Maternal and fetal plasma amino acid concentrations during gestation and in retarded fetal growth

Comparison of Diagnostic Values of Maternal Arginine Concentration for Different Pregnancy Complications: A Systematic Review and Meta-Analysis

Abnormal arginine metabolism contributes to the development of intrauterine growth restriction (IUGR), preeclampsia (PE), and gestational diabetes mellitus (GDM), which increase the health burden of mothers and induce adverse birth outcomes. However, associations between maternal arginine concentration and different pregnancy complications have not been systematically compared. The PubMed, ScienceDirect, and Web of Science databases were searched for peer-reviewed publications to evaluate the diagnostic value of plasma arginine concentration in complicated pregnancies. Standardized mean difference (SMD) of the arginine concentration was pooled by a random effects model. The results show that increased maternal arginine concentrations were observed in IUGR (SMD: 0.48; 95% CI: 0.20, 0.76; I² = 47.0%) and GDM (SMD: 0.46; 95% CI: 0.11, 0.81; I² = 82.3%) cases but not in PE patients (SMD: 0.21; 95% CI: −0.04, 0.47; I² = 80.3%) compared with the normal cohorts. Subgroup analyses indicated that the non-fasting circulating arginine concentration in third trimester was increased significantly in GDM and severe IUGR pregnancies, but the change mode was dependent on ethnicity. Additionally, only severe PE persons were accompanied by higher plasma arginine concentrations. These findings suggest that maternal arginine concentration is an important reference for assessing the development of pregnancy complications.

A Nutrient-Sensing Transition at Birth Triggers Glucose-Responsive Insulin Secretion

A drastic transition at birth, from constant maternal nutrient supply in utero to intermittent postnatal feeding, requires changes in the metabolic system of the neonate. Despite their central role in metabolic homeostasis, little is known about how pancreatic β cells adjust to the new nutritional challenge. Here, we find that after birth β cell function shifts from amino acid- to glucose-stimulated insulin secretion in correlation with the change in the nutritional environment. This adaptation is mediated by a transition in nutrient sensitivity of the mTORC1 pathway, which leads to intermittent mTORC1 activity. Disrupting nutrient sensitivity of mTORC1 in mature β cells reverts insulin secretion to a functionally immature state. Finally, manipulating nutrient sensitivity of mTORC1 in stem cell-derived β cells in vitro strongly enhances their glucose-responsive insulin secretion. These results reveal a mechanism by which nutrients regulate β cell function, thereby enabling a metabolic adaptation for the newborn.

A Primary Role for α-Cells as Amino Acid Sensors

Glucagon and its partner insulin are dually linked in both their secretion from islet cells and their action in the liver. Glucagon signaling increases hepatic glucose output, and hyperglucagonemia is partly responsible for the hyperglycemia in diabetes, making glucagon an attractive target for therapeutic intervention. Interrupting glucagon signaling lowers blood glucose but also results in hyperglucagonemia and α-cell hyperplasia. Investigation of the mechanism for α-cell proliferation led to the description of a conserved liver-α-cell axis where glucagon is a critical regulator of amino acid homeostasis. In return, amino acids regulate α-cell function and proliferation. New evidence suggests that dysfunction of the axis in humans may result in the hyperglucagonemia observed in diabetes. This discussion outlines important but often overlooked roles for glucagon that extend beyond glycemia and supports a new role for α-cells as amino acid sensors.

Analysis of sequential hair segments reflects changes in the metabolome across the trimesters of pregnancy

The hair metabolome has been recognized as a valuable source of information in pregnancy research, as it provides stable metabolite information that could assist with studying biomarkers or metabolic mechanisms of pregnancy and its complications. We tested the hypothesis that hair segments could be used to reflect a metabolite profile containing information from both endogenous and exogenous compounds accumulated during the nine months of pregnancy. Segments of hair samples corresponding to the trimesters were collected from 175 pregnant women in New Zealand. The hair samples were analysed using gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. In healthy pregnancies, 56 hair metabolites were significantly different between the first and second trimesters, while 62 metabolites were different between the first and third trimesters (p < 0.05). Additionally, three metabolites in the second trimester hair samples were significantly different between healthy controls and women who delivered small-for-gestational-age infants (p < 0.05), and ten metabolites in third trimester hair were significantly different between healthy controls and women with gestational diabetes mellitus (p < 0.01). The findings from this pilot study provide improved insight into the changes of the hair metabolome during pregnancy, as well as highlight the potential of the maternal hair metabolome to differentiate pregnancy complications from healthy pregnancies.

Maternal and newborn infants amino acid concentrations in obese women born themselves with normal and small for gestational age birth weight

This study was undertaken to compare amino acid concentrations in maternal and newborn infants' serum in normal pregnancy and two groups of obese women who were born themselves with normal and small for gestational age (SGA) birth weight. Maternal cholesterol, lipoproteins concentrations and maternal and infants amino acid concentrations were evaluated at the time of delivery in 28 normal pregnancies, 46 obese pregnant women with normal birth weight (Ob-AGA group) and 44 obese pregnant women born themselves SGA (Ob-SGA group). Mean birth weight of newborn infants in Ob-SGA group was significantly less than in normal and Ob-AGA groups. Cholesterol and lipoproteins were significantly elevated in obese women (more prominent in Ob-SGA group). Most amino acid concentrations and fetal-maternal amino acid gradients were significantly lower in Ob-SGA group. These data suggest significant changes in placental amino acid transport/synthetic function in obese women who were born themselves SGA.

Relationship between glutamate, GOT and GPT levels in maternal and fetal blood: a potential mechanism for fetal neuroprotection

BACKGROUND

Excess glutamate in the brain is thought to be implicated in the pathophysiology of fetal anoxic brain injury, yet little is known about the mechanisms by which glutamate is regulated in the fetal brain. This study examines whether there are differences between maternal and fetal glutamate concentrations, and whether a correlation between them exists.

METHODS

10 ml of venous blood was extracted from 87 full-term (>37 weeks gestation) pregnant women in active labor. Immediately after delivery of the neonate, 10 ml of blood from the umbilical artery and vein was extracted. Samples were analyzed for levels of glutamate, glutamate-oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT).

RESULTS

Fetal blood glutamate concentrations in both the umbilical artery and vein were found to be significantly higher than maternal blood (p<0.001). Similarly, fetal serum GOT levels in the umbilical artery and vein were found to be significantly higher than maternal GOT levels (p<0.001). The difference in GPT levels between maternal and fetal serum was not statistically significant. There was no difference in fetal glutamate, GOT or GPT between the umbilical artery and vein. There was an association observed between glutamate levels in maternal blood and glutamate levels in both venous (R=0.32, p<0.01) and arterial (R=0.33, p<0.05) fetal blood.

CONCLUSIONS

This study demonstrated that higher baseline concentrations of blood glutamate are present in fetal blood compared with maternal blood, and this was associated with elevated GOT, but not GPT levels. An association was observed between maternal and fetal blood glutamate levels.

Blood glutamate scavenging: insight into neuroprotection

Brain insults are characterized by a multitude of complex processes, of which glutamate release plays a major role. Deleterious excess of glutamate in the brain's extracellular fluids stimulates glutamate receptors, which in turn lead to cell swelling, apoptosis, and neuronal death. These exacerbate neurological outcome. Approaches aimed at antagonizing the astrocytic and glial glutamate receptors have failed to demonstrate clinical benefit. Alternatively, eliminating excess glutamate from brain interstitial fluids by making use of the naturally occurring brain-to-blood glutamate efflux has been shown to be effective in various animal studies. This is facilitated by gradient driven transport across brain capillary endothelial glutamate transporters. Blood glutamate scavengers enhance this naturally occurring mechanism by reducing the blood glutamate concentration, thus increasing the rate at which excess glutamate is cleared. Blood glutamate scavenging is achieved by several mechanisms including: catalyzation of the enzymatic process involved in glutamate metabolism, redistribution of glutamate into tissue, and acute stress response. Regardless of the mechanism involved, decreased blood glutamate concentration is associated with improved neurological outcome. This review focuses on the physiological, mechanistic and clinical roles of blood glutamate scavenging, particularly in the context of acute and chronic CNS injury. We discuss the details of brain-to-blood glutamate efflux, auto-regulation mechanisms of blood glutamate, natural and exogenous blood glutamate scavenging systems, and redistribution of glutamate. We then propose different applied methodologies to reduce blood and brain glutamate concentrations and discuss the neuroprotective role of blood glutamate scavenging.

Maternal and fetal amino acid concentrations in normal pregnancies and in pregnancies with gestational diabetes mellitus

OBJECTIVE

This study was undertaken to compare amino acid concentrations in normal pregnancies and pregnancies with gestational diabetes (GDM), a condition associated with altered fetal growth.

STUDY DESIGN

Maternal and fetal amino acids were evaluated by high-performance liquid chromatograph at the time of delivery in 16 normal and 17 GDM pregnancies. Fetal weights were not different, but placental weights were significantly higher and fetal/placental weight ratios were significantly lower in GDM compared with normal.

RESULTS

Ornithine was significantly increased in GDM mothers. In umbilical vein and artery of GDM significant increases were observed for valine, methionine, phenylalanine, isoleucine, leucine, ornithine, glutamate, proline, and alanine, whereas glutamine was significantly decreased.

CONCLUSION

Placental amino acid exchange is altered in GDM pregnancies. Moreover, the changes observed for glutamine and glutamate in the umbilical samples suggest that in GDM the fetal hepatic production of glutamate is increased, likely as a consequence of the endocrine changes in the fetal compartment.

Plasma amino acid concentrations throughout normal pregnancy and early stages of intrauterine growth restricted pregnancy

OBJECTIVES

Assessment of maternal plasma amino acids during normal gestation and in early stages of intrauterine growth restriction (IUGR).

STUDY DESIGN

Plasma amino acid concentrations were measured in: (1) non-pregnant women (n=7); (2) normal pregnant women in the first (n=13), second (n=17) and third (n=12) trimester; and (3) pregnant women in the first trimester with later development of IUGR (n=8). Amino acid levels were quantified by electrochemical detection in a reversed-phase high-performance liquid chromatography (HPLC) system.

RESULTS

The levels of most essential and non-essential amino acids changed markedly in the first trimester during normal pregnancy and thereafter remained almost constant. In the first trimester of IUGR, a number of both essential and non-essential amino acids were significantly different from those observed in normal pregnancies, with values more similar to those observed in non-pregnant women.

CONCLUSIONS

Levels of most maternal amino acids decrease and some increase during early gestation reflecting a metabolic adaptation that occurs in normal pregnancies. Pregnancies that later develop IUGR show a lack of these adaptations for a significant number of both essential and non-essential amino acids, suggesting a lack of adaptation.

Reproductive fitness in maternal homocystinuria due to cystathionine beta-synthase deficiency

Early diagnosis and improved treatment are leading to the potential for increased reproductive capability in homocystinuria due to cystathionine beta-synthase (CbetaS) deficiency, but information about reproductive outcome and risk of thromboembolism in pregnancy is limited. To provide further information, clinical and biochemical information was obtained on women with maternal homocystinuria, on their pregnancies and on the offspring. This information included blood sulphur amino acids and total homocysteine, CbetaS gene mutations and developmental and cognitive scores in the offspring. The study involved 15 pregnancies in 11 women, of whom 5 were pyridoxine-nonresponsive and 6 were pyridoxine-responsive. Complications of pregnancy included pre-eclampsia at term in two pregnancies and superficial venous thrombosis of the leg in a third pregnancy. One pregnancy was terminated and two pregnancies resulted in first-trimester spontaneous abortions. The remaining 12 pregnancies produced live-born infants with normal or above-normal birth measurements. One offspring has multiple congenital anomalies that include colobomas of the iris and choroid, neural tube defect and undescended testes. He is also mentally retarded and autistic. A second offspring has Beckwith-Wiedemann syndrome. The remaining 10 offspring were normal at birth and have remained normal. There was no relationship between the severity of the biochemical abnormalities or the therapies during pregnancy to either the pregnancy complications or the offspring outcomes. The infrequent occurrences of pregnancy complications, offspring abnormalities and maternal thromboembolic events in this series suggest that pregnancy and outcome in maternal homocystinuria are usually normal. Nevertheless, a cautious approach would include careful monitoring of these pregnancies with attention to metabolic therapy and possibly anticoagulation.

Protein metabolism in pregnancy

Adaptation to pregnancy involves major changes in maternal metabolism to provide for the growing demands of the conceptus. Although changes in glucose metabolism, and possibly in fatty acid metabolism, occur in parallel with the increasing energy demands of the mother and the fetus, adaptation of protein metabolism appears to be in anticipation of maternal and fetal needs. During pregnancy, there is an excess of maternal nitrogen in the form of lean body mass over that deposited in the fetus and the products of conception; there is also a pregnancy-induced hypoaminoacidemia and a diminished amino acid response to protein intake, suggesting an increased uptake of amino acids in the splanchnic compartment. With the use of stable-isotope-labeled tracers, it was shown that there is a decreased rate of urea synthesis during pregnancy that is evident early in gestation. Kinetic studies of leucine metabolism showed no significant change in leucine carbon turnover but a significantly lower rate of leucine nitrogen turnover, suggesting a lower rate of leucine transamination. These data suggest an integral regulation of whole-body protein and nitrogen metabolism starting early in gestation and aimed at conservation and accretion of nitrogen by the mother and the fetus.

Mechanisms of amino acid supply to the rat conceptus in normal and abnormal development

Using in vitro and in vivo models, we have shown that protein is an important source of amino acids from 8.5 to 17.5 d postconception, a significant portion of postimplantation development in the rat. This satisfactorily explains why inhibition of protein pinocytosis and digestion by the visceral yolk sac may lead to congenital malformations, growth retardation, and intrauterine death during organogenesis and growth retardation and death during fetal stages. In humans, this process may be just as important and possibly just as vulnerable to inhibition, but other placental or paraplacental tissues may be involved in addition to the secondary yolk sac.

Maternal concentrations and fetal-maternal concentration differences of plasma amino acids in normal and intrauterine growth-restricted pregnancies

OBJECTIVES

Our purpose was to determine whether maternal amino acid concentration changes during gestation in pregnancies with intrauterine growth restriction as in normal pregnancies and to verify whether these changes are related to changes in fetal-maternal differences.

STUDY DESIGN

Amino acid concentrations were measured in 5 nonpregnant women, in 11 second-trimester and 10 third-trimester pregnant women with appropriate-for-gestational-age fetuses, and in 23 pregnant women with intrauterine growth restriction. Umbilical venous amino acids were measured at the time of fetal blood sampling. The severity of intrauterine growth restriction was assessed by Doppler velocimetry and fetal heart rate and by evaluation of oxygenation and acid-base balance.

RESULTS

In normal pregnant women the maternal concentration of most amino acids was significantly lower in both the second and third trimesters compared with nonpregnant women. In intrauterine growth restriction the maternal concentrations of most essential amino acids were significantly higher than in appropriate-for-gestational-age pregnancies. This observation, coupled with lower fetal amino acid concentrations in intrauterine growth restriction, leads to significantly lower fetal-maternal differences.

CONCLUSIONS

Normal pregnant women have a significant decrease in amino acid concentrations compared with nonpregnant women, whereas in intrauterine growth restriction maternal amino acids are reduced less, Significantly lower fetal-maternal concentration differences are present in intrauterine growth restriction, independent of the degree of severity.

Fuel metabolism in deviant fetal growth in offspring of diabetic women

Fetal growth and development from its very first stages of intrauterine life is significantly influenced by the metabolic environment in which the conceptus develops. Maternal disease states such as gestational diabetes and hypertensive pregnancy, representing maternal conditions involved in extremes of impaired fetal growth (macrosomia versus growth restriction), can serve as excellent examples of the various factors that are involved in intrauterine growth.

Free amino acid concentrations in normal and abnormal third trimester placental villi

Homogenates of placental villi were obtained from normotensive pregnancies and from pregnancies complicated by pre-eclampsia and growth retardation. The homogenates were analysed for free amino acid concentrations using high performance liquid chromatography (HPLC). The study shows that there are significantly higher concentrations of two essential amino acids, L-arginine and phenylalanine (P < 0.05), in the growth-retarded group compared to the term normotensive and pre-eclamptic groups. There are significantly higher concentrations of the non-essential amino acids: glutamic acid in the growth retarded group compared to the normotensive group, and of tyrosine in the growth-retarded group compared to the pre-eclamptic group. However, there is no increase in the glycine/valine ratio, a characteristic marker for kwashiorkor or a reduction in total protein concentration in the pre-eclamptic or growth-retarded groups. These findings suggest that there may be abnormalities in placental metabolism, amino acid transfer across the basal membrane into the fetal circulation, and also fetoplacental perfusion in pregnancies complicated by pre-eclampsia and growth retardation.

Two major pathways of zinc(II) acquisition by human placental syncytiotrophoblast

Uptake of zinc into placental villous syncytiotrophoblast is the first step in its transfer from mother to fetus. To help characterise physiologically significant pathways of zinc accumulation by these cells, we incubated cultured layers of syncytiotrophoblast cells derived from human near-term placental tissue with serum ultrafiltrate (containing the zinc complexed with low molecular mass serum constituents), dialysed serum (containing the zinc bound to the serum proteins) and whole serum, each of whose endogenous zinc was tracer-labelled with 65Zn(II). Zinc label from both fractions of serum readily entered a rapidly labelled EDTA-sensitive cellular compartment, probably representing zinc bound to the outside cell surface and in accumulative fashion, an EDTA-resistant compartment, probably consisting largely of internalised cellular zinc. Movement of zinc into the EDTA-resistant pool was strongly temperature-dependent and did not occur via the EDTA-sensitive pool from either serum source. Transfer of zinc from the low molecular mass serum fraction into the EDTA-resistant pool was saturable, the concentration giving half-maximal rate being 1.2 mumol/l nonprotein-bound zinc. No nonsaturable component was detected. Zinc from the serum protein-bound fraction entered by a saturable component, already saturated at physiological total protein-bound zinc concentration, and by an apparently nonsaturable component, not appreciably accounted for by nonspecific fluid-phase endocytosis. The results show that zinc is acquired by placental syncytiotrophoblast from the low molecular mass serum zinc pool probably by a carrier-mediated process, and at least as importantly, from the zinc bound to serum protein, possibly by an endocytic mechanism.

Placental amino acid transport

Normal fetal growth and development depend on a continuous supply of amino acids from the mother to the fetus. The placenta is responsible for the transfer of amino acids between the two circulations. The human placenta is hemomonochorial, meaning that the maternal and fetal circulations are separated by a single layer of polarized epithelium called the syncytiotrophoblast, which is in direct contact with maternal blood. Transport proteins located in the microvillous and basal membranes of the syncytiotrophoblast are the principal mechanism for transfer from maternal blood to fetal blood. Knowledge of the function and regulation of syncytiotrophoblast amino acid transporters is of great importance in understanding the mechanism of placental transport and potentially improving fetal and newborn outcomes. The development of methods for the isolation of microvillous and basal membrane vesicles from human placenta over the past two decades has contributed greatly to this understanding. Now a primary cultured trophoblast model is available to study amino acid transport and regulation as the cells differentiate. The types of amino acid transporters and their distribution between the syncytiotrophoblast microvillous and basal membranes are somewhat unique compared with other polarized epithelia. These differences may reflect the unusual circumstance of this epithelium that is exposed to blood on both sides. The current state of knowledge as to the types of transport systems present in syncytiotrophoblast, their regulation, and the effects of maternal consumption of drugs on transport are discussed.

Protein turnover in the human fetus studied at term using stable isotope tracer amino acids

Before elective cesarean delivery (4 h), we infused L-[1-13C]leucine and L-[15N]phenylalanine into the maternal circulation and measured enrichment and concentration of amino acids and carbon dioxide in cord blood of six normal human fetuses at delivery. There were net fetal uptakes of leucine (2.22 +/- 0.29 mumol.kg-1.min-1) and phenylalanine (0.80 +/- 0.11 mumol.kg-1.min-1) with net outputs of CO2 (6.11 +/- 1.12 ml.kg-1.min-1) and the transamination product of leucine, alpha-ketoisocaproate (1.04 +/- 0.32 mumol.kg-1.min-1). Fetal amino acid oxidation accounted for a substantial proportion of the flux from the mother (leucine, 0.36 +/- 0.09 mumol.kg-1.min-1 and phenylalanine, 0.18 +/- 0.04 mumol.kg-1.min-1). Fetal whole body accretion of leucine carbon (0.82 +/- 0.21 mumol.kg-1.min-1) was 69% of the umbilical uptake, and that of phenylalanine (0.62 +/- 0.08 mumol.kg-1.min-1) was 78%. Fetal whole body protein synthesis was approximately 13 g.kg-1.day-1, i.e., much faster than in adults but similar to that in the newborn. Net protein accretion was 2-4 g.kg-1.day-1. The placental supply of leucine and phenylalanine exceeds the fetal demand for protein synthesis by only a small amount, suggesting that the safety margin of placental transfer may be small for these amino acids. The results suggest that the method could be applied safely to studies of fetal growth retardation.

Case reports of successful pregnancy in women with maple syrup urine disease and propionic acidemia

We report on 2 women with organic acidemias, one with classical maple syrup urine disease and another with mild propionic acidemia in which protein restricted diets and carnitine supplementation were successfully employed to manage pregnancies. Healthy infants were delivered without maternal metabolic decompensation.

Taurine uptake in chicken leukocytes and erythrocytes

1. The intracellular taurine concentration and rate of taurine uptake of chicken erythrocytes and two leukocyte populations were determined from one to six weeks of age. 2. Plasma taurine concentrations increased significantly from the time of hatching to week 2 and remained constant thereafter. 3. Intracellular taurine concentrations in both leukocyte populations increased significantly with age without any significant change in the erythrocytes. 4. Taurine uptake rate for erythrocytes was significantly higher at weeks 1-3 while both leukocyte populations showed no significant change during the six week period studied.

Umbilical amino acid concentrations in normal and growth-retarded fetuses sampled in utero by cordocentesis

Fetal plasma amino acid concentrations were obtained by cordocentesis at midgestation in 11 normal (appropriate for gestational age) fetuses and at late gestation in 12 small-for-gestational-age fetuses, and at cesarean section in 14 normal term infants. In normal fetuses total molar amino acid concentrations and fetal/maternal total molar concentration ratios did not change significantly between the second and third trimesters. Fetal and maternal concentrations of most amino acids were significantly correlated at both midgestation and late gestation. Small-for-gestational-age fetuses had significantly lower concentrations of total alpha-aminonitrogen; this was mainly because of a reduction of the branched chain amino acids valine, leucine, and isoleucine, and of lysine and serine. Maternal arterial concentrations of phenylalanine, arginine, histidine, and alanine were elevated in small-for-gestational-age pregnancies. Thus there are only minor changes in amino acid concentrations between midgestation and late gestation in normal fetuses with a constant fetal/maternal ratio. In small-for-gestational-age infants a significant reduction in alpha-aminonitrogen and in most essential amino acids was demonstrable in utero weeks before delivery.

Plasma amino acids in appropriate- and small-for-gestational-age fetuses

The fetal plasma amino acid profiles of 28 small-for-gestational-age fetuses were established in umbilical venous blood samples obtained by cordocentesis and the values were compared with those of 62 appropriate-for-gestational age fetuses. In the appropriate-for-gestational-age group fetal levels were significantly correlated with but were higher than the maternal levels, which indicates that amino acids are actively transported by the placenta. In the small-for-gestational-age group, the fetal plasma concentration and the fetomaternal ratio of essential amino acids was decreased and this decrease was significantly correlated with the degree of fetal hypoxemia. There was a variable response (e.g., alanine was increased, whereas serine and tyrosine were decreased) involved with nonessential amino acids. In umbilical venous hypoxemia the plasma ratio of nonessential/essential amino acids was increased, and the maternal plasma concentrations of both essential and nonessential amino acids were increased. These findings suggest that in uteroplacental insufficiency there is intrauterine starvation.

Cordocentesis in the diagnosis of intrauterine starvation

Glycine and valine were measured in umbilical venous blood obtained by cordocentesis from 28 small-for-gestational-age fetuses. The values were compared with those from 62 appropriate-for-gestational-age fetuses. The ratio of glycine to valine was higher in the small-for-gestational-age fetuses and correlated significantly with the degree of fetal hypoxemia. These findings indicate that placental insufficiency is associated with a biochemical disturbance in the fetus that is similar to that observed in children with protein deprivation and kwashiorkor syndrome.

Umbilical amino acid concentrations in appropriate and small for gestational age infants: a biochemical difference present in utero

Plasma amino acid concentrations were determined in 28 pregnant women and their infants at term. Samples were obtained from 17 appropriate for gestational age and eight small for gestational age infants at cesarean section, while three small for gestational age fetuses were studied in utero by transabdominal cord sampling by means of ultrasonic guidance. Small for gestational age fetuses have significantly lower concentrations of alpha-aminonitrogen, compared with those of appropriate for gestational age fetuses, in both the umbilical artery and vein. Most of the difference is accounted for by the branched chain amino acids valine, leucine, and isoleucine. In contrast, hydroxyproline concentration is significantly higher in both the umbilical artery and vein of small for gestational age fetuses. The sum of the branched chain amino acid concentrations in the umbilical vein is directly related to maternal arterial values in both appropriate for gestational age and small for gestational age fetuses. Maternal arterial concentrations were slightly lower in small for gestational age fetuses and the regression analysis of umbilical venous versus maternal arterial branched chain amino acid concentrations was significantly different for small for gestational age and appropriate for gestational age infants. Umbilical venoarterial concentration differences in normal fetuses are significantly positive for most essential amino acids and for total alpha-aminonitrogen. In contrast, these differences were significant only for four essential amino acids in small for gestational age infants, while the total alpha-aminonitrogen venoarterial difference was not significant. The data obtained by transabdominal cord sampling from relatively undisturbed fetuses were in agreement with the data obtained at cesarean section; this information suggests that these differences between small for gestational age and appropriate for gestational age infants reflected steady-state conditions.

Maternal Hartnup disorder

We describe childbearing in two unrelated women with Hartnup disorder, an inborn error of neutral amino acid transport. Two living, unaffected offspring born after untreated and uneventful pregnancies, one from each woman, have had normal growth and development. The older one had an IQ of 92 at 4 years while the younger one at 4 months had a Development Quotient of 107 on the Mental Scale and 102 on the Motor Scale. A third offspring had a neural tube defect complicated by hydrocephalus and died at 3 months. This mother had a family history of major congenital anomalies. We think that this experience supports the view that Hartnup disorder in the mother, unlike phenylketonuria, does not have an adverse effect on the fetus. The presence of normal ratios of the amino acid concentrations between maternal and umbilical veins in one mother also suggests that placental transport of free amino acids, unlike renal transport, may not be reduced in maternal Hartnup disorder.

Amino acid profiles in early diabetic and non-diabetic pregnancy

Plasma amino acid concentrations were measured in six insulin-dependent diabetic women and seven non-diabetic women in early pregnancy while fasting and one hour after a standard meal. Fasting plasma levels of total amino acids and individual amino acids were similar in the two groups, excepting isoleucine, which was raised in the diabetics. One hour post-prandially total amino acid concentrations were similar in the two groups; however, mean concentrations of total branched chain amino acids and mean concentration of the individual amino acids, serine, valine, isoleucine, leucine and tyrosine were elevated in the diabetics. Amino acids are important in early islet development and in insulin secretion from fetal pancreas in vitro. The elevated post-prandial amino acid levels found in pregnant diabetics in early pregnancy may contribute to fetal islet hypertrophy and hyperinsulinaemia.

Acute versus chronic conditions for studies of fetal nutrient requirements: applicability to the human

In order to validate results obtained in 'acute' versus 'chronic' experimental conditions, two fetal sheep nutrients, lactate and glucose, have been determined in 'acute' conditions and compared with the 'chronic' data in the literature. Maternal and fetal blood glucose in 'acute' conditions was in the range of published 'chronic' data. Fetal blood lactate was similar in 'acute' and during 'chronic' conditions. Maternal and fetal veno-arterial (VA) differences were in the same direction in 'acute' and in 'chronic' conditions for both lactate and glucose and of the same magnitude for lactate. For glucose, a good relationship was observed between umbilical VA differences and maternal arterial concentrations for all 'acute' and 'chronic' values. Thus no fundamental differences appear in the results obtained in 'acute' or during 'chronic' conditions. The applicability of such animal results to the human and the use of acute conditions to study fetal nutrition in the human are discussed.

Determination of cysteinesulfinate, hypotaurine and taurine in physiological samples by reversed-phase high-performance liquid chromatography

Cysteinesulfinate, hypotaurine and taurine, which are key metabolites of cysteine, can be separated from each other and other closely eluting amino acids in biological samples by reversed-phase high-performance liquid chromatography on a Waters Nova-Pak C18 column. Samples were derivatized with o-phthalaldehyde-2-mercaptoethanol prior to injection. The elution system consisted of 100 mM potassium phosphate buffer, pH 7.0, with 3% (v/v) tetrahydrofuran with an initial isocratic phase at 1.2% acetonitrile and a gradient from 1.2 to 12.8% acetonitrile. This method is suitable for measurement of the production of metabolites from cysteine by isolated cells and for analysis of plasma and tissue extracts. Low levels of hypotaurine in rat tissues were easily measured with this method and are reported here for the first time.

Free amino acids in human fetal plasma

Free amino acids were determined on fetal plasma samples in 28 pregnancies between 20 and 33 wk gestation. No correlation can be observed between these concentrations and the age of gestation.

An enzymatic fluorometric assay for L-lysine in plasma and tissue

A simple, specific, and reliable method has been developed for the determination of L-lysine in blood plasma and tissue. The L-lysine in the sample is decarboxylated enzymatically, and fluorescamine is added to a pentan-1-ol extract of the cadaverine formed. This produces a stable product which is measured fluorometrically.

Tryptophan, cortisol and puerperal mood

Plasma cortisol, free and total tryptophan were determined in 71 subjects on 8 occasions between 36 weeks gestation and 6 weeks post-partum. Affect was measured by rating scales and clinical interview. Twenty-eight subjects were judged to have experienced post-partum 'blues'. Seasonal variation occurred in the incidence of 'blues' and in cortisol and free tryptophan levels. Puerperally-depressed mood was correlated with high cortisol at 38 weeks irrespective of season. Free tryptophan was reduced in 'blues' subjects but only at the time of year when free tryptophan was normally high. Total tryptophan was low antenatally; a rapid rise on days 1 and 2 post-partum was superimposed on a slower return to normal. This initial peak was clearly absent in 37 per cent of subjects. Its absence was significantly related to occurrence of post-partum 'blues' and of complaints of depression in the ensuing 6 months. This finding is discussed in relation to the possible occurrence of an occult disturbance of tryptophan handling in subjects susceptible to depression.

Alanine-stimulated insulin secretion in the fetal and neonatal lamb

Standardized rapid infusions of alanine were performed in six fetal lambs and three neonatal lambs to test the hypothesis that elevations of circulating amino acids may induce insulin secretion. Fetal insulin secretion was induced and exhibited a biphasic pattern with maximal elevation (61.8 +/- 18.5 microunits/ml) by 60 minutes of infusion. Alanine infusion was not associated with elevation of plasma glucose. Linear regression analysis delineated a significant relationship between steady state infusion concentrations of alanine and insulin (r = 0.70, p less than 0.01); the correlation was improved by adding glucose as an additional variable (r = 0.80). Alanine infusions into the neonatal lamb demonstrated a similar early pattern of secretion. Two combined glucose-alanine infusions were performed in two fetal lambs and demonstrated a significant effect on the timing of insulin release although no synergy could be demonstrated. Insulin secretion may be important in the modulation of fetal and neonatal amino acid utilization for fuel or protein accretion. Alanine-induced insulin secretion could have the effect of sparing alanine as a glucose precursor and would allow enhanced tissue uptake for transamination and protein synthesis.

Free and bound tryptophan in human plasma during the perinatal period

The concentration of tryptophan and the degree of binding of the amino acid to protein were examined in human plasma during the perinatal period. Both total and unbound (free) tryptophan were higher in cord vein plasma than in the maternal circulation, the concentration gradient being approximately 1 : 2. The proportion of the total plasma tryptophan concentration that was not bound to protein was less in cord vein plasma than in the maternal circulation. After birth the proportion in infant plasma fell significantly. Both total and free tryptophan fell during the first 24 hours of postnatal life. Total tryptophan returned to the cord vein plasma level 6--8 days after birth whilst free tryptophan failed to increase during the period of the observations. In premature infants total and free tryptophan also declined in concentration 12--24 hours after birth, suggesting the phenomenon to be related to birth rather than to gestational age. Phenylalanine remained unchanged whilst tyrosine increased in concentration during the first 80 hours of postnatal life. Thus, the availability of tryptophan to the tissues appears to decline during the immediate postnatal period and the results suggest that the requirement for tryptophan during this time may exceed the supply from standard artifical milk preparations.

Transport and accumulation of alpha-aminoisobutyric acid (A.I.B.) in the guinea pig placenta

Active transport of A.I.B. from mother to fetus was studied. This was done in the intact animal and using the isolated placenta, artificially perfused at both sides. It was shown that A.I.B. is actively accumulated in the placental cells. An estimate of the kinetic constants is given. It is shown that this accumulation takes place predominantly from the maternal side of the placenta. A.I.B. that has been accumulated is cleared to the maternal and fetal circulation in equal amounts. So the netto active transport from mother to fetus is brought about by an unequal distribution of carriers, the maternal side being most active.

Tissue concentrations of free amino acids in term human placentas

Five human term placentas were analyzed for total free amino acid concentrations. Calculation of tissue fluid distribution via 14C-inulin space enabled an estimation of placental intracellular amino acid concentrations based upon cord and maternal plasma concentrations. Maximum and minimum estimates for amino acid concentration in intracellular water are given. Data are compared to concentrations in organs of various species. Taurine was present in the highest concentration (3.529 +/- 1.120 mumoles per gram wet weight). Glutamic and aspartic acids, alanine, glycine, and glutamine were all present in concentrations greater than 0.5 mumoles per gram wet weight.