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Biomedical subjects

R R Wolfe

Publications and source records attributed to R R Wolfe.

At least 145 records · Page 8Linked to original sources
PubMed1994

Determinants of free-living energy expenditure in normal weight and obese women measured by doubly labeled water.

Total free-living energy expenditure (TEE) was measured in 9 normal weight controls and 5 obese women using the doubly labeled water (DLW) method. Resting energy expenditure (REE) and the thermic effect of food (TEF) were measured by indirect calorimetry and the energy cost of physical activity (PA) calculated by deduction, in order to quantify the components and identify determinants of free-living TEE. Although REE was quantitatively the major component of TEE in both groups, PA best explained the variability, contributing 76% to the variance in free-living TEE. The obese women had elevated values for TEE (12397 +/- 2565 vs. 8339 +/- 1787 kJ/d, mean +/- SD; p < 0.005), compared with the control women. PA (5071 +/- 2385 vs. 2552 +/- 1452; p < 0.05) and REE (6393 +/- 678 vs. 5084 +/- 259; p < 0.0005) were also raised in the obese, whereas TEF was not significantly different between the groups, accounting for 7.6% of energy expenditure for the obese and 8% for the control subjects. Body weight was the single best determinant of mean daily free-living TEE across both groups. We conclude that PA and body weight are the main determinants of free-living TEE.

Adult↗
PubMed1994

Effect of hepatectomy on glucose metabolism in the dog.

The response of whole-body glucose uptake and oxidation and hindlimb glucose and lactate balance was investigated using the hyperinsulinemic, euglycemic clamp in 12 sham-operated control dogs and 10 hepatectomized dogs. A combination of radioactive (NaH14CO3) and stable (U-13C-glucose) isotope tracers was used to quantify glucose kinetics and oxidation. The insulin concentration was increased to approximately 5,000 microU/mL. Mean glucose uptake rates across the hindlimb were similar, 7.72 and 8.06 mumol.kg-1.min-1 for hepatectomy and sham-operated groups, respectively. Lactate release across the hindlimb also showed no significant differences between the two groups. Therefore, it was concluded that the liver did not affect peripheral glucose uptake in response to supramaximal insulin infusion under these experimental conditions. On the other hand, the mean glucose infusion rate during the last 60 minutes of the insulin clamp in the hepatectomy group was significantly decreased compared with that in the sham-operated group, 57.11 versus 46.29 mumol.kg-1.min-1, respectively (P < .05). Consequently, the maximal capacity of the liver of the anesthetized dog to clear glucose in response to supramaximal insulin infusion appears to be approximately 10.8 mumol.kg-1.min-1, which is about 20% of the total glucose infused. Isotopic data showed that most hepatic glucose uptake was oxidized. In contrast, most peripheral glucose uptake appeared to be stored as glycogen.

Animals↗
PubMed1994

Changes in lipolytic sensitivity following repeated epinephrine infusion in humans.

The lipolytic response to epinephrine is increased in lean but not obese subjects during conditions of increased circulating catecholamines such as starvation and critical illness. We evaluated the effect of repeated epinephrine treatment (0.03 micrograms.kg-1.min-1 for 30 min thrice daily) on basal lipolysis and the lipolytic response to epinephrine in lean and obese subjects. Lipolytic rates were determined using [2H5]glycerol during basal conditions and 60 min of epinephrine infusion before and after 6 days of repeated epinephrine treatment. Basal lipolysis and the lipolytic response to epinephrine were higher in obese (2.47 +/- 0.51 mumol.kg-1.min-1 and 106 +/- 21 mumol/kg, respectively) than lean (1.45 +/- 0.15 mumol.kg-1.min-1 and 70 +/- 12 mumol/kg, respectively; P = 0.08 obese vs. lean) subjects. Repeated epinephrine treatment decreased basal glycerol rate of appearance and the lipolytic response to epinephrine in lean and obese subjects. Plasma insulin concentration increased after repeated epinephrine treatment in both obese (14.3 +/- 0.6 to 18.2 +/- 1.6 microU/ml; P < 0.05) and lean (8.4 +/- 1.3 to 11.1 +/- 1.5 microU/ml; P < 0.01) subjects. Repeated epinephrine treatment suppresses basal and epinephrine-stimulated lipolysis. Increased plasma insulin concentration may be the mechanism.

Adult↗
PubMed1994

Lactate-pyruvate interconversion in blood: implications for in vivo tracer studies.

We have evaluated lactate and pyruvate kinetics in whole blood or plasma by the addition of [1-13C]lactate (n = 5) or [1-13C]pyruvate (n = 5) and application of compartmental modeling to the resulting data. Pyruvate and lactate concentrations and tracer-to-tracee ratios were measured at frequent intervals for 45 min. Pyruvate and lactate tracer-to-tracee ratios equilibrated almost completely within 3-4 min in whole blood, whereas there was no isotopic exchange in plasma. The average rate of interconversion between unlabeled lactate and pyruvate was four to five times (pyruvate to lactate) and three to four times (lactate to pyruvate) the net production rate of lactate. We conclude that there is a very rapid interconversion between lactate and pyruvate in blood that has to be considered in the interpretation of in vivo tracer studies.

Adult↗
PubMed1994

Effect of tumor necrosis factor on substrate and amino acid kinetics in conscious dogs.

Two groups of conscious dogs were studied using isotopic tracer techniques to test the hypothesis that tumor necrosis factor (TNF) affects glucose production, lipolysis, amino acid, and protein kinetics. [1-13C]leucine, [15N2]urea, [6,6-2H2]glucose, and [2H5]glycerol were infused to determine the leucine, urea, glucose, and lipid kinetics, and NaH14CO3 was infused to determine the rate of CO2 production. In one group, after a 2-h basal period (period 1), recombinant human TNF was infused (prime, 2.5 micrograms/kg; constant, 62.5 ng.kg-1.min-1) for 2 h (period 2; group 1, n = 15). Group 2 received saline rather than TNF in period 2 (n = 3). TNF infusion caused a significant increase in endogenous glucose production, a significant increase in glucose clearance rate, and a decrease in glycerol flux. Although TNF infusion did not change leucine flux, leucine oxidation increased by 49% (P < 0.0001), and nonoxidative leucine disappearance decreased during TNF infusion by 13% (P < 0.0001). TNF infusion also caused a significant increase (18%) in endogenous urea production. TNF significantly increased plasma glucagon concentration. We conclude that TNF causes a shift toward carbohydrate metabolism and stimulates the oxidation of amino acids. Whereas whole body protein breakdown is not affected by TNF, protein synthesis is impaired, leading to an increase in net protein breakdown.

Amino Acids↗
PubMed1994

Measurement of pyruvate and lactate kinetics across the hindlimb and gut of anesthetized dogs.

We have developed a new model to quantify regional pyruvate and lactate transmembrane transport, shunting, exchange, production, and oxidation in vivo. The method is based on the systemic continuous infusion of pyruvate or lactate stable isotopic carbon tracers and the measurement of pyruvate and lactate enrichment and concentration in the artery and vein of that region (e.g., leg or gut), the pyruvate and lactate enrichment of intracellular free water in the tissue as measured by biopsy, and the rate of blood flow through the tissue. The purpose of the experiment was to measure the pyruvate and lactate kinetics in leg muscle and gut in anesthetized dogs (n = 6). The transmembrane transport and degree of shunting of pyruvate and lactate were comparable in muscle and gut. When modified for substrate inflow, interconversion between pyruvate and lactate took place at a rate twice as fast in muscle as in the gut, and production and oxidation of pyruvate was approximately 50% greater in muscle than in the gut. Thus our new model enables quantitation of many aspects of lactate and pyruvate kinetics. We conclude that in anesthetized animals the muscle is the tissue most responsible for whole body peripheral pyruvate and lactate kinetics.

Anesthesia↗
PubMed1994

Protein synthesis and breakdown in skin and muscle: a leg model of amino acid kinetics.

In the postabsorptive state, amino acids are released from the periphery to provide precursors for protein synthesis in the splanchnic organs. To evaluate the differential role of the most important peripheral tissues, i.e., skin and muscle, in the interorgan amino acid exchange, we have developed a model to simultaneously measure the rates of protein synthesis and degradation in these tissues. Anesthetized dogs were studied using the arteriovenous catheterization of the leg in combination with muscle and skin biopsies. L-[alpha-15N]lysine and L-[ring-2H5]phenylalanine were infused as independent markers of both skin and muscle protein kinetics. Model structure described leg skin and muscle as tissues arranged in parallel and accounted for blood flow distribution. Lysine data show that, in the postabsorptive state, the fractional rate (%/h) of skin protein synthesis (0.543 +/- 0.218) was comparable to the fractional rate of degradation (0.507 +/- 0.157), whereas, in muscle, degradation (0.454 +/- 0.116) was greater (P < 0.05) than synthesis (0.318 +/- 0.109). Similar conclusions were apparent from the phenylalanine data. Skin protein synthesis and degradation accounted for approximately 10-15% of the total leg protein kinetics.

Amino Acids↗
PubMed1994

Fat metabolism during low-intensity exercise in endurance-trained and untrained men.

Whole body lipid kinetics were evaluated during basal resting conditions, 4 h of treadmill exercise eliciting an oxygen uptake of 20 ml.kg-1.min-1, and 1 h of recovery in five untrained and five endurance-trained men. Glycerol and free fatty acid (FFA) rate of appearance (Ra) values in plasma were determined by infusing [2H5]glycerol and [1-13C]palmitate, respectively, and lipid oxidation was determined by indirect calorimetry. The lipolytic response to 4 h of exercise, expressed as the average glycerol and FFA Ra values, was similar in both trained (9.85 +/- 1.02 and 24.64 +/- 3.76 mumol.kg-1.min-1, respectively) and untrained subjects (11.29 +/- 0.99 and 24.13 +/- 0.39 mumol.kg-1.min-1, respectively). However, mean triglyceride oxidation was greater during exercise in the trained than in the untrained group (7.51 +/- 0.26 and 5.67 +/- 0.51 mumol.kg-1.min-1, respectively; P < 0.001). During recovery, glycerol and FFA Ra values decreased more rapidly in trained than in untrained subjects. We conclude that highly trained male endurance runners use more fat as a fuel during low-intensity exercise than do untrained healthy men despite similar rates of lipolysis and FFA uptake from plasma. Therefore, the increase in fat oxidation must be related to an increased percentage of FFA uptake oxidized, a greater contribution from intramuscular triglyceride stores, or both. Additionally, lipid kinetics return to baseline more rapidly in trained than in untrained subjects after completing an exercise bout of the same absolute intensity.

Adult↗
PubMed1994

Alanine kinetics in humans during low-intensity exercise.

There is little doubt that pyruvate contributes to the increased alanine flux in exercise, but the role of protein breakdown is less clear. To quantify the relative contributions of pyruvate and protein breakdown to the increase in alanine flux observed in exercise, we used a primed, constant infusion of 15N-alanine and 1-13C-lactate. The rate of appearance of alanine, the de novo synthesis of alanine, and rate of alanine release from protein breakdown were determined in five healthy subjects at rest and during exercise. The exercise was performed for 120 min on a treadmill at 45% of the subject's VO2max. The total rate of appearance of alanine, calculated with the 15N-alanine tracer, increased significantly during exercise from 4.9 +/- 0.5 to 7.9 +/- 0.9 mumol.kg-1. The amount of alanine derived from pyruvate also significantly increased during exercise (3.2 +/- 0.3 vs 4.5 +/- 0.7), but the proportion of the total decreased from 65% at rest to 57% during exercise (statistically significant, P < 0.05). Consequently, the alanine derived from protein breakdown significantly increased (1.7 +/- 0.5 vs 3.4 +/- 0.8) and was also increased as percent of total alanine flux. Thus, we conclude that during low-intensity exercise, whole body protein catabolism is accelerated.

Adult↗
PubMed1993

Concentration dependence of methyl palmitate isotope ratios by electron impact ionization gas chromatography/mass spectrometry.

Isotope ratios must be measured precisely when stable isotopic tracers are used for in vivo metabolic kinetic studies since low enrichments are generally achieved above relatively high natural abundance backgrounds. We have observed that the (m + 1)/(m + 0) isotope ratio for the molecular ion of methyl palmitate (measured by electron impact ionization selected ion monitoring gas chromatography/mass spectrometry) is limited by a dependence of the isotope ratio on the quantity of sample analyzed. Since it is not practical to analyze exactly the same quantity of sample in a series of samples, this concentration dependence decreases the apparent precision of the isotope ratio measurement. The apparent natural abundance (m + 1)/(m + 0) isotope ratio increased from approximately 0.185 (0.2 nmol analyzed) to 0.20 (2.0 nmol). The concentration dependence was not altered as the quadrupole tuning resolution was varied and did not appear to arise from system non-linearity. The major source of concentration dependence derived from hydrogen abstraction during ion-molecule collisions within the ionization chamber. The concentration dependence was decreased as the repeller voltage increased and ion residence times in the source were reduced. Furthermore, the integrated (m + 1) peak ares increased with the square of the (m + 0) peak area, consistent with a bimolecular ion-molecule collision process. A simple mathematical correction for the concentration dependence afforded a ten-fold improvement in the coefficient of variation of the isotope ratio measurement.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas Chromatography-Mass Spectrometry↗
PubMed1993

Measurement of 15N enrichment in multiple amino acids and urea in a single analysis by gas chromatography/mass spectrometry.

A precise and accurate procedure to measure the 15N isotopic enrichment of 18 common plasma amino acids and singly (15N1) and doubly (15N2) labeled urea in a single analysis by selected ion monitoring electron impact ionization gas chromatography/mass spectrometry analysis is presented. The choice of tert-butyldimethylsilyl derivatives allowed the enrichments in the amide and amino nitrogens of glutamine to be resolved. The ions monitored contained all the nitrogen atoms from the parent compounds except for arginine, which lost one guanidino nitrogen. Isotope ratios were determined with a coefficient of variation (within-assay precision) of 0.35% (range, 0.1-1.0%) on replicate measures averaged over all components; thus, the standard deviation associated with a nominal [m + 1]/[m + 0] isotope ratio of 0.2000 was 0.0007. The average error between measured and theoretical [m + 1]/[m + 0] isotope ratios was +0.0001 +/- 0.0086 for samples at natural abundance isotopic composition. The utility of the procedure is demonstrated by monitoring the incorporation of 15N into 18 plasma amino acids and urea during a 6 h oral administration of 15NH4Cl to a human volunteer. Highest levels of enrichment were achieved in arginine and urea, followed by glutamine. Approximately 80% of the label in glutamine was in the amino nitrogen. Excess 15N enrichment was observed in all plasma amino acids monitored with the exception of the essential amino acids phenylalanine, lysine and histidine. This method will facilitate the measurement of isotopic enrichment of multiple amino acids by a single analysis when it is necessary to monitor multiple stable-isotopically labeled amino acids in studies of amino acid and protein metabolic kinetics.

Administration, Oral↗
PubMed1993

Variation in total energy expenditure in young healthy free-living men.

Interindividual and intraindividual variation in total energy expenditure (TEE) were examined in 17 healthy, free-living men (weight, 56.4 to 82.4 kg; age, 18 to 30 years). TEE over 14 days, resting metabolic rate (RMR), and body composition were measured two or three times during 77 days of fixed caloric intake using doubly labeled water, respiratory gas analysis, and isotope dilution, respectively. When individual data were averaged, TEE was most significantly related to fat-free mass ([FFM] r = .73, P = .001), body mass (r = .70, P = .002), and RMR (r = .63, P = .006). After adjusting TEE for BM, a significant inverse relation with age was found (partial r = -.52, P = .032). Stepwise regression analysis showed that 69% of individual variation in TEE was explained by BM, age, and fasting respiratory exchange ratio (RER). TEE/RMR averaged 1.73 +/- 0.25 (range, 1.38 to 2.32), and was independent of age and body composition. In 10 subjects in whom triplicate observations of TEE were performed, the average experimental variation for TEE was +/- 11.9% (range, 6.1% to 19.6%) compared with a theoretical estimate of precision of +/- 5.9% based on the reported isotope dose and analytical uncertainty. The difference between theoretical estimates of precision and observed experimental variation suggests that inherent random variation in free-living TEE is +/- 10% (ie, square root of 12(2)-6(2)) in subjects maintained on fixed caloric intake. We conclude that in young free living men (1) BM, age, and RER are important determinants of TEE; and (2) intraindividual variation in TEE is approximately +/- 10% due to fluctuations in physical activity levels within individuals over time.

Adolescent↗
PubMed1993

Insulin action on protein metabolism.

On the basis of the preceding observations, the following sequence of events can be postulated during insulin deficiency or excess. The main feature of insulin deficiency is the disruption of protein balance in muscle that rapidly leads to emaciation and wasting. Muscle protein degradation is greatly enhanced while increased amino acid availability maintains protein synthesis. In splanchnic tissues, both degradation and synthesis are increased but with an altered pattern, so that the levels of some proteins are increased (e.g. proteins of the acute-phase response), while those of others are decreased (e.g. albumin). As a result, intracellular protein content in liver is maintained but secretion of plasma proteins is abnormal. In healthy subjects, an acute increase in insulin concentration, as occurs after a meal, leads to a rapid suppression of protein breakdown in the splanchnic area. If hyperinsulinaemia is not supported by an exogenous amino acid supply, as might occur during a protein-free meal or experimentally during euglycaemic hyperinsulinaemic clamping, the plasma as well as muscle free amino acid concentration drops, owing to reduced splanchnic release. With reduced amino acid availability, insulin is not anabolic in muscle. If amino acid concentrations are maintained at normal or high levels, e.g. following a mixed meal, a net protein deposition in muscle may occur, primarily because of a stimulation of synthesis and possibly owing to inhibition of breakdown.

Amino Acids↗
PubMed1993

Assessment of the mathematical issues involved in measuring the fractional synthesis rate of protein using the flooding dose technique.

1. The fractional synthesis rate of protein is commonly measured by either the constant infusion method or the flooding dose method. The two methods often give different results. 2. An underlying assumption of the traditional flooding dose formula is that the protein synthesis rate is not stimulated by the flooding dose. A new formula for calculation of the fractional synthesis rate is derived with the alternative assumption that the protein synthesis rate is stimulated by an amount proportional to the change in the intracellular concentration of the infused amino acid. The alternative formula is: Fractional synthesis rate = [formula: see text] where EB and EF are the enrichments of bound and free amino acid, respectively (atom per cent excess), and C = 1-(EF/EI), where EI is the enrichment of the infusate. This approach defines the lowest possible value for the fractional synthesis rate. The traditional equation gives a maximal value for the fractional synthesis rate. 3. When data from the literature are considered, the fractional synthesis rate of muscle protein as calculated by the constant infusion technique falls between the values of fractional synthesis rate calculated by the two flooding dose formulae when leucine is the tracer, suggesting that a flooding dose of leucine exerts a stimulatory effect on the rate of protein synthesis, but that the increase is not as great as the increase in the intracellular concentration of leucine.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1993

The role of the renin-angiotensin system in insulin sensitivity in normotensive subjects.

Nonobese patients with essential hypertension have been reported to be insulin resistant. Because blockade of the renin-angiotensin system has been demonstrated to improve insulin sensitivity in hypertensive patients, the authors evaluated the effects of angiotensin-II administration and of angiotensin-converting enzyme inhibition with enalapril on insulin-mediated glucose uptake in normotensive men. The results showed no change in insulin sensitivity with either 0.3 ng/kg/min or 1 ng/kg/min angiotensin-II administration or with enalapril therapy. The authors conclude that neither physiologic amounts of angiotensin-II nor converting enzyme inhibition alter insulin sensitivity in normotensive men.

Adult↗
PubMed1993

Acute response of human muscle protein to catabolic hormones.

OBJECTIVE: The purpose of this study was to determine the acute in vivo response of human muscle protein to stress. SUMMARY BACKGROUND DATA: Prior animal and human in vitro studies have suggested that physiologic stress increases muscle protein turnover. In contrast, recent publications using a polyribosomal methodology have demonstrated a reduction in human muscle protein synthesis in vivo after surgery. METHODS: Five healthy volunteers were given a stable isotopic infusion of 1,2(13)C leucine that allowed for determination of the fractional rate of muscle protein synthesis by measuring the rate of incorporation of 13C label into vastus lateralis muscle biopsies. Simultaneous infusion of 15N lysine and quantitation of leg blood flow by indocyanine green dye dilution allowed for estimation of leg muscle protein breakdown rate (Lys Ra) and synthesis rate (Lys Rd). These measurements were performed before and then at the conclusion of a 4-hour femoral arterial infusion of the catabolic hormones epinephrine, cortisol, and glucagon. RESULTS: The catabolic hormone infusion elicited a significant (65%) increase in the leg muscle protein breakdown rate and a significant but less marked increase in the rate of muscle protein synthesis, as assessed by both an increase in the fractional rate of muscle protein synthesis of 48.5% and in lysine uptake within the leg of 32%. CONCLUSIONS: This study conclusively demonstrates that a hormonally induced stress results in a net catabolism of human muscle protein by increasing the rate of protein breakdown in excess of an increased protein synthetic rate.

Adult↗
PubMed1993

Carbohydrate metabolism during pregnancy in control subjects and women with gestational diabetes.

The purpose of this study was to characterize carbohydrate metabolism associated with the development of gestational diabetes. Six control (Ctl) and ten women with gestational diabetes mellitus (GDM) were evaluated using an intravenous glucose tolerance test and hyperinsulinemic-euglycemic clamp with [6,6-2H2]glucose prior to conception (P) and at 12-14 (E), and 34-36 wk of gestation (L). There was an increase (P = 0.0001) in first-phase insulin response in Ctl (P 174 +/- 133, E 388 +/- 120, and L 587 +/- 303 microU/ml) and GDM (P 197 +/- 94, E 267 +/- 77, and L 376 +/- 162 microU/ml) but a significant (P = 0.02) lag in change in GDM with advancing gestation. Basal endogenous glucose production increased during gestation [Ctl: P 2.74 +/- 0.23, E 2.62 +/- 0.38, and L 3.14 +/- 0.36; GDM: P 2.68 +/- 0.51, E 2.78 +/- 0.45, and L 2.98 +/- 0.48 mg.kg fat-free mass (FFM)-1 x min-1; P = 0.02], but there was resistance to suppression by insulin infusion (P = 0.03) in late gestation (GDM: 0.61 +/- 0.44 vs. Ctl: 0.16 +/- 0.17 mg.kg FFM-1 x min-1). Insulin sensitivity decreased during gestation (Ctl: P 10.78 +/- 2.78, E 8.34 +/- 2.36, and L 4.75 +/- 1.22; GDM: P 7.49 +/- 2.13, E 7.40 +/- 1.45, and L 4.21 +/- 1.01 mg.kg FFM-1 x min-1; P = 0.0001) and was primarily decreased (P = 0.04) in GDM compared with Ctl from P through E. These findings closely resemble those of non-insulin-dependent, predominantly insulin-resistant diabetes, which is often a sequel of GDM.

Adult↗