摘要:

ABSTRACT.Neonatal hypoglycemia is a frequent complication in immature infants. This may be due to small substrate stores, a high brain:body weight ratio, and immature enzyme systems. The purpose of the present study was to investigate the rate of glucose production in newborn infants with gestational ages of less than 28 wk. The subjects were 10 newborn infants delivered after 25 to 26 gestational wk. Their mean birth weight was 772 g (range 588–1000 g), and their mean postnatal age at the time of the study was 15 h (range 4–24 h). An isotopic compound (d-6,6-2H2-glucose) was given as a constant-rate i.v. infusion. In addition to dideuteroglucose, eight of the infants also received an i.v. infusion of unlabeled glucose at a rate of 1.4–2.6 mg·kg−1·min−1. Blood samples for determination of the concentration and isotopic enrichment of plasma glucose were obtained every 15 min in a 2-h period. Isotopic enrichment, measured by gas chromatography/mass spectrometry, was used for calculating the glucose production rate. The mean glucose production rate related to body weight (± SD) was 6.1 ± 1.5 mg·kg−1·min−1. The results show that infants born at <28 gestational wk have a capacity to produce glucose on their 1st d of life at rates close to or even exceeding those reported in term infants.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

ABSTRACT.Several formulas for preterm infants contain medium-chain triglycerides (MCT) to enhance fat absorption. Although fat absorption with MCT was slightly higher in several studies in preterm infants, a beneficial effect on growth has only been reported in one publication. We hypothesized that when part of the fat blend of preterm formula is substituted by MCT oil, this might lead to a different metabolic pattern in which, due to the preferential oxidation of MCT, an increase in lipogenesis from glucose could lead to an increase in metabolic rate. To study the impact of MCT on glucose metabolism, 18 preterm infants were randomized to receive either an MCT or an LCT formula containing 38- and 6%-by-weight medium-chain fatty acids, respectively, in their fat blend. At 4 wk of age, the metabolic rate, substrate utilization, glucose kinetics, and oxidation were measured by indirect respiratory calorimetry in combination with a constant-rate oral infusion of [U-13C]glucose. The “true” rate of appearance of glucose (Ra “true”) was measured from the dilution of the uniformly labeled (m + 6) species of infused tracer, whereas “apparent” rate of appearance of glucose (Ra “apparent”) was measured from the dilution of infused tracer C (carbon). The latter was measured by an on-line combustion method using a gas chromatograph-isotope ratio mass spectrometer. At a carbohydrate intake of 8.4 mg·kg−1·min−1, total utilization of carbohydrate was equal in both groups at 7.6 mg·kg−1·-min−1. However, glucose oxidation, as measured by the appearance of13C in breath CO2was significantly lower in the MCT group (4.5 ± 0.83versus5.7 ± 0.67 mg·kg−1· min−1, MCTversusLCT). Therefore, it can be assumed that a larger proportion of the glucose intake in the MCT group was used in the nonoxidative pathway,e.g.synthesis of fat as compared with the LCT group. There was no difference in the rate of endogenous glucose production and glucose C recycling between the two groups. In addition, the metabolic rate calculated from the rate of oxygen consumption was also similar (59 ± 5versus62 ± 4 kcal·kg−1·d−1MCTversusLCT). We conclude that, in preterm infants fed a formula containing 38% MCT in their fat blend, glucose oxidation is significantly decreased whereas lipogenesis is probably increased. These findings may provide a mechanism for the so-called metabolic inefficiency of MCT.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

ABSTRACT.Twenty-three preterm infants with respiratory distress syndrome (mean birth weight 1.07 kg, SD 0.24 kg) were randomly assigned to receive glucose alone or glucose with amino acids (1.5 g·kg−1·d−1) i.v. beginning on the 1st d of life. Blood ammonia and serum urea, CO2content, sodium, potassium, chloride, and ionized calcium concentrations were normal and did not differ between treatment groups. Nitrogen balance was significantly greater in the group that received amino acids [88 (SD 54)versus[135 (SD 45) mg·kg−1d−1]. In 12 infants (seven, glucose-only; five, glucose and amino acids), leucine kinetic studies were also performed on the 3rd d of life. These 12 infants received a 4-h primed constant infusion of l-[1-13C] leucine. Blood and breath were collected and analyzed for [1-13C]ketoisocaproate and13CO2, respectively. Leucine turnover and oxidation were calculated. Both leucine turnover and oxidation were significantly higher in the group receiving amino acids than in the glucose-only group [241 (SD 38)versus164 (SD 25)μmol·kg−1·h−1and 71 (SD 22)versus40 (SD 17)μmol·kg−1·h−1, respectively]. In addition, the calculated rate of protein synthesis was higher in the group receiving amino acids [6.9 (SD 1.1)versus5.0 (SD 1.2) g·kg−1·d−1]. These data indicate that the i.v. administration of amino acids (1.5 g·kg−1·d−1) to ill preterm infants beginning on the 1st d of life improves whole-body protein balance as a result of increased protein synthesis.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

ABSTRACT.Newborn infants (n= 26), subdivided into three groups in which only the nonprotein energy was manipulated, were studied during continuously administered total parenteral nutrition. Nonprotein energy intake was provided as a glucose/fat mixture, and fat energy represented 18% (group A), 29% (group B), and 40% (group C). Energy expenditure and substrate utilization were measured by indirect calorimetry during a 6-h period. Other analyses included 24-h urinary nitrogen excretion, glycemia, and lipid profile. The results showed that glucose oxidation increased with increasing total glucose intake (p< 0.05). Net fat oxidation was observed in all groups and increased with increasing percentage of energy infused as fat. The maximal oxidative glucose disposal rate observed was in group A (11.2 g/kg/d). Maximal fat oxidation observed was in group C (2 g/kg/d), in which energy delivered by fat represented 40%. This group was more energy efficient than the others. Oxygen consumption was not affected by modification of the source of energy, but carbon dioxide production was higher in group A (p< 0.05), as was the nonprotein respiratory quotient (p< 0.05). Despite differences in carbon dioxide production, arterial capillary PCO2was not affected and, together with the higher (p< 0.05) minute ventilation, suggests that adequate pulmonary compensation occurred during the low-fat regimen. Arterial capillary PO2was lower during the high-fat regimen (p< 0.05). Protein oxidation was greater in group A (1.14 ± 0.32 g/kg/d) than in group B (0.70 ± 0.21 g/kg/d) or group C (0.78 ± 0.28 g/kg/d). These data suggest that total parenteral nutrition regimens containing between 29 and 40% of calories as fat emulsion result in enhanced protein retention.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

ABSTRACT.Premature infants receive high dietary zinc and often glucocorticoids as a treatment for chronic lung disease. A piglet model was developed to investigate intestinal zinc transport and distribution of tissue zinc in response to treatment with short-term (5 d) glucocorticoid therapy or a high zinc diet. Piglets (13–15 d old;n= 21) were randomly allocated to:1) dexamethasone (DEX) therapy (1.5 mg/kg intramuscularly twice a day),2) high zinc diet (15.3 mmol/kg), or3) control group (0.3 mmol dietary zinc/kg and saline intramuscularly twice a day). Pig weight, formula intake, urine volume, and blood glucose were monitored. At necropsy, tissue samples were obtained to measure zinc in plasma and zinc and metallothionein in liver and small intestinal mucosa. Velocity of zinc uptake by intestinal brush border membrane vesicles was measured using65Zn tracer. Maximum uptake rate and Km for zinc uptake by brush border membrane vesicles were significantly greater (p< 0.05) in DEX compared with control and high zinc groups. DEX-treated piglets had a significantly lower (p< 0.05) zinc efflux rate across brush border membrane vesicles compared with that of the control. The high zinc group had a higher liver (p< 0.05) and mucosal (p< 0.05) zinc content and higher liver metallothionein concentration (p< 0.001) compared with the control and DEX groups. Weight gain over 5 d was not different among groups. Daily blood glucose was higher (p< 0.05) in DEXversuscontrol and high zinc groups. Short-term DEX treatment induced changes in mucosal uptake of zinc that are consistent with up-regulation of specific mucosal proteins, but this was not the case with metallothionein. These alterations in zinc metabolism may have consequences for zinc status in premature infants who receive glucocorticoids such as DEX and/or high zinc diets.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

ABSTRACT.It is now widely accepted that tetrahydrobiopterin (BH4), the natural cofactor of aromatic amino acid hydroxylases, in the absence of its regenerating enzyme dihydropteridine reductase (DHPR), will function only stoichiometrically in the phenylalanine (Phe) hydroxylating system. This has limited the use of pterin cofactor in diagnosis and treatment of patients suffering from inherited DHPR deficiency, one of the most common forms of hyperphenylalaninemia caused by BH4 deficiency. This is despite the observation of a dramatic fall in serum Phe concentration after BH4 loading in such patients. In this study, quantitation of this phenomenon was obtained by comparing the kinetics of serum Phe after either a simple Phe or a combined Phe plus BH4 oral loading in patients with Phe hydroxylase or with DHPR deficiency. Only in the latter was the total body clearance of Phe enhanced up to 5 times by the cofactor administration, resulting in the molar equivalent of Phe hydroxylated/mol of BH4 ranging from at least 6 to 10, against the postulated 1. As a consequence, BH4 administration should be attempted therapeutically in DHPR-deficient patients, thus avoiding a lifelong Phe-restricted diet. Preliminary experience with such treatment is given with two cases.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

ABSTRACT.Multiple acyl-CoA dehydrogenation disorders result from generalized defects in intramitochondrial acyl-CoA dehydrogenation. Fibroblasts from a riboflavin-responsive multiple acyl-CoA dehydrogenation disorder patient catabolized14C-butyrate, -octanoate, and -leucine normally after culture in riboflavin-supplemented medium (2 mg/L). After culture in riboflavin-depleted medium (≤1.4μg/L)his cells oxidized the same substrates poorly at 20 to 33% of control (p< 0.05). Patient cells incubated in a wide range of d-[2-14C]riboflavin concentrations (3, 31.4, and 100μg/L) synthesized14C-flavin mononucleotide and14C-flavin adenine dinucleotide (FAD) normally and had normal cytosolic14C-flavin mononucleotide and14C-FAD contents, which argues against defects in cellular riboflavin uptake and conversion to flavin mononucleotide and FAD. After culture in 31.4μg14C-riboflavin/L for 2 wk,14C-FAD specific radioactivities plateaued and were similar in patient and control cells. However, culturing these uniformly labeled cells in riboflavin-depleted medium for 2 wk lowered the patient's cellular14C-FAD content to only 23% of control levels. Similarly, after incubation in low14C-riboflavin concentrations (4.4μg/L), the patient's mitochondrial14C-FAD content was only 51% of control after 1 h and 29% of control at 4 h. After a 4-h incubation in a high physiologic concentration of14C-riboflavin (31.4μg/L), which raised the patient's cellular14C-FAD levels 3- to 4-fold, his mitochondrial14C-FAD content rose to normal; control values did not change. We also investigated possible defective FAD binding to flavoenzymes essential for acyl-CoA dehydrogenation. Medium-chain acyl-CoA dehydrogenase activities did not fall significantly in either patient or control mitochondria from cells cultured in riboflavin-depleted medium. However, after culture in riboflavin-depleted medium, the patient's electron transfer flavoprotein activity fell to 59% of control in mitochondrial preparations, which is compatible with decreased matrix FAD content. We postulate that defective maintenance of mitochondrial FAD levels explains this patient's riboflavin-responsive multiple acyl-CoA dehydrogenation disorder phenotype.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

ABSTRACT.IGF-binding protein-3 (IGFBP-3), usually found as glycosylated 41- and 38-kD forms, is the major serum IGFBP during extrauterine life. In normal serum IGFBP-3 binds one IGF peptide and one acid-labile (α) subunit in a high-molecular-weight (MW) complex of 150 kD. By RIA, an excess of IGFBP-3 is present in chronic renal failure (CRF) serum, where it reportedly accumulates at low MW (25–55 kD) rather than as part of the 150-kD complex. To further evaluate IGFBP-3 forms in CRF, sera were obtained from seven healthy adolescents and seven adolescents with CRF. By RIA, IGFBP-3 levels were higher in CRF than normal sera (15.4 ± 2.2versus10.1 ± 2.1μg/mL). High-MW (150-kD) fractions of CRF and normal sera, obtained by neutral size-exclusion chromatography, had equal amounts of IGFBP-3 by RIA. However, a second RIA peak of IGFBP-3, present in low-MW (35-kD) fractions of CRF but not normal sera, could account for the higher IGFBP-3 levels of CRF serum. [l25I]IGF ligand blots of whole serum and serum fractions, either with or without prior precipitation by IGFBP-3 antiserum, found levels of 41- and 38-kD IGFBP-3 forms to be similar between CRF and normal whole sera and located these forms in the high-MW (150-kD) fractions of CRF and normal sera. [125I]IGF ligand blots also identified excess IGFBP in low-MW CRF serum fractions; cross-linking these IGFBP with [125I]IGF-I, followed by precipitation with IGFBP-1, -2, and -3 antibodies, identified high levels of unsaturated IGFBP-1, IGFBP-2, and 19- and 14-kD forms of IGFBP-3 in CRF serum. These studies indicate that1) normal levels of functional 41- and 38-kD IGFBP-3 forms are present in CRF serum, and these forms can be incorporated into the 150-kD serum complex; and2) high RIA levels of IGFBP-3 in low-MW fractions of CRF serum are at least in part due to 19- and 14-kD IGFBP-3 forms. These studies suggest that the excess unsaturated IGFBP of CRF serum are small enough to enter interstitial tissue spaces where they may modulate IGF-I-mediated mitogenic, metabolic, and differentiative effects.

ISSN:0031-3998    

出版商:OVID    

年代:1993

数据来源: OVID