The transfer of free palmitic and linoleic acids across the ovine placenta

Following the injection of3H‐16∶0 and14C‐18∶2 (n−6) into the jugular vein of the ewe, the rates of disappearance of these fatty acids from the maternal plasma and their rates of appearance in the fetal plasma have been studied. The rates of disappearance of both labeled acids from the maternal circulation were similar. The appearance of radioactivity in the fetal plasma was rapid and could be detected within 2.5 min after injection into the mother. In contrast to the similar rates of disappearance of the fatty acids from the maternal plasma, the rate of accumulation of3H‐16∶0 within the fetal plasma was appreciably greater than that of14C‐18∶2 (n−6). The absolute concentrations of the total lipid and unesterified fatty acid fractions within the fetal plasma were significantly lower than that of the maternal plasma. In comparison to that of maternal plasma, fetal plasma lipid contained an extremely low proportion of 18∶2 (n−6) accompanied by an appreciable accumulation of 20∶3 (n−9). On the other hand, the proportion of 20∶4 (n−6) within the fetal plasma was about twice that present within the maternal plasma. The obvious inability of the placenta to be as freely permeable to the passage of 18∶2 (n−6) as to 16∶0 is discussed in relation to these differences in fatty acid composition between the maternal and fetal plasmas and the known poor essential fatty acid status of the developing fetus.