The transfer of free fatty acids across the rabbit placenta

Dietary Phospholipid-Bound Conjugated Linoleic Acid and Docosahexaenoic Acid Incorporation Into Fetal Liver and Brain Modulates Fatty Acid and N-Acylethanolamine Profiles

We evaluated whether maternal intake of conjugated linoleic acid (CLA) and docosahexaenoic acid (DHA) in the phospholipid (PL) form (CLA-DHA PL) affects maternal and fetal brain and liver fatty acids (FAs) profile and the biosynthesis of FA-derived bioactive lipid mediators N-acylethanolamines (NAEs) involved in several neurophysiological functions. We fed rat dams during the first 2/3 of their pregnancy a CLA-DHA PL diet containing PL-bound 0.5% CLA and 0.2% DHA. FA and NAE profiles were analyzed in maternal and fetal liver and brain by Liquid Chromatography diode array detector (LC-DAD) and MS/MS in line. We found that CLA and DHA crossed the placenta and were readily incorporated into the fetal liver and brain. CLA metabolites were also found abundantly in fetal tissues. Changes in the FA profile induced by the CLA-DHA PL diet influenced the biosynthesis of NAE derived from arachidonic acid (ARA; N-arachidonoylethanolamine, AEA) and from DHA (N-docosahexaenoylethanolamine, DHEA). The latter has been previously shown to promote synaptogenesis and neuritogenesis. The reduced tissue n6/n3 ratio was associated to a significant decrease of AEA levels in the fetal and maternal liver and an increase of DHEA in the fetal and maternal liver and in the fetal brain. Maternal dietary CLA-DHA PL by promptly modifying fetal brain FA metabolism, and thereby, increasing DHEA, might represent an effective nutritional strategy to promote neurite growth and synaptogenesis and protect the offspring from neurological and psychiatric disorders with neuroinflammatory and neurodegenerative basis during the critical prenatal period.

Regulation of placental nutrient transport and implications for fetal growth

Fetal macronutrient requirements for oxidative metabolism and growth are met by placental transport of glucose, amino acids, and, to a lesser extent that varies with species, fatty acids. It is becoming possible to relate the maternal–fetal transport kinetics of these molecules in vivo to the expression and distribution of specific transporters among placental cell types and subcellular membrane fractions. This is most true for glucose transport, although apparent inconsistencies among data on the roles and relative importance of the predominant placenta glucose transporters, GLUT-1 and GLUT-3, remain to be resolved. The quantity of macronutrients transferred to the fetus from the maternal bloodstream is greatly influenced by placental metabolism, which results in net consumption of large amounts of glucose and, to a lesser extent, amino acids. The pattern of fetal nutrient supply is also altered considerably by placental conversion of glucose to lactate and, in some species, fructose, and extensive transamination of amino acids. Placental capacity for transport of glucose and amino acids increases with fetal demand as gestation advances through expansion of the exchange surface area and increased expression of specific transport molecules. In late pregnancy, transport capacity is closely related to placental size and can be modified by maternal nutrition. Preliminary evidence suggests that placental expression and function of specific transport proteins are influenced by extracellular concentrations of nutrients and endocrine factors, but, in general, the humoral regulation of placental capacity for nutrient transport is poorly understood. Consequences of normal and abnormal development of placental transport functions for fetal growth, especially during late gestation, and, possibly, for fetal programming of postnatal disorders, are discussed.

Effects of dietary energy level and source on foetal development and energy balance in concurrently pregnant and lactating primiparous rabbit does

The aim of this experiment was to study the effects of dietary energy level and source on foetal growth and survival and mobilization of body stores in concurrently pregnant and lactating primiparous rabbit does. Does were given a moderate-energy diet (≍9·9 MJ digestible energy (DE) per kg dry matter (DM); group M, no. = 23) or a high-energy diet (-12·2 MJ DE per kg DM). In this latter case, additional energy came from starch (group S, no. = 23) or starch and fat (group F, no. = 22). Primiparous rabbit does were mated within 12 h after parturition and were slaughtered on day 28 of gestation-lactation. During the first 21 days, the DE intake and milk production were higher in the group F than in the groups S and M (P < 0·05). On day 28 of pregnancy, the weight of adipose tissues and liver, as well as the lipid content of the carcass, were higher in the groups S and F than in the group M (P < 0·05). Foetal survival and weight were similar in the three groups. These results indicate that increased energy level of the diet did not improve foetal survival or growth in concurrently pregnant and lactating primiparous does. On the contrary, it could reduce the mobilization offat stores, especially if the energy source is starch.

Placental invasiveness and brain-body allometry in eutherian mammals

Brain growth is a key trait in the evolution of mammalian life history. Brain development should be mediated by placentation, which determines patterns of resource transfer from mothers to fetal offspring. Eutherian placentation varies in the extent to which a maternal barrier separates fetal tissues from maternal blood. We demonstrate here that more invasive forms of placentation are associated with substantially steeper brain-body allometry, faster prenatal brain growth and slower prenatal body growth. On the basis of the physiological literature we suggest a simple mechanism for these differences: in species with invasive placentation, where the placenta is bathed directly in maternal blood, fatty acids essential for brain development can be readily extracted by the fetus, but in species with less invasive placentation they must be synthesized by the fetus. Hence, with regard to brain-body allometry and prenatal growth patterns, eutherian mammals are structured into distinct groups differing in placental invasiveness.

Effect of selection for litter size and feeding programme on the performance of young rabbit females during rearing and first pregnancy

A total of 166 crossbred young female rabbits were used to study the effect of two types of crossbred does (H1 v. H2, old and current generations, respectively) from the cross of different generations of maternal lines selected for litter size, the use of a feeding programme based on a low energy rearing diet (F) and the presentation of a high-energy dietpre-partum(E) on the performance of young rabbit females until their first parturition and on the main litter traits at first kindling. Perirenal fat was thicker at the age of 3 months for H2 than for H1 does, but this difference disappeared at the first insemination (4·5 months). H2 does had a significantly larger total number and number of live pups at birth (+2·06 live pups) than H1, higher than expected (+1·06). As this greater foetal growth was obtained for a similar energy intake of does, possible differences may exist in partitioning and/or effficiencies of dietary and body energies in favour of foetal growth as the genetic propensity for litter size increased. The use of a low-energy diet significantly reduced the growth of does during the rearing period (−294 g), but they showed a greater compensatory growth during the first 4 weeks of gestation (+79 g) as a consequence of their higher energy intake, without any retardation in their reproductive development. Does receiving diet F until 28th day of gestation showed a significantly greaterpre-partumenergy intake and their number of pups born alive was lower (−1·3 pups). Finally, the litters of females receiving diet Epre-partumand during lactation had lower mortality during the 1st week (26·9 v. 42·9% dead pups) and throughout lactation than those receiving a moderate energy diet.

Influence of a maternal cholesterol-enriched diet on [1-14C]-linoleic acid and L-[4, 5-3H]-leucine entry in plasma of rabbit offspring

Fetal development requires an important entry of essential free fatty acids (EFFA) and essential amino acids (EAA) into the fetal circulation. We have reported that a 0.2% enriched-cholesterol diet (ECD) during rabbit gestation significantly reduces fetus weight compared to control diet. It is known that dietary linoleic acid deficiency, an EFFA, during the fetal development induces an important impair to the somatic development. Moreover, intrauterine growth retardation induced a reduction of the flux of leucine, an EAA, from maternal to fetal circulation. Therefore, we hypothesized that the administration of an ECD induces modifications of placental lipid composition concomitant alterations of the transfer of linoleic acid and leucine in fetal circulation. Quantification of placental lipids revealed that in the ECD group a reduction of total-cholesterol (TC) and free-cholesterol (FC) is observed, however an increased in FFA and phospholipids is noticed when compared to the control group. In placenta from the ECD group, the FC/ TC ratio is significantly reduced compared to the control group. In the ECD group, the liver shows an increase of TC, FC and FFA compared to the control group. However, the quantity of triacylglycerol present in the liver from the ECD is significantly reduced compared to the control group. To evaluate the placental transfer of some essential nutrients, intravenous injection of [1-14C]-linoleic acid or L-[4, 5-3H]-leucine to term rabbit (control and ECD group) were done. Two hours later, rabbits were euthanized and we collected placenta, livers and blood from dams and offspring. The concentrations of both radiolabeled molecules (linoleic acid and its esterified form or leucine) were higher in the plasma of ECD offspring than those found in offspring from control diet. Despite such alteration of placental lipid composition, linoleic acid and leucine transfer by the placenta was not compromised but rather increased.

The fetal origins of atherosclerosis: maternal hypercholesterolemia, and cholesterol-lowering or antioxidant treatment during pregnancy influence in utero programming and postnatal susceptibility to atherogenesis

It has long been postulated that pathogenic events during fetal development influence atherosclerosis-related diseases later in life, but the mechanisms involved are unknown. This review focuses on the evidence indicating that maternal hypercholesterolemia during pregnancy is responsible for one cascade of pathogenic events. Maternal hypercholesterolemia is associated with greatly increased fatty streak formation in human fetal arteries and accelerated progression of atherosclerosis during childhood. Recent experiments in genetically more homogeneous rabbits established that temporary diet-induced maternal hypercholesterolemia is sufficient to enhance fetal lesion formation. More important, maternal hypercholesterolemia or ensuing pathogenic events in the fetus increase postnatal atherogenesis in response to hypercholesterolemia. Maternal treatment with cholesterol-lowering agents or antioxidants greatly reduces fetal and postnatal atherogenesis, indicating a pathogenic role of lipid peroxidation and a potential involvement of oxidation-sensitive signaling pathways. Experiments in a murine model showed that differences in arterial gene expression between offspring of normo- and hypercholesterolemic mothers persist long after birth, supporting the assumption that fetal lesion formation is associated with genetic programming, which may in turn affect postnatal atherogenesis. A better understanding of pathogenic programming events in utero may lead to the identification of genes determining the susceptibility to atherosclerosis and define novel preventive approaches.

Maternal hypercholesterolemia enhances atherogenesis in normocholesterolemic rabbits, which is inhibited by antioxidant or lipid-lowering intervention during pregnancy: an experimental model of atherogenic mechanisms in human fetuses

Maternal hypercholesterolemia during pregnancy is associated with a marked increase in aortic fatty streak formation in human fetuses and faster progression of atherosclerosis during normocholesterolemic childhood. However, the mechanisms responsible are unknown, and the contribution of genetic differences is difficult to assess in humans. The goal of this study was to determine whether maternal hypercholesterolemia per se may cause enhanced fatty streak formation in offspring and whether interventions during pregnancy can reduce it. During pregnancy, 1 group of New Zealand White rabbits was fed control chow and 8 groups were fed hypercholesterolemic diets Chol 1 (yielding plasma cholesterol of 153 mg/dL) or Chol 2 (yielding 359 mg/dL) without or with cholestyramine, vitamin E, or both. Offspring (n=15 to 25 per group) were killed at birth. Maternal hypercholesterolemia enhanced mean lesion size in the aorta of their offspring at birth from 44+/-18x10(3) micrometer(2) per section in controls to 85+/-26x10(3) in Chol 1 and 156+/-49x10(3) in Chol 2 groups (P<0.0001 for both). Cholestyramine or vitamin E treatment of mothers significantly reduced atherosclerosis at birth by up to 39% compared with controls on the same diet. Oxidized fatty acids and malondialdehyde in aortic atherosclerotic lesions and plasma were similarly affected by diets and treatment as atherosclerosis. Our results establish the causal role of hypercholesterolemia and peroxidation in fetal atherogenesis and demonstrate that both lipid-lowering and antioxidant interventions during pregnancy can reduce it. If it can be established that interventions in mothers also affect progression of lesions after birth, this may indicate a novel approach for the prevention of atherosclerosis.

Kinetics of palmitic acid transport in insulin-dependent diabetic pregnancies: in vitro study

BACKGROUND

The paucity of data relating to transport kinetics of free fatty acids (FFA) in pregnant diabetic women prompted the undertaking of the present study.

METHODS

Transport kinetics of a model FFA, palmitic acid, have been investigated in Type I diabetic pregnancies, using in vitro perfusion of isolated placental lobules. National Cancer Tissue Culture medium diluted with Earle's buffered salt solution was used as the perfusate and control placental lobules were perfused for comparison.

RESULTS

In five Type I diabetic women, the palmitic acid transport fraction (TF) averaged 5.6 +/- 0.42% of injected maternal bolus dose, representing 11.8 +/- 2.1% that of tritiated water used as reference. In control perfusions (n = 5), the palmitic acid TF represented 10.2 +/- 1.3% of tritiated water TF. Differential transport rates of palmitic acid for 10, 25, 50, 75 and 90% of efflux in fetal veins differed significantly from the corresponding values for tritiated water in both study and control series. However, palmitic acid transport rates for the various efflux fractions in the two series were not significantly different. For kinetic parameters, such as area under the curve, clearance, elimination constant, time for maximum response, absorption rate and elimination rate, the values for palmitic acid in the diabetic and control series also did not differ significantly.

CONCLUSION

Transport kinetics of palmitic acid in Type I human diabetic pregnancies in in vitro conditions do not differ significantly from those observed in normal pregnancies.

Effect of glucose load on the transport kinetics of palmitic acid in the human placenta: an in vitro study

1. A paucity of data relating to free fatty acid (FFA) transport in the human placenta in non-steady state conditions prompted us to undertake the present study. 2. The transport kinetics of palmitic acid in non-steady state conditions have been investigated in vitro using human perfused placental lobules. The effects of varying glucose concentrations on maternal-foetal transport of the FFA were also investigated to mimic the hyperglycaemic states of human diabetic pregnancies. 3. National Cancer Tissue Culture medium diluted with Earle's buffered salt solution was used as the perfusate. [14C]-Palmitic acid, along with tritiated water as a reference, was injected as a bolus into the maternal arterial perfusate and perfusate samples were collected from the venous outflow for a period of 5 min. 4. The transport fraction (TF) of palmitic acid, expressed as percentage of the injected bolus, averaged 3.45 +/- 0.15% in five perfusions, representing 9.2 +/- 1.3% of the corresponding reference marker TF. Kinetic parameters, as well as TF indices of palmitic acid expressed in relation to the reference substance, did not differ significantly between perfusions with a physiological glucose load and those with hyperglycaemic concentrations of glucose of 27.8 and 55.6 mmol/L. 5. The present study shows that hyperglycaemia per se does not significantly alter palmitic acid transport kinetics in vitro in the human perfused placental lobule.

Impact of a cholesterol enriched diet on maternal and fetal plasma lipids and fetal deposition in pregnant rabbits

Pregnancy is associated with a hypercholesterolemic and a hyperlipidemic state. The totality of the essential fatty acids and 50% of the lipids needed by the fetus are transferred by the placenta from the maternal circulation. The hypothesis of this study is that an augmentation of the maternal plasmatic cholesterol is modifying the fetal lipids accumulation and development during rabbit pregnancy. To demonstrate the impact of a cholesterol enriched diet on plasma lipids during rabbit's pregnancy and on their fetus, we have established two groups: control and hypercholesterolemic rabbits (fed with a 0.2% cholesterol diet). Blood samples were collected before mating and at each trimester of pregnancy for analysis of lipid fractions and their lipoproteins. Plasma analysis shows that starting the 10th day of pregnancy the concentration of total-cholesterol and lipoproteins decreases for both groups. We have demonstrated that for the hypercholesterolemic group, concentrations of total-cholesterol (631%) and lipoproteins are significantly higher at the end of pregnancy than those for the control group. For both groups, after 20 days of pregnancy, triglycerides metabolism was biphasic showing a significant increase followed by a diminution in their concentration. In both groups, free fatty acids increases significantly at the end of the pregnancy (537.5% for the control group and 462.5% for the hypercholesterolemic group). Furthermore, the offsprings of hypercholesterolemic dams manifest a lower birth weight (15.5%) than those of control group. Our results demonstrate that a cholesterol enriched diet modifies greatly the fetal development and lipid metabolism during rabbit's pregnancy. These modifications could be useful for the understanding of the interaction between diet and fetal development in rabbit and probably during human pregnancy.

Maternal and umbilical venous plasma lipid concentrations at delivery in the mare

The concentrations and fatty acid composition of the plasma free fatty acid, triacylglycerol and phospholipid fractions were determined in maternal and umbilical cord vein blood samples taken at delivery from 17 mares. Maternal and umbilical vein plasma free fatty acid concentrations were of a similar order and a positive correlation was found between the two levels suggesting that the equine placenta is permeable to fatty acid. Substantial amounts of the essential fatty acids and their longer chain derivatives were seen in both umbilical vein plasma free fatty acid and phospholipid fractions supporting this view. Certain long chain polyunsaturated derivatives of the essential fatty acids found in the umbilical venous plasma phospholipid fraction were not seen in the maternal circulating lipids. The precursor fatty acids were readily available to both foetal and placental tissues and therefore must have been elongated and incorporated into phospholipid by either or both. Very small amounts of the essential fatty acids were found in adipose stores in the newborn foal and virtually no fat stores at all in the newborn foal liver.

High arachidonic acid levels in the cord blood of infants of mothers on vegetarian diets

1. Maternal and umbilical cord plasma samples were collected from forty-seven Asian women, twenty-eight life-long vegetarians and seventeen non-vegetarians, during delivery of their babies. The concentrations and fatty acid profiles of the plasma free fatty acid and triacylglycerol fractions were determined. 2. There were no significant differences between the levels of free fatty acid and triacylglycerol in either maternal or cord plasma from vegetarian compared with non-vegetarian Asian women. The fatty acid profiles of the lipid fractions in the two groups were similar. Total plasma free fatty acid levels in the maternal circulation correlated with umbilical cord levels. 3. The levels of linoleic acid in the maternal plasma free fatty acid fraction of the Asian women were much higher than previous reports on mixed populations of European women. In the Asian women arachidonic acid concentrations in both maternal and umbilical circulations were over four times higher than those reported for women unselected for race and diet.

The effects of dietary supplementation with fish oil in patients with psoriasis

Ten patients with psoriasis resistant to conventional topical treatment were given dietary supplements of fish oil, providing approximately 12 g of eicosapentaenoic acid daily for a period of at least 6 weeks. In eight patients there was a modest improvement in their psoriasis, the principal effects being a diminution of erythema and scaling. The dietary treatment resulted in a substantial inhibition of leukotriene B4 production by the peripheral blood polymorphonuclear leukocytes in vitro. The discrepancy between the high degree of inhibition of leukotriene B4 synthesis and the modest therapeutic effect suggests that leukotriene B4 is not the only mediator involved in the development of the psoriatic lesion. Furthermore, the in vivo cutaneous levels of leukotriene B4 might not have been inhibited to the same extent as the polymorphonuclear leukocyte levels in vitro. Further studies on the use of fish oil supplements, both on their own and in conjunction with other forms of treatment in psoriasis are warranted. It will also be important to determine whether the altered profile of 5-lipoxygenase products found in the blood is also seen in the skin.

The transfer of free fatty acids across the human placenta

Thirty-three matched maternal venous and umbilical cord vein and artery plasma samples were obtained at elective caesarean section and the concentrations of the individual free fatty acids determined. The maternal levels were 1.009 (SEM 0.043) and the umbilical vein-artery difference was 0.036 (SEM 0.011) mmol/l. There was a significant correlation between the mean concentration in maternal venous blood and the vein-artery difference for myristic, palmitic, stearic, linoleic and docosahexaenoic acids but not for oleic acid. When arachidonic acid concentration in the fetus was high, then the vein-artery difference was negative (flow to the placenta), when it was low, the difference was positive (flow to the fetus). Thus whilst there appears in general to be a flow of fatty acid to the fetus dependent on maternal free fatty acid concentrations, the transfer of arachidonic acid is largely determined by other factors. The reasons why oleic acid does not behave like the other fatty acids is not clear.

The role of the placenta in the supply of essential fatty acids to the fetal sheep: studies of lipid compositions at term

A study has been made of the comparative distribution and fatty acid compositions of the major lipid fractions of maternal plasma, placenta and fetal plasma of the sheep at approximately 120 days of gestation. Cholesteryl esters and phospholipids constituted the major lipid fractions present in both maternal and fetal plasmas. In the placenta, phospholipids accounted for some 60 per cent of the total lipid present. Within the phospholipids of the maternal and fetal plasmas and placenta, phosphatidylcholine comprised the largest component. Whereas maternal plasma contained high levels of linoleic and arachidonic acids, fetal plasma contained a low proportion only a linoleic acid and high proportions of delta 5,8,11 eicosatrienoic acid and arachidonic acid. In the maternal plasma the arachidonic acid:linoleic acid ratio was only 0.17, but in the fetal plasma the ratio was 3.32. The differences in the lipid and fatty acid compositions between the maternal plasma, fetal plasma and placenta are discussed in relationship to the distinctive polyunsaturated fatty acid metabolism of the fetal and newborn lamb.

Placental uptake and transfer of lipid in the postterm rabbit

Gonadotropin-injected pregnant rabbits were delivered by cesarean section near term (30 days after conception (term, 31 days) and 3 1/2 and 4 days post term. Lipid metabolism of the postterm and near-term fetus was compared. Fetal and placental uptake of radioactivity and rate of lipid entry into the fetus, as well as fetal and maternal plasma free fatty acid (FFA) specific activities (at equilibrium) were determined following a single maternal injection of [1-14C]palmitate (50 muCi) administered at cesarean section. Evidence of placental malfunction in the postterm period includes decreased placental uptake and transport of labeled FFA occurring while maternal and fetal FFA dynamics (half times) remain unchanged and a loss in "organization": The strong positive correlation (p less than 0.001) between placental uptake and transfer to the fetus at 30 days' gestation is lost 5 days later. A comparison of maternal and fetal plasma FFA specific activities indicates a substantial (62%) near-term fetal contribution to its own circulating FFA pool. Total plasma FFA is elevated in the postterm fetus concomitant with a decreasing maternal supply. A postterm fetus must therefore contribute lipid from its own reserves (probably liver) in excess of amounts attributed to a near-term fetus, i.e., greater than 62%.

The passage of fat emulsion across the human placenta

Six patients near term were given an intravenous infusion of a fat emulsion (Intralipid) a few hours before normal delivery or Caesarean section. Six other non-infused patients were studied as controls. Maternal venous and umbilical venous and arterial blood samples were taken at delivery and analyzed for individual fatty acid concentrations in triglyceride, free fatty acid (FFA) and phospholipid fractions. The emulsion, being rich in oleic and linoleic acids, affected the composition of the maternal triglycerides. The fetal lipids were also altered and the infusions resulted in large positive umbilical venous-arterial (v-a) differences in FFA and triglyceride fatty acid concentrations, but this was not the case for phospholipid concentrations. The fatty acids with the largest v-a differences were those prominent in the emulsion.

Cord blood hypertriglyceridaemia as an index of fetal stress: use of a simple screening test and results of further biochemical analysis

In this preliminary study, 120 cord blood samples were subjected to a simple on-the-ward triglyceride screening procedure and 15 were designated as being high and another 15 randomly selected as controls. All the samples were then subjected to detailed biochemical analysis for fatty acid profiles and/or concentrations of free fatty acids, triglycerides (TG), phospholipids, cholesterol esters and glycerol. Eleven of the samples designated 'high' were associated with one or more of the following clinical conditions: family history of ischaemic heart disease, maternal starvation, fetal distress, light-for-dates babies and excessive weight gain during pregnancy. There was an association between high TG levels and high glycerol levels. The fatty acid pattern of the TG was altered when at abnormally high concentration, in particular oleic acid was increased relative to the others, and this was associated with an increase in cholesterol ester oleic acid. The possible mechanisms resulting in cord hypertriglyceridaemia are discussed.

The distribution of arachidonic acid in plasma and tissues of patients near term undergoing elective or emergency Caesarean section

The distribution of arachidonic acid in both the free and the bound state was measured in the maternal circulation, the fetal circulation and tissues within the pregnant uterus in 16 patients undergoing Caesarean section. Half of the patients had an elective Caesarean section and half had a Caesarean section during labour. No differences in arachidonic acid concentrations were found between the maternal or fetal circulations in women having elective Caesarean section and those having a Caesarean section in labour. The total and bound values of arachidonic acid in myometrium were higher in patients undergoing Caesarean section in labour. There was also an increased amount of arachidonic acid when expressed as an arachidonic acid/palmitic acid ratio between the fetal circulation and the maternal circulation, suggesting an active transport mechanism for arachidonic acid across the placenta. Levels of free arachidonic acid were in microgram quantities in both plasma and tissues, suggesting that the availability of free arachidonic acid was not the limiting factor in prostaglandin production.

Rabbit placental clearing-factor lipase and transfer to the foetus of fatty acids derived from triglycerides injected into the mother

1. Lipase activity was measured in rabbit placental tissue fragments in late pregnancy. The activity in incubated tissue was greater with heparin (69%), reduced by NaCl (90%), but not affected by acetone or ether. 2. Pregnant rabbits (28-days gestation) were given triglyceride emulsions intravenously and the change in profile of fatty acids in the maternal and umbilical artery and vein plasma free fatty acid (FFA) measured. 3. Those fatty acids predominant in the emulsion were higher in concentration in the umbilical vein FFA than in the maternal plasma FFA and the venous-arterial difference was altered such that the placental transfer of FFA was enriched in a pattern corresponding to the profile of the fatty acids in the emulsion. 4. It is concluded that (i) the rabbit placenta shows considerable lipase activity and the lipase has the same characteristics as clearing-factor (lipoprotein) lipase, (ii) triglyceride infused into the mother is taken up by the placenta and hydrolysed, and (iii) the fatty acids so released pass through the placenta and are taken up by the foetus.