Protein metabolism in human obesity: relationship with glucose and lipid metabolism and with visceral adipose tissue

It is controversial whether metabolic disorders of human obesity include protein metabolism. Even less information is available concerning the effect of fat distribution on protein metabolism. Therefore, a comprehensive evaluation of glucose, lipid, and protein metabolism was performed in 11 obese nondiabetic and 9 normal women whose body composition and regional fat distribution were determined. [1-14C]Leucine and [3-3H]glucose were infused in the postabsorptive state and during an euglycemic hyperinsulinemic (35-40 microU/mL) clamp combined with indirect calorimetry for assessment of leucine flux, oxidation, and nonoxidative disposal, glucose turnover and oxidation, and lipid oxidation. Fat-free mass (FFM) was estimated by a bolus of 3H2O. Subcutaneous abdominal and visceral adipose tissues were determined by nuclear magnetic resonance imaging. During the clamp, obese women had lower glucose turnover (4.51 +/- 0.41 vs. 6.63 +/- 0.40 mg/min.kg FFM; P < 0.05), with a defect in both oxidation (3.27 +/- 0.22 vs. 3.89 +/- 0.21) and nonoxidative disposal (1.24 +/- 0.27 vs. 2.74 +/- 0.41; P < 0.005), whereas lipid oxidation was higher during the clamp (0.49 +/- 0.15 vs. 0.17 +/- 0.09 mg/min.kg FFM). There was no difference in leucine flux (basal, 2.23 +/- 0.17 vs. 2.30 +/- 0.29; clamp, 2.06 +/- 0.19 vs. 2.10 +/- 0.24 mumol/min.kg FFM), oxidation (basal, 0.37 +/- 0.04 vs. 0.36 +/- 0.05; clamp, 0.34 +/- 0.04 vs. 0.39 +/- 0.06) and nonoxidative leucine disposal (basal, 1.86 +/- 0.17 vs. 1.94 +/- 0.26; clamp, 1.72 +/- 0.20 vs. 1.71 +/- 0.19) in the two groups. In obese women, basal leucine oxidation was directly related with glucose oxidation and inversely to lipid oxidation (both P < 0.05), whereas visceral adipose tissue was inversely related to leucine flux both in the basal state and during the clamp (P < 0.05). In conclusion, in human obesity, 1) rates of protein metabolism in the basal state and in the range of insulin concentrations encountered after a meal are normal; 2) protein oxidation is positively related to glucose oxidation and negatively related to lipid oxidation; and 3) visceral adipose tissue is inversely related to all parameters of protein metabolism.     

Diurnal changes in plasma amino acids in maple syrup urine disease

Protein turnover is a cyclic process with a net loss of protein in the (catabolic) fasted state and a net gain in the (anabolic) fed state. In maple syrup urine disease (MSUD) the early block of degradation of the branched-chain amino acids (BCAA) brings about the opportunity for evaluation of the diurnal variation in net protein anabolism and catabolism by studying cyclic changes in the plasma concentrations of BCAA. The alterations in plasma BCAA in a 3-y-old boy with classical MSUD were studied in the fed and fasted state over a period of 19 months. For each amino acid a total of 34 data pairs was calculated. The plasma concentrations of the BCAA leucine, valine and isoleucine were constantly higher in the fasted than in the fed state. Plasma concentrations of alloisoleucine, being a non-protein amino acid, did not participate in cyclic changes. In contrast, the essential amino acid pair tyrosine and phenylalanine increased after meals. The fasting concentration of alanine increased after feeding, while glycine did not change significantly. Healthy subjects show a decrease in all amino acids in the fasted (mild catabolic) state and an increase in the fed state. These findings in MSUD suggest a net decrease in non-BCAA as result of a greater rate of amino acid oxidation rate than of protein breakdown and a net entry of BCAA into plasma in the fasted state due to the specific metabolic block. Such changes in amino acid plasma pools have to be taken into account during monitoring of treatment and especially when in vivo leucine oxidation is assessed.     

Heritable disorder resembling neuronal storage disease in mice expressing prion protein with deletion of an alpha-helix

Ethanol abuse is frequently associated with protein malnutrition. To assess the acute effects of ethanol on whole-body protein metabolism, [1-13C]leucine kinetics were measured in eight postabsorptive normal male subjects three times, ie, during administration of two doses of ethanol (dose 1, 0.52 g/kg during 2 hours and 0.3 g/kg during 3 hours; dose 2, 0.69 g/kg during 2 hours and 0.3 g/kg during 3 hours) and during saline (controls). During the last 2 hours of the studies, glucose, insulin, and amino acids were infused to assess the effects of ethanol on protein kinetics under anabolic conditions (euglycemic clamp). The decreases in leucine flux (reflecting whole-body protein breakdown) and nonoxidative leucine disappearance (a parameter of protein synthesis) during saline infusion were abolished in both ethanol protocols (P < .05 or less v saline). The rate of leucine oxidation decreased during the higher dose of ethanol compared with saline (P < .005), indicating an anticatabolic effect. During anabolic conditions (clamp), leucine flux and nonoxidative leucine disappearance were significantly higher in both ethanol studies compared with saline (P < .05). Resting energy expenditure (REE) and oxygen consumption (VO2) during the euglycemic clamp increased to a greater degree during both ethanol studies than during saline (P < .05 or less). Thus, an elevation of blood ethanol concentrations to the levels observed in social drinking results in a net anticatabolic effect (diminished leucine oxidation) when ethanol is administered alone. However, during administration of other nutritional substrates, the anticatabolic effect was not detectable, possibly because ethanol enhanced nutrient-induced thermogenesis.     

Intracerebroventricular administration of leptin markedly enhances insulin sensitivity and systemic glucose utilization in conscious rats

This study examines the acute, subacute (overnight), and chronic (7-day) effects of intracerebroventricular (i.c.v.) administration of r-metMuLeptin on insulin sensitivity and systemic glucose turnover in conscious unrestrained rats (body weight, 250 to 300 g). Under postabsorptive conditions, acute i.c.v. leptin ([AL] 10 microg bolus) did not affect tracer (3-(3)H-glucose)-determined glucose production (GP) and utilization (GU) rates during the 2-hour hyperinsulinemic (2 mU x kg(-1) x min(-1)) euglycemic clamp. Chronic i.c.v. leptin ([CL] 10 microg/d for 7 days) administered by osmotic pumps markedly reduced the daily food consumption (P < .05), body weight (P < .05), and postabsorptive basal plasma glucose level (P < .01). During the glucose clamp, GP was markedly suppressed (55%) with CL (P < .001 v vehicle and pair-fed control groups). The insulin-induced increment in GU was significantly greater with CL (23.3 +/- 1.8 mg(-1) x kg(-1) x min(-1)) than with vehicle (16.9 +/- 0.2) and pair-feeding (17.1 +/- 0.6, both P < .001). Subacute i.c.v. leptin ([SL] 10 microg bolus) moderately but insignificantly decreased overnight food consumption (-18%) and body weight (-2.5 +/- 1.5 g). The glucose infusion rate during the final 60 minutes of the glucose clamp was 43% greater than for the vehicle group (P < .0001). SL also significantly increased GU (P < .005) and suppressed GP (P < .05) during the glucose clamp. Thus, we conclude that i.c.v. administered leptin has strong actions on the central nervous system that result in significant increases in insulin sensitivity and systemic GU, and these effects are achieved as early as overnight after leptin administration.     

Inhibition of lipolysis reduces beta1-adrenoceptor-mediated thermogenesis in man

The purpose of the study was to investigate whether the increase in energy expenditure and lipid oxidation during beta1-adrenergic stimulation is caused by the concomitant increase in lipolysis. Twelve healthy male subjects participated in three trials: no-LIP/-, inhibition of lipolysis by pretreatment with acipimox followed by saline infusion; -/BETA, no pretreatment, with dobutamine infusion to stimulate beta1-adrenoceptors; and no-LIP/BETA, pretreatment with acipimox followed by dobutamine infusion. Inhibition of lipolysis did not affect baseline energy expenditure, but decreased lipid oxidation and increased carbohydrate oxidation. Energy expenditure and lipid oxidation increased significantly during beta1-adrenergic stimulation, but this increase was significantly smaller when lipolysis was inhibited ([baseline v infusion period] energy expenditure: -/BETA, 5.15 +/- 0.16 v 6.11 +/- 0.26 kJ/min, P < .001; no-LIP/BETA, 5.28 +/- 0.17 v 5.71 +/- 0.19 kJ/min, P < .01; lipid oxidation: -/BETA, 0.059 +/- 0.004 v 0.073 +/- 0.006 g/min, P < .01; no-LIP/BETA, 0.034 +/- 0.005 v 0.039 +/- 0.006 g/min, P < .05). Baseline plasma glycerol and nonesterified fatty acid (NEFA) concentrations decreased after inhibition of lipolysis. Glycerol and NEFA increased significantly during beta1-adrenergic stimulation alone (glycerol, 65.0 +/- 5.3 v 117.0 +/- 10.9 micromol/L; NEFA, 362 +/- 24 v 954 /- 89 micromol/L; both P < .001). Concomitant administration of acipimox prevented a substantial part of the increase in lipolysis during beta1-adrenergic stimulation, but the increase in plasma glycerol and NEFA remained significant (glycerol, 40.4 +/- 2.2 v 44.8 +/- 2.2 micromol/L; NEFA, 118 +/- 18 v 160 +/- 19 micromol/L; both P < .05). In conclusion, a reduced availability of plasma NEFA was associated with a reduced increase in energy expenditure and lipid oxidation during beta1-adrenergic stimulation in man.     

The influence of bicarbonate supplementation on plasma levels of branched-chain amino acids in haemodialysis patients with metabolic acidosis

BACKGROUND: It has been hypothesized that correction of metabolic acidosis might improve the nutritional state of acidotic haemodialysis (HD) patients partly because of a reduced oxidation of branched-chain amino acids (BCAA). AIM: We investigated whether bicarbonate (Bic) supplementation in acidotic HD patients results in increased plasma levels of BCAA. METHODS: In a longitudinal study (run-in period, 2 months; study period, 6 months), the effect of Bic supplementation on plasma levels of BCAA was studied in 12 acidotic HD patients (7 men, 5 women, mean age 54 +/- 18 years) with a predialysis bicarbonate (Bic) concentration smaller or equal to 22 mmol/l. Bic was supplemented by increasing Bic concentration of the dialysate and by oral Bic supplementation. RESULTS: Predialysis Bic increased significantly during the study period (18.7 +/- 2.7 vs. 23.1 +/- 11.5 mmol/l). There was no change in nutritional parameters. However, plasma levels of the BCAA valine, leucine, and isoleucine increased significantly. CONCLUSIONS: In haemodialysis patients with metabolic acidosis, Bic supplementation over a 6-months period resulted in an increase in plasma levels of BCAA. Further study is needed to elucidate the mechanisms behind, and the clinical importance of the observed changes in plasma BCAA levels.     

A preliminary placebo-controlled crossover trial of fludrocortisone for chronic fatigue syndrome

To investigate the time course of the hepatic glucose metabolism in non-insulin-dependent diabetes (NIDDM), we measured hepatic glucose production (HGP) and first-pass uptake of portal glucose infusion by the liver (HGU) using dual-tracer methods in a NIDDM model, Otsuka Long-Evans Tokushima Fatty (OLETF) rats, and in normal controls, Long-Evans Tokushima Otsuka (LETO) rats, at 8, 14, and 28 weeks of age (n = 5, respectively). The fasting plasma glucose level in OLETF rats was significantly higher than in LETO rats at 28 weeks of age (8.9 +/- 1.7 v 6.3 +/- 0.4 mmol/L, P < .01), while there was no significant difference at 8 and 14 weeks. Hyperinsulinemia in OLETF rats appeared at > or = 8 weeks of age. Basal HGP was significantly higher in OLETF than in LETO rats at 8 and 28 weeks (8 weeks, 12.7 +/- 1.7 v 9.4 +/- 1.8 mg x kg(-1) x min(-1), P < .05; 28 weeks, 10.9 +/- 1.6 v 7.1 +/- 1.3 mg x kg(-1) x min(-1), P < .01). At 14 weeks, basal HGP was not significantly different between OLETF and LETO rats. However, at all study points, HGU during a portal glucose infusion was significantly lower in OLETF than in LETO rats (8 weeks, 0.9 +/- 0.2 v 2.3 +/- 0.5, P < .01; 14 weeks, 0.8 +/- 0.3 v 1.4 +/- 0.3, P < .05; 28 weeks, 0.7 +/- 0.2 v 1.4 +/- 0.3 mg x kg(-1) x min(-1), P < .01). Fasting plasma free fatty acid (FFA) levels were not significantly different between OLETF and LETO, except at 8 weeks. Suppression of plasma FFA levels by endogenous insulin during a portal glucose infusion was impaired in OLETF rats compared with LETO rats. In summary, this study demonstrates that derangement of hepatic glucose handling, such as increased basal HGP and decreased HGU, is observed in obese NIDDM model OLETF rats at the prediabetic phase when hyperglycemia is still not apparent. Furthermore, these derangements may be accompanied by impaired lipid metabolism.     

Circadian rhythmicity of heart rates in centenarians]

Insulin and branched-chain amino acid (BCAA) metabolism was studied in 14 adolescents with uremia on hemodialysis. Glucose tolerance was measured by intravenous glucose tolerance tests. Insulin sensitivity was measured by the euglycemia clamp technique. Insulin secretion during constant hyperglycemia was measured by the hyperglycemic clamp technique. Fasting plasma BCAA concentrations were compared with data from 8 adolescent controls, whereas insulin indices were compared with 8 young adults controls and with published normal data in adolescents. The patients could be further sub-divided into two groups with respect to their growth velocity standard deviation score (GVSDS). Group 1 consisted of 7 patients with GVSDS less than -2. This group demonstrated insulin resistance, glucose intolerance, and low insulin secretion. This group also had low plasma valine, leucine, and isoleucine concentrations compared with control values. Group 2 consisted of 7 patients with GVSDS more than -2. This group demonstrated insulin resistance, but normal glucose tolerance and normal insulin secretion. Plasma valine, leucine, and isoleucine concentrations in group 2 were not different from control values. Total plasma BCAA correlated with glucose tolerance index and with insulin secretion, but not with insulin sensitivity. Growth failure in uremia is associated with glucose intolerance, hypoinsulinemia, and low plasma BCAA concentrations. Impaired utilization of conventional energy sources leading to preferential oxidation of BCAA may contribute to reduced anabolism and growth failure in uremia.     

Removal of branched-chain amino acids by peritoneal dialysis, continuous arteriovenous hemofiltration, and continuous arteriovenous hemodialysis in rabbits: implications for maple syrup urine disease treatment

Renal elimination of branched-chain amino acids (BCAA) is low in maple syrup urine disease, and peritoneal dialysis may be required in an emergency situation for removal of the three BCAA (leucine, isoleucine, and valine). However, failures of BCAA removal by peritoneal dialysis have been reported, especially in neonates. Therefore, we tested the ability of continuous hemofiltration and continuous hemodialysis to remove BCAA as compared with peritoneal dialysis. Experiments were conducted in 15 anesthetized adult rabbits infused with leucine, isoleucine, and valine. In group 1 (n = 7), peritoneal dialysis (dialysate = 75 mL/kg) and continuous arteriovenous hemofiltration with a polysulfone 800-cm2 hemofilter were simultaneously performed during 40 min. In group 2 (n = 8), continuous arteriovenous hemofiltration and continuous arteriovenous hemodialysis were successively performed during 30 min in a randomly settled order. Animals had high and stable BCAA plasma levels during the experimental procedure. As compared with peritoneal dialysis, continuous arteriovenous hemofiltration constantly showed a significant increase in clearances of leucine (+159 +/- 99%), isoleucine (+176 +/- 107%), and valine (+125 +/- 76%). In comparison with continuous arteriovenous hemofiltration, continuous arteriovenous hemodialysis constantly showed significant increased values in clearances of leucine (+90 +/- 43%), isoleucine (+95 +/- 45%), and valine (+99 +/- 52%). During continuous arteriovenous hemofiltration and continuous arteriovenous hemodialysis, a significant positive correlation was established between urea clearance and clearances of leucine (r2 = 0.953 and 0.927, respectively), isoleucine (r2 = 0.948 and 0.910, respectively), and valine (r2 = 0.953 and 0.864, respectively).     

Sympathetic nervous system activity and resting metabolic rate in vegetarians

We examined the resting metabolic rate (RMR) and sympathetic nervous system activity of young male vegetarians (n = 17) and nonvegetarians (n = 40). Subjects were characterized for RMR by indirect calorimetry, norepinephrine kinetics from infusions of tritiated norepinephrine, energy and macronutrient intake from a 3-day food diary, and body composition by underwater weighing. Vegetarians reported a greater relative intake of carbohydrates (62% +/- 5% v 51% +/- 6%, P < .01) and a lower relative intake of fat (25% +/- 5% v 33% +/- 6%, P < .01) than nonvegetarians, whereas no differences were observed in daily energy intake, body composition, or maximal aerobic capacity (VO2max) between groups. Vegetarians exhibited an 11% higher absolute RMR (1.29 +/- 0.15 v 1.16 +/- 0.13 kcal/min, P < .01), a higher plasma concentration of norepinephrine (216 +/- 33 v 165 +/- 18 pg/mL, P < .01), and a greater norepinephrine appearance rate (0.50 +/- 0.08 v 0.36 +/- 0.09 micrograms/min, P < .01) than nonvegetarians. After statistically controlling for differences in relative amounts of carbohydrate and fat in the diet and for norepinephrine concentrations, no significant differences in adjusted RMR between vegetarians and nonvegetarians were noted. These results suggest that the higher RMR observed in young male vegetarians is partially mediated by differences in dietary macronutrient composition and increased sympathetic nervous system activity.     

ISCOMs: an adjuvant with multiple functions

Glucagon causes transient hyperglycemia and persistent hypoaminoacidemia, but the mechanisms of this action are unclear. To address this question, the present study measured the effects of glucagon on glucose, leucine, phenylalanine, and glutamine kinetics. Seven healthy subjects each underwent three pancreatic clamp studies (octreotide 30 ng/kg/min, insulin 0.15 mU/kg/min, and glucagon 1.4 ng/kg/min) lasting 7 hours. During the last 3.5 hours of the studies, glucagon infusion was either unchanged (study 0) or increased to 4 and 7 ng/kg/min (studies 1 and 2). The higher glucagon infusion rates increased the glucagon concentration by 50% and 100%, respectively. [6,6-(2)H2]glucose, [2-(15)N]glutamine, 2H5-phenylalanine, and 2H3-leucine were infused to quantify the respective fluxes. Glucagon transiently increased glucose concentrations by stimulating glucose production, which peaked in 15 minutes to 3.82 +/- 0.36 and 4.21 +/- 0.33 mg/kg/min in studies 1 and 2 and then returned to the postabsorptive levels. Glucagon decreased the glutamine concentration (-10% +/- 2% and -22% +/- 2% in studies 1 and 2 v study 0, P < .05), because glutamine uptake became greater than glutamine release (balance from -1.9 +/- 0.9 in study 0 to -8.1 +/- 1.1 and -13.6 +/- 1.0 micromol/kg/h in studies 1 and 2, P < .01). Glucagon decreased the leucine concentration (-11% +/- 3% in study 2 v study 0, P < .02) and caused a small increment in proteolysis (+6% in study 2 v study 0, P < .01) that was related to the decrement in glutamine concentrations. Phenylalanine kinetics were not significantly affected. These results show that glucagon promotes the uptake of gluconeogenic substrates but does not increase their release, suggesting that glucagon-induced hyperglycemia is short-lived because glucagon fails to provide more fuel for gluconeogenesis. The small increase in proteolysis and the depletion of circulating glutamine prove that physiologic hyperglucagonemia can contribute to protein catabolism.     

Alterations in skeletal muscle gene expression in the rat with chronic congestive heart failure

Congestive heart failure is often associated with skeletal muscle abnormalities that contribute to early fatigue and acidosis. Up to the present time, however, the mechanisms responsible for these changes are unclear. Myocardial infarctions were produced by coronary ligation in adult Sprague-Dawley rats. At 20 weeks, 10 control rats, and 15 animals with heart failure [defined by elevated LVEDP (26.1 +/- 3.1 v 2.5 +/- 0.5 mmHg) and RV hypertrophy (300 +/- 21 g v 158 +/- 9 mg)] underwent in vivo measurements of total body, and soleus total protein and myosin heavy chain (MHC) synthesis by [3H]leucine constant infusion. Soleus muscle was also analysed for protein content, and MHC isoenzyme content by SDS-PAGE. Northern blotting also was used to determine levels of the mRNA's encoding type I, IIa, IIb, and IIx MHC, alpha-skeletal actin, COX III, SDH and GAPDH. Soleus muscles in heart failure rats were smaller than controls (112 +/- 6 v 126 +/- 5 mg) and the degree of atrophy was significant when corrected for body mass (0.38 +/- 0.02 v 0.46 +/- 0.02 mg/g. P = 0.007). Although there was no significant difference in plasma leucine flux (an index of whole-body protein synthesis), soleus muscle total and MHC synthesis was reduced in heart failure animals. Whereas the Type I MHC isoenzyme (beta MHC) was the only MHC detected in the soleus of control animals, type II MHC isoenzyme comprised 11.8 +/- 3.1% of the MHC in the heart failure group. Furthermore, steady-state mRNA levels encoding beta MHC were significantly depressed in the heart failure rats, where those encoding Types IIb and IIx MHC were increased. Steady-state mRNA levels of alpha-skeletal actin, cytochrome C oxidase (COX III) and succinate dehydrogenase (SDH) were also significantly depressed. This animal model of chronic heart failure is associated with quantitative and qualitative alterations in skeletal muscle gene expression that are similar to those reported in skeletal muscle of patients with chronic heart failure. The altered phenotype and impaired metabolic capacity may contribute to exercise intolerance in CHF.     

Renal blood flow velocity in acute renal failure following cardiopulmonary bypass surgery

Two lysosomal storage diseases, aspartylglucosaminuria and mannosidosis, are associated with highly elevated serum dolichol concentrations. To elucidate possible mechanisms leading to elevated serum dolichols, we studied the effects of Triton WR 1339 (known to increase serum cholesterol) and orotic acid (known to decrease serum cholesterol) on blood and biliary dolichol and beta-hexosaminidase levels in rats. In Triton WR 1339-treated rats, serum dolichol was markedly increased compared with saline-treated controls 1 (400 +/- 70 ng/mL, n = 7 v 85 +/- 11 ng/mL, n = 8, P < .001), 4 (789 +/- 70 ng/mL, n = 10 v 110 +/- 10 ng/mL, n = 7, P < .0001), and 8 (549 +/- 43 ng/mL, n = 8 v 87 +/- 8 ng/mL, n = 7, P < .001) days after administration of the drug. By contrast, serum dolichol was decreased (64 +/- 5 ng/mL, n = 8 v 119 +/- 7 ng/mL, n = 8, P < .0001) after a 7-day orotic acid feeding compared with controls. Serum beta-hexosaminidase was unaffected by both treatments. Orotic acid also increased biliary dolichol (280 +/- 47 ng/100 g body weight [BW]/h, n = 7 v 83 +/- 15 ng/100 g BW/h, n = 7, P < .01) and beta-hexosaminidase (21 +/- 3 mU/100 g BW/h, n = 7 v 8.3 +/- 2 mU/100 g BW/h, n = 9, P < .01) excretion compared with controls. Thus, both Triton WR 1339 and orotic acid have an effect on dolichol metabolism, and it is conceivable--based on our results--that serum dolichol concentrations are regulated, at least in part, by a mechanism similar to that for serum cholesterol levels.     

Pre-exercise branched-chain amino acid administration increases endurance performance in rats

This study investigated the effects of pre-exercise branched-chain amino acid (BCAA) administration on blood ammonia levels and on time to exhaustion during treadmill exercise in rats. Adult female Wistar rats were trained on a motor driven treadmill. After a 24-h fast, rats were injected intraperitoneally (i.p.) with 1 mL of placebo or BCAA (30 mg), 5 min before performing 30 min of submaximal exercise (N = 18) or running to exhaustion (N = 12). In both cases, rats were sacrificed immediately following exercise, and blood was collected for the measurement of glucose, nonesterified fatty acid (NEFA), lactic acid, BCAA, ammonia, and free-tryptophan (free-TRP) levels. Control values were obtained from sedentary rats that were subjected to identical treatments and procedures (N = 30). Plasma BCAA levels increased threefold within 5 min after BCAA administration. Mean run time to exhaustion was significantly longer (P < 0.01) after BCAA administration (99 +/- 9 min) compared with placebo (76 +/- 4 min). During exercise, blood ammonia levels were significantly higher (P < 0.01) in the BCAA treated compared with those in the placebo treated rats both in the 30-min exercise bout (113 +/- 25 mumol.L-1 (BCAA) vs 89 +/- 16 mumol.L-1) and following exercise to exhaustion (186 +/- 44 mumol.L-1 (BCAA) vs 123 +/- 19 mumol.L-1). These data demonstrate that BCAA administration in rats results in enhanced endurance performance and an increase in blood ammonia during exercise.     

Effect of theophylline on substrate metabolism during exercise

We tested the hypothesis that adenosine is involved in regulating substrate metabolism during exercise. Seven trained cyclists were studied during 30 minutes of exercise at approximately 75% maximal oxygen uptake (VO2max). Lipid metabolism was evaluated by infusing [2H5]glycerol and [1-13C]palmitate, and glucose kinetics were evaluated by infusing [6,6-2H]glucose. Fat and carbohydrate oxidation were also measured by indirect calorimetry. The same subjects performed two identical exercise tests, but in one trial theophylline, a potent adenosine receptor antagonist, was infused for 1 hour before and throughout exercise. Theophylline did not increase whole-body lipolysis (glycerol rate of appearance [Ra]) or free fatty acid (FFA) release during exercise, but fat oxidation was lower than control values (9.5 +/- 3.0 v 18.0 +/- 4.2 micromol x min(-1) x kg(-1), P < .01). Glucose Ra was not affected by theophylline infusion, but glucose uptake was lower (31.6 +/- 4.1 v 40.4 +/- 5.0 micromol x min(-1) x kg(-1), P < .05) and glucose concentration was higher (6.4 +/- 0.6 v 5.8 +/- 0.4 mmol/L, P < .05) than in the control trial. Total carbohydrate oxidation (302.3 +/- 26.2 v 265.5 +/- 11.7 micromol x min(-1) x kg(-1), P < .06), estimated muscle glycogenolysis (270.7 +/- 23.1 v 225.1 +/- 9.7 micromol x min(-1) x kg(-1), P < .05), and plasma lactate concentration (7.9 +/- 1.6 v 5.9 +/- 1.1 mmol/L, P < .001) were also higher during the theophylline trial. These data suggest that adenosine may play a role in stimulating glucose uptake and restraining glycogenolysis but not in limiting lipolysis during exercise.     

Integrated nutritional, hormonal, and metabolic effects of recombinant human growth hormone (rhGH) supplementation in trauma patients

An anabolic stimulus is needed in addition to conventional nutritional support in the catabolic "flow" phase of severe trauma. One promising therapy appears to be rhGH infusion which has direct as well as hormonal mediated substrate effects. We investigated on a whole-body level, the basic metabolic effects of trauma within 48-60 h after injury in 20 severely injured (injury severity score [ISS] = 31 +/- 2), highly catabolic (N loss = 19 +/- 2 g/d), hypermetabolic (resting energy expenditure [REE] = 141 +/- 5% basal energy expenditure [BEE]), adult (age 46 +/- 5 y) multiple-trauma victims, before starting nutrition therapy and its modification after 1 wk of rhGH supplementation with TPN (1.1 x REE calories, 250 mg N.kg-1.d-1). Group H (n = 10) randomly received at 8:00 a.m. on a daily basis rhGH (0.15 mg.kg-1.d-1) and Group C (n = 10) received the vehicle of infusion. Protein metabolism (turnover, synthesis and breakdown rates, and N balance); glucose kinetics (production, oxidation, and recycling); lipid metabolism, (lipolysis and fat oxidation rates), daily metabolic and fuel substrate oxidation rate (indirect calorimetry); and plasma levels of hormones, substrates, and amino acids were quantified. In group H compared to group C: N balance is less negative (-41 +/- 18 vs -121 +/- 19 mg N.kg-1.d-1, P = 0.001); whole body protein synthesis rate is 28 +/- 2% (P = 0.05) higher; protein synthesis efficiency is higher (62 +/- 2% vs 48 +/- 3%, P = 0.010); plasma glucose level is significantly elevated (256 +/- 25 vs 202 +/- 17 mg/dL, P = 0.05) without affecting hepatic glucose output (1.51 +/- 0.20 vs 1.56 +/- 0.6 mg N.kg-1.min-1), glucose oxidation and recycling rates; significantly enhanced rate of lipolysis (P = 0.006) and free fatty acid reesterification (P = 0.05); significantly elevated plasma levels of anabolic GH, IGF-1, IGFBP-3, and insulin; trauma induced counter-regulatory hormone (cortisol, glucagon, catecholamines) levels are not altered; trauma induced hypoaminoacidemia is normalized (P < 0.05) and 3-methylhistidine excretion is significantly low (P < 0.001). Improved plasma IGF-1 levels in Group H compared with Group C account for protein anabolic effects of adjuvant rhGH and may be helpful in promoting tissue repair and early recovery. Skeletal muscle protein is spared by rhGH resulting in the stimulation of visceral protein breakdown. The hyperglycemic, hyperinsulinemia observed during rhGH supplementation may be due to defective nonoxidative glucose disposal, as well as inhibition of glucose transport activity into tissue cells. The simultaneous operation of increased lipolytic and reesterification processes may allow the adipocyte to respond rapidly to changes in peripheral metabolic fuel requirements during injury. This integral approach helps us to better understand the mechanism of the metabolic effects of rhGH.     

Protein balance in the first week of life in ventilated neonates receiving parenteral nutrition

BACKGROUND: Protein intake is frequently delayed in ill neonates because of concerns about their ability to metabolize substrates. OBJECTIVE: We aimed to determine the factors affecting protein balance in ventilated, parenterally fed newborns during the first week of life. DESIGN: Leucine kinetic studies were performed in 19 neonates by using the [1-(13)C]leucine tracer technique after 24 h of a stable total parenteral nutrition (TPN) regimen. TPN intakes were prescribed by rotating attending physicians, enabling assessment of protein metabolism over a range of clinically used nutrient intakes. RESULTS: Mean (+/-SD) birth weight was 1.497 +/- 0.779 kg, gestational age at birth was 30.3 +/- 4.0 wk, and age at study was 3.9 +/- 1.4 d. Amino acid intakes (AAIs) ranged from 0.0 to 2.9 g x kg(-1) x d(-1). Based on leucine kinetic data, protein balance was calculated as the difference between protein synthesis and catabolism. By multiple regression analysis, AAI was the only predictor associated independently with protein balance (P < 0.01); energy intake, lipid intake, glucose intake, birth weight, and gestational age were not. Both leucine oxidation and nonoxidative leucine disposal rates were significantly correlated with leucine intake (P < 0.0005 and P < 0.01, respectively). Of the 12 infants with AAIs > 1 g x kg(-1) x d(-1), only 1 infant was significantly catabolic (protein balance <-1 g x kg(-1) x d(-1)). There was no evidence of protein intolerance as determined by elevated creatinine (69 +/- 31 micromol/L), plasma urea nitrogen (6.7 +/- 2.53 mmol/L), or metabolic acidosis (pH: 7.36 +/- 0.05). CONCLUSIONS: Ill neonates can achieve a positive protein balance in the first days of life without laboratory evidence of protein toxicity.     

Lipoic acid reduces glycemia and increases muscle GLUT4 content in streptozotocin-diabetic rats

Alpha lipoic acid (lipoate [LA]), a cofactor of alpha-ketodehydrogenase, exhibits unique antioxidant properties. Recent studies suggest a direct effect of LA on glucose metabolism in both human and experimental diabetes. This study examines the possibility that LA positively affects glucose homeostasis in streptozotocin (STZ)-induced diabetic rats by altering skeletal muscle glucose utilization. Blood glucose concentration in STZ-diabetic rats following 10 days of intraperitoneal (i.p.) injection of LA 30 mg/kg was reduced compared with that in vehicle-treated diabetic rats (495 +/- 131 v 641 +/- 125 mg/dL in fed state, P = .003, and 189 +/- 48 v 341 +/- 36 mg/dL after 12-hour fast, P = .001). No effect of LA on plasma insulin was observed. Gastrocnemius muscle crude membrane GLUT4 protein was elevated both in control and in diabetic rats treated with LA by 1.5- and 2.8-fold, respectively, without significant changes in GLUT4 mRNA levels. Gastrocnemius lactic acid was increased in diabetic rats (19.9 +/- 5.5 v 10.4 +/- 2.8 mumol/g muscle, P < .05 v nondiabetic rats), and was normal in LA-treated diabetic rats (9.1 +/- 5.0 mumol/g muscle). Insulin-stimulated 2-deoxyglucose (2 DG) uptake into isolated soleus muscle was reduced in diabetic rats compared with the control group (474 +/- 15 v 568 +/- 52 pmol/mg muscle 30 min, respectively, P = .05). LA treatment prevented this reduction, resulting in insulin-stimulated glucose uptake comparable to that of nondiabetic animals. These results suggest that daily LA treatment may reduce blood glucose concentrations in STZ-diabetic rats by enhancing muscle GLUT4 protein content and by increasing muscle glucose utilization.     

Pulsatile growth hormone and prolactin: effects of (+) butaclamol, a dopamine receptor blocking agent

Growth hormone (rGH) and prolactin (rPRL) secretory profiles were obtained before and after treatment with a dopamine receptor blocking agent, (+) butaclamol, in 10 male rats chronically implanted with right atrial cannulae. Mean rGH plasma concentrations, determined by planimetry, were reduced (202 +/- 20 ng/ml vs. 135 +/- 20ng/ml, P less than .01), but the basic configuration and periodicity of rGH secretory bursts were unaltered. Mean rPRL plasma concentrations were elevated (11.1 +/- 2.1 ng/ml vs 65.5 +/- 8.1 ng/ml, P less than .0005), but rPRL episodic secretion was still apparent. It is concluded that dopaminergic neurons have a minor role in facilitating episodic rGH secretion. Furthermore, persisting episodic rPRL secretion in rats administered a dopamine antagonist suggests that rPRL feedback inhibition does not inactivitate the neural mechanism generating episodic rPRL secretion.     

Further evidence for a central role of adipose tissue in the antihyperglycemic effect of metformin

OBJECTIVE: To evaluate further the relative roles played by liver and adipose tissue in the therapeutic response to metformin in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: A total of 11 patients with diet-treated type 2 diabetes were given metformin for approximately 3 months. Measurements were made before and after treatment of 1) fasting and postprandial plasma glucose, insulin, and free fatty acid (FFA) concentrations; 2) glucose appearance (Ra) and disappearance (Rd) rates measured overnight with 3-[3H]glucose; and 3) plasma FFA concentrations during a 195-min infusion period at relatively low insulin (approximately 12-24 microU/ml) concentrations. RESULTS: Mean +/- SEM fasting plasma glucose concentration was significantly lower (175 +/- 11 vs. 224 +/- 15 mg/dl; P < 0.01) after treatment with metformin. Mean +/- SEM insulin concentrations measured from 8:00 A.M. to 5:00 P.M. did not change with treatment. However, both glucose and FFA concentrations were significantly lower (P < 0.01) when measured over the same time period, and the decreases in plasma FFA and glucose concentration were highly correlated (r = 0.81; P = 0.03). Overnight glucose turnover studies indicated that neither Ra (hepatic glucose production [HGP]) nor Rd changed significantly with treatment in association with metformin treatment. Since plasma glucose concentration was much lower after metformin treatment, the overnight glucose metabolic clearance rate (MCR) was significantly lower (P < 0.01). Finally, the ability of insulin to inhibit isoproterenol-stimulated increases in plasma FFA concentration was enhanced in metformin-treated patients (P < 0.05). CONCLUSIONS: Metformin treatment was associated with significantly lower fasting plasma glucose concentrations and lower day-long plasma glucose and FFA concentrations. Although overnight HGP was unchanged after treatment with metformin, the overnight glucose MCR was significantly increased, and the antilipolytic activity of insulin was also enhanced. Given these findings, it is suggested that at least part of the antihyperglycemic effect of metformin is due to a decrease in release of FFA from adipose tissue, leading to lower circulating FFA concentrations and an increase in glucose uptake.