bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucose and insulin-induced inhibition of fatty acid oxidation: the glucose-fatty acid cycle reversed
Authors: Sidossis L. S. , Wolfe R. R.
Published: December 2017

In this study we have investigated a hypothesis that proposes the reverse of the so-called "glucose-fatty acid cycle, " i.e., that accelerated carbohydrate metabolism directly inhibits fatty acid oxidation. We studied normal volunteers in the basal state and during a hyperinsulinemic, hyperglycemic clamp (plasma insulin = 1,789 +/- 119 pmol/l, plasma glucose = 7.7 +/- 0.2 mmol/l). We quantified fat oxidation using indirect calorimetry and stable isotopes ([1-13C]oleate). Plasma oleate enrichment and free fatty acid (FFA) concentration were kept constant by means of infusion of lipids and heparin. Glucose oxidation increased from basal 6.2 +/- 0.8 to 22.3 +/- 1.4 mumol.kg-1.min-1 during the clamp (P < 0.01). Total (indirect calorimetry) and plasma fatty acid oxidation (isotopic determination) decreased from 2.6 +/- 0.2 to 0.4 +/- 0.3 (P < 0.01) and 2.2 +/- 0.2 to 1.4 +/- 0.1 mumol.kg-1.min-1 (P <0.05), respectively. We conclude that under the conditions of the present experiment, glucose and/or insulin directly inhibits fatty acid oxidation. Our findings suggest that, contrary to the prediction of the glucose-fatty acid cycle, the intracellular availability of glucose (rather than FFA) determines the nature of substrate oxidation in human subjects.
Rapid enhancement of acyl-CoA synthetase, LPL, and GLUT-4 mRNAs in adipose tissue of VMH rats
Authors: Shimomura I. , Takahashi M. , Tokunaga K. , Keno Y. , Nakamura T. , Yamashita S. , Takemura K. , Yamamoto T. , Funahashi T. , Matsuzawa Y.
Published: December 2017

Obesity is frequently accompanied by metabolic and cardiovascular complications. The accumulation of intra-abdominal visceral fat has been shown to be more closely related to various complications of obesity than that of subcutaneous fat. To elucidate the metabolic characteristics of visceral fat during fat accumulation, we examined the changes of acyl-CoA synthetase (ACS) mRNA abundance and its activity, glucose transporter (GLUT)-4, lipoprotein lipase (LPL), and very-low-density lipoprotein (VLDL) receptor mRNA abundances in mesenteric and subcutaneous fat in early stages of ventromedial hypothalamus (VMH)-lesioned rats. ACS activity increased 4.9-fold in the mesenteric fat on the 1st day, remaining unchanged in the subcutaneous fat. ACS, GLUT-4, and LPL mRNA levels were all increased in both fat tissues of VMH rats. The relative increase of mRNAs in VMH day 1 was greater in the mesenteric fat, suggesting that mesenteric fat shows rapid response during fat accumulation. VLDL receptor mRNA levels showed no significant change in either fat tissue. We conclude that ACS, GLUT-4, and LPL may contribute to fat accumulation at the gene expression level from a very early stage during the development of obesity.
Creatine ingestion favorably affects performance and muscle metabolism during maximal exercise in humans
Authors: Casey A. , Constantin-Teodosiu D. , Howell S. , Hultman E. , Greenhaff P. L.
Published: December 2017

Nine male subjects performed two bouts of 30-s maximal isokinetic cycling before and after ingestion of 20 g creatine (Cr) monohydrate/day for 5 days. Cr ingestion produced a 23.1 +/- 4.7 mmol/kg dry matter increase in the muscle total creatine (TCr) concentration. Total work production during bouts 1 and 2 increased by approximately 4%, and the cumulative increases in both peak and total work production over the two exercise bouts were positively correlated with the increase in muscle TCr. Cumulative loss of ATP was 30.7 +/- 12.2% less after Cr ingestion, despite the increase in work production. Resting phosphocreatine (PCr) increased in type I and II fibers. Changes in PCr before exercise bouts 1 and 2 in type II fibers were positively correlated with changes in PCr degradation during exercise in this fiber type and changes in total work production. The results suggest that improvements in performance were mediated via improved ATP resynthesis as a consequence of increased PCr availability in type II fibers.
Increased lipid oxidation but normal muscle glycogen response to epinephrine in humans with IDDM
Authors: Cohen N. , Halberstam M. , Rossetti L. , Shamoon H.
Published: December 2017

The effects of physiological increments in epinephrine and insulin on glucose production (GP), skeletal muscle glycogen metabolism, and substrate oxidation were studied in eight insulin-dependent diabetes mellitus (IDDM) and nine control subjects. Epinephrine was coinfused for the final 120 min of a 240-min euglycemic, hyperinsulinemic clamp. In both groups, insulin increased glucose uptake, glycogen synthesis, and whole body carbohydrate (CHO) oxidation and inhibited GP (by 70-80%) and lipid oxidation (by approximately 50%), whereas epinephrine antagonized the effect of insulin on glucose uptake and glycogen synthesis. In contrast, GP increased in IDDM subjects (P < 0.02) but remained suppressed by insulin in controls. CHO oxidation fell (1.37 +/- 0.25 vs. 2.08 +/- 0.32 mg.kg-1.min-1) and lipid oxidation increased to baseline in IDDM subjects, with increments in plasma free fatty acids (FFA) and glycerol. In contrast, in controls, plasma FFA and glycerol remained suppressed and lipid oxidation decreased further with epinephrine (P < 0.005). Epinephrine completely reversed insulin's activation of muscle glycogen synthase in both groups. Thus, during hyperinsulinemia, the hepatic response to epinephrine in IDDM subjects may be dependent on activation of lipid oxidation. Skeletal muscle glycogen metabolism is exquisitely sensitive to epinephrine despite the presence of hyperinsulinemia.
Cavernosal nerve stimulation in the rat reverses castration-induced decrease in penile NOS activity
Authors: Lugg J. , Ng C. , Rajfer J. , Gonzalez-Cadavid N.
Published: December 2017

Castration in the rat reduces both the erectile response and penile nitric oxide synthase (NOS) activity, and these effects are prevented by androgen administration. In this study we determined that the decrease of penile NOS in the castrated rat is due to NOS enzyme inhibition rather than to a reduction of its content and that this inhibition may be reversed. Adult rats were either castrated or left intact, and, after 1 wk, electrical field stimulation (EFS) was applied to the cavernosal nerve and the penises were excised either at the peak of erection or after detumescence. Penile NOS activity in the non-EFS castrates decreased by 70% as compared with the intact non-EFS-treated controls, but neuronal NOS content remained unaffected despite changes in regional distribution. NOS activity in the castrated penis was restored to normal values by EFS at the peak of stimulation, and then decreased on detumescence. This was in contrast to the intact controls in which EFS did not stimulate penile NOS activity. These data indicate that androgen depletion in the rat reduces penile NOS activity rather than NOS content and that this enzyme inhibition is reversed by cavernosal nerve stimulation.
Contributions of modeling to understanding stimulus-secretion coupling in pancreatic beta-cells
Authors: Sherman A.
Published: December 2017

Mechanisms of ionic control of insulin secretion in beta-cells of the pancreatic islets of Langerhans are reviewed. The focus is on aspects that have been treated by mathematical models, especially those related to bursting electrical activity. The study of these mechanisms is difficult because of the need to consider ionic fluxes, calcium handling, metabolism, and electrical coupling with other cells in the islet. The data come either from islets, where experimental maneuvers tend to have multiple effects, or from isolated cells, which have degraded electrical activity and secretory sensitivity. Modeling aids in the process by integrating data on individual components such as channels and calcium handling and testing hypotheses for coherence and quantitative plausibility. The study of a variety of models has led to some general mathematical results that have yielded qualitative model-independent insights.
Aluminum potentiates P(i) transport stimulation induced by fluoride in osteoblast-like cells
Authors: Imai T. , Burgener D. , Zhen X. , Benjour J. P. , Caverzasio J.
Published: December 2017

The effect of aluminum (AI) on inorganic phosphate (P(i)) transport stimulation induced by fluoride (F) was investigated in MC3T3-E1 osteoblast-like cells. Al potentiated the increase in P(i) transport activity induced by F in a dose- and time-dependent manner. Results obtained with deferoxamine mesylate, an Al chelator, suggest that a fluoroalumino complex is probably the active F molecule responsible for the change in P(i) transport observed in this study. The signaling pathway responsible for the stimulation of P(i) transport by F+Al likely involves a tyrosine phosphorylation process but neither a protein kinase C nor a mitogen-activated protein kinase pathway. As previously found in UMR-106 cells for F alone, F+Al potentiated the change in P(i) transport induced by fetal calf serum. A similar interaction was found between F+Al and thrombin acting through a G protein-coupled receptor. These observations are compatible with the hypothesis that F+Al could interact with G protein-coupled receptors associated with a signaling tyrosine phosphorylation process involved in the regulation of P(i), transport in osteoblast-like cells.
Glucose-induced transmigration of monocytes is linked to phosphorylation of PECAM-1 in cultured endothelial cells
Authors: Rattan V. , Shen Y. , Sultana C. , Kumar D. , Kalra V. K.
Published: December 2017

The adherence of circulating monocytes to the endothelium, their migration into the subendothelium, and the subsequent formation of foam cells are initial events in the pathogenesis of atherosclerosis. However, the effect of hyperglycemia on the transendothelial migration of monocytes is not known. Exposure of human umbilical vein endothelial cells (HUVEC) cultured in a Transwell chamber to 25 mM D-glucose (a concentration representing a hyperglycemic state) for 2 h resulted in a twofold increase in the migration of vitamin D3-differentiated monocyte-like HL-60 cells. The migration was inhibited by addition of either an antibody to platelet-endothelial cell adhesion molecule-1 (PECAM-1) or a protein kinase C inhibitor, GF-109203X. In HUVEC, high concentrations of D-glucose (25 mM), but not of other sugars such as L-glucose, 2-deoxyglucose, D-galactose, or D-mannitol, caused a sevenfold increase in the phosphorylation of PECAM-1 as a result of activation of protein kinase C. The 25 mM D-glucose-induced PECAM-1 phosphorylation and transmigration of monocyte-like HL-60 cells were further increased by treatment of HUVEC with the phosphatase inhibitor calyculin A. These results suggest that direct phosphorylation of PECAM-1 in response to elevated glucose promotes transendothelial migration of monocytes, contributing to accelerated atherogenesis in diabetics.
Impaired insulin secretion and excessive hepatic glucose production are both early events in the diabetic GK rat
Authors: Picarel-Blanchot F. , Berthelier C. , Bailbe D. , Portha B.
Published: December 2017

Adult Goto-Kakisaki Wistar (GK) rats exhibit a spontaneous non-insulin-dependent diabetes characterized by impaired glucose-induced insulin secretion, decreased beta-cell mass, hepatic glucose overproduction, and moderate insulin resistance in muscles and adipose tissues. To elucidate the pathogenesis of hyperglycemia in this animal model, we have studied insulin secretion and insulin action in 4-wk-old GK pups, just before weaning. In the postabsorptive state, their basal plasma glucose level was elevated (P < 0.001), and their tolerance to intravenous glucose was impaired. Their kinetics of insulin release in response to glucose was impaired, with a low acute phase of insulin release in vivo and in vitro (perfused pancreas). Basal glucose production was increased in the GK pups by 40% (P < 0.05). During euglycemic clamp performed at submaximal hyperinsulinemia, suppression of liver glucose production was less effective (P < 0.01) in the GK rats, whereas their overall glucose utilization was similar to that of the control group. This was correlated with a normal insulin-stimulated glucose utilization by epitrochlearis, soleus, and extensor digitorum longus muscles, diaphragm, and white adipose tissues. These data give body to the primacy of the beta-cell defects in the etiology of non-insulin-dependent diabetes mellitus in the GK rat. They also highlight a possible primary role of the liver defect. Peripheral insulin resistance does not contribute to the development of postnatal glucose intolerance in this diabetes model.
Effect of low-level basal plus marked "pulsatile" hyperglycemia on insulin secretion in fetal sheep
Authors: Carver T. D. , Anderson S. M. , Aldoretta P. W. , Hay W. W.
Published: December 2017

We compared fetal glucose- and arginine-stimulated insulin secretion (delta I, pM) among four groups of pregnant sheep after 10-11 days of different maternal glycemic patterns: 1) control, euglycemic; 2) low-level basal plus "pulsatile" hyperglycemic (PHG group); 3) markedly hyperglycemic (HG) group); 4) markedly hypoglycemic (LG group). Mean delta I during a hyperglycemic clamp was greatest in the PHG group (190 +/- 28 pM, P < 0.01) and least in the HG (64 +/- 13 pM, P < 0.05) and LG groups (68 +/- 15 pM, P < 0.05) compared with the control group (126 +/- 18 pM). After an arginine bolus, insulin concentration was greater in the PHG group at two of four sampling times over 30 min compared with the control group and at all times compared with the HG and LG groups. The trend in mean delta I over the postarginine sampling period (PHG 1,092 +/- 114 pM; control 921 +/- 86 pM; HG897 +/- 117 pM; LG831 +/- 57 pM) was in the same direction as for glucose and was significant (P < 0.05). Thus glucose-stimulated fetal insulin secretion is regulated by the duration and pattern, as well as the magnitude, of maternal and fetal hyperglycemia; this regulation may also extend to insulin-secretion capacity.
NONMEM improves group parameter estimation for the minimal model of glucose kinetics
Authors: De Gaetano A. , Mingrone G. , Castageneto M.
Published: December 2017

The minimal model of glucose kinetics interprets blood glucose and insulin concentrations after an interprets blood glucose and insulin concentrations after an intravenous glucose tolerance test (IVGTT) and provides parameters describing tissue insulin sensitivity and glucose-dependent tissue glucose disposal. In the standard application, the model is fitted to each experimental subject's points by nonlinear least squares, with suitable weighing. The variability of parameter estimates may, however, represent a problem, making the model in practice unidentifiable on a group of experimental subjects undergoing some treatment of interest. To obviate this problem, a specific modification to the original protocol has been introduced: administering tolbutamide 20 min after the glucose bolus has been shown to improve parameter stability. With this modification, however, the converse model of pancreatic secretion can no more be fitted on the collected series of concentrations. The application of the nonlinear mixed effects model (NONMEM) loss function allows estimation of parameter population means, variances, and covariances to be made on all sampled subjects simultaneously. Although this procedure does not allow an individual subject's parameters to be estimated, the variability of the group parameter estimates is greatly reduced compared with the standard method. In the present work, 20 healthy volunteers have been studied with an IVGTT, and group parameters have been computed in both standard and NONMEM ways: asymptotic parameter coefficients of variation with NONMEM were at least twenty times smaller than the corresponding sample parameter coefficients of variation obtained with the classical method.
Altered muscle insulin sensitivity in the male offspring of protein-malnourished rats
Authors: Ozanne S. E. , Wang C. L. , Coleman N. , Smith G. D.
Published: December 2017

Insulin sensitivity of skeletal muscle was studied in male offspring of rat dams fed either a 20% (control) or 8% (low-protein) diet during pregnancy and lactation. Freshly isolated muscle strips took up more [3H]methylglucose from low-protein animals than from controls (19.2 +/- 2.5 and 4.26 +/- 0.45 nmol.min-1.mg muscle-1, respectively, P < 0.001). However, after a 60-min preincubation there was no significant difference in basal glucose transport (4.02 +/- 0.42 and 4.23 +/- 0.35 nmol.min-1.mg-1 for control and low-protein animals, respectively). Insulin (300 pM) had a significantly greater (P < 0.001) effect on stimulation of glucose transport into preincubated low-protein muscle strips than into controls (to 14.14 +/- 1.25 and 9.61 +/- 0.71 nmol.min-1.mg-1, respectively). There were no differences in total GLUT-4 protein content. However, subcellular fractionation revealed significantly (P < 0.001) more GLUT-4 in muscle plasma membranes of low-protein animals compared with controls. Insulin increased (P < 0.001) the GLUT-4 content of control plasma membranes but had no effect in low-protein animals. There were twofold more insulin receptors in low-protein muscle membranes compared with controls (2.35 +/- 0.17 x 10(11) and 1.28 +/- 0.10 x 10(11) and insulin receptors/mg muscle membrane protein, respectively, P < 0.01). These results suggest that programming of muscle insulin sensitivity can occur during fetal life.
Dual-energy X-ray absorptiometry body composition model: review of physical concepts
Authors: Pietrobelli A. , Formica C. , Wang Z. , Heymsfield S. B.
Published: December 2017

Although dual-energy X-ray absorptiometry (DXA) is widely used in clinical research as a means of quantifying body composition, there remains at present little published information that reviews the method's underlying physical basis. Because a clear understanding of DXA physical concepts is integral to appropriate use and interpretation, we present here a three-section review that includes both relevant in vitro and in vivo experimental demonstrations. In the first section we describe the main physical principles on which DXA is based. The section that follows presents a step-by-step analysis of the DXA two-component soft tissue model. In the final section we demonstrate how knowledge of physical concepts can lead to resolution of important methodological concerns, such as the influence of hydration changes on DXA fat estimates. A thorough understanding of DXA physical concepts provides a basis for appropriate interpretation of measurement results and stimulates many new and important research questions.
Postprandial leg and splanchnic fatty acid metabolism in nonobese men and women
Authors: Nguyen T. T. , Mijares A. H. , Johnson C. M. , Jensen M. D.
Published: December 2017

These studies were conducted to determine whether there are gender-specific regional differences in meal triglyceride fatty acid uptake. Systemic and regional oleate ([3H]oleate) kinetics were measured in nine nonobese men and eight nonobese women before and at the end of a 6-h meal, administered as small frequent feedings to achieve steady-state chylomicronemia. Chylomicron uptake in the splanchnic bed accounted for 71 +/- 15% of meal triglyceride disappearance in men and 20 +/- 7% in women (P < 0.01), whereas leg chylomicron uptake could only account for 12 +/- 2 and 8 +/- 4% (P not significant in men vs. women) of meal triglyceride disappearance. Meal ingestion suppressed (P < 0.05) systemic and regional free fatty acid release in both men and women. Splanchnic nonchylomicron triglyceride release and leg nonchylomicron triglyceride uptake were not significantly different in men and women. In summary, the largest quantitative difference between men and women in fatty acid kinetics during meal ingestion is a substantially greater splanchnic uptake of meal triglyceride fatty acids in men. This could represent greater meal fatty acid storage in visceral adipose tissue.
Time course of insulin resistance associated with feeding dogs a high-fat diet
Authors: Rocchini A. P. , Marker P. , Cervenka T.
Published: December 2017

The current study evaluated both the time course of insulin resistance associated with feeding dogs a high-fat diet and the relationship between the development of insulin resistance and the increase in blood pressure that also occurs. Twelve adult mongrel dogs were chronically instrumented and randomly assigned to either a control diet group (n = 4) or a high-fat diet group (n = 8). Insulin resistance was assessed by a weekly, single-dose (2 mU.kg-1.min-1) euglycemic-hyperinsulinemic clamp on all dogs. Feeding dogs a high-fat diet was associated with a 3.7 +/- 0.5 kg increase in body weight, a 20 +/- 4 mmHg increase in mean blood pressure, a reduction in insulin-mediated glucose uptake [(in mumol-kg-1.min-1) decreasing from 72 +/- 6 before to 49 +/- 7 at 1 wk, 29 +/- 3 at 3 wk, and 30 +/- 2 at 6 wk of the high-fat diet, P < 0.01]. and a reduced insulin-mediated increase in cardiac output. In eight dogs (4 high fat and 4 control), the dose-response relationship of insulin-induced glucose uptake also was studied. The whole body glucose uptake dose-response curve was shifted to the right, and the rate of maximal whole body glucose uptake was significantly decreased (P < 0.001). Finally, we observed a direct relationship between the high-fat diet-induced weekly increase in mean arterial pressure and the degree to which insulin resistance developed. In summary, the current study documents that feeding dogs a high-fat diet causes the rapid development of insulin resistance that is the result of both a reduced sensitivity and a reduced responsiveness to insulin.
Differential regulation of macrophage arginine metabolism: a proposed role in wound healing
Authors: Shearer J. D. , Richards J. R. , Mills C. D. , Caldwell M. D.
Published: December 2017

Nitric oxide (NO) and ornithine, products of NO synthase or arginase, respectively, have opposing biological activities. The effect of mediators of leukocyte activation and inhibition on arginine metabolism of resident mouse peritoneal exudate cells (MPEC) was determined. Factors that increased basal NO synthase activity, interferon (IFN)-gamma and lipopolysaccharide (LPS), decreased arginase activity in intact cells. Transforming growth factor (TGF)-beta1 decreased IFN-gamma-stimulated NO synthase activity and produced a reciprocal increase in urea and ornithine release. TGF-beta1 had no effect on the activity of these enzymes in LPS-stimulated MPEC. Corticosterone (Cort, 100 ng/ml) decreased the basal activity of both enzymes. However, Cort inhibited NO synthase activity and increased ornithine release in MPEC exposed to IFN-gamma or LPS. The difference between arginase activity in intact cells vs. that of cell lysates suggested intracellular inhibition of arginase activity. Products of NO synthase, NO and citrulline, were shown to inhibit MPEC arginase activity under maximal assay conditions. Intracellular pH was not altered by exposure of MPEC to LPS, IFN-gamma, TGF-beta, and Cort. This reciprocal change in arginine metabolism is proposed to be an important component of wound healing. Expression of NO synthase creates a cytotoxic environment that may be important to the early phase of wound healing. As wound healing progresses, increased arginase activity produces an environment favorable for fibroblast replication and collagen production.
Decline in muscle insulin-dependent and -independent glucose uptake but not GLUT-4 in 21- vs. 28-day-old rats
Authors: Cartee G. D. , Wetter T. J. , Guerra A. N. , Cox T. N.
Published: December 2017

The most rapid age-related decrease in insulin-stimulated glucose uptake in skeletal muscle occurs between 3 and 5 wk of age in rats. Therefore, we studied unstimulated, insulin-stimulated, and in vitro hypoxia-stimulated 2-deoxy-D-[G-3H]glucose (2-DG) uptake in isolated soleus, flexor digitorum brevis (FDB), and epitrochlearis muscles from rats at 21, 28, and 35 days of age. Age-related decrements in insulin- (approximately 40-60%) and hypoxia-stimulated (approximately 50%) 2-DG uptake occurred in all muscles, and most of the decline was evident by 28 days. Unstimulated 2-DG uptake declined significantly with advancing age in the epitrochlearis (73%) and FDB (60%) and tended to decrease in the soleus (38%). The time course and relative magnitude of these decrements were similar under unstimulated, insulin-stimulated, and hypoxic conditions. GLUT-4 protein concentration was unaltered by age in each muscle. These results indicate that a substantial age-related decrement in 2-DG uptake occurs in several limb muscles from rats at 21 vs. 28-35 days by a mechanism that is independent of GLUT-4 levels and not specific for the insulin-dependent pathway.
Regulation of insulin secretion via ATP-sensitive K+ channel independent mechanisms: role of phospholipase C
Authors: Zawalich W. S. , Zawalich K. C.
Published: December 2017

Groups of rat or mouse islets were isolated and perifused with 20 mM glucose plus 200 microM diazoxide. The further addition of 30 mM K+ resulted in a rapid and sustained biphasic insulin secretory response. The onset of secretion in response to the addition of K+ was comparable in both species, but the magnitude of the response was significantly greater from rat islets. After the labeling of islet phosphoinositide pools with 2-[3H]inositol, the accumulation of labeled inositol phosphates (IP) in response to 30 mM K+ addition in the simultaneous presence of 20 mM glucose plus diazoxide was assessed. The addition of 30 mM K+ significantly increased IP accumulation approximately 300% in rat islets, whereas only an insignificant 25-30% increase was observed in mouse islets. The protein kinase C inhibitor staurosporine (50 nM) dramatically reduced the sustained secretory response from rat islets in the presence of 30 mM K+, 20 mM glucose, and diazoxide. Its effect was minimal on mouse islets and a significant inhibitory effect on insulin secretion was observed only during the final 5 min of the perifusion. The further addition of carbachol, an agonist that activates an isozyme of phospholipase C distinct from that activated by glucose, together with K+, 20 mM glucose, plus diazoxide resulted in a sustained amplification of insulin secretion from mouse but not rat islets. K+ (30 mM)-induced insulin secretion in the presence of 3 mM glucose was similar from perifused rat or mouse islets, a finding that would seem to preclude the activation of voltage-regulated Ca2+ channels as the pertinent difference. These results confirm previous observations with these species and document another anomaly that exists between the responses of rat islets compared with mouse islets. The inability to activate a nutrient- and calcium-regulated phospholipase C isozyme in mouse islets to the same extent as in rat islets appears to account, at least in part, for these different insulin secretory responses under these unique conditions.
Involvement of MAP kinase and c-fos signaling in the inhibition of cell growth by somatostatin
Authors: Yoshitomi H. , Fujii Y. , Miyazaki M. , Nakajima N. , Inagaki N. , Seino S.
Published: December 2017

Somatostatin significantly suppressed cell growth of the mouse insulinoma-derived cell line MIN6. MIN6 cells exhibited high-affinity binding of somatostatin with 50% inhibitory concentration value of 0.9 nM. RNA blot analysis revealed that MIN6 cells expressed only SSTR3 among the five somatostatin receptors so far identified. Treatment of MIN6 cells with somatostatin significantly reduced the serum-induced c-fos expression levels. On the other hand, somatostatin (100 nM) treatment of MIN6 cells cultured in medium containing 10% serum transiently increased c-fos expression levels to 282 +/- 4.7% and then significantly decreased them to 27 +/- 7.6% of the levels before treatment. Mitogen-activated protein (MAP) kinase activity transiently increased to 656 +/- 91.2% and decreased thereafter to 39 +/- 13.3% of the activity before the addition of somatostatin (100 nM) into the medium. In addition, the stimulatory effect of somatostatin on c-fos expression and MAP kinase activity (early effect) was not altered by pertussis toxin (PTX), whereas the suppressive effect of somatostatin on c-fos expression and MAP kinase activity (late effect) was mitigated by PTX. These findings suggest that an inhibition of c-fos expression mediated by cross talk between PTX-sensitive G protein signaling and receptor tyrosine kinase signaling is one of the mechanisms by which somatostatin inhibits cell growth in MIN6 cells.
Role of the autonomic nervous system in the thermogenic response to food in lean individuals
Authors: De Jonge L. , Garrel D. R.
Published: December 2017

The aim of this study was to determine the role of the autonomic nervous system (ANS) in obligatory and facultative components of the thermogenic response to food (TRF). Nineteen lean, healthy subjects participated in this study, which comprised two protocols, each exploring one component of the ANS. In the first experimental group, propranolol (prime: 80 micrograms/kg; continuous: 1 microgram.kg-1.min-1) was infused intravenously to inhibit sympathetic nervous activity (SNA), whereas in the second group atropine (prime: 5 micrograms/kg; continuous: 5 micrograms.kg-1.min-1) was used to inhibit parasympathetic nervous activity (PNA). The TRF was measured on four occasions: 1) after oral ingestion of a breakfast, during 0.9% NaCl perfusion, 2) after oral ingestion of the same breakfast, during the perfusion of one of the drugs, 3) after intragastric injection of a pureed form of the same meal as in part 1, during 0.9% NaCl perfusion, and 4) after intragastric feeding, during the administration of one of the drugs. Energy expenditure was measured by indirect calorimetry for 30 min before and 6 h after ingestion of the meal. Facultative TRF was defined as the difference between oral and intragastric TRF. Intragastric feeding significantly reduced TRF in both studies: 6.6 +/- 1.0 vs. 8.7 +/- 0.8% of the ingested energy in the SNA study and 5.5 +/- 1.6 vs. 7.4 +/- 3.1% in the PNA study. During propranolol infusion, TRF was significantly lower than it was during saline infusion after oral feeding (6.9 +/- 1.0% vs. 8.7 +/- 0.8% of ingested energy) but not after intragastric feeding. During atropine administration, TRF was reduced after both oral and intragastric feeding, although statistical significance was not reached in the latter. Atropine administration decreased gastric emptying (measured with an isotopic method) 2 h postingestion by 50%. These results show that the SNA is necessary for the facultative component of TRF to occur in humans. The role of the PNA appears to be related to its action on gastric emptying.
Blockade of the renin-angiotensin-aldosterone system prevents growth hormone-induced fluid retention in humans
Authors: Moller J. , Moller N. , Frandsen E. , Wolthers T. , Jorgensen J. O. , Christiansen J. S.
Published: December 2017

To test if the renin-angiotensin-aldosterone system (RAAS) is involved in growth hormone (GH)-associated fluid retention, we examined the effect of GH administration in the presence or absence of RAAS blockade at different levels on body fluid homeostasis. Eight subjects were examined in a controlled, randomized double-blinded trial. During four 6-day periods they received subcutaneous GH (6 IU-m-2) or placebo injections and tablets as follows: 1) placebo and placebo, 2) GH and placebo, 3) GH and captopril, and 4) GH and spironolactone. GH increased extracellular volume (liters; placebo 18.87 +/- 0.85; GH + placebo 20.43 +/- 1.01) but this effect was abolished by captopril (GH + captopril 18.82 +/- 0.67) and spironolactone (GH + spironolactone 18.99 +/- 0.85). Correspondingly, the GH-induced reduction in bioimpedance was blocked by captopril and spironolactone. Plasma renin and angiotensin II concentrations increased during all three GH treatment regimens, whereas plasma aldosterone was increased only after GH plus spironolactone. The data demonstrate that GH activates the RAAS and that blockade of the RAAS by two separate mechanisms prevents fluid retention normally encountered after GH exposure. These observations suggest that the RAAS plays a key role in GH-induced regulation of fluid homeostasis.
Prostaglandin-endoperoxide H synthase-2 expression and activity increases with term labor in human chorion
Authors: Mijovic J. E. , Zakar T. , Nairn T. K. , Olson D. M.
Published: December 2017

We investigated the changes in prostaglandin-endoperoxide H synthase (PGHS) specific activity and the levels and distribution of PGHS-1 and PGHS-2 mRNA in chorion collected at term before the onset of labor (CS) and after term labor and delivery (SL). PGHS specific activity and PGHS-2 mRNA abundance were higher in chorion collected after SL compared with that obtained at CS (P < 0.001); there was no difference in the levels of PGHS-1 mRNA between CS and SI, tissues. The increase in PGHS specific activity at SL was significantly correlated with PGHS-2 mRNA expression (P < 0.05) but not with PGHS-1 mRNA levels. In situ hybridization indicated that the pervasiveness of staining for PGHS-1 mRNA throughout full-thickness membranes did not change with labor onset; however, a greater number of cells expressed PGHS-2 in SL tissues. Our results demonstrate a selective increase in PGHS-2 expression and activity in chorion trophoblasts and mesenchymal cells with term labor onset. These observations are similar to those concerning amnion and imply that a concerted mechanism may exist in the fetal membranes to induce PGHS-2 expression at labor.
Coupling of oxytocin receptor to G proteins in rat myometrium during labor: Gi receptor interaction
Authors: Strakova Z. , Soloff M. S.
Published: December 2017

Occupancy of oxytocin receptor (OTR) binding sites in pregnant rat myometrial membranes with iodinated oxytocin antagonist (OTA), followed by detergent solubilization and size selection, showed that radioactivity eluted in two distinct peaks: one corresponding in size to the isolated receptor (approximately 60 kDa) and the other ranging from 240 to 320 kDa. The unliganded 240- to 320-kDa fraction contained OTRs coupled to G proteins, as the addition of oxytocin (OT) increased guanosine 35S-labeled 5'-O-(3-thiotriphosphate) binding up to twofold in a dose-dependent manner. The effects of OT were blocked by coincubation with OTA. G protein alpha-subunits associated with OTRs in the 240- to 320-kDa peak were identified by immunoadsorption. Significant amounts of both G alpha q/11 and G alpha i3 were associated with the OTR; a lesser amount of G alpha s was complexed. Using the same approach but with antibodies to effector enzymes, we observed that phospholipase C beta 1 (PLC beta 1) and PLA2 were also associated with the OTR. The results corroborate the well-established interaction of OTR with Gq and further show that Gi coupling might be an important component of OTR signal transduction. To further investigate the interaction of Gi with the OTR, we showed that OT stimulation of guanosine 5'-triphosphatase activity in intact myometrial membranes was inhibited by pertussis toxin. Pertussis toxin-stimulated ADP ribosylation of G alpha i in myometrial membranes was also decreased by OT treatment. These findings with pertussis toxin strongly indicate that OTR is coupled to Gi in rat myometrial membranes. The 60-kDa OTR peak (noncoupled receptor) was demonstrable in the myometrium only before the end of gestation and after parturition and accounted for about one-half the 125I-OTA binding activity. At term, there was about a fivefold increase in binding and almost a complete shift to the 240- to 320-kDa-size complex. Thus the established increased sensitivity of the myometrium to OT at term could be the result of both upregulation of OTRs and an increase in the fraction of receptors coupled to signal transduction components, one of which is Gi.
Altered energy balance and cytokine gene expression in a murine model of chronic infection with Toxoplasma gondii
Authors: Arsenijevic D. , Girardier L. , Seydoux J. , Chang H. R. , Dulloo A. G.
Published: December 2017

The temporal pattern of changes in energy balance and cytokine mRNA expression in spleen and brain were examined in a mouse model of infection with Toxoplasma gondii. During days 1-7 postinfection, food intake was unaltered, but energy expenditure was significantly increased, and this was associated with elevated tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1, IL-5, and interferon (IFN)-gamma. The hypermetabolic state persisted during subsequent anorexia, whose onset coincided with elevated IL-2, and at the end of the acute phase of cachexia, the dual anorexic and hypermetabolic states were associated with the cytokines examined: TNF-alpha, IL-1 beta, IL-2, IL-4, IL-5, IL-6, IL-10, and IFN-gamma. In the chronic phase of the infection, the mice showed either partial weight recovery (gainers) or no weight regain (nongainers). The infected gainers, though still hypophagic, were no longer hypermetabolic, and their cytokine mRNA was no longer elevated, except for TNF-alpha and IL-10. In contrast, the infected nongainers continued to show both anoroxia and hypermetabolism, which were associated with elevations in all cytokines examined and particularly those of the TH2 profile (IL-4 and IL-5) and IL-6. Taken together, these studies reveal a distinct pattern of cytokine mRNA expression underlying 1) hypermetabolism vs. anorexia, 2) acute vs. chronic cachexia, and 3) stable weight loss vs. partial weight recovery.
Effect of amino acid and glucose administration during postexercise recovery on protein kinetics in dogs
Authors: Okamura K. , Doi T. , Hamada K. , Sakurai M. , Matsumoto K. , Imaizumi K. , Yoshioka Y. , Shimizu S. , Suzuki M.
Published: December 2017

To examine the effect of the timing of amino acids (AA) and glucose (G) administration after exercise on protein kinetics, ten dogs fitted with chronic catheters in the artery and the femoral vein ran on a treadmill for 150 min. They were intraportally infused with a solution containing AA and G either right after (E) or 2 h after (L) the exercise. The protein kinetics were estimated using the arteriovenous difference of phenylalanine (Phe) coupled with the [2H5]Phe dilution method. The net balance of Phe across the hindlimb (HL) was negative after exercise. It became positive in E within 15 min after the start of the infusion, and it remained negative in L until the infusion was initiated. The uptake of Phe by the HL during the second half of the infusion period was higher in E than in L (10.9 +/- 6.6 vs. 5.4 +/- 2.3 nmol.kg-1.min-1, P = 0.049). During the infusion, protein synthesis in the HL was higher in E than in L (29.7 +/- 9.6 vs. 22.0 +/- 10.1 nmol.kg-1.min-1, P = 0.028), whereas proteolysis was comparable (18.7 +/- 5.7 vs. 16.5 +/- 11.1 nmol.kg-1.min-1. These results suggest that the early provision of the nutrients after exercise more effectively enhances protein accretion than nutrients administered later.
beta 3-Adrenergic-mediated suppression of leptin gene expression in rats
Authors: Li H. , Matheny M. , Scarpace P. J.
Published: December 2017

To investigate the role of beta 3-adrenergic receptors in the suppression of leptin gene expression, we fasted F-344 rats to decrease leptin mRNA levels, refed the rats to stimulate leptin mRNA production, and examined the ability of the beta 3-adrenergic agonist CGP-12177 to prevent the rise in leptin mRNA levels. In the initial 2 h after CGP-12177 (0.75 mg/kg), there were significant reductions in both food consumption and leptin mRNA levels in epididymal, perirenal, and interscapular white adipose tissue. We were unable to detect leptin mRNA in interscapular brown adipose tissue (IBAT), whereas there was a significant increase in uncoupling protein mRNA levels in IBAT after CGP-12177. The suppression of leptin mRNA and food intake by CGP-12177 was confirmed in a second experiment using another rat strain, the F-344 x BN. Furthermore, refeeding after a period of fasting increased leptin mRNA, which was prevented by CGP-12177. These data indicate a role for beta 3-adrenergic-mediated regulation of leptin gene expression in nonmutant rodents and are consistent with other reports suggesting that beta 3-adrenergic agonists suppress food intake.
Growth hormone-induced insulin resistance: role of the insulin receptor, IRS-1, GLUT-1, and GLUT-4
Authors: Smith T. R. , Elmendorf J. S. , David T. S. , Turinsky J.
Published: December 2017

Treatment of rats with growth hormone (GH; 1 mg/kg sc) twice daily over 2.5 days did not alter fasting plasma glucose or glucose tolerance but increased fasting plasma insulin levels 65% and peak insulin response to a glucose load 35% over controls, indicating the development of insulin resistance. Studies on partially purified insulin receptors from soleus muscles showed that GH increased the abundance of insulin receptor beta-subunits by 48% as measured by immunoblotting. Despite this increase, GH abolished the increase in autophosphorylation of the insulin receptor beta-subunit in response to physiological hyperinsulinemia and diminished by 28% the response to supraphysiological hyperinsulinemia. Similarly, insulin-stimulated phosphorylation of insulin receptor substrate-1 (IRS-1) was decreased 25% by GH, but the abundance of IRS-1 was not affected. Studies on rats pretreated with streptozotocin suggested that the effects of GH are direct and not secondary to GH-induced hyperinsulinemia. GH decreased basal GLUT-1 abundance in the low-density microsome and plasma membrane fractions of epididymal adipocytes by 50 and 42%, respectively, but decreased basal GLUT-4 abundance only in the low-density microsome fraction by 24%. Despite these alterations, the abundance of both transporters in the plasma membrane fraction of adipocytes incubated with 0.1 U insulin/ml was not diminished by GH.
IGF-I regulation of Na(+)-K(+)-ATPase in rat arterial smooth muscle
Authors: Standley P. R. , Zhang F. , Zayas R. M. , Muniyappa R. , Walsh M. F. , Cragoe E. , Sowers J. R.
Published: December 2017

Insulin-like growth factor I (IGF-I) is vasodilatory and mitogenic for vascular smooth muscle cells (VSMC). Alteration in VSMC Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) activity is hypothesized to underlie abnormal vascular tone and growth in hypertension and diabetes. Therefore, we investigated effects of IGF-I on Na(+)-K(+)-ATPase activity in rat aortic VSMC. IGF-I increases pump activity in a dose- and time-dependent manner: the minimal dose required was 10(-10) M, and the minimal time required was 20 min (at 10(-8) M) to increase activity. Similar effects persisted through 12 h. In Na(+)-loaded cells, IGF-I does not further stimulate activity. Blockade of Na+/H+ exchange attenuates IGF-I-induced increases in activity after 30 min but has no effect after 12 h. Northern blot analyses reveal that expression of the alpha 1- and the alpha 2-subunits of the pump were unaffected by IGF-I. Plasma membrane alpha 1- and alpha 2-protein were also unaffected, suggesting translocation of preformed pools was not responsible for the increases. Inhibitors revealed that neither tyrosine kinase activity, RNA transcription, protein synthesis, nitric oxide synthase activity, or protein kinase C activity mediated this IGF-I effect. Therefore, IGF-I regulates Na pump activity in the short term by an Na+/H+ exchange-dependent but transcription/translocation-independent mechanism. These data suggest that IGF-I, known to be produced by VSMC, may regulate tone and growth responses abnormal in disease states such as hypertension and diabetes.
Accelerated glycogenolysis in uremia and under sucrose feeding: role of phosphorylase alpha regulators
Authors: Bakkour Z. , Laouari D. , Dautrey S. , Yvert J. P. , Kleinknecht C.
Published: December 2017

To understand the mechanism of hepatic glycogen depletion found in uremia and under sucrose feeding, we examined net hepatic glycogenolysis-associated active enzymes and metabolites during fasting. Liver was taken 2, 7, and 18 h after food removal in uremic and pair-fed control rats fed either a sucrose or cornstarch diet for 21 days. Other uremic and control rats fasted for 18 h were refed a sucrose meal to measure glycogen increment. Glycogen storage in uremia was normal, suggesting effective glycogen synthesis. During a short fast, sucrose feeding and uremia enhanced net glycogenolysis through different but additive mechanisms. Under sucrose feeding, there were high phosphorylase alpha levels associated with hepatic insulin resistance. In uremia, phosphorylase alpha levels were low, but the enzyme was probably activated in vivo by a fall of inhibitors (ATP, alpha-glycerophosphate, fructose-1,6-diphosphate, and glucose) and a rise of Pi, as verified in vitro. Enhanced gluconeogenesis was also suggested, but excessive hepatic glucose production was unlikely in uremia. During fasting, hypoglycemia occurred in uremia due to reduced glycogenolysis, inefficient hepatic gluconeogenesis, and impaired renal gluconeogenesis. This may be relevant to poor fasting tolerance in uremia, which could be aggravated under excessive sucrose intake.
Phorbol esters stimulate muscle glucose transport by a mechanism distinct from the insulin and hypoxia pathways
Authors: Hansen P. A. , Corbett J. A. , Holloszy J. O.
Published: December 2017

Glucose transport in skeletal muscle can be stimulated by insulin and also by contractions and hypoxia. Activation of protein kinase C (PKC) stimulates glucose transport in muscle and other insulin-responsive cells. This study was performed to determine if the diacylglycerol (DAG)/phorbol ester-sensitive PKC isoforms participate in insulin and/or hypoxia-stimulated glucose transport in skeletal muscle. The phorbol ester 12-deoxyphorbol 13-phenylacetate 20-acetate (dPPA) induced a three- to fourfold increase in glucose transport in rat epitrochlearis muscle. The effects of dPPA on glucose transport and on cell surface GLUT-4 were completely additive to the maximal effects of insulin or hypoxia. Phorbol ester treatment induced 5- to 10-fold increases in phosphorylation of the myristoylated alanine-rich C kinase substrate protein in muscle, whereas insulin and hypoxia had negligible effects. Calphostin C, an inhibitor of DAG-sensitive PKC isoforms, decreased glucose transport stimulation by dPPA but not by insulin or hypoxia. These results provide evidence that activation of DAG/phorbol ester-sensitive PKCs is not involved in the pathways by which either insulin or hypoxia stimulates muscle glucose transport. They also show that activation of this group of PKCs increases glucose transport by a mechanism that is independent of and additive to the effects of insulin or hypoxia.
Poor fetal nutrition causes long-term changes in expression of insulin signaling components in adipocytes
Authors: Ozanne S. E. , Nave B. T. , Wang C. L. , Shepherd P. R. , Prins J. , Smith G. D.
Published: December 2017

Insulin action on adipocytes was studied in the offspring of mothers who had been fed either a control (20% protein) or a low (8%)-protein diet during pregnancy and lactation. Adipocytes isolated from low-protein offspring had significantly higher basal and insulin-stimulated glucose uptakes than controls. This may be related to a threefold increase in insulin receptors in low-protein adipocytes. Consistent with these observed changes in glucose transport, adipocytes from low-protein animals had significantly higher basal and insulin-stimulated insulin receptor substrate (IRS)-1-associated phosphatidylinositol 3-kinase (PI 3-kinase) activities. There was also more p85-associated PI 3-kinase activity in these adipocytes. There was no difference in expression in the p85 regulatory subunit or the p110-alpha catalytic subunit of PI 3-kinase. In contrast, there was a sixfold reduction in the p110-beta catalytic subunit of PI 3-kinase in adipocytes from low-protein animals. These results suggest that poor fetal nutrition during pregnancy and lactation can have long-term effects on glucose transport and on the expression of key components of the insulin signaling pathway in adipocytes.