Estimation of gluconeogenesis in newborn infants

Satish C. Kalhan1, Prabhu Parimi1, Ron Van Beek2, Carol Gilfillan1, Firas Saker1, Lourdes Gruca1, and Pieter J. J. Sauer2

1 Schwartz Center for Metabolism and Nutrition, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland, Ohio 44109; and 2 Erasmus University and Sophia Children's Hospital, 3000 CB Rotterdam, The Netherlands


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

The rate of glucose turnover (Ra) and gluconeogenesis (GNG) via pyruvate were quantified in seven full-term healthy babies between 24 and 48 h after birth and in twelve low-birth-weight infants on days 3 andby use of [13C6]glucose and 2H2O. The preterm babies were receiving parenteral alimentation of either glucose or glucose plus amino acid with or without lipids. The contribution of GNG to glucose production was measured by the appearance of 2H on C-6 of glucose. Glucose Ra in full-term babies was 30 ± 1.7 (SD) µmol · kg-1 · min-1. GNG via pyruvate contributed ~31% to glucose Ra. In preterm babies, the contribution of GNG to endogenous glucose Ra was variable (range 6-60%). The highest contribution was in infants receiving low rates of exogenous glucose infusion. In an additional group of infants of normal and diabetic mothers, lactate turnover and its incorporation into glucose were measured within 4-24 h of birth by use of [13C3]lactate tracer. The rate of lactate turnover was 38 µmol · kg-1 · min-1, and lactate C, not corrected for loss of tracer in the tricarboxylic acid cycle, contributed ~18% to glucose C. Lactate and glucose kinetics were similar in infants that were small for their gestational age and in normal infants or infants of diabetic mothers. These data show that gluconeogenesis is evident soon after birth in the newborn infant and that, even after a brief fast (5 h), GNG via pyruvate makes a significant contribution to glucose production in healthy full-term infants. These data may have important implications for the nutritional support of the healthy and sick newborn infant.

gluconeogenesis; lactate; stable isotopes; newborn infants; 2H2O


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

THE FETUS IN UTERO, under normal unperturbed physiological circumstances, is entirely dependent on the mother for a continuous supply of glucose, and no significant production of glucose by the fetus has been demonstrated, either in human or in other mammalian species (see review in Ref. 15). In addition, although significant activity of key enzymes involved in gluconeogenesis has been documented early in gestation in human fetal liver, gluconeogenesis in vivo has not been documented (11, 19, 29, 32, 33). Whether cytosolic phosphoenolpyruvate carboxykinase, the key regulatory enzyme involved in gluconeogenesis, is expressed in human fetal liver is not known. In rodents, cytosolic phosphoenolpyruvate carboxykinase is first expressed immediately after birth and is associated with the appearance of gluconeogenesis (12, 15). Thus the newborn at birth relies entirely on the mobilization of accumulated hepatic glycogen stores and the initiation of gluconeogenesis for a continuous supply of glucose. Both of these processes, i.e., glycogenolysis and gluconeogenesis, are stimulated by the birth-associated surges of catecholamines and pancreatic glucagon (20). That the human newborn can incorporate alanine carbon into glucose as early as 6 h of age has been demonstrated by Frazer et al. with a 13C-labeled tracer (10). However, the contribution of gluconeogenesis to glucose production in healthy full-term newborns has not been quantified. In the present study, with stable isotopic tracers, we have quantified the turnover rate of lactate and its incorporation into glucose in the period immediately after birth. In addition, using the recently developed deuterium-labeled water method (4, 22, 27), we have quantified the contribution of gluconeogenesis via pyruvate to total glucose production in healthy, normal full-term babies. During adaptation to the extrauterine environment, perturbations in glucose homeostasis are often observed in preterm infants, in those born small for gestational age, and in those born to mothers with diabetes (20). Because both hyperglycemia and hypoglycemia are often seen in these babies, we also quantified the rates of glucose turnover and gluconeogenesis in clinically stable infants in these groups. Our data show that gluconeogenesis from lactate and pyruvate is established by 4-6 h after birth. Gluconeogenesis from pyruvate contributes as much as 30% to total glucose production in healthy term babies between 5 and 6 h after a feed.


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

Gluconeogenesis (GNG) was measured in normal, preterm, small-for-gestational-age (SGA) infants, and in infants of diabetic mothers either by use of the deuterium labeling of body water or by quantifying the incorporation of 13C from labeled lactate into glucose.

Deuterium-Labeled Water Studies

GNG was quantified in seven full-term infants and thirteen preterm infants with the method of deuterium labeling of body water (4, 27). The study protocol was approved by the institutional review board. Written informed consent was obtained from the mother and, when available, the father, after the procedure had been fully explained. The full-term infants were appropriate for gestational age, had normal Apgar scores, had no clinical problems, and were receiving either formula feeds or maternal breast milk (Table 1). Two infants (nos. 6 and 7) were born to mothers with gestational and insulin-dependent diabetes mellitus (IDDM). They had normal plasma glucose concentrations and did not develop any neonatal problems.

                              
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Table 1.   Clinical characteristics of full-term infants

A majority of the term infants were studied on the 2nd day after birth in the General Clinical Research Center at MetroHealth Medical Center (Cleveland, OH). Two indwelling cannulas were placed in the superficial vein of each hand to draw blood samples and infuse the isotopic tracer [13C6]glucose (99% 13C; Isotec, Miamisburg, OH). The study protocol is displayed in Fig. 1. Approximately 3 h after the last feed, an oral dose (4 g/kg body wt) of 2H2O (99% 2H; Isotec) mixed with sterile distilled water was administered. Two hours later, three blood samples for the measurement of [2H]enrichment of C-6 of plasma glucose were obtained at 20-min intervals. This was followed by intravenous administration of a prime constant-rate infusion of [13C6]glucose for the next 120 min to quantify the rate of appearance (Ra) of glucose. The bolus prime was 0.6 mg/kg body weight, and the constant rate infusion was 30 µg · kg-1 · min-1. Blood samples were obtained for the measurement of glucose m6 enrichment at 90, 105, and 120 min of [13C6]glucose infusion. The infants were comfortable throughout the study period and did not show any evidence of stress. Cardiopulmonary monitoring was performed and plasma glucose concentration measured with each blood sampling. Their plasma glucose concentration remained unchanged throughout the study. The blood samples were centrifuged at 4°C, and plasma was stored at -70°C for later analysis. The study was completed at ~8 h after the last feed. In one infant (no. 8, not reported here), the study was discontinued because of inability to obtain venous blood samples.


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Fig. 1.   Study design for the quantification of gluconeogenesis using 2H2O. Three hours after the last feed, the infants were given 2H2O (4.0 g/kg body weight) mixed in sterile water. Plasma samples for the measurement of 2H enrichment in body water and on C-6 of glucose were obtained starting at 120 min after 2H2O administration. A prime constant-rate infusion of [13C6]glucose was started at 180 min and continued for 2 h to quantify the rate of appearance of glucose. The plasma glucose concentration () mg/dl, glucose m6 enrichment, and 2H enrichment on C-6 glucose from 1 study are displayed.

The preterm infants were studied between 48 and 72 h after birth with a similar protocol as described above, with minor modifications. As anticipated, all preterm infants were initially on ventilatory support. At the time of study, three infants were on ventilatory support and one required continuous positive airway pressure. No babies were on vasopressors at the time of study. All were receiving antibiotics, and three were on caffeine due to apnea or prematurity. All had indwelling vascular cannulas for clinical indications. Within 24 h after birth, they were assigned to either glucose, glucose plus amino acids (1.2 g · kg-1 · day-1), or glucose, amino acids (1.2 g · kg-1 · day-1), and lipids (1.25 g · kg-1 · day-1 = ~1 µmol · kg-1 · min-1). The rate of glucose infusion was based on the clinical protocol and adjusted by the patient's physician on the basis of clinical and laboratory information. However, the rate of glucose infusion was constant for several hours before and throughout the tracer infusion study. Plasma samples for deuterium enrichment on C-6 of glucose were obtained 3, 4, and 5 h after the nasogastric dose of 2H2O. [13C6]glucose infusion was started at 5 h, and blood samples for the 13C enrichment of glucose were obtained at 6.5, 6.75, and 7 h of the study. The doses of 2H2O and [13C6]glucose were the same per kilogram of body weight as for term infants. These studies were performed at the Sophia Children's Hospital (Rotterdam, The Netherlands). The study protocol was approved by the institutional review board, and written informed consent was obtained from the parents after the protocol had been fully explained. The investigators were not responsible for the clinical care of the infants.

Lactate Kinetics

Glucose and lactate kinetics were quantified in ten normal infants of a size appropriate for their gestational age (AGA), six infants of IDDM mothers, and four SGA infants (Table 2). The mothers with IDDM were managed with multiple insulin doses per day or by continuous subcutaneous insulin infusion to maintain normoglycemia throughout the day. Their hemoglobin A1 concentrations at delivery were within the normal range. All infants were born at term gestation and had no intrapartum or neonatal problems. They had normal physical examinations and no apparent clinical problems. The tracer isotope infusions were started within 4-5 h after birth in eight normal AGA infants and three IDDM infants. Other infants were studied between 8 and 24 h after birth. Tracer infusion in the latter group was started 4-5 h after the last feed and continued for the next 4 h. [6,6-2H2]glucose [98 atom % excess (APE) 2H enrichment; Merck, Dorvall, QC, Canada] and [13C3]lactate (90 APE 13C; Merck) were each infused at a prime constant-rate infusion. For both [6,6-2H2]glucose and [13C3]lactate, the infusion rate was 30 µg · kg-1 · min-1 after a prime of 1.8 mg/kg. Heparinized blood samples were drawn from an indwelling cannula at 30-min intervals; plasma was separated and stored at -20°C for later analysis. An aliquot of the whole blood was also precipitated with an equal volume of 10% perchloric acid and neutralized with 10% potassium carbonate for the measurement of blood lactate.

                              
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Table 2.   Clinical characteristics of the infants; lactate kinetics

Analytical Methods

Plasma glucose was measured by the glucose oxidase method. Blood lactate levels were measured using lactate dehydrogenase. Deuterium enrichment of hydrogens on C-6 of glucose was measured as described previously (4, 22). Briefly, C-6 of glucose with its hydrogens, after preparatory isolation and purification, was cleaved by periodate oxidation to formaldehyde, which, when condensed with ammonium hydroxide, forms hexamethylenetetramine. The latter was analyzed on a gas chromatography-mass spectrometry (GC-MS) system (HP 5970 equipped with an HP 5890 gas chromatograph; Hewlett-Packard, Palo Alto, CA). The GC-MS conditions were as follows: a nonpolar cross-linked methyl siloxane capillary column (HP-1, Hewlett-Packard) was used. Its dimensions were 30 m in length, 0.25 mm ID, 0.25 µm film thickness, 220°C injection temperature, 105°C oven initial temperature for 5.6 min, final temperature 230°C, and 45°C/min ramp rate. The retention time for hexamethylenetetramine was ~4.2 min. Electron impact ionization (70 eV) was used, and ions of mass-to-charge ratios 140 and 141 were monitored using selective ion monitoring technique. Standard solutions of glucose of known enrichment were run along with those of unknown enrichment to calibrate for instrumental variations.

The (m+6) enrichment of glucose (glucose m6, i.e., all carbons of glucose labeled with 13C) was measured using chemical ionization MS as described previously (1, 40). The (m+2) enrichment of glucose in [6,6-2H2]glucose was measured using a pentaacetate derivative, as previously described (23). The deuterium enrichment of glucose was corrected for the contribution of 13C from lactate. Plasma lactate enrichment was measured using an n-propylamide heptafluorobutyrate derivative (38). The 13C incorporation into glucose was estimated from the enrichment of C-1 of plasma glucose with the enzymatic decarboxylation method (21). 2H enrichment of total body water (plasma sample) was measured using the zinc reduction method on an isotope ratio mass spectrometer (Dr. W. Wong; Children's Nutrition Research Center, Baylor College of Medicine, Houston, TX).

Calculations

The rates of appearance (Ra) of glucose and lactate were calculated from the dilution of tracer glucose in plasma, as described (39)
R<SUB>a</SUB> (<IT>&mgr;</IT>mol<IT>·</IT>kg<SUP><IT>−</IT>1</SUP><IT>·</IT>min<SUP><IT>−</IT>1</SUP>)<IT>=</IT>[(E<SUB>i</SUB><IT>/</IT>E<SUB>p</SUB>)<IT>−</IT>1]<IT>×</IT>I
where Ei and Ep are the enrichments of isotopic tracer infused and of the substrate in plasma, respectively, and I is the rate of tracer infusion (in µmol · kg-1 · min-1).

The contribution of GNG from pyruvate was calculated as
GNG from pyruvate<IT> =</IT><FR><NU>100<IT>×</IT>0.5<IT>×</IT><SUP>2</SUP>H enrichment of glucose C-6</NU><DE><SUP> 2</SUP>H enrichment in H<SUB>2</SUB>O</DE></FR>
As discussed previously (16, 27), it is assumed that methyl hydrogens of pyruvate C-3, which forms C-6 of glucose, exchange with hydrogens in body water, so that 2H enrichment of hydrogens bound to C-3 of pyruvate or to that of phosphoenolpyruvate becomes similar to that of water. This exchange reaction in fasting adults has been shown to be over 80% complete. It has not been examined in the neonate.

The enrichment in C-6 is multiplied by 0.5 because of two hydrogens on C-6. Total GNG is calculated by multiplying the fractional contribution of GNG with total glucose Ra.

The Ra of lactate was calculated using the tracer dilution equation, as in the first equation and in Ref. 39. The incorporation of lactate carbon into glucose was estimated by precursor-product relationship. The fraction of glucose from lactate equals the 13C/12C ratio of glucose C-1 divided by the 13C/12C ratio of plasma lactate. It was assumed that the 13C/12C ratio of glucose C-1 represents the enrichment of all carbons of glucose. No correction was made for the loss of tracer carbon via exchange in the tricarboxylic acid cycle and, therefore, the estimates of lactate C incorporation into glucose represent minimal estimates.

All data are reported as means ± SD. Group comparisons were made using parametric and nonparametric statistical methods with Statistix software (Analytical Software, La Jolla, CA).


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Gluconeogenesis via Pyruvate 2H2O Studies

Term infants. As displayed in Table 1, the term infants were appropriate for gestational age and were studied at a mean age of 46 h. They maintained normal plasma glucose concentration throughout the 8 h of fasting. The mean plasma glucose concentration was 68 mg/dl (3.8 mM).

The 2H enrichment of plasma water and that of hydrogens on C-6 of glucose are displayed in Table 3. Infant no. 6 had received a smaller dose of 2H2O due to spillage. Also displayed are the m6 enrichments of glucose and the calculated contribution of GNG via pyruvate. A steady-state isotopic enrichment was evident in all infants. The Ra of glucose as measured by [13C6]glucose tracer dilution ranged between 4.9 and 5.9 mg · kg-1 · min-1 (28-33 µmol · kg-1 · min-1). GNG from pyruvate contributed between 22 and 40% to the total glucose production, or an average of 1.7 mg · kg-1 · min-1 (9.3 µmol · kg-1 · min-1). There was no correlation (r = 0.025; P = 0.96) between glucose Ra and the contribution of GNG.

                              
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Table 3.   GNG in the full-term newborn infant

Preterm babies. The preterm infants were studied between days 3 and 4 after birth. As anticipated in this group, because of clinical considerations, they were receiving a wide range of total calories (64-143 kcal · kg-1 · day-1). The rate of exogenous glucose infusion (I) ranged between 3 and 10.6 mg · kg-1 · min-1 (16-59 µmol · kg-1 · min-1; Table 4). Their plasma glucose concentration ranged between 4 and 7 mmol/l. Total Ra of glucose quantified by [13C6]glucose tracer dilution was 6-16 mg · kg-1 · min-1 (33-83 µmol · kg-1 · min-1), and the rate of endogenous glucose production (Re) was 0-7 mg · kg-1 · min-1.

                              
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Table 4.   GNG in the preterm babies

In the infants receiving glucose alone, the contribution of GNG via pyruvate ranged between 6 and 60% of endogenous glucose production. The highest contributions (53 and 60%) were observed in the two infants (nos. 4 and 5) who were receiving glucose at 3 mg · kg-1 · min-1 (17 µmol · kg-1 · min-1), a rate much lower than the Re seen in normal-term infants.

There was no difference in glucose Ra, glucose Re, and the contribution of GNG in infants receiving glucose plus amino acids with or without intravenous lipids. There was no correlation (r = 0.12) between glucose Re and the contribution of GNG.

Glucose and Lactate Kinetics

The plasma glucose and lactate levels were unchanged throughout the study period, and no significant difference was evident among normal infants, SGA infants, and infants of IDDM mothers (Table 5). The plasma C-peptide levels were slightly higher (P = nonsignificant) in the infants of diabetic mothers. The Ra of glucose was also similar in the three groups. The measured rates of glucose Ra when [6,6-2H2]glucose was used were slightly lower than those estimated using [13C6]glucose tracer. The reason for this difference remains undetermined (17). The estimated rate of plasma lactate turnover was 38 µmol · kg-1 · min-1 in normal babies. It was slightly lower in the SGA babies and higher in the infants of IDDM mothers (P = 0.07 by one-way ANOVA). The fractional contribution of GNG estimated from the incorporation of lactate carbon into glucose was also similar in the three groups and accounted for 18% of glucose Ra. This (uncorrected) estimation does not take into consideration the loss of tracer carbon via exchange in the tricarboxylic acid cycle intermediates. There was no significant correlation (r = 0.29; P = 0.23) between glucose Ra and lactate Ra, or between glucose Ra and the fractional contribution of lactate.

                              
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Table 5.   Glucose and lactate kinetics in newborn infants


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

In the present study, we have documented for the first time that healthy full-term neonates establish GNG from lactate 4-6 h after birth, and that GNG from pyruvate contributes ~30% of total glucose release at ~5 h after the last feed. In preterm infants, even in the presence of exogenous glucose and other nutrient administration, GNG is a significant contributor to the total glucose turnover. These data are important for the nutritional management of sick newborns and contribute to our understanding of extrauterine adaptation of the human neonate.

Although GNG has been estimated indirectly in the human newborn by quantifying the glucose carbon recycling (8, 18), or in the SGA infants by estimating incorporation of alanine C into glucose (10), no data exist documenting the contribution of GNG or the appearance of GNG in the full-term healthy newborn infant. In the present study, using the method of deuterium labeling of body water, we have documented that, in the healthy newborn between 35 and 68 h after birth and 5 h after the last feed, GNG contributed ~30% to the total glucose Ra. These estimates are of a similar magnitude to those seen in normal healthy adults after an overnight fast (13, 37). The deuterium incorporation in the hydrogens of C-6 of glucose quantifies the contribution of pyruvate to glucose and does not include the contribution of glycerol (4, 27). In addition, because of a lack of complete equilibrium between deuterium in body water and methyl hydrogens (C-3) of pyruvate, the measurement of 2H enrichment on C-6 of glucose results in underestimation (by ~10%) of the contribution of GNG via pyruvate to total glucose Ra. The incorporation of 2H on C-5 of glucose, although more precise for the estimation of total GNG, is difficult to use in neonates because of the very large sample size requirements (3, 4).

These measurements of GNG via pyruvate are similar to the estimates of glucose carbon recycling made by us in similar neonates with [13C6]glucose (8). In that study, the estimated glucose Ra from tracer dilution in eleven healthy full-term infants after an 8- to 9-h fast was 28 µmol · kg-1 · min-1, and glucose C recycling amounted to 35% or 10.4 µmol · kg-1 · min-1. Because glucose carbon recycling involves return of lactate and pyruvate from the periphery back to the liver and their incorporation into glucose, estimation of glucose C recycling gives an estimation of GNG via pyruvate. If the contribution of glycerol, ~4.5 µmol · kg-1 · min-1 (31, 35), is also included, then the total GNG in a healthy newborn will amount to ~14 µmol · kg-1 · min-1, or ~46% of the total glucose Ra of 30 µmol · kg-1 · min-1. This is significant and implies an important role of GNG in glucose homeostasis even after a brief fast. The quantitative contribution of various precursors to GNG via pyruvate remains undetermined.

The data in preterm babies, although variable, are also significant in that they underscore the quantitatively large contribution of GNG to glucose production, even when the endogenous rate of glucose production was low, e.g., infants infused with glucose plus amino acids with or without lipids. It is of interest that, in these babies also, GNG via pyruvate contributed 20-40% to endogenous production of glucose. In babies who were receiving glucose alone parenterally, the contribution of GNG was variable. It was highest (~50%) in the two infants (nos. 4 and 5) who were receiving intravenous glucose at the lowest rate. These measurements are of similar magnitude to those reported by Sunehag et al. (36) and Keshen et al. (25) in studies of low-birth-weight babies in which different isotopic tracer methods were used.

These data suggest that GNG should be considered as one of the several substrate cycles, like the triglyceride fatty acid cycle and protein turnover, which are active at all times and which can be rapidly accelerated at the time of acute demand.

Only one other study has quantified lactate turnover in the human newborn. Cowett and Wolfe (7), using the [13C3]lactate tracer dilution technique, reported the rate of lactate turnover to be 77.2 ± 13.0 µmol · kg-1 · min-1 in full-term infants between 9 and 42 h after birth, and 100 ± 19.2 µmol · kg-1 · min-1 in preterm infants. Their estimates are much higher than those reported in the present study. The differences may be related to age of the infants, intercurrent illness, or relationship to the last feed. Whereas a majority of the infants in the present study were investigated during the first few hours after birth (8/10 normal and 4/6 IDDM) and were not receiving any intravenous fluids or antibiotics, such was not the case in the study of Cowett and Wolfe. Our data on lactate turnover are similar to those reported in infants and children aged 1-25 mo, which range between 25 and 44 µmol · kg-1 · min-1 (2), and they are much higher than those reported in normal and diabetic adult subjects on the basis of similar tracer methods (9). The calculated contribution of lactate to glucose in our study, without account for loss of tracer in the tricarboxylic acid cycle, was ~18%. Correction for the loss of tracer (correction factor ~1.5) (14, 24) would yield lactate's contribution to be ~27%, similar to that observed using the 2H2O method.

Of interest, the Ra of lactate turnover was almost twofold the Ra of glucose turnover. This is in contrast to the data in adults, in which lactate turnover has been reported to be much lower than the rate of glucose turnover (in lactate equivalents) (5, 6, 9, 14, 24, 26, 28, 34). This would suggest either a rapid rate of equilibrium of the tracer between various compartments of lactate (plus pyruvate plus alanine) in babies or an influx of carbon into the lactate pool from nonglucose sources, e.g., amino acids. Such an hypothesis remains to be examined. The high rate of lactate turnover is also significant, because lactate has been suggested to be an important metabolic fuel for the brain in the newborn period (30). Finally, the lack of any significant difference among normal infants, SGA infants, and infants of IDDM mothers was not surprising. It essentially reflects the clinical practice of rigorous intrapartum regulation of maternal metabolism. Furthermore, because a large fraction of lactate C is derived from glucose, a difference in lactate kinetics will not be anticipated in the presence of similar rates of glucose turnover (41).

In summary, the present data show that GNG from lactate is apparent soon after birth in the healthy newborn infant and that it contributes ~30% of the total glucose produced. Significant contribution of GNG to glucose Ra could be observed in healthy babies within 5 hours of last feed and was also seen in preterm infants while they received parenteral glucose and other nutrients.


    ACKNOWLEDGEMENTS

We appreciate the assistance of the nursing staff of the General Clinical Research Center at MetroHealth Medical Center, the expert support of Alicia O'Brien and Ed Burkett, and the secretarial support of Joyce Nolan.


    FOOTNOTES

This work was financially supported by National Institutes of Health Grants HD-11089 and RR-00080.

Address for reprint requests and other correspondence: S. Kalhan, MetroHealth Medical Center, 2500 MetroHealth Dr., Cleveland, OH 44109-1998 (E-mail: sck{at}po.cwru.edu).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 1 February 2001; accepted in final form 10 July 2001.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Assel, B, Rossi K, and Kalhan S. Glucose metabolism during fasting through human pregnancy: comparison of tracer method with respiratory calorimetry. Am J Physiol Endocrinol Metab 265: E351-E356, 1993[Abstract/Free Full Text].

2.   Bougneres, P, Rocchiccioli F, Nurjhan N, and Zeller J. Stable isotope determination of plasma lactate conversion into glucose in fasting infants. Am J Physiol Endocrinol Metab 268: E652-E659, 1995[Abstract/Free Full Text].

3.   Bugianesi, E, Kalhan S, Burkett E, Marchesini G, and McCullough A. Quantification of gluconeogenesis in cirrhosis: response to glucagon. Gastroenterology 115: 1530-1540, 1998[ISI][Medline].

4.   Chandramouli, V, Ekberg K, Schumann WC, Kalhan SC, Wahren J, and Landau BR. Quantifying gluconeogenesis during fasting. Am J Physiol Endocrinol Metab 273: E1209-E1215, 1997[ISI][Medline].

5.   Consoli, A, Kennedy F, Miles J, and Gerich J. Determination of Krebs cycle metabolic carbon exchange in vivo and its use to estimate the individual contributions of gluconeogenesis and glycogenolysis to overall glucose output in man. J Clin Invest 80: 1303-1310, 1987[ISI][Medline].

6.   Consoli, A, Nurjhan N, Reilly JJ, Jr, Bier DM, and Gerich JE. Mechanism of increased gluconeogenesis in noninsulin-dependent diabetes mellitus. Role of alterations in systemic, hepatic, and muscle lactate and alanine metabolism. J Clin Invest 86: 2038-2045, 1990[ISI][Medline].

7.   Cowett, RM, and Wolfe RR. Glucose and lactate kinetics in the neonate. J Dev Physiol 16: 341-347, 1991[Medline].

8.   Denne, SC, and Kalhan SC. Glucose carbon recycling and oxidation in human newborns. Am J Physiol Endocrinol Metab 251: E71-E77, 1986[Abstract/Free Full Text].

9.   Diraison, F, Large V, Brunengraber H, and Beylot M. Non-invasive tracing of liver intermediary metabolism in normal subjects and in moderately hyperglycaemic NIDDM subjects. Evidence against increased gluconeogenesis and hepatic fatty acid oxidation in NIDDM. Diabetologia 41: 212-220, 1998[ISI][Medline].

10.   Frazer, TE, Karl IE, Hillman LS, and Bier DM. Direct measurement of gluconeogenesis from [2,3-13C2]alanine in the human neonate. Am J Physiol Endocrinol Metab 240: E615-E621, 1981[Abstract/Free Full Text].

11.   Greengard, O. Enzymic differentiation of human liver: comparison with the rat model. Pediatr Res 11: 669-676, 1977[Abstract].

12.   Hanson, RW, and Reshef L. Regulation of phosphoenolpyruvate carboxykinase (GTP) gene expression. Annu Rev Biochem 66: 581-611, 1997[ISI][Medline].

13.   Haymond, MW, and Sunehag AL. The reciprocal pool model for the measurement of gluconeogenesis by use of [U-13C]glucose. Am J Physiol Endocrinol Metab 278: E140-E145, 2000[Abstract/Free Full Text].

14.   Hetenyi, G, Jr. Correction factor for the estimation of plasma glucose synthesis from the transfer of 14C-atoms from labelled substrate in vivo: a preliminary report. Can J Physiol Pharmacol 57: 767-770, 1979[ISI][Medline].

15.   Kalhan, S, and Parimi P. Gluconeogenesis in the fetus and neonate. Sem Perinatol 24: 94-106, 2000[ISI].

16.   Kalhan, S, Rossi K, Gruca L, Burkett E, and O'Brien A. Glucose turnover and gluconeogenesis in human pregnancy. J Clin Invest 100: 1775-1781, 1997[Abstract/Free Full Text].

17.   Kalhan, SC. Stable isotopic tracers for studies of glucose metabolism. J Nutr 126: 362S-368S, 1996[Medline].

18.   Kalhan, SC, Bier DM, Savin SM, and Adam PAJ Estimation of glucose turnover and 13-C recycling in the human newborn by simultaneous [1-13C]glucose and [6,6-2H2]glucose tracers. J Clin Endocrinol Metab 50: 456-460, 1980[Abstract].

19.   Kalhan, SC, D'Angelo LJ, Savin SM, and Adam PAJ Glucose production in pregnant women at term gestation. Sources of glucose for human fetus. J Clin Invest 63: 388-394, 1979[ISI][Medline].

20.   Kalhan, SC, and Raghavan CV. Metabolism of glucose in the fetus and newborn. In: Fetal and Neonatal Physiology (2nd ed.), edited by Polin RA, and Fox WW. Philadelphia, PA: Saunders, 1998, p. 543-558.

21.   Kalhan, SC, Savin SM, Adam PAJ, and Campbell GT. Estimation of glucose turnover with stable tracer glucose-1-13C. J Lab Clin Med 89: 285-294, 1977[ISI][Medline].

22.   Kalhan, SC, Trivedi R, Singh S, Chandramouli V, Schumann WC, and Landau BR. A micromethod for the measurement of deuterium bound to carbon-6 of glucose to quantify gluconeogenesis in vivo. J Mass Spectrom 30: 1588-1592, 1995[ISI].

23.   Kalhan, SC, Tserng K, Gilfillan C, and Dierker LJ. Metabolism of urea and glucose in normal and diabetic pregnancy. Metabolism 31: 824-833, 1982[ISI][Medline].

24.   Katz, J. Determination of gluconeogenesis in vivo with 14C-labeled substrates. Am J Physiol Regulatory Integrative Comp Physiol 248: R391-R399, 1985[Abstract/Free Full Text].

25.   Keshen, T, Miller R, Jahoor F, Jaksic T, and Reeds PJ. Glucose production and gluconeogenesis are negatively related to body weight in mechanically ventilated, very low birth weight neonates. Pediatr Res 41: 132-138, 1997[Abstract].

26.   Kreisberg, RA, Pennington LF, and Boshell BR. Lactate turnover and gluconeogenesis in normal and obese humans. Effect of starvation. Diabetes 19: 53-63, 1970[ISI][Medline].

27.   Landau, BR, Wahren J, Chandramouli V, Schumann WC, Ekberg K, and Kalhan SC. Use of 2H2O for estimating rates of gluconeogenesis. Application to the fasted state. J Clin Invest 95: 172-178, 1995[ISI][Medline].

28.   Lecavalier, L, Bolli G, and Gerich J. Glucagon-cortisol interactions on glucose turnover and lactate gluconeogenesis in normal humans. Am J Physiol Endocrinol Metab 258: E569-E575, 1990[Abstract/Free Full Text].

29.   Marconi, AM, Cetin I, Davoli E, Baggiani AM, Fanelli R, Fennessey PV, Battaglia FC, and Pardi G. An evaluation of fetal glucogenesis in intrauterine growth-retarded pregnancies. Metabolism 42: 860-864, 1993[ISI][Medline].

30.   Medina, JM, Tabernero A, Tovar JA, and Martin-Barrientos J. Metabolic fuel utilization and pyruvate oxidation during the postnatal period. J Inher Metab Dis 19: 432-442, 1996[ISI][Medline].

31.   Patel, D, and Kalhan S. Glycerol metabolism and triglyceride-fatty acid cycling in the human newborn: effect of maternal diabetes and intrauterine growth retardation. Pediatr Res 31: 52-58, 1992[Abstract].

32.   Raiha, N, and Lindros KO. Development of some enzymes involved in gluconeogenesis in human liver. Ann Med Exp Biol Fenn 47: 146-150, 1969[ISI][Medline].

33.   Sadava, D, Frykman P, Harris E, Majerus D, Mustard J, and Bernard B. Development of enzymes of glycolysis and gluconeogenesis in human fetal liver. Biol Neonate 62: 89-95, 1992[ISI][Medline].

34.   Searle, GL, and Cavalieri RR. Determination of lactate kinetics in the human analysis of data from single injection vs. continuous infusion methods. Proc Soc Exp Biol Med 139: 1002-1006, 1972.

35.   Sunehag, A, Gustafsson J, and Ewald U. Glycerol carbon contributes to hepatic glucose production during the first eight hours in healthy term infants. Acta Paediatr 85: 1339-1343, 1996[ISI][Medline].

36.   Sunehag, AL, Haymond MW, Schanler RJ, Reeds PJ, and Bier DM. Gluconeogenesis in very low birth weight infants receiving total parenteral nutrition. Diabetes 48: 791-800, 1999[Abstract].

37.   Tayek, JA, and Katz J. Glucose production, recycling, and gluconeogenesis in normals and diabetics: a mass isotopomer [U-13C]glucose study. Am J Physiol Endocrinol Metab 270: E709-E717, 1996[Abstract/Free Full Text].

38.   Tserng, K, Gilfillan CA, and Kalhan SC. Determination of carbon-13 labeled lactate in blood by gas chromatography/mass spectrometry. Anal Chem 56: 517-523, 1984[ISI][Medline].

39.   Tserng, K, and Kalhan SC. Calculation of substrate turnover rate in stable isotope tracer studies. Am J Physiol Endocrinol Metab 245: E308-E311, 1983[Abstract/Free Full Text].

40.   Tserng, K, and Kalhan SC. Estimation of glucose carbon recycling and glucose turnover with [U-13C]glucose. Am J Physiol Endocrinol Metab 245: E476-E482, 1983[Abstract/Free Full Text].

41.   Virkamäki, A, Puhakainen I, Nurjhan N, Gerich JE, and Yki-Järvinen H. Measurement of lactate formation from glucose using [6-3H]- and [6-14C]glucose in humans. Am J Physiol Endocrinol Metab 259: E397-E404, 1990[Abstract/Free Full Text].


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