1,720,976 research outputs found
Effects of [15N]leucine infused at low rates on leucine metabolism in humans.
No full textThe present studies were carried out to determine whether infusions of [15N]leucine at low rates affect estimates of leucine oxidation and of proteolysis and protein synthesis in humans. Three groups of normal subjects were infused for 3 h with either [15N]leucine at a rate of 0.16 or 0.26 mumol X kg-1 X min-1 or saline using [2H3]leucine and alpha-[14C]ketoisocaproate as isotopic tracers of leucine metabolism. Data were analyzed at steady state using both single- and dual-isotope models. Preliminary studies were carried out to characterize the dual-isotope model in humans using infusions of [3H]leucine and alpha-[14C]ketoisocaproate. In the postabsorptive state estimates of leucine appearance, disappearance, and oxidation derived from the two isotope models were in good agreement. Infusion of stable isotope up to approximately 10% of the leucine carbon flux do not have a significant effect on leucine metabolism, but the data derived from such studies must be properly controlled and interpreted with care because these tracers are not massless
Glucose production, gluconeogenesis and insulin sensitivity in children and adolescents: an evaluation of their reproducibility
No full textThe prevalence of overweight and obese children has doubled, and the incidence of type 2 diabetes in children (0-19 y) has increased 4-fold during the past several decades. As a result we can anticipate an increased number of metabolic studies in children. There are few data on measures of glucose metabolism in normal children, and virtually none relating to their reproducibility. The aims of this study were 1) to provide new data on energy expenditure and glucose, lipid, and protein metabolism in nonobese, healthy children and adolescents; 2) to evaluate their reproducibility; and 3) on the basis of these data, to perform power calculations for metabolic studies. Eight nonobese subjects (8-16 y) were studied on two occasions, preceded by 7 d of a diet with identical energy content and macronutrient distribution. Gluconeogenesis, measured by deuterium oxide, accounted for 50% of glucose production. Insulin sensitivity, measured by the labeled minimal model, averaged 4.9 x 10(-4) mL(mU x min)(-1). Glucose appearance rate was significantly higher (p < 0.01) in the children than in the adolescents. Furthermore, we demonstrated that for energy intake and expenditure, plasma concentrations of glucose and C-peptide, and rates of appearance of glucose and leucine, a 10% difference can be detected in fewer than five subjects with a power of 80% and a type I error of 5%. Insulin concentration, gluconeogenesis, insulin secretory indices, insulin sensitivity, and glucose effectiveness were more variable, but with the above power a difference of 25% could be detected in 7-11 subjects using a paired study design
Abnormal meal carbohydrate disposition in insulin-dependent diabetes. Relative contributions of endogenous glucose production and initial splanchnic uptake and effect of intensive insulin therapy.
No full textPostprandial hyperglycemia in insulin-deficient, insulin-dependent diabetic subjects may result from impaired suppression of endogenous glucose production and/or abnormal disposition of meal-derived glucose. To investigate the relative contributions of these processes and to determine whether 2 wk of near normoglycemia achieved by using intensive insulin therapy could restore the pattern of glucose disposal to normal, meal-related and endogenous rates of glucose appearance were measured isotopically after ingestion of a mixed meal that contained deuterated glucose in seven lean insulin-dependent and five lean nondiabetic subjects. Diabetic subjects were studied once when insulin deficient and again during intensive insulin therapy after 2 wk of near normoglycemia. Total glucose production was determined by using tritiated glucose and the contribution of meal-related glucose was determined by using the plasma enrichment of deuterated glucose. The elevated basal and peak postprandial plasma glucose concentrations (252 +/- 33 and 452 +/- 31 mg/dl) of diabetic subjects when insulin deficient were decreased by intensive insulin therapy to values (82 +/- 6 and 193 +/- 10 mg/dl, P less than 0.01) that approximated those of nondiabetic subjects (93 +/- 3 and 140 +/- 15 mg/dl, respectively). Total and endogenous rates of glucose appearance (3,091 +/- 523 and 1,814 +/- 474 mg/kg per 8 h) in the diabetic subjects were significantly (P less than 0.02) greater than those in non-diabetic subjects (1,718 +/- 34 and 620 +/- 98 mg/kg per 8 h, respectively), whereas meal-derived rates of glucose appearance did not differ. Intensive insulin therapy decreased (P less than 0.01) both total (1,581 +/- 98 mg/kg per 8 h) and endogenous (478 +/- 67 mg/kg per 8 h) glucose appearance to rates that approximated those observed in the nondiabetic subjects, but did not alter meal-related glucose appearance. Thus, excessive entry of glucose into the peripheral circulation in insulin-deficient diabetic patients after ingestion of a mixed meal resulted from a lack of appropriate suppression of endogenous glucose production rather than impairment of initial splanchnic glucose uptake. Intensive insulin therapy restored postprandial suppression of endogenous glucose production to rates observed in nondiabetic subject
Effects of dietary macronutrient content on glucose metabolism in children
No full textEffects of carbohydrate, fat, and fructose intake on substrate and hormone concentrations, glucose production, gluconeogenesis, and insulin sensitivity were determined in healthy, nonobese prepubertal children (n = 12) and adolescents (n = 24) using a cross-over design. In one group (12 prepubertal children and 12 adolescents), subjects were studied after 7 d of isocaloric, isonitrogenous diets providing either 60% carbohydrate and 25% fat [high carbohydrate (H(CHO))/low fat (L(F))] or 30% carbohydrate and 55% fat [low carbohydrate (L(CHO))/high fat (H(F))], and in a second group (12 adolescents) H(CHO)/L(F) diets containing either 40% or 10% fructose was used. All subjects adapted to changes in carbohydrate and fat intakes primarily by appropriately adjusting their substrate oxidation rates to match the intakes, with only minor changes in parameters of glucose metabolism. Changing from a L(CHO)/H(F) to H(CHO)/L(F) diet resulted in increased insulin sensitivity (stable labeled iv glucose tolerance test) in adolescents [from 3.2 +/- 0.7 x 10(-4) to 5.0 +/- 1.4 x 10(-4) (min(-1))/( micro U.ml(-1)) (mean +/- SE)] but not in prepubertal children [9.4 +/- 2.5 x 10(-4) to 9.9 +/- 1.5 x 10(-4) (min(-1))/( micro U.ml(-1))], whereas beta-cell sensitivity was unaffected in both groups. Insulin sensitivity was higher in prepubertal children than in adolescents (P < 0.05). The dietary fructose content did not affect any measured parameter. We conclude that in the short term, dramatic changes in fat and carbohydrate intakes (regardless of fructose content) did not adversely affect glucose and lipid metabolism in healthy nonobese children. In the adolescents, the high carbohydrate diet resulted in increased insulin sensitivity, thus facilitating insulin-mediated glucose uptake
Short-term high dietary fructose intake had no effects on insulin sensitivity and secretion or glucose and lipid metabolism in healthy, obese adolescents
No full textThere is virtually no information on the metabolic impact of dietary fructose intake in adolescents despite their high fructose consumption, particularly via sweetened beverages.
AIM:
To determine the short-term metabolic effects of dietary fructose intake in obese adolescents.
METHODS:
Six volunteers (3 M/3 F; 15.2 +/- 0.5 yr; 35 +/- 2 kg/m2; 39 +/- 2% body fat) were studied twice following 7 d of isocaloric, isonitrogenous high carbohydrate (60% CHO; 25% fat) diets with fructose accounting for 6% and 24% of total energy intake, respectively (random order). Insulin sensitivity and secretion were analyzed by the stable labeled intravenous glucose tolerance test and glucose and lipid kinetics using GCMS.
RESULTS:
A fourfold increase in dietary fructose intake did not affect insulin sensitivity or secretion, glucose kinetics, lipolysis or glucose, insulin, C-peptide, triglycerides, HDL- and LDL-cholesterol concentrations.
CONCLUSIONS:
In the short term, when energy intake is constant, dietary fructose per se is not a contributor to insulin resistance and hypersecretion in obese adolescents
Regulation of whole-body leucine metabolism with insulin during mixed-meal absorption in normal and diabetic humans.
No full textTo determine the effects of insulin on dietary and endogenous leucine metabolism, five normal subjects, seven insulin-insufficient insulin-dependent (IDDM) diabetic patients, and five diabetic patients controlled with continuous subcutaneous insulin infusion (CSII) were studied before and for 8 h after ingestion of a chemically defined elemental test meal (10 cal/kg) containing crystalline amino acids. L-[1-14C]leucine was included in the meal to trace the entry and oxidation of the dietary leucine. Total (meal + endogenous) entry of leucine into the circulation was estimated with a constant infusion of [2H3]leucine. Postabsorptive and meal-related increases in the plasma leucine concentration were greater (P less than .05) in the insulin-insufficient IDDM than in the normal subjects but returned to near-normal values with CSII. Baseline leucine flux was approximately 40% greater in the insulin-insufficient IDDM than in normal subjects (2.17 +/- 0.17 vs. 1.55 +/- 0.15 mumol.kg-1.min-1, respectively; .05 less than P less than .01) but were near normal during CSII treatment (1.85 +/- 0.25 mumol.kg-1.min-1). Furthermore, total leucine entry during meal absorption was greater in the insulin-insufficient IDDM (1.41 +/- 0.10 mmol.kg-1.8 h-1) than in either normal (0.96 +/- 0.08 mmol.kg-1.8 h-1, P less than .01) or IDDM subjects during CSII treatment (1.09 +/- 0.11 mmol.kg-1.8 h-1, P less than .05). Fractional oxidation (approximately 40-50%) and entry of dietary leucine were similar in all three group
Apparent decreased oxidation and turnover of leucine during infusion of medium-chain triglycerides.
No full textA potential effector of the protein-sparing adaptation to fasting could be the increased availability of endogenous long-chain fatty acids. Were this hypothesis correct, infusion of medium-chain triglycerides to increase the plasma concentration of medium-chain fatty acids might also result in protein sparing. However, in most in vitro studies in rat muscle, octanoate increases the oxidation of the essential amino acid leucine. Therefore leucine metabolism was assessed with infusions of [3H]leucine and a-[14C]ketoisocaproate ([14C]KIC) before and during an infusion of trioctanoin in conscious dogs. Plasma octanoate increased from less than 30 to 528 microM over the 3 h of infusion. Plasma leucine and KIC concentrations decreased by 65-70% (P less than 0.01) over the first 2 h of infusion. Leucine oxidation, estimated from the expired 14CO2 and the plasma [14C]KIC specific activity, as well as from an open two-pool model, decreased. By use of these isotope models, the rates of leucine coming from and going to protein decreased (P less than 0.05 to P less than 0.01). Interconversion of leucine and KIC estimated from the open two-pool model decreased by 80% (P less than 0.01). These changes were accompanied by a 36% decrease in the plasma concentration of total plasma amino acids. Within the confines of the isotope models employed, these data are consistent with the hypothesis that increased fatty acid oxidation decreases protein turnover and may spare essential amino acids
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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