Amino acid and protein metabolism in diabetes mellitus.

In normal man, the fasting state is characterized by release of alanine and glutamine from muscle and in situ muscle catabolism of branched chain amino acids (lecucine, isoleucine, and valine). The alanine released by muscle is utilized by the liver for gluconeogenesis. Muscle nitrogen repletion occurs during protein feeding primarily by means of selective hepatic escape and muscle uptake of branched chain amino acids in ingested protein. In the diabetic, amino acid catabolism is exaggerated in the fasting state as reflected by increased uptake of alanine by the liver for gluconeogenesis and accelerated branched chain amino acid catabolism in muscle. After protein feeding, uptake of branched chain amino acids by muscle is reduced and these amino acids accumulate in increased amounts in arterial blood. Protein feeding also exaggerates the hyperglycemia of diabetes by causing an increase in hepatic glucose production. Diabetes is thus characterized by accelerated protein catabolism during fasting as well as diminished nitrogen repletion and hyperglycemia after protein feeding. The hyperketonemia of diabetes may however, have a restraining influence on protein catabolism thereby reducing alanine availability for gluconeogenesis.     

Amino acid and glucose metabolism in the postabsorptive state and following amino acid ingestion in the dog

Amino acid and glucose metabolism was studied in nine awake 18-hour fasted dogs with chronic portal, arterial, and hepatic venous catheters before and for three hours after oral ingestion of amino acids. The meal was composed of a crystalline mixture of free amino acid, containing neither carbohydrate nor lipid. Following the amino acid meal, plasma glucose concentration declined slowly and this occurred despite a rise in hepatic glucose release. Portal plasma insulin rose transiently (30 +/- 7 to 50 +/- 11 microU/mL, P less than 0.05) while the increase in portal glucagon was more striking and persisted throughout the study (162 +/- 40 to 412 +/- 166 pg/mL). Over the three hours following amino acid ingestion, the entire ingested load of glycine, serine, phenylalanine, proline, and threonine was recovered in portal blood as was 80% of the ingested branched chain amino acids (BCAA). The subsequent uptake of these glucogenic amino acids by the liver was equivalent to the amount ingested, while hepatic removal of BCAA could account for disposal of 44% of the BCAA absorbed; the remainder was released by the splanchnic bed. During this time, ongoing gut production of alanine was observed and the liver removed 1,740 +/- 170 mumol/kg of alanine, which was twofold greater than combined gut output of absorbed and synthesized alanine. In the postcibal state, the total net flux of alanine and five other glucogenic amino acids from peripheral to splanchnic tissues (1,480 mumol/kg 3 h) exceeded the net movement of branched chain amino acids from splanchnic to peripheral tissues (590 mumol/kg/3 h).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of insulin on blood levels of branched chain keto and amino acids in man

Branched chain keto acids, their corresponding amino acids, glucose, glucagon, growth hormone, C-peptide and gastric inhibitory polypeptide were determined in 8 healthy subjects after an intravenous bolus injection of 0.1 U/kg insulin. Branched chain keto acids declined within 60 min, the corresponding amino acids within 20 min or later. Amino acids tended to return towards normal earlier than their keto acids. Blood glucose levels were normal 2 hr after insulin injection while keto and amino acids remained diminished for more than 3 hr. In 8 healthy controls, given physiological saline instead of insulin, the branched chain keto acids did not decline throughout the test. It is suggested that insulin diminishes blood levels of branched chain keto acids, that the intraorgan flux of branched chain keto acids is different from the flux of branched chain amino acids and that branched chain keto acids may serve to correct for hypoglycemia.     

The effect of diabetes and the redox potential on amino acid content and release by isolated rat hemidiaphragms

The free amino acid content of diaphragm muscles of control and diabetic rats was studied 5 days after the injection of streptozotocin. Muscles were prepared for analysis either immediately after sacrifice or following incubation in balanced salt solution containing 5.5 mM glucose, with or without an electron acceptor, 0.02 mM methylene blue. Diaphragms of diabetic rats contained significantly more free taurine, glutamate, and branched chain amino acids than the controls at sacrifice, and significantly less glutamine, serine, asparagine, lysine, arginine, histidine, threonine, citrulline, and carnosine. Alanine decreased in plasma of diabetic rats but not in diaphragms before incubation. Hemidiaphragms of diabetic rats produced less alanine and more glutamate during incubation than controls. After incubation they contained less than half as much alanine and glutamine and twice as much glutamate than the controls, having released approximately 40% less alanine and 25% more glutamate into the medium than the controls. Glutamine release was not significantly different between the two groups. Methylene blue increased the free alanine content in the tissue water as well as alanine release by control and by diabetic muscles; the glutamate content of muscles decreased concomitantly. The effects of methylene blue were greater in the diabetic group. Branched chain amino acid release by diabetic muscles decreased during incubation with methylene blue. Muscles of diabetic rats contained more α-ketoglutarate than the controls after incubation with or without methylene blue. Methylene blue increased the α-ketoglutarate content of muscles and its release into the medium, the effect being greater in diabetics than in controls. Hemidiaphragms from diabetic rats released less pyruvate during incubation than controls, while lactate release by the two groups was not significantly different. Incubation with methylene blue caused a marked increase in pyruvate release by diabetic muscles, and a lesser stimulation in controls; lactate release increased in both groups. After incubation the lactate/pyruvate ratio in muscles was lower in the methylene blue treated group. The in vitro effect of 0.02 mM phenazine methosulfate on alanine production was similar to that of methylene blue. The data is compatible with the hypothesis that the $\text{NADH}\text{NAD}$ ratio may exert a restraining effect on alanine production and release by muscle. The progressive increase in this ratio may play a role in the eventual deceleration of gluconeogenesis during a prolonged fast and may restrain this process in uncompensated diabetes.     

The disposal of an intravenously administered amino acid load across the human forearm

This study was designed to examine the role of the skeletal muscle in man in the disposal of an intravenously administered L-amino acid solution. Arterio-deep venous differences of amino acids, glucose and lactate, and blood flow across the human forearm were measured in 9 healthy normal male volunteers (age = 27 ± 2 yr, weight = 79 ± 4 kg and height = 180 ± 2 cms) after an overnight fast (12 hr). Glucose and alanine turnover rates were estimated using a continuous infusion of 3-³H-glucose and U-¹⁴C-alanine isotopes. All measurements were obtained during steady state conditions, basally and two hours after the start of an L-amino acid infusion (8.5% solution). During the control period there was a significant release of total alpha amino nitrogen (AAN) equal to $\text{300 ± 97 nmole}\text{100 g}$ forearm muscle/min with alanine and glutamine accounting for over 80% of that amount ($\text{260 ± 24 nmole}\text{100 g}\text{forearm muscle/min}$). The release of the branched chain amino acids (BCAA) was only significant for valine, while the release of each of the keto acids of leucine and valine, α-ketoisocaproate and α-ketoisovalerate ($\text{37 ± 12 and 36 ± 7 nmole}\text{100 ml}\text{forearm muscle/min respectively}$) was significant from zero and exceeded the release of the corresponding amino acids ($\text{13 ± 17 and 24 ± 7 nmole}\text{100 g}\text{forearm muscle/min for leucine and valine respectively}$). The infusion of the L-amino acid solution resulted in a reversal of amino acid balance across the forearm. There was a net uptake of AAN of $\text{1195 ± 209 nmole}\text{100 g}$ forearm muscle/min with the BCAA accounting for $\text{513 ± 75 nmole}\text{100 g}$ forearm muscle/min or 49 ± 6% of the uptake. The net uptake of BCAA by skeletal muscle did not exceed 35% of the amount infused. The release of α-ketoisocaproate and α-ketoisovalerate showed no significant change from basal levels. The output of alanine and glutamine persisted in response to the infusion; while alanine output dropped by 40%, glutamine output increased by 50% ($\text{68 ± 23 and 218 ± 42 nmole}\text{100 g}\text{forearm muscle/min respectively}$), yet the combined release of alanine and glutamine did not change significantly from basal levels. Amino acid infusion resulted in a twofold increase in insulin and glucagon. Plasma glucose fell from 5.3 ± 0.05 mM basally to 5.04 ± 0.06 mM (p < 0.05), while blood lactate increased from 0.587 ± 0.03 mM to 0.639 ± 0.025 mM (p < 0.05); similarly there was a time dependent increase in glucose uptake by muscle ($\text{from}\text{0.857 ± 0.08}\text{to}\text{1.27 ± 0.07 μ}\text{mole}\text{100 g}\text{forearm muscle/min}$, p < 0.05) and lactate release ($\text{0.226 ± 0.03}\text{to}\text{0.297 ± 0.045 μ}\text{mole}\text{100 g}\text{forearm muscle/min}\text{, p < 0.05}$). These results indicate that a significant amount of the amino acids infused, and specifically the BCAA are extracted by human skeletal muscle, and mostly retained as such for later use. The data obtained under the conditions of the present study also indicate that tissues other than skeletal muscle are as important in the overall handling of these amino acids. However, it remains to be seen whether these findings can be extrapolated to other physiological conditions.     

Alcohol Intake and Withdrawal: Effects on Branched Chain Amino Acids and Alanine

The effects of chronic alcohol consumption on plasma branched chain amino acids and alanine concentrations were evaluated, and basal blood concentrations of these amino acids were determined after chronic ethanol intake and following a withdrawal period in 30 admitted alcoholics. After ethanol intake, alcoholics showed increased branched chain amino acid concentrations; the blood alanine concentrations were depressed after the withdrawal period. To evaluate the effect of ethanol on diurnal variations of these amino acids in the blood, a group of these patients underwent two isocaloric diets with and without wine. The diet with alcohol induced a sustained increase of branched chain amino acids persisting even after the postprandial phase with a decrease of alanine as compared to the diet without.     

Muscle nitrogen metabolism in chronic hepatic insufficiency.

Whole blood arterio-venous (A-V) differences for ammonia (NH3) and amino acids were determined across the forearm in 14 patients with decompensated alcoholic cirrhosis and hyperammonemia. NH3 was extracted by the forearm in all patients; however, the fractional extraction of NH3 was significantly less in five individuals with gross muscle wasting (13.3% versus 25.3%). There was neither a significant uptake nor release of NH3 in normal control subjects. The arterial concentrations of 12 out of 20 amino acids were strikingly diminished in the patient group. In contrast to normal subjects, in whom the release of alanine exceeds that of glutamine, the A-V difference for glutamine in the patients was threefold greater than that for alanine. The A-V differences for all other amino acids were not significantly different from zero. The results suggest that (1) muscle plays an important role in disposing of NH3 in patients with hepatic insufficiency and (2) a major fraction of NH3 taken up by muscle is released as glutamine.     

Correction of altered plasma amino acid pattern in cirrhosis of the liver by somatostatin.

The purpose of our study was to evaluate the effect of somatostatin (500 microgram/h intravenously) upon insulin, c-peptide, glucagon and plasma amino acids concentrations in patients with and without cirrhosis of the liver. The typical plasma amino acid pattern in cirrhosis is characterised by increased concentrations of the aromatic amino acids and decreased concentrations of the branched chain amino acids and of alanine and glycine. After administration of somatostatin insulin, c-peptide and glucagon concentrations decreased and those of the branched chain amino acids in both groups increased; in addition in patients with cirrhosis the plasma concentrations of threonine, serine, glycine, alanine, lysine, and arginine increased also. Infusion of somatostatin plus insulin in patients with cirrhosis succeeded in preventing the increase in the branched chain amino acid concentrations, while the infusion of somatostatin plus glucagon decreased threonine, serine, glycine, alinine, phenylalanine, tyrosine, lysine and arginine concentrations. It is therefore suggested that the effect of somatostatin on the plasma amino acids may be because of the reduction of insulin and glucagon concentrations; however, other effects of somatostatin cannot be excluded at present.     

Branched chain amino acid metabolism in the retina of diabetic rats

Summary Diabetes is known to produce increased levels of the branched chain amino acids in plasma, heart and muscle as well as increased oxidation of [¹⁴C]-leucine by nerves and muscles from rats. Plasma and retinas from streptozotocin diabetic rats had significant elevations in branched chain amino acid levels compared to control. Retinas from diabetic rats have been found to oxidize significantly more of the branched chain amino acids, leucine, isoleucine and valine than did control retinas when incubated in media containing 16.5 mmol/1 glucose. Neither the extracellular space nor the tissue pool of leucine was significantly different in the two groups. The addition of 19 amino acids, at normal plasma concentrations, to the incubation media resulted in 80 percent suppression of leucine oxidation without significant change in incorporation of [¹⁴C] into protein. These results suggest that the major role for the branched chain amino acids in the rat retina is in protein synthesis which is not affected by short-term diabetes.This investigation was supported by a grant-in-aid from Fight-For-Sight, Inc., New York City, and by USPHS grant AM02001 from the National Institute of Arthritis, Metabolism and Digestive Diseases.     

Serum hepatocyte growth factor as an index of extensive catabolism of patients awaiting liver transplantation

BACKGROUND: Whole body catabolism as the result of intrahepatic metabolic derangement is common in liver transplant candidates. However, individual nutritional assessment parameters lack sensitivity and specificity in determining energy status of these patients. Recently, serum hepatocyte growth factor (HGF) has been shown to reflect the recovery of hepatic energy metabolism after liver transplantation. AIMS: The relation between preoperative levels of serum HGF and metabolic variables was investigated to clarify the clinical value of measuring HGF in evaluations of the catabolism. PATIENTS/METHODS: Blood samples were obtained from 30 liver transplant recipients, and biopsy specimens were taken from each recipient's rectus muscle and the explanted liver. Preoperative serum concentration of HGF was determined. Whole body energy metabolism was assessed by measuring glycogen contents of biopsy specimens and plasma or serum levels of glucose, insulin, total ketone bodies, total carnitine, and amino acids. RESULTS: Serum HGF concentration was elevated in 22 of 30 patients and correlated with the Child-Pugh score. It showed a negative association with muscle glycogen content, and a positive correlation with serum levels of glucose, total carnitine, and total ketone bodies. Patients with elevated serum HGF concentrations had higher preoperative plasma levels of aromatic amino acids and branched chain amino acids, associated with lower branched chain to aromatic amino acid ratios. CONCLUSIONS: The elevated serum concentration of HGF in liver transplant candidates reflected inhibition of peripheral glucose storage, enhanced lipid oxidation, and increased peripheral release of branched chain amino acids, and thus extensive energy catabolism.     

Evidence of Inter-organ Amino-Acid Transport by Blood Cells in Humans

To evaluate the contribution of blood cellular elements to inter-organ transport of amino acids, net exchange across the leg and splanchnic bed of 17 amino acids was determined in seven healthy postabsorptive subjects by use of both whole blood and plasma for analysis. Arterial-portal venous differences were measured in five additional subjects undergoing elective cholecystectomy. By use of whole blood, significant net release of amino acids was noted from the leg and gut, while a consistent uptake was observed by the splanchnic bed. The output of alanine from the leg and gut and the uptake of this amino acid by the splanchnic bed exceeded that of all other amino acids and accounted for 35-40% of total amino-acid exchange. Transport by way of plasma could not account for total tissue release or uptake of alanine, threonine, serine, glutamine, methionine, leucine, isoleucine, tyrosine, and citrulline. For each of these amino acids, significant tissue exchange was calculated to occur by way of the blood cellular elements, the direction of which generally paralleled the net shifts occurring in plasma. For alanine, 30% of its output from the leg and gut and 22% of its uptake by the splanchnic area occurred by way of blood cells. We conclude that the blood cellular elements, presumably erythrocytes, contribute substantially to the net flux of amino acids from muscle and gut to liver in normal postabsorptive humans. Alanine predominates in the inter-organ transfer of amino acids occurring by way of blood cells as well as plasma.     

Splanchnic, renal, and muscle clearance of alanylglutamine in man and organ fluxes of alanine and glutamine when infused in free and peptide forms

The present study was designed to investigate organ metabolism of intravenously (IV) infused (100 mumol.h-1.kg-1) alanylglutamine and its amino acid constituents in a group of healthy subjects. The dipeptide clearance (mumol/min) by kidney (51 +/- 3) was significantly (P less than .01) greater than the clearance by either splanchnic organs (19 +/- 6) or skeletal muscle (21 +/- 8). Infusion of alanylglutamine significantly (P less than .01) increased arterial plasma concentrations of free alanine (260 +/- 31 v 330 +/- 38 mumol/L) and free glutamine (620 +/- 66 v 764 +/- 65 mumol/L) when compared with the baseline period. Concurrently, splanchnic uptake of alanine and glutamine increased and muscle release of alanine ceased. However, muscle release of glutamine remained unaffected. Renal balances of alanine and glutamine changed from neutral to negative (net release) and from positive (net uptake) to neutral, respectively. Infusion of a corresponding mixture of alanine and glutamine had similar effects on arterial plasma concentrations and splanchnic and muscle balances of alanine and glutamine, but had no effect on renal balances of these amino acids. From these studies in man, we conclude that kidney predominates over other organs in clearance of alanylglutamine from plasma and that this may account for the different effect of infusion of alanine and glutamine in free and peptide forms on renal fluxes of these amino acids.     

Effects of oral alanine administration in fasting obese subjects

The effects of administration of oral alanine to therapeutically starved obese subjects is described. Fifty grams of alanine administered daily in divided doses after 2 wk of fasting caused reversal of hypoglycemia and ketosis. Since urinary and blood urea nitrogen increased, these effects appeared secondary to increased hepatic glucose production from alanine. Reduction of muscle catabolism during alanine administration was suggested by decreased plasma levels of essential branched chain amino acids and diminished urinary losses of phosphorus and potassium. Small rises in plasma insulin occurred and may have mediated these effects. Hyperuricemia was diminished, and urinary uric acid excretion was increased by alanine as ketosis disappeared. These data suggest that alanine supply may be one important regulator of hepatic gluconeogenesis during fasting. Additionally, it was observed that a single oral 50-g dose of alanine produced hyperinsulinemia and hypoglycemia in the postabsorptive state. After 2 wk of fasting, the same dose produced hyperglycemia and lesser hyperinsulinemia.     

Effect of intraarterial infusion of the ketoanalogue of leucine on amino acid release by forearm muscle

α-Ketoanalogues of most essential amino acids can be converted to the corresponding amino acids in man and appear to be useful dietary supplements in protein-intolerant patients. Recently, the branchedchain amino acids, especially leucine, have been found to promote protein synthesis in isolated muscle. The present studies were designed to assess the capacity of skeletal muscle to aminate the keto-analogue of leucine and determine if the metabolism of the ketoacid promotes protein synthesis. Six normal postabsorptive males received a 30-min brachial intraarterial infusion of ketoleucine (34.4 μmoles/min). Changes in ipsilateral muscle balance were estimated from whole blood concentrations and flow for 1 hr. Brachial arterial blood ketoleucine concentration increased by an average of 1.02 mM. In a single passage across forearm muscle, 52% of the ketoacid was extracted. Leucine was the only amino acid released in increased amounts, accounting for 31% of ketoleucine extracted. The remainder was apparently oxidized. No one donor capable of supplying all the nitrogen needed for leucine production could be identified, but significant reductions in the release of alanine, glycine, and histidine, and changes from release to uptake of valine and isoleucine, suggest possible contributions from these amino acids. Glutamine-asparagine release did not change. Lysine, tyrosine, and phenylalanine balances were also unchanged, suggesting no anabolic effect of ketoleucine on muscle protein under these conditions. The results demonstrate rapid transamination and utilization of ketoleucine by skeletal muscle in postabsorptive man.     

Alterations in alanine metabolism in diabetic dogs during short-term treatment with an artificial B cell

Summary The flux rates of plasma glucose and alanine were studied isotopically (6-³H-glucose and U-¹⁴C-alanine simultaneously) in resting chronically diabetic dogs during short-term treatment with an artificial B cell where the insulin was infused into a peripheral vein. Despite perfect blood glucose control and normal glucose flux rates, the concentration and rates of appearance and disappearance of alanine were significantly elevated in the diabetic animals before, during and after an exogenous glucose load. The incorporation of the carbon moiety of alanine into circulating glucose was also increased, but diminished to a near-normal extent when exogenous glucose was given. The plasma clearance rates for alanine in the diabetic dogs were normal throughout the study. It is concluded that normal blood glucose control in diabetes does not necessarily mean normalization of the entire metabolic network. On the basis of peripheral hyperinsulinaemia alanine formation from glucose and branched chain amino acids is elevated in muscle. This may explain increased flux of alanine despite normal blood glucose control.     

Controlled trial of nutritional supplementation, with and without branched chain amino acid enrichment, in treatment of acute alcoholic hepatitis

Sixty-four patients admitted with acute alcoholic hepatitis, with or without underlying cirrhosis, were randomized regardless of encephalopathy to receive a controlled diet either alone, or supplemented orally, nasogastrically, or intravenously as necessary, with 2000 kCal and 10 g nitrogen daily. Whether this came from a conventional protein source or a branched chain amino acid enriched formulation was also randomly determined. In the absence of renal failure, nitrogen intakes of 10 g or more daily were invariably associated with positive nitrogen balance, but complications of liver dysfunction prevented the attainment of significantly more positive balance in the supplemented groups than in controls. Neither in the series as a whole, nor in any identifiable subgroup of patients, was mortality affected by treatment. Changes in prothrombin time and in measured nutritional parameters during the study did not differ between supplemented and control groups, and the observed changes in midarm muscle circumference appeared to reflect changes in degree of fluid retention. Neither enteral nor parenteral branched chain amino acids showed any consistent effect upon encephalopathy.     

Serum branched chain amino and keto acid response to fasting in humans

Eight healthy individuals were fasted for 72 hours. The concentrations of the branched chain keto acids (BCKA), branched chain amino acids (BCAA), C peptide, and glucagon were determined in peripheral venous blood. alpha-ketoisocaproic acid, alpha-keto-beta-methyl-n-valeric acid, and alpha-ketoisovaleric acid increased significantly within 36 hours along with the corresponding amino acids. After 60 hours of starvation, the concentrations of BCKA and BCAA declined despite the fact that the subjects were still in the fasting state. These changes were accompanied by a decrease in the concentrations of C peptide and an increase in glucagon levels. It is suggested that in starving man insulinopenia may contribute to the rise in BCKA concentrations and that the increase in BCKA may be a mechanism to reduce proteolysis.     

Effects of pharmacologic hyperglucagonemia on plasma amino acid concentrations in normal and diabetic man

Four normal and five insulin dependent diabetic men received a 2 h pharmacologic glucagon infusion (50 ng/kg/min) resulting in plasma glucagon levels (4400 pg/ml) similar to those seen in glucagonoma patients. In normal subjects in whom plasma insulin concentrations rose significantly (239 uU/ml) and the blood level of 15 of the 18 amino acids measured fell significantly. In contrast, in the diabetic men who secreted no insulin in response to glucagon (no rise in C-peptide levels), only 10 of 18 amino acid levels fell significantly. The branched chain amino acids valine, leucine and isoleucine, as well as tyrosine and phenylalanine were among the 8 amino acids which showed no change in response to glucagon in the diabetics. Thus, glucagon appears to have no acute affect on branched chain amino acid levels in man.     

Protein metabolism during total parenteral nutrition (TPN) in injured rats using medium-chain triglycerides

There are metabolic limitations to the infusion of large quantities of dextrose in critically ill patients receiving total parenteral nutrition. Of the alternative, nonprotein lipid sources, medium chain triglycerides (carbon chain length 8 and 10) are more rapidly oxidized and are deposited in the adipose tissue at rates much less than long chain triglycerides. In rats with burn injury receiving hypocaloric (dextrose and amino acids) parenteral feeding, we studied the changes in protein metabolism as a result of increasing the caloric intake by 33% by the addition of either dextrose, a soybean oil emulsion, a medium chain triglyceride emulsion, or a structured lipid emulsion of triglycerides synthesized from safflower oil (40%) and medium chain triglycerides (60%). Changes in body weight, blood glucose concentration, beta-hydroxybutyrate, lactate, amino acids, insulin, albumin, liver protein content, and nitrogen balance were measured during three days of feeding. Whole body leucine kinetics and muscle protein fractional synthetic rate were evaluated using a constant intravenous infusion of L-[1-14C]leucine. The addition of dextrose or soybean oil emulsion produced a significant increase in body weight and liver nitrogen but did not change albumin concentrations or leucine kinetics compared to those of the hypocaloric feeding group. Rats receiving medium chain triglycerides and structured lipid emulsions showed a reduction in branched chain amino acid concentrations and an improvement in serum albumin levels. However, the rats receiving the structured lipid emulsion also showed increased body weight, had a significant decrease in leucine oxidation, and showed a three day cumulative nitrogen balance significantly greater than zero.(ABSTRACT TRUNCATED AT 250 WORDS)     

Placenta as a link between amino acids, insulin-IGF axis, and low birth weight: evidence from twin studies.

Current evidence suggests that reduced placental transport of amino acids regulates fetal growth. We determined the association between fetal nutrition and the insulin-IGF axis by measuring the plasma concentrations of amino acids, insulin, IGF-I and IGF-binding protein-1 (IGFBP-1) in maternal and cord blood from gestational age-matched dichorionic (DC) twins with (n = 10) and without discordant birth weights (n = 10). In the growth-restricted (IUGR) twins, fetal concentrations of total essential (P < 0.01), nonessential (P < 0.01), and branched chain amino acids (P < 0.01) were lower than those in the appropriate for gestational age co-twins and concordant twin pairs. The IUGR twins had lower fetal concentrations of insulin (P < 0.001) and IGF-I (P < 0.05) and higher concentrations of IGFBP-1 (P < 0.01) than their appropriate for gestational age co-twins. In the discordant group, fetal IGFBP-1 had a negative association with fetal insulin (r = 0.71; P < 0.001), total essential amino acids (r = 0.78; P < 0.001), and branched chain amino acids (r = 0.64; P < 0.01). There was a positive correlation between total essential amino acids (r = 0.63; P < 0.001) and branched chain amino acids (r = 0.58; P < 0.01) and plasma insulin. However, there were no associations among fetal insulin, IGFBP-1 and nonessential amino acids. These data demonstrate the link between the reduction in certain essential and nonessential amino acids and alterations in fetal circulating levels of insulin and IGFBP-1, in growth-restricted twins.