Transfer of long-chain fatty acids to the fetal and neonatal lamb

The transfer across the ovine placenta of [3H] palmitic acid, 1-[14C] oleic acid, 1-[14C] linoleic acid and 1-[14C] linolenic acid has been studied in chronically catheterized ewes and fetuses using continuous infusion and single injection techniques. No radioactivity was detected in fetal plasma lipids after continuous infusion of isotope into the maternal circulation and a maximum of 0.04% of the injected radioactivity was transferred to the fetal plasma lipids in a 30 min period following the single injection of isotope into the ewe. No detectable radioactivity was transferred to the maternal circulation after injection of isotope into the fetus. The concentration of fetal plasma free fatty acids was very low (less than 50 mumol/1) and that of esterified lipids was about a third of the concentrations in maternal plasma. Two ewes lambed shortly after the infusion of isotope into the maternal circulation and an appreciable amount of radioactivity was subsequently secreted in milk and transferred to the sucking lamb. It was calculated that up to 50% of the radioactivity from 1-[14C] linoleic acid injected into the maternal circulation could have been secreted in milk in the first month of lactation. About 2 g of linoleic acid was secreted in milk daily. It is concluded that the syndesmochorial placenta is virtually impermeable to long chain fatty acids in both directions and that the most important source of linoleic acid for the developing lamb is from milk during the neonatal period.