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Biol Reprod 2004, 10.1095/biolreprod.104.029645
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BIOLOGY OF REPRODUCTION 71, 901–908 (2004)
DOI: 10.1095/biolreprod.104.029645
© 2004 by the Society for the Study of Reproduction, Inc.

Pregnancy

Maternal Nutrient Restriction Reduces Concentrations of Amino Acids and Polyamines in Ovine Maternal and Fetal Plasma and Fetal Fluids1

Hyukjung Kwon3, Stephen P. Ford4, Fuller W. Bazer3, Thomas E. Spencer3, Peter W. Nathanielsz4,5, Mark J. Nijland4,5, Bret W. Hess4, and Guoyao Wu2,3

Department of Animal Science and Center for Animal Biotechnology and Genomics,3 Texas A&M University, College Station, Texas 77843 Center for the Study of Fetal Programming and Department of Animal Science,4 University of Wyoming, Laramie, Wyoming 82071 Department of Obstetrics and Gynecology,5 New York University School of Medicine, New York, New York 10016


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Amino acids and polyamines are essential for placental and fetal growth, but little is known about their availability in the conceptus in response to maternal undernutrition. We hypothesized that maternal nutrient restriction reduces concentrations of amino acids and polyamines in the ovine conceptus. This hypothesis was tested in nutrient-restricted ewes between Days 28 and 78 (experiment 1) and between Days 28 and 135 (experiment 2) of gestation. In both experiments, ewes were assigned randomly on Day 28 of gestation to a control group fed 100% of National Research Council (NRC) nutrient requirements and to an nutrient-restricted group fed 50% of NRC requirements. Every 7 days beginning on Day 28 of gestation, ewes were weighed and rations adjusted for changes in body weight. On Day 78 of gestation, blood samples were obtained from the uterine artery and umbilical vein for analysis. In experiment 2, nutrient-restricted ewes on Day 78 of gestation either continued to be fed 50% of NRC requirements or were realimented to 100% of NRC requirements until Day 135. Fetal weight was reduced in nutrient-restricted ewes at both Day 78 (32%) and Day 135 (15%) compared with controls. Nutritional restriction markedly reduced (P < 0.05) concentrations of total {alpha}-amino acids (particularly serine, arginine-family amino acids, and branched-chain amino acids) and polyamines in maternal and fetal plasma and in fetal allantoic and amniotic fluids at both mid and late gestation. Realimentation of nutrient-restricted ewes increased (P < 0.05) concentrations of total {alpha}-amino acids and polyamines in all the measured compartments and prevented intrauterine growth retardation. These novel findings demonstrate that 50% global nutrient restriction decreases concentrations of amino acids and polyamines in the ovine conceptus that could adversely impact key fetal functions. The results have important implications for understanding the mechanisms responsible for both intrauterine growth retardation and developmental origins of adult disease.

amino acids, nutrition, pregnancy, sheep


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Intrauterine growth retardation (IUGR) occurs in response to maternal undernutrition in humans, sheep, pigs, and rats [1–4]. Nutrient restriction in pregnant women may result from low dietary intake of nutrients owing to either a limited supply of food or severe nausea and vomiting known as hyperemesis gravidarum [5]. Epidemiological studies in humans suggest that alterations in fetal nutrition and endocrine status may result in developmental adaptations that permanently change the structure, physiology, and metabolism of the offspring, thereby predisposing individuals to cardiovascular, metabolic, and endocrine diseases in adult life [6]. Maternal nutrient restriction can also occur in domestic animals [7, 8]. For example, unsupplemented grazing ewes lose a significant amount of body weight during pregnancy, and their health, fetal growth, and lactation performance are compromised [7]. Thus, studies of the mechanisms responsible for IUGR brought about by maternal nutrient restriction have important implications for both human medicine and animal agriculture.

Amino acids play a vital role in the development of the conceptus (embryo/fetus and associated placental membranes). In addition to serving as building blocks for tissue protein synthesis, amino acids function as antioxidants, regulators of hormone secretion, major fuels for fetal growth, and cell signaling molecules [9, 10]. Furthermore, amino acids are essential precursors for the synthesis of nonprotein substances with biological importance, including nitric oxide, polyamines, neurotransmitters, amino sugars, purine and pyrimidine nucleotides, creatine, carnitine, porphyrins, melatonin, melanin, and sphingolipids [11, 12]. For example, nitric oxide, a product of arginine catabolism, plays a crucial role in regulating placental angiogenesis and fetal-placental blood flows during gestation [13–15]. Polyamines (polycationic molecules) regulate gene expression, signal transduction, ion channel function, and DNA and protein synthesis, as well as cell proliferation, differentiation, and function [10]. Surprisingly, little is known about the effect of maternal nutrient restriction on concentrations of amino acids and polyamines in the conceptus of any species.

The sheep is a widely used animal model for studying fetal and placental development [14–17]. We have recently reported striking changes in concentrations of both amino acids [18] and polyamines [19], as well as polyamines and nitric oxide synthesis [19, 20] in the ovine conceptus during pregnancy. In the present study, we used an established ovine model of IUGR [21] to test the hypothesis that maternal nutrient restriction reduces the availability of amino acids and polyamines in the conceptus.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Animals

Two series of experiments were conducted with multiparous ewes of mixed breeding. In both experiments 1 and 2, maternal nutrient restriction (50% of National Research Council [NRC] nutrient requirements) was carried out between Days 28 and 78 of gestation, as described previously [21]. Briefly, the diet consisted of a pelleted beet pulp (93.5% dry matter, 79.7% total digestible nutrient, 10% crude protein) and a mineral-vitamin mixture. On Day 20 of gestation, 16 ewes were weighed so that individual diets could be calculated on a metabolic body weight basis (weight0.75). On Day 21 of gestation, all ewes were placed in individual pens and provided all nutrients that met NRC maintenance requirements for early gestation. On Day 28 of gestation, ewes were assigned randomly to a control group (n = 8) fed 100% of NRC nutrient requirements or to a nutrient-restricted group (n = 8) fed 50% of NRC nutrient requirements. Every 7 days beginning on Day 28 of gestation, ewes were weighed and rations adjusted for changes in body weight. On Day 45 of gestation, the number of fetuses carried by each ewe was determined by ultrasonography (Ausonics Microimager 1000 sector scanning instrument; Ausonics Pty Ltd., Sydney, Australia). At Day 78 of gestation, each ewe in experiment 1 was administered an overdose of sodium pentobarbital (Abbott Laboratories, Abbott Park, IL) and exsanguinated. After the tip of the gravid uterine horn was exposed, blood samples were withdrawn from the uterine artery and umbilical vein into cooled heparinized tubes. The tubes were immediately centrifuged at 4°C and 3000 x g for 10 min to obtain plasma. Allantoic and amniotic fluids were obtained through the amniochorion and chorioallantoic membranes, respectively [18]. All plasma and fetal fluid samples were stored at –80°C until analyzed. At Day 78 of gestation in experiment 2, nutrient-restricted ewes either continued to be fed 50% of NRC nutrient requirements (n = 5) or were realimented to 100% of NRC nutrient requirements (n = 8). At Day 135 of gestation, blood samples were obtained from the uterine artery and umbilical vein of all ewes, and allantoic and amniotic fluids were collected as described for experiment 1. This study was approved by the University of Wyoming Animal Care and Use Committee.

Analysis of Amino Acids

Plasma and fetal fluids were analyzed for amino acids, as described previously [18, 22]. Briefly, amino acids, except for proline, were determined by HPLC methods involving precolumn derivatization with o-phthaldialdehyde. The values for total cysteine in plasma and fluids represent free cysteine plus one-half cystine. Proline was measured using an HPLC method involving precolumn derivatization with 9-fluorenylmethyl chloroformate. Amino acids in samples were quantified on the basis of known amounts of standards (Sigma Chemical Co., St. Louis, MO) using Millenium-32 Software (Waters, Milford, MA).

Analysis of Polyamines

Plasma and fetal fluids were analyzed for polyamines by an ion-pairing HPLC method involving precolumn derivatization with o-phthaldialdehyde [23, 24]. Putrescine, spermidine, and spermine in samples were quantified on the basis of known amounts of standards (Sigma) using Millenium-32 Software (Waters).

Statistics Analyses

Statistical comparisons between the two groups of ewes killed on Day 78 of gestation were performed using the Student unpaired t-test. Statistical comparisons among the three groups of ewes killed on Day 135 of gestation were completed using a one-way ANOVA. Post hoc analysis was performed with a Tukey test for highly significant differences. All statistical analyses were performed using the SAS V8.2 program for Windows (SAS Institute Inc., Cary, NC), and significance was accepted when P ≤ 0.05. Data are presented as mean ± standard error of the mean (SEM).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Maternal Undernutrition Between Days 28 and 78 of Gestation

At Day 78 of gestation, fetuses from control ewes were heavier (P < 0.05) than fetuses from nutrient-restricted ewes, averaging 326.4 ± 20.0 g and 221.7 ± 7.9 g (n = 8), respectively. Table 1 summarizes concentrations of amino acids in maternal and fetal plasma at Day 78 of gestation. Glycine was the most abundant amino acid in both maternal and fetal plasma. Compared with control ewes, maternal nutrient restriction between Days 28 and 78 of gestation increased (P < 0.01) plasma concentration of glycine, but decreased (P < 0.05) plasma concentrations of most amino acids (arginine, citrulline, cysteine, glutamine, isoleucine, leucine, ornithine, phenylalanine, proline, serine, and valine) in both maternal and fetal plasma. Nutrient restriction also decreased (P < 0.05) concentrations of lysine, methionine, threonine, tryptophan, and tyrosine in maternal plasma, but had no effect (P > 0.05) on these amino acids in fetal plasma. Maternal nutrient restriction had no effect (P > 0.05) on concentrations of ß-alanine, asparagine, aspartate, glutamate, histidine, and taurine in either maternal or fetal plasma. Concentrations of total {alpha}-amino acids were 8.8% and 8.3% lower (P < 0.01), respectively, in plasma from nutrient-restricted ewes and their fetuses when compared with control ewes. At Day 78 of gestation, concentrations of total polyamines (putrescine plus spermidine plus spermine) were 3.1 ± 0.25 and 2.6 ± 0.14 µmol/L (n = 8, P < 0.05) in maternal plasma of control and nutrient-restricted ewes, and were 4.5 ± 0.28 and 3.2 ± 0.21 µmol/L (n = 8, P < 0.05) in fetal plasma of control and nutrient-restricted ewes, respectively.


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  		TABLE 1. Amino acid concentrations (µmol/L) in ovine maternal and fetal plasma at Day 78 of gestation.*

Concentrations of amino acids in allantoic and amniotic fluids at Day 78 of gestation are summarized in Table 2. Alanine, citrulline, glutamine, glycine, and serine represented 73% and 76% of total {alpha}-amino acids in the allantoic fluid of control and nutrient-restricted ewes, respectively. Compared with control ewes, maternal nutrient restriction between Days 28 and 78 of gestation increased (P < 0.01) concentrations of glycine more than two-fold but decreased (P < 0.05) concentrations of many amino acids (arginine, citrulline, glutamine, isoleucine, leucine, proline, serine, and valine; Table 2) and polyamines (Table 3) in both allantoic and amniotic fluids. Nutrient restriction had no effect (P > 0.05) on concentrations of cysteine, lysine, and taurine in allantoic fluid, but decreased (P < 0.05) concentrations of these amino acids in amniotic fluid; the opposite was observed for ornithine. Concentrations of alanine, ß-alanine, asparagine, aspartate, glutamate, histidine, methionine, phenylalanine, threonine, tryptophan, and tyrosine in allantoic and amniotic fluids did not differ (P > 0.05) between control and nutrient-restricted ewes. At Day 78 of gestation, maternal nutrient restriction had no effect (P > 0.05) on concentrations of total {alpha}-amino acids in allantoic fluid, but decreased (P < 0.05) concentrations of total {alpha}-amino acids by 5% in amniotic fluid.


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  		TABLE 2. Amino acid concentrations (µmol/L) in ovine fetal fluids at Day 78 of gestation.*


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  		TABLE 3. Polyamine concentrations (nmol/L) in ovine fetal fluids at Day 78 of gestation.*

Maternal Undernutrition Between Days 28 and 135 of Gestation

At Day 135 of gestation, weights of fetuses from control and nutrient-restricted realimented ewes were similar (P > 0.05), averaging 4782.0 ± 165.1 g (n = 8) and 4639.6 ± 236.4 g (n = 8), respectively, whereas weights of the fetuses of ewes that were continuously nutrient-restricted (4047.0 ± 175.5 g; n = 5) were reduced (P < 0.05) when compared with control ewes. Concentrations of amino acids in maternal and fetal plasma at Day 135 of gestation are summarized in Table 4. Maternal nutrient restriction between Days 28 and 135 of gestation markedly reduced (P < 0.05) concentrations of most amino acids (alanine, arginine, asparagine, citrulline, cysteine, glutamine, histidine, isoleucine, leucine, lysine, methionine, ornithine, phenylalanine, proline, taurine, threonine, tryptophan, tyrosine, and valine) in both maternal and fetal plasma. Concentrations of ß-alanine, aspartate, glutamate, glycine, and serine in maternal plasma, and concentrations of ß-alanine and aspartate in fetal plasma did not differ (P > 0.05) between control and nutrient-restricted ewes. Concentrations of total {alpha}-amino acids were 28% and 34% lower (P < 0.05), respectively, in maternal and fetal plasma of ewes fed 50% of NRC nutrient requirements between Days 28 and 135 of gestation when compared with control ewes.


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  		TABLE 4. Amino acid concentrations (µmol/L) in ovine maternal and fetal plasma at Day 135 of gestation.*

Realimentation of underfed ewes beginning on Day 78 of gestation increased (P < 0.05) concentrations of several amino acids (alanine, cysteine, methionine, proline, taurine, and tryptophan) in both maternal and fetal plasma by Day 135 of gestation compared with ewes underfed between Days 28 and 135 of gestation. Realimentation of underfed ewes completely restored concentrations of alanine and asparagine in maternal plasma and of alanine, asparagine, histidine, taurine, and tyrosine in fetal plasma to values in control ewes. However, in both maternal and fetal plasma, concentrations of most amino acids remained lower (P < 0.05) in realimented ewes in comparison with control ewes. In maternal and fetal plasma, concentrations of total {alpha}-amino acids in realimented ewes were 10%–16% higher (P < 0.01) than those in underfed ewes, but were 21%–23% lower (P < 0.01) than those in control ewes.

At Day 135 of gestation, concentrations of total polyamines (putrescine plus spermidine plus spermine) were 3.4 ± 0.19 (n = 8), 2.5 ± 0.13 (n = 5), and 2.9 ± 0.17 µmol/ L (n = 8) in maternal plasma of control, nutrient-restricted, and realimented ewes, and were 4.3 ± 0.20 (n = 8), 2.9 ± 0.11 (n = 5), and 3.6 ± 0.15 µmol/L (n = 8) in fetal plasma of control, nutrient-restricted, and realimented ewes, respectively. Concentrations of total polyamines in realimented ewes were higher (P < 0.05) than those in nutrient-restricted ewes, but were lower (P < 0.05) than those in control ewes.

Table 5 summarizes concentrations of amino acids in allantoic and amniotic fluids on Day 135 of gestation. Maternal nutrient restriction between Days 28 and 135 of gestation markedly reduced (P < 0.05) concentrations of most amino acids (arginine, citrulline, cysteine, glutamate, histidine, isoleucine, leucine, lysine, methionine, ornithine, phenylalanine, proline, serine, taurine, tryptophan, tyrosine, and valine) in both allantoic and amniotic fluids. The decrease in allantoic fluid serine (84%) was the most striking. Surprisingly, concentrations of alanine, glutamine, glycine, and threonine in allantoic fluid increased (P < 0.01) in nutrient-restricted ewes compared with control ewes. Concentrations of alanine, ß-alanine, asparagine, aspartate, and taurine in allantoic fluid or concentrations of ß-alanine in amniotic fluid did not differ (P > 0.05) between control and nutrient-restricted ewes. Concentrations of total {alpha}-amino acids were 55% and 67% lower (P < 0.01), respectively, in allantoic and amniotic fluids of nutrient-restricted ewes when compared with control ewes. Realimentation of nutrient-restricted ewes beginning on Day 78 of gestation increased (P < 0.05) concentrations of arginine, citrulline, cysteine, histidine, proline, serine, tryptophan, and valine in both allantoic and amniotic fluids in comparison with nonrealimented ewes. However, in these fetal fluids, concentrations of most amino acids in allantoic and amniotic fluids remained lower (P < 0.05) in realimented ewes in comparison with control ewes. Realimentation of underfed ewes completely restored, to values for control ewes, concentrations of glutamate and histidine in allantoic fluid and of asparagine and tryptophan in amniotic fluid. In both allantoic and amniotic fluids, concentrations of total {alpha}-amino acids (Table 5) and polyamines (Table 6) in realimented ewes were higher (P < 0.01) than those in nutrient-restricted ewes, but were lower (P < 0.01) than those in control ewes.


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  		TABLE 5. Amino acid concentrations (µmol/L) in ovine fetal fluids at Day 135 of gestation.*


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  		TABLE 6. Polyamine concentrations (nmol/L) in ovine fetal fluids at Day 135 of gestation.*


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This is the first report of changes in concentrations of amino acids and polyamines in the ovine conceptus in response to precisely controlled maternal nutrient restriction. Although maternal and fetal plasma concentrations of amino acids in human IUGR have been documented, it is not known whether these changes were directly caused by maternal nutrient restriction or other environmental factors acting on a self-selected genetic population [25–29]. There are five major findings from this study: 1) 50% global nutrient restriction of pregnant ewes for both the first half of gestation and throughout gestation until just prior to term leads to IUGR, which can be reversed by realimentation during the second half of gestation; 2) maternal nutrient restriction markedly reduced concentrations of arginine-family amino acids and branched-chain amino acids in maternal and fetal plasma and in fetal fluids; 3) serine exhibited the most striking decrease in allantoic fluid (84%) and amniotic fluid (73%) by late gestation; 4) concentrations of polyamines in maternal and fetal plasma and in fetal allantoic and amniotic fluids were reduced in nutrient-restricted ewes compared with control ewes; and 5) realimentation of underfed ewes increased concentrations of total {alpha}-amino acids and polyamines in maternal and fetal plasma and in fetal fluids in association with compensatory fetal growth.

The marked decrease in all essential amino acids in maternal plasma (except for histidine at Day 78 of gestation) at both mid and late gestation in response to maternal nutrient restriction is in contrast to the reported elevation in concentrations of most essential amino acids in maternal plasma in women with IUGR of unknown etiology [28]. Concentration of urea (a major nitrogenous product of protein catabolism [30]) is reduced in maternal and fetal plasma of nutrient-restricted ewes [21], suggesting a decrease in amino acid catabolism by the whole body and/or possibly enhanced recycling of urea-nitrogen into the rumen to support microbial protein synthesis. Despite this mechanism of nitrogen conservation, the mobilization of maternal protein reserve (mainly from skeletal muscle) in ewes fed 50% of NRC requirements during the first half of gestation and throughout gestation did not appear to sufficiently compensate for the decreased supply of metabolizable protein from diet. Our finding that concentrations of total {alpha}-amino acids decreased to similar extents in both maternal and fetal plasma of underfed ewes supports the view that placental transport is a major mechanism responsible for fetal amino acid homeostasis [31–33].

Each amino acid has its own unique and tissue-specific metabolic pathways [9, 12]. Consistent with this notion, maternal undernutrition differentially affected concentrations of amino acids in maternal and fetal plasma. For example, at Day 78 of gestation, the concentration of glycine in both maternal and fetal plasma of nutrient-restricted ewes increased, but concentrations of most amino acids decreased compared with control ewes. Despite the elevated fetal glycine levels, serine concentration was markedly reduced in fetal plasma and fluids by maternal nutrient restriction. The uterus derives serine from maternal plasma, but there is little transplacental transport of serine to the ovine fetus owing to its extensive catabolism by uteroplacental tissues [16, 34]. Thus, in fetal lambs large amounts of serine are synthesized from glycine and N5,N10-methylenetetrahydrofolate as well as from 3-phosphoglycerate (an intermediate of glycolysis) and glutamate [16, 35]. Reduction in serine synthesis as a result of maternal nutrient restriction may indicate a decrease in liver and/or kidney function, which would have long-term metabolic and cardiovascular consequences later in life [36]. Serine is a major glucogenic amino acid in humans [9] and ewes [37]. It also plays an important role in one-carbon unit metabolism essential for 2'-deoxythymidylate synthesis and methylation of biomolecules [38]. In addition, serine participates in the synthesis of phosphatidylserine and ceramide (signaling molecules) [9]. All of these events are critical for cell metabolism and function. Therefore, reduced availability of serine in the conceptus of underfed ewes may impair the synthesis of glucose, DNA, and protein, thereby contributing to IUGR.

Another interesting finding of this study is that concentrations of branched-chain amino acids and arginine-family amino acids were consistently decreased in all of the measured compartments of underfed ewes at mid and late gestation. Likewise, IUGR in humans is associated with reduced fetal plasma concentrations of branched-chain amino acids [25–28] and arginine [33]. A reduced availability of branched-chain amino acids would impair placental and fetal glutamine synthesis [39]. In support of this view, glutamine concentrations were markedly reduced in ovine fetal plasma at both mid and late gestation. This may have an important impact on fetal growth, because glutamine is a major fuel for the growing fetus, a primary transporter of carbon and nitrogen among fetal organs, and an essential substrate for DNA and aminosugar syntheses [10, 32]. In addition, decreased arginine availability would reduce endothelial nitric oxide synthesis [40], and therefore placental-fetal blood flows, which in turn would decrease the transfer of nutrients and oxygen from maternal to fetal blood.

Amniotic fluid is essential for fetal growth and development [41]. Interestingly, we have shown that glutamine and polyamines are abundant in ovine amniotic fluid [18, 19]. The swallowing of amniotic fluid provides a source of rich nutrients for utilization by the fetal intestine and other tissues [42], and therefore the prevention of amniotic fluid entry into the small intestine by esophageal ligation results in IUGR in sheep [43]. Amniotic fluid is derived from both the fetus (kidneys, lungs, and epidermis) and fetal placental blood vessels [41]. Thus, a fall in concentrations of glutamine and polyamines in maternal and fetal plasma resulted in a decrease in their availability in fetal amniotic fluid. The latter would contribute to retarded growth of the small intestine and other tissues in fetuses of nutrient-restricted ewes [21].

Available evidence shows that increasing maternal plasma levels of amino acids can increase their availability in fetal plasma and fluids [32]. Remarkably, realimentation of nutrient-restricted ewes increased serine concentrations in allantoic fluid four-fold compared with restricted ewes, suggesting an increase in intrafetal synthesis of serine. However, in all of the measured compartments, concentrations of total {alpha}-amino acids and polyamines remained lower in realimented ewes compared with control ewes. There are several possible explanations for these findings. First, utilization of dietary amino acids for tissue protein synthesis in realimented ewes increases during compensatory growth of both the mother and the fetus. Second, because nutrient-restricted ewes exhibit compensatory growth of placentomes in response to realimentation during late gestation [44], an increased amount of amino acids would be directed toward placentomal protein synthesis, thereby reducing their transfer from maternal to fetal blood. Third, arginine, ornithine, and methionine, as well as proline and glutamine (precursors of ornithine), are important substrates for the synthesis of putrescine, spermidine, and spermine [11], and therefore the reduced availability of these amino acids in fetal plasma and fluids would contribute to a decrease in polyamine synthesis by placental, uterine, and fetal tissues [19]. Whatever the mechanisms, our results indicate that realimentation of nutrient-restricted ewes increased the availability of amino acids (substrates for the synthesis of protein and other biologically important molecules) and polyamines (key regulators of DNA and protein synthesis as well as cell function) in the conceptus, which prevented IUGR brought about by maternal undernutrition.

In conclusion, concentrations of total {alpha}-amino acids (particularly serine, arginine-family amino acids, and branched-chain amino acids) and polyamines were severely reduced in maternal plasma, fetal plasma, and fetal allantoic and amniotic fluids of nutrient-restricted ewes at both mid and late gestation. Realimentation of underfed ewes beginning from mid-gestation increased concentrations of total {alpha}-amino acids and polyamines in all of the measured compartments and prevented IUGR. These findings establish a foundation for further studies to define the roles of amino acids and polyamines in the prevention and treatment of IUGR brought about by maternal nutrient restriction.


   ACKNOWLEDGMENTS
 
We thank research personnel in our laboratories for technical assistance.


   FOOTNOTES
 
1 Supported, in part, by grants from USDA/NRI 2001-02259 and 2001-02166, the Texas A&M University Life Science Program, the University of Wyoming BRIN P20, RR16474, and NIH HD 21350. Back

2 Correspondence: Guoyao Wu, Department of Animal Science, Room 212, Kleberg Building, Texas A&M University, 2471 TAMU, College Station, TX 77843-2471. FAX: 979 845 6057; g-wu{at}tamu.edu Back

Received: 11 March 2004.

First decision: 2 April 2004.

Accepted: 4 May 2004.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
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