bluuebunny/crossref_metadata_2025 huggingface dataset:
Glutamate transport and not cellular content modulates paracellular permeability in LLC-PK1-F+ cells
Authors: Welbourne T. C. , Chevalier D.
Published: December 2017

Uptake of glutamate modulates two cellular processes: 1) glutamine flux through the cellular glutaminase (GA) and 2) paracellular permeability (PP). Because both responses are the result of a decreased glutamate uptake, the present study was designed to determine whether the transport step or resulting fall in cellular glutamate modulates PP. To do so, advantage was taken of the ability of D-glutamate to competitively displace the natural L-isomer yet maintain transporter activity at or even above that normally occurring with L-glutamate. As a consequence cellular L-glutamate would fall while transporter fluxes remained. Accordingly, LLC-PK1-F+ cells were grown to confluent monolayers on porous supports in Dulbecco's modified Eagle's medium containing 50 microM L-glutamate and 1.8 mM L-glutamine with and without 1 mM D-glutamate. After a 90-min exposure to D-glutamate monolayer, L-glutamate content had fallen 38%. D-Glutamate was transported in place of the L-isomer as evidenced by the accumulation of L-glutamate in the media and uptake of the D-isomer. Although GA activation occurs as the result of the fall in cellular L-glutamate, PP did not increase; in fact, it slightly decreased as evidenced by an increased electrical resistance (from 180 +/- 12 to 210 +/- 10 omega x cm2, P < 0.02) and reduction in L-[(14)C]glucose permeability (2.72 +/- 0.75 to 2.28 +/- 0.37%, P = 0.10). Thus glutamate transporter activity and associated ionic fluxes rather than the fall in cellular glutamate and GA activation appear to play the critical role in modulating PP.
Progressive increase in glucose transport and GLUT-4 in human sarcolemmal vesicles during moderate exercise
Authors: Kristiansen S. , Hargreaves M. , Richter E. A.
Published: December 2017

Muscle glucose uptake increases progressively during moderate-intensity exercise. To elucidate whether this is due to a progressive increase in sarcolemmal glucose transport capacity, nine men exercised for 40 min at 75% maximal oxygen uptake on a bicycle ergometer. Muscle biopsies were obtained from the vastus lateralis at rest (0 min) and after 5 and 40 min of exercise and used for production of sarcolemmal giant (SG) vesicles. SG vesicle glucose transport at 5 mM increased (P < 0.05) by 38 and 93% after 5 and 40 min of exercise, respectively, compared with glucose transport at rest. The SG vesicle GLUT-4 protein content increased (P < 0.05) by 36 and 91% after 5 and 40 min of exercise, respectively, compared with rest. Thus the increase in vesicle glucose transport was accompanied by a similar increase in SG vesicle GLUT-4 protein content. Muscle glucose and glucose 6-phosphate were low at rest, increased (P < 0.05) 2.2- and 2.3-fold, respectively, after 5 min of exercise, and returned to resting values after 40 min of exercise. It is concluded that the progressive increase in muscle glucose uptake during moderate-intensity exercise may be due at least in part to a progressive increase in sarcolemmal glucose transport and GLUT-4 protein content.
Regulation of gluconeogenesis by glutamine in normal postabsorptive humans
Authors: Perriello G. , Nurjhan N. , Stumvoll M. , Bucci A. , Welle S. , Dailey G. , Bier D. M. , Toft I. , Jenssen T. G. , Gerich J. E.
Published: December 2017

There is evidence that glutamine may act as a regulator of protein, free fatty acid, and glycogen metabolism. To test the hypothesis that glutamine may act as a physiological regulator of gluconeogenesis, we infused 16 normal postabsorptive volunteers with glutamine at a rate (11.4 micromol kg(-1) x min(-1)) estimated to approximate its appearance in plasma after a protein meal and assessed changes in production of glucose from glutamine, systemic glucose appearance and disposal, and uptake and release of glucose, glutamine, and alanine by forearm skeletal muscle. Although infusion of glutamine increased plasma glutamine concentration and turnover only threefold (from 0.63 +/- 0.03 to 1.95 +/- 0.10 mmol/l and from 5.43 +/- 0.24 to 14.85 +/- 0.66 micromol x kg(-1) x min(-1), respectively; P < 0.001), formation of glucose from glutamine increased sevenfold from 0.55 +/- 0.03 to 3.74 +/- 0.28 micromol x kg(-1) x min(-1) (P < 0.001). Formation of glucose from alanine was also stimulated (0.52 +/- 0.05 vs. 0.75 +/- 0.04 micromol x kg(-1) x min(-1); P < 0.001) in the absence of a change in plasma alanine concentration. Furthermore, glutamine infusion decreased its own de novo synthesis (4.55 +/- 0.22 vs. 2.81 +/- 0.62 micromol x kg(-1) x min(-1);P < 0.02) while increasing that of alanine (2.82 +/- 0.32 vs. 3.56 +/- 0.32 micromol x kg(-1) x min(-1); P < 0.002). Systemic glucose appearance, systemic glucose disposal, and forearm balance of glucose and alanine were not altered. Because the stimulatory effects of glutamine on gluconeogenesis occurred in the absence of changes in plasma insulin and glucagon levels, these results provide evidence that, in humans, glutamine may act both as a substrate and as a regulator of gluconeogenesis as well as a modulator of its own metabolism.
Glucose kinetics in interstitial fluid can be predicted by compartmental modeling
Authors: Gastaldelli A. , Schwarz J. M. , Caveggion E. , Traber L. D. , Traber D. L. , Rosenblatt J. , Toffolo G. , Cobelli C. , Wolfe R. R.
Published: December 2017

The purposes of this study were to define in sheep a compartmental model for glucose kinetics in the basal condition and to test the hypothesis that interstitial fluid obtained by sampling thoracic duct lymph (TDL) represents one or more peripheral compartments of the glucose model. A bolus of [6,6-(2)H]glucose was injected in nine animals, followed by frequent sampling of blood and TDL. Linear kinetic modeling has been applied to plasma data, indicating that a three-compartment model adequately describes glucose kinetics. Both catenary and mammillary models were identified, and their predictions for the tracer behavior in nonaccessible pools were evaluated. In all experiments, regardless of the model structure, predictions in the compartment most rapidly exchanging with blood (pool 2) well matched the measured tracer-to-tracee ratio in TDL. Furthermore, modeling analysis showed that 90-95% of the tracer in TDL comes from this pool. This supported the physiological identification of a peripheral pool of glucose kinetics as extracellular fluid represented by TDL measurements.
Interaction of exercise, insulin, and hypoglycemia studied using euglycemic and hypoglycemic insulin clamps
Authors: Zinker B. A. , Allison R. G. , Lacy D. B. , Wasserman D. H.
Published: December 2017

Hyperinsulinemic euglycemic and hypoglycemic clamps were used to study the interaction of exercise, insulin, and hypoglycemia at rest and during exercise in the dog. Sampling (artery and portal, hepatic, and iliac veins) and infusion (vena cava) catheters and a flow probe (external iliac artery) were implanted surgically >16 days before study. After an 18-h fast and an 80-min tracer equilibration period, dogs were studied in the basal state (t = -40 to 0 min) and during a moderate treadmill exercise (t = 0-150 min) period or an equivalent duration sedentary period. Insulin was infused at 1 mU x kg(-1) x min(-1) from t = 0-150 min. In one group of sedentary (n = 7) and one group of exercised (n = 6) dogs, glucose was clamped at basal during the insulin infusion. In another group of sedentary (n = 6) and another group of exercised (n = 6) dogs, arterial glucose was clamped at hypoglycemic levels (approximately 65 mg/dl) during the insulin infusion. Arteriovenous difference and isotopic ([3-(3)H]glucose, [U-(14)C]glucose) techniques were used to assess glucose metabolism. Insulin levels were approximately 40 microU/ml in all groups. Data show that 1) counterregulatory hormone (glucagon, catecholamines, and cortisol) responses to exercise and hypoglycemia combined are synergistically higher than the response to either stimulus alone; 2) exercise-induced increases in insulin action are negated during hypoglycemia by the counterregulatory response; 3) decreased need for exogenous glucose during hypoglycemic compared with euglycemic exercise is due to stimulation of endogenous glucose production, which accounts for approximately 30% of the decrease, and reduction of glucose utilization, which accounts for approximately 70%; and 4) insulin-stimulated nonoxidative glucose metabolism is unaffected by exercise or hypoglycemia, whereas insulin-stimulated oxidative glucose metabolism is selectively increased by exercise and decreased by hypoglycemia. In conclusion, the marked rise in insulin action during exercise is matched, under insulin-induced hypoglycemic conditions, by an equally profound increase in counterregulation. The effectiveness of the potent insulin counterregulatory response may be important in decreasing the magnitude and frequency of exercise-induced hypoglycemia.
Malonyl-CoA regulation in skeletal muscle: its link to cell citrate and the glucose-fatty acid cycle
Authors: Saha A. K. , Vavvas D. , Kurowski T. G. , Apazidis A. , Witters L. A. , Shafrir E. , Ruderman N. B.
Published: December 2017

Malonyl-CoA is an inhibitor of carnitine palmitoyltransferase I, the enzyme that controls the oxidation of fatty acids by regulating their transfer into the mitochondria. Despite this, knowledge of how malonyl-CoA levels are regulated in skeletal muscle, the major site of fatty acid oxidation, is limited. Two- to fivefold increases in malonyl-CoA occur in rat soleus muscles incubated with glucose or glucose plus insulin for 20 min [Saha, A. K., T. G. Kurowski, and N. B. Ruderman. Am. J. Physiol. 269 (Endocrinol. Metab. 32): E283-E289, 1995]. In addition, as reported here, acetoacetate in the presence of glucose increases malonyl-CoA levels in the incubated soleus. The increases in malonyl-CoA in all of these situations correlated closely with increases in the concentration of citrate (r2 = 0.64) and to an even greater extent the sum of citrate plus malate (r2 = 0.90), an antiporter for citrate efflux from the mitochondria. Where measured, no increase in the activity of acetyl-CoA carboxylase (ACC) was found. Inhibition of ATP citrate lyase with hydroxycitrate markedly diminished the increases in malonyl-CoA in these muscles, indicating that citrate was the major substrate for the malonyl-CoA precursor, cytosolic acetyl-CoA. Studies with enzyme purified by immunoprecipitation indicated that the observed increases in citrate could have also allosterically activated ACC. The results suggest that in the presence of glucose, insulin and acetoacetate acutely increase malonyl-CoA levels in the incubated soleus by increasing the cytosolic concentration of citrate. This novel mechanism could complement the glucose-fatty acid cycle in determining how muscle chooses its fuels. It could also provide a means by which glucose acutely modulates signal transduction in muscle and other cells (e.g., the pancreatic beta-cell) in which its metabolism is determined by substrate availability.
Direct quantification of norepinephrine spillover and hormone output from the pancreas of the conscious dog
Authors: Dunning B. E. , Scott M. F. , Neal D. W. , Cherrington A. D.
Published: December 2017

To estimate pancreatic neural activity and to assess the potential role of the pancreatic nerves in the regulation of hormone secretion, the methodology necessary to quantify neurotransmitter spillover and hormone output in the conscious dog was developed. A femoral artery and the superior pancreaticoduodenal vein (SPDV) were chronically cannulated, and a flow probe was placed on the SPDV. Hormone output was calculated using the pancreatic arteriovenous concentration difference and the SPDV plasma flow. Basal glucose levels were 103 +/- 1 mg/dl; the pancreatic outputs of insulin, glucagon, and pancreatic polypeptide (PP, an index of parasympathetic neural activity) were 2,900 +/- 700 microU/min, 1,900 +/- 400 pg/min, and 9.3 +/- 4.6 ng/min, respectively. Pancreatic norepinephrine (NE) spillover was calculated similarly; however, pancreatic extraction of epinephrine was used as an index of NE extraction. Basal NE spillover was 3,600 +/- 700 pg/min, greatly exceeding that reported using anesthetized, laparotomized dogs. Intravenous glucose infusion increased plasma glucose to 146 +/- 13 mg/dl, increased insulin output approximately twofold, and suppressed glucagon output by approximately 50%. Hyperglycemia markedly reduced PP output. Hyperglycemia failed to influence pancreatic NE spillover. Insulin-induced hypoglycemia (36 +/- 2 mg/dl) completely suppressed insulin output and stimulated glucagon output (> 10-fold). Hypoglycemia increased NE spillover and PP output to 19,900 +/- 4,600 pg/min and 117 +/- 22 ng/min, respectively. We conclude that pancreatic neurotransmitter spillover in the basal state is much higher than previously appreciated and that neural signaling to the pancreas is responsive to physiological and pathophysiological changes in the metabolic state.
Decreased plasma glutamine level and CD4+ T cell number in response to 8 wk of anaerobic training
Authors: Hack V. , Weiss C. , Friedmann B. , Suttner S. , Schykowski M. , Erbe N. , Benner A. , Bartsch P. , Droge W.
Published: December 2017

The purpose of the present study was to investigate the role of plasma amino acids and glutathione (GSH) on the absolute number of leukocyte and lymphocyte subpopulations in response to different training programs. Healthy untrained subjects were randomly assigned to an 8-wk aerobic (AET) or anaerobic (ANT) exercise training program. Absolute number of cell counts did not significantly change in AET, whereas a decrease of CD4+ T cell counts (P < 0.05), a fall in cells expressing CD45RA+ antigen (P < 0.05), and a marked increase in CD8+ T cell numbers (P < 0.01) were noted in ANT at the end of the training period compared with baseline values. Furthermore, ANT demonstrated a marked rise (P < 0.001) in plasma glutamate from 27.6 +/- 2.8 to 49.8 +/- 5.2 microM and a considerable reduction (P < 0.001) of the plasma glutamine pool from 713 +/- 22 to 601 +/- 30 microM after 8 wk of training. The decrease in glutamine showed a strong positive correlation to the individual loss of CD4+ T cells (r = 0.67, P < 0.001). AET demonstrated a rise (P < 0.05) in GSH from 20.7 +/- 2.5 to 28.1 +/- 1.5 nmol/mg protein at terminal examination. In conclusion, our data indicate impairment of the number and activity of CD4+ T cells in response to 8 wk of ANT, which might be linked to metabolic factors such as glutamine.
Assessment of insulin sensitivity with minimal model: role of model assumptions
Authors: Mari A.
Published: December 2017

Insulin sensitivity is frequently assessed with the minimal model (MM) and the insulin-modified intravenous glucose tolerance test (MIVGTT). To ascertain the validity of this approach, the mechanisms by which the MM estimates glucose effectiveness and insulin sensitivity (SG and SI, respectively) from the data are analyzed theoretically. Published data and new labeled MIVGTTs in normal and non-insulin-dependent diabetic (NIDDM) subjects are used as reference data. One reason for the reported difficulty in estimating SI in NIDDM is the inadequacy of the MM to describe the data. SG is a biased estimate of the fractional glucose clearance (FGC) at basal insulin, and SI is a biased estimate of the average slope of the insulin concentration-FGC curve. The monocompartmental assumption and the role of glucose production in the MM are causes of bias. The bias is fairly constant across the spectrum of glucose tolerance (SG: approximately 150% overestimate; SI: approximately 30% underestimate). Also, SI is not expected to account satisfactorily for hepatic insulin sensitivity. Finally, by the use of SG and SI, FGC at a target insulin level (FGCMM) can be estimated. FGCMM agrees well with the analogous clamp index (difference 10%; correlation: r = 0.88, P < 0.002) and, in NIDDM, has a lower coefficient of variation than SI (57 vs. 82%). In conclusion, this analysis indicates that the MM is a sufficiently reliable method for the assessment of insulin sensitivity if it is used cautiously.
Quantitative analysis of acetoacetate metabolism in AS-30D hepatoma cells with 13C and 14C isotopic techniques
Authors: Holleran A. L. , Fiskum G. , Kelleher J. K.
Published: December 2017

Experimental hepatoma cells utilize acetoacetate as an oxidative energy source and as a precursor for lipid synthesis. The significance of ketone body metabolism in tumors lies in the study of tumor-host metabolism and the ketoneMic condition that is often present in cancer patients. The quantitative importance of acetoacetate and glucose was investigated in AS-30D cells with use of 13C and 14C isotopic methods. In addition, the effects of acetoacetate were compared with those of dichloroacetic acid (DCA), an activator of pyruvate dehydrogenase (PDH). The 14CO2 ratio method evaluated the entry of pyruvate into the tricarboxylic acid (TCA) cycle and revealed that acetoacetate diverted pyruvate from PDH to pyruvate carboxylation. In contrast, DCA increased the oxidation of glucose largely through PDH, indicating that PDH is not maximally active in the absence of DCA. Isotopomer spectral analysis of lipid synthesis demonstrated that, in the absence of acetoacetate, glucose supplied 65% of the acetyl-CoA used for de novo lipogenesis. When 5 mM acetoacetate was included in the incubation, glucose was displaced as a lipogenic precursor and acetoacetate supplied 85% of the acetyl-CoA for lipogenesis vs. only 2% for glucose. Thus AS-30D cells have a large capacity for acetoacetate utilization for de novo lipogenesis.
Effects of endotoxin on zinc metabolism in human volunteers
Authors: Gaetke L. M. , McClain C. J. , Talwalkar R. T. , Shedlofsky S. I.
Published: December 2017

After stress or trauma, the serum zinc concentration decreases. This study evaluated possible mechanisms for hypozincemia with the use of a human endotoxemia model. Two doses of endotoxin [lipopolysaccharide (LPS)] were administered on consecutive mornings to 12 healthy volunteers, and each subject was also studied after saline injection. Blood was analyzed for zinc, cytokines (tumor necrosis factor-alpha and interleukin-6), albumin, albumin-zinc binding, and C-reactive protein (CRP). Serial 24-h urine collections were analyzed for zinc. Each LPS dose briefly increased plasma cytokine concentrations and decreased the serum zinc concentration. Serum albumin, the major zinc binding protein, did not decrease, but a progressive increase in CRP was found. LPS did not alter zinc binding affinity to serum albumin. Urine zinc losses were not increased. We conclude that hypozincemia in this model cannot be explained by decreased serum albumin, changes in serum albumin-zinc binding, or increased urinary zinc excretion. Because hypozincemia was transient and followed cytokine peaks, we postulate that LPS-stimulated hypozincemia is mediated, at least partly, by a cytokine-directed internal redistribution of zinc.
Cholate inhibits high-fat diet-induced hyperglycemia and obesity with acyl-CoA synthetase mRNA decrease
Authors: Ikemoto S. , Takahashi M. , Tsunoda N. , Maruyama K. , Itakura H. , Kawanaka K. , Tabata I. , Higuchi M. , Tange T. , Yamamoto T. T. , Ezaki O.
Published: December 2017

The effects of sodium cholate on high-fat diet-induced hyperglycemia and obesity were investigated. Insulin resistance was estimated by measuring 2-deoxyglucose uptake in epitrochlearis muscles incubated in vitro. Addition of 0.5% cholate to high-safflower oil diet completely prevented high fat-induced hyperglycemia and obesity in C57BL/6J mice with a slight decrease of energy intake but with no inhibition of fat absorption. Furthermore, the addition of cholate decreased blood insulin levels and prevented high-fat diet-induced decrease of glucose uptake in epitrochlearis. However, there was no change in the unsaturation index of fatty acids in skeletal muscles and in GLUT-4 levels by cholate. In liver, cholate addition resulted in cholesterol accumulation and completely prevented high-fat diet-induced triglyceride accumulation. The changes of triglyceride level in the liver were paralleled to the changes of acyl-CoA synthetase (ACS) mRNA. ACS catalyzes the formation of acyl-CoA from fatty acid, and acyl-CoA is utilized for triglyceride formation in liver. ACS has a sterol-responsive element 1 in its promoter region. These data indicate that the favorable effects of cholate could be partly the result of downregulation of ACS mRNA.
Modulation of gliquidone action by forskolin in the pancreas of normal and GK rats
Authors: Leclercq-Meyer V. , Malaisse W. J.
Published: December 2017

This study aims to investigate whether agents that stimulate adenosine 3',5'-cyclic monophosphate (cAMP) formation could be used to increase insulin release evoked by hypoglycemic sulfonylureas in non-insulin-dependent diabetes mellitus. For this purpose, the effect of gliquidone (1.0 microM) on insulin and glucagon release was examined in the perfused pancreas of either normal or Goto-Kakizaki (GK) rats at a low concentration of D-glucose (2.8 mM) and in the absence or presence of forskolin (1.3 microM). In normal rats, the diterpene exerted relatively little effect on basal insulin release but markedly augmented the insulinotropic action of gliquidone. In GK rats, forskolin dramatically augmented both basal and gliquidone-stimulated insulin output. In mirror image of its effect on insulin release, forskolin augmented basal glucagon output and failed to increase the secretory response of the A cell to gliquidone, at least in normal rats. On the contrary, in GK rats, forskolin, while slightly enhancing basal glucagon output, unmasked the glucagonotropic potential of gliquidone that was otherwise not detected in the diabetic animals. These findings are interpreted in light of a dual metabolic and energy-independent response of islet cells to the forskolin-induced generation of cAMP. They document the optimalization by endogenous cAMP of the B cell secretory response to gliquidone in non-insulin-dependent diabetes.
Interleukin-6 secretion in mice is associated with reduced glucose-6-phosphatase and liver glycogen levels
Authors: Metzger S. , Goldschmidt N. , Barash V. , Peretz T. , Drize O. , Shilyansky J. , Shiloni E. , Chajek-Shaul T.
Published: December 2017

Mice bearing interleukin-6 (IL-6)-secreting tumor were used to study the chronic effect of IL-6 on carbohydrate metabolism. Mice were injected with allogeneic tumor cells transduced with the murine IL-6 gene. Serum IL-6 levels were correlated exponentially with tumor weight. Secretion of IL-6 from the developed tumors was associated with decreased food consumption, reduced body weight, and reduced blood glucose levels. Insulin levels did not change, and 2-deoxyglucose uptake was not affected in most tissues examined. A significant increase of 2-deoxyglucose uptake was measured in the liver. Glycogen content in the liver determined 0, 6, 12, and 18 days after tumor inoculation was 42, 23, 12, and 3 mg/g, respectively. The activity of phosphoenolpyruvate carboxykinase was not affected. The activity of glucose-6-phosphatase (G-6-Phase) determined 6, 12, and 18 days after tumor injection was 84, 70, and 50% of G-6-Pase activity in pair-fed mice bearing nonsecreting tumors, respectively. G-6-Pase mRNA levels were markedly reduced due to inhibition of G-6-Pase gene transcriptional rate.
Insulin-stimulated amino acid utilization during glucose and amino acid clamps decreases with development
Authors: Wray-Cahen D. , Beckett P. R. , Nguyen H. V. , Davis T. A.
Published: December 2017

Neonatal animals utilize their dietary amino acids for protein accretion with high efficiency, and this efficiency declines during early life. The factors responsible for this developmental change are unknown. Our objectives were to determine whether amino acid (AA) utilization is stimulated by insulin in the neonate and whether this response changes during the suckling period. Two hyperinsulinemic-euglycemic clamp infusion studies, using 10-2,000 ng insulin.kg-0.66.min-1, were performed in 7- and 26-day-old pigs. In study I, no AA were provided during the infusion, and the resultant decline in plasma AA levels was defined. In study II, plasma AA were clamped at near-fasting levels, and whole body utilization of exogenous AA was determined by measuring the rate of infusion of an AA mixture necessary to maintain basal plasma lysine concentrations. In study I, the half-maximal effective dose (ED50) for the fall in AA concentrations with increasing plasma insulin concentration was lower in 7- than in 26-day-old pigs, and the nadir in AA concentration was achieved by only 20 microU/ml insulin. In study II, the utilization of exogenous AA during hyperinsulinemic-euglycemic AA clamps exhibited a higher maximum response (Rmax) (49 vs. 26 mumol AAtotal.min-1.kg-1) and a lower ED50 (18 vs. 45 microU insulin/ml) in 7- than in 26-day-old pigs. Plasma urea nitrogen concentrations did not rise with increasing insulin and AA infusion rates. These results indicate that insulin stimulates the utilization of exogenous AA in neonatal pigs and that both the insulin sensitivity and responsiveness of AA utilization decline over the suckling period. The infused AA were likely utilized for protein accretion.
Muscle glycogen synthesis in recovery from intense exercise in humans
Authors: Bangsbo J. , Madsen K. , Kiens B. , Richter E. A.
Published: December 2017

The present study examined the role of lactate and glucose as substrates for glyconeogenesis in muscle in recovery from high-intensity exercise in humans. Seven subjects performed approximately 100 min of intense intermittent one-legged knee extensor exercise on two occasions: with [high lactate (HL)] and without [control (C)] intense arm exercise between the leg exercise bouts, leading to end exercise arterial plasma lactate concentrations of 16.0 +/- 1.6 and 9.2 +/- 1.6 mmol/l, respectively (P < 0.05). At the end of exercise, muscle lactate and glycogen were similar in HL and C (20.5 +/- 1.3 vs. 17.3 +/- 2.0 mmol/kg wet wt and 48.1 +/- 11.3 vs. 56.3 +/- 8.6 mmol/kg wet wt, respectively). Muscle glycogen increased (P < 0.05) during the first 5 min of recovery only in HL, but after 90 min of recovery the muscle glycogen concentration was the same in C and HL (61.2 +/- 12.0 vs. 71.5 +/- 10.9 mmol/kg wet wt). Muscle lactate not released to the blood could maximally account for 28 (C) and 54% (HL) of the increase in muscle glycogen during 90 min of recovery or < 10% of glycogen synthesis after full recovery. The total net glucose uptake corresponded to 84 (C) and 57% (HL) of the glycogen synthesized. Apparently, muscle glyconeogenesis may occur in humans, but the role of lactate as a substrate is minor. Instead, blood glucose appears to be the most important precursor for muscle glycogen synthesis after intense exercise.
Relationship of visceral adipose tissue and glucose disposal is independent of sex in black NIDDM subjects
Authors: Banerji M. A. , Lebowitz J. , Chaiken R. L. , Gordon D. , Kral J. G. , Lebovitz H. E.
Published: December 2017

To determine the interrelationship among insulin action, total or regional adiposity, and sex, we measured insulin-mediated glucose disposal by the euglycemic insulin clamp and adipose distribution using computed axial tomography (22 scans) in 32 black men and 20 black women with non-insulin-dependent diabetes mellitus (age 48 +/- 9 and 54 +/- 9 yr, body mass index 26.3 +/- 2.3 and 27.2 +/- 2.6 kg/m2, respectively). Women had approximately 80% more total and subcutaneous fat volume than men (31.8 +/- 8.3 vs. 18.6 +/- 6.1 and 28.5 +/- 7.3 vs. 14.7 +/- 4.6 liters) and less muscle volume (22.9 +/- 3.7 vs. 35.1 +/- 3.8 liters). Visceral fat volume did not differ between men and women (3.49 +/- 1.65 vs. 2.96 +/- 1.22 liters). Despite these body composition differences, an inverse nonlinear relationship existed between glucose disposal and visceral fat independent of sex (r = -0.58, P < 0.0001; men r = -0.60 and women r = -0.59; the slope and intercept were not different in men and women). Visceral fat explained a significant portion (34%) of variance in insulin-mediated glucose disposal, whereas total or subcutaneous fat and sex did not. Visceral fat appears to affect glucose disposal over a restricted range (up to approximately 2.5 l/m2 body surface area.
Glucose ingestion affects cardiac ANS in healthy subjects with different amounts of body fat.
Authors: Paolisso G , Manzella D , Ferrara N , Gambardella A , Abete P , Tagliamonte M R , De Lucia D , Furgi G , Picone C , Gentile S , Rengo F , Varricchio M
Published: December 2017

Low-to-high frequency ratio (LF/HF) is an indirect index of sympathovagal balance derived by heart rate spectral analysis. We investigated the effect of glucose ingestion on LF/HF in 17 healthy, normotensive young subjects (9 male, 8 female) with a wide body fat content range (body fat = 29 +/- 5.9%; range = 19-42%) and a normal thyroid hormone status. Before and after an oral glucose tolerance test (OGTT), the Holter technique and indirect calorimetry allowed us to determine heart rate and substrate oxidation in all subjects. At baseline, LF/HF correlated with body fat (r = 0.60, P < 0.005), waist-to-hip ratio (r = 0.57, P < 0.01), fasting plasma insulin (r = 0.55, P < 0.04), leptin (r = 0.56, P < 0.01), and norepinephrine (r = 0.58, P < 0.009) concentrations. Age-, body fat-, content-, and fat-free mass-adjusted respiratory quotient (r = 0.59, P < 0.007) and basal metabolic rate (r = 0.61, P < 0.001) were also correlated with basal LF/HF. Along with OGTT plasma glucose, insulin and norepinephrine concentrations and basal LF/HF significantly rose at 60 min and then declined throughout the test. Area under the curve (AUC) for LF/HF correlated with body fat (r = -0.66, P < 0.004), fasting plasma leptin concentration (r = -0.57, P < 0.01), glucose induced thermogenesis (r = 0.62, P < 0.001), glucose uptake (r = 0.59, P < 0.007), and AUC for plasma norepinephrine concentration (r = 0.63, P < 0.001). Water instead of glucose ingestion does not significantly affect LF/HF (n = 8). In conclusion, our study supports the hypothesis that glucose ingestion affects LF/HF and that such change is related to the amount of body fat.
Dexamethasone increases G alpha q-11 expression and hormone-stimulated phospholipase C activity in UMR-106-01 cells.
Authors: Mitchell J , Bansal A
Published: December 2017

Glucocorticoids regulate responsiveness of many cells to hormones that bind to G protein-coupled receptors. We examined the effect of glucocorticoids on parathyroid hormone (PTH) activation of two G protein-activated signal transduction pathways, phospholipase C (PLC) and adenylyl cyclase, in osteosarcoma UMR-106-01 cells. Dexamethasone (100 nM) increased PTH-stimulated and NaF-stimulated PLC activity by > 100% over 4 days (223 +/- 8 and 293 +/- 8.2% of control after 4 days for PTH and NaF-stimulated activity, respectively). The increase in PTH-stimulated adenylyl cyclase response in the same cells was more modest (162 +/- 5.4 and 171 +/- 6.8% of control after 4 days for PTH and NaF-stimulated activity, respectively). PTH activation of PLC was blocked by antiserums to G alpha q-11 and activation of adenylyl cyclase by G alpha s antiserums. Quantification of these G protein subunits in control and dexamethasone-treated cells showed a 78% increase in G alpha q-11 (from 18.1 +/- 1.2 to 32.2 +/- 1.5 pmol/mg), whereas G alpha s was increased only 34% (from 6.2 +/- 0.5 to 8.2 +/- 0.3 pmol/mg) and G beta-subunits were increased 40% (from 54 +/- 2.3 to 75.2 +/- 3.8 pmol/mg). These results suggest that glucocorticoids are more potent regulators of PLC activity than adenylyl cyclase activity in UMR cells, and this is mediated, at least in part, by differential increases in G alpha q-11 proteins.
Functional heterogeneity of leucine pools in human skeletal muscle.
Authors: Ljungqvist O H , Persson M , Ford G C , Nair K S
Published: December 2017

Current models to measure muscle protein synthesis in humans assume a homogeneous intracellular amino acid pool. This assumption was tested by measuring the isotopic enrichment of leucine and its transamination product alpha-ketoisocaproate (KIC) in plasma and muscle tissue fluid and comparing them with that of leucyl-tRNA during a continuous infusion of L-[1-13C]leucine in 12 healthy subjects. Six subjects were studied twice while drinking a carbohydrate (0.42 kcal/kg) drink every 20 min for 11 h or the same volume of water. Six others took an isocaloric mixed meal providing 14 mg protein/kg every 20 min and water. Enrichment of plasma and tissue fluid KIC and plasma leucine was consistently higher than that of leucyl-tRNA and tissue fluid leucine (P < 0.01), whereas the enrichment of leucyl-tRNA was equivalent to that of tissue fluid leucine in all experiments. Furthermore, the ratio of enrichment of leucyl-tRNA to that of plasma leucine and KIC decreased after the mixed meal, whereas that of leucyl-tRNA to tissue fluid leucine remained constant. The enrichment of KIC was closer (approximately 17% lower) to that of plasma leucine than that of leucyl-tRNA (approximately 43% higher), indicating that the transamination pool derived more leucine from extracellular sources than the acylation pool. We conclude that the use of plasma KIC enrichment as a surrogate measure of leucyl-tRNA enrichment substantially underestimates muscle protein synthetic rates in humans, whereas tissue fluid leucine enrichment is a valid surrogate measure. In addition, the differences in enrichment of leucyl-tRNA and KIC support a regulated cytoplasmic trafficking of leucine in muscle cells.
Where is the "inverting factor" in hormone secretion from parathyroid cells?
Authors: Cohen Y , Rahamimov R , Naveh-Many T , Silver J , Rahamimoff R
Published: December 2017

Secretion of hormones and transmitters in the body fall into two general categories. In the majority of the secreting cells, including the presynaptic terminals in the nervous system, an increase in the extracellular calcium causes an increase in secretion. There are two notable exceptions to this general rule: the parathyroid cells and the renal juxtaglomerular cells, where an increase in extracellular calcium leads to a decrease in secretion. Because these two cell types have a cardinal role in a wide variety of physiological and pathophysiological functions, it is of great importance to understand the regulation of their hormone secretion process. A key element to such an understanding is the identification of the location of the "inverting step," which makes the parathyroid cells behave in a fashion contrary to most other secretory cells. Whole cell imaging studies strongly suggested that the inversion factor is between the changes in intracellular calcium concentration ([Ca2+]i) and the secretion of the hormone. Surprisingly, confocal calcium imaging of the parathyroid cells did not support this dogma. It revealed that the interior of the parathyroid cell is a nonhomogeneous medium and that an increase in the extra-cellular calcium concentration produces changes in [Ca2+]i, in both the same and opposite directions, in different parts of the parathyroid cell.
Abnormal regulation of HGP by hyperglycemia in mice with a disrupted glucokinase allele
Authors: Rossetti Luciano , Chen Wei , Hu Meizhu , Hawkins Meredith , Barzilai Nir , Efrat Shimon
Published: December 2017

Glucokinase (GK) catalyzes the phosphorylation of glucose in β-cells and hepatocytes, and mutations in the GK gene have been implicated in a form of human diabetes. To investigate the relative role of partial deficiencies in the hepatic vs. pancreatic GK activity, we examined insulin secretion, glucose disposal, and hepatic glucose production (HGP) in response to hyperglycemia in transgenic mice 1) with one disrupted GK allele, which manifest decreased GK activity in both liver and β-cells (GK+/−), and 2) with decreased GK activity selectively in β-cells (RIP-GKRZ). Liver GK activity was decreased by 35–50% in the GK+/− but not in the RIP-GKRZ compared with wild type (WT) mice. Hyperglycemic clamp studies were performed in conscious mice with or without concomitant pancreatic clamp. In all studies [3-3H]glucose was infused to measure the rate of appearance of glucose and HGP during 80 min of euglycemia (Glc ∼5 mM) followed by 90 min of hyperglycemia (Glc ∼17 mM). During hyperglycemic clamp studies, steady-state plasma insulin concentration, rate of glucose infusion, and rate of glucose disappearance (Rd) were decreased in both GK+/− and RIP-GKRZ compared with WT mice. However, whereas the basal HGP (at euglycemia) averaged ∼22 mg ⋅ kg−1⋅ min−1in all groups, during hyperglycemia HGP was suppressed by only 48% in GK+/− compared with ∼70 and 65% in the WT and RIP-GKRZ mice, respectively. During the pancreatic clamp studies, the ability of hyperglycemia per se to increase Rdwas similar in all groups. However, hyperglycemia inhibited HGP by only 12% in GK+/−, vs. 42 and 45%, respectively, in the WT and RIP-GKRZ mice. We conclude that, although impaired glucose-induced insulin secretion is common to both models of decreased pancreatic GK activity, the marked impairment in the ability of hyperglycemia to inhibit HGP is due to the specific decrease in hepatic GK activity.
Regional differences in interstitial glycerol concentration in subcutaneous adipose tissue of women
Authors: Hickner R. C. , Fisher J. S. , Kohrt W. M.
Published: December 2017

The aims of this study were to 1) compare two methods of determining interstitial glycerol concentration in subcutaneous adipose tissue (AT) and 2) determine whether there are regional differences in interstitial glycerol concentration in subcutaneous AT of nonobese, premenopausal women. Microdialysis probes were inserted under local anesthesia into the abdominal (2 probes) and femoral (1 probe) subcutaneous AT in each subject ( n = 5) and perfused with a Ringer solution containing 2.5 mM glucose and glycerol in concentrations ranging from 0 to 900 μM. Microdialysis probe relative recoveries and interstitial glycerol concentrations were determined by the no-net-flux method (NNF) and the internal reference method (IR) with the use of [13C]glycerol. Microdialysis probe relative recoveries were 57.4 ± 3.6% by NNF and 61.2 ± 10.1% by IR in femoral AT [ P = not significant (NS)] and were 55.2 ± 6.0% by NNF and 66.6 ± 4.2% by IR in abdominal AT ( P = NS). The calculated interstitial glycerol concentrations determined by NNF and IR were 236.4 ± 42.7 and 241.1 ± 39.6 μM ( P = NS) in femoral AT and 151.4 ± 29.7 and 129.4 ± 18.7 μM in abdominal AT (NNF vs. IR, P = NS; femoral vs. abdominal, P < 0.05). It can be concluded that the interstitial glycerol concentration in the femoral AT of nonobese, premenopausal females is ∼240 μM and is higher than in abdominal AT (140 μM). Furthermore, the use of a stable isotope of glycerol as an internal reference is suitable for determining interstitial glycerol concentrations in subcutaneous adipose tissue in humans at rest.
Exercise regulation of glucose transport in skeletal muscle
Authors: Hayashi Tatsuya , Wojtaszewski Jørgen F. P. , Goodyear Laurie J.
Published: December 2017

Exercise increases the rate of glucose uptake into the contracting skeletal muscles. This effect of exercise is similar to the action of insulin on glucose uptake, and the mechanism through which both stimuli increase skeletal muscle glucose uptake involves the translocation of GLUT-4 glucose transporters to the plasma membrane and transverse tubules. Most studies suggest that exercise and insulin recruit distinct GLUT-4-containing vesicles and/or mobilize different “pools” of GLUT-4 proteins originating from unique intracellular locations. There are different intracellular signaling pathways that lead to insulin- and exercise-stimulated GLUT-4 translocation. Insulin utilizes a phosphatidylinositol 3-kinase-dependent mechanism, whereas the exercise signal may be initiated by calcium release from the sarcoplasmic reticulum leading to the activation of other signaling intermediaries, and there is also evidence for autocrine- or paracrine-mediated activation of transport. The period after exercise is characterized by increased sensitivity of muscle glucose uptake to insulin, which can be substantially prolonged in the face of carbohydrate deprivation. The ability of exercise to utilize insulin-independent mechanisms to increase glucose uptake in skeletal muscle has important clinical implications, especially for patients with diseases that are associated with peripheral insulin resistance, such as non-insulin-dependent diabetes mellitus.
Effects of marginal iodine deficiency during pregnancy: iodide uptake by the maternal and fetal thyroid
Authors: Versloot P. M. , Elst J. P. Schröder-Van Der , Van Der Heide D. , Boogerd L.
Published: December 2017

Iodide uptake by the thyroid is an active process. Iodine deficiency and pregnancy are known to influence thyroid hormone metabolism. The aim of this study was to clarify the effects of iodine deficiency and pregnancy on iodide uptake by the thyroid. Radioiodide was injected intravenously into nonpregnant and 19-day pregnant rats receiving a normal or marginally iodine-deficient diet. The uptake of radioiodide by the thyroid was measured continuously for 4 h. The absolute iodide uptake by the maternal and fetal thyroid glands at 24 h was calculated by means of the urinary specific activity. Pregnancy resulted in a decrease in the absolute thyroidal iodide uptake. Marginal iodine deficiency had no effect on the absolute iodide uptake by the maternal thyroid. The decreased plasma inorganic iodide was compensated by an increase in thyroidal clearance. A similar compensation was not found for the fetus; the uptake of iodide by the fetal thyroid decreased by 50% during marginal iodine deficiency. This can lead to diminished thyroid hormone production, which will have a negative effect on fetal development, especially of the brain.
Quantifying gluconeogenesis during fasting
Authors: Chandramouli Visvanathan , Ekberg Karin , Schumann William C. , Kalhan Satish C. , Wahren John , Landau Bernard R.
Published: December 2017

The use of2H2O in estimating gluconeogenesis’ contribution to glucose production (%GNG) was examined during progressive fasting in three groups of healthy subjects. One group ( n = 3) ingested2H2O to a body water enrichment of ≈0.35% 5 h into the fast. %GNG was determined at 2-h intervals from the ratio of the enrichments of the hydrogens at C-5 and C-2 of blood glucose, assayed in hexamethylenetetramine. %GNG increased from 40 ± 8% at 10 h to 93 ± 6% at 42 h. Another group ingested2H2O over 2.25 h, beginning at 11 h ( n = 7) and 19 h ( n = 7) to achieve ≈0.5% water enrichment. Enrichment in plasma water and at C-2 reached steady state ≈1 h after completion of2H2O ingestion. The C-5-to-C-2 ratio reached steady state by the completion of 2H2O ingestion. %GNG was 54 ± 2% at 14 h and 64 ± 2% at 22 h. A 3-h [6,6-2H2]glucose infusion was also begun to estimate glucose production from enrichments at C-6, again in hexamethylenetetramine. Glucose produced by gluconeogenesis was 0.99 ± 0.06 mg ⋅ kg−1 ⋅ min−1at both 14 and 22 h. In a third group ( n = 3) %GNG reached steady state ≈2 h after2H2O ingestion to only ≈0.25% enrichment. In conclusion, %GNG by 2 h after2H2O ingestion and glucose production using [6,6-2H2]glucose infusion, begun together, can be determined from hydrogen enrichments at blood glucose C-2, C-5, and C-6. %GNG increases gradually from the postabsorptive state to 42 h of fasting, without apparent change in the quantity of glucose produced by gluconeogenesis at 14 and 22 h.
Effect of cholinergic blockade on inhibited GH secretion by feeding and intraruminal SCFA infusion in sheep
Authors: Matsunaga N. , Wakiya M. , Roh S. G. , Hirota M. , He M. L. , Hidaka S. , Hidari H.
Published: December 2017

The effect of cholinergic blockade on suppressed growth hormone (GH) secretion caused by feeding or the intraruminal infusion of an acetate, propionate, and butyrate mixture (107 and 214 μmol ⋅ kg−1⋅ min−1over 6 h) was examined in ovariectomized ewes. Intraruminal infusion at the rate of 107 μmol ⋅ kg−1⋅ min−1increased peripheral plasma short-chain fatty acid (SCFA) concentrations to approximately the physiological levels noted after feeding. Plasma GH was markedly suppressed by feeding and at both the 107 and 214 μmol ⋅ kg−1⋅ min−1SCFA infusion rates; however, cholinergic blocking agents completely blocked the suppressed GH secretion after feeding and only at the 107 μmol ⋅ kg−1⋅ min−1infusion rate. Plasma glucose increased at both infusion rates, and the plasma free fatty acids decreased after feeding and at both infusion rates. However, both metabolites were unchanged relative to the saline control after the injection of the cholinergic antagonists. It is suggested that the decrease in plasma GH observed after feeding and a near-physiological ruminal SCFA increment is mediated via the parasympathetic nerve and not by pharmacological ruminal SCFA increments attributed to other pathways.
Differential effects of rat pregnancy on uterine and lung atrial natriuretic factor receptors
Authors: Vaillancourt Patrice , Omer Saeed , Deng Xing-Fei , Mulay Shree , Varma Daya R.
Published: December 2017

We investigated if the refractoriness to the tocolytic effects of atrial natriuretic factor (ANF) during rat pregnancy is due to a downregulation of one or both guanylyl cyclase (GC)-coupled GC-A and GC-B ANF receptors; lungs were used as controls. Uteri and lungs of virgin, pregnant ( days 7, 16, and 21), and day 2postpartum rats expressed mRNAs for GC-A and GC-B as well as GC-uncoupled ANF-C receptors. GC-B receptor protein was more abundant than GC-A in uteri; the reverse was the case in lungs. Pregnancy decreased uterine mRNAs and proteins for GC-A and GC-B receptors as well as the effects of ANF and C-type natriuretic peptide (CNP) on uterine GC activity; lung ANF receptors and effects of ANF and CNP on lung GC activity were not modulated by pregnancy. It is concluded that pregnancy induces organ-specific modulation of ANF receptors and a downregulation of ANF-GC receptors would minimize interference with uterine motility during pregnancy.
Effects of acute α2-blockade on insulin action and secretion in humans
Authors: Natali Andrea , Gastaldelli Amalia , Galvan Alfredo Quiñones , Sironi Anna Maria , Ciociaro Demetrio , Sanna Giovanna , Rosenzweig Pierre , Ferrannini Ele
Published: December 2017

We tested whether acute α2-blockade affects insulin secretion, glucose and fat metabolism, thermogenesis, and hemodynamics in humans. During a 5-h epinephrine infusion (50 ng ⋅ min−1 ⋅ kg−1) in five volunteers, deriglidole, a selective α2-receptor inhibitor, led to a more sustained rise in plasma insulin and C-peptide levels (+59 ± 14 vs. +28 ± 6, and +273 ± 18 vs. +53 ± 14 pM, P < 0.01 vs. placebo) despite a smaller rise in plasma glucose (+0.90 ± 0.4 vs. +1.5 ± 0.3 mM, P < 0.01). Another 10 subjects were studied in the postabsorptive state and during a 4-h hyperglycemic (+4 mM) clamp, coupled with the ingestion of 75 g of glucose at 2 h. In the postabsorptive state, hepatic glucose production, resting energy expenditure, and plasma insulin, free fatty acid (FFA), and potassium concentrations were not affected by acute α2-blockade. Hyperglycemia elicited a biphasic rise in plasma insulin (to a peak of 140 ± 24 pM), C-peptide levels (1,520 ± 344 pM), and insulin secretion (to 410 ± 22 pmol/min); superimposed glucose ingestion elicited a further twofold rise in insulin and C-peptide levels, and insulin secretion. However, α2-blockade failed to change these secretory responses. Fasting blood β-hydroxybutyrate and glycerol and plasma FFA and potassium concentrations all declined with hyperglycemia; time course and extent of these changes were not affected by α2-blockade. Resting energy expenditure (+25 vs. +16%, P < 0.01) and external cardiac work (+28% vs. +19%, P < 0.01) showed larger increments after α2-blockade. We conclude that acute α2-blockade in humans 1) prevents epinephrine-induced inhibition of insulin secretion, 2) does not potentiate basal or intravenous- or oral glucose-induced insulin release, 3) enhances thermogenesis, and 4) increases cardiac work.