Effects of antenatal steroids on protein metabolism in preterm infants on the first day of life

OBJECTIVE: To analyze, in an existing cohort of infants, whether antenatal administered corticosteroids influence protein metabolism in preterm infants on the first day of life. Study design Three groups of infants were studied. The mothers of 25 infants had received 2 or more doses of corticosteroids, the mothers of 5 had received 1 dose, and there was no antenatal steroid exposure for 8 infants. Within a few hours after birth, a double-tracer leucine infusion was started by intravenous and intragastric routes and continued for 5 hours while the infants received only intravenous glucose. RESULTS: The plasma alpha-keto-isocaproic acid (KIC) enrichment (mol percent excess, MPE) from the intravenous tracer was not different between infants who reveived no antenatal steroids (8.58+/-1.64), 1 dose (7.60+/-0.78), and 2 or more doses (7.61+/-1.29). From the intragastric tracer, the plasma KIC enrichment from the intragastric tracer was different among the 3 groups, 7.62+/-2.35 for 0 doses, 5.78+/-0.85 for 1 dose, and 5.53+/-1.58 for 2 or more doses of antenatal steroids.Plasma KIC enrichment from the intravenous tracer was significantly higher than from the intragastric tracer in infants who received antenatal steroids, whereas there was no difference in infants who had not received antenatal steroids. Plasma leucine enrichment showed the same results. CONCLUSIONS: Antenatal corticosteroid administration to the fetus has no effect on whole-body leucine metabolism on the first day of life. However, it is associated with an increase in splanchnic leucine uptake at birth.     

Splanchnic oxidation is the major metabolic fate of dietary glutamate in enterally fed preterm infants

The intestine is a major site of amino acid metabolism, especially in neonates. The energy needed for the metabolic processes in neonatal animals is derived from dietary glucose and amino acids. No data are available showing that dietary amino acids function as intestinal fuel source in human neonates as well. We hypothesized that preterm infants show a high splanchnic first-pass glutamate metabolism and the primary metabolic fate of glutamate is oxidation. Five preterm infants (birth weight 1.2+/-0.2 kg, gestational age 29+/-1 wk) were studied by dual tracer ([U-(13)C]glutamate and [D3]glutamate) techniques on two study days (within postnatal d 14-19). Splanchnic and whole-body glutamate kinetics were assessed by plasma isotopic enrichment of [U-(13)C]glutamate and [D3]glutamate and breath CO2 enrichment. Fractional first-pass glutamate uptake was 77+/-18% on d 1, and 70+/-7% on d 2, mean 74+/-13%. Almost all (86+/-7%) of the glutamate used in the first pass is directed toward oxidation. There is a high splanchnic fractional first-pass uptake and a high oxidation rate of glutamate in preterm infants. Glutamate is an important source of energy for the splanchnic tissues in preterm infants receiving full enteral feeding.     

Whole-body protein parameters in premature infants: a comparison of different 15N tracer substances and different methods.

[15N]glycine, [15N]leucine, and [15N]yeast protein thermitase hydrolysate (YPTH) as tracers for investigating the protein turnover rates in premature infants were studied in nine human milk-fed neonates (born after 32 to 34 wk of gestation) by paired comparison of the tracers. The 15N enrichment of total urinary nitrogen and ammonia after administration of a single oral dose of 15N was measured by emission spectrometry. Flux rates were calculated using a three-compartment model and the ammonia end product method. The mean whole-body protein synthesis rates, as determined by the three-compartment model derived from the three 15N tracers, differed significantly (p less than 0.01) among [15N]glycine (15.9 g/kg/d), [15N] leucine (9.1 g/kg/d), and 15N-YPTH (5.9 g/kg/d). When the corresponding rates were determined from the excretion of label in ammonia, the results showed the opposite tendency; the lowest apparent synthesis rates were found after [15N]glycine (7.5 g/kg/d), followed by [15N]leucine (14.4 g/kg/d), and the highest figure resulted after [15N] YPTH (16.7 g/kg/d). The results of this comparison substantiate the assumption that there are methodologic errors in connection with the use of different tracers and models for the calculation of whole-body protein parameters in preterm infants, with respect to the main requirement for tracer kinetic studies; the tracer nitrogen must be representative of total amino acid nitrogen. Seen in this light, mixtures of completely labeled amino acids such as YPTH may represent the most reliable tracer substance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Persistently low blood retinol levels during and after parenteral feeding of very low birth weight infants: examination of losses into intravenous administration sets and a method of prevention by addition to a lipid emulsion

Very low birth weight infants have little storage of hepatic retinol and are, therefore, highly dependent upon an exogenous supply. The recent association between low serum retinol level and bronchopulmonary dysplasia and the persistently low serum levels of retinol during total parenteral nutrition prompted a prospective study to evaluate serial changes in serum retinol levels during 1 month of total parenteral nutrition (retinol dose 455 micrograms/d) and again during 1 month of total enteral feeding (retinol dose 200 to 300 micrograms/d) in the same infants. Infants were divided into two groups. Group 1 consisted of infants weighing less than 1,000 g (n = 24) and group 2 consisted of infants weighing 1,000 to 1,500 g (n = 17). Although initial mean levels of retinol were similar in both groups (14.8 +/- 0.9 and 13.5 +/- 0.7 micrograms/dL), there was wide variation between infants. In group 1 infants, there was a significant (P less than .01) decline in retinol level by the second week of life (to 9.2 +/- 1 micrograms/dL), which persisted during total parenteral nutrition, but increased to 13.4 +/- 2 after 1 week of enteral feeding. This level was maintained throughout enteral feeding. In group 2 infants, there was no significant change in serum retinol level throughout the study. During total parenteral nutrition, several infants had retinol levels below 10 micrograms/dL, a level associated with signs of retinol deficiency in older children. Because losses of retinol are known to occur in smaller volume total parenteral nutrition solutions, it was speculated that losses of retinol in our patients were due to retinol losses in the total parenteral nutrition delivery system.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma and urine riboflavin during riboflavin-free nutrition in very-low-birth-weight infants

BACKGROUND: Very-low-birth-weight (VLBW; birth weight <1500 g) infants receive enteral and parenteral nutriture that provides greater daily riboflavin (vitamin B2) than does term infant nutriture, and elevated plasma riboflavin develops in these infants after birth. The purpose of this study was to measure plasma and urine riboflavin concentrations in VLBW infants during riboflavin-free nutrition. Our hypothesis was that elevated plasma riboflavin develops in VLBW infants because of high daily intake and immature renal riboflavin elimination. METHODS: Eighteen clinically healthy VLBW infants received parenteral nutrition and preterm infant formula during the first postnatal month. On postnatal days 10 and 28, the infants received specially prepared riboflavin-free enteral and parenteral nutrition for the 24-hour study period. Serial collections of plasma were made at time 0 and at 12 and 24 hours. Urine was collected continuously for the 24-hour period in 4-hour aliquots. Samples were analyzed for riboflavin concentration. RESULTS: During the 24-hour riboflavin-free study period on postnatal day 10, plasma riboflavin decreased 56% from 185 +/- 37 ng/mL (mean +/- SEM), and urine riboflavin decreased 75% from 3112 +/- 960 mg/mL. Similarly, on postnatal day 28, plasma riboflavin decreased 79% from 184 +/- 32 ng/mL, and urine riboflavin concentration decreased 91% from 5092 +/- 743 ng/mL during the 24-hour riboflavin-free study period. Riboflavin half-life (t(1/2)) was 18.5 hours on postnatal day 10 and decreased 48% by postnatal day 28. Riboflavin elimination was 145.1 +/- 20.6 mg/kg per day on postnatal day 10 and increased 40% by postnatal day 28. CONCLUSION: The VLBW infants who received parenteral nutrition and preterm infant formula had elevated plasma riboflavin on postnatal days 10 and 28. Plasma riboflavin t(1,2) was shorter and renal riboflavin elimination was greater on postnatal day 28 than on postnatal day 10. Plasma riboflavin was normal after 24 hours of riboflavin-free nutrition. The pattern of plasma and urine riboflavin in VLBW infants suggests a lower daily intake would maintain plasma riboflavin close to normal.     

影响极低出生体重儿体重增长的多因素分析

目的探讨影响极低出生体重儿(VLBW)体重增长的相关因素。方法对1998年7月—2004年3月重庆医科大学儿童医院新生儿病房收治的51例VLBW进行回顾性分析。结果单因素分析发现,早开奶、热卡摄入量和蛋白质摄入量对体重增长有显著性影响(P<0·05)。多元逐步回归分析结果示,热卡摄入量和蛋白质摄入量是影响体重增长的显著因素,回归方程为Y(体重增长)=-6·426+0·120X1(热卡摄入量)+3·737X2(蛋白质摄入量)(P<0·01)。达到体重增长目标对象中单纯胃肠内营养组和部分胃肠外营养组热卡摄入量分别为(520·62±21·59)kJ/(kg·d)[(124·43±5·16)kcal/(kg·d)]、(451·49±68·41)kJ/(kg·d)[(107·98±16·35)kcal/(kg·d)],差异有统计学意义(P<0·05)。早开奶组出生体重恢复时间、住院时间和胃肠外营养液体量占总液量比例>75%时间平均秩分别为18·58、20·24、20·11,晚开奶组分别为33·00、32·48、31·83,差异有统计学意义(P<0·05)。结论VLBW在生后应保证足量热卡和蛋白质的供给,对于小于胎龄儿和有严重并发症的患儿更应该加强营养的补充,对VLBW应尽早喂养,同时需要胃肠外营养作为肠内营养的补充。     

Changes in protein turnover after the introduction of parenteral nutrition in premature infants: comparison of breast milk and egg protein-based amino acid solutions.

Rates of protein turnover were measured in 20 infants receiving either Vamin Infant (group A) or Vamin 9 glucose (group B) as the amino acid source in total parenteral nutrition. A constant infusion of L-[1-13C]leucine was used to measure whole body leucine flux, and leucine oxidation rates were derived from measurements of total urinary nitrogen excretion. Infants were first studied when receiving only i.v. glucose and again on each of the next 4 d as total parenteral nutrition was gradually increased to a maximum of 430 mg nitrogen/kg/d and 90 nonprotein kcal/kg/d. Net protein gain and protein synthesis and breakdown rates increased progressively for all infants taken together over the study period as i.v. nutrition was increasing (p less than 0.001). There were no differences between groups in the changes in net protein gain and rates of protein synthesis and breakdown throughout the study period. Nitrogen retention on d 5 for the two groups was similar (60 +/- 16% and 67 +/- 11% in groups A and B, respectively). In a subgroup of infants, measurements were repeated on d 8, when the intake had been constant for 3 d. Protein retention was the same as on d 5, but both synthesis and breakdown were increased. It is concluded that rates of protein turnover increase significantly in response to increasing i.v. nutrition and that this elevation was not influenced by the composition of the amino acid mixture given.     

Effect of early low-volume enteral substrate on subsequent feeding tolerance in very low birth weight infants

To determine the effect of small enteral feedings on small bowel function, 46 infants with birth weight less than 1500 g, selected on the basis of risk factors for feeding intolerance, were assigned randomly to one of two feeding groups. Group 1 received low-volume enteral feeds (12 ml/kg/day) in addition to parenteral alimentation for 10 days beginning on day 8 of life; group 2 received parenteral alimentation alone until day 18 of life. After this trial period feedings were increased by 15 ml/kg/day in all infants. Four infants (9%) developed necrotizing enterocolitis (one prior to any feeds, two in group 1, and one in group 2); two others were dropped from the study for reasons unrelated to feeding. The remaining 18 infants in group 1 had improved feeding tolerance compared with the 22 in group 2, as manifested by fewer days that gastric residuum totalled more than 10% of feedings (1.3 +/- 0.5 days vs 3.2 +/- 0.6 days, respectively, p less than 0.05) and fewer days that feedings were discontinued because of feeding intolerance (2.7 +/- 0.8 days vs 5.5 +/- 0.9 days, respectively, p less than 0.05). Consequently, 17 of 18 (94%) infants who had received the early low-volume enteral feedings achieved an enteral intake of 120 kcal/kg/day by 6 weeks of life, whereas only 14 of 22 (64%) infants in the delayed feeding group reached this intake (p less than 0.05). Peak total serum bilirubin concentrations were comparable in the two groups. The initiation of hypocaloric enteral substrate as an adjunct to parenteral nutrition improved subsequent feeding tolerance in sick infants with very low birth weight.     

Effect of two amino acid solutions on leucine turnover in preterm infants

OBJECTIVE: To assess the effect of two different parenteral amino acid mixtures, Trophamine and Primene, on leucine turnover in preterm infants. METHOD: Leucine kinetics were measured with [5,5,5 D3]leucine tracer in 15 infants receiving Trophamine (group 'T') (mean birth weight 1,263 g) and 22 who received Primene (group 'P') (mean birth weight 1,336 g) during two study periods, within a few hours after birth but before introduction of parenteral amino acid solution, and again at postnatal day 7. The rate of appearance of leucine was calculated from the enrichment of alpha-ketoisocaproic acid in plasma. RESULTS: There were no significant differences in leucine turnover within a few hours after birth in the two groups. In the infants who received Primene leucine turnover on day 7 was significantly lower than in those who received Trophamine (269 +/- 43 vs. 335 +/- 27, p < 0.05). Despite a higher intake of leucine in the Trophamine group (108 +/- 10 vs. 77 +/- 8 micromol.kg(-1).h(-1)), leucine released from proteins at day 7 was higher in this group compared to Primene (227 +/- 27 vs. 192 +/- 42 micromol.kg(-1).h(-1)). CONCLUSIONS: Primene administration results in lower leucine released from proteins, an estimate of protein breakdown, than Trophamine in preterm infants. Increases in whole body leucine turnover in response to administration of i.v. amino acids is influenced by the composition of the amino acid mixture. The factors responsible for this difference remain to be elucidated.     

Chemotherapy does not influence intestinal amino acid uptake in children

Chemotherapy will frequently induce intestinal damage (mucositis). Enteral nutrition is then often withheld for fear of impaired intestinal absorption as shown in animal models. There is no clinical evidence, however, that absorption is indeed compromised during chemotherapy-induced mucositis. The aim of this study was to evaluate systemic availability of dietary amino acids (leucine) during chemotherapy-induced mucositis. We studied eight childhood cancer patients (age 1.5-16 y) on 2 d, i.e. the day before chemotherapy and 3-5 d after. Chemotherapy-induced oral mucositis and diarrhea were scored on a World Health Organization toxicity scale. Stable isotope tracers were used to measure first-pass splanchnic leucine uptake and whole-body leucine kinetics. Patients showed increased mucositis and/or diarrhea toxicity scores (p < 0.0001) after chemotherapy. Systemic availability of enterally administered leucine was not significantly affected by chemotherapy (before 60%, after 90%, p = 0.46). Interestingly, five patients already showed a negative leucine balance before chemotherapy. In conclusion, most children receiving chemotherapy are already catabolic before start of a new cycle of chemotherapy. Amino acid transport as measured by leucine uptake in the intestine is not affected by chemotherapy-induced mucositis.     

The fear of necrotizing enterocolitis versus achieving optimal growth in preterm infants--an opinion

Very-low-birthweight (VLBW) infants suffer marked growth delay despite well-intentioned efforts at combining enteral and parenteral nutrition. Fear of necrotizing enterocolitis (NEC) has traditionally influenced neonatologists toward delaying and progressing slowly with enteral feeding, while supporting the infant with parenteral nutrition. Current evidence suggests significant benefits of enteral feeding that is started early and advanced at rates of 20-35 ml/kg/d. Conclusion: We conclude that fear of inadequate growth should replace the fear of NEC in guiding nutritional strategies for these infants.     

Evaluation of a pediatric multiple vitamin preparation for total parenteral nutrition in infants and children. I. Blood levels of water-soluble vitamins

This study represents the first attempt to evaluate the response to the only intravenous vitamin preparation (MVI Pediatric) for infants and children receiving total parenteral nutrition. Eighteen preterm infants (group 1), 26 term infants and children receiving total parenteral nutrition for 2 to 4 weeks (group 2A), and eight infants and children receiving total parenteral nutrition for 3 to 6 months (group 2B) were studied. Term gestation infants and children up to 11 years of age received daily vitamin doses that approximated the 1974 Recommended Dietary Allowances and coincided with the 1975 American Medical Association Nutrition Advisory Group total parenteral nutrition dosage guidelines for children weighing more than 10 kg. Preterm infants received 65% of these dosages. RBC transketolase (vitamin B1), glutathione reductase (B2), and glutamic oxaloacetic transaminase (B6) activities were maintained at normal levels, and niacin levels were maintained within the reference range (7.1 +/- 0.32 micrograms/mL) in all study patients. Pantothenate, biotin, and ascorbate were maintained at reference levels in groups 2A and 2B. In group 1, ascorbic acid was increased significantly during treatment from 1.53 +/- 0.16 to 3.60 by seven days and to 2.54 +/- 0.62 by day 28 of treatment (reference normals = 0.99 +/- 0.1 mg/dL). RBC folate was maintained within the reference range of 411 +/- 76 pg/mL; however, pantothenate and biotin levels increased significantly to more than 2 SD above reference values during treatment, and vitamin B12 levels, which were above the reference range initially, were maintained at more than 2 SD above the reference range throughout treatment. The elevation in vitamin B12 was seen in both group 1 and 2 patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute effects of intravenous glutamine supplementation on protein metabolism in very low birth weight infants: a stable isotope study.

Although very low birth weight infants are subjected to severe stress and glutamine is now considered a conditionally essential amino acid that may attenuate stress-induced protein wasting in adults, current amino acid solutions designed for neonatal parenteral nutrition do not contain glutamine. To determine whether a short-term supplementation with i.v. glutamine would affect protein metabolism in very low birth weight infants, 13 preterm neonates (gestational age, 28-30 wk; birth weight, 820-1610 g) receiving parenteral nutrition supplying 1.5 g x kg(-1) x d(-1) amino acids and approximately 60 nonprotein kcal x kg(-1) x d(-1) were randomized to receive an i.v. supplement made of either 1) natural L-glutamine (0.5 g x kg(-1) x d(-1); glutamine group), or 2) an isonitrogenous glutamine-free amino acid mixture (control group), for 24 h starting on the third day of life. On the fourth day of life, they received a 2-h infusion of NaH(13)CO(3) to assess the recovery of (13)C in breath, immediately followed by a 3-h L-[1-(13)C]leucine infusion. Plasma ammonia did not differ between the groups. Glutamine supplementation was associated with 1) higher plasma glutamine (629 +/- 94 versus 503 +/- 83 microM, mean +/- SD; p < 0.05, one-tailed unpaired t test), 2) lower rates of leucine release from protein breakdown (-16%, p < 0.05) and leucine oxidation (-35%, p < 0.05), 3) a lower rate of nonoxidative leucine disposal, an index of protein synthesis (-20%, p < 0.05), and 4) no change in protein balance (nonoxidative leucine disposal - leucine release from protein breakdown, NS). We conclude that although parenteral glutamine failed to enhance rates of protein synthesis, glutamine may have an acute protein-sparing effect, as it suppressed leucine oxidation and protein breakdown, in parenterally fed very low birth weight infants.     

非营养性吸吮对早产儿营养及胃肠道转运时间的影响

目的　评估非营养性吸吮 (NNS)对早产儿营养、胃肠道转运时间 (WGTT)及喂养相关并发症的影响。方法　将 3 8例需经鼻胃管喂养 (INGF)的健康早产适于胎龄儿 (出生体重 10 5 0～1790g) ,根据是否辅以非营养性吸吮随机分成单纯鼻胃管喂养组和非营养性吸吮组 ,用同一种配方乳喂养。记录喂养 2周的生长发育指标 (体重、身长、头围 )的变化及恢复出生体重的时间 ;入液量、奶量、热能、肠道营养热能达 418 4kJ/(kg·d)的时间、鼻胃管留置时间 ;大便次数、性状 ;喂养相关并发症 ;测定胃肠道转运时间。结果　非营养性吸吮组恢复出生体重时间 [( 8 8± 3 7)d]较单纯鼻胃管喂养组 [( 11 1± 3 0 )d]显著缩短 (P <0 0 5 ) ;喂养前及 2周后体重、身长、头围的变化差异无显著性 (P>0 0 5 )。非营养性吸吮组肠道营养热能达 418 4kJ/(kg·d)的时间 [( 12 3± 5 1)d]较单纯鼻胃管喂养组 [( 15 7± 5 2 )d]明显缩短 (P <0 0 5 ) ;鼻胃管留置时间 [( 13± 10 )d]缩短 4d [( 17± 12 )d],但差异无显著性 (P >0 0 5 )。非营养性吸吮组胃残留的发生率 ( 16 7% )较单纯鼻胃管喂养组 ( 5 0 % )显著减少(P <0 0 5 ) ,两组其他并发症的发生率差异无显著性 (P >0 0 5 ) ;非营养性吸吮组第 2周的全胃肠道转运时间 [( 3 3     

Amino acids, glutamine, and protein metabolism in very low birth weight infants

Glutamine has been proposed to be conditionally essential for premature infants, and the currently used parenteral nutrient mixtures do not contain glutamine. De novo glutamine synthesis (DGln) is linked to inflow of carbon into and out of the tricarboxylic acid (TCA) cycle. We hypothesized that a higher supply of parenteral amino acids by increasing the influx of amino acid carbon into the TCA cycle will enhance the rate of DGln. Very low birth weight infants were randomized to receive parenteral amino acids either 1.5 g/kg/d for 20 h followed by 3.0 g/kg/d for 5 h (AA1.5) or 3.0 g/kg/d for 20 h followed by 1.5 g/kg/d for 5 h (AA3.0). A third group of babies received amino acids 1.5 g/kg/d for 20 h followed by 3.0 g/kg/d for 20 h (AA-Ext). Glutamine and protein/nitrogen kinetics were examined using [5-(15)N]glutamine, [2H5]phenylalanine, [1-(13)C,15N]leucine, and [15N2]urea tracers. An acute increase in parenteral amino acid infusion for 5 h (AA1.5) resulted in decrease in rate of appearance (Ra) of phenylalanine and urea, but had no effect on glutamine Ra. Infusion of amino acids at 3.0 g/kg/d for 20 h resulted in increase in DGln, leucine transamination, and urea synthesis, but had no effect on Ra phenylalanine (AA-Ext). These data show an acute increase in parenteral amino acid-suppressed proteolysis, however, such an effect was not seen when amino acids were infused for 20 h and resulted in an increase in glutamine synthesis.     

Intestinal protein and LPH synthesis in parenterally fed piglets receiving partial enteral nutrition and enteral insulinlike growth factor 1

BACKGROUND: Providing partial enteral nutrition (PEN) supplemented with insulinlike growth factor-1 (IGF-1) to parenterally fed piglets increases lactase-phlorizin hydrolase (LPH) activity, but not LPH mRNA. The current aim was to investigate potential mechanisms by which IGF-1 up-regulates LPH activity. METHODS: Newborn piglets (n = 15) received 100% parenteral nutrition (TPN), 80% parenteral nutrition + 20% parenteral nutrition (PEN), or PEN + IGF-1 (1.0 mg. kg-1. d-1) for 7 days. On day 7, [2H3]-leucine was intravenously administered to measure mucosal protein and brush border LPH (BB LPH) synthesis. RESULTS: Weight gain, nutrient intake, and jejunal weight and length were similar among the treatment groups. Partial enteral nutrition alone increased mucosal weight, villus width and cross-sectional area, LPH activity, mRNA expression, and high mannose LPH precursor (proLPHh) abundance compared with TPN (P<0.05). Insulinlike growth factor-1 further increased mucosal weight, LPH activity, and LPH activity per unit BB LPH approximately twofold over PEN alone (P < 0.05) but did not affect LPH mRNA or the abundance of proLPHh (one of the LPH isoforms) or mature LPH. Isotopic enrichment of [2H3]-leucine in plasma, mucosal protein, and LPH precursors, and the fractional and absolute synthesis rates of mucosal protein and LPH were similar among the treatment groups. Insulinlike growth factor-1 treatment increased total mucosal protein synthesis (60%, P < 0.05) but not LPH synthesis compared with the other two groups. CONCLUSIONS: Because IGF-1 did not affect the fractional synthesis rate of either mucosal protein or LPH, the authors suggest that enteral IGF-1 increases mucosal protein mass and LPH activity by suppressing mucosal proteolytic degradation.     

Glucose production and oxidation in preterm infants during total parenteral nutrition

During total parenteral nutrition in preterm infants, glucose may be infused at high rates, but it is not known if the endogenous glucose production is fully suppressed under these circumstances. Eight preterm appropriate for gestational age (AGA) (birth wt: 1613 +/- 151 g, gestational age: 31.1 +/- 1.5 wk) and eight preterm small for gestational age (SGA) newborn infants (1185 +/- 241 g, 32.9 +/- 2.6 wk) receiving a glucose infusion rate of 7.55 +/- 0.56 and 8.16 +/- 0.65 mg/kg.min, respectively, were studied during continuous total parenteral nutrition at postnatal d 8. Glucose oxidation rate was determined with a primed constant infusion of [U-13C] glucose, measuring the 13CO2 production in breath gas by isotope ratio mass spectrometry and the glucose production rate in plasma by gas chromatography mass spectrometry. In breath gas of AGA and SGA infants, 60 and 65%, respectively, of the infused tracer appeared as 13CO2. The glucose production rates were 7.97 +/- 1.61 and 8.12 +/- 1.84 mg/kg.min in AGA and SGA infants, respectively, indicating that no significant endogenous glucose production occurred. The glucose oxidation calculated from the glucose production and 13CO2 production was 4.74 +/- 0.99 mg/kg.min in AGA infants and was significantly different from the carbohydrate oxidation rate of 6.62 +/- 1.23 mg/kg.min measured by simultaneous indirect calorimetry. In SGA infants, however, the glucose and carbohydrate oxidation rates were not significantly different at 5.33 +/- 1.56 and 6.16 +/- 2.45 mg/kg.min. It is concluded that 1-wk-old AGA or SGA preterm infants receiving total parenteral nutrition of 80 kcal/kg.d produce no endogenous glucose and their glucose oxidation rates are similar at 63-65% of the glucose infused. It is suggested that the significant difference between glucose and carbohydrate oxidation rates observed in AGA but not in SGA infants is due either to a higher rate of lipogenesis from carbohydrates, or, less likely, to a higher rate of glycogen oxidation.     

Continuous nasogastric drip elemental feeding. Alternative for prolonged parenteral nutrition in severe prolonged diarrhea

Eighteen infants with severe prolonged diarrhea were fed successfully by continuous drip enteral feedings with an elemental diet. The mean weight gain was 6.4 +/- 0.7 g/kg/day, using a solution containing up to 87 kcal/dL at volumes up to 260 mL/kg/day. No cardiovascular or metabolic abnormalities occurred. Advantages of the continuous drip regimen were demonstrated by an adaptation phase with a plateau or even a decline in body weight in 12 patients, with weaning from continuous periodic feedings without changing the total caloric or volume intake. Continuous drip feeding provides an alternative for total parenteral nutrition in patients with severe prolonged diarrhea and intolerance to even an elemental diet given as periodic feedings.     

Leucine kinetics during feeding in normal newborns

To examine how leucine and protein metabolism is affected by feeding, leucine kinetics were determined in 11 normal term newborns during feeding using a prime constant tracer infusion of 1-13C leucine combined with respiratory calorimetry. Fed newborns were compared with previously studied fasting newborns. Feeding and fasting newborns had similar rates of leucine oxidation (34 +/- 3 mumol/kg/h versus 31 +/- 4 mumol/kg/h) and leucine release from existing protein (156 +/- 16 mumol/kg/h versus 164 +/- 8 mumol/kg/h). In contrast, nonoxidative disposal rates of leucine (a reflection of protein synthesis) were significantly greater in feeding newborns (170 +/- 13 mumol/kg/h versus 129 +/- 9 mumol/kg/h). A significant positive correlation between birth weight and leucine flux was demonstrated in both feeding and fasting newborns. These results suggest that 1) newborns may accomplish protein accretion primarily by increases in protein synthesis rather than suppression of protein breakdown; 2) an estimate can be made of the minimal leucine intake required to replace irreversible leucine oxidative losses (816 mumol/kg/d, 107 mg/kg/d); and 3) the positive correlation between birth weight and leucine flux in both feeding and fasting newborns may be a result of differences in previous protein and energy supplies.     

Acute effects of enteral nutrition on protein turnover in adolescents with Crohn disease

Adults with inactive Crohn disease have been shown to have normal rates of protein turnover when compared with healthy adults. It is not known whether this is true for adolescents with inactive Crohn disease, when rate of protein synthesis must be greater than that of breakdown for normal development. The objective of this study was to determine whether enteral nutrition acutely suppresses proteolysis and increases protein synthesis in adolescents with inactive Crohn disease. Six adolescents (five males/one female; mean age, 15.8 +/- 1.9 y; range, 13.2-17.6 y; mean bone age, 14.6 +/- 1.8 y; range, 12.5-17 y) participated. Leucine (Leu) and phenylalanine (Phe) kinetics were measured using stable isotopes under fasted and fed conditions during a single study visit. In response to enteral nutrition, the endogenous rates of appearance (Ra) of Leu and Phe (reflecting proteolysis) decreased significantly by 40%. The percentages of splanchnic uptake of Leu and Phe were 35 +/- 10% and 13 +/- 12%, respectively. Under fed conditions, utilization of Phe for protein synthesis increased significantly. We conclude that in clinically stable adolescents with Crohn disease, enteral nutrition promotes anabolism by suppressing proteolysis and increasing protein synthesis. Rates of suppression of proteolysis were similar to those reported previously in normal children.