Incorporation in vivo of 1-14C-palmitic acid into placental and fetal liver lipids of the rabbit.

The incorporation of free fatty acid into the placental and fetal liver lipids of rabbits was studied after fetal injections of albumin-bound 1-14C-palmitic acid. The fetuses were killed either 5--10 or 10--20 min after the injection. The placentas and livers were extracted for lipids and the specific activities of triglycerides (TG), phospholipids (PL), free fatty acids (FFA), monoglycerides (MG) and diglycerides (DG) measured. The lipids of the liver and placenta took up 17.0 and 3.6% of the dose, respectively, and of that liver TG accounted for 74% and the placental TG 34% of the label in each tissue. Most of the remaining counts were in the PL fraction with the rest more or less evely distributed between the FFA, DG and MG fractions. No activity was recorded in the cholesterol esters. The placental TG, PL, DG and MG specific activities reached the same level as that of the placental FFA, while in the liver these esters had higher specific activities (than the liver FFA). The liver TG, DG and PL had higher specific activities when compared with those of the placenta. The specific activity of the placental FFA was lower at 10--20 min than at 5--10 min; the opposite was seen for the placental TG. No time-related changes were seen in the liver lipids. It is concluded that (i) both placenta and fetal liver incorporate FFA into glycerides and PL; (ii) the liver incorporates FFA more rapidly and to a greater extent than the placenta; (iii) most of the FFA is incorporated into TG and to a lesser extent (PL; (iv) in both organs hydrolysis of PL or TG occurs. These results are discussed with reference to placental transport of FFA and fetal fat metabolism.