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D M Bier

Publications and source records attributed to D M Bier.

At least 73 records · Page 4Linked to original sources
PubMed1990

Amino acid metabolism after intense exercise.

We studied postexercise amino acid metabolism, in the whole body and across the forearm. Seven volunteers were infused with L-[alpha-15N]lysine and L-[1-13C]-leucine twice [one time during 3 h after cycle exercise (75% VO2max), and one time in the resting state]. Whole body protein breakdown was estimated from dilution of L-[alpha-15N]lysine and L-[1-13C]ketoisocaproic acid (KIC) enrichments in plasma. Leucine oxidation was calculated from 13CO2 enrichments in expired air. Whole body protein breakdown was not increased above resting levels during the recovery period. Leucine oxidation was decreased after exercise (postexercise 13 +/- 2.3 vs. resting 19 +/- 3.2 mumol.kg-1.h-1; P less than 0.02), while nonoxidative leucine disposal was increased (115 +/- 6.1 vs. 103 +/- 5.6 micrograms.kg-1.min-1; P less than 0.02). After exercise, forearm net lysine balance was unchanged (87 +/- 25 vs. 93 +/- 28 nmol.100 ml-1.min-1), but there were decreases in forearm muscle protein degradation (219 +/- 51 vs. 356 +/- 85 nmol.100 ml-1.min-1; P less than 0.05) and synthesis (132 +/- 41 vs. 255 +/- 69 nmol.100 ml-1.min-1; P less than 0.01). In conclusion, after exercise 1) whole body protein degradation is not increased, 2) leucine disposal is directed away from oxidative and toward nonoxidative pathways, 3) forearm protein synthesis is decreased. Postexercise increases in whole body protein synthesis occur in tissues other than nonexercised muscle.

Adult↗
PubMed1990

Contribution of liver and skeletal muscle to alanine and lactate metabolism in humans.

To quantitate alanine and lactate gluconeogenesis in postabsorptive humans and to test the hypothesis that muscle is the principal source of these precursors, we infused normal volunteers with [3-14C]lactate, [3-13C]alanine, and [6-3H]glucose and calculated alanine and lactate incorporation into plasma glucose corrected for tricarboxylic acid cycle carbon exchange, the systemic appearance of these substrates, and their forearm fractional extraction, uptake, and release. Forearm alanine and lactate fractional extraction averaged 37 +/- 3 and 27 +/- 2%, respectively; muscle alanine release (2.94 +/- 0.27 mumol.kg body wt-1.min-1) accounted for approximately 70% of its systemic appearance (4.18 +/- 0.31 mumol.kg body wt-1.min-1); muscle lactate release (5.51 +/- 0.42 mumol.kg body wt-1.min-1) accounted for approximately 40% of its systemic appearance (12.66 +/- 0.77 mumol.kg body wt-1.min-1); muscle alanine and lactate uptake (1.60 +/- 0.7 and 3.29 +/- 0.36 mumol.kg body wt-1.min-1, respectively) accounted for approximately 30% of their overall disappearance from plasma, whereas alanine and lactate incorporation into plasma glucose (1.83 +/- 0.20 and 4.24 +/- 0.44 mumol.kg body wt-1.min-1, respectively) accounted for approximately 50% of their disappearance from plasma. We therefore conclude that muscle is the major source of plasma alanine and lactate in postabsorptive humans and that factors regulating their release from muscle may thus exert an important influence on hepatic gluconeogenesis.

Alanine↗
PubMed1990

Endurance training decreases plasma glucose turnover and oxidation during moderate-intensity exercise in men.

To assess the effects of endurance training on plasma glucose kinetics during moderate-intensity exercise in men, seven men were studied before and after 12 wk of strenuous exercise training (3 days/wk running, 3 days/wk cycling). After priming of the glucose and bicarbonate pools, [U-13C] glucose was infused continuously during 2 h of cycle ergometer exercise at 60% of pretraining peak O2 uptake (VO2) to determine glucose turnover and oxidation. Training increased cycle ergometer peak VO2 by 23% and decreased the respiratory exchange ratio during the final 30 min of exercise from 0.89 +/- 0.01 to 0.85 +/- 0.01 (SE) (P less than 0.001). Plasma glucose turnover during exercise decreased from 44.6 +/- 3.5 mumol.kg fat-free mass (FFM)-1.min-1 before training to 31.5 +/- 4.3 after training (P less than 0.001), whereas plasma glucose clearance (i.e., rate of disappearance/plasma glucose concentration) fell from 9.5 +/- 0.6 to 6.4 +/- 0.8 ml.kg FFM-1.min-1 (P less than 0.001). Oxidation of plasma-derived glucose, which accounted for approximately 90% of plasma glucose disappearance in both the untrained and trained states, decreased from 41.1 +/- 3.4 mumol.kg FFM-1.min-1 before training to 27.7 +/- 4.8 after training (P less than 0.001). This decrease could account for roughly one-half of the total reduction in the amount of carbohydrate utilized during the final 30 min of exercise in the trained compared with the untrained state.

Adult↗
PubMed1990

Mechanism of increased gluconeogenesis in noninsulin-dependent diabetes mellitus. Role of alterations in systemic, hepatic, and muscle lactate and alanine metabolism.

To assess the mechanisms responsible for increased gluconeogenesis in noninsulin-dependent diabetes mellitus (NIDDM), we infused [3-14C]lactate, [3-13C]alanine, and [6-3H]glucose in 10 postabsorptive NIDDM subjects and in 9 age- and weight-matched nondiabetic volunteers and measured systemic appearance of alanine and lactate, their release from forearm tissues, and their conversion into plasma glucose (corrected for Krebs cycle carbon exchange). Systemic appearance of lactate and alanine were both significantly greater in diabetic subjects (18.2 +/- 0.9 and 5.8 +/- 0.4 mumol/kg/min, respectively) than in the nondiabetic volunteers (12.6 +/- 0.7 and 4.2 +/- 0.3 mumol/kg/min, respectively, P less than 0.001 and P less than 0.01). Conversions of lactate and alanine to glucose were also both significantly greater in NIDDM subjects (8.6 +/- 0.5 and 2.4 +/- 0.1 mumole/kg/min, respectively) than in nondiabetic volunteers (4.2 +/- 0.4 and 1.8 +/- 0.1 mumol/kg/min, respectively, P less than 0.001 and P less than 0.025). The proportion of systemic alanine appearance converted to glucose was not increased in NIDDM subjects (42.7 +/- 1.9 vs. 44.2 +/- 2.9% in nondiabetic volunteers), whereas the proportion of systemic lactate appearance converted to glucose was increased in NIDDM subjects (48.3 +/- 3.8 vs. 34.2 +/- 3.8% in nondiabetic volunteers, P less than 0.025); the latter increased hepatic efficiency accounted for approximately 40% of the increased lactate conversion to glucose. Neither forearm nor total body muscle lactate and alanine release was significantly different in NIDDM and nondiabetic volunteers. Therefore, we conclude that increased substrate delivery to the liver and increased efficiency of intrahepatic substrate conversion to glucose are both important factors for the increased gluconeogenesis of NIDDM and that tissues other than muscle are responsible for the increased delivery of gluconeogenic precursors to the liver.

Alanine↗
PubMed1990

Whole body nitrogen kinetics and their relationship to growth in short children treated with recombinant human growth hormone.

We studied the effects of growth hormone on retention of 15N-labeled amino acids in 34 short, prepubertal, growth hormone-sufficient children and three growth hormone-deficient subjects. All 34 non-growth hormone-deficient children had apparently normal circulating growth hormone molecules and no mutations were detected in the growth hormone or IGF-I genes of any subjects. Fibroblasts from 34 children responded normally when challenged with recombinant human IGF-I. During the last 72 h of a 4-d challenge with recombinant human growth hormone (16 micrograms/kg body wt), retention of a mixed 15N-amino acid dose varied between 5.7 and 50.5%. Whole body protein synthesis, breakdown, and net anabolism calculated from the 15N kinetics were all increased by the acute growth hormone challenge. However, no routine clinical feature or laboratory determination correlated with the nitrogen retention response. After subsequent treatment (75 micrograms/kg three times a week) with recombinant human growth hormone for 1 y, there was a significant increase in height velocity, but this increase was not related significantly to pretreatment variables other than inversely to pretreatment height velocity. There was a significant (p = 0.03) correlation between the change in height velocity Z score and the degree of nitrogen retention to acute challenge with growth hormone, but this correlation was too weak (r = 0.37) to be of practical value in predicting the treatment growth response in an individual child.

Adolescent↗
PubMed1990

Low prevalence of insulin-like growth factor-I gene mutations in human growth disorders.

In an attempt to identify genetic lesions contributing to human growth disorders, we evaluated a prospectively recruited group of children with growth failure for mutations in the insulin-like growth factor-I (IGF-I) gene. Two complementary approaches were used: Southern blot analysis to examine the large scale organization of the gene, and a solution hybridization, nuclease protection assay to identify small alterations, such as point mutations. From a total of 61 subjects studied, 52 had no organic basis for their short stature. Analysis of chromosomal DNA from these individuals failed to reveal any variation in the IGF-I gene except for a HindIII site polymorphism which maps near the 3' end of the last IGF-I exon. No single nucleotide substitutions were found within IGF-I-coding regions. Since the frequency of the length polymorphism was the same for both normal-sized and short individuals, it is unlikely to be associated with growth abnormalities. Our results suggest that there is minimal DNA sequence variability in the human IGF-I gene and that mutations in IGF-I exons are infrequent causes of growth failure.

Blotting, Southern↗
PubMed1990

Modeling glucose metabolism in man: theory and practice.

Quantitative assessment of whole-body and regional glucose metabolism from in vivo kinetic data requires a model of the system, i.e. specific assumptions about the structure and functioning of the system. We discuss here models which allow the measurement and understanding of the kinetics of glucose metabolism in vivo in man and of the effect of insulin upon them. Discussed models include: a whole-body description of glucose distribution and metabolism to quantitate insulin effect; a model to measure in vivo glucose transport in the forearm; physiological models to assess glucose kinetics in the non-steady state; the insulin and C-peptide IVGTT minimal models to assess beta-cell function; the labelled IVGTT minimal models to assess insulin sensitivity and hepatic production. Emphasis is on models of the compartmental type and on the crucial role of modeling methodology. Aspects of improved experiment design are also discussed.

Biological Transport, Active↗
PubMed1989

[Incorporation of 15N in VLDL and LDL: in vivo synthesis of apolipoprotein B in the post-absorptive and fasting state].

In vivo synthesis of apolipoprotein B 100 (ApoB) was recently determined in man using stable isotopes. With this procedure we analyzed (1) the effect of fasting on synthesis of ApoB from very low density lipoprotein (VLDL) and (2) tracer enrichment in low density lipoprotein (LDL). After a 36-hour fasting period and in the post-absorptive state 4 healthy subjects were given a priming dose (8.7 mumol/kg) of 15N glycine followed by a constant infusion (10 mumol/kg/h for 8 h) to achieve 5% tracer enrichment in the plasma pool of glycine. The K-values, i.e. fractional synthetic rates/hr of ApoB from VLDL were 0.53 +/- 0.26 vs. 0.43 +/- 0.16 (p greater than 0.05). Tracer enrichment in ApoB from LDL at the end of the infusions was 0.19% vs. 1.46% in ApoB from VLDL. The results indicate that (1) in young healthy postabsorptive individuals about 40% of ApoB from VLDL in plasma is synthesized per hour, (2) fasting does not materially affect fractional ApoB synthesis and (3) at 5% 15N enrichment in plasma glycine, tracer enrichment in ApoB from LDL is at the lower limit of detection for the procedure employed.

Adult↗
PubMed1989

Use of multiple 13C-labeling strategies and 13C NMR to detect low levels of exogenous metabolites in the presence of large endogenous pools: measurement of glucose turnover in a human subject.

A significant problem which may be encountered in 13C NMR studies of metabolism is the contribution that background levels of 13C may make to the observed spectra when low or tracer levels of the 13C label are used. We propose that the introduction of two or more labeled sites in the same tracer molecule is an effective strategy for eliminating or reducing this difficulty and demonstrate its feasibility in an isotope dilution study of glucose turnover in a human volunteer. This approach has two significant advantages over the more common use of a singly enriched labeling strategy: (i) as a consequence of the scalar coupling interactions, multiple-labeled metabolites will yield spectra distinct from those containing natural abundance 13C, and (ii) at a 99% level of enrichment for the precursor, concentration levels which are approximately 1% of the endogenous pools can be detected with approximately equal sensitivity. As a demonstration of this strategy, glucose production in a human subject was determined by continuous infusion of tracer levels of [U-13C6]glucose over a 4-h period and subsequent analysis of plasma levels of the tracer in vitro by NMR. Mass spectroscopy was used on the same samples to provide a basis for comparison of the precision and accuracy of the NMR technique. The results demonstrate the feasibility of the multiply labeled approach for detection by NMR of tracer amounts of label in the presence of a much larger endogenous pool of glucose. The NMR and mass spectrometric data gave quantitatively identical results for the glucose production rate demonstrating that equivalent data may be obtained by both methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

A theoretical basis for increasing current estimates of the amino acid requirements in adult man, with experimental support.

Estimates of the minimum (obligatory) rates of loss of indispensable acids via irreversible oxidation in healthy young adults are predicted from published data for obligatory nitrogen losses and from published values for whole-body protein turnover and the efficiency of amino acid recycling. The estimates obtained by these two different approaches are consistent and equal to or in most cases considerably higher than current values for the upper range of the individual amino acid requirements in healthy adults. From these estimates of the obligatory, or minimum, rates of amino acid oxidation, the minimum requirements for indispensable amino acids are predicted. These are about two to three times higher than current requirement figures. Experimental support for these higher requirement figures is presented, based on published 13C-labeled amino acid tracer studies. When these revised estimates are expressed per unit of protein need, the amino acid pattern is similar to the 1985 Food and Agriculture Organization/World Health Organization/United Nations University amino acid scoring pattern for the preschool child (aged 2-5 y).

Adult↗
PubMed1989

Leucine metabolism in aging humans: effect of insulin and substrate availability.

To elucidate the relative roles of insulin (I) and amino acid (AA) availability on body protein economy and AA kinetics, we compared whole body leucine kinetic responses, using a 360-min constant infusion of L-[1-13C]leucine, during administration of an L-AA solution to six healthy young (21-25 yr) and six healthy old (72-87 yr) men (study 1) to those when the AA solution was given in conjunction with a euglycemic I clamp (study 2). In study 1, serum I increased significantly (P less than 0.02) by 4 +/- 1 and 4 +/- 2 microU/ml in young (Y) and old (O) men, respectively. In study 2, I was raised to 91 +/- 7 (Y) and 88 +/- 7 (O) microU/ml; the glucose infusion to maintain euglycemia in the Y was significantly greater than in the O (8.0 +/- 0.1 vs. 6.8 +/- 1.9 mg.kg-1.min-1). Leucine flux and oxidation increased significantly in both age groups during the administration of AA. Estimates of leucine released from protein breakdown declined (P less than 0.01) by 18 and 20% in study 1 and 2, respectively, in the young and by 12 and 44%, respectively, in the elderly. Rates of leucine incorporation into protein increased (P less than 0.01) similarly in both age groups and in both studies. These findings emphasize the importance of AA availability in the stimulation of protein synthesis and suggest that insulin's major role in vivo is to repress whole body proteolysis. Furthermore, despite evidence of an age-related decline in glucose disposal, the elderly had similar leucine kinetic responses to hyperaminoacidemia.

Adult↗
PubMed1989

Epinephrine's effect on metabolic rate is independent of changes in plasma insulin or glucagon.

Epinephrine's effect to increase metabolic rate is accompanied by changes in the plasma concentrations of insulin, glucagon, and metabolic substrates. Because both glucagon and insulin have been reported to affect thermogenesis, these hormones might contribute to or modify the thermogenic response to epinephrine. To determine if the epinephrine-induced increase in metabolic rate is secondary to changes in glucagon or insulin or to changes in the fuels modulated by these hormones, metabolic rate was measured by indirect calorimetry in five normal weight post-absorptive young men on three occasions: study A, an intravenous epinephrine infusion alone; study B, a 4-h "islet clamp" consisting of somatostatin infusion with basal insulin and glucagon replacement; and study C, an intravenous epinephrine infusion combined with the islet clamp. A 1-h base-line period preceded 2 h of epinephrine infusion. During the 4-h islet clamp (study B), metabolic rate and plasma concentrations of epinephrine, insulin, glucagon, and glucose remained unchanged. During the infusion of epinephrine alone (study A), metabolic rate and concentrations of glucagon, free fatty acids, and C-peptide increased as expected. Also as expected, the glycemic response to epinephrine infusion was much larger when insulin and glucagon levels were fixed with the islet clamp (study C). In contrast, the metabolic rate and the free fatty acid concentration responded similarly to epinephrine infusion when insulin and glucagon were fixed (study C) and when they were changing (study A). We conclude that epinephrine increases metabolic rate independently of physiological changes in plasma glucagon or insulin or the circulating fuels they modulate.

Adult↗
PubMed1989

Stable-label intravenous glucose tolerance test minimal model.

The minimal model approach to estimating insulin sensitivity (Sl) and glucose effectiveness in promoting its own disposition at basal insulin (SG) is a powerful tool that has been underutilized given its potential applications. In part, this has been due to its inability to separate insulin and glucose effects on peripheral uptake from their effects on hepatic glucose inflow. Prior enhancements, with radiotracer labeling of the dosage, permit this separation but are unsuitable for use in pregnancy and childhood. In this study, we labeled the intravenous glucose tolerance test (IVGTT) dosage with [6,6-2H2]glucose, [2-2H]glucose, or both stable isotopically labeled glucose tracers and modeled glucose kinetics in six postabsorptive, nonobese adults. As previously found with the radiotracer model, the tracer-estimated S*l derived from the stable-label IVGTT was greater than Sl in each case except one, and the tracer-estimated SG* was less than SG in each instance. More importantly, however, the stable-label IVGTT estimated each parameter with an average precision of +/- 5% (range 3-9%) compared to average precisions of +/- 74% (range 7-309%) for SG and +/- 22% (range 3-72%) for Sl. In addition, because of the different metabolic fates of the two deuterated tracers, there were minor differences in basal insulin-derived measures of glucose effectiveness, but these differences were negligible for parameters describing insulin-stimulated processes. In conclusion, the stable-label IVGTT is a simple, highly precise means of assessing insulin sensitivity and glucose effectiveness at basal insulin that can be used to measure these parameters in individuals of all ages, including children and pregnant women.

Adult↗
PubMed1989

Contribution of 3-hydroxyisobutyrate to the measurement of 3-hydroxybutyrate in human plasma: comparison of enzymatic and gas-liquid chromatography-mass spectrometry assays in normal and in diabetic subjects.

In this study we employed a capillary gas-liquid chromatographic-mass spectrometric (GLC-MS) method to measure the plasma concentrations of 3-hydroxybutyrate (3-OHB) and 3-hydroxyisobutyrate (3-OHIB) in overnight fasted diabetic subjects and in normal subjects. Plasma contents of 3-hydroxybutyrate measured in this fashion were identical to those obtained by enzymatic assay using a commercial preparation of beta-hydroxybutyrate dehydrogenase, indicating no significant contamination of this enzyme preparation with 3-hydroxyisobutyrate dehydrogenase. In normal individuals, plasma 3-OHIB concentration was 21 +/- 2 microM in the overnight fasted state and was higher in diabetic subjects (38 +/- 5 microM) and in subjects fasted for 72 h (97 +/- 4 microM). In the postabsorptive state, 3-OHIB was 33% the concentration of 3-OHB in normals and 17% that of 3-OHB in the diabetics.

3-Hydroxybutyric Acid↗
PubMed1988

Glutamine and glutamate nitrogen exchangeable pools in cultured fibroblasts: a stable isotope study.

Glutamine's role as an energetic fuel has been extensively studied in the past using 14C- and 3H-labeled tracers in cultured human cells. Yet another prominent role of glutamine, that of a nitrogen shuttle, cannot be approached without an N-tracer. We therefore used 15N-labeled glutamine and glutamate to address the following questions: 1) is it possible to study the exchangeable pools of intracellular free glutamine and glutamate nitrogen with stable isotope methods? and 2) to what extent is intracellular glutamine pool regulated by extracellular glutamine? We observed that: 1) intracellular [15N]-glutamine enrichment reached a plateau at 80% within 20 min of incubation in a buffer containing 0.7 mM pure 15N-glutamine and no glutamate; in contrast, intracellular 15N-glutamate enrichment rose only to 40% after 4 hours of incubation in a buffer containing 0.5 mM pure 15N-glutamate and no glutamine; 2) the cell-free glutamine content was tightly dependent on extracellular glutamine level, while the cell-free glutamate remained steady irrespective of the extracellular glutamate level; 3) the cells took up glutamine and glutamate against a concentration gradient; the rate of glutamine uptake accounted for 90% of the cell glutamine turnover rate; and 4) when cells were confronted with a glutamine-free medium, only one fourth of intracellular glutamine was derived from the exchangeable glutamate. We conclude that: 1) The size and turnover rate of the intracellular pool of free glutamine nitrogen are measureable using stable isotope methodology; 2) glutamine uptake from the extracellular medium accounts for most of glutamine turnover rate in cultured fibroblasts; and 3) intracellular free glutamate is divided up between several pools in cultured human fibroblasts.

Body Fluids↗