Early treatment of the pregnant guinea pig with IGFs promotes placental transport and nutrient partitioning near term

Appropriate partitioning of nutrients between the mother and conceptus is a major determinant of pregnancy success, with placental transfer playing a key role. Insulin-like growth factors (IGFs) increase in the maternal circulation during early pregnancy and are predictive of fetal and placental growth. We have previously shown in the guinea pig that increasing maternal IGF abundance in early to midpregnancy enhances fetal growth and viability near term. We now show that this treatment promotes placental transport to the fetus, fetal substrate utilization, and nutrient partitioning near term. Pregnant guinea pigs were infused with IGF-I, IGF-II (both 1 mg.kg-1.day-1) or vehicle subcutaneously from days 20-38 of pregnancy (term=69 days). Tissue uptake and placental transfer of the nonmetabolizable radio analogs [3H]methyl-D-glucose (MG) and [14C]aminoisobutyric acid (AIB) in vivo was measured on day 62. Early pregnancy exposure to elevated maternal IGF-I increased placental MG uptake by>70% (P=0.004), whereas each IGF increased fetal plasma MG concentrations by 40-50% (P<0.012). Both IGFs increased fetal tissue MG uptake (P<0.048), whereas IGF-I also increased AIB uptake by visceral organs (P=0.046). In the mother, earlier exposure to either IGF increased AIB uptake by visceral organs (P<0.014), whereas IGF-I also enhanced uptake of AIB by muscle (P=0.044) and MG uptake by visceral organs (P=0.016) and muscle (P=0.046). In conclusion, exogenous maternal IGFs in early pregnancy sustainedly increase maternal substrate utilization, placental transport of MG to the fetus, and fetal utilization of substrates near term. This was consistent with the previously observed increase in fetal growth and survival following IGF treatment.     

Maternal lipid metabolism and placental lipid transfer

During early pregnancy, long-chain polyunsaturated fatty acids (LC-PUFA) may accumulate in maternal fat depots and become available for placental transfer during late pregnancy, when the fetal growth rate is maximal and fetal requirements for LC-PUFAs are greatly enhanced. During this late part of gestation, enhanced lipolytic activity in adipose tissue contributes to the development of maternal hyperlipidaemia; there is an increase in plasma triacylglycerol concentrations, with smaller rises in phospholipid and cholesterol concentrations. Besides the increase in plasma very-low-density lipoprotein, there is a proportional enrichment of triacylglycerols in both low-density lipoproteins and high-density lipoproteins. These lipoproteins transport LC-PUFA in the maternal circulation. The presence of lipoprotein receptors in the placenta allows their placental uptake, where they are hydrolysed by lipoprotein lipase, phospholipase A(2) and intracellular lipase. The fatty acids that are released can be metabolized and diffuse into the fetal plasma. Although present in smaller proportions, maternal plasma non-esterified fatty acids are also a source of LC-PUFA for the fetus, their placental transfer being facilitated by the presence of a membrane fatty acid-binding protein. There is very little placental transfer of glycerol, whereas the transfer of ketone bodies may become quantitatively important under conditions of maternal hyperketonaemia, such as during fasting, a high-fat diet or diabetes. The demands for cholesterol in the fetus are high, but whereas maternal cholesterol substantially contributes to fetal cholesterol during early pregnancy, fetal cholesterol biosynthesis rather than cholesterol transfer from maternal lipoproteins seems to be the main mechanism for satisfying fetal requirements during late pregnancy.     

Vitamin D-dependent calcium-binding protein. Changes during gestation, prenatal and postnatal development in rats

During the perinatal period, calcium metabolism is stressed. As intestinal Ca-binding protein is considered as a molecular expression of the hormonal effect of 1,25-dihydroxycholecalciferol (1,25(OH)2D3), Ca-binding protin measurements may document the vitamin D roles during this period. We describe the variations of Ca-binding protein concentrations in the rat during the last 5 days of gestation, in the maternal duodenum, placentas, fetal membranes and fetal intestines. We also report intestinal Ca-binding protein changes from birth until weaning. The evolution of the maternal intestinal Ca-binding protein, which increases on day 19.5 of gestation, is consistent with that of calcium intestinal absorption and may be explained by increased 1,25(OH)2D3 production. Placental Ca-binding protein rises from day 17.5 until the end of gestation, and may be related to the profile of calcium transfer from mother to fetuses. It is noteworthy that the placental Ca-binding protein is predominantly found in the fetal part of the organ where materno-fetal exchanges occur. The yolk sac synthesizes substantial amounts of Ca-binding protein. In the fetal membranes, Ca-binding protein plateaus from day 17.5 until day 20.5 and decreases on day 21.5. The Ca-binding protein presence in the fetal placenta and in the yolk sac may suggest that these tissues are also targets for vitamin D. In the fetus the intestinal Ca-binding protein s is detected as early as day 17.5 of gestation and increases markedly during the last day of gestation. From birth and during the first 3 weeks of postnatal life, the intestinal Ca-binding protein concentration does not change. It undergoes a sharp rise just at the time of weaning. We have also shown that the specific distribution of Ca-binding protein along the intestine is acquired during intrauterine life and does not change with sucking or weaning. The two main changes of intestinal Ca-binding protein, observed just before birth and at weaning, may reflect the intestinal maturation and/or variations in vitamin D metabolism.     

Low iron diet and parenteral cadmium exposure in pregnant rats: the effects on trace elements and fetal viability

The effects of latent iron deficiency combined with parenteral subchronic or acute cadmium exposure during pregnancy on maternal and fetal tissue distribution of cadmium, iron and zinc, and on fetal viability were evaluated. Timed-pregnant Sprague-Dawley rats were fed on semisynthetic test diets with either high iron (240 mg kg) or low iron (10 mg kg), and concomitantly exposed to 0, 3 or 5 mg cadmium (as anhydrous CdCl₂) per kilogram body weight. Animals were exposed to cadmium from gestation day 1 through 19 by subcutaneously implanted mini pumps (Subchronic exposure) or on gestation day 15 by a single subcutaneous injection (Acute exposure). All rats were killed on gestation day 19. Blood samples, selected organs and fetuses were removed and prepared for element analyses by atomic absorption spectrometry. Low iron diet caused decreases in maternal body weight, maternal and fetal liver weights, placental weights and tissue iron concentrations. By cadmium exposure, both subchronic and acute, tissue cadmium concentrations were increased and the increase was dose-related, maternal liver and kidney zinc concentrations were increased, and fetal zinc concentration was decreased. Cadmium concentration in maternal liver was additionally increased by low iron diet. Acute cadmium exposure caused lower maternal body and organ weights, high fetal mortality, and decreased fetal weights of survivors. In conclusion, parenteral cadmium exposure during pregnancy causes perturbations in essential elements in maternal and fetal compartments. Acute cadmium exposure in the last trimester of gestation poses a risk for fetal viability especially when combined with low iron in maternal diet.     

Prostaglandin F and E levels in the conceptus, uterus and plasma during early pregnancy in the ewe

Concentrations of prostaglandins E and F (PGE and PGF) were measured in the embryo or fetus, extra embryonic or fetal membranes (membranes), intercaruncular and caruncular endometrium and plasma collected from uterine and ovarian arterial and venous vessels from separate groups of ewes laparotomized at 5 day intervals from day 10 to day 55 of pregnancy. Our purpose was to investigate the role of prostaglandins E and F in the maternal recognition of pregnancy, implantation and early placental function. Our data suggest that the initial maintenance of the corpus luteum in the pregnant ewe does not involve a reduction in PGF production, compared to pregnant ewes; but a change in the pattern of PGF secretion. This is accompanied by an elevation in PGE production of similar magnitude to that observed in non pregnant ewes. The extra embryonic/fetal membranes appear to be the major source of elevated PGF levels in the maternal circulation prior to day 30 of pregnancy. Between days 35 and 55 of gestation the rising PGF levels in maternal serum probably come from the fetus. Over the same period PGE levels rise in the fetus and intercaruncular endometrium, but PGE secretion into the maternal circulation is not enhanced. A role for PGF and PGE in fetal, placental and uterine growth is suggested; placental and uterine endocrine function may also be targets.     

Prostaglandin F and E levels in the conceptus, uterus and plasma during early pregnancy in the ewe

Concentrations of prostaglandins E and F (PGE and PGF) were measured in the embryo or fetus, extra embryonic or fetal membranes (membranes), intercaruncular and caruncular endometrium and plasma collected from uterine and ovarian arterial and venous vessels from separate groups of ewes laparotomized at 5 day intervals from day 10 to day 55 of pregnancy. Our purpose was to investigate the role of prostaglandins E and F in the maternal recognition of pregnancy, implantation and early placental function. Our data suggest that the initial maintenance of the corpus luteum in the pregnant ewe does not involve a reduction in PGF production, compared to pregnant ewes; but a change in the pattern of PGF secretion. This is accompanied by an elevation in PGE production of similar magnitude to that observed in non pregnant ewes. The extra embryonic/fetal membranes appear to be the major source of elevated PGF levels in the maternal circulation prior to day 30 of pregnancy. Between days 35 and 55 of gestation the rising PGF levels in maternal serum probably come from the fetus. Over the same period PGE levels rise in the fetus and intercaruncular endometrium, but PGE secretion into the maternal circulation is not enhanced. A role for PGF and PGE in fetal, placental and uterine growth is suggested; placental and uterine endocrine function may also be targets.     

Iron,zinc, and copper content in the tissues of the rat during pregnancy

The levels of iron, zinc, and copper in the tissues of the pregnant rat, on d 12, 19, and 21 after impregnation have been determined and compared with controls. Iron levels decreased considerably in late pregnancy as a result of increased fetal requirements, thus diminishing iron stores in rat tissues, but maintaining the circulating plasma levels. Copper levels increased slightly at midpregnancy, but returned to control levels at the end of gestation. Zinc stores also increased slightly during early pregnancy, yet were decreased at the end of pregnancy, but to a lesser extent than those of iron. The data are explained on the basis of equilibrium between assimilation and fetal needs for copper, a slightly higher demand for zinc with altered equilibrium, and a much altered equilibrium for iron that provokes a dwindling of iron maternal reserves that is not compensated by dietary iron.     

Iron and copper concentrations in the maternal and fetal serum, placenta and amniotic fluid during the reproductive stadium as well as in the milk of rabbits

Serum concentrations of iron and copper from rabbits (New Zealand White hybrids; N = 12) were determined during the reproductive stadium (gestation and four weeks of lactation). Samples of serum from fetuses, placental tissue and amniotic fluid were also examined. Iron: a decrease of iron in the maternal serum during the second half of gestation was observed, whilst a significant rise occurred in the first week of lactation. The content of iron in the fetal serum dropped from day 21 to day 28 of gestation. The iron concentration in the placental tissue decreased during this time. A rise of the iron level in the amniotic fluid was determined from day 21 to day 28 of gestation. The iron content in the milk was about 33 mumol/l (first and second day of lactation). Copper: in the first half of pregnancy the copper level diminished slightly compared with the content of non-pregnant, non-lactating rabbits, while a rise was observed in the fourth week of this period. The copper concentration decreased in the first week of lactation and then reached the peak level in the second week of this phase. The copper level in the fetal serum declined from day 21 to day 28 of gestation, while the copper content in the amniotic fluid increased significantly on day 28, in comparison with day 21 of gestation. In contrast, a decline of the copper concentration in the placental tissue was noticed from day 21 to day 28 of this period. The copper content in the milk was nearly 25 mumol/l (first and second day of lactation).     

A study of the relationship between placental non-haem iron and iron transfer in the guinea pig: the maturation of the transfer process

The relationship between placental non-haem iron and placental iron transfer has been studied in the guinea pig. From day 25 to day 50, non-haem iron and iron transfer increase. Expressed on placental wet weight or per g of placental DNA, iron transfer and non-haem iron were inversely related; an increase of transfer was accompanied by a decrease of the non-haem iron content. The results are discussed in terms of the hypothesis, that accumulation of non-haem iron in early pregnancy is caused by an imbalance between iron uptake and iron transfer. The steady increase of total non-haem iron till term which has been demonstrated in this study is in contradiction with this hypothesis. The paper describes an alternative hypothesis in which placental non-haem iron, most likely ferritin iron, is assumed to play an active role in the regulation of placental iron transfer.     

The relationship between human cytomegalovirus infection and atherosclerosis development

Transport characteristics of essential trace elements as zinc, copper, selenium and iron have been studied in maternal–fetal direction in normal pregnancies, using in vitro perfusion of human placental lobules. Solutions of trace elements corresponding to twice the physiological concentrations were injected (100 l bolus) into the maternal arterial perfusate. Serial perfusate samples were collected every 30 sec from venous outflows for a study period of 5 min. Concentrations of these trace elements and their transport kinetics were determined. Transport fractions (TF) of zinc, copper, selenium and iron averaged 0.21, 0.49, 0.55 and 0.10% of maternal load respectively. Other parameters such as area under the curve, clearance, elimination constant, absorption and elimination rates showed some significant differences between the various elements. Copper and selenium appear to be transported passively in maternal–fetal direction, while for iron and zinc, role of active transport for transfer across the human placental membrane cannot be discounted. We speculate that alterations in copper: zinc TR50 (transport rate for 50% efflux) and TF ratios could serve as useful indicators for assessing placental transport status of these essential elements in complicated pregnancy states.     

The effect of elevation of maternal plasma catecholamines on the fetus and placenta of the pregnant sheep

To study the effects of reduced uterine blood flow on fetal and placental metabolism, adrenaline has been infused at physiological doses (0.5 microgram/min per kg) into the circulation of the pregnant sheep. This gives a reduction of about one third of uterine blood flow at days 120-143 of pregnancy, but causes no significant change in umbilical blood flow. In contrast to the effects of constricting the uterine artery to reduce blood flow to a similar degree, placental oxygen consumption was reduced and that, together with a large increase in lactate production, indicated the placenta became hypoxic. The fetal blood gas status and hence oxygen consumption was not affected significantly. A consistent arterio-venous difference for glucose across the umbilical or uterine circulations was not detected unless the uterine blood flow was comparatively high. Glucose balance across the uterus showed a close linear relationship with uterine blood flow and more particularly with the supply of glucose to the uterus. There was clear evidence for glucose uptake by the placenta and fetus and also glucose output by both. The latter was more common when uterine blood flow was comparatively low or reduced by adrenaline infusion. The results are consistent with the concept that glucose supply has to be maintained to the placenta even at the expense of fetal stores, although lactate can substitute if there is enhanced output because of fetal hypoxia. They indicate that placental mobilisation of glycogen can lead to a net output of glucose to the mother. The manner of communicating to the fetus changes in placental state that occur during maternal adrenaline infusion is not clear. However towards the end of the 60 min infusion, elevation of fetal plasma adrenaline, probably resulting from a breakdown of the placental permeability barrier, may be an important signal.     

Immunologic consequences of vaccination against abortion in mice

CBA/J female mice have a high rate of fetal resorption when mated with DBA/2J males. This fetal wastage can be dramatically reduced by immunizing the female with BALB/cJ but not DBA/2J spleen cells. We report here that immunization with BALB/cJ (but not DBA/2J) spleen cells leads to 1) anti-paternal MHC antibody that is predominantly of the IgG1 isotype, and which disappears from the serum during pregnancy; 2) increased active suppression in both the spleen and placenta; and 3) an ability to adoptively transfer the fetal protection and placental suppression with serum from the immunized mice. Congenic absorption studies before adoptive transfer indicate that the active component of the serum is also directed against the paternal MHC haplotype. These results indicate that maternal humoral immunity can lead to increased fetal protection in correlation with local active suppression in the placenta. They also suggest an expansion of the placental immunoabsorbent hypothesis to include the induction of active suppression against maternal cell-mediated immunity.     

Growth and in-vitro metabolism of placental tissues of cows from day 100 to day 250 of gestation.

Weight of placental tissues of cows increased exponentially from Day 100 to Day 250 of gestation, but at much slower relative and absolute rates than fetal weight. In addition, growth rate of fetal placental tissues was less than that of maternal placental tissues. Concentrations of DNA, RNA and protein, however, increased in fetal placental but not in maternal placental tissues. Fetal placental tissues therefore exhibited hyperplasia, which probably contributes to increased functional capacity of the placenta during late gestation. The rate of O2 uptake in vitro was greatest for maternal placental tissues, suggesting that the maternal portion of the placenta accounts for most of the large rate of placental O2 utilization in vivo. Compared with other placental tissues, rate of secretion of macromolecules by intercaruncular endometrium was high, but decreased from Day 100 to 250, suggesting that uterine glandular secretory activity may decrease as gestation advances. Rate of secretion of macromolecules also was high for intercotyledonary tissues and increased with day of gestation, suggesting a role for secretory products of chorioallantois in gravid uterine function.     

Factors affecting gas transfer across the placenta and the oxygen supply to the fetus

The factors that affect placental gas exchange are reviewed, with particular reference to recent measurements of the effect of changes in one or more of these factors on O2 delivery to the fetus and on fetal O2 uptake. Fetal or maternal placental blood flows and blood O2 capacities can be altered by 50% without any major change occurring in fetal O2 uptake: umbilical venous O2 content and fetal O2 delivery fall, but the O2 consumption of the fetus is maintained by increasing the fractional extraction of O2 from the blood. There is evidence that the fetus can also cope with a reduction in blood O2 affinity resulting from replacement of fetal with maternal blood. The critical level of O2 delivery is about 0.6 mmol.min-1.kg-1 in the fetal sheep. When O2 delivery is reduced below this level, by decreasing maternal placental blood flow, raising or lowering fetal haematocrit, decreasing maternal O2 capacity, or decreasing fetal O2 affinity, fetal O2 uptake tends to fall. The resultant tissue hypoxia and inability to maintain oxidative metabolism is reflected in a lowering of arterial blood pH and base excess. Whilst the results of short-term experiments suggest that there exists a large reserve for placental O2 transfer and fetal O2 supply, there is evidence that fetal O2 uptake is more tightly linked to O2 delivery when the latter is reduced for a period of days or weeks. In the long term, restriction of the supply of O2 and nutrients leads to a reduced rate of fetal growth and a reprogramming of tissue development.     

Intestinal and placental calcium-binding proteins in vitamin D-deprived or -supplemented rats

In rats, at day 20 of pregnancy, the placenta and the fetal intestine contain calcium-binding proteins (CaBPs) which closely resemble the vitamin D-dependent CaBP of the adult rat duodenal mucosa. A significant and specific increase of the dam intestinal CaBP likely synthesized as a result of pregnancy, is observed. A 5 week-vitamin D-depletion promoted a decrease of the CaBP content of the dam intestine and of its calcemia. No changes were detected in the non-pregnant animals. Likewise, neither fetal calcemia nor CaBP contents of the feto-placental unit were affected. Such findings suggest i) that pregnancy elicits the vitamin D-sensitivity of rats and ii) that a slight vitamin D-deficiency acts only on the maternal compartment. Although the vitamin D-dependence of placental and fetal CaBPs remains to be demonstrated, our results suggest that these proteins act in concert with the maternal CaBP, to favour a mother to fetus transfer of calcium in order to satisfy the needs of the mineralizing fetal skeleton.     

Important aspects of placental-specific gene transfer

The placenta is a unique and highly complex organ that develops only during pregnancy and is essential for growth and survival of the developing fetus. The placenta provides the vital exchange of gases and wastes, the necessary nutrients for fetal development, acts as immune barrier that protects against maternal rejection, and produces numerous hormones and growth factors that promote fetal maturity to regulate pregnancy until parturition. Abnormal placental development is a major underlying cause of pregnancy-associated disorders that often result in preterm birth. Defects in placental stem cell propagation, growth, and differentiation are the major factors that affect embryonic and fetal well-being and dramatically increase the risk of pregnancy complications. Understanding the processes that regulate placentation is important in determining the underlying factors behind abnormal placental development. The ability to manipulate genes in a placenta-specific manner provides a unique tool to analyze development and eliminates potentially confounding results that can occur with traditional gene knockouts. Trophoblast stem cells and mouse embryos are not overly amenable to traditional gene transfer techniques. Most viral vectors, however, have a low infection rate and often lead to mosaic transgenesis. Although the traditional method of embryo transfer is intrauterine surgical implantation, the methodology reported here, combining lentiviral blastocyst infection and nonsurgical embryo transfer, leads to highly efficient and placental-specific gene transfer. Numerous advantages of our optimized procedures include increased investigator safety, a reduction in animal stress, rapid and noninvasive embryo transfer, and higher a rate of pregnancy and live birth.     

Effect of oxygen concentrations on sodium iodide symporter expression and iodide uptake and hCG expression in human choriocarcinoma BeWo cells

Normal human fetal development requires an adequate supply of thyroid hormone from conception. Until about 16 wk gestation this is supplied entirely by placental transfer of maternal hormone. Subsequently, the fetal thyroid synthesizes thyroid hormones, requiring a supply of maternal iodide. Trophoblast iodide transfer is mediated by the apical sodium iodide symporter (NIS). Placental oxygen levels are low in early pregnancy (~1%), rising with placental vascularisation to a plateau of ~8% at about 16 wk. Although the impact of these changing oxygen levels on placental implantation is well recognized, effects on trophoblast materno-fetal exchange are less understood. We investigated expression of the NIS regulator hCG, NIS mRNA expression, and I(125) uptake in choriocarcinoma BeWo cells (a model of the trophoblast) cultured in 1 and 8% oxygen and in room air (21% oxygen). Expression of NIS and hCG mRNA and protein was low at 1% oxygen but rose significantly at 8 and at 21%. This was reflected in significant increases in I(125) uptake. Desferrioxamine, an iron chelator and hypoxia mimic, decreased NIS and hCG expression and I(125) uptake in BeWo cells. NIS expression and I(125) uptake in cells grown at 1% oxygen were not increased by addition of hCG (2,500 IU/l). We infer that placental NIS mRNA and protein expression are regulated by oxygen, rising with vascularization of the placenta in the late first trimester, a time when fetal iodide requirements are increasing.     

The interrelationships between circulating maternal esterified and non-esterified fatty acids in pregnant guinea pigs and their relative contributions to the fetal circulation

The relative contributions of esterified and non-esterified fatty acids to placental lipid transfer were estimated in 7 pregnant guinea-pigs. The fetal side of the placenta was perfused in situ whilst a constant infusion of a mixture of [3H]triacylglycerol emulsion (Intralipid) and [14C]non-esterified fatty acid was given i.v. to the anaesthetised mother. Considerable interconversion of the lipid moieties circulating in the mother was observed. Metabolic turnover rates of triacylglycerol and non-esterified fatty acid were found to be 14.6 mmol/day and 55 mmol/day respectively. No intact triacylglycerol was found to cross the placenta from the mother. Relatively more [3H]non-esterified fatty acid than [14C]non-esterified fatty acid was found in the perfusion fluid when compared with simultaneous circulating maternal levels of these non-esterified fatty acids indicating hydrolysis and direct transfer of [3H]triacylglycerol within the placental tissue. This hydrolysis resulted in the transfer of approximately 0.2 mmol non-esterified fatty acid/day across each placenta at this gestational age (53 days). This is in contrast to the transfer of circulating maternal non-esterified fatty acids, these can be calculated to give a mother to fetus unidirectional transport value of 3.62 mmol/day/placenta, but the total maternal to fetal flux taking into account back transfer to the mother is 1.26 mmol/day/placenta. Results from simultaneous carotid artery and uterine vein samples showed that approximately 40% of the maternal arterial triacylglycerol is removed during a pass through the uterine bed, but the majority of the triacylglycerol re-emerges in the uterine vein as non-esterified fatty acids, and masks the uterine vein uptake of circulating maternal non-esterified fatty acid. The uterine vein non-esterified fatty acid concentration is highly dependent upon levels of circulating maternal triacylglycerols and apparent uterine bed production of non-esterified fatty acid occurs when maternal triacylglycerols are high relative to non-esterified fatty acids.     

Role of transferrin in iron transport between maternal and fetal circulations of a perfused lobule of human placenta

The transfer of iron between the maternal and fetal circulations of an isolated perfused lobule of term human placenta was investigated using 125I-labelled or 59Fe-labelled diferric transferrin. There was negligible transplacental transfer of intact transferrin whereas nearly 4 per cent of the added 59Fe was transferred into the fetal circulation after 2 h, where it became associated with fetal transferrin. Over 20 per cent of the added 59Fe radioactivity was sequestered within the placental tissue during this period, associated with transferrin, ferritin and other uncharacterized molecules. This suggests an important role for an intracellular pool in regulating transfer. The presence of 10 mM chloroquine in the maternal circulation substantially reduced tissue accumulation of 59Fe and totally inhibited transfer to the fetus. It is concluded that the initial stages of iron transfer to the fetus involve the internalization of maternal iron-saturated transferrin bound to membrane receptors by receptor-mediated endocytosis, which can be inhibited by the drug chloroquine. Subsequently, the transplacental transfer of iron to the fetus does not involve the concomitant movement of transferrin.     

A novel pattern of placental leucine transfer during mid to late gestation in a highly placentotrophic viviparous lizard

Placentotrophy is the nourishment of embryos by resources provided via the placenta during gestation. The magnitude and timing of placental nutrient support during pregnancy are important for embryonic growth, especially in highly placentotrophic animals such as mammals. However, no study has yet investigated how placental organic nutrient support may change during pregnancy in highly placentotrophic viviparous reptiles. Amino acids are essential nutrients for embryonic growth and leucine is a common amino acid. The magnitude and timing of placental leucine transfer may affect embryonic growth and mass and, therefore, offspring phenotype. In this study, female Pseudemoia entrecasteauxii, a highly placentotrophic viviparous skink, were collected throughout gestation. We injected (3)H-leucine into these gravid females and assessed the transfer of (3)H-leucine into maternal compartments (i.e., the blood and the liver), and into embryonic compartments (i.e., the embryo, the yolk, and the amniotic fluid). At either 60 or 120 min post-injection, the radioactivity in each sample was extracted and then counted, and the transfer ratio was calculated. Our results provide direct evidence that circulating maternal leucine passes through the placenta into the embryos in this species. The relative rate of placental leucine transfer did not alter during mid to late gestation. This suggests the steady somatic growth of the embryos during mid-late pregnancy is dependent upon the placental transfer of nutrients rather than yolk stores. This pattern of placental nutrient support may determine offspring body size at birth and, therefore, offspring fitness in P. entrecasteauxii.