bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of protein intake on plasma and erythrocyte free amino acids and serum IGF-I and IGFBP-1 levels in rats
Authors: Filho J. C. Divino , Hazel S. J. , Anderstam B. , Bergström J. , Lewitt M. , Hall K.
Published: December 2017

Amino acid (AA) levels in plasma and erythrocytes (RBC) were determined in rats ( n = 29) fed diets with 6, 21, and 35% protein, and their association with insulin-like growth factor I (IGF-I), insulin, or IGF-binding protein (IGFBP)-1 levels was studied. Free AA in plasma and RBC were determined by reversed-phase high-pressure liquid chromotography, and IGF-I, IGFBP-1, and insulin plasma levels were determined by RIA. Rats fed the low-protein (6%) diet were growth-retarded and had lower serum IGF-I levels and higher serum IGFBP-1 levels than the other two groups ( P < 0.0001). In rats fed the low-protein diet, most of the nonessential AA (NEAA) in both plasma and RBC increased, whereas the essential AA (EAA), with the exception of threonine, decreased. When the groups were combined, both RBC and plasma EAA-to-NEAA ratios were positively correlated to IGF-I ( r = 0.76 and 0.80, respectively; P < 0.0001) and inversely correlated to IGFBP-1 levels ( r = −0.67, P < 0.001 and r = −0.78, P < 0.0001, respectively). A significant inverse correlation was found between RBC glutamate and IGF-I ( r = −0.85, P < 0.0001, n = 25) and insulin ( r = −0.72, P < 0.001, n = 21), and a positive correlation was found for IGFBP-1 ( r = 0.78, P < 0.0001, n = 24). In multiple regression analysis, only IGF-I remained as an independent variable. Threonine was the only EAA with a significant inverse correlation to insulin ( r = −0.66, P < 0.001). We hypothesize that AA metabolism is associated to changes in IGF-I, insulin, and IGFBP-1 levels in rats on different protein intakes.
Acute effect of growth hormone to induce peripheral insulin resistance is independent of FFA and insulin levels in rats
Authors: Kim Jason K. , Choi Cheol S. , Youn Jang H.
Published: December 2017

To examine whether growth hormone (GH) induces peripheral insulin resistance by altering plasma free fatty acid (FFA) or insulin levels, the effects of GH infusion on insulin-stimulated glucose fluxes were studied in conscious rats under two protocols. In study 1, either saline ( n = 7) or human recombinant GH (21 μg ⋅ kg−1⋅ h−1; n = 8) was infused for 300 min, and insulin-stimulated glucose fluxes were estimated during the final 150-min period of hyperinsulinemic euglycemic clamps. In study 2, hyperinsulinemic euglycemic clamps were first conducted for 150 min (to raise plasma insulin and suppress FFA levels), and saline or GH ( n = 7 for each) was subsequently infused for the following 300-min clamp period. In study 1, GH infusion in the basal state did not significantly alter plasma FFA or insulin levels. In contrast, GH infusion decreased insulin-stimulated glucose uptake, glycolysis, and glycogen synthesis by 32, 27, and 40%, respectively ( P < 0.05). In study 2, GH infusion during hyperinsulinemic euglycemic clamps did not alter plasma FFA or insulin levels ( P > 0.05). GH infusion had no effect on insulin-stimulated glucose uptake during the initial 150 min but eventually decreased insulin-stimulated glucose uptake by 37% ( P < 0.05), similar to the results in study 1. These data indicate that GH induces peripheral insulin resistance independent of plasma FFA and insulin levels. The induction of insulin resistance was preceded by suppression of glycogen synthesis, consistent with the hypothesis that metabolic impairment precedes and causes development of peripheral insulin resistance.
Downregulation of the human taurine transporter by glucose in cultured retinal pigment epithelial cells
Authors: Stevens Martin J. , Hosaka Yoshiyuki , Masterson Jennifer A. , Jones Sandra M. , Thomas Thommey P. , Larkin Dennis D.
Published: December 2017

In diabetes, activation of the aldose reductase (AR) pathway and alterations of glucose-sensitive signal transduction pathways have been implicated in depletion of intracellular taurine, an endogenous antioxidant and compatible osmolyte. Cellular taurine accumulation occurs by an osmotically induced, protein kinase C (PKC)-regulated Na+-taurine cotransporter (hTT). The effects of ambient glucose on taurine content, hTT activity, and hTT gene expression were therefore evaluated in low and high AR-expressing human retinal pigment epithelial cell lines. In low AR-expressing cells, 20 mM glucose decreased taurine content, hTT transporter activity, and mRNA levels, and these effects were unaffected by AR inhibition (ARI). In these cells, the inhibitory effects of high glucose on hTT appeared to be posttranscriptionally mediated, because 20 mM glucose decreased hTT mRNA stability without affecting hTT transcriptional rate. Inhibition of PKC overcame the decrease in hTT activity in high glucose-exposed cells. In high AR-expressing cells, prolonged exposure to 20 mM glucose resulted in intracellular taurine depletion, which paralleled sorbitol accumulation and was prevented by ARI. In these cells exposed to 5 mM glucose, hTT mRNA abundance was decreased and declined further in 20 mM glucose but was corrected by ARI. In 5 mM glucose, hTT transcriptional rate was markedly decreased in high AR-expressing cells, did not decline further in 20 mM glucose, but was increased by ARI to levels above those observed in low AR-expressing cells. Therefore, glucose rapidly and specifically decreases taurine content, hTT activity, and mRNA abundance by AR-unrelated and AR-related posttranscriptional and transcriptional mechanisms.
Trifluoroacetate, a contaminant in purified proteins, inhibits proliferation of osteoblasts and chondrocytes
Authors: Cornish J. , Callon K. E. , Lin C. Q.-X. , Xiao C. L. , Mulvey T. B. , Cooper G. J. S. , Reid I. R.
Published: December 2017

Peptides purified by HPLC are often in the form of a trifluoroacetate (TFA) salt, because trifluoroacetic acid is used as a solvent in reversed-phase HPLC separation. However, the potential effects of this contaminant in culture systems have not been addressed previously. TFA (10−8 to 10−7 M) reduced cell numbers and thymidine incorporation into fetal rat osteoblast cultures after 24 h. Similar effects were found in cultures of articular chondrocytes and neonatal mouse calvariae, indicating that the effect is not specific to one cell type or to one species of origin. When the activities of the TFA and hydrochloride salts of amylin, amylin-(1—8), and calcitonin were compared in osteoblasts, cell proliferation was consistently less with the TFA salts of these peptides, resulting in failure to detect a proliferative effect or wrongly attributing an antiproliferative effect. This finding is likely to be relevant to all studies of purified peptides in concentrations above 10−9 M in whatever cell or tissue type. Such peptides should be converted to a hydrochloride or biologically equivalent salt before assessment of their biological effects is undertaken.
Influence of obesity and body fat distribution on growth hormone kinetics in humans
Authors: Langendonk Janneke G. , Meinders A. Edo , Burggraaf Jacobus , Frölich Marijke , Roelen Corné A. M. , Schoemaker Rik C. , Cohen Adam F. , Pijl Hanno
Published: December 2017

We studied the kinetics of exogenous recombinant 22-kDa human growth hormone (rhGH) in premenopausal women with upper body obesity (UBO), lower body obesity (LBO), or normal body weight. A bolus of 100 mU rhGH was administered during a continuous infusion of somatostatin to suppress endogenous GH secretion. GH kinetics were investigated with noncompartmental analysis of plasma GH curves. GH peak values in response to GH infusion and plasma half-life of GH were not significantly different between normal weight and obese subjects. In contrast, GH clearance was 33% higher in LBO women and 51% higher in UBO women compared with clearance in normal weight controls. The difference in clearance between LBO and UBO was not statistically significant. Altered GH clearance characteristics contribute to low circulating GH levels in obese humans. Body fat distribution does not appear to affect GH kinetics.
Regulations of gonadotropin secretion by circulating inhibin, estradiol, and progesterone in cyclic hamsters
Authors: Kishi Hisashi , Itoh Mariko , Ohshima Ken-Ichi , Wang Ming-Wei , Watanabe Gen , Taya Kazuyoshi
Published: December 2017

The physiological importance of gonadal hormones in feedback control of gonadotropin secretion during the estrous cycle in golden hamsters was investigated with immunoneutralization methods. Anti-inhibin serum (inhibin-AS) treatment always induced a drastic increase in follicle-stimulating hormone (FSH) secretion and occasionally raised luteinizing hormone (LH) secretion. Anti-estradiol-17β serum (estradiol-AS) treatment increased LH secretion typically. Although estradiol-AS elevated FSH secretion occasionally, the elevation was much less than that by inhibin-AS. Plasma FSH reached ovariectomized levels by a synergistic effect of both antisera. Elevated plasma LH with both antisera was much less pronounced than in ovariectomized animals. Plasma LH increased dramatically to the levels in the ovariectomized group when antibody against progesterone (progesterone-AB) was given together with inhibin-AS and estradiol-AS, although progesterone-monoclonal antibody alone did not alter plasma gonadotropin levels. These results indicate that in hamsters FSH secretion is mainly regulated by inhibin and LH secretion is regulated by estradiol-17β and progesterone during the estrous cycle.
Glucagon-like peptide 2 decreases mortality and reduces the severity of indomethacin-induced murine enteritis
Authors: Boushey Robin P. , Yusta Bernardo , Drucker Daniel J.
Published: December 2017

Glucagon-like peptides (GLPs) are secreted from enteroendocrine cells in the gastrointestinal tract. GLP-1 actions regulate blood glucose, whereas GLP-2 exerts trophic effects on intestinal mucosal epithelium. Although GLP-1 actions are preserved in diseases such as diabetes, GLP-2 action has not been extensively studied in the setting of intestinal disease. We have now evaluated the biological effects of a human GLP-2 analog in the setting of experimental murine nonsteroidal antiinflammatory drug-induced enteritis. Human (h)[Gly2]GLP-2 significantly improved survival whether administered before, concomitant with, or after indomethacin. h[Gly2]GLP-2-treated mice exhibited reduced histological evidence of disease activity, fewer intestinal ulcerations, and decreased myeloperoxidase activity in the small bowel ( P < 0.05, h[Gly2]GLP-2- vs. saline-treated controls). h[Gly2]GLP-2 significantly reduced cytokine induction, bacteremia, and the percentage of positive splenic and hepatic bacterial cultures ( P < 0.05). h[Gly2]GLP-2 enhanced epithelial proliferation ( P < 0.05 for increased crypt cell proliferation in h[Gly2]GLP-2- vs. saline-treated mice after indomethacin) and reduced apoptosis in the crypt compartment ( P < 0.02). These observations demonstrate that a human GLP-2 analog exerts multiple complementary actions that serve to preserve the integrity of the mucosal epithelium in experimental gastrointestinal injury in vivo.
Rates of small intestinal mucosal protein synthesis in human jejunum and ileum
Authors: Nakshabendi Imad M. , McKee Ruth , Downie Shaun , Russell Robin I. , Rennie Michael J.
Published: December 2017

We investigated possible differences in the rates of mucosal protein synthesis between the proximal and distal regions of the small intestine. We took advantage of access to the gut mucosa available in otherwise healthy patients with ileostomy in whom the terminal ileum was histologically normal. All subjects received primed, continuous intravenous infusions ofl-[1-13C]leucine after an overnight fast. After 4 h of tracer infusion, jejunal biopsies were obtained using a Crosby-Kugler capsule introduced orally; ileal biopsies were obtained via endoscopy via the ileostomy. Protein synthesis was calculated from protein labeling relative to intracellular leucine enrichment obtained by appropriate mass spectrometric measurements. Rates of jejunal and ileal mucosal protein synthesis were significantly different ( P < 0.001) at 2.14 ± 0.2 and 1.2 ± 0.2 %/h (means ± SD). These are lower than rates in normal healthy duodenum (2.53 ± 0.25 %/h), suggesting a gradation of rates of synthesis along the bowel. Together with other data, these results suggest that mucosae of the bowel contribute not more than 10% to whole body protein turnover.
Amino acid-induced stimulation of translation initiation in rat skeletal muscle
Authors: Vary Thomas C. , Jefferson Leonard S. , Kimball Scot R.
Published: December 2017

Amino acids stimulate protein synthesis in skeletal muscle by accelerating translation initiation. In the two studies described herein, we examined mechanisms by which amino acids regulate translation initiation in perfused skeletal muscle hindlimb preparation of rats. In the first study, the effects of supraphysiological amino acid concentrations on eukaryotic initiation factors (eIF) 2B and 4E were compared with physiological concentrations of amino acids. Amino acid supplementation stimulated protein synthesis twofold. No changes were observed in eIF2B activity, in the amount of eIF4E associated with the eIF4E-binding protein (4E-BP1), or in the phosphorylation of 4E-BP1. The abundance of eIF4E bound to eIF4G and the extent of phosphorylation of eIF4E were increased by 800 and 20%, respectively. In the second study, we examined the effect of removing leucine on translation initiation when all other amino acids were maintained at supraphysiological concentrations. Removal of leucine from the perfusate decreased the rate of protein synthesis by 40%. The inhibition of protein synthesis was associated with a 40% decrease in eIF2B activity and an 80% fall in the abundance of eIF4E ⋅ eIF4G complex. The fall in eIF4G binding to eIF4E was associated with increased 4E-BP1 bound to eIF4E and a reduced phosphorylation of 4E-BP1. In contrast, the extent of phosphorylation of eIF4E was unaffected. We conclude that formation of the active eIF4E ⋅ eIF4G complex controls protein synthesis in skeletal muscle when the amino acid concentration is above the physiological range, whereas removal of leucine reduces protein synthesis through changes in both eIF2B and eIF4E.
Use of a single13C NMR resonance of glutamate for measuring oxygen consumption in tissue
Authors: Jeffrey F. Mark H. , Reshetov Alexander , Storey Charles J. , Carvalho Rui A. , Sherry A. Dean , Malloy Craig R.
Published: December 2017

A kinetic model of the citric acid cycle for calculating oxygen consumption from13C nuclear magnetic resonance (NMR) multiplet data has been developed. Measured oxygen consumption (MV˙o2) was compared with MV˙o2predicted by the model with13C NMR data obtained from rat hearts perfused with glucose and either [2-13C]acetate or [3-13C]pyruvate. The accuracy of MV˙o2measured from three subsets of NMR data was compared: glutamate C-4 and C-3 resonance areas; the doublet C4D34 (expressed as a fraction of C-4 area); and C-4 and C-3 areas plus several multiplets of C-2, C-3, and C-4. MV˙o2determined by set 2(C4D34 only) gave the same degree of accuracy as set 3(complete data); both were superior to set 1(C-4 and C-3 areas). Analysis of the latter suffers from the correlation between citric acid cycle flux and exchange between α-ketoglutarate and glutamate, resulting in greater error in estimating MV˙o2. Analysis of C4D34 is less influenced by correlation between parameters, and this single measurement provides the best opportunity for a noninvasive measurement of oxygen consumption.
Endothelium-specific activation of NAD(P)H oxidase in aortas of exogenously hyperinsulinemic rats
Authors: Kashiwagi Atsunori , Shinozaki Kazuya , Nishio Yoshihiko , Maegawa Hiroshi , Maeno Yasuhiro , Kanazawa Akio , Kojima Hideto , Haneda Masakazu , Hidaka Hideki , Yasuda Hitoshi , Kikkawa Ryuichi
Published: December 2017

To examine the effects of chronic hyperinsulinemia on vascular tissues, we examined the production of superoxide anion ([Formula: see text]) in the aortic tissues of control and exogenously hyperinsulinemic rats performed by the implantation of an insulin pellet for 4 wk. [Formula: see text]production by aortic segments from hyperinsulinemic rats was 2.4-fold (lucigenin chemiluminescence method) and 1.7-fold (cytochrome c method) of that of control rats without any differences in [Formula: see text]degrading activities in aortic tissues, respectively ( P < 0.025). The increment was completely abolished in the presence of either 100 μmol/l apocynin (an inhibitor of NADPH oxidase) or 10 μmol/l diphenyleneiodonium (an inhibitor of flavin-containing enzyme) and was exclusively endothelium dependent. Consistently, NAD(P)H oxidase activities in endothelial homogenate in hyperinsulinemic rats were dose dependently stimulated above the values of control rats, although these activities in nonendothelial homogenate were not significantly stimulated by insulin. Furthermore, an insulin effect was also demonstrated 1 h after exposing aortic tissues to insulin. These results indicate that[Formula: see text] production specifically increases in endothelium of aortic tissues in chronic hyperinsulinemic rats through the activation of NAD(P)H oxidase.
Low energy availability, not exercise stress, suppresses the diurnal rhythm of leptin in healthy young women
Authors: Hilton L. K. , Loucks A. B.
Published: December 2017

Because the effect of exercise on leptin was not established, we controlled energy intake (I) and exercise energy expenditure (E) to distinguish the independent effects of energy availability (A = I − E) and exercise stress (everything associated with exercise except its energy cost) on the diurnal leptin rhythm in healthy young women. In random order, we set A = 45 and 10 kcal ⋅ kg lean body mass−1(LBM) ⋅ day−1 for 4 days during the early follicular phase of separate menstrual cycles in sedentary (S, n = 7) and exercising (X, n = 9: E = 30 kcal ⋅ kg LBM−1 ⋅ day−1) women. Low energy availability suppressed the 24-h mean ( P < 10−6) and amplitude ( P < 10−5), whereas exercise stress did not (both P> 0.2). Suppressions of the 24-h mean (−72 ± 3 vs. −53 ± 3%, P < 0.001) and amplitude (−85 ± 3 vs. −58 ± 6%, P < 0.001) were more extreme in S vs. X than previously reported effects on luteinizing hormone pulsatility and carbohydrate availability. Thus the diurnal rhythm of leptin depends on energy, or carbohydrate, availability, not intake, and exercise has no suppressive effect on the diurnal rhythm of leptin beyond the impact of its energy cost on energy availability.
Role of eIF4E in stimulation of protein synthesis by IGF-I in perfused rat skeletal muscle
Authors: Vary Thomas C. , Jefferson Leonard S. , Kimball Scot R.
Published: December 2017

Insulin-like growth factor I (IGF-I) promotes anabolism by stimulating protein synthesis in skeletal muscle. In the present study, we have examined mechanisms by which IGF-I stimulates protein synthesis in skeletal muscle with a perfused rat hindlimb preparation. IGF-I (10 nM) stimulated protein synthesis over 2.7-fold. Total RNA content was unaffected, but translational efficiency was increased by IGF-I. We next examined the effect of IGF-I on eukaryotic initiation factor (eIF) 4E as a mechanism regulating translation initiation. IGF-I did not alter either the amount of eIF4E associated with the eIF4E binding protein 4E-BP1 or the phosphorylation state of 4E-BP1. Likewise, the phosphorylation state of eIF4E was unaltered by IGF-I. In contrast, the amount of eIF4E bound to eIF4G was increased threefold by IGF-I. We conclude that IGF-I regulates protein synthesis in skeletal muscle by enhancing formation of the active eIF4E ⋅ eIF4G complex.
Effect of regional hyperemia on myocardial uptake of 2-deoxy-2-[18F]fluoro-d-glucose
Authors: McFalls Edward O. , Baldwin Douglas , Marx David , Fashingbauer Peggy , Ward Herbert B.
Published: December 2017

2-Deoxy-2-[18F]fluoro-d-glucose (FDG) may be used to predict glucose kinetics when the factor relating differences in transport and phosphorylation between compounds remains constant (“lumped constant”). It is not clear whether hyperemia alters that factor. In anesthetized swine, myocardial FDG uptake was estimated by positron emission tomography, during an intracoronary infusion of either adenosine, ATP, or bradykinin (40 μg ⋅ kg−1 ⋅ min−1, 40 μg ⋅ kg−1 ⋅ min−1, and 2 nmol ⋅ kg− 1 ⋅ min− 1, respectively; n = 6 for all groups). In controls during normal perfusion ( n = 6), FDG uptake was 0.78 ± 0.32 μmol ⋅ g− 1 ⋅ min− 1, whereas glucose uptake by Fick was 0.71 ± 0.25 μmol ⋅ g− 1 ⋅ min− 1( r = 0.73; P < 0.05). Adenosine increased blood flow from 1.29 ± 0.43 to 4.80 ± 2.19 ml ⋅ g− 1 ⋅ min− 1( P < 0.05) and glucose uptake from 1.16 ± 1.10 to 3.35 ± 2.12 μmol ⋅ g− 1 ⋅ min− 1( P < 0.05), whereas FDG uptake in the hyperemic region was lower than remote regions (0.46 ± 0.29 and 0.95 ± 0.55 μmol ⋅ g− 1 ⋅ min− 1, respectively; P < 0.05). In the ATP and bradykinin groups, blood flow increased four- and twofold, respectively, with no net change in glucose uptake. FDG uptake in the hyperemic region was also significantly lower than remote regions. For all animals, the ratio of blood flow in the hyperemic region relative to remote region was inversely proportional to the ratio of FDG uptake in the same regions ( r 2=0.73; P < 0.001). Because nitric oxide elaboration during hyperemia could potentially alter substrate preference and FDG kinetics, six additional swine were studied during maximal adenosine before and after intracoronary N G-monomethyl-l-arginine (1.5 mg/kg). Inhibition of nitric oxide had no effect on either regional myocardial substrate uptake or FDG accumulation. In conclusion, hyperemia decreased regional myocardial FDG uptake relative to normally perfused regions and this effect on the lumped constant was independent of nitric oxide.
Greater potency of IGF-I than IGF-I/BP-3 complex in catabolic parenterally fed rats
Authors: Kritsch K. R. , Huss D. J. , Ney D. M.
Published: December 2017

We compared the anabolic effects of recombinant human insulin-like growth factor I (rhIGF-I, 2.5 mg/kg) and equimolar amounts of rhIGF-I prebound to rhIGF binding protein-3 (rhIGF-I/BP-3) coinfused continuously with total parenteral nutrition (TPN) solution in dexamethasone (Dex, 70 μg/day ip)-treated male rats for 6 days. The four TPN groups included control, Dex, Dex + IGF-I, and Dex+IGF-I/BP-3. Pharmacokinetic analysis indicated reduced clearance of IGF-I when infused as IGF-I/BP-3 compared with free IGF-I (0.91 ± 0.09 vs. 2.01 ± 0.19 ml serum/min, P < 0.001) and this was associated with significantly greater serum IGF-I concentrations in the Dex+IGF-I/BP-3 group. Despite greater total serum IGF-I levels, infusion of free IGF-I produced greater anabolic responses than IGF-I/BP-3 based on body weight, nitrogen balance, and jejunal cellularity. Treatment with free IGF-I, but not IGF-I/BP-3, significantly reduced serum insulin and glucose levels that were elevated due to Dex. There were no significant differences in liver IGF-I mRNA levels between groups. Serum IGFBP-3 levels were elevated with infusion of IGF-I/BP-3 compared with IGF-I. These results indicate greater anabolic potency of IGF-I compared with IGF-I/BP-3 when administered by continuous parenteral infusion with TPN solution in catabolic rats.
Twenty-four-hour rhythms of plasma glucose and insulin secretion rate in regular night workers
Authors: Simon C. , Weibel L. , Brandenberger G.
Published: December 2017

To determine whether the ultradian and circadian rhythms of glucose and insulin secretion rate (ISR) are adapted to their permanent nocturnal schedule, eight night workers were studied during their usual 24-h cycle with continuous enteral nutrition and a 10-min blood sampling procedure and were compared with 8 day-active subjects studied once with nocturnal sleep and once with an acute 8-h-shifted sleep. The mean 24-h glucose and ISR levels were similar in the three experiments. The duration and the number of the ultradian oscillations were influenced neither by the time of day nor by the sleep condition or its shift, but their mean amplitude increased during sleep whenever it occurred. In day-active subjects, glucose and ISR levels were high during nighttime sleep and then decreased to a minimum in the afternoon. After the acute sleep shift, the glucose and ISR rhythms were split in a biphasic pattern with a slight increase during the night of deprivation and another during daytime sleep. In night workers, the glucose and ISR peak levels exhibited an 8-h shift in accordance with the sleep shift, but the onset of the glucose rise underwent a shift of only 6 h and the sleep-related amplification of the glucose and ISR oscillations did not occur simultaneously. These results demonstrate that despite a predominant influence of sleep, the 24-h glucose and ISR rhythms are only partially adapted in permanent night workers.
High-frequency oscillations in circulating amylin concentrations in healthy humans
Authors: Juhl Claus B. , Pørksen Niels , Sturis Jeppe , Hansen Åge Prange , Veldhuis Johannes D. , Pincus Steven , Fineman Mark , Schmitz Ole
Published: December 2017

Amylin is stored in the pancreatic β-cell granules and cosecreted with insulin in response to nutrient stimuli. To gain further insight into control of hormonal release in β-cell physiology, we examined whether amylin, like insulin, circulates in a high-frequency oscillatory pattern, and if it does, to compare the secretory patterns of the two hormones. Eight overnight-fasted healthy individuals were studied during intravenous glucose infusion (2.0 mg ⋅ kg−1⋅ min−1). Blood was collected every minute for 90 min and analyzed in triplicate for amylin, total amylin immunoreactivity (TAI), and insulin. Mean plasma concentrations of amylin (nonglycosylated), TAI (nonglycosylated plus glycosylated), insulin, and glucose were 2.77 ± 1.21 pmol/l, 7.60 ± 1.73 pmol/l, 50.4 ± 17.5 pmol/l, and 5.9 ± 0.3 mmol/l, respectively. The 90-min time series of amylin, TAI, and insulin were analyzed for periodicity (by spectral analysis, autocorrelation analysis, and deconvolution analysis) and regularity [by approximate entropy (ApEn)]. Significant spectral density peaks were demonstrated by a random shuffling technique in 7 (out of 7), 8 (out of 8), and 8 (out of 8) time series, respectively, whereas autocorrelation analysis revealed significant pulsatility in 5 (out of 7), 7 (out of 8), and 5 (out of 8), respectively. The dominant periodicity of oscillations determined by spectral analysis was 4.6 ± 0.3, 4.6 ± 0.4, and 6.5 ± 1.1 min/pulse, respectively (amylin vs. insulin, P = 0.017, TAI vs. insulin, P = 0.018). By deconvolution analysis, amylin and insulin periodicities were, respectively, 6.3 ± 1.0 and 5.5 ± 0.6 min. By application of the regularity statistic, ApEn, 6 (out of 7), 7 (out of 8), and 6 (out of 8), respectively, were found to be significantly different from random. In conclusion, like several other hormones, circulating amylin concentrations exhibit oscillations in the secretory patterns for nonglycosylated as well as glycosylated forms. Whether the high-frequency pulsatile release of amylin is disturbed in diabetes is not known.
Inhibin is an important factor in the regulation of FSH secretion in the adult male hamster
Authors: Kishi Hisashi , Itoh Mariko , Wada Sachiko , Yukinari Yoko , Tanaka Yumiko , Nagamine Natsuko , Jin Wanzhu , Watanabe Gen , Taya Kazuyoshi
Published: December 2017

We investigated the importance of inhibin and testosterone in the regulation of gonadotropin secretion in adult male golden hamsters ( Mesocricetus auratus). After castration, plasma concentrations of inhibin and testosterone were reduced to undetectable, whereas plasma follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were increased. After hemicastration, plasma FSH and LH increased moderately and plasma inhibin decreased to one-half its initial level. Plasma testosterone levels in hemicastrated animals decreased 3 h after hemicastration but returned to those in sham-operated animals at 6 h. Plasma LH in the castrated hamster declined comparably to intact animals with testosterone treatment; plasma FSH also decreased but still remained at levels higher than those in intact animals. After treatment with inhibin in long-term-castrated animals, plasma FSH decreased, whereas plasma LH was not altered. Intact males treated with flutamide, an anti-androgen, showed a significant increase in plasma LH but not in FSH. On the other hand, treatment with anti-inhibin serum induced a significant elevation in plasma FSH, but not in LH. Using immunohistochemistry, we showed that the inhibin α-subunit was localized to both Sertoli and Leydig cells. The present study in adult male hamsters indicates that FSH secretion is regulated mainly by inhibin, presumably from Sertoli and Leydig cells, and that LH secretion is controlled primarily by androgens produced from the Leydig cells. This situation is more similar to that of primates than of rats.
Role of C-peptide in human physiology
Authors: Wahren John , Ekberg Karin , Johansson Jan , Henriksson Mikael , Pramanik Aladdin , Johansson Bo-Lennart , Rigler Rudolf , Jörnvall Hans
Published: December 2017

The C-peptide of proinsulin is important for the biosynthesis of insulin but has for a long time been considered to be biologically inert. Data now indicate that C-peptide in the nanomolar concentration range binds specifically to cell surfaces, probably to a G protein-coupled surface receptor, with subsequent activation of Ca2+-dependent intracellular signaling pathways. The association rate constant, Kass, for C-peptide binding to endothelial cells, renal tubular cells, and fibroblasts is ∼3 ⋅ 109M−1. The binding is stereospecific, and no cross-reaction is seen with insulin, proinsulin, insulin growth factors I and II, or neuropeptide Y. C-peptide stimulates Na+-K+-ATPase and endothelial nitric oxide synthase activities. Data also indicate that C-peptide administration is accompanied by augmented blood flow in skeletal muscle and skin, diminished glomerular hyperfiltration, reduced urinary albumin excretion, and improved nerve function, all in patients with type 1 diabetes who lack C-peptide, but not in healthy subjects. The possibility exists that C-peptide replacement, together with insulin administration, may prevent the development or retard the progression of long-term complications in type 1 diabetes.
Triiodothyronine amplifies the adrenergic stimulation of uncoupling protein expression in rat brown adipocytes
Authors: Hernández Arturo , Obregón Maria Jesús
Published: December 2017

Uncoupling protein (UCP), the mitochondrial protein specific to brown adipose tissue, is activated transcriptionally in response to cold and adrenergic agents. We studied the role of triiodothyronine (T3) on the adrenergic stimulation of UCP mRNA expression by use of primary cultures of rat brown adipocytes. Basal UCP mRNA levels are undetectable. Norepinephrine (NE) increases UCP mRNA during differentiation, not during proliferation. In hypothyroid conditions, UCP mRNA response to NE is almost absent. The presence of T3(0.2–20 nM) greatly increases the adrenergic response (30-fold). The sensitivity of UCP mRNA responses to NE is potentiated ∼100-fold by the presence of T3. The effect is proportional to the dose and time of preexposure to T3. The increases obtained with NE and T3are prevented by actinomycin and cycloheximide. T3greatly stabilizes UCP mRNA transcripts. The effects of thyroxine and retinoic acid are weaker than those of T3. In conclusion, in cultured rat brown adipocytes, T3is required and both synergizes with NE to increase UCP mRNA and stabilizes its mRNA transcripts.
Citrate release by perfused rat hearts: a window on mitochondrial cataplerosis
Authors: Vincent Geneviève , Comte Blandine , Poirier Myriame , Rosiers Christine Des
Published: December 2017

Cytosolic citrate is proposed to play a crucial role in substrate fuel selection in the heart. However, little is known about factors regulating the transfer of citrate from the mitochondria, where it is synthesized, to the cytosol. Further to our observation that rat hearts perfused under normoxia release citrate whose13C labeling pattern reflects that of mitochondrial citrate (B. Comte, G. Vincent, B. Bouchard, and C. Des Rosiers. J. Biol. Chem. 272: 26117–26124, 1997), we report here data indicating that this citrate release is a specific process reflecting the mitochondrial efflux of citrate, a process referred to as cataplerosis. Indeed, measured rates of citrate release, which vary between 2 and 21 nmol/min, are modulated by the nature and concentration of exogenous substrates feeding acetyl-CoA (fatty acid) and oxaloacetate (lactate plus pyruvate) for the mitochondrial citrate synthase reaction. Such release rates that represent at most 2% of the citric acid cycle flux are in agreement with the activity of the mitochondrial tricarboxylate transporter whose participation is also substantiated by 1) parallel variations in citrate release rates and tissue levels of citrate plus malate, the antiporter, and 2) a lowering of the citrate release rate by 1,2,3-benzenetricarboxylic acid, a specific inhibitor of the transporter. Taken together, the results from the present study indicate that citrate cataplerosis is modulated by substrate supply, in agreement with the role of cytosolic citrate in fuel partitioning, and occurs, at least in part, through the mitochondrial tricarboxylate transporter.
Dual regulation of leptin secretion: intracellular energy and calcium dependence of regulated pathway
Authors: Levy James R. , Gyarmati Judit , Lesko John M. , Adler Robert A. , Stevens Wayne
Published: December 2017

Rodent leptin is secreted by adipocytes and acutely regulates appetite and chronically regulates body weight. Mechanisms for leptin secretion in cultured adipocytes were investigated. Acutely, energy-producing substrates stimulated leptin secretion about twofold. Biologically inert carbohydrates failed to stimulate leptin secretion, and depletion of intracellular energy inhibited leptin release. There appears to be a correlation between intracellular ATP concentration and the rate of leptin secretion. Insulin increased leptin secretion by an additional 25%. Acute leptin secretion is calcium dependent. When incubated in the absence of calcium or in the presence of intracellular calcium chelators, glucose plus insulin failed to stimulate leptin secretion. In contrast, basal leptin secretion is secreted spontaneously and is calcium independent. Adipocytes from fatter animals secrete more leptin, even in the absence of calcium, compared with cells from thinner animals. Acute stimulus-secretion coupling mechanisms were then investigated. The potassium channel activator diazoxide and the nonspecific calcium channel blockers nickel and cadmium inhibited acute leptin secretion. These studies demonstrate that intracellular energy production is important for acute leptin secretion and that potassium and calcium flux may play roles in coupling intracellular energy production to leptin secretion.
Epinephrine infusion during moderate intensity exercise increases glucose production and uptake
Authors: Kreisman Stuart H. , Mew Nicholas Ah , Arsenault Mylène , Nessim Sharon J. , Halter Jeffrey B. , Vranic Mladen , Marliss Errol B.
Published: December 2017

The glucoregulatory response to intense exercise [IE, >80% maximum O2 uptake (V˙o 2 max)] comprises a marked increment in glucose production (Ra) and a lesser increment in glucose uptake (Rd), resulting in hyperglycemia. The Ra correlates with plasma catecholamines but not with the glucagon-to-insulin (IRG/IRI) ratio. If epinephrine (Epi) infusion during moderate exercise were able to markedly stimulate Ra, this would support an important role for the catecholamines' response in IE. Seven fit male subjects (26 ± 2 yr, body mass index 23 ± 0.5 kg/m2,V˙o 2 max 65 ± 5 ml ⋅ kg− 1 ⋅ min− 1) underwent 40 min of postabsorptive cycle ergometer exercise (145 ± 14 W) once without [control (CON)] and once with Epi infusion [EPI (0.1 μg ⋅ kg− 1 ⋅ min− 1)] from 30 to 40 min. Epi levels reached 9.4 ± 0.8 nM (20× rest, 10× CON). Ra increased ∼70% to 3.75 ± 0.53 in CON but to 8.57 ± 0.58 mg ⋅ kg− 1 ⋅ min− 1in EPI ( P < 0.001). Increments in Ra and Epi correlated ( r 2 = 0.923, P ≤ 0.01). In EPI, peak Rd (5.55 ± 0.54 vs. 3.38 ± 0.46 mg ⋅ kg− 1 ⋅ min− 1, P = 0.006) and glucose metabolic clearance rate (MCR, P= 0.018) were higher. The Ra-to-Rdimbalance in EPI caused hyperglycemia (7.12 ± 0.22 vs. 5.59 ± 0.22 mM, P = 0.001) until minute 60 of recovery. A small and late IRG/IRI increase ( P = 0.015 vs. CON) could not account for the Ra increase. Norepinephrine (∼4× increase at peak) did not differ between EPI and CON. Thus Epi infusion during moderate exercise led to increments in Ra and Rd and caused rises of plasma glucose, lactate, and respiratory exchange ratio in fit individuals, supporting a regulatory role for Epi in IE. Epi's effects on Rd and MCR during exercise may differ from its effects at rest.
Effects of high-fat diet and exercise training on intracellular glucose metabolism in rats
Authors: Kim Chul-Hee , Youn Jang H. , Park Joong-Yeol , Hong Sung K. , Park Kyong S. , Park Sung W. , Suh Kyo I. , Lee Ki-Up
Published: December 2017

We examined the effects of high-fat diet (HFD) and exercise training on insulin-stimulated whole body glucose fluxes and several key steps of glucose metabolism in skeletal muscle. Rats were maintained for 3 wk on either low-fat (LFD) or high-fat diet with or without exercise training (swimming for 3 h per day). After the 3-wk diet/exercise treatments, animals underwent hyperinsulinemic euglycemic clamp experiments for measurements of insulin-stimulated whole body glucose fluxes. In addition, muscle samples were taken at the end of the clamps for measurements of glucose 6-phosphate (G-6- P) and GLUT-4 protein contents, hexokinase, and glycogen synthase (GS) activities. Insulin-stimulated glucose uptake was decreased by HFD and increased by exercise training ( P < 0.01 for both). The opposite effects of HFD and exercise training on insulin-stimulated glucose uptake were associated with similar increases in muscle G-6- P levels ( P < 0.05 for both). However, the increase in G-6- Plevel was accompanied by decreased GS activity without changes in GLUT-4 protein content and hexokinase activities in the HFD group. In contrast, the increase in G-6- P level in the exercise-trained group was accompanied by increased GLUT-4 protein content and hexokinase II (cytosolic) and GS activities. These results suggest that HFD and exercise training affect insulin sensitivity by acting predominantly on different steps of intracellular glucose metabolism. High-fat feeding appears to induce insulin resistance by affecting predominantly steps distal to G-6- P (e.g., glycolysis and glycogen synthesis). Exercise training affected multiple steps of glucose metabolism both proximal and distal to G-6- P. However, increased muscle G-6- P levels in the face of increased glucose metabolic fluxes suggest that the effect of exercise training is quantitatively more prominent on the steps proximal to G-6- P(i.e., glucose transport and phosphorylation).
Involvement of tyrosine kinase in citrate-stimulated aldosterone production in bovine glomerulosa cells
Authors: Kigoshi Toshikazu , Imaizumi Noriko , Yoshida Junko , Nakagawa Atsushi , Nakano Shigeru , Nishio Matomo , Uchida Kenzo
Published: December 2017

The present study was designed to assess whether citrate stimulates aldosterone production by isolated bovine adrenal glomerulosa cells in vitro. When the cells were incubated with graded concentrations of citrate up to 4.0 mM, basal aldosterone production was significantly elevated, with a gradual reduction of extracellular ionized calcium concentration. Without citrate, however, adding increasing amounts of calcium chloride to a calcium-free medium did not reproduce the citrate's effect on basal aldosterone production. Genistein, an inhibitor of tyrosine kinases, inhibited the citrate (4 mM)-induced aldosterone production in a dose-dependent manner, with 89.8% of inhibition at a concentration of 10 μM. When the cells were exposed to citrate (4 mM) for 5, 10, and 30 min, tyrosine in Mr 105,000 endogenous protein was dominantly phosphorylated. This study demonstrates for the first time that citrate stimulates aldosterone production in bovine adrenal glomerulosa cells in vitro and also suggests a crucial involvement of protein tyrosine kinase in the steroidogenic action of citrate in the cells.
Plasma FFA utilization and fatty acid-binding protein content are diminished in type 2 diabetic muscle
Authors: Blaak Ellen E. , Wagenmakers Anton J. M. , Glatz Jan F. C. , Wolffenbuttel Bruce H. R. , Kemerink Gerrit J. , Langenberg Chris J. M. , Heidendal Guido A. K. , Saris Wim H. M.
Published: December 2017

In this study, we investigated the hypothesis that impairments in forearm skeletal muscle free fatty acid (FFA) metabolism are present in patients with type 2 diabetes both in the overnight fasted state and during β-adrenergic stimulation. Eight obese subjects with type 2 diabetes and eight nonobese controls (Con) were studied using the forearm balance technique and indirect calorimetry during infusion of the stable isotope tracer [U-13C]palmitate after an overnight fast and during infusion of the nonselective β-agonist isoprenaline (Iso, 20 ng · kg lean body mass−1 · min−1). Additionally, activities of mitochondrial enzymes and of cytoplasmatic fatty acid-binding protein (FABP) were determined in biopsies from the vastus lateralis muscle. Both during fasting and Iso infusion, the tracer balance data showed that forearm muscle FFA uptake (Con vs. type 2: fast 449 ± 69 vs. 258 ± 42 and Iso 715 ± 129 vs. 398 ± 70 nmol · 100 ml tissue−1 · min−1, P < 0.05) and FFA release were lower in type 2 diabetes compared with Con. Also, the oxidation of plasma FFA by skeletal muscle was blunted during Iso infusion in type 2 diabetes (Con vs. type 2: Iso 446 ± 274 vs. 16 ± 70 nmol · 100 ml tissue−1 · min−1, P < 0.05). The net forearm glycerol release was increased in type 2 diabetic subjects ( P < 0.05), which points to an increased forearm lipolysis. Additionally, skeletal muscle cytoplasmatic FABP content and the activity of muscle oxidative enzymes were lowered in type 2 diabetes. We conclude that the uptake and oxidation of plasma FFA are impaired in the forearm muscles of type 2 diabetic subjects in the overnight fasted state with and without Iso stimulation.
Insulin stimulation of muscle protein synthesis in obese Zucker rats is not via a rapamycin-sensitive pathway
Authors: Fluckey James D. , Pohnert Steven C. , Boyd S. Greg , Cortright Ronald N. , Trappe Todd A. , Dohm G. Lynis
Published: December 2017

The obese Zucker rat is resistant to insulin for glucose disposal, but it is unknown whether this insulin resistance is accompanied by alterations of insulin-mediated muscle protein synthesis. We examined rates of muscle protein synthesis either with or without insulin in lean and obese Zucker rats with the use of a bilateral hindlimb preparation. Additional experiments examined insulin's effect on protein synthesis with or without rapamycin, an inhibitor of protein synthesis. Protein synthesis in red and white gastrocnemius was stimulated by insulin compared with control (no insulin) in obese ( n = 10, P < 0.05) but not in lean ( n = 10, P > 0.05) Zucker rats. In white gastrocnemius, rapamycin significantly reduced rates of protein synthesis compared with control in lean ( n = 6) and obese ( n = 6) rats; however, in red gastrocnemius, the attenuating effect of rapamycin occurred only in obese rats. The addition of insulin to rapamycin resulted in rates of synthesis that were similar to those for rapamycin alone for lean rats and to those for insulin alone (augmented) for obese rats in both tissues. Our results demonstrate that insulin enhances protein synthesis in muscle that is otherwise characterized as insulin resistant. Furthermore, rapamycin inhibits protein synthesis in muscle of obese Zucker rats; however, stimulation of protein synthesis by insulin is not via a rapamycin-sensitive pathway.
Cytokines and endotoxin induce cytokine receptors in skeletal muscle
Authors: Zhang Yan , Pilon Geneviève , Marette André , Baracos Vickie E.
Published: December 2017

Proinflammatory cytokines are important factors in the regulation of diverse aspects of skeletal muscle function; however, the muscle cytokine receptors mediating these functions are uncharacterized. Binding kinetics (dissociation constant = 39 ± 4.7 × 10−9M, maximal binding = 3.5 ± 0.23 × 10−12mol/mg membrane protein) of muscle tumor necrosis factor (TNF) receptors were obtained. Skeletal muscle was found to express mRNAs encoding interleukin-1 type I and II receptors, interleukin-6 receptor (IL-6R), and interferon-γ receptor by RT-PCR, but these receptors were below limits of detection of ligand-binding assay (≥1 fmol binding sites/mg protein). Twenty-four hours after intraperitoneal administration of endotoxin to rats, TNF receptor type II (TNFRII) and IL-6R mRNA were increased in skeletal muscle ( P < 0.05). In cultured L6 cells, the expression of mRNA encoding TNFRII and IL-6R receptors was induced by TNF-α, and all six cytokine receptor mRNA were induced by a mixture of TNF-α, IFN-γ, and endotoxin ( P < 0.05). This suggests that the low level of cytokine receptor expression is complemented by a capacity for receptor induction, providing a clear mechanism for amplification of cytokine responses at the muscle level.
Fetal origins of hyperphagia, obesity, and hypertension and postnatal amplification by hypercaloric nutrition
Authors: Vickers Mark H. , Breier Bernhard H. , Cutfield Wayne S. , Hofman Paul L. , Gluckman Peter D.
Published: December 2017

Environmental factors and diet are generally believed to be accelerators of obesity and hypertension, but they are not the underlying cause. Our animal model of obesity and hypertension is based on the observation that impaired fetal growth has long-term clinical consequences that are induced by fetal programming. Using fetal undernutrition throughout pregnancy, we investigated whether the effects of fetal programming on adult obesity and hypertension are mediated by changes in insulin and leptin action and whether increased appetite may be a behavioral trigger of adult disease. Virgin Wistar rats were time mated and randomly assigned to receive food either ad libitum (AD group) or at 30% of ad libitum intake, or undernutrition (UN group). Offspring from UN mothers were significantly smaller at birth than AD offspring. At weaning, offspring were assigned to one of two diets [a control diet or a hypercaloric (30% fat) diet]. Food intake in offspring from UN mothers was significantly elevated at an early postnatal age. It increased further with advancing age and was amplified by hypercaloric nutrition. UN offspring also showed elevated systolic blood pressure and markedly increased fasting plasma insulin and leptin concentrations. This study is the first to demonstrate that profound adult hyperphagia is a consequence of fetal programming and a key contributing factor in adult pathophysiology. We hypothesize that hyperinsulinism and hyperleptinemia play a key role in the etiology of hyperphagia, obesity, and hypertension as a consequence of altered fetal development.