Investigation of [14C] linoleic acid conversion into [14C] arachidonic acid and placental transfer of linoleic and palmitic acids across the perfused human placenta.

In five separate experiments in which single placental lobes were perfused, [14C] antipyrine, [3H] dextran and a fatty acid mixture containing [14C] linoleic and [3H] palmitic acids were added to the maternal circuit. Samples of fetal and maternal perfusate, taken at intervals, were analysed for radioactivity and fatty acid content. The relative placental transport rates of antipyrine, linoleic and palmitic acids and the changes in maternal and fetal circuit content of linoleic, palmitic and arachidonic acids were measured. Mean transfer rates of 150, 0.023 and 0.034 mumol min-1 were obtained for [14C] antipyrine, [3H] palmitic and [14C] linoleic acids, respectively. The transfer of [3H] dextran was negligible. The transfer rates of linoleic and palmitic acids did not differ significantly from one another. The maternal circuit content of palmitic and arachidonic acids increased, whereas linoleic acid content decreased. The fetal content of all three acid increased but in the case of arachidonic and palmitic acids the increase was not as great as that seen in the maternal circuit. In no experiment was radioactivity detected in maternal or fetal perfusate arachidonic acid. It is concluded that linoleic and palmitic acids cross the placenta from the maternal to the fetal side. This transfer appears to be non-selective. The large amounts of arachidonic acid that are released into the perfusate probably originate from placental lipids other than free linoleic acid.