The role of glucose, long-chain triglycerides and amino acids for promotion of amino acid balance across peripheral tissues in man

The role of amino acids, glucose and lipids in improving amino acid balance in peripheral tissues was evaluated. Primed constant infusion of L-[ring-2H5]phenylalanine in combination with flux measurements of glucose, free fatty acids (FFA) and amino acids across arm and leg tissues were applied in male volunteers after an overnight fast with subsequent primed constant infusions of amino acids (0.2 g N kg-1 body weight day-1), long-chain triglycerides (0.98-1.079 g kg-1 day-1) and glucose (3.13-3.62 g kg-1 day-1). Amino acids and phenylalanine tracer infusion continued for 6 h; the lipid infusion was provided during 2-6 h from the start, and glucose infusion was provided between 4 and 6 h. Flux measurements were performed at steady state before the next infusion started. Arterial concentrations of infused substrates increased during provision, but remained constant thereafter. Plasma insulin increased when glucose was provided, whereas insulin-like growth factor (IGF) I was unchanged during all infusions. Blood flow was unchanged in arm tissue during all infusions, while leg blood flow increased during fat and glucose infusion. FFA and glucose balance were unchanged during amino acid infusion but improved during lipid and glucose infusions. Amino acid balance was negative across arm and leg tissues in the fasted state, but reached balance during amino acid infusion. This effect was equally dependent on protein synthesis and protein degradation without any contribution from lipids and glucose. 3-Methylhistidine release from tissues was not influenced by any substrate. Our results suggest that extracellular amino acid concentrations determine amino acid balance across peripheral tissues independently of non-protein calories, insulin and IGF-I.

Splanchnic utilization of enteral alanine in humans

The splanchnic bed extracts the majority of the enteral nonessential amino acids glutamine and glutamate, while extracting a much smaller proportion of essential amino acids such as leucine and phenylalanine. Alanine is an abundant nonessential amino acid that plays an important role in hepatic gluconeogenesis and ureagenesis. However, its enteral fate has not been studied. Twelve normal healthy postabsorptive adults received a 7-hour infusion of [1-13C]alanine, 3.5 hours intravenously (IV) and 3.5 hours via a nasogastric tube (NG). The order of infusion was randomized among subjects. Alanine kinetics were calculated from the enrichments of plasma alanine 13C and expired 13CO2. The alanine appearance rate (Ra), measured during the IV tracer infusion, was 279+/-17 micromol/kg/h; 92%+/-2% of the IV-infused and 86%+/-2% of the NG-infused [1-13C]alanine tracer was recovered as 13CO2. From the difference in plasma alanine 13C enrichment between IV-infused and NG-infused tracers, we determined that the splanchnic bed extracted 69%+/-1% of the enterally delivered alanine tracer on the first pass during absorption. Only one third of the enteral alanine passed intact through the splanchnic bed and was made available to systemic tissues. Of the enteral alanine extracted, 83%+/-3% of the carboxyl-carbon label was recovered as CO2, leaving only 17% of the sequestered alanine available for use in splanchnic protein synthesis. Thus, the splanchnic bed, presumably the liver, extracts and metabolizes most of the enterally delivered alanine.

Obesity-related phenotypes and the beta3-adrenoceptor gene variant in postmenopausal women

We examined the hypothesis that postmenopausal women with the beta3-adrenoceptor gene variant (Trp64Arg) have reduced total daily energy expenditure (TEE), altered free fatty acid kinetics, and increased intra-abdominal fat. A secondary objective was to examine whether the obese state masks the effect of the variant on resting metabolic rate (RMR). There were 23 obese heterozygous women with the genetic variant (age 58 +/- 6 years; BMI 36 +/- 7 kg/m2) who were compared with 19 homozygous obese women with the normal allele (age 56 +/- 4 years; BMI 36 +/- 3 kg/m2). Daily energy expenditure was determined from doubly labeled water and indirect calorimetry, lipolysis from infusion of [1-13C]palmitate, and body fat distribution from computed tomography. No significant differences were found in TEE, RMR, energy expenditure of physical activity, the thermic effect of a meal, fat oxidation as estimated by fasting and postprandial respiratory quotients (RQs), or rate of lipolysis. Similarly, no difference was found in visceral adipose tissue and abdominal subcutaneous fat areas. When RMR was compared between obese (n = 23) and never-obese women with the Trp64Arg variant (n = 16), we found a 317 kcal/day lower RMR in never-obese women after controlling for fat mass, fat-free mass, and age (P < 0.0017). These results do not support the hypothesis that already obese women with the Trp64Arg polymorphism of the beta3-adrenergic receptor gene have lower daily energy expenditure, altered lipolysis, and increased abdominal obesity. On the other hand, the lower RMR in never-obese women suggests that the obese state may mask a moderate effect of the Trp64Arg variant on energy expenditure. Although these results need to be confirmed in other populations, the obese state may have been a confounding factor in previous studies of the beta3-adrenoceptor Trp64Arg variant and energy expenditure.

Assessment of physical activity in older individuals: a doubly labeled water study

We compared the accuracy of two physical activity recall questionnaires and a motion detector in 45- to 84-yr-old women (n = 35) and men (n = 32), using doubly labeled water (DLW) in conjunction with indirect calorimetry as the criterion measure. Subjects were administered the Yale Physical Activity Survey (YPAS) and Minnesota Leisure Time Physical Activity Questionnaire (LTA). Physical activity energy expenditure was determined over a 10-day period by using a Caltrac uniaxial accelerometer and DLW in conjunction with indirect calorimetry. In older women, Minnesota LTA (386 +/- 228 kcal/day) and Caltrac (379 +/- 162 kcal/day) underestimated physical activity by approximately 55% compared with DLW (873 +/- 244 kcal/day). No difference was observed between daily physical activity measured by the YPAS (863 +/- 447 kcal/day) and DLW in older women. In older men, Minnesota LTA (459 +/- 288 kcal/day) and Caltrac (554 +/- 242 kcal/day) underestimated daily physical activity by approximately 50-60% compared with DLW (1,211 +/- 429 kcal/day). No difference was found between physical activity measured by the YPAS (1,107 +/- 612 kcal/day) and DLW in older men. Despite no difference in mean physical activity levels between YPAS and DLW in women and men, Bland and Altman (Lancet 1: 307-310, 1986) analyses demonstrated poor concordance between DLW and YPAS (i.e., limits of agreement = -1,310-1,518 kcal/day). Our data suggest that the Minnesota LTA recall and Caltrac uniaxial accelerometer may significantly underestimate free-living daily physical activity energy expenditure in older women and men. Although the YPAS compares favorably with DLW on a group basis, its use as a proxy measure of individual daily physical activity energy expenditure may be limited in older women and men.

Epinephrine produces a prolonged elevation in metabolic rate in humans

BACKGROUND

Epinephrine increases the metabolic rate and contributes to the hypermetabolic state in severe illness.

OBJECTIVE

We sought to determine the effect of prolonged elevation of epinephrine on resting energy expenditure (REE).

DESIGN

Thirteen healthy men were placed on a well-defined diet for 5 d. Beginning on the morning of the second diet day, the subjects were infused for 24 h with saline, then for 23 h with epinephrine (0.18 nmol x kg(-1) x min(-1)) to increase plasma epinephrine concentrations into the high physiologic range (4720 +/- 340 pmol/L). REE and the respiratory quotient (RQ) were measured by indirect calorimetry in the postabsorptive state at the same time every morning.

RESULTS

Infusion of epinephrine significantly increased heart rate and systolic blood pressure, but the response was transient (values after 23 h of epinephrine infusion were not significantly different from those on the day saline was infused). Infusion of epinephrine significantly increased REE by 12% and increased the RQ. These changes were apparent at the end of the 23-h infusion (REE: 97.5 +/- 2.3 kJ x kg(-1) x d(-1) with saline infusion and 108.9 +/- 2.3 kJ x kg(-1) x d(-1) with epinephrine infusion; RQ: 0.832 +/- 0.012 with saline infusion and 0.879 +/- 0.013 with epinephrine infusion). REE returned to baseline by 24 h after the epinephrine infusion ended, but the postabsorptive RQ remained modestly elevated. Infusion of epinephrine also produced a transient increase in urine flow and in urinary nitrogen excretion. This diuresis was compensated for by a drop in urine volume and nitrogen excretion after the epinephrine infusion was stopped.

CONCLUSIONS

Epinephrine produced a prolonged increase in REE in healthy subjects. The fuel for this increase in REE, determined by the RQ, was from increased carbohydrate oxidation, not from that of fat or protein.

Trp64Arg variant of the beta3-adrenoceptor and insulin resistance in obese postmenopausal women

There is controversy regarding the role of the Trp64Arg variant of the beta3-adrenergic receptor (beta3AR) gene in the pathogenesis of insulin resistance. The modest effect of the variant as well as differences in study design, gender, age, and genetic background may contribute to divergent results among investigations. Insulin sensitivity (euglycemic clamp and tracers) was measured in 13 obese women (57 +/- 6 yr old) heterozygous for the beta3AR variant and in 14 women (57 +/- 4 yr old) homozygous for the normal gene. Groups were matched for age, body composition, intraabdominal fat, sc abdominal fat, physical activity level, and aerobic capacity. Exogenous glucose infusion during the clamp was significantly lower (P = 0.03) in beta3AR heterozygotes (241 +/- 135 mg/min) vs. normal homozygotes (379 +/- 172 mg/min). Basal endogenous glucose production was not different (P = 0.20) between heterozygotes (175 +/- 27 mg/min) and normal homozygotes (164 +/- 14 mg/min). Endogenous glucose production during hyperinsulinemia was also not different (P = 0.22) between heterozygotes (77 +/- 57 mg/min) and normal homozygotes (56 +/- 16 mg/min). Total glucose disposal adjusted for residual endogenous glucose production was lower (P = 0.049) for heterozygotes (320 +/- 111 mg/min) than for normal homozygotes (441 +/- 183 mg/min). Our results suggest that obese postmenopausal women who are heterozygous for the Trp64Arg variant in the beta3AR gene have greater insulin resistance than age-, body composition-, and physical activity-matched women homozygous for the normal gene.

Literacy and body fatness are associated with underreporting of energy intake in US low-income women using the multiple-pass 24-hour recall: a doubly labeled water study

OBJECTIVE

The accuracy of the multiple-pass 24-hour recall method for estimating energy intake in low-income women in the United States was ascertained by comparing the method with measurements of total energy expenditure. The multiple-pass 24-hour recall is designed to provide respondents with multiple cues and opportunities to report their food intake. It consists of 3 distinct passes: the quick list, detailed description, and review. Predictors of energy intake misreporting (energy intake--total energy expenditure) in the sample were determined.

DESIGN

Four multiple-pass 24-hour recalls (2 in person, 2 by telephone) were obtained over a 14-day period to estimate energy intake. Total energy expenditure was measured over the same 14-day period using the doubly labeled water method. Body composition was measured using dual energy x-ray absorptiometry, and literacy was measured by the Wide Range Achievement Test (WRAT) for reading and spelling.

SUBJECTS/SETTINGS

Thirty-five low-income women between the ages of 19 and 46 years were tested at the General Clinical Research Center at the University of Vermont, Burlington. Low income was defined as a household income at or below 130% of the federal poverty level.

STATISTICAL ANALYSIS

Pearson product moment correlation coefficients, t tests, paired t tests, and stepwise multiple regression analysis were used to test the relationships among study variables.

RESULTS

Mean energy intake was significantly lower than mean total energy expenditure (2,197 +/- 607 vs 2,644 +/- 503 kcal, P = .001) and the correlation between the 2 measures was poor (r = .22, P = .20). Percentage body fat and the combined age-adjusted reading and spelling WRAT scores were the best predictors of misreporting of energy intake (R = .52, P = .006).

CONCLUSIONS

The multiple-pass 24-hour recall did not generate a group measure of energy intake that was accurate or unbiased in this sample. Underreporting was strongly associated with increased body fatness. The ability to read and spell as measured by the WRAT improved the accuracy of the women's recall of their food intake.

APPLICATIONS

Dietetics professionals should take into consideration the problem of underreporting whenever conclusions are made about associations between diet and health and/or when evaluating the impact of food assistance programs on dietary intake.

Energy requirements and physical activity in free-living older women and men: a doubly labeled water study

Determinants of daily energy needs and physical activity are unknown in free-living elderly. This study examined determinants of daily total energy expenditure (TEE) and free-living physical activity in older women (n = 51; age = 67 +/- 6 yr) and men (n = 48; age = 70 +/- 7 yr) by using doubly labeled water and indirect calorimetry. Using multiple-regression analyses, we predicted TEE by using anthropometric, physiological, and physical activity indexes. Data were collected on resting metabolic rate (RMR), body composition, peak oxygen consumption (VO2 peak), leisure time activity, and plasma thyroid hormone. Data adjusted for body composition were not different between older women and men, respectively (in kcal/day): TEE, 2,306 +/- 647 vs. 2,456 +/- 666; RMR, 1,463 +/- 244 vs. 1,378 +/- 249; and physical activity energy expenditure, 612 +/- 570 vs. 832 +/- 581. In a subgroup of 70 women and men, RMR and VO2 peak explained approximately two-thirds of the variance in TEE (R2 = 0.62; standard error of the estimate = +/-348 kcal/day). Crossvalidation of this equation in the remaining 29 women and men was successful, with no difference between predicted and measured TEE (2,364 +/- 398 and 2,406 +/- 571 kcal/day, respectively). The strongest predictors of physical activity energy expenditure (P < 0.05) for women and men were VO2 peak (r = 0.43), fat-free mass (r = 0.39), and body mass (r = 0.34). In summary, RMR and VO2 peak are important independent predictors of energy requirements in the elderly. Furthermore, cardiovascular fitness and fat-free mass are moderate predictors of physical activity in free-living elderly.

Absence of glutamine isotopic steady state: implications for the assessment of whole-body glutamine production rate

1. During infusion of [5-15N]glutamine in patients with gastrointestinal cancer we unexpectedly observed a gradual decrease in time of the appearance rate (Ra) of glutamine in plasma. Here we investigate whether the failure to achieve a plateau isotopic enrichment in plasma is, among other factors, due to incomplete equilibration of the glutamine tracer with the large intramuscular free glutamine pool.2. Plasma and intramuscular glutamine enrichment were measured during 6-11 h infusions of L-[5-15N]glutamine and L-[1-13C]glutamine in post-absorptive patients admitted to hospital for elective abdominal surgery. L-[1-13C]Leucine and L-[ring-2H5]phenylalanine were infused to measure the proportion of glutamine appearing in plasma directly due to its release from protein.3. The glutamine tracer entered muscle, but the rise in intramuscular glutamine enrichment was small, presumably as a result of the enormous size of the intramuscular glutamine pool and the limited speed of entry of glutamine into muscle. In each patient the intramuscular glutamine enrichment was lower than that in plasma (P<0.001), and both increased with tracer infusion time (P<0.001), indicating incomplete equilibration of the glutamine tracer.4.A comparison of the results obtained by the two glutamine tracers indicated that recycling of the nitrogen label contributed to about 15% of the decrease in Ra.5. There was a gradual reduction in the glutamine release from proteolysis, which contributed to 16-21% of the decline in Ra.6. We conclude that slow equilibration of the glutamine tracer with the large muscle glutamine pool significantly contributes to the absence of isotopic steady state. Consequently, the appearance rate of glutamine in plasma measured during short tracer infusion periods (hours) considerably overestimates the whole-body glutamine flux.

Insulin resistance in cirrhosis: prolonged reduction of hyperinsulinemia normalizes insulin sensitivity

Insulin resistance is present in nearly all patients with cirrhosis, but its etiology remains unknown. Chronic hyperinsulinemia has been suspected as a potential candidate, and we therefore tested the hypothesis that, in cirrhosis, prolonged reduction of the hyperinsulinemia restores insulin sensitivity. Whole-body insulin sensitivity (euglycemic insulin-clamp technique), glucose turnover (6,6-2H2-glucose isotope dilution), glucose oxidation (indirect calorimetry), non-oxidative glucose disposal, and fractional glycogen synthase activity in muscle (biopsies) were measured in eight clinically stable patients with cirrhosis before and at the end of a 4-day continuous subcutaneous infusion of the somatostatin-analogue octreotide (200 microg/24 h) designed to continuously reduce plasma insulin levels. Baseline data were compared with results obtained in healthy individuals matched for sex, age, and weight (n = 8). During the baseline (pre-octreotide) study, patients demonstrated a significant decrease in insulin-mediated glucose uptake compared with controls (5.75 +/- 0.21 vs. 7.98 +/- 0.84 mg/kg/min; P < .03), which was entirely accounted for by an impairment in non-oxidative glucose disposal (P < .04). Four-day infusion of octreotide to cirrhotic patients: 1) reduced postabsorptive and meal-stimulated plasma insulin levels by approximately 35% to 45% without significantly affecting glucose tolerance; 2) did not significantly alter plasma free fatty acids (FFA), growth hormone, and glucagon levels in the postabsorptive state and during the meal test; 3) normalized insulin-mediated whole-body glucose disposal (7.63 +/- 0.72 mg/kg/min post-octreotide; P = not significant vs. control). Restoration of insulin-mediated glucose utilization was entirely caused by normalization of non-oxidative glucose disposal; 4) was associated with a considerably more pronounced stimulation by insulin of the fractional glycogen synthase in muscle compared with pre-octreotide results (increment above baseline pre: 0.035 +/- 0.010 vs. post: 0.060 +/- 0.023 nmol/min/mg protein; P < .04). Fractional glycogen activity significantly correlated with non-oxidative glucose disposal during insulin infusion (r = .69; P < .03). Prolonged reduction of hyperinsulinemia for 96 hours in cirrhotic patients normalizes insulin-mediated glucose uptake and glycogen synthesis in muscle. We conclude that chronic hyperinsulinemia causes insulin resistance in cirrhosis.

Glucagon increases glutamine uptake without affecting glutamine release in humans

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.

Energy requirements and physical activity of older free-living African-Americans: a doubly labeled water study

We examined daily energy requirements and determinants of physical activity in older, free-living African-American women (n = 37; age, 64 +/- 8 yr) and men (n = 28; age, 64 +/- 7 yr). Total daily energy expenditure and its components [i.e. resting metabolic rate (RMR) and physical activity energy expenditure] were determined using doubly labeled water and indirect calorimetry. Body composition from dual energy x-ray absorptiometry, maximal oxygen consumption from a graded treadmill test, and leisure time physical activity from a structured interview were determined. Total daily energy expenditure adjusted for body composition was lower (P < 0.05) for women (2198 +/- 621 kcal/d) than for men (2633 +/- 669 kcal/d) due to a lower RMR (1431 +/- 240 vs. 1576 +/- 259 kcal/d; P = 0.07) and physical activity energy expenditure (548 +/- 559 vs. 794 +/- 603 kcal/d; P = 0.19), respectively. The physical activity level ratio (i.e. total daily energy expenditure/RMR) was not different from Food and Agriculture Organization/World Health Organization/United Nations University recommendations (i.e. 1.51) for women (1.51 +/- 0.25), but was higher for men (1.71 +/- 0.32). The strongest correlates with physical activity energy expenditure were age for women (r = -0.44; P < 0.01) and maximal oxygen consumption for men (r = 0.39; P < 0.05). These data show that daily energy requirements are significantly lower in African-American women compared to men, primarily due to lower levels of physical activity energy expenditure. Furthermore, lower levels of cardiovascular fitness in men and advancing age in women are associated with lower physical activity energy expenditure.

Metabolism of parenterally administered fat emulsions in the rat: studies of fatty acid oxidation with 1-13C- and 8-13C-labelled triolein

To reassess the hypothesis that fatty acid catabolism occurs to completion via beta-oxidation, male Sprague-Dawley rats receiving continuous total parenteral nutrition (TPN) including 43% energy as fat were infused with [1-(13)C]- or [8-(13)C]triolein. Expired CO2 was collected continuously for 4 h and its 13C:12C ratio determined by isotope-ratio mass spectrometry. Bicarbonate retention was also assessed over 4 h by infusion of NaH14CO3 and measurement of the expired 14CO2. A possible loss of label from [8-(13)C]oleic acid from the citric acid cycle via labelled acetyl-CoA without oxidation to CO2 was assessed by infusing further animals with acetate labelled with 14C either at C atoms 1 or 2 and determination of its conversion to expired 14CO2. At isotopic steady state, 63.2 (SE 1.6)% (n 8) of the infused [1-(14)C]acetate and 46.0 (SE 1.2)% (n 8) of [2-(14)C]acetate was recovered as expired 14CO2. After correction for bicarbonate retention and non-oxidative isotope loss, 37.3 (SE 1.2)% (n 20) of the [1-(13)C]triolein was found to have been oxidized, whereas 32.6 (SE 1.0)% (n 20) of the [8-(13)C]triolein was oxidized (P < or = 0.01). The lower oxidation of the C atom at position 8 of oleic acid than that at position 1 indicates incomplete oxidative breakdown of the fatty acid after entering beta-oxidation.

Urinary 3-methylhistidine excretion: association with total body skeletal muscle mass by computerized axial tomography

BACKGROUND

The urinary excretion of endogenous 3-methylhistidine (3-MH) has been proposed as a predictor of skeletal muscle mass (SM). In this study, we report the relationship between 24-hour urinary 3-MH excretion and SM.

METHODS

Total body SM was measured by multiscan computerized axial tomography (CT) in a sample of 10 healthy adult men who followed a meat-free diet for 7 days. 3-MH was measured during the last 3 days of the meat-free diet protocol on consecutive 24-hour urine collections.

RESULTS

The 3-MH excretion was 216.3 +/- 44.7 mumol/d (mean +/- SD) and was found well associated with SM (in kilograms), SM = 0.0887 x 3-MH + 11.8; r = .88, p < .001. Compared with CT, the previous 3-MH-SM prediction equation suggested by Lukaski et al underestimated SM by an average of 8.9 kg in the 10 healthy men. This difference was caused by the Burkinshaw-Cohn neutron activation model, which underestimated SM and was used as the reference in the Lukaski method.

CONCLUSIONS

Twenty-four-hour urinary 3-MH excretion can be applied for estimating SM in healthy adult men on a meat-free diet.

Effect of moderate exercise on insulin sensitivity and substrate metabolism during post-exercise recovery in cirrhosis

We examined whether a single bout of moderate exercise has a beneficial effect on insulin sensitivity and fuel homeostasis in cirrhosis. Clinically stable cirrhotic patients and age-, sex-, and weight-matched controls participated in insulin clamp studies (either euglycemic hyperinsulinemic or hyperglycemic hyperinsulinemic) in combination with indirect calorimetry and [6,6-2H2]glucose. Three to seven days later, studies were repeated following a single bout of exercise (30 minutes of treadmill exercise at 60% of maximal aerobic capacity). After an overnight fast, following exercise, both cirrhotic and control individuals showed a shift in fuel utilization to enhanced lipid oxidation, decreased glucose oxidation, and increased nonoxidative glucose disposal rates (i.e., glycogen synthesis in muscle) when compared with pre-exercise rates but differences were statistically significant only in the patient group. During euglycemic hyperinsulinemia, insulin-mediated glucose disposal was significantly reduced in cirrhotic patients (3.43 +/- 0.26 vs. 7.36 +/- 0.48 mg/kg/min, P < .01). Following exercise, glucose uptake increased significantly in cirrhotic patients when compared with pre-exercise levels (P < .05) but remained unchanged in the control group. The increase in total body glucose disposal in cirrhotic patients was entirely accounted for by an increase in nonoxidative glucose disposal (0.81 +/- 0.20 vs. 0.51 +/- 0.15 mg/kg/min, P < .05). During combined hyperglycemia/hyperinsulinemia, however, insulin sensitivity was unaffected by exercise in both patients and control individuals. In summary, in cirrhotic patients, a single bout of moderate exercise 1) causes a shift in substrate utilization with an increase in lipid oxidation in the postexercise period that is significantly more pronounced than in controls, and 2) increases insulin sensitivity only during euglycemia but not during the more physiological condition of hyperglycemia. Single bouts of moderate exercise therefore may not have a beneficial effect on the metabolic status of patients with chronic liver disease.

Epinephrine does not impair utilization of exogenous amino acids in humans

The effect of epinephrine on leucine and phenylalanine kinetics was measured by using the stable isotope amino acid tracers L-[1-(13)C]leucine and L-[phenyl-2H5]-phenylalanine in the postabsorptive state and during the intravenous administration of a standard amino acid solution with respect to the amino acid load. Infusion of epinephrine (plasma concentration: approximately 3600 pmol/L) decreased leucine and phenylalanine and increased ketoisocaproate plasma concentrations and increased the metabolic clearance rate of leucine and phenylalanine. Epinephrine neither influenced leucine or phenylalanine flux nor leucine oxidation or leucine net balance. Hyperaminoacidemia from amino acid infusion reduced endogenous leucine release and stimulated leucine oxidation and nonoxidative disposal of leucine, resulting in a dose-dependent increase in leucine net balance. Epinephrine did not influence any changes in amino acid kinetics during parenteral amino acid administration. Therefore, we conclude that epinephrine had no catabolic effects on amino acid metabolism and no negative effect on the utilization of a parenterally offered amino acid solution in healthy humans.

Effects of amino acids on synthesis and degradation of skeletal muscle proteins in humans

Synthesis and degradation of globular and myofibrillar proteins across arm and leg muscles were examined during stepwise increased intravenous infusion of amino acids (0.1, 0.2, 0.4, and 0.8 g N.kg-1.day-1) to healthy volunteers. Protein dynamics were measured by a primed constant infusion of L-[ring-2H5]phenylalanine and the release of 3-methylhistidine from skeletal muscles. Arterial concentrations and flux of glucose, lactate, and free fatty acids were unchanged despite increasing concentrations of plasma amino acids from 2.6 to 5.7 mM. Plasma insulin, insulin-like growth factor I (IGF-I), and plasma concentrations of IGF-I-binding proteins-1 and -3 remained at fasting levels throughout the investigation. Amino acid infusion caused a significant uptake of the majority of amino acids across arm and leg tissues, except tyrosine, tryptophan, and cysteine, probably due to low concentrations of these amino acids in the formulation. The balance of globular proteins improved significantly (P < 0.01) due to stimulation of synthesis and attenuation of degradation across arm and leg tissues, despite insignificant uptake of tyrosine, tryptophan, and cysteine. Degradation of myofibrillar proteins was uninfluenced by provision of amino acids. The results demonstrate that neither insulin nor circulating IGF-I explained improved protein balance in skeletal muscles after elevation of plasma amino acids. Rather, some amino acids in themselves trigger cellular reactions that initiate peptide formation. Limited availability of some extracellular amino acids was overcome by increased reutilization of the intracellular amino acid.

Total-body skeletal muscle mass: evaluation of 24-h urinary creatinine excretion by computerized axial tomography

A classic body-composition method is estimation of total-body skeletal muscle mass (SM, in kg) from 24-h urinary creatinine excretion (in g). Two approaches of unknown validity have been used to calculate SM from creatinine: one assumes a constant ratio of SM to creatinine, the so-called creatinine equivalence (k), and that SM = k x creatinine; the other suggests a highly variable ratio of SM to creatinine and is based on regression equations of the form SM = b + a x creatinine. We explored these two extreme possibilities by measuring SM with whole-body computerized axial tomography and collecting urinary creatinine during meat-free dietary conditions in 12 healthy adult men. Prediction equations were developed in the men that fit these two models: SM = 21.8 x creatinine (SD and CV of the ratio of SM to creatinine: 1.3 kg and 6.0%, respectively) and SM = 18.9 x creatinine + 4.1 (r = 0.92, P = 2.55 x 10(-5), SEE = 1.89 kg). The validity of each model is reviewed in the context of theoretical aspects of creatine-creatinine metabolism. This first investigation of the method of measuring urinary creatinine excretion to determine SM by using modern techniques raises important practical and basic questions related to SM prediction.

Analysis of blood donor return behaviour using survival regression methods

The acquisition of a sufficient and safe supply of blood products is required to support modern medical care; in most countries this has meant a reliance on voluntary, nonremunerated blood donors. Recent reported shortages in the United States and elsewhere have highlighted the need for a method to measure and evaluate blood donor return behaviour. This paper describes a framework within which standard time-to-outcome methods can be used to analyse blood donor return behaviour. Survival curves and relative risk estimates derived from a proportional hazards analysis of a large administrative dataset are reported. In addition to assessing the effect of sex, age and other key donor demographic factors on the probability of a subsequent donation attempt, the analysis reveals that the relative risks are time-dependent. This suggests that the likelihood of attempting a subsequent donation may also depend on the time since the index donation attempt. The implications for blood collection agencies and transfusion researchers of this new perspective on donor behaviour are discussed.

A comparative study of different means of assessing long-term energy expenditure in humans

We compared three independent techniques for measurement of total energy expenditure (TEE) in human subjects: 1) weight-maintaining energy intake (dietTEE), 2) 24-h chamber calorimetry (chamberTEE), and 3) differential elimination rates 2H2O and H(2)18O (isotopeTEE). Twenty-three healthy adult in-patients [19 never obese (NO), 2 obese (OB), and 2 formerly-obese (RO); 9 female, 14 malel] ingested a liquid formula diet (40% of calories as fat, 45% carbohydrate, 15% protein), the volume of which was adjusted until body weight was stable for at least 14 days. Body composition was then determined by hydrodensitometry, isotope dilution, and dual photon beam absorptiometry (DXA). The thermic effect of feeding (TEF) and resting energy expenditure [REE; measured before arising (dietREE) and after arising (chamberREE)] were determined by indirect calorimetry. Non-resting energy expenditure (NREE) was calculated as NREE = TEE - (REE + TEF). Subjects then gained or lost 10% of their body weight and were restudied as described above. All measures of TEE were significantly correlated (dietTEE vs. chamberTEE r2 = 0.75; dietTEE vs. isotopeTEE r2 = 0.88; isotopeTEE vs. chamberTEE r2 = 0.73; P < 0.0001). ChamberTEE (mean +/- SE = 2,107 +/- 64 kcal/day) was approximately 20% lower than either dietTEE (2,536 +/- 94 kcal/day, P < 0.0001) or isotopeTEE (2,564 +/- 83 kcal/day, P < 0.0001). When data were normalized to metabolic mass, weight gain of 10% was associated with significant increases in dietTEE (P < 0.005) and isotopeTEE (P < 0.05) but not chamberTEE; weight loss of 10% was associated with significant reductions in dietTEE (P < 0.005) and isotopeTEE (P < 0.05) but not chamberTEE. We conclude that measures of energy expenditure obtained in a highly controlled environment by caloric titration (dietTEE) or differential excretion rates of 2H2O and H(2)18O (isotopeTEE) are not significantly different and that measurements of TEE obtained in a respiratory chamber (chamberTEE) are significantly lower than dietTEE or isotopeTEE, probably largely due to limitations on physical activity in the chamber.

Unexplained disturbance in body weight regulation: diagnostic outcome assessed by doubly labeled water and body composition analyses in obese patients reporting low energy intakes

SUBJECTS

Ten patients who had long-term disturbances in body weight regulation, were referred over a 3-year period for obesity evaluation, and reported low energy intakes (< 1,200 kcal/day).

OBJECTIVE

To ascertain whether these patients had a low energy expenditure and thus reduced energy requirement, and/or whether they were misreporting their energy intake.

DESIGN

Comparison of outcome measures in referred patients and in obese control patients who did not report low energy intakes and disturbances in body weight regulation.

MAIN OUTCOME MEASURES

Low energy expenditure was evaluated with serum thyroid hormone levels, resting metabolic rate (RMR), thermic effect of food (TEF), and total energy expenditure (TEE) by doubly labeled water technique. Misreporting of energy intake was evaluated by comparing patients' self-reported energy intake with energy intake estimated by doubly labeled water and body composition analyses over a 14-day period.

STATISTICAL ANALYSES PERFORMED

Low energy expenditure was considered present in a patient if RMR or TEE was more than 15% below predicted values according to results from the control group. Patient group TEF was compared with TEF results observed in the control group.

RESULTS

All patients had normal serum thyroid hormone levels. Eight patients had RMR and TEE values within 15% of predicted values and were substantially underreporting their energy intake. One patient had low TEE (-19%) and a normal RMR, a finding that implies a low level of physical activity. This patient also underreported energy intake as estimated by the doubly labeled water technique during the study (-38%). The 10th patient had a low RMR (-23.2%) and TEE (-25.0%), the mechanism of which was uncertain. This patient's reported food intake over the 14-day period was accurate but was less than her long-term intake over months or years as suggested by doubly labeled water TEE estimates. The TEF response in patients was not significantly different from that observed in the control group.

CONCLUSIONS

Underreporting of energy intake from foods is a frequent finding in patients with disturbances in body weight regulation who are referred for obesity evaluation. Severe underreporting may be detectable by means of screening measures available to most dietitians. Low energy expenditure, due either to physical inactivity or to metabolic factors, is also observed. Modern evaluation methods provide new insights into patients with weight regulatory disturbances and at the same time stimulate important new research questions.

Metabolic and clinical response to recombinant human insulin-like growth factor I in myotonic dystrophy--a clinical research center study

Muscle weakness and wasting in myotonic dystrophy (MyD) are believed to be due to a decrease in muscle protein synthesis, secondary to insulin resistance. A 4-month, randomized, double blind, placebo-controlled trial was undertaken to assess whether recombinant human insulin-like growth factor I (rhIGF-I) may overcome the insulin resistance. Patients received either 5 mg rhIGF-I (n = 7) or placebo (n = 9), sc, twice daily. Glucose metabolism was assessed by stable label iv glucose tolerance test, amino acid metabolism by L-[13C] leucine turnover, body composition by dual energy x-ray absorptiometry and N excretion, and muscle response by manual muscle strength and neuromuscular function. In the treated group, the insulin sensitivity index, insulin action, and glucose disposal all increased (P < 0.05). Leucine flux and leucine incorporation into protein increased (P < 0.05), and the rate of leucine oxidation to leucine turnover decreased (P < 0.05), findings indicative of increased protein synthesis. Body weight and lean body mass increased, whereas percent body fat decreased (P < 0.05). An increase in manual muscle strength of 0.42 +/- 0.30 (P < 0.02) and in neuromuscular function of 17.5 +/- 11.7 (P < 0.02) occurred in the four patients who received a rhIGF-I dose greater than 70 micrograms/kg, whereas a more modest response occurred in the three patients who received a dose less than 70 micrograms/kg. Two patients showed dramatic improvement. Long term rhIGF-I therapy appears to cause metabolic and muscle improvement in optimally treated MyD patients.

Oxidation of glutamic acid by the splanchnic bed in humans

[1,2-13C2]glutamate and [ring-2H5]phenylalanine were infused for 7 h into postabsorptive healthy subjects on two occasions. The tracer infusion was by the intravenous route for 3.5 h and by the nasogastric route for 3.5 h. The order of tracer infusion routes was switched between the two occasions. From the plasma tracer enrichment measurements at plateau during the intravenous and enteral infusion periods, we determined that 33 +/- 3% of the enterally delivered phenylalanine and 96 +/- 1% of the glutamate were removed on the first pass by the splanchnic bed; 78 +/- 3% of the enterally delivered [13C]glutamate tracer was recovered as exhaled CO2 compared with 79 +/- 2% of the intravenously infused tracer. The fraction of the enterally delivered tracer that was sequestered specifically on the first pass by the splanchnic bed was 75 +/- 2%. These results verify the previously reported large uptake of [15N]glutamate by the splanchnic bed [Matthews et al. Am. J. Physiol. 264 (Endocrinol. Metab. 27): E848-E854, 1993] and demonstrate that the uptake of tracer is not due to an artifactual loss of the 15N tracer by reversible transamination but to glutamate uptake for oxidation.

Effect of cortisol on energy expenditure and amino acid metabolism in humans

Hydrocortisone was infused overnight into nine normal healthy adults on three occasions at 0, 80, and 200 micrograms.kg-1.h-1, producing plasma cortisol concentrations of 10.6 +/- 1.2, 34.0 +/- 2.0, and 64.9 +/- 4.3 micrograms/dl, respectively. L-[1-13C]leucine, L-[phenyl-2H5]phenylalanine, and L-[2-15N]glutamine were infused during the last 7 h of hypercortisolemia to measure amino acid kinetics. During the last 3.5 h, somatostatin, glucagon, and insulin were infused to reduce the cortisol-induced elevation in plasma insulin to basal. Hypercortisolemia increased plasma glucose, free fatty acid (FFA), and insulin concentrations. Institution of the somatostatin clamp returned insulin to basal but increased glucose and FFA. Acute hypercortisolemia increased protein breakdown 5-20%, as measured by increases in leucine and phenylalanine appearance rates. Normalizing insulin during hypercortisolemia did not alter phenylalanine flux but enhanced leucine appearance rate, the latter result indicating that insulin was affecting leucine metabolism during hypercortisolemia. The fraction of the leucine flux that was oxidized was not significantly increased with hypercortisolemia, but disposal by the nonoxidative route of leucine uptake for protein synthesis was increased. Hypercortisolemia increased cycling of amino acids by increasing protein breakdown and synthesis, but the increase in this process could have increased resting energy expenditure (REE) only 1-2%. Hypercortisolemia increased glutamine flux in a dose-dependent fashion through an increase in de novo synthesis, which presumably reflects increased release from skeletal muscle. Hypercortisolemia increased REE 9-15% at the 80 and 200 micrograms.kg-1.h-1 infusion rates. Respiratory quotient did not rise with cortisol infusion but tended to decrease, suggesting that the increase in REE was fueled by increased oxidation of fat. These data demonstrate that hypercortisolemia increases metabolic rate and may be in part responsible for the hypermetabolic state in injury.