Fate of orally administered radioactive fatty acids in the late-pregnant rat.

To investigate the biodisponibility of placental transfer of fatty acids, rats pregnant for 20 days were given tracer amounts of [(14)C]palmitic (PA), oleic (OA), linoleic (LA), α-linolenic (LNA), or docosahexaenoic acid (DHA) orally and euthanized at 0.5, 1.0, 2.0, or 8.0 h thereafter. Maternal plasma radioactivity in lipids initially increased only to decline at later times. Most of the label appeared first as triacylglycerols (TAG); later, the proportion in phospholipids (PhL) increased. The percentage of label in placental lipids was also always highest shortly after administration and declined later; again, PhL increased with time. Fetal plasma radioactivity increased with time, with its highest value at 8.0 h after DHA or LNA administration. DHA initially appeared primarily in the nonesterified fatty acids (NEFA) and PA, OA, LA, and LNA as TAG followed by NEFA; in all cases, there was an increase in PhL at later times. Measurement of fatty acid concentrations allowed calculation of specific (radio)activities, and the ratio (fetal/maternal) of these in the plasmas gave an index of placental transfer activity, which was LNA > LA > DHA = OA > PA. It is proposed that a considerable proportion of most fatty acids transferred through the placenta are released into the fetal circulation in the form of TAG.