Endothelial colony-forming cells and mesenchymal stem cells from ECMO circuits of term infants.

OBJECTIVE: Endothelial progenitor cells (EPCs) have been examined in numerous adult diseases and have been suggested as a cellular-based therapy. However, there are no reports describing EPCs being isolated from newborn peripheral blood. STUDY DESIGN: Endothelial colony-forming cells (ECFCs), a subtype of EPCs, were isolated from blood collected from 12 neonatal extracorporeal membrane oxygenation (ECMO) circuits. RESULT: ECFCs were isolated in all samples. We unexpectedly isolated a distinctly different colony of mesenchymal stem cells (MSCs) in seven samples. Both cell types expressed the expected endothelial or mesenchymal cell surface antigens. CONCLUSION: To our knowledge, this is the first report of ECFCs and MSCs isolated from peripheral blood of critically ill term newborns. Both cells types may be mobilized in response to critical illness or to the ECMO circuit. Further studies evaluating the role of stem cells in various newborn conditions are warranted.

Amino acids do not suppress proteolysis in premature neonates.

To determine whether increased amino acid availability can reduce proteolysis in premature neonates and to assess the capacity of infants born prematurely to acutely increase the irreversible catabolism of the essential amino acids leucine (via oxidation) and phenylalanine (via hydroxylation to form tyrosine), leucine and phenylalanine kinetics were measured under basal conditions and in response to a graded infusion of intravenous amino acids (1.2 and 2.4 g. kg(-1). day(-1)) in clinically stable premature (approximately 32 wk gestation) infants in the 1st wk of life. In contrast to the dose-dependent suppression of proteolysis seen in healthy full-term neonates, the endogenous rates of appearance of leucine and phenylalanine (reflecting proteolysis) were unchanged in response to amino acids (297 +/- 21, 283 +/- 19, and 284 +/- 31 micromol. kg(-1). h(-1) for leucine and 92 +/- 6, 92 +/- 4, and 84 +/- 7 micromol. kg(-1). h(-1) for phenylalanine). Similar to full-term neonates, leucine oxidation (40 +/- 5, 65 +/- 6, and 99 +/- 7 micromol. kg(-1). h(-1)) and phenylalanine hydroxylation (12 +/- 1, 16 +/- 1, and 20 +/- 2 micromol. kg(-1). h(-1)) increased in a stepwise fashion in response to graded amino acids. This capacity to increase phenylalanine hydroxylation may be crucial to meet tyrosine needs when exogenous supply is limited. Finally, to determine whether amino acids stimulate glucose production in premature neonates, glucose rate of appearance was measured during each study period. In response to amino acid infusion, rates of endogenous glucose production were unchanged (and near zero).

Energy expenditure in infants with pulmonary insufficiency: is there evidence for increased energy needs?

The observed growth failure in infants with pulmonary insufficiency is postulated to be a consequence of elevated rates of energy expenditure. Assessment of energy expenditure by the classical technique of indirect calorimetry has yielded conflicting results. The adoption of the newer, doubly labeled water technique has provided evidence to support increased rates of energy expenditure in infants with chronic lung disease, congenital heart disease and in minimally ill, extremely low birth weight infants. The doubly labeled water technique holds great promise for the detailed study of energy expenditure in a variety of clinical conditions, including very ill as well as free-living subjects.

Protein and energy requirements in preterm infants.

Although protein and energy requirements in healthy growing and enterally fed infants are relatively well established, the nutritional requirements of extremely low birth weight infants are considerably less certain. New and emerging data in ELBW infants suggest high rates of energy expenditure and protein losses, which results in significant nutritional deficits and high rates of growth failure. Based on the limited and incomplete available data, energy intakes of 125-130 kcal/kg/d and protein intakes of 3.5-4 g/kg/d appear to be necessary to produce normal growth in ELBW infants. Although these intakes may be difficult to achieve in clinical practice, there is clear evidence that aggressive early nutrition can improve growth outcomes in these infants.

Energy expenditure after surgical repair in children with cyanotic congenital heart disease.

OBJECTIVE: Infants with cyanotic congenital heart disease (CCHD) have previously been shown to have similar resting energy expenditures (REEs) and elevated total energy expenditures (TEEs) compared with age-matched healthy infants. The purpose of this investigation was to re-examine the REE and TEE of the same individuals at 5 years of age, after surgical repair of the heart defect was done, to determine whether metabolic differences persist. STUDY DESIGN: Seven children were studied approximately 2.6 years after they underwent surgical repair of CCHD along with 10 age-matched healthy children. Indirect calorimetry was used to determine REE, and the doubly labeled water method was used to determine TEE and body composition. RESULTS: Results were compared with single-factor repeated measures analysis of variance. No significant differences were found between groups in weight or body composition. No significant differences were found between groups in REE, TEE, or the energy expended in physical activity. CONCLUSION: We conclude that differences in TEE observed during infancy are no longer present in 5-year-old children after they undergo surgical repair of CCHD. Furthermore, the individual components of energy expenditure of children with CCHD after repair are indistinguishable from those of healthy age-matched children.

Energy expenditure in the extremely low-birth weight infant.

Information about energy requirements of extremely low-birth weight infants is sparse, despite the rapidly improving survival rates of this population. Metabolizable energy intake can be estimated from energy balance studies and the percentage of caloric intake that is actually absorbed by these infants is approximately 87%. Data on energy expenditure in extremely premature infants is limited; however, energy expenditure has been shown to increase with postnatal age. Because both intake and expenditure are affected by multiple factors, there is significant variability in estimates of the energy requirements in extremely low-birth weight infants. At present, no valid recommendations can be made regarding optimal energy requirements for the extremely low-birth weight infant, except that their requirements probably exceed those of stable, growing very low-birth weight infants, currently estimated at 105 to 135 kcal.kg-1d-1.

Glucose and amino acid kinetic response to graded infusion of rhIGF-I in the late gestation ovine fetus.

Insulin-like growth factor I (IGF-I) has anabolic effects and is thought to be important in fetal development. The present study was designed to determine the dose response of recombinant human (rh) IGF-I on ovine fetal glucose and amino acid kinetics. Chronically catheterized fetal lambs were studied at 122-127 days gestation. The kinetics of leucine, phenylalanine, and glucose were measured before and during the infusion of rhIGF-I. rhIGF-I was infused into the fetal inferior vena cava at low, medium, or high rates (9.9, 20.1, or 40.2 nmol/h, respectively). A stepwise increase in serum IGF-I was achieved (164 +/- 3, 222 +/- 7, and 275 +/- 5 ng/ml). Insulin concentrations were decreased at the medium and high rhIGF doses. The rate of appearance (Ra) of leucine and phenylalanine and leucine oxidation decreased. Phenylalanine appearance from protein breakdown was decreased, with a maximal suppression of 30% observed at the highest rate of infusion. Glucose Ra was increased at the medium and high doses; other aspects of glucose metabolism were unchanged. The change in both glucose Ra and suppression of proteolysis was significantly correlated to the rhIGF-I infusion rate. It is concluded that rhIGF-I exerts dose-related effects in the ovine fetus, increasing fetoplacental glucose turnover and causing significant suppression of both proteolysis and amino acid oxidation.

Energy expenditure and energy intake during dexamethasone therapy for chronic lung disease.

Dexamethasone is commonly administered to ventilator-dependent preterm infants with chronic lung disease. Infants receiving dexamethasone therapy frequently exhibit decreased rates of weight gain. The purpose of this investigation was to determine whether decreased growth in infants receiving dexamethasone therapy is caused by increased energy expenditure. Twelve infants were studied: 6 received dexamethasone treatment at 2 wk of age and crossed over to receive placebo treatment at 4 wk; the treatment order was reversed in the other 6 infants. The doubly labeled water method was used to determine energy expenditure for a 1-wk period during each treatment phase. The rate of weight gain during dexamethasone treatment was 6.5+/-10.6 and 20.0+/-5.7 g/kg/d during placebo treatment. Energy expenditure was 93.1+/-34.6 kcal/kg/d during dexamethasone treatment and 88.3+/-37.1 kcal/kg/d during placebo treatment. Energy intake was 119.2+/-29.0 kcal/kg/d during dexamethasone treatment and 113.8+/-23.7 kcal/kg/d during placebo treatment. The difference between intake and expenditure, or the energy available for growth, was 26.2+/-36.8 kcal/kg/d during dexamethasone treatment and 25.5+/-37.4 kcal/kg/d during placebo treatment. No significant differences were found in energy expenditure or energy intake between the treatment phases. The reduced growth seen in infants receiving dexamethasone treatment cannot be explained by increased energy expenditure or decreased energy intake, but may be due to differences in the composition of newly accreted tissue.

Aromatic amino acids are utilized and protein synthesis is stimulated during amino acid infusion in the ovine fetus.

The purpose of this study was to determine whether the ovine fetus is capable of increased disposal of an amino acid load; if so, would it respond by increased protein synthesis, amino acid catabolism or both? A further purpose of the study was to determine whether the pathways of aromatic amino acid catabolism are functional in the fetus. Late gestation ovine fetuses of well-nourished ewes received an infusion of Aminosyn PF alone (APF), and Aminosyn PF + glycyl-L-tyrosine (APF+GT) at rates estimated to double the intake of these amino acids. The initial study, using APF, was performed at 126 +/- 1.4 d; the APF+GT study was performed at 132 +/- 1.7 d (term = 150 d). Phenylalanine and tyrosine kinetics were determined using both stable and radioactive isotopes. Plasma concentrations of most amino acids, but not tyrosine, increased during both studies; tyrosine concentration increased only during the APF+GT study. Phenylalanine rate of appearance and phenylalanine hydroxylation increased during both studies. Tyrosine rate of appearance increased only during the APF+GT study; tyrosine oxidation did not increase during either study. Fetal protein synthesis increased significantly during both studies, producing a significant increase in fetal protein accretion. Fetal proteolysis was unchanged in response to either amino acid infusion. These results indicate that the fetus responds to an acute increase in amino acid supply primarily by increasing protein synthesis and accretion, with a smaller but significant increase in amino acid catabolism also. Both phenylalanine hydroxylation and tyrosine oxidation are active in the fetus, and the fetus is able to increase phenylalanine hydroxylation rapidly in response to increased supply.

Splanchnic uptake of leucine in healthy children and in children with cystic fibrosis.

Interpretation of tracer studies of amino acid kinetics in the fed state is dependent on knowledge of splanchnic uptake of diet-derived amino acids. We studied five healthy control children and five children with cystic fibrosis (CF). After an overnight fast, the children ingested, hourly, a formula diet for 11 h. 5,5,5-[2H3]Leucine was added to the feedings during the last 6 h, and an i.v. infusion of 1-[13C]leucine was administered during the last 2 h of the formula feeding. The mean rate of splanchnic uptake of leucine was similar in the CF and control group, 23.8 +/- 24.0 and 21.5 +/- 21.2 mumol.kg-1.h-1, respectively. Fractional splanchnic uptake of leucine was not significantly different in the patients with CF (0.16 +/- 0.112 mean +/- SD) compared with the control children (0.244 +/- 0.256(-1)). The rate of whole body protein breakdown was not significantly different between the groups (CF versus control) with (159 +/- 18 versus 135 +/- 28 mumol.kg-1.h-1) or without (135 +/- 14 versus 114 +/- 20 mumol.kg-1.h-1) correction for splanchnic leucine uptake. However, for the 10 cases combined, protein breakdown corrected for splanchnic leucine uptake (147 +/- 26 mumol.kg-1.h-1) was 18% greater than uncorrected protein breakdown (124 +/- 20 mumol.kg-1.h-1) (p = 0.009). The data suggest that companion studies of splanchnic uptake might enhance the interpretation of leucine kinetics in the fed state.

Effect of rhIGF-I infusion on whole fetal and fetal skeletal muscle protein metabolism in sheep.

Insulin-like growth factor I (IGF-I) has been shown to have significant anabolic effects in the regulation of fetal protein metabolism. To investigate the tissue-specific effects of IGF-I on fetal skeletal muscle metabolism, we infused recombinant human (rh) IGF-I directly into the hindlimb of nine chronically catheterized, late-gestation fetal sheep. Substrate balance and amino acid kinetics were measured across the hindlimb and were compared with the effects at the whole body level before and during a 3-h infusion of rhIGF-I into the external iliac artery at 150 microgram/h. Infusion of rhIGF-I resulted in increases in IGF-I concentrations by 2- to 5. 75-fold in the ipsilateral iliac vein and by nearly 3-fold in the abdominal aorta. In the study limb, IGF-I had no effect on protein synthesis (phenylalanine rate of disposal 0.88 +/- 0.13 before vs. 0. 73 +/- 0.19 micromol/min during IGF-I) or breakdown (phenylalanine rate of appearance 0.67 +/- 0.13 before vs. 0.60 +/- 0.17 micromol/min during IGF-I) and did not alter net phenylalanine balance. IGF-I also did not affect hindlimb oxygen or glucose uptake. In contrast, at the whole body level, the rate of appearance of leucine, indicative of fetal protein breakdown, decreased during IGF-I infusion (rate of appearance of leucine 41.1 +/- 3.3 to 37.6 +/- 2.7 micromol/min) as did fetal leucine oxidation (8.4 +/- 0.8 to 6.8 +/- 0.6 micromol/min). There was no change in the umbilical uptake of leucine, and although not statistically significant, fetal leucine accretion increased 2.4-fold. These results provide further evidence that IGF-I promotes fetal protein accretion; however, its site of action is in tissues other than skeletal muscle.

Increased energy expenditure in infants with cyanotic congenital heart disease.

Infants with cyanotic congenital heart disease (CCHD) often have reduced weight gain compared with infants in control groups. Our purpose was to conduct a longitudinal study of energy intake, resting energy expenditure (REE), and total energy expenditure (TEE) of a group of infants with CCHD. We hypothesized that increased REE and TEE and decreased energy intake in these infants would lead to reduced growth. Ten infants with uncorrected CCHD and 12 infants in a control group were studied at 2 weeks of age and again at 3 months. Indirect calorimetry was used to determine REE; the doubly labeled water method was used to determine TEE and intake. At 2 weeks and 3 months of age, infants with CCHD weighed significantly less than infants in the control group. No significant difference was seen in energy intake or REE between groups during either period. TEE was slightly but not statistically increased in the CCHD group at 2 weeks (72.6 +/- 17.4 vs 59.8 +/- 10.9 kcal/kg/d) and significantly increased at 3 months (93.6 +/- 23.3 vs 72.2 +/- 13.2 kcal/kg/d, P

Total but not resting energy expenditure is increased in infants with ventricular septal defects.

OBJECTIVE: The purpose of this study was to determine the effect of left-to-right shunting on the resting energy expenditure (REE), total energy expenditure (TEE), and energy intake in a group of 3- to 5-month-old infants with moderate to large unrepaired ventricular septal defects (VSDs) compared with age-matched, healthy infants. METHODS: Eight infants with VSDs and 10 healthy controls between 3 to 5 months of age participated in the study. Indirect calorimetry was used to measure REE and the doubly-labeled water method was used to measure TEE and energy intake. An echocardiogram and anthropometric measurements were performed on all study participants. Daily urine samples were collected at home for 7 days. Samples were analyzed by isotope ratio mass spectrometry. Data were compared using analysis of variance. RESULTS: No significant differences were found in REE (VSD, 42.2 +/- 8.7 kcal/kg/d; control, 43.9 +/- 14.1 kcal/kg/d) or energy intake (VSD, 90.8 +/- 19.9 kcal/kg/d; control, 87.1 +/- 11.7 kcal/kg/d) between the groups. The percent total body water was significantly higher in the VSD infants and the percent fat mass was significantly lower. TEE was 40% higher in the VSD group (VSD, 87.6 +/- 10.8 kcal/kg/d; control, 61.9 +/- 10.3 kcal/kg/d). The difference between TEE and REE, reflecting the energy of activity, was 2.5 times greater in the VSD group. CONCLUSIONS: REE and energy intake are virtually identical between the two groups. Despite this, infants with VSDs have substantially higher TEE than age-matched healthy infants. The large difference between TEE and REE in VSD infants suggests a substantially elevated energy cost of physical activity in these infants. These results demonstrate that, although infants with VSDs may match the energy intake of healthy infants, they are unable to meet their increased energy demands, resulting in growth retardation.

Exogenous insulin reduces proteolysis and protein synthesis in extremely low birth weight infants.

OBJECTIVE: To determine the effect of a continuous insulin infusion on protein and glucose metabolism in extremely low birth weight (ELBW) infants. STUDY DESIGN: We measured the rate of appearance (Ra) of the essential amino acids leucine and phenylalanine (reflecting proteolysis), utilization of phenylalanine for protein synthesis, and glucose Ra using stable isotope tracers during a basal infusion of glucose (6 mg/kg/min) and in response to a continuous infusion of insulin (0.05 U/kg/hr) by means of the euglycemic hyperinsulinemic clamp technique. Four clinically stable, euglycemic ELBW infants (26 +/- 0 weeks' gestation, 894 +/- 44 gm birth weight, 2.8 +/- 0.8 days of age) were studied. RESULTS: In response to a greater than tenfold increase in insulin concentration (from 7 +/- 2 to 79 +/- 13 microU/ml), there was a 20% decrease in leucine Ra (Basal: 272 +/- 27 mumol/kg/hr; Insulin: 226 +/- 29 mumol/kg/hr; p < 0.01) and in phenylalanine Ra (Basal: 91 +/- 5 mumol/kg/hr; Insulin: 72 +/- 2 mumol/kg/hr; p < 0.05). Use of phenylalanine for protein synthesis also decreased by a similar magnitude (Basal: 77 +/- 4 mumol/kg/hr; Insulin: 62 +/- 1 mumol/kg/hr; p < 0.05). Glucose utilization doubled (from 8 +/- 0.9 to 15.7 +/- 1.1 mg/kg/min; p = 0.0003) and plasma lactate concentrations tripled (from 2.1 +/- 0.5 to 5.7 +/- 1.0 mmol/L; p < 0.05) during the insulin infusion. CONCLUSIONS: During an infusion of glucose alone, pharmacologic concentrations of insulin in ELBW infants produced no net protein anabolic effect. Furthermore, euglycemic hyperinsulinemia was accompanied by development of significant metabolic acidosis.

Regulation of fetal amino acid metabolism: substrate or hormonal regulation?

Insulin is regarded as the primary fetal growth-promoting hormone, but direct in vivo experimental data supporting this conjecture are sparse. Data obtained from studies in in vivo, chronically catheterized fetal lambs under a variety of experimental circumstances demonstrate that glucose availability is the primary modulator of fetal protein accretion, via its ability to diminish amino acid catabolism. The ovine fetus is shown to be resistant to insulin-induced suppression of proteolysis, relative to the adult. Data from studies in the human premature infant show that the findings in the ovine fetus are similar to those in the ex utero premature human.

Acute changes in leucine and phenylalanine kinetics produced by parenteral nutrition in premature infants.

To determine the effect of parenteral nutrition on the balance and catabolism of leucine (by oxidation) and phenylalanine (by hydroxylation) and to assess any acute changes in proteolysis and/or protein synthesis, leucine and phenylalanine kinetics were measured by stable isotope tracer infusions in nine 32-wk gestation premature infants under both basal conditions and in response to an i.v. infusion of glucose, lipid, and amino acids. Leucine and phenylalanine balance both changed from negative to positive during parenteral nutrition. However, leucine and phenylalanine catabolism were differently affected by parenteral nutrition; the rate of leucine oxidation increased 2-fold, whereas the rate of phenylalanine hydroxylation was unchanged from basal values. Phenylalanine utilization for protein synthesis and leucine utilization for protein synthesis (based on both plasma leucine and alpha-ketoisocaproic acid enrichments) increased significantly during parenteral nutrition. The endogenous rates of release of leucine (based on plasma leucine enrichment) and phenylalanine (both reflecting proteolysis) were significantly reduced during parenteral nutrition. The endogenous rate of release of leucine (based on alpha-ketoisocaproic acid enrichment) was slightly but not significantly lower during parenteral nutrition. The substantial increase in leucine oxidation without changes in phenylalanine hydroxylation suggests a possible limitation in the phenylalanine/tyrosine supply during parenteral nutrition. In addition, these results suggest that premature infants respond to parenteral nutrition with acute increases in whole body protein synthesis as well as a probable reduction in proteolysis.

Amino acids suppress proteolysis independent of insulin throughout the neonatal period.

To determine how increased amino acid availability alters rates of whole body proteolysis and the irreversible catabolism of the essential amino acids leucine and phenylalanine throughout the neonatal period, leucine and phenylalanine kinetics were measured under basal conditions and in response to intravenous amino acids in two separate groups of healthy, full-term newborns (at 3 days and 3 wk of age). The endogenous rates of appearance of leucine and phenylalanine (reflecting proteolysis) were suppressed equally in both groups and in a dose-dependent fashion (by approximately 10% with 1.2 g x kg(-1) x day(-1) and by approximately 20% with 2.4 g x kg(-1) x day(-1)) in response to intravenous amino acid delivery. Insulin concentrations remained unchanged from basal values during amino acid administration. The irreversible catabolism of leucine and phenylalanine increased in a stepwise fashion in response to intravenous amino acids; again, no differences were observed between the two groups. This study clearly demonstrates that the capacity to acutely increase rates of leucine oxidation and phenylalanine hydroxylation is fully present early in the neonatal period in normal newborns. Furthermore, these data suggest that amino acid availability is a primary regulator of proteolysis in normal newborns throughout the neonatal period.

Effects of feeding on protein turnover in healthy children and in children with cystic fibrosis.

We hypothesized that there is less suppression of whole-body protein breakdown with feeding in patients with cystic fibrosis (CF) who exhibit decreased insulin secretion after a single meal. Using [1-13C]leucine, we measured rates of nonoxidative leucine disappearance (whole-body protein synthesis) and protein breakdown in nine CF patients (6-11 y of age) and five healthy control subjects (8-10 y of age) during feeding and fasting. In the CF patients, synthesis and breakdown (x +/- SD) were 172 +/- 61 and 157 +/- 67 mumol.kg-1.h-1 during feeding and 140 +/- 24 and 178 +/- 26 mumol.kg-1.h-1 during fasting. The respective control values were 129 +/- 27 and 114 +/- 20 mumol.kg-1.h-1 during feeding and 136 +/- 13 and 173 +/- 18 mumol.kg-1.h-1 during fasting. Leucine balance was nearly identical in the two groups. By analysis of variance, there was a significant effect of feeding on protein breakdown but no difference between the groups. However, when each group was analyzed separately, feeding resulted in a 34% decrease in breakdown in the control subjects (P = 0.001) and a 23% increase in synthesis in the CF group (P = 0.058). Plasma insulin concentrations did not differ in the two groups. Thus, feeding may affect protein turnover differently in children with CF than in control children independently of plasma insulin concentration.

Effects of circulating IGF-I on glucose and amino acid kinetics in the ovine fetus.

To investigate the role of insulin-like growth factor I (IGF-I) in the regulation of fetal metabolism, the kinetics of leucine, phenylalanine, and glucose were assessed in the chronically catheterized ovine fetus (0.85 gestation) before and during infusion of recombinant human IGF-I (rhIGF-I). Substrate kinetics were determined by tracer dilution. rhIGF-I was infused at 6.7 nmol.kg fetus-1.h-1. Fetal insulin and growth hormone concentrations were significantly decreased by 50% during rhIGF-I infusion. Net umbilical glucose uptake was unchanged, and glucose rate of appearance increased in the fed state only. There were no changes in the net umbilical uptakes of leucine or phenylalanine, but the rates of appearance of both declined during rhIGF-I infusion, indicative of decreased fetal protein breakdown (Ra,Leu 45.4 +/- 1.40 to 40 +/- 1.4 mumol/min in the fed state, 43 +/- 1.5 to 37 +/- 1.5 mumol/min in the fasted state; Ra,Phe 10.7 +/- 0.3 to 10.4 +/- 0.3 mumol/min in the fed state and from 10.7 +/- 0.3 to 9.8 +/- 0.3 mumol/min in the fasted state). Leucine oxidation was also decreased (8.90 +/- 0.76 to 6.52 +/- 0.81 mumol/min, P = 0.025), more so in the fasted than the fed state. These results indicate a significant antiproteolytic endocrine effect for IGF-I in the late-gestation mammalian fetus.

Glucose and amino acid turnover in untreated gestational diabetes.

OBJECTIVE: Although gestational diabetes affects as many as 3% of all pregnant women, specific aspects of glucose and protein metabolism in this population have not been clearly delineated. We tested the hypothesis that gestational diabetes mellitus (GDM) results in increased glucose production and proteolysis during fasting. RESEARCH DESIGN AND METHODS: Using tracer isotope infusions, the rate of appearance (Ra) of glucose, leucine, phenylalanine and tyrosine, phenylalanine hydroxylation, leucine oxidation, and urea nitrogen excretion were determined after an overnight fast in 10 GDM subjects, within 2 weeks of diagnosis and before initiation of treatment, and in a matched control group of nine healthy nondiabetic pregnant women. RESULTS: Fasting glucose Ra was similar in GDM patients and control subjects (GDM, 12.8 +/- 1.1 vs. control subjects, 12.8 +/- 0.9 mumol . kg-1 . min-1). Leucine and phenylalanine Ra (reflecting proteolysis) also were not different between GDM patients and control subjects (GDM leucine Ra, 128 +/- 14 vs. control subjects, 124 +/- 5; phenylalanine Ra GDM, 35 +/- 4 vs. control subjects, 40 +/- 2 mumol . kg-1 . h-1). Furthermore, leucine oxidation and phenylalanine hydroxylation were not increased in GDM subjects, urea nitrogen excretion was actually lower in GDM patients. However, fasting insulin concentrations were significantly elevated in GDM subjects (GDM, 165 +/- 35 vs. control subjects, 30 +/- 5 pmol/l; P < 0.01). CONCLUSIONS: Hepatic glucose release and whole-body proteolysis in GDM patients were remarkably similar to matched pregnant control subjects. This was achieved with insulin concentrations three- to fivefold higher than normal, suggesting significant insulin resistance for both glucose and protein metabolism in GDM.