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M J Rennie

Publications and source records attributed to M J Rennie.

At least 19 recordsLinked to original sources
PubMed1992

A role for membrane transport in modulation of intramuscular free glutamine turnover in streptozotocin diabetic rats.

We wished to examine the effects of diabetes on muscle glutamine kinetics. Accordingly, female Wistar rats (200 g) were made diabetic by a single injection of streptozotocin (85 mg/kg) and studied 4 days later; control rats received saline. In diabetic rats, glutamine concentration of gastrocnemius muscle was 33% less than in control rats: 2.60 +/- 0.06 mumol/g vs. 3.84 +/- 0.13 mumol/g (P < 0.001). In gastrocnemius muscle, glutamine synthetase activity (Vmax) was unaltered by diabetes (approx. 235 nmol/min per g) but glutaminase Vmax increased from 146 +/- 29 to 401 +/- 94 nmol/min per g; substrate Km values of neither enzyme were affected by diabetes. Net glutamine efflux (A-V concentration difference x blood flow) from hindlimbs of diabetic rats in vivo was greater than control values (-30.0 +/- 3.2 vs. -1.9 +/- 2.6 nmol/min per g (P < 0.001)) and hindlimb NH3 uptake was concomitantly greater (about 27 nmol/min per g). The glutamine transport capacity (Vmax) of the Na-dependent System Nm in perfused hindlimb muscle was 29% lower in diabetic rats than in controls (820 +/- 50 vs. 1160 +/- 80 nmol/min per g (P < 0.01)), but transporter Km was the same in both groups (9.2 +/- 0.5 mM). The difference between inward and net glutamine fluxes indicated that glutamine efflux in perfused hindlimbs was stimulated in diabetes at physiological perfusate glutamine (0.5 mM); ammonia (1 mM in perfusate) had little effect on net glutamine flux in control and diabetic muscles. Intramuscular Na+ was 26% greater in diabetic (13.2 mumol/g) than control muscle, but muscle K+ (100 mumol/g) was similar. The accelerated rate of glutamine release from skeletal muscle and the lower muscle free glutamine concentration observed in diabetes may result from a combination of: (i), a diminished Na+ electrochemical gradient (i.e., the net driving force for glutamine accrual in muscle falls); (ii), a faster turnover of glutamine in muscle and (iii), an increased Vmax/Km for sarcolemmal glutamine efflux.

Amino Acids↗
PubMed1992

Biochemical and immunocytochemical localization of the 'GLUT5 glucose transporter' in human skeletal muscle.

Using biochemical and immunocytochemical techniques, we have assessed both the protein expression and the cellular localization of the GLUT5 transporter in human skeletal muscle. Human muscle membranes, prepared by subcellular fractionation, were subjected to SDS/PAGE and Western-blot analyses using antiserum raised against a specific C-terminal amino acid sequence of the human GLUT5 transporter. GLUT5 was detected as a discrete 49 kDa protein band in a plasma-membrane-enriched fraction prepared from either soleus or gracilis muscle. In contrast, GLUT5 protein was not detectable to any significant extent in fractions which were devoid of muscle plasma membranes (mean GLUT5 abundance in intracellular fractions from three muscle preparations amounted to approximately 10% of that in the plasma-membrane-enriched fraction). Immunofluorescence studies using cryostat sections of human triceps muscle supported the biochemical observations and revealed that GLUT5 antibody selectivity labelled the plasma membrane of muscle cells. This immuno-labelling was significantly suppressed after tissue incubation with antiserum in the presence of a 14-amino-acid synthetic peptide corresponding to a specific C-terminus sequence of human GLUT5. These results indicate that human skeletal muscle expresses the GLUT5 transporter and that it is specifically localized to the plasma membrane, where it may participate in regulating hexose transfer across the sarcolemma.

Blotting, Western↗
PubMed1992

Transport of L-glutamine and L-glutamate across sinusoidal membranes of rat liver. Effects of starvation, diabetes and corticosteroid treatment.

There is increasing evidence that membrane transporters for glutamine and glutamate are involved in control of liver metabolism in health and disease. We therefore investigated the effects of three catabolic states [starvation (60 h), diabetes (4 days after streptozotocin treatment) and corticosteroid (8-day dexamethasone) treatment] associated with altered hepatic amino acid metabolism on the activity of glutamine and glutamate transporters in sinusoidal membrane vesicles from livers of treated rats. In control preparations, L-[14C]glutamine uptake was largely Na(+)-dependent, but L-[14C]glutamate uptake was largely Na(+)-independent. Vmax. values for Na(+)-dependent uptake of glutamine and/or glutamate exceeded control values (by about 2- and 12-fold respectively) in liver membrane vesicles from starved (glutamine), diabetic (glutamate) or steroid-treated (glutamine and glutamate) rats. The Km values for Na(+)-dependent transport of glutamine or glutamate and the rates of their Na(+)-independent uptake were not significantly altered by any treatment. Na(+)-independent glutamate uptake appeared to include a dicarboxylate-exchange component. The patterns of inhibition of glutamine and glutamate uptake by other amino acids indicated that the apparent induction of Na(+)-dependent amino acid transport in catabolic states included increased functional expression of systems A, N (both for glutamine) and X-ag (for glutamate). The results demonstrate that conditions resulting in increased secretion of catabolic hormones (e.g. corticosteroid, glucagon) are associated with increased capacity for Na(+)-dependent transport of amino acids into liver cells from the blood. The modulation of hepatic permeability to glutamine and glutamate in these situations may control the availability of amino acids for intrahepatic metabolic processes such as ureagenesis, ammonia detoxification and gluconeogenesis.

Amino Acids↗
PubMed1992

Expression of rat liver glutamine transporters in Xenopus laevis oocytes.

As a first step in attempting to isolate the Na(+)-dependent System N transporter from rat liver we have investigated the use of prophase-arrested oocytes from Xenopus laevis for the functional expression of rat liver glutamine transporters. Individual oocytes, defolliculated by collagenase treatment, were injected with 50 nl of a 1 mg.ml-1 solution of poly(A)+ RNA (mRNA) isolated from rat liver. 50 microM L-[3H]glutamine uptake was measured 1-5 days post-injection: after 48 h, poly(A)+ RNA-injected oocytes showed a 60 +/- 12% increase in Na(+)-dependent glutamine uptake compared to controls. This increased uptake showed characteristic features of hepatic System N: that is, it tolerated Li(+)-for-Na+ substitution and was inhibited by the System N substrate L-histidine (5 mM) in Li medium, unlike endogenous Na(+)-dependent glutamine transport. In subsequent experiments rat liver poly(A)+ RNA, size-fractionated by density gradient fractionation, was injected into oocytes. Injection of poly(A)+ RNA of 1.9-2.8 kilobases (kb) in size resulted in a significant stimulation of Na(+)-dependent glutamine transport to 0.362 +/- 0.080 pmol.min-1/oocyte from 0.178 +/- 0.060 pmol.min-1/oocyte in vehicle-injected oocytes (p less than 0.01). A lighter fraction, with poly(A)+ RNA of less than 1.9 kilobases size resulted in a similar increase in Na(+)-dependent glutamine uptake which was largely Li(+)-tolerant: Li(+)-stimulated glutamine uptake in oocytes injected with this fraction increased to 0.230 +/- 0.070 pmol.min-1/oocyte from 0.098 +/- 0.029 pmol.min-1/oocyte in controls (p less than 0.05). This enhanced rate of Li(+)-stimulated glutamine uptake was inhibited 28 and 70%, respectively, by 1 and 5 mM L-histidine. Na(+)-independent uptake of glutamine rose by 72 +/- 12% in oocytes injected with poly(A)+ RNA of 2.8-3.6 kb (p less than 0.001). These results demonstrate that glutamine transporters, with characteristics associated with hepatic Systems N, L, and A (or ASC), can be expressed in X. laevis oocytes injected with specific size fractions of rat liver mRNA.

Animals↗
PubMed1992

Measurement of muscle protein fractional synthetic rate by capillary gas chromatography/combustion isotope ratio mass spectrometry.

The measurement of skeletal muscle protein fractional synthetic rate using an infusion of (1-13C)leucine and measuring the isotopic abundance of the tracer in skeletal muscle protein by preparative gas chromatography (GC)/ninhydrin isotope ratio mass spectrometry (IRMS) is laborious and subject to errors owing to contamination by 12C. The purpose of this study was to compare muscle (13C)leucine enrichment measured with the conventional preparative GC/ninhydrin IRMS approach to a new, continuous-flow technique using capillary GC/combustion IRMS. Quadriceps muscles were removed from four Sprague-Dawley rats after each was infused at a different rate with (1-13C)leucine for 6-8 h. Muscle leucine enrichment (at. % excess) measured by both methods differed by less than 4%, except at low (13C)leucine enrichments (less than 0.03 at. % excess). In addition, capillary GC/combustion IRMS was used to assess muscle (13C)leucine enrichment and fractional muscle protein synthesis rate in ten normal young men and women infused with (1,2-13C2)leucine for 12-14 h. This approach reduced the variability of the isotope abundance measure and gave estimates of muscle protein synthesis rate (0.050 +/- 0.011% h-1 (mean +/- SEM); range = 0.023-0.147% h-1) that agree with published values determined using the standard analytical approach. The measurement of (13C)leucine enrichment from skeletal muscle protein by capillary GC/combustion IRMS provides a simple, acceptable and practical alternative to preparative GC/ninhydrin IRMS.

Adult↗
PubMed1992

Transport and membrane binding of the glutamine analogue 6-diazo-5-oxo-L-norleucine (DON) in Xenopus laevis oocytes.

We have examined transport and membrane binding of 6-diazo-5-oxo-L-norleucine (DON, a photoactive diazo-analogue of glutamine) and their relationships to glutamine transport in Xenopus laevis oocytes. DON uptake was stereospecific and saturable (Vmax of 0.44 pmol/oocyte.min and a Km of 0.065 mM). DON uptake was largely Na+ dependent (80% at 50 microM DON) and inhibited (greater than 75%) by glutamine and arginine (substrates of the System B0,+ transporter) at 1 mM. Glutamine and DON show mutual competitive inhibition of Na(+)-dependent transport. Preincubation of oocytes in medium containing 0.1 mM DON for 24 or 48 hr depressed the Vmax for System B0,+ transport (as measured by Na(+)-dependent glutamine uptake), this effect was highly specific (neither D-DON nor the System B0,+ substrates glutamine and D-alanine showed any independent effect) and required Na+ ions. Glutamine (1 mM in preincubation medium) protected transport from inhibition by DON. The possibility that specific inactivation of System B0,+ by DON reflects attachment of DON to the transporter was tested by examining the binding of [14C]DON to Xenopus oocyte membranes. Oocytes incubated in 100 mM NaCl in the presence of [14C]DON for up to 48 hr showed 2.4-fold higher 14C-binding to membranes than oocytes incubated in choline chloride. Na(+)-dependent DON binding (31 +/- 11 fmol/micrograms membrane protein) was suppressed by external glutamine, arginine or alanine and was largely confined to a membrane protein fraction of 48-65 kDa (as assessed by SDS-polyacrylamide gel electrophoresis). The present studies indicate that DON and glutamine uptake in oocytes are both mediated by System B0,+ and demonstrate the DON binding to a particular membrane protein fraction is associated with inactivation of the transporter, offering the prospect of using [14C]DON as a covalent label for the transport protein in order to facilitate its isolation and subsequent biochemical characterization.

Animals↗
PubMed1992

Effects of oral testosterone undecanoate on growth, body composition, strength and energy expenditure of adolescent boys.

OBJECTIVE: We determined the effect of 3 months of daily, 40 mg oral testosterone undecanoate on growth, body composition, hand grip and quadriceps muscle strength, and total free-living daily energy expenditure in boys with constitutionally delayed puberty. DESIGN: Double blind, placebo controlled study. PATIENTS: Eighteen boys with constitutionally delayed puberty, mean (SD) age 13.2 (1.6) years. MEASUREMENTS: Body composition measurements were made by skinfold thickness, bioelectrical impedance and stable isotope dilution (H2(18)O) methods. Energy expenditure was assessed by the doubly-labelled water (2H2(18)O) technique. RESULTS: Height velocity increased from 5.4 (0.8) to 8.1 (0.6) cm/year (P < 0.05) in the 3 months after active therapy. Fat-free mass increased more with therapy (2.7 (0.3) kg) over the 6-month study period than with placebo (1.7 (0.4) kg, P < 0.5). Height velocity increases correlated with daily increases in fat-free mass (r = 0.68, P = 0.005) in the study group as a whole. Energy expenditure and muscle strength increased similarly in both groups. Predicted adult height decreased in the group which was treated with testosterone undecanoate. CONCLUSIONS: Testosterone undecanoate (40 mg daily for 3 months) significantly increased height velocity and fat-free mass velocities after 6 months but not muscle strength, endurance or total daily energy expenditure.

Administration, Oral↗
PubMed1992

Whole body protein turnover in childhood Crohn's disease.

In order to investigate the effects of treatment on protein metabolism in childhood Crohn's disease whole body protein turnover was measured using a primed constant intravenous infusion of L-[1-13C]leucine and mass spectrometry in 10 children with active disease. Mean rates of protein synthesis and breakdown markedly decreased after treatment with steroids (four) or an elemental diet (six). This suggests that protein synthesis and breakdown are increased during active Crohn's disease in children and are reduced after induction of remission regardless of the type of treatment.

Adolescent↗
PubMed1992

Effect of growth hormone and resistance exercise on muscle growth in young men.

The purpose of this study was to determine whether growth hormone (GH) administration enhances the muscle anabolism associated with heavy-resistance exercise. Sixteen men (21-34 yr) were assigned randomly to a resistance training plus GH group (n = 7) or to a resistance training plus placebo group (n = 9). For 12 wk, both groups trained all major muscle groups in an identical fashion while receiving 40 micrograms recombinant human GH.kg-1.day-1 or placebo. Fat-free mass (FFM) and total body water increased (P less than 0.05) in both groups but more (P less than 0.01) in the GH recipients. Whole body protein synthesis rate increased more (P less than 0.03), and whole body protein balance was greater (P = 0.01) in the GH-treated group, but quadriceps muscle protein synthesis rate, torso and limb circumferences, and muscle strength did not increase more in the GH-treated group. In the young men studied, resistance exercise with or without GH resulted in similar increments in muscle size, strength, and muscle protein synthesis, indicating that 1) the larger increase in FFM with GH treatment was probably due to an increase in lean tissue other than skeletal muscle and 2) resistance training supplemented with GH did not further enhance muscle anabolism and function.

Adipose Tissue↗
PubMed1992

Flooding with L-[1-13C]leucine stimulates human muscle protein incorporation of continuously infused L-[1-13C]valine.

To investigate why flooding methods give higher rates than constant-infusion methods for muscle protein synthesis, we studied seven healthy postabsorptive male volunteers (20-42 yr; 67-74 kg) during a 7.5-h primed constant infusion of L-[1-13C]valine (99 atoms %, 1.5 mg/kg prime, 1.5 mg.kg-1.h-1); at 6.5 h they were given a flood of L-[1-13C]leucine (20 atoms %, 0.05 g/kg). Musculus tibialis anterior biopsies were taken at 0.5, 6, and 7.5 h, and blood was sampled as appropriate. The enrichment of valine and leucine in muscle protein (isotope ratio mass spectrometry of protein amino acid-derived 13CO2) was compared with the average enrichment of various amino acid pools (gas chromatography-mass spectrometry). During infusion of [13C] valine the rate of muscle protein synthesis measured using alpha-ketoisovalerate (alpha-KIV) as precursor surrogate was 0.043 +/- 0.002%/h (SE). After flooding with leucine, the incorporation rate of [13C]valine increased by 70% (P less than 0.05), i.e., apparent muscle protein synthetic rate (based on alpha-[13C]KIV) increased to 0.065 +/- 0.009%/h (P less than 0.05); the rate calculated from the [13C]leucine flood was 0.060 +/- 0.005%/h (P less than 0.01). The synthetic rates calculated using the constant-infusion method were higher after flooding, irrespective of the precursor chosen, raising serious concern about the validity of the flooding-dose method.

Adult↗
PubMed1992

Stimulation of protein synthesis in pig skeletal muscle by infusion of amino acids during constant insulin availability.

Incorporation of L-[1-13C]leucine into muscle protein and leg exchange of L-[15N]phenylalanine were used to assess the effects over 240 min of amino acid supply on leg protein turnover in anesthetized, overnight-fasted (Landrace x Great White) female pigs. In all pigs, plasma insulin and glucagon stability was ensured by infusion of somatostatin (8 micrograms.kg-1.h-1), insulin (6 mU.kg-1.h-1), and glucagon (72 ng.kg-1.h-1). Mixed amino acid infusion (260 mg.kg-1.h-1) caused a 2- to 2.5-fold elevation of arterial plasma phenylalanine and leucine; in a control group (no amino acid infusion), an increase in phenylalanine and leucine concentration was observed as a result of the hormone clamp. Plasma insulin and glucagon concentrations were steady and not significantly different between control and amino acid-infused groups during the final 240 min, but plasma glucose fell (P less than 0.05) in both groups (4.57 +/- 0.17 to 3.15 +/- 0.73 mM). Muscle protein synthetic rate (estimated from the change in L-[1-13C]leucine incorporation compared with labeling of [13C]leucyl-tRNA) was greater in amino acid-infused (0.076%/h) than in control (0.053%/h) pigs. In the control group, leg amino acid balance was negative (Phe alone, -10.2 +/- 9.4 nmol Phe.100 g-1.min-1; total amino acids, -0.27 +/- 1.04 micrograms amino N.100 g-1.min-1), but during amino acid infusion, balance was positive (Phe alone, +33.6 +/- 8.8 nmol Phe.100 g-1.min-1; total amino acids, +58.2 +/- 4.9 micrograms amino N.100 g-1.min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1992

Metabolic effects of three weeks administration of the beta-adrenoceptor agonist BRL 26830A.

BRL 26830A is a thermogenic beta-adrenergic agonist drug which has an anti-obesity effect in animals and diet-restricted obese man. This study was undertaken in obese subjects who were not calorie restricted to assess the effect of three weeks drug administration on energy expenditure and glucose, amino acid and fatty acid metabolism in the post-absorptive and fed states. Stable isotope tracers were employed to determine kinetic data both at baseline and during adrenaline infusion. There was no evidence of BRL 26830A causing a major shift in fuel metabolism or having an anabolic effect. Baseline plasma concentrations of glycerol (P less than 0.01) and palmitate (P less than 0.01) were reduced, glucose remained within the normal range, whereas insulin decreased after BRL 26830A. The hypoaminoacidaemic effect of adrenaline was attenuated by BRL 26830A (P less than 0.01 for branched-chain amino acids, P less than 0.05 for total amino acids). The results suggest that BRL 26830A improves insulin sensitivity and causes selective down-regulation of adrenergic receptors. The increased insulin sensitivity may be a useful therapeutic effect for this class of drug and suggests a possible role in the treatment of obese non-insulin dependent diabetic patients.

Adrenergic beta-Agonists↗
PubMed1991

Substrate-specificity of glutamine transporters in membrane vesicles from rat liver and skeletal muscle investigated using amino acid analogues.

We investigated the effects of glutamine and histidine analogues on glutamine transport processes in membrane vesicles prepared from rat liver (sinusoidal membrane) and skeletal muscle (sarcolemma). L-[14C]Glutamine is transported in these membranes predominantly by Systems N/Nm (liver and muscle respectively), and to a lesser extent by Systems A and L (e.g. about 60, 20 and 20% of total flux respectively via Systems N, A and L at 0.05 mM-glutamine in liver membrane vesicles). The glutamine anti-metabolites 6-diazo-5-oxo-L-norleucine and acivicin were relatively poor inhibitors of glutamine uptake into liver membrane vesicles (less than 25% inhibition at 20-fold excess) and appeared primarily to inhibit System A activity (i.e. N-methylaminoisobutyric acid-inhibitable glutamine uptake). In similar experiments azaserine (also a glutamine anti-metabolite) inhibited approx. 50% of glutamine uptake, apparently by inhibition of System A and also of System L (i.e. 2-amino-2-carboxybicyclo[2,2,1]heptane-inhibitable glutamine uptake). Glutamate gamma-hydroxamate, aspartate beta-hydroxamate, histidine and N'-methylhistidine were all strong inhibitors of glutamine uptake into liver membrane vesicles (greater than 65% inhibition at 20-fold excess), but neither homoglutamine nor N'-methylhistidine produced inhibition. L-Glutamate-gamma-hydroxamate was shown to be a competitive inhibitor of glutamine transport via System N (Ki approximately 0.6 mM). Glutamine uptake in sarcolemmal vesicles showed a similar general pattern of inhibition as in liver membrane vesicles. The results highlight limits on the substrate tolerance of System N; we suggest that the presence of both an L-alpha-amino acid group and a nitrogen group with a delocalized lone-pair of electrons (amide or pyrrole type), separated by a specific intramolecular distance (C2-C4 chain equivalent), is important for substrate recognition by this transporter.

Amino Acids↗
PubMed1991

Isolation of aminoacyl-tRNA and its labeling with stable-isotope tracers: Use in studies of human tissue protein synthesis.

We isolated aminoacyl-tRNA (60-70% yield) from human and rat tissues and measured, by GC/MS, its labeling in vivo by [15N]- and [13C]leucine. Tracer dilution artifacts seemed unlikely since, after infusion of L-[1-13C,15N]leucine into rats, (i) muscle leucyl-tRNA labeling exceeded tissue free leucine labeling, (ii) values were largely unaffected by storing over 5 min at 22 degrees C, and (iii) L-[2,4,5-methyl-13C]leucine was not incorporated into leucyl-tRNA during homogenization. Leucyl-tRNA labeling in liver and muscle suggested charging from extra- and intracellular pools: e.g., after infusing L-[1-13C,15N]leucine, rat muscle tissue free leucine 13C labeling (8.97 +/- 0.30 atom % excess) exceeded that by 15N (3.37 +/- 0.33 atom % excess), and both were significantly lower (P less than 0.02) than venous plasma (13C, 12.1 +/- 1.8; 15N, 5.54 +/- 0.6 atom % excess) indicating tracer dilution by transamination and by proteolysis; however, leucyl-tRNA labeling by either isotope (13C, 10.26 +/- 0.50; 15N, 4.72 +/- 0.72 atom % excess) was significantly above mixed tissue free leucine (P less than 0.05). Labeling of leucyl-tRNA in human erector spinae muscle (obtained after preoperative L-[1-13C]leucine infusion) was, at 4.98 +/- 0.43 atom % excess, lower (27%) than venous plasma leucine (P less than 0.05) and intermediate between muscle free leucine (9% lower; P less than 0.01) and venous alpha-ketoisocaproate (11% higher; P less than 0.02). Human placental leucyl-tRNA labeling (after predelivery tracer infusion) was 37% lower (P less than 0.05) than maternal uterine vein labeling but not significantly different from placental free leucine or umbilical arterial leucine.

Animals↗
PubMed1991

Effects of corticosteroid on the transport and metabolism of glutamine in rat skeletal muscle.

Intramuscular glutamine falls with injury and disease in circumstances associated with increases in blood corticosteroids. We have investigated the effects of corticosteroid administration (0.44 mg/kg dexamethasone daily for 8 days, 200 g female rats) on intramuscular glutamine and Na+, muscle glutamine metabolism and sarcolemmal glutamine transport in the perfused hindlimb. After dexamethasone treatment intramuscular glutamine fell by 45% and Na+ rose by 25% (the respective muscle/plasma distribution ratios changed from 8.6 to 4.5 and 0.12 to 0.15); glutamine synthetase and glutaminase activities were unchanged at 475 +/- 75 and 60 +/- 19 nmol/g muscle per min. Glutamine output by the hindlimb of anaesthetized rats was increased from 31 to 85 nmol/g per min. Sarcolemmal glutamine transport was studied by paired-tracer dilution in the perfused hindlimb: the maximal capacity (Vmax) for glutamine transport into muscle (by Na(+)-glutamine symport) fell from 1058 +/- 310 to 395 +/- 110 nmol/g muscle per min after dexamethasone treatment, accompanied by a decrease in the Km (from 8.1 +/- 1.9 to 2.1 +/- 0.4 mM glutamine). At physiological plasma glutamine concentration (0.75 mM) dexamethasone appeared to cause a proportional increase in sarcolemmal glutamine efflux over influx. Addition of dexamethasone (200 nM) to the perfusate of control rat hindlimbs caused acute changes in Vmax and Km of glutamine transport similar to those resulting from 8-day dexamethasone treatment. The reduction in muscle glutamine concentration after dexamethasone treatment may be primarily due to a reduction in the driving force for intramuscular glutamine accumulation, i.e., in the Na+ electrochemical gradient. The prolonged increase in muscle glutamine output after dexamethasone treatment (which occurs despite a reduction in the size of the intramuscular glutamine pool) appears to be due to a combination of (a) accelerated sarcolemmal glutamine efflux and (b) increased intramuscular synthesis of glutamine.

Amino Acids↗
PubMed1991

Effect of adrenaline infusion on fatty acid and glucose turnover in lean and obese human subjects in the post-absorptive and fed states.

1. Energy expenditure, plasma glucose and palmitate kinetics and leg glycerol release were determined simultaneously both before and during adrenaline infusion in lean and obese human subjects. Seven lean subjects (mean 96.5% of ideal body weight) were studied in the post-absorptive state and also during mixed nutrient liquid feeding, eight obese subjects (mean 165% of ideal body weight) were studied in the post-absorptive state and six obese subjects (mean 174% of ideal body weight) were studied during feeding. 2. Resting energy expenditure was higher in the obese subjects, but the thermic response to adrenaline, both in absolute and percentage terms, was similar in lean and obese subjects. Plasma adrenaline concentrations attained (3 nmol/l) were comparable in all groups and the infusion had no differential effects on the plasma insulin concentration. Before adrenaline infusion the plasma glucose flux was higher in the obese than in the lean subjects in the fed state only (45.8 +/- 3.8 versus 36.6 +/- 1.0 mmol/h, P less than 0.05); it increased to the same extent in both groups with the adrenaline infusion. 3. Before the adrenaline infusion plasma palmitate flux was higher in the obese than in the lean subjects (by 51%, P less than 0.01, in the post-absorptive state and by 78%, P less than 0.05, in the fed state). However, there was no significant change during adrenaline infusion in the obese subjects (from 13.5 +/- 1.00 to 15.0 +/- 1.84 mmol/h, not significant, in the post-absorptive state and from 14.4 +/- 2.13 to 15.7 +/- 1.74 mmol/h, not significant, in the fed state), whereas there were increases in the lean subjects (from 8.93 +/- 1.10 to 11.2 +/- 1.19 mmol/h, P less than 0.05, in the post-absorptive state, and from 8.06 +/- 1.19 to 9.86 +/- 0.93 mmol/h, P less than 0.05, in the fed state). 4. Before adrenaline infusion the palmitate oxidation rate was also higher in the obese than in the lean subjects (1.86 +/- 0.14 versus 1.22 +/- 0.09 mmol/h, P less than 0.01, in the post-absorptive state and 1.73 +/- 0.25 versus 1.12 +/- 0.12 mmol/h, P less than 0.05, in the fed state). However, in response to adrenaline the fractional oxidation rate (% of flux) increased less in the obese than in the lean subjects, especially in the post-absorptive state (from 13.8 +/- 1.02 to 14.9 +/- 1.39%, not significant, versus from 13.7 +/- 0.98 to 19.3 +/- 1.92%, P less than 0.05). These effects were independent of feeding.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗