bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucoregulatory responses to intense exercise performed in the postprandial state
Authors: Kreisman Stuart H. , Manzon Anthony , Nessim Sharon J. , Morais José A. , Gougeon Réjeanne , Fisher Simon J. , Vranic Mladen , Marliss Errol B.
Published: December 2017

A seven- to eightfold increment in hepatic glucose production (endogenous Ra) occurs in postabsorptive (PA) intense exercise (IE). A similar response is likely present in the postprandial (PP) state, when most such exercise is performed, because 1) little evidence for increased intestinal absorption of glucose during exercise exists, and 2) intravenous glucose does not prevent it. We investigated IE in 10 PA and 8 PP fit, lean, young males who had exercised for 15 min at >84% maximum O2uptake, starting 3 h after a 412-kcal mixed meal. The meal induced a small rise in glycemia with sustained insulin and glucagon increases. Preexercise glucose total Ra and utilization (Rd) were equal and ∼130% of the PA level. Exercise hyperglycemia in PP was delayed and diminished and, in early recovery, was of shorter duration and lesser magnitude ( P = 0.042). Peak catecholamine (12- to 16-fold increase) and Ra (PP: 11.5 ± 1.4, PA: 13.8 ± 1.4 mg ⋅ kg− 1 ⋅ min− 1) responses did not differ, and their responses during exercise were significantly correlated. Exercise glucagon, insulin, and glucagon-to-insulin responses were small or not significant. Rd reached the same peak (PP: 8.0 ± 0.6, PA: 9.3 ± 0.8 mg ⋅ kg− 1 ⋅ min− 1) but was greater at 20–120 min of recovery in PP ( P = 0.001). Therefore, the total Ra response to IE is preserved despite the possibility of prior PP suppression of endogenous Ra and is consistent with catecholamine mediation. Post-IE hyperglycemia is reduced in the postprandial state.
Dose-response characteristics of insulin action on glucose metabolism: a non-steady-state approach
Authors: Natali Andrea , Gastaldelli Amalia , Camastra Stefania , Sironi Anna Maria , Toschi Elena , Masoni Antonio , Ferrannini Ele , Mari Andrea
Published: December 2017

The traditional methods for the assessment of insulin sensitivity yield only a single index, not the whole dose-response curve information. This curve is typically characterized by a maximally insulin-stimulated glucose clearance (Clmax) and an insulin concentration at half-maximal response (EC50). We developed an approach for estimating the whole dose-response curve with a single in vivo test, based on the use of tracer glucose and exogenous insulin administration (two steps of 20 and 200 mU ⋅ min− 1 ⋅ m− 2, 100 min each). The effect of insulin on plasma glucose clearance was calculated from non-steady-state data by use of a circulatory model of glucose kinetics and a model of insulin action in which glucose clearance is represented as a Michaelis-Menten function of insulin concentration with a delay ( t 1/2). In seven nondiabetic subjects, the model predicted adequately the tracer concentration: the model residuals were unbiased, and their coefficient of variation was similar to the expected measurement error (∼3%), indicating that the model did not introduce significant systematic errors. Lean ( n= 4) and obese ( n = 3) subjects had similar half-times for insulin action ( t 1/2 = 25 ± 9 vs. 25 ± 8 min) and maximal responses (Clmax = 705 ± 46 vs. 668 ± 259 ml ⋅ min− 1 ⋅ m− 2, respectively), whereas EC50 was 240 ± 84 μU/ml in the lean vs. 364 ± 229 μU/ml in the obese ( P < 0.04). EC50 and the insulin sensitivity index (ISI, initial slope of the dose-response curve), but not Clmax, were related to body adiposity and fat distribution with r of 0.6–0.8 ( P < 0.05). Thus, despite the small number of study subjects, we were able to reproduce information consistent with the literature. In addition, among the lean individuals, t 1/2 was positively related to the ISI ( r = 0.72, P < 0.02). We conclude that the test here presented, based on a more elaborate representation of glucose kinetics and insulin action, allows a reliable quantitation of the insulin dose-response curve for whole body glucose utilization in a single session of relatively short duration.
Effect of enteral glutamine on leucine, phenylalanine and glutamine metabolism in hypercortisolemic subjects
Authors: Claeyssens Sophie , Bouteloup-Demange Corinne , Gachon Pierre , Hecketsweiler Bernadette , Lerebours Eric , Lavoinne Alain , Déchelotte Pierre
Published: December 2017

The effect of enteral Gln on protein and Gln metabolism was investigated during experimental hypercortisolemia. Four groups of subjects that had received corticosteroids and either enteral Gln (0.5 g ⋅ kg−1 ⋅ day−1for 2 days) or isonitrogenous Ala-Gly were studied in a fasted or in a fed state. In either state, enteral Gln, compared with Ala-Gly, induced no statistically significant change in the endogenous rate of Leu appearance, an index of proteolysis, Leu oxidation, and nonoxidative Leu disposal, an index of protein synthesis, as studied by kinetics of [1-13C]Leu. Similar data were obtained from kinetics of [2H5]Phe, resulting in an unchanged protein balance in both cases. In contrast, enteral Gln significantly decreased the endogenous rate of Gln appearance and Gln de novo synthesis in the fed state ( P < 0.05) as estimated by the kinetics of [15N]Gln. This decrease in Gln de novo synthesis induced by Gln could contribute to spare amino acids in hypercatabolic patients.
Effect of dexamethasone on fetal hepatic glutamine-glutamate exchange
Authors: Timmerman Michelle , Teng Cecilia , Wilkening Randall B. , Fennessey Paul , Battaglia Frederick C. , Meschia Giacomo
Published: December 2017

Intravenous infusion of dexamethasone (Dex) in the fetal lamb causes a two- to threefold increase in plasma glutamine and other glucogenic amino acids and a decrease of plasma glutamate to approximately one-third of normal. To explore the underlying mechanisms, hepatic amino acid uptake and conversion ofl-[1-13C]glutamine tol-[1-13C]glutamate and13CO2were measured in six sheep fetuses before and in the last 2 h of a 26-h Dex infusion. Dex decreased hepatic glutamine and alanine uptakes ( P < 0.01) and hepatic glutamate output ( P < 0.001). Hepatic outputs of the glutamate (RGlu,Gln) and CO2formed from plasma glutamine decreased to 21 ( P < 0.001) and 53% ( P= 0.009) of control, respectively. RGlu,Gln, expressed as a fraction of both outputs, decreased ( P < 0.001) from 0.36 ± 0.02 to 0.18 ± 0.04. Hepatic glucose output remained virtually zero throughout the experiment. We conclude that Dex decreases fetal hepatic glutamate output by increasing the routing of glutamate carbon into the citric acid cycle and by decreasing the hepatic uptake of glucogenic amino acids.
Protein turnover modifications induced by the protein feeding pattern still persist after the end of the diets
Authors: Arnal M. A. , Mosoni L. , Boirie Y. , Gachon P. , Genest M. , Bayle G. , Grizard J. , Arnal M. , Antoine J. M. , Beaufrère B. , Mirand P. Patureau
Published: December 2017

This study was undertaken to determine whether the protein feeding pattern could induce chronic adaptation of protein turnover. After a 15-day adaptive period, elderly (68 yr) and young (26 yr) women received, for 14 days, a diet providing 200 KJ ⋅ kg fat-free mass (FFM)− 1 ⋅ day− 1, where the daily protein intake (1.7 g protein ⋅ kg FFM− 1 ⋅ day− 1) was either spread over 4 meals in the spread pattern or mainly (80%) consumed at noon in the pulse pattern. One day after the end of the dietary treatment, whole body leucine kinetics were measured by use of a continuous [13C]leucine infusion, both in the postabsorptive state and in the same fed state. The pulse pattern was able to induce, in young as in elderly women, a lower postabsorptive leucine oxidation and endogenous leucine flux than the spread pattern and improved the responsiveness of nonoxidative leucine disposal during 4-h oral feeding. Thus the pulse pattern was able to induce chronic regulation of protein metabolism in young as in elderly women.
Acute response of IGF-I and IGF binding proteins induced by thermal injury
Authors: Lang Charles H. , Liu Xiaoli , Nystrom Gerald J. , Frost Robert A.
Published: December 2017

Previous studies demonstrate that thermal injury decreases circulating levels of insulin growth factor I (IGF-I) and alters the plasma concentration of several IGF binding proteins (IGFBP), but the mechanisms for these alterations have not been elucidated. In the current study, a 30% total body surface area full-thickness scald burn was produced in anesthetized rats, and animals were studied 24 h later. The plasma concentration of both total and free IGF-I was decreased (38 and 65%, respectively) in burn rats compared with values from time-matched control animals. Thermal injury decreased the IGF-I peptide content in liver ∼40%, as well as in fast-twitch skeletal muscle (56–69%) and heart (28%). In contrast, IGF-I content in kidney was elevated by 36% in burn rats. Northern blot analysis of liver indicated that burn decreased the expression of small (1.7- and 0.9- to 1.2-kb) IGF-I mRNA transcripts but increased the expression of the 7.5-kb transcript. In contrast, there was a coordinate decrease in all IGF-I mRNA transcripts in muscle and kidney of ∼30%. For liver, muscle, and kidney, there was no significant difference in the expression of growth hormone receptor mRNA between control and burn rats. Thermal injury increased plasma IGFBP-1 levels, and this change was associated with increased IGFBP-1 mRNA in both liver and kidney. IGFBP-3 levels in plasma were concomitantly decreased by burn injury. This change was associated with a reduction in IGFBP-3 mRNA in liver but an increased expression of IGFBP-3 in kidney and muscle. Thermal injury also decreased the concentration of the acid-labile subunit (ALS) in plasma and ALS mRNA expression in liver. Finally, hepatic expression of IGFBP-related peptide-1 was increased twofold in liver but was unchanged in kidney or muscle of burn rats. These results characterize burn-induced changes in various components of the IGF system in select tissues and thereby provide potential mechanisms for alterations in the circulating IGF system and for changes in tissue metabolism.
Isoproterenol and cAMP regulation of the human brain natriuretic peptide gene involves Src and Rac
Authors: He Quan , Wu Guiyun , Lapointe Margot C.
Published: December 2017

Brain natriuretic peptide (BNP) gene expression and chronic activation of the sympathetic nervous system are characteristics of the development of heart failure. We studied the role of the β-adrenergic signaling pathway in regulation of the human BNP (hBNP) promoter. An hBNP promoter (−1818 to +100) coupled to a luciferase reporter gene was transferred into neonatal cardiac myocytes, and luciferase activity was measured as an index of promoter activity. Isoproterenol (ISO), forskolin, and cAMP stimulated the promoter, and the β2-antagonist ICI 118,551 abrogated the effect of ISO. In contrast, the protein kinase A (PKA) inhibitor H-89 failed to block the action of cAMP and ISO. Pertussis toxin (PT), which inactivates Gαi, inhibited ISO- and cAMP-stimulated hBNP promoter activity. The Src tyrosine kinase inhibitor PP1 and a dominant-negative mutant of the small G protein Rac also abolished the effect of ISO and cAMP. Finally, we studied the involvement of M-CAT-like binding sites in basal and inducible regulation of the hBNP promoter. Mutation of these elements decreased basal and cAMP-induced activity. These data suggest that β-adrenergic regulation of hBNP is PKA independent, involves a Gαi-activated pathway, and targets regulatory elements in the proximal BNP promoter.
Partial saturation and regional variation in the blood-to-brain transport of leptin in normal weight mice
Authors: Banks William A. , Clever Cecilia M. , Farrell Catherine L.
Published: December 2017

Impaired blood-brain barrier transport of leptin into the arcuate nucleus has been suggested to underlie obesity in humans and outbred aging mice. Here, we used a brain perfusion method in mice to measure transport rates and kinetic parameters for leptin at vascular concentrations between 0.15 and 130 ng/ml. Transport into whole brain was partially saturated at all concentrations, not only those seen in obesity. Leptin entered all regions of the brain, not only the hypothalamus, with entry and saturation rates differing among the brain regions. The value of the Michaelis-Menten constant of the transporter approximates normal serum levels and the maximum velocity value varies significantly among brain regions. These results suggest an important role for low serum levels signaling starvation status to the brain and show that the levels of leptin seen in obesity greatly saturate the transporter. Differences in regional uptake and saturation provide a mechanism by which leptin can control events mediated at the arcuate nucleus and other regions of the central nervous system with different regional thresholds for optimal function.
Glucagon-like peptide-1 improves insulin and proinsulin binding on RINm5F cells and human monocytes
Authors: Ebinger Martin , Jehle Daniela R. , Fussgaenger Rolf D. , Fehmann Hans C. , Jehle Peter M.
Published: December 2017

Glucagon-like peptide-1-(7—36) amide (GLP-1) is a potent incretin hormone secreted from distal gut. It stimulates basal and glucose-induced insulin secretion and proinsulin gene expression. The present study tested the hypothesis that GLP-1 may modulate insulin receptor binding. RINm5F rat insulinoma cells were incubated with GLP-1 (0.01–100 nM) for different periods (1 min-24 h). Insulin receptor binding was assessed by competitive ligand binding studies. In addition, we investigated the effect of GLP-1 on insulin receptor binding on monocytes isolated from type 1 and type 2 diabetes patients and healthy volunteers. In RINm5F cells, GLP-1 increased the capacity and affinity of insulin binding in a time- and concentration-dependent manner. The GLP-1 receptor agonist exendin-4 showed similar effects, whereas the receptor antagonist exendin-(9—39) amide inhibited the GLP-1-induced increase in insulin receptor binding. The GLP-1 effect was potentiated by the adenylyl cyclase activator forskolin and the stable cAMP analog Sp-5,6-dichloro-1- β-d-ribofuranosyl-benzimidazole-3′,5′-monophosphorothioate but was antagonized by the intracellular Ca2+chelator 1,2-bis(0-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid-AM. Glucagon, gastric inhibitory peptide (GIP), and GIP-(1—30) did not affect insulin binding. In isolated monocytes, 24 h incubation with 100 nM GLP-1 significantly ( P < 0.05) increased the diminished number of high-capacity/low-affinity insulin binding sites per cell in type 1 diabetics (9,000 ± 3,200 vs. 18,500 ± 3,600) and in type 2 diabetics (15,700 ± 2,100 vs. 28,900 ± 1,800) compared with nondiabetic control subjects (25,100 ± 2,700 vs. 26,200 ± 4,200). Based on our previous experiments in IEC-6 cells and IM-9 lymphoblasts indicating that the low-affinity/high-capacity insulin binding sites may be more specific for proinsulin (Jehle, PM, Fussgaenger RD, Angelus NK, Jungwirth RJ, Saile B, and Lutz MP. Am J Physiol Endocrinol Metab276: E262–E268, 1999 and Jehle, PM, Lutz MP, and Fussgaenger RD. Diabetologia 39: 421–432, 1996), we further investigated the effect of GLP-1 on proinsulin binding in RINm5F cells and monocytes. In both cell types, GLP-1 induced a significant increase in proinsulin binding. We conclude that, in RINm5F cells and in isolated human monocytes, GLP-1 specifically increases the number of high-capacity insulin binding sites that may be functional proinsulin receptors.
Synthesis rate of plasma albumin is a good indicator of liver albumin synthesis in sepsis
Authors: Ruot Benoît , Breuillé Denis , Rambourdin Fabienne , Bayle Gerard , Capitan Pierre , Obled Christiane
Published: December 2017

Plasma albumin is well known to decrease in response to inflammation. The rate of albumin synthesis from both liver and plasma was measured in vivo by use of a large dose ofl-[2H3-14C]valine in rats injected intravenously with live Escherichia coli and in pair-fed control rats during the acute-phase period (2 days postinfection). The plasma albumin concentration was reduced by 50% in infected rats compared with pair-fed animals. Infection induced a fall in both liver albumin mRNA levels and albumin synthesis relative to total liver protein synthesis. However, absolute liver albumin synthesis rate (ASR) was not affected by infection. In plasma, albumin fractional synthesis rate was increased by 50% in infected animals compared with pair-fed animals. The albumin ASR estimated in the plasma was similar in the two groups. These results suggest that hypoalbuminemia is not due to reduced albumin synthesis during sepsis. Moreover, liver and plasma albumin ASR were similar. Therefore, albumin synthesis measured in the plasma is a good indicator of liver albumin synthesis.
Individual severity of dietary obesity in unselected Wistar rats: relationship with hyperphagia
Authors: Harrold Joanne A. , Widdowson Peter S. , Clapham John C. , Williams Gareth
Published: December 2017

We investigated the relative importance of overeating, thermogenesis, and uncoupling protein (UCP) expression in determining the severity of obesity in male Wistar rats fed a highly palatable diet. After 2 wk of feeding, body weight did not differ significantly from controls (248 ± 4 vs. 229 ± 3 g; P > 0.3), but rectal temperature, brown adipose tissue (BAT) mass, UCP3 expression in gastrocnemius muscle, and UCP2 expression in white adipose tissue (WAT) were all elevated in diet-fed animals. In a further study, rats fed a palatable diet for 8 wk exhibited higher energy intake and rectal temperature than controls. Dietary-obese rats were divided into high (427–490 g; n = 8) and low (313–410 g; n = 10) weight gainers. The high gainers ate significantly more than the low gainers, and energy intake was positively correlated with weight gain ( r 2 = 0.72, P < 0.01). UCP2 and UCP3 mRNA levels in gastrocnemius muscle were significantly increased above lean controls in all diet-fed animals, whereas UCPs in WAT and BAT did not differ significantly from controls. Whereas rats fed palatable food exhibited a thermogenic response, there was no significant difference in core temperature between high and low gain groups (37.5 ± 0.1 vs. 37.6 ± 0.1°C; P > 0.5). We conclude that a higher energy intake is the critical factor determining susceptibility to dietary obesity in unselected Wistar rats.
Weight stability masks sarcopenia in elderly men and women
Authors: Gallagher Dympna , Ruts Else , Visser Marjolein , Heshka Stanley , Baumgartner Richard N. , Wang Jack , Pierson Richard N. , Pi-Sunyer F. Xavier , Heymsfield Steven B.
Published: December 2017

Skeletal muscle loss or sarcopenia in aging has been suggested in cross-sectional studies but has not been shown in elderly subjects using appropriate measurement techniques combined with a longitudinal study design. Longitudinal skeletal muscle mass changes after age 60 yr were investigated in independently living, healthy men ( n = 24) and women ( n = 54; mean age 73 yr) with a mean ± SD follow-up time of 4.7 ± 2.3 yr. Measurements included regional skeletal muscle mass, four additional lean components (fat-free body mass, body cell mass, total body water, and bone mineral), and total body fat. Total appendicular skeletal muscle (TSM) mass decreased in men (−0.8 ± 1.2 kg, P = 0.002), consisting of leg skeletal muscle (LSM) loss (−0.7 ± 0.8 kg, P = 0.001) and a trend toward loss of arm skeletal muscle (ASM; −0.2 ± 0.4 kg, P = 0.06). In women, TSM mass decreased (−0.4 ± 1.2 kg, P = 0.006) and consisted of LSM loss (−0.3 ± 0.8 kg, P = 0.005) and a tendency for a loss of ASM (−0.1 ± 0.6 kg, P = 0.20). Multiple regression modeling indicates greater rates of LSM loss in men. Body weight in men at follow-up did not change significantly (−0.5 ± 3.0 kg, P = 0.44) and fat mass increased (+1.2 ± 2.4 kg, P = 0.03). Body weight and fat mass in women were nonsignificantly reduced (−0.8 ± 3.9 kg, P= 0.15 and −0.8 ± 3.5 kg, P = 0.12). These observations suggest that sarcopenia is a progressive process, particularly in elderly men, and occurs even in healthy independently living older adults who may not manifest weight loss.
Role of adrenoceptors and cAMP on the catecholamine-induced inhibition of proteolysis in rat skeletal muscle
Authors: Navegantes Luiz Carlos C. , Resano Neusa M. Z. , Migliorini Renato H. , Kettelhut Ísis C.
Published: December 2017

The role of adrenoceptor subtypes and of cAMP on rat skeletal muscle proteolysis was investigated using a preparation that maintains tissue glycogen stores and metabolic activity for several hours. In both soleus and extensor digitorum longus (EDL) muscles, proteolysis decreased by 15–20% in the presence of equimolar concentrations of epinephrine, isoproterenol, a nonselective β-agonist, or clenbuterol, a selective β2-agonist. Norepinephrine also reduced proteolysis but less markedly than epinephrine. No change in proteolysis was observed when muscles were incubated with phenylephrine, a nonselective α-agonist. The decrease in the rate of protein degradation induced by 10−4 M epinephrine was prevented by 10−5 M propranolol, a nonselective β-antagonist, and by 10−5 M ICI 118.551, a selective β2-antagonist. The antiproteolytic effect of epinephrine was not inhibited by prazosin or yohimbine (selective α1-and α2-antagonists, respectively) or by atenolol, a selective β1-antagonist. Dibutyryl cAMP and isobutylmethylxanthine reduced proteolysis in both soleus and EDL muscles. The data suggest that catecholamines exert an inhibitory control of skeletal muscle proteolysis, probably mediated by β2-adrenoceptors, with the participation of a cAMP-dependent pathway.
Age-related decrease of somatostatin receptor number in the normal human thymus
Authors: Ferone Diego , Pivonello Rosario , Van Hagen P. Martin , Waaijers Marlijn , Zuijderwijk Joke , Colao Annamaria , Lombardi Gaetano , Bogers Ad J. J. C. , Lamberts Steven W. J. , Hofland Leo J.
Published: December 2017

The thymus exhibits a pattern of aging oriented toward a physiological involution. The structural changes start with a steady decrease of thymocytes, whereas no major variations occur in the number of thymic epithelial cells (TEC). The data concerning the role of hormones and neuropeptides in thymic involution are equivocal. We recently demonstrated the presence of somatostatin (SS) and three different SS receptor (SSR) subtypes in the human thymus. TEC selectively expressed SSR subtype 1 (sst1) and sst2a. In the present study we investigated whether SSR number is age related in the thymus. Binding of the sst2-preferring ligand125I-Tyr3-octreotide was evaluated in a large series of normal human thymuses of different age by SSR autoradiography and ligand binding on tissue homogenates. The score at autoradiography and the number of SSR at membrane homogenate binding (Bmax) were inversely correlated with the thymus age ( r = −0.84, P < 0.001; r = −0.82, P < 0.001, respectively). The autoradiographic score was positively correlated with the Bmaxvalues ( r = 0.74, P < 0.001). Because the TEC number in the age range considered remains unchanged, the decrease of octreotide binding sites might be due to a reduction of sst2areceptor number on TEC. The age-related expression of a receptor involved mainly in controlling secretive processes is in line with the evidence that the major changes occurring in TEC with aging are related to their capabilities in producing thymic hormones. In conclusion, SS and SSR might play a role in the involution of the human thymus. These findings underline the links between the neuroendocrine and immune systems and support the concept that neuropeptides participate in development of cellular immunity in humans.
Calcium-dependent activation of phospholipase C by mechanical distension in renin-expressing As4.1 cells
Authors: Ryan Michael J. , Gross Kenneth W. , Hajduczok George
Published: December 2017

One of the major physiological regulators for the production and release of renin from the kidney is blood pressure. The juxtaglomerular (JG) cells, located primarily at the afferent arterioles leading to the glomerulus, are thought to be the baroreceptor of the kidney and adjust their ability to secrete renin in an inverse relationship to changes in pressure (mechanical force). The characteristics of JG cells that allow them to sense and respond to changes in mechanical force at the cellular level are not clear. By use of a renin-expressing clonal cell line (As4.1) as a model for JG cells, it was the purpose of this paper to identify cellular pathways that are activated by mechanical distension. Fura 2-labeled As4.1 cells were mechanically probed to observe changes of intracellular calcium concentration ([Ca2+]i). Mechanical distension of As4.1 cells resulted in an influx of Ca2+to the cytosol, mediated by stretch-activated ion channels and dependent on the presence of extracellular Ca2+. Furthermore, cyclic mechanical distension elevated total inositol phosphates (IP) in As4.1 cells. This response was also dependent on the presence of extracellular Ca2+, and the addition of U-73122, a phospholipase C (PLC) antagonist, significantly attenuated the increase of IP. Taken together, these findings demonstrate the calcium-dependent activation of PLC and the subsequent increase of IP and [Ca2+]ito be a potentially important pathway for the modality of pressure sensing by renin-expressing cells in response to mechanical stimulation.
Fat oxidation, lipolysis, and free fatty acid cycling in obesity-prone and obesity-resistant rats
Authors: Commerford S. Renee , Pagliassotti Michael J. , Melby Christopher L. , Wei Yuren , Gayles Ellis C. , Hill James O.
Published: December 2017

Defects in fat metabolism may contribute to the development of obesity, but what these defects are and where they occur in the feeding/fasting cycle are unknown. In the present study, basal fat metabolism was characterized using a high-fat diet (HFD)-induced model of obesity development. Male rats consumed a HFD (45% fat, 35% carbohydrate) ad libitum for either 1 or 5 wk (HFD1 or HFD5). After 1 wk on the HFD, rats were separated on the basis of body weight gain into obesity-prone (OP, ≥48 g) or obesity-resistant (OR, ≤40 g) groups. Twenty-four-hour-fasted rats were studied either at this time (OP1, OR1) or after 5 wk (OP5, OR5). Fat pad weight (sum of epididymal, retroperitoneal, and mesenteric fat pads) at HFD1 was 26% greater and at HFD5 was 43% greater ( P≤0.05) in OP vs. OR. Free fatty acid rates of appearance (FFA Ra) and oxidation were not significantly different between OP and OR at 1 or 5 wk. Glycerol Ra, when expressed in absolute terms (μmol/min), increased from 1 to 5 wk of HFD feeding in both OP and OR, but significantly so only in OP. Likewise, increased rates of intracellular FFA cycling [estimated as (3 × glycerol Ra) − FFA Ra] were observed in both OP and OR rats from 1 to 5 wk of HFD feeding, but significantly so in OP rats only. When expressed relative to fat cell volume (μmol · pl−1· min−1), neither lipolysis nor intracellular cycling was significantly different between OP and OR, regardless of time on HFD. These data suggest that 1) if low rates of fat oxidation contribute to obesity development in OP rats, the contribution does not occur at times when fat oxidation is at or near maximum rates (i.e., 24-h fasted conditions), and 2) between 1 and 5 wk of HFD feeding, basal lipolysis and reesterification may work to expand fat cell volume and increase fat pad weight in both OP and OR rats, although more so in OP rats.
Prior exercise and postprandial substrate extraction across the human leg
Authors: Malkova D. , Evans R. D. , Frayn K. N. , Humphreys S. M. , Jones P. R. M. , Hardman A. E.
Published: December 2017

Prior exercise decreases postprandial plasma triacylglycerol (TG) concentrations, possibly through changes to skeletal muscle TG extraction. We measured postprandial substrate extraction across the leg in eight normolipidemic men aged 21–46 yr. On the afternoon preceding one trial, subjects ran for 2 h at 64 ± 1% of maximal oxygen uptake (exercise); before the control trial, subjects had refrained from exercise. Samples of femoral arterial and venous blood were obtained, and leg blood flow was measured in the fasting state and for 6 h after a meal (1.2 g fat, 1.2 g carbohydrate/kg body mass). Prior exercise increased time averaged postprandial TG clearance across the leg (total TG: control, 0.079 ± 0.014 ml · 100 ml tissue−1 · min−1; exercise, 0.158 ± 0.023 ml · 100 ml tissue−1 · min−1, P<0.01), particularly in the chylomicron fraction, so that absolute TG uptake was maintained despite lower plasma TG concentrations (control, 1.53 ± 0.13 mmol/l; exercise, 1.01 ± 0.16 mmol/l, P < 0.001). Prior exercise increased postprandial leg blood flow and glucose uptake (both P < 0.05). Mechanisms other than increased leg TG uptake must account for the effect of prior exercise on postprandial lipemia.
Limitations to basal and insulin-stimulated skeletal muscle glucose uptake in the high-fat-fed rat
Authors: Halseth Amy E. , Bracy Deanna P. , Wasserman David H.
Published: December 2017

Rats fed a high-fat diet display blunted insulin-stimulated skeletal muscle glucose uptake. It is not clear whether this is due solely to a defect in glucose transport, or if glucose delivery and phosphorylation are also impaired. To determine this, rats were fed standard chow (control rats) or a high-fat diet (HF rats) for 4 wk. Experiments were then performed on conscious rats under basal conditions or during hyperinsulinemic euglycemic clamps. Rats received primed constant infusions of 3- O-methyl-[3H]glucose (3- O-MG) and [1-14C]mannitol. Total muscle glucose concentration and the steady-state ratio of intracellular to extracellular 3- O-MG concentration [which distributes based on the transsarcolemmal glucose gradient (TSGG)] were used to calculate glucose concentrations at the inner and outer sarcolemmal surfaces ([G]imand [G]om, respectively) in soleus. Total muscle glucose was also measured in two fast-twitch muscles. Muscle glucose uptake was markedly decreased in HF rats. In control rats, hyperinsulinemia resulted in a decrease in soleus TSGG compared with basal, due to increased [G]im. In HF rats during hyperinsulinemia, [G]imalso exceeded zero. Hyperinsulinemia also decreased muscle glucose in HF rats, implicating impaired glucose delivery. In conclusion, defects in extracellular and intracellular components of muscle glucose uptake are of major functional significance in this model of insulin resistance.
Altered metabolism causes cardiac dysfunction in perfused hearts from diabetic (db/db) mice
Authors: Belke Darrell D. , Larsen Terje S. , Gibbs E. Michael , Severson David L.
Published: December 2017

Contractile function and substrate metabolism were characterized in perfused hearts from genetically diabetic C57BL/KsJ- leprdb / leprdb ( db/db) mice and their non-diabetic lean littermates. Contractility was assessed in working hearts by measuring left ventricular pressures and cardiac power. Rates of glycolysis, glucose oxidation, and fatty acid oxidation were measured using radiolabeled substrates ([5-3H]glucose, [U-14C]glucose, and [9,10-3H]palmitate) in the perfusate. Contractile dysfunction in db/db hearts was evident, with increased left ventricular end diastolic pressure and decreased left ventricular developed pressure, cardiac output, and cardiac power. The rate of glycolysis from exogenous glucose in diabetic hearts was 48% of control, whereas glucose oxidation was depressed to only 16% of control. In contrast, palmitate oxidation was increased twofold in db/db hearts. The hypothesis that altered metabolism plays a causative role in diabetes-induced contractile dysfunction was tested using perfused hearts from transgenic db/db mice that overexpress GLUT-4 glucose transporters. Both glucose metabolism and palmitate metabolism were normalized in hearts from db/db-human insulin-regulatable glucose transporter (hGLUT-4) hearts, as was contractile function. These findings strongly support a causative role of impaired metabolism in the cardiomyopathy observed in db/db diabetic hearts.
Evidence for physiological coupling of insulin-mediated glucose metabolism and limb blood flow
Authors: Mather Kieren , Laakso Markku , Edelman Steven , Hook Ginger , Baron Alain
Published: December 2017

We hypothesized that the vasodilation observed during insulin stimulation is closely coupled to the rate of glucose metabolism. Lean (L, n = 13), obese nondiabetic (OB, n = 13), and obese type 2 diabetic subjects (Type 2 DM, n = 16) were studied. Leg blood flow (LBF) was examined under conditions of euglycemic hyperinsulinemia (EH) and hyperglycemic hyperinsulinemia (HH), which produced a steady-state whole body glucose disposal rate (GDR) of ∼2,000 μmol · m−2 · min−1. At this GDR, under both conditions, subjects across the range of insulin sensitivity exhibited equivalent LBF (l/min EH: L, 0.42 ± 0.03; OB, 0.43 ± 0.03; Type 2 DM, 0.38 ± 0.07; P= 0.72 by ANOVA. HH: L, 0.44 ± 0.04; OB, 0.39 ± 0.05; Type 2 DM, 0.41 ± 0.04; P = 0.71). The continuous relationship between LBF and GDR did not differ across subject groups [slope × 10−5l/(μmol · m−2 · min−1) by ANOVA. EH: L, 8.6; OB, 9.2; Type 2 DM, 7.9; P = 0.91. HH: L, 4.2; OB, 2.5; Type 2 DM, 4.1; P = 0.77], although this relationship did differ between the EH and HH conditions ( P = 0.001). These findings support a physiological coupling of LBF and insulin-mediated glucose metabolism. The mechanism(s) linking substrate delivery and metabolism appears to be intact in insulin-resistant states.
Altered TNF-α, glucose, insulin, and amino acids in islets of Langerhans cultured in a microgravity model system
Authors: Tobin Brian W. , Leeper-Woodford Sandra K. , Hashemi Brian B. , Smith Scott M. , Sams Clarence F.
Published: December 2017

The present studies were designed to determine effects of a microgravity model system upon lipopolysaccharide (LPS)-stimulated tumor necrosis factor-α (TNF-α) activity and indexes of insulin and fuel homeostasis of pancreatic islets of Langerhans. Islets (1,726 ± 117, 150 islet equivalent units) from Wistar-Furth rats were treated as 1) high aspect ratio vessel (HARV) cell culture, 2) HARV plus LPS, 3) static culture, and 4) static culture plus LPS. TNF-α (L929 cytotoxicity assay) was significantly increased in LPS-induced HARV and static cultures; yet the increase was more pronounced in the static culture group ( P < 0.05). A decrease in insulin concentration was demonstrated in the LPS-stimulated HARV culture ( P< 0.05). We observed a greater glucose concentration and increased disappearance of arginine in islets cultured in HARVs. Although nitrogenous compound analysis indicated a ubiquitous reliance on glutamine in all experimental groups, arginine was converted to ornithine at a twofold greater rate in the islets cultured in the HARV microgravity model system ( P < 0.05). These studies demonstrate alterations in LPS-induced TNF-α production of pancreatic islets of Langerhans, favoring a lesser TNF activity in the HARV. These alterations in fuel homeostasis may be promulgated by gravity-averaged cell culture methods or by three-dimensional cell assembly.
PTH and PTH-related peptide enhance steroid secretion from human adrenocortical cells
Authors: Mazzocchi Giuseppina , Aragona Francesco , Malendowicz Ludwik K. , Nussdorfer Gastone G.
Published: December 2017

Parathyroid hormone (PTH) and PTH-related peptide (PTH-RP) are two hypercalcemic hormones that share a common receptor subtype, the PTH/PTH-RP receptor. PTH and PTH-RP concentration dependently enhanced basal aldosterone and cortisol secretion from dispersed human adrenocortical cells, with a maximal effective concentration (∼2-fold increase) of 10−8 M. The secretagogue effect of 10−8 M PTH or PTH-RP was abolished by the PTH/PTH-RP receptor antagonist [Leu11,d-Trp12]-PTH-RP-(7–34)-amide (10−6 M). PTH and PTH-RP (10−8 M) raised cAMP and inositol-triphosphate release by dispersed adrenocortical cells, and these effects were blocked by the adenylate cyclase inhibitor SQ-22536 (10−4 M) and the phospholipase C (PLC) inhibitor U-73122 (10−5 M), respectively. SQ-22536 (10−4 M) and U-73122 (10−5 M) partially inhibited aldosterone and cortisol response to 10−8 M PTH and PTH-RP; when added together, they abolished it. Similar results were obtained by using the protein kinase (PK)A and PKC inhibitors H-89 and calphostin C (10−5 M). It is concluded that PTH and PTH-RP exert a sizeable secretagogue action on the human adrenal cortex, probably acting through the PTH/PTH-RP receptor coupled with both adenylate cyclase/PKA- and PLC/PKC-dependent signaling cascades.
Regulatory responses to an orald-glutamate load: formation ofd-pyrrolidone carboxylic acid in humans
Authors: Raj Dominic , Langford Maryln , Krueger Stephan , Shelton Martin , Welbourne Tomas
Published: December 2017

Previously published studies have shown d-glutamate to be the most potent natural inhibitor of glutathione synthesis known, yet how d-glutamate is handled in humans is unknown. Therefore, we administered an oral d-glutamate load to four healthy volunteers and monitored the plasma d-glutamate concentration and excretion over a 3-h postload period. Compared with time controls, the plasma d-glutamate concentration increased 10-fold in the 1st h and then reached a plateau over the remaining time course. In contrast, plasma d-pyrrolidone carboxylic acid increased progressively throughout the 3-h time course to a level 10-fold higher than the d-glutamate plasma concentration. Excretion of d-glutamate progressively increased despite a constant filtered d-glutamate load rising from only 5 to 95% of the filtered amount. Excretion ofd-pyrrolidone carboxylic acid increased with the rise in filtered load without significant reabsorption. The amount ofd-pyrrolidone carboxylic acid excreted over the 3-h time course was 10 times the amount excreted as d-glutamate and accounted for almost 20% of the administered d-glutamate. These findings indicate that plasma d-glutamate concentration is tightly regulated through two mechanisms: 1) the transport into cells and metabolic conversion tod-pyrrolidone carboxylic acid and excretion, and 2) the enhancement of d-glutamate clearance by the kidneys.
Reduced free IGF-I and increased IGFBP-3 proteolysis in Turner syndrome: modulation by female sex steroids
Authors: Gravholt Claus Højbjerg , Frystyk Jan , Flyvbjerg Allan , Ørskov Hans , Christiansen Jens Sandahl
Published: December 2017

The bioactivity of the growth hormone-insulin-like growth factor (IGF) system is reduced in Turner syndrome and may explain the reduction seen in final height. We compared levels of free and total IGF-I, immunoreactive and Western ligand blot IGF-binding protein (IGFBP)-3, and IGFBP-3 proteolysis in women with Turner syndrome ( n = 23) before (TB) and during 6 mo treatment with 17β-estradiol and norethisterone. An age-matched group of controls ( n = 24) was included. Total IGF-I and immunoreactive levels of IGFBP-3 were comparable in TB and controls, whereas free IGF-I ( P = 0.02) in TB was less than in controls. Western ligand blotting (WLB)-IGFBP-3 was significantly lower in TB than in controls ( P = 0.0005). Accordingly, IGFBP-3 proteolysis was greater in Turner syndrome ( P = 0.001). Female sex steroid treatment increased WLB-IGFBP-3 ( P = 0.0005), whereas immunoreactive IGFBP-3 and IGFBP-3 proteolysis were normalized ( P = 0.004). Free IGF-I remained unchanged ( P = 0.8), with a tendency toward a decrease in total IGF-I ( P = 0.1). In conclusion, despite normal total IGF-I and immunoreactive IGFBP-3, free serum IGF-I is less and IGFBP-3 proteolysis is greater in Turner syndrome than in controls. During sex steroid treatment, IGFBP-3 proteolysis normalized, without any change in free IGF-I.
Increased weight gain after ovariectomy is not a consequence of leptin resistance
Authors: Chen Yanyun , Heiman Mark L.
Published: December 2017

The positive correlation between leptin and body fat mass has caused some investigators to speculate that leptin resistance contributes to obesity. Loss of ovarian function in human and rat is associated with increased fat mass gain and increased circulating leptin levels. To study whether ovariectomy produces leptin resistance, Sprague-Dawley female rats were ovariectomized or sham operated and injected with leptin for 35 days. Ovariectomy (OVX) produced hyperphagia and increased gain in both lean and fat mass. Daily leptin injections initially decreased food intake significantly, but feeding gradually increased to a stable level by day 16and remained at that level for the duration of study. Body composition analysis indicated that chronic injection of leptin to OVX rats dramatically decreased ( P < 0.05) fat mass [30 ± 2 (SE) g, vehicle, to 3 ± 1 g, leptin]. Using indirect calorimetry, we observed that OVX did not change energy expenditure or total level of fuel utilization. Leptin administration increased fat utilization and prevented reduction in calorie expenditure that is typically associated with food restriction. Leptin treatment to OVX rats decreased plasma triglyceride, free fatty acid, and insulin concentrations, whereas glucose concentration was normal. Withdrawal of leptin triggered hyperphagia, indicating that leptin biology remained throughout the duration of the chronic treatment. The same dose of leptin produced qualitatively similar data in sham-operated rats. Thus we concluded that the loss of ovarian function in rats is not associated with a change in leptin sensitivity.
Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans
Authors: Bamman Marcas M. , Shipp James R. , Jiang Jie , Gower Barbara A. , Hunter Gary R. , Goodman Ashley , McLafferty Charles L. , Urban Randall J.
Published: December 2017

The mechanism(s) of load-induced muscle hypertrophy is as yet unclear, but increasing evidence suggests a role for locally expressed insulin-like growth factor I (IGF-I). We investigated the effects of concentric (CON) vs. eccentric (ECC) loading on muscle IGF-I mRNA concentration. We hypothesized a greater IGF-I response after ECC compared with CON. Ten healthy subjects (24.4 ± 0.7 yr, 174.5 ± 2.6 cm, 70.9 ± 4.3 kg) completed eight sets of eight CON or ECC squats separated by 6–10 days. IGF-I, IGF binding protein-4 (IGFBP-4), and androgen receptor (AR) mRNA concentrations were determined in vastus lateralis muscle by RT-PCR before and 48 h after ECC and CON. Serum total testosterone (TT) and IGF-I were measured serially across 48 h, and serum creatine kinase activity (CK), isometric maximum voluntary contraction (MVC), and soreness were determined at 48 h. IGF-I mRNA concentration increased 62% and IGFBP-4 mRNA concentration decreased 57% after ECC ( P < 0.05). Changes after CON were similar but not significant ( P = 0.06–0.12). AR mRNA concentration increased ( P < 0.05) after ECC (63%) and CON (102%). Serum TT and IGF-I showed little change. MVC fell 10% and CK rose 183% after ECC ( P < 0.05). Perceived soreness was higher ( P < 0.01) after ECC compared with CON. Results indicate that a single bout of mechanical loading in humans alters activity of the muscle IGF-I system, and the enhanced response to ECC suggests that IGF-I may somehow modulate tissue regeneration after mechanical damage.
Glucose metabolism in perfused mouse hearts overexpressing human GLUT-4 glucose transporter
Authors: Belke Darrel D. , Larsen Terje S. , Gibbs E. Michael , Severson David L.
Published: December 2017

Glucose and fatty acid metabolism was assessed in isolated working hearts from control C57BL/KsJ- m+/+db mice and transgenic mice overexpressing the human GLUT-4 glucose transporter ( db/+-hGLUT-4). Heart rate, coronary flow, cardiac output, and cardiac power did not differ between control hearts and hearts overexpressing GLUT-4. Hearts overexpressing GLUT-4 had significantly higher rates of glucose uptake and glycolysis and higher levels of glycogen after perfusion than control hearts, but rates of glucose and palmitate oxidation were not different. Insulin (1 mU/ml) significantly increased glycogen levels in both groups. Insulin increased glycolysis in control hearts but not in GLUT-4 hearts, whereas glucose oxidation was increased by insulin in both groups. Therefore, GLUT-4 overexpression increases glycolysis, but not glucose oxidation, in the heart. Although control hearts responded to insulin with increased rates of glycolysis, the enhanced entry of glucose in the GLUT-4 hearts was already sufficient to maximally activate glycolysis under basal conditions such that insulin could not further stimulate the glycolytic rate.
Depletion of mitochondrial DNA alters glucose metabolism in SK-Hep1 cells
Authors: Park Kyu-Sang , Nam Kyung-Jay , Kim Jun-Woo , Lee Youn-Bok , Han Chang-Yeop , Jeong June-Key , Lee Hong-Kyu , Pak Youngmi Kim
Published: December 2017

Maternally inherited mitochondrial DNA (mtDNA) has been suggested to be a genetic factor for diabetes. Reports have shown a decrease of mtDNA content in tissues of diabetic patients. We investigated the effects of mtDNA depletion on glucose metabolism by use of ρ0 SK-Hep1 human hepatoma cells, whose mtDNA was depleted by long-term exposure to ethidium bromide. The ρ0 cells failed to hyperpolarize mitochondrial membrane potential in response to glucose stimulation. Intracellular ATP content, glucose-stimulated ATP production, glucose uptake, steady-state mRNA and protein levels of glucose transporters, and cellular activities of glucose-metabolizing enzymes were decreased in ρ0 cells compared with parental ρ+ cells. Our results suggest that the quantitative reduction of mtDNA may suppress the expression of nuclear DNA-encoded glucose transporters and enzymes of glucose metabolism. Thus this may lead to diabetic status, such as decreased ATP production and glucose utilization.
Use of sulfate production as a measure of short-term sulfur amino acid catabolism in humans
Authors: Hamadeh Mazen J. , Hoffer L. John
Published: December 2017

There is no fully satisfactory method for measuring amino acid catabolism in the nonsteady state that follows normal protein consumption. Because sulfate is the major product of sulfur amino acid catabolism, we tested whether its production can be accurately depicted using simple tracer or nontracer approaches under basal conditions and after the intravenous administration of a known amount of sulfate. In the basal postabsorptive state, serum sulfate concentration and urinary sulfate excretion remained constant for many hours, but the apparent steady-state serum sulfate rate of appearance achieved with primed continuous oral administration of sodium [34S]sulfate was 20% higher than urinary sulfate excretion. By contrast, after magnesium sulfate infusion, the increase in sulfate production above basal accounted for 95% over 6 h and 98% over 9 h of the administered dose when measured simply as urinary inorganic sulfate excretion corrected for changes in its extracellular fluid content. Using the latter method, we measured sulfate production after oral methionine and intravenous infusion of methionine in a mixture of other essential amino acids. Sulfate production above basal accounted for 59% over 6 h and 75% over 9 h of the oral methionine dose. Similar results were obtained with the mixed amino acid infusion, but interpretation of the latter experiment was limited by the mild protein sparing (and, hence, reduced endogenous sulfate production) induced by the amino acid infusion. We conclude that a simple nontracer method can provide an accurate measure of sulfate production and, hence, sulfur amino acid catabolism over collection periods as short as 6 h after a test meal. A significant portion of the sulfur derived from methionine appears to be retained in nonprotein compounds immediately after its ingestion.