the placenta.