The transfer of free fatty acids across the rabbit placenta.

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Abstract
The passage of fatty acids across the placenta was studied in 28 day pregnant rabbits by comparing the fatty acid distribution in plasma free fatty acids (FFA) of umbilical cord artery and vein with that in maternal plasma and by infusing the doe at a constant rate with labeled palmitic, linoleic or arachidonic acids. During the infusion maternal and fetal plasma FFA specific activities were measured. The mean levels of all the fatty acids studied (12-20 C atoms) were similar in both the umbilical vein plasma and maternal arterial plasma FFA, except for arachidonic acid, which was higher in fetal blood. The relative distribution of the fatty acids in umbilical arterial plasma was similar to that in the vein, but at lower concentrations. The mean cord venous-arterial difference for each fatty acid correlated positively with the mean maternal arterial levels, with the exception of arachidonic acid. During the constant infusion experiments the specific activities of the fatty acids in the maternal and fetal circulating FFA pools rose rapidly during the first 4 min then rose only slowly. Palmitic and linoleic acids were cleared from the maternal circulation in a similar manner and crossed the placenta at similar rates. The average fetal specific activity in plasma FFA reached 15% of the maternal level for both palmitate and linoleate. The figure for arachidonic acid was half that for palmitic acid infused at the same time. All the major fatty acids present in fetal adipose tissue cross the placenta, the net transport of each fatty acid depends in part on maternal concentrations and the rate of metabolism of palmitic and linoleic acids is the same and both cross the placenta at the same rate. Proportionately less fetal arachidonic acid was derived from maternal FFA. The results suggested a 2nd placental source of arachidonic acid and possibly also of other fatty acids.