Incorporation <i>in vivo</i> of 1-¹⁴C-Palmitic Acid into Placental and Fetal Liver Lipids of the Rabbit

Abstract

The incorporation of free fatty acid into the placental and fetal liver lipids of rabbits was studied after fetal injections of albumin-bound l-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 the 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 evenly 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.

The effects of energy intake during pregnancy in doe rabbits on pup birth weight, milk output and maternal body composition change in the ensuing lactation

“…It should be noted that on both treatments does were above their predicted maintenance requirements for DE (approximately 1-2 MJ DE/day, from the data of Partridge et al 1983). One confounding factor in rabbits could be that FFA can cross the haemochorial placenta and be directly incorporated into foetal adipose tissue (Elphick & Hull, 1977;Stammers, Elphick & Hull, 1981). In contrast in sheep the epitheliochorial placenta appears to allow negligible direct transport.…”

Effect of Maternal Glucose Infusions on Fatty Acid Transport across the Placenta in Rabbits

“…The human placenta in vitro incorporates FFA into triglyceride (35,39), but this incorporation is apparently independent of glucose concentration and the presence of in sulin (2). Esterification of labelled FFA into rabbit placental triglyceride in vitro and in vivo is small compared with that of the human placenta and compared with incorporation by the fetal liver (7,15). The significance of placental triglyceride esterification in terms of active fatty acid transport is not known.…”

Distribution of Label in Maternal Plasma, Placenta, Fetal Plasma and Tissues after Injection of ¹⁴C-Palmitate into the Circulation of 21- and 28-Day-Pregnant Rabbits

“…Studies during late pregnancy in guinea pigs (Balmier et al, 1972;Bcjhmer and Havel, 1975) and rabbits (Edson et a l, 1975) suggest that maternal plasma FFA enter the fetal circulation and contribute to the triglyceride stores of fetal adipose tissue and liver. The ability of fetal liver and brown adipose tissue (BAT) to take up and esterify 14C-palmitate has been demonstrated in vitro {Hudson and after fetal injection of 14C-palmitate (Elphick and Hull, 1977). It therefore seemed likely that maternal plasma FFA could be important in the anabolic metabolism of the fetus.…”