Postexercise nutrient intake timing in humans is critical to recovery of leg glucose and protein homeostasis.

Although the importance of postexercise nutrient ingestion timing has been investigated for glycogen metabolism, little is known about similar effects for protein dynamics. Each subject (n = 10) was studied twice, with the same oral supplement (10 g protein, 8 g carbohydrate, 3 g fat) being administered either immediately (EARLY) or 3 h (LATE) after 60 min of moderate-intensity exercise. Leg blood flow and circulating concentrations of glucose, amino acids, and insulin were similar for EARLY and LATE. Leg glucose uptake and whole body glucose utilization (D-[6,6-2H(2)]glucose) were stimulated threefold and 44%, respectively, for EARLY vs. LATE. Although essential and nonessential amino acids were taken up by the leg in EARLY, they were released in LATE. Although proteolysis was unaffected, leg (L-[ring-2H(5)]phenylalanine) and whole body (L-[1-13C]leucine) protein synthesis were elevated threefold and 12%, respectively, for EARLY vs. LATE, resulting in a net gain of leg and whole body protein. Therefore, similar to carbohydrate homeostasis, EARLY postexercise ingestion of a nutrient supplement enhances accretion of whole body and leg protein, suggesting a common mechanism of exercise-induced insulin action.

Determination of stable isotopic enrichment and concentration of glycerol in plasma via gas chromatography-mass spectrometry for the estimation of lipolysis in vivo.

Measuring glycerol's rate of appearance into the plasma compartment provides an excellent estimation of whole-body lipolysis. The glycerol rate of appearance can be calculated by estimating the plasma dilution of continuously infused stable or radioactive isotopes of glycerol. Previously, determination of glycerol stable isotopic enrichment has required either chemical ionization gas chromatography-mass spectrometry (GC-MS) or electron impact ionization GC-MS in which a fragment containing only a portion of the glycerol molecule was measured. The present method uses tert.-butyldimethylsilyl (tBDMS) derivatization and electron impact ionization to measure a fragment including the entire glycerol molecule. The method determines concentration and enrichment of plasma glycerol in a simple, precise, and cost-efficient manner, providing a basis from which lipid homeostasis can be assessed.

A comparison of air displacement plethysmography with three other techniques to determine body fat in healthy adults.

BACKGROUND: This study compared air displacement plethysmography (ADP), which relies on measurements of body density to estimate body fat, with three other techniques that measure body composition: (1) hydrostatic weighing (HW), which also measures body density; (2) bioelectrical impedance (BIA), which determines electrical resistance and total body water to estimate fat-free mass; and (3) dual-energy x-ray absorptiometry (DXA), which measures bone, fat, and fat-free soft tissue masses. METHODS: ADP, HW, BIA, and DXA were performed on 20 healthy volunteers (10 males and 10 females). The subjects were within 20% of ideal body weight, 31.1 +/- 1.8 years of age, and 75.4 +/- 2.7 kg with body mass index values of 25.2 +/- 0.9 (kg/m2) and percent body fat by ADP ranging from 6.0% to 41.0%. RESULTS: Percent body fat measurements by the four methods were highly correlated (r > .90, p < .0001). Mean body fat as determined by ADP, HW, BIA, and DXA were 23.4% +/- 2.3%, 23.9% +/-1.8%, 23.1% +/- 1.9%, and 26.4% +/- 2.4%, respectively (* p < .05 vs ADP). There was a significantly positive slope (+0.23) for the individual differences vs the average of ADP and HW percent body fat, demonstrating a slightly negative difference at lower body fat levels and a slightly positive difference at greater body fat levels. Although the average percent body fat determined by ADP was similar to that by HW for the entire population, there was a significant gender difference with the average body fat measured by ADP being 16% less in males and 7% greater in females than that determined by HW. CONCLUSIONS: Body fat measurements using ADP were highly correlated with those using HW, BIA, and DXA across a relatively wide range of body fat levels in healthy adults. These results support the utility of ADP as a relatively new technique in the estimation of percent body fat in healthy adults. However, the error associated with gender and the level of body fat is not negligible and requires further investigation.

Parenteral glutamine infusion alters insulin-mediated glucose metabolism.

BACKGROUND: Glutamine is a conditionally essential amino acid that is critical for many basic cellular processes. Its supplementation has been found to be beneficial during several critical illnesses. This study examines the effects of increased glutamine availability on insulin-mediated glucose homeostasis in vivo in multicatheterized conscious canines (n = 5). METHODS: Two weeks before the study, catheters were placed in the femoral artery and the portal, hepatic, femoral, and renal veins for blood sampling and in the splenic vein for intraportal infusion of insulin and glucagon. Doppler probes were placed to measure blood flow. The metabolic study consisted of equilibration, basal, and experimental periods during which [3-3H]glucose was infused to measure glucose kinetics. During the 5-hour experimental period, a hyperinsulinemic-euglycemic clamp was performed by infusing somatostatin, basal glucagon, fivefold basal insulin, and glucose to maintain euglycemia. The experimental period was divided evenly into two subperiods performed in random order: (1) i.v. glutamine infusion (0.72 mmol kg(-1) h(-1)) and (2) i.v. saline infusion. RESULTS: With glutamine, the glucose required to maintain euglycemia was increased 46% over saline (6.8 +/- 1.0 to 9.9 +/- 1.7 mg kg(-1) min(-1). In addition, whole-body glucose production and utilization were increased by 1.4 and 4.6 mg kg(-1) min(-1), respectively. Finally, the increase in whole-body glucose utilization was manifested by increased hepatic and hindlimb glucose utilization. CONCLUSIONS: Increased glutamine availability blunted insulin's action on glucose production and enhanced insulin-mediated glucose utilization with the changes in utilization being threefold greater than the changes in production. Thus parenteral glutamine has potential benefit as a nutrient adjuvant during clinical situations associated with insulin resistance.

Protein turnover and energy expenditure increase during exogenous nutrient availability in sickle cell disease.

In the present study, energy expenditure (EE) and rates of whole-body protein, glucose, and lipid metabolism were assessed in 8 African American sickle cell disease (SCD) patients and in 6 healthy African American control subjects during the infusion of amino acids, glucose, and lipid. Whole-body protein, glucose, and lipid kinetics were estimated by using L-[1-(13)C]leucine, D-[6,6-(2)H2]glucose, and [(2)H5]glycerol, respectively. After a 2-h tracer equilibration period and a 0.5-h basal period, nutrients were administered intravenously for 3 h with 16% of the energy as protein, 52% as carbohydrate, and 32% as fat. Breath and blood were collected during the last 30 min of nutrient infusion and EE was measured by indirect calorimetry. EE was 14% greater (P < or = 0.05) in SCD patients [145.0 +/- 3.5 kJ x kg fat-free mass (FFM)(-1) x d(-1)] than in control subjects (126.8 +/- 3.8 kJ x kg FFM(-1) x d(-1)). Whole-body protein breakdown (4.4 +/- 0.4 compared with 3.1 +/- 0.1 mg x kg FFM(-1) x min(-1), P < or = 0.05) and protein synthesis (4.6 +/- 0.4 compared with 3.2 +/- 0.1 g x kg FFM(-1) x min(-1), P < or = 0.05) were 42% and 44% greater, respectively, in the SCD patients than in control subjects, but whole-body amino acid oxidation (0.90 +/- 0.05 compared with 1.03 +/- 0.09 mg x kg FFM(-1) x min(-1)) was not significantly different between the 2 groups. Whole-body glucose and lipid kinetics did not differ significantly between the groups. EE increased in SCD patients during exogenous nutrient availability, and the additional energy required for the accelerated rates of whole-body protein breakdown and synthesis made a significant contribution to the increase in EE. These metabolic aberrations may increase the dietary energy and protein requirements of SCD patients.

Alterations in basal nutrient metabolism increase resting energy expenditure in sickle cell disease.

Basal rates of whole body protein, glucose, and lipid metabolism and resting energy expenditure (REE) were measured in eight African-American sickle cell disease (SCD) patients and in six African-American controls. Catheters were placed 1) in an antecubital vein for stable isotope infusion and 2) in a heated hand vein for arterialized venous blood. Breath and blood were collected during the last 30 min of the 2.5-h study, and REE was measured by indirect calorimetry. REE [128 +/- 5 vs. 111 +/- 1 kJ.kg fat-free mass (FFM)-1.day-1; P < 0.05 vs. controls] was 15% greater in the SCD patients. Whole body protein breakdown (5.0 +/- 0.3 vs. 3.8 +/- 0.2 mg.kg FFM-1.min-1; P < 0.05 vs. controls) and protein synthesis (4.4 +/- 0.3 vs. 3.2 +/- 0.2 mg.kg FFM-1.min-1; P < 0.05 vs. controls) were 32 and 38% greater, respectively, in the SCD patients, but whole body amino acid oxidation was similar (0.58 +/- 0.03 vs. 0.66 +/- 0.03 mg.kg FFM-1.min-1). Measures of whole body glucose and lipid metabolism were not significantly different between the groups. The additional energy required for the greater rates of whole body protein breakdown and synthesis caused by SCD contributes significantly to the observed increase in REE, suggesting that dietary energy and protein requirements are enhanced in SCD patients.

Maintaining muscle protein anabolism after a metabolic stress: role of dextrose vs. amino acid availability.

The effect of chronic hypocaloric parenteral infusions of amino acids (AA) vs. dextrose (D) on protein homeostasis after a generalized metabolic stress was examined. Multicatheterized mongrel dogs were metabolically challenged by a 4-day fast and then administered a 4-day intravenous infusion of saline (S, n = 8), D (n = 8), or isocaloric AA (n = 7). Although nitrogen balance (g.kg.1.day-1) was similarly negative with S (-0.37 +/- 0.05), D (-0.28 +/- 0.03), and AA (-0.37 +/- 0.04) during the fasting period, it was less negative (P < or = 0.05) with AA (-0.06 +/- 0.04) than with D (-0.20 +/- 0.03) or S (-0.23 +/- 0.04) during nutrient infusion. AA resulted in net hindlimb uptake and D in net hindlimb release of essential AA (570 +/- 261 vs. -248 +/- 59 nmol.kg-1.min-1). Whereas S and D infusions led to net hindlimb muscle protein loss (-37 +/- 24 and -89 +/- 33 micrograms.kg-1.min-1, respectively, P < or = 0.05 vs. AA), parenteral AA resulted in net deposition (169 +/- 62 micrograms.kg-1.min-1) as measured using L-[ring-2H5]phenylalanine. Thus hypocaloric parenteral D infusion after a metabolic stress does not favor nitrogen conservation, because net whole body nitrogen loss, skeletal muscle protein catabolism, and hindlimb AA release were not blunted compared with S infusion. Conversely, hypocaloric AA infusion preserves whole body and muscle protein stores.

The role of glucagon in the control of protein and amino acid metabolism in vivo.

The relative contribution of hyperglucagonemia to the mechanisms of nitrogen loss during catabolic states has not been clearly established. The present study examines the independent effect of physiologic elevations of plasma glucagon on whole-body protein kinetics, as well as on net amino acid balance across the liver and gastrointestinal tract tissues, in conscious 18-hour-fasted dogs (n = 7). Each study consisted of a 120-minute equilibration period, a 30-minute basal period, and a 150-minute experimental period. Leucine kinetics were measured using L-[1-14C]leucine. Pancreatic hormones were maintained by infusing intravenous somatostatin (0.8 micrograms/kg.min), intraportal insulin (275 microU/kg.min), and intraportal glucagon (0.65 ng/kg.min basally and 2.5 experimentally). Dextrose was infused to maintain plasma glucose constant (14.1 +/- 0.3 mumol/L), thereby providing a consistent metabolic steady state for the study of protein and amino acid metabolism. In the experimental period, plasma glucagon was fourfold basal levels (112 +/- 10 v 32 +/- 6 pg/mL), whereas plasma insulin remained stable (mean, 10 +/- 1 microU/mL). Hepatic glucose production was increased 30%, but leucine rates of appearance ([Ra] proteolysis), oxidative disappearance (Rd), and nonoxidative Rd (protein synthesis) were not altered during the experimental period. Furthermore, the net release of amino acids by the gastrointestinal tract was not increased by glucagon. However, uptake and extraction of amino acids by the liver were increased, resulting in a 17% decrease in total plasma amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic glucose production and insulin sensitivity and responsiveness in iron-deficient anemic rats.

We performed euglycemic hyperinsulinemic glucose clamps at insulin infusion rates of 1.9, 4.0, 9.3, and 19.3 mU.kg-1 x min-1 in rats with varying severities of iron deficiency anemia (IDA; mean hemoglobin concentrations of 59, 79, 107, and 137 g/l) to assess the effect of IDA on insulin sensitivity and responsiveness. Glucose appearance and disappearance (Rd) rates were determined using a primed continuous infusion of [3-3H]glucose. Basal plasma glucose and insulin concentrations were similar between the IDA and control rats. Basal hepatic glucose production was significantly (P = 0.0001) elevated in the two most anemic groups (13.6 +/- 2.4 and 12.6 +/- 3.1 vs. 10.6 +/- 2.2 and 10.2 +/- 2.0 mg.kg-1 x min-1). A significant upward shift in the insulin dose-response curves for Rd indicated an increase in peripheral insulin responsiveness in the two most anemic groups while a slight leftward shift was suggestive of an increase in insulin sensitivity in all three anemic groups. Hepatic insulin sensitivity and responsiveness were unaffected by IDA. We conclude that increased glucose utilization rates in IDA rats are due primarily to an increase in peripheral insulin responsiveness.

Day-to-day variation in iron-status indices in healthy men and women.

We evaluated the day-to-day variation of four iron-status indices: hemoglobin (Hb), hematocrit (Hct), plasma ferritin (PF), and plasma iron (PI). Finger-prick blood samples were collected for 31 consecutive days in 20 healthy men and women. Replicate (sigma 2rep) and day-to-day (sigma 2day) variance components were estimated. Day-to-day variation in the iron-status measures was similar between men and women except for PF, for which the variation was greater in women. The CVs for a single future determination for Hb, Hct, PF, and PI were 4.6%, 3.0%, 15.2%, and 26.7% for males and 4.4%, 3.2%, 26.8%, and 29.0% for females, respectively. Three to 10 independent measurements are required to accurately determine PF and PI whereas one is adequate for Hb and Hct. Thus, day-to-day biological variation is a major component of the variability in these iron-status indicators and must be considered when assessing iron status.

The impact of varying degrees of iron nutriture on several functional consequences of iron deficiency in rats.

The impact of varying severities of iron-deficiency anemia on fasting blood glucose, plasma triiodothyronine, heart norepinephrine concentrations and resting oxygen consumption were evaluated. Male weanling Sprague-Dawley rats were assigned to one of six dietary groups (4, 6, 11, 16, 23 or 40 mg Fe/kg diet) for 6 wk. Hemoglobin, liver iron and transferrin saturation were significantly lower in the 4 and 6 mg Fe/kg diet groups relative to the other groups and were indicative of anemia, low tissue iron stores and impaired erythropoiesis. Fasting blood glucose and heart norepinephrine concentrations were significantly higher and lower, respectively, in the 4 and 6 mg Fe/kg diet groups than the three highest dietary Fe groups. Although fasting blood glucose was significantly inversely correlated (r = -0.89, P = 0.0001) with hemoglobin concentration; a significant quadratic relationship (R 2 = 0.70, P = 0.0001) existed between hemoglobin and heart norepinephrine concentration. Differences in plasma triiodothyronine concentrations and resting oxygen consumption were not significant among the groups. Thus, base on hemoglobin concentration as an index of the severity of iron deficiency, these findings demonstrate that certain physiological manifestations of iron deficiency occur at even moderate-to-mild degrees of anemia.

Impaired thermoregulation and thyroid function in iron-deficiency anemia.

Ten women with iron-deficiency anemia, 8 with depleted iron stores (nonanemic), and 12 control women, all of similar body fatness, were exposed to a 28 degrees C water bath to test the hypothesis that iron-deficiency anemia impairs thermoregulatory performance. The anemic women had lower rectal temperatures than did control women (36.0 +/- 0.2 vs 36.2 +/- 0.1 degree C, respectively, P = 0.001) and a lower rate of oxygen consumption (5.28 +/- 0.26 vs 5.99 +/- 0.29 mL.min-1.kg body wt-1, respectively, P = 0.04) at 100 min of cold exposure. Plasma thyroxine and triiodothyronine concentrations were significantly (P less than 0.002) lower in anemic than in control women at baseline and during cold exposure. Responses of iron-depleted subjects were similar to those of control subjects. Iron supplementation corrected the anemia, significantly (P = 0.03) improved rectal temperature at 100 min, and partially normalized plasma thyroid hormone concentrations. Plasma catecholamines were unaffected by iron status. This experiment demonstrates a functional consequence of iron-deficiency anemia in the balance of heat production and loss and suggests that thyroid-hormone metabolism may be responsible.

Estimation of energy expenditure and maintenance energy requirements of college-age men and women.

Data from two nationwide dietary surveys have led to the suggestion that human energy requirements have been overestimated. A 5-wk energy balance study was conducted to estimate the energy expenditure and maintenance energy requirements of 12 college-age men and women, 20 to 29 yr of age, by the factorial method and by measurement of energy intake and changes in body energy content (intake/balance technique). Mean daily energy expenditure estimated by the intake/balance technique and the factorial method, respectively, was 3081 and 3040 kcal (r = 0.90) for the male subjects and 2183 and 2283 kcal (r = 0.53) for the female subjects. Although differences between the intake/balance and factorial estimations of energy expenditure tended to be greater for individuals than groups and for females than males, the factorial method as performed in this study provided accurate estimations of energy expenditure. In addition, the estimated energy requirements of the college-age subjects in this study provide evidence to support the Recommended Dietary Allowances for energy for this age group.