bluuebunny/crossref_metadata_2025 huggingface dataset:
Islet amyloid polypeptide tonally inhibits β-, α-, and δ-cell secretion in isolated rat pancreatic islets
Authors: Wang Feng , Adrian Thomas E. , Westermark Gunilla T. , Ding Xianzhong , Gasslander Thomas , Permert Johan
Published: December 2017

Islet amyloid polypeptide (IAPP, or amylin) is produced in pancreatic β-cells. The intraislet significance of IAPP is still uncertain. In the present study, paracrine effects of endogenous IAPP and somatostatin were investigated in isolated rat pancreatic islets. The intraislet IAPP activity was inhibited with an IAPP antiserum or a specific antagonist [IAPP-(8—37)]. Somatostatin activity was inhibited by immunoneutralization. Basal insulin and glucagon secretion were not affected by the somatostatin and/or IAPP blockade. Arginine-stimulated insulin and glucagon secretion were dose dependently increased by IAPP antiserum, IAPP-(8—37), and somatostatin antiserum, respectively. Arginine-stimulated somatostatin secretion was dose dependently potentiated by IAPP antiserum. Insulin secretion induced by 16.7 mM glucose was enhanced by IAPP antiserum and IAPP-(8—37), respectively. A combination of somatostatin antiserum with IAPP antiserum or IAPP-(8—37) further enhanced the arginine-stimulated insulin and glucagon secretion compared with effects when the blocking reagents were used individually. These results indicate that endogenously produced IAPP tonally inhibits stimulated insulin, glucagon, and somatostatin secretion. Furthermore, the paracrine effects of IAPP and somatostatin are additive.
DHEA improves glucose uptake via activations of protein kinase C and phosphatidylinositol 3-kinase
Authors: Ishizuka Tatsuo , Kajita Kazuo , Miura Atsushi , Ishizawa Masayoshi , Kanoh Yoshinori , Itaya Satomi , Kimura Mika , Muto Naoya , Mune Tomoatsu , Morita Hiroaki , Yasuda Keigo
Published: December 2017

We have examined the effect of adrenal androgen, dehydroepiandrosterone (DHEA), on glucose uptake, phosphatidylinositol (PI) 3-kinase, and protein kinase C (PKC) activity in rat adipocytes. DHEA (1 μM) provoked a twofold increase in 2-[3H]deoxyglucose (DG) uptake for 30 min. Pretreatment with DHEA increased insulin-induced 2-[3H]DG uptake without alterations of insulin specific binding and autophosphorylation of insulin receptor. DHEA also stimulated PI 3-kinase activity. [3H]DHEA bound to purified PKC containing PKC-α, -β, and -γ. DHEA provoked the translocation of PKC-β and -ζ from the cytosol to the membrane in rat adipocytes. These results suggest that DHEA stimulates both PI 3-kinase and PKCs and subsequently stimulates glucose uptake. Moreover, to clarify the in vivo effect of DHEA on Goto-Kakizaki (GK) and Otsuka Long-Evans fatty (OLETF) rats, animal models of non-insulin-dependent diabetes mellitus (NIDDM) were treated with 0.4% DHEA for 2 wk. Insulin- and 12- O-tetradecanoyl phorbol-13-acetate-induced 2-[3H]DG uptakes of adipocytes were significantly increased, but there was no significant increase in the soleus muscles in DHEA-treated GK/Wistar or OLETF/Long-Evans Tokushima (LETO) rats when compared with untreated GK/Wistar or OLETF/LETO rats. These results indicate that in vivo DHEA treatment can result in increased insulin-induced glucose uptake in two different NIDDM rat models.
Bone and hormonal changes induced by skeletal unloading in the mature male rat
Authors: Dehority Walter , Halloran Bernard P. , Bikle Daniel D. , Curren Tracy , Kostenuik Paul J. , Wronski Thomas J. , Shen Ying , Rabkin Brian , Bouraoui Abderrahman , Morey-Holton Emily
Published: December 2017

To determine whether the rat hindlimb elevation model can be used to study the effects of spaceflight and loss of gravitational loading on bone in the adult animal, and to examine the effects of age on bone responsiveness to mechanical loading, we studied 6-mo-old rats subjected to hindlimb elevation for up to 5 wk. Loss of weight bearing in the adult induced a mild hypercalcemia, diminished serum 1,25-dihydroxyvitamin D, decreased vertebral bone mass, and blunted the otherwise normal increase in femoral mass associated with bone maturation. Unloading decreased osteoblast numbers and reduced periosteal and cancellous bone formation but had no effect on bone resorption. Mineralizing surface, mineral apposition rate, and bone formation rate decreased during unloading. Our results demonstrate the utility of the adult rat hindlimb elevation model as a means of simulating the loss of gravitational loading on the skeleton, and they show that the effects of nonweight bearing are prolonged and have a greater relative effect on bone formation in the adult than in the young growing animal.
Direct access to interstitial fluid in adipose tissue in humans by use of open-flow microperfusion
Authors: Schaupp L. , Ellmerer M. , Brunner G. A. , Wutte A. , Sendlhofer G. , Trajanoski Z. , Skrabal F. , Pieber T. R. , Wach P.
Published: December 2017

To gain direct access to the interstitial fluid (ISF), a new technique called open-flow microperfusion has been evaluated. This method is based on a double-lumen catheter with macroscopic (0.3–0.5 mm diameter) perforations that is inserted into the subcutaneous adipose tissue and constantly perfused. Thus partial equilibration between the ISF and the perfusion fluid occurs. The glucose concentration of the ISF was determined by established (zero flow rate, no net flux, and recirculation procedures) and new (ionic reference and suction technique) calibration methods by use of open-flow microperfusion. The data show that 1) the glucose concentration in the ISF is significantly lower than the corresponding arterialized venous plasma values during basal steady-state conditions (adipose tissue 3.2 ± 0.10 mM, plasma 5.27 ± 0.12 mM) as well as during hyperglycemic clamp experiments (adipose tissue 7.3 ± 0.13 mM, plasma 9.91 ± 0.16 mM), and 2) it is possible to determine the recovery continuously by using the ion concentration of the ISF as an internal standard (ionic reference).
Leukemia inhibitory factor and oncostatin M stimulate collagenase-3 expression in osteoblasts
Authors: Varghese Samuel , Yu Kyung , Canalis Ernesto
Published: December 2017

Leukemia inhibitory factor (LIF) and oncostatin M (OSM) have multiple effects on skeletal remodeling. Although these cytokines modestly regulate collagen synthesis in osteoblasts, their effects on collagenase expression and collagen degradation are not known. We tested whether LIF and OSM regulate the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in osteoblast-enriched cells isolated from fetal rat calvariae. LIF and OSM increased collagenase-3 (MMP-13) mRNA and immunoreactive protein levels in a time- and dose-dependent manner. LIF and OSM enhanced the rate of transcription of the collagenase gene and stabilized collagenase mRNA in transcriptionally arrested cells. LIF and OSM failed to regulate the expression of gelatinase A (MMP-2) and B (MMP-9). LIF and OSM modestly stimulated the expression of TIMP-1 but did not alter the expression of TIMP-2 and -3. In conclusion, LIF and OSM stimulate collagenase-3 and TIMP-1 expression in osteoblasts, and these effects may be involved in mediating the bone remodeling actions of these cytokines.
HaCaT human keratinocytes express IGF-II, IGFBP-6, and an acid-activated protease with activity against IGFBP-6
Authors: Marinaro Joe A. , Hendrich Elke C. , Leeding Kerri S. , Bach Leon A.
Published: December 2017

The insulin-like growth factor (IGF) system plays an important role in skin. HaCaT human keratinocytes proliferate in response to IGFs and synthesize IGF-binding protein-3 (IGFBP-3). Recently, IGFBP-6 was also identified by NH2-terminal sequencing, but it has not been identified by Western ligand blotting. In the present study, IGFBP-6 was detected in HaCaT-conditioned medium by use of immunoblotting and Western ligand blotting with125I-labeled IGF-II. Proteolytic activity against IGFBPs, an important mechanism for regulation of their activity, was then studied. An acid-activated, cathepsin D-like protease that cleaved both IGFBP-6 and IGFBP-3 was detected. Although proteolysis did not substantially reduce the size of immunoreactive IGFBP-6, it greatly reduced the ability of IGFBP-6 to bind125I-IGF-II as determined by Western ligand blotting and solution assay. HaCaT keratinocytes do not express IGF-I mRNA, but IGF-II mRNA and protein expression was detected. These observations suggest the possibility of an autocrine IGF-II loop that is regulated by the relative expression of IGF-II, IGFBP-3, and IGFBP-6, and IGFBP proteases in these keratinocytes, although demonstration of this loop requires further study.
Insulin but not growth hormone stimulates protein anabolism in skin wound and muscle
Authors: Zhang Xiao-Jun , Chinkes David L. , Wolf Steve E. , Wolfe Robert R.
Published: December 2017

We have measured protein kinetics in the scalded skin and normal muscle in anesthetized rabbits. On the 7th day after ear scald,l-[ ring-13C6]phenylalanine was infused as a tracer, and the ear and hindlimb were used as arteriovenous units to reflect skin and muscle protein kinetics. Insulin was infused at 0.6 or 2.3–3.4 mU ⋅ kg−1⋅ min−1in the low-dose and high-dose insulin groups. In the growth hormone group, recombinant human growth hormone was administered at 2 mg ⋅ kg−1⋅ day−1after the ear was scalded. The results were compared with a control group in which the ear was scalded but otherwise was not treated. In the control group, net protein loss in the scalded skin and muscle was 23.1 ± 21.4 and 3.9 ± 1.5 μmol ⋅ 100 g−1⋅ h−1, respectively. Insulin infusion at either high or low dose reduced net protein loss to near zero by inhibiting proteolysis. In contrast, growth hormone treatment had no anabolic effect on either tissue. In conclusion, insulin but not growth hormone has an anabolic effect on scalded skin and normal muscle; low-dose insulin is as effective in achieving an anabolic effect on both tissues, with less hypoglycemic response than high-dose insulin.
Glucose effectiveness is the major determinant of intravenous glucose tolerance in the rat
Authors: McArthur M. Dawn , You Dan , Klapstein Kim , Finegood Diane T.
Published: December 2017

To determine the importance of insulin for glucose disposal during an intravenous glucose tolerance test in rats, experiments were performed in four cohorts of conscious unrestrained rats fasted overnight. In cohorts 1- 3, a bolus of tracer ([3-3H]glucose, 50 μCi) was given alone, with glucose (0.3 g/kg) to induce an endogenous insulin response (∼1,100 pmol/l), or with exogenous insulin to give physiological (1,700 pmol/l) or supraphysiological (12,000 pmol/l) plasma levels. Raising plasma insulin within the physiological range had no effect ( P > 0.05), but supraphysiological levels induced hypoglycemia (7.3 ± 0.2 to 3.6 ± 0.2 mmol/l) and increased [3H]glucose disappearance rate ( P < 0.001). In cohort 4, a primed, continuous tracer infusion was started 120 min before saline or glucose bolus injection. [3H]glucose levels fell 15–20%, and the disappearance rate rose 36% ( P < 0.05) after glucose injection. These results indicate that in fasted rats a tracer bolus injection protocol is not sufficiently sensitive to measure the physiological effect of insulin released in response to a bolus of glucose because this effect of insulin is small. Glucose itself is the predominant mediator of glucose disposal after a bolus of glucose in the fasted rat.
Effect of intravenous glutamine on duodenal mucosa protein synthesis in healthy growing dogs
Authors: Marchini J. Sérgio , Nguyen Patrick , Deschamps Jack-Yves , Maugère Pascale , Krempf Michel , Darmaun Dominique
Published: December 2017

To determine whether glutamine acutely stimulates protein synthesis in the duodenal mucosa, five healthy growing dogs underwent endoscopic biopsies of duodenal mucosa at the end of three 4-h primed, continuous intravenous infusions ofl-[1-13C]leucine on three separate days, while receiving intravenous infusion of 1) saline, 2)l-glutamine (800 μmol ⋅ kg−1 ⋅ h−1), and 3) isonitrogenous amounts of glycine. The three infusions were performed after 24 h of fasting, a week apart from each other and in a randomized order. Glutamine infusion induced a doubling in plasma glutamine level, and glycine caused a >10-fold rise in plasma glycine level. During intravenous infusions of [13C]leucine, the plasma leucine labeling attained a plateau value between 3.22 and 3.68 mole % excess (MPE) and [13C]ketoisocaproate ([13C]KIC) of 2.91–2.84 MPE; there were no significant differences between glutamine, glycine, and saline infusion days. Plasma leucine appearance rate was 354 ± 33 (SE), 414 ± 28, and 351 ± 35 μmol ⋅ kg−1 ⋅ h−1(not significant) during glycine, saline, and glutamine infusion, respectively. The fractional synthetic rate (FSR) of duodenal mucosa protein was calculated from the rise in protein-bound [13C]leucine enrichment in the biopsy sample, divided by time and with either plasma [13C]KIC or tissue free [13C]leucine as precursor pool enrichment. Regardless of the precursor pool used in calculations, duodenal protein FSR failed to rise significantly during glutamine infusion (65 ± 11%/day) compared either with saline (84 ± 18%/day) or glycine infusion days (80 ± 15%/day). We conclude that 1) plasma [13C]KIC and tissue free [13C]leucine can be used interchangeably as precursor pools to calculate gut protein FSR; and 2) short intravenous infusion of glutamine does not acutely stimulate duodenal protein synthesis in well-nourished, growing dogs.
Leptin responsiveness and gene dosage for leptin receptor mutation (fa) in newborn rats
Authors: Kraeft Susanne , Schwarzer Knut , Eiden Sandra , Nuesslein-Hildesheim Barbara , Preibisch Gerald , Schmidt Ingrid
Published: December 2017

To determine the degree to which the leptin receptor mutation ( fa) influences the responsiveness to leptin during the first postnatal week, we injected recombinant leptin (600 pmol ⋅ g−1⋅ day−1sc from day 1 to day 7) into wild-type (+/+), heterozygous (+/ fa), and fatty ( fa/fa) rat pups. Growth and final body fat content of these leptin-treated pups were compared with those of saline-treated littermates of the same genotype. The body mass of the leptin-treated +/+ pups, but not that of the +/ fa and fa/fa pups, increased more slowly than that of their respective controls, and fat content at day 7was reduced by 37% in +/+ pups, by 22% in +/ fa pups, but not at all in fa/fa pups. Plasma leptin remained excessively high throughout the day under this treatment, but a 30-fold lower leptin dose, causing only moderate changes of plasma leptin, still reduced the body fat of +/+ pups significantly. We conclude that leptin participates in the control of even the earliest stages of fat deposition and that the response to supraphysiological doses of leptin is markedly reduced in 1-wk-old pups with one fa allele and absent in pups with two fa alleles.
Rapid reversal of the effects of the portal signal under hyperinsulinemic conditions in the conscious dog
Authors: Hsieh Po-Shiuan , Moore Mary Courtney , Neal Doss W. , Emshwiller Maya , Cherrington Alan D.
Published: December 2017

Experiments were performed on two groups of 42-h-fasted conscious dogs ( n = 6/group). Somatostatin was given peripherally with insulin (4-fold basal) and glucagon (basal) intraportally. In the first experimental period, glucose was infused peripherally to double the hepatic glucose load (HGL) in both groups. In the second experimental period, glucose (21.8 μmol ⋅ kg−1⋅ min−1) was infused intraportally and the peripheral glucose infusion rate (PeGIR) was reduced to maintain the precreating HGL in the portal signal (PO) group, whereas saline was given intraportally in the control (CON) group and PeGIR was not changed. In the third period, the portal glucose infusion was stopped in the PO group and PeGIR was increased to sustain HGL. PeGIR was continued in the CON group. The glucose loads to the liver did not differ in the CON and PO groups. Net hepatic glucose uptake was 9.6 ± 2.5, 11.6 ± 2.6, and 15.5 ± 3.2 vs. 10.8 ± 1.8, 23.7 ± 3.0, and 15.5 ± 1.1 μmol ⋅ kg−1⋅ min−1, and nonhepatic glucose uptake (non-HGU) was 29.8 ± 1.1, 40.1 ± 4.5, and 49.5 ± 4.0 vs. 26.6 ± 4.3, 23.2 ± 4.0, and 40.4 ± 3.1 μmol ⋅ kg−1⋅ min−1in the CON and PO groups during the three periods, respectively. Cessation of the portal signal shifted NHGU and non-HGU to rates similar to those evident in the CON group within 10 min. These results indicate that even under hyperinsulinemic conditions the effects of the portal signal on hepatic and peripheral glucose uptake are rapidly reversible.
Redox-dependent and redox-independent subcomponents of protein degradation in perfused myocardium
Authors: Lockwood Thomas D.
Published: December 2017

The integration of proteolytic pathways with metabolism was investigated in perfused rat myocardium. After a 10-min incorporation period, the minute-to-minute release of [3H]leucine from myocardial proteins was measured in nonrecirculating effluent perfusate. The nontoxic pro-oxidant probe diamide (100 μM) or a supraphysiological concentration of the endogenous oxidative metabolite dehydroascorbic acid (200 μM) reversibly inhibited 75% of myocardial proteolysis consisting of several known subcomponents (redox dependent); however, 25% of proteolysis was diamide insensitive (redox independent). Decrease in extracellular glucose concentration from 10 to 0.1 mM strongly increased the potencies of minimally effective concentrations of diamide (10 μM) or dehydroascorbic acid (15 μM) by ∼10-fold to the respective potencies maximally inhibiting proteolysis. The reversal of diamide action was also strongly dependent on the perfusate glucose concentration observed at 0.1, 0.2, 1.0 and 10 mM glucose. Proteolytic inhibition caused by diamide (100 μM) was not accompanied by change in basal tissue ATP content of 5 μmol/g wet wt. Conversely, nearly lethal 60% ATP depletion caused by sodium azide (0.4 mM) was not accompanied by change in total [3H]leucine release. Results indicate that a large proteolytic subcomponent (75%) is maintained by redox chains fed by glucose; however, there is no apparent linkage of this proteolysis to short-term ATP fluctuations. A distinct major proteolytic subcomponent (25%) does not vary in response to experimental intervention in either ATP content or redox chains.
Acute enhancement of insulin secretion by FFA in humans is lost with prolonged FFA elevation
Authors: Carpentier André , Mittelman Steven D. , Lamarche Benoǐt , Bergman Richard N. , Giacca Adria , Lewis Gary F.
Published: December 2017

The in vivo effect of elevated free fatty acids (FFA) on β-cell function in humans remains extremely controversial. We examined, in healthy young men, the acute (90 min) and chronic (48 h) effects of an approximately twofold elevation of plasma FFA vs. control on glucose-stimulated insulin secretion (GSIS). GSIS was studied in response to a graded intravenous glucose infusion (peak plasma glucose, ∼10 mmol/l, n = 8) and a two-step hyperglycemic clamp (10 and 20 mmol/l, n = 8). In the acute studies, GSIS was significantly higher, insulin sensitivity index (SI) was lower, and disposition index (DI = insulin sensitivity × insulin secretion) was unchanged with elevated FFA vs. control [2-step clamp: DI = 8.9 ± 1.4 × 10−3l2 ⋅ kg−1 ⋅ min−2in control vs. 10.0 ± 1.9 × 10−3l2 ⋅ kg−1 ⋅ min−2with high FFA, P = nonsignificant (NS)]. In the chronic studies, there was no difference in absolute GSIS between control and high FFA studies, but there was a reduction in SI and a loss of the expected compensatory increase in insulin secretion as assessed by the DI (2-step clamp: DI = 10.0 ± 1.2 × 10−3l2 ⋅ kg−1 ⋅ min−2in control vs. 6.1 ± 0.7 × 10−3l2 ⋅ kg−1 ⋅ min−2with high FFA, P = 0.01). In summary, 1) acute and chronic FFA elevation induces insulin resistance; 2) with acute FFA elevation, this insulin resistance is precisely countered by an FFA-induced increase in insulin secretion, such that DI does not change; and 3) chronic FFA elevation disables this β-cell compensation.
Effect of tension on contraction-induced glucose transport in rat skeletal muscle
Authors: Ihlemann Jacob , Ploug Thorkil , Hellsten Ylva , Galbo Henrik
Published: December 2017

We questioned the general view that contraction-induced muscle glucose transport only depends on stimulation frequency and not on workload. Incubated soleus muscles were electrically stimulated at a given pattern for 5 min. Resting length was adjusted to achieve either no force (0% P), maximum force (100% P), or 50% of maximum force (50% P). Glucose transport (2-deoxy-d-glucose uptake) increased directly with force development ( P < 0.05) [27 ± 2 (basal), 45 ± 2 (0% P), 68 ± 3 (50% P), and 94 ± 3 (100% P) nmol ⋅ g−1⋅ 5 min−1]. Glycogen decreased at 0% P but did not change further with force development ( P > 0.05). Lactate, AMP, and IMP concentrations were higher ( P < 0.05) and ATP concentrations lower ( P < 0.05) when force was produced than when it was not. 5′-AMP-activated protein kinase (AMPK) activity increased directly with force [20 ± 2 (basal), 60 ± 11 (0% P), 91 ± 12 (50% P), and 109 ± 12 (100% P) pmol ⋅ mg−1⋅ min−1]. Passive stretch (∼86% P) doubled glucose transport without altering metabolism. In conclusion, contraction-induced muscle glucose transport varies directly with force development and is not solely determined by stimulation frequency. AMPK activity is probably an essential determinant of contraction-induced glucose transport. In contrast, glycogen concentrations per se do not play a major role. Finally, passive stretch per se increases glucose transport in muscle.
Inhibition of muscle protein synthesis by alcohol is associated with modulation of eIF2B and eIF4E
Authors: Lang Charles H. , Wu Duanqing , Frost Robert A. , Jefferson Leonard S. , Kimball Scot R. , Vary Thomas C.
Published: December 2017

The present study examined potential mechanisms for the inhibition of protein synthesis in skeletal muscle after chronic alcohol consumption. Rats were maintained on an alcohol-containing diet for 14 wk; control animals were pair fed. Alcohol-induced myopathy was confirmed by a reduction in lean body mass as well as a decrease in the weight of the gastrocnemius and psoas muscles normalized for tibial length. No alcohol-induced decrease in total RNA content (an estimate of ribosomal RNA) was detected in any muscle examined, suggesting that alcohol reduced translational efficiency but not the capacity for protein synthesis. To identify mechanisms responsible for regulating translational efficiency, we analyzed several eukaryotic initiation factors (eIF). There was no difference in the muscle content of either total eIF2α or the amount of eIF2α in the phosphorylated form between alcohol-fed and control rats. Similarly, the relative amount of eIF2Bε in muscle was also not different. In contrast, alcohol decreased eIF2B activity in psoas (fast-twitch) but not in soleus or heart (slow-twitch) muscles. Alcohol feeding also dramatically influenced the distribution of eIF4E in the gastrocnemius (fast-twitch) muscle. Compared with control values, muscle from alcohol-fed rats demonstrated 1) an increased binding of the translational repressor 4E-binding protein 1 (4E-BP1) with eIF4E, 2) a decrease in the phosphorylated γ-form of 4E-BP1, and 3) a decrease in eIF4G associated with eIF4E. In summary, these data suggest that chronic alcohol consumption impairs translation initiation in muscle by altering multiple regulatory sites, including eIF2B activity and eIF4E availability.
Concurrent reductions of serum leptin and lipids during weight loss in obese men with type II diabetes
Authors: Halle Martin , Berg Aloys , Garwers Ulrich , Grathwohl Dominik , Knisel Werner , Keul Joseph
Published: December 2017

The aim of the study was to examine the effects of weight reduction by exercise and diet on metabolic control in obese subjects with insulin resistance, particularly investigating if changes in serum leptin concentrations were directly associated with improvements in metabolic control. Twenty obese men (48 ± 8 yr; body mass index 32.1 ± 3.9 kg/m2) with previously diagnosed type II diabetes mellitus were assigned to a 4-wk intervention program of exercise (2,200 kcal/wk) and diet (1,000 kcal/day; 50% carbohydrates, 25% protein, 25% fat; polyunsaturated-to-saturated fatty acid ratio 1.0). Intervention induced significant reductions in body weight and serum leptin levels, and improvements in lipoprotein profile and glucose control. Reductions in leptin levels were directly associated with reductions in serum triglycerides and cholesterol, a finding that was independent of improvements in glucose control. These data show that serum leptin concentrations can be reduced with caloric restriction and exercise in male patients with type II diabetes, and they suggest a direct relationship between leptin and lipoprotein metabolism that is not solely due to weight reduction.
Insulin-like growth factor I rapidly enhances acid efflux from osteoblastic cells
Authors: Santhanagopal Anu , Dixon S. Jeffrey
Published: December 2017

Insulin-like growth factor I (IGF-I) is thought to stimulate bone resorption indirectly through a primary effect on osteoblasts, which in turn activate osteoclasts by as-yet-unidentified mechanisms. Small decreases in extracellular pH (pHo) dramatically increase the resorptive activity of osteoclasts. Our purpose was to characterize the effect of IGF-I on acid production by osteoblastic cells. When confluent, UMR-106 osteoblast-like cells and rat calvarial cells acidified the compartment beneath them. Superfusion with IGF-I caused a further decrease in pHo. To investigate the mechanism, we monitored acid efflux from subconfluent cultures. IGF-I rapidly increased net efflux of H+ equivalents in a concentration-dependent manner. IGF-II (10 nM) evoked a smaller response than IGF-I (10 nM). The response to IGF-I was partially dependent on extracellular Na+, but not glucose, and exhibited little if any desensitization. Wortmannin, an inhibitor of phosphatidylinositol 3-kinase, abolished the response to IGF-I but not to parathyroid hormone. Thus IGF-I enhances acid efflux from osteoblastic cells, via a signaling pathway dependent on activation of phosphatidylinositol 3-kinase. In vivo, acidification of the compartment between the osteogenic cell layer and the bone matrix may affect diverse processes, including mineralization and osteoclastic bone resorption.
Availability of intestinal microbial lysine for whole body lysine homeostasis in human subjects
Authors: Metges Cornelia C. , El-Khoury Antoine E. , Henneman Lidewij , Petzke Klaus J. , Grant Ian , Bedri Shahinaze , Pereira Paulo P. , Ajami Alfred M. , Fuller Malcolm F. , Young Vernon R.
Published: December 2017

We have investigated whether there is a net contribution of lysine synthesized de novo by the gastrointestinal microflora to lysine homeostasis in six adults. On two separate occasions an adequate diet was given for a total of 11 days, and a 24-h (12-h fast, 12-h fed) tracer protocol was performed on the last day, in which lysine turnover, oxidation, and splanchnic uptake were measured on the basis of intravenous and oral administration ofl-[1-13C]lysine andl-[6,6-2H2]lysine, respectively. [15N2]urea or15NH4Cl was ingested daily over the last 6 days to label microbial protein. In addition, seven ileostomates were studied with15NH4Cl. [15N]lysine enrichment in fecal and ileal microbial protein, as precursor for microbial lysine absorption, and in plasma free lysine was measured by gas chromatography-combustion-isotope ratio mass spectrometry. Differences in plasma [13C]- and [2H2]lysine enrichments during the 12-h fed period were observed between the two15N tracer studies, although the reason is unclear, and possibly unrelated to the tracer form per se. In the normal adults, after15NH4Cl and [15N2]urea intake, respectively, lysine derived from fecal microbial protein accounted for 5 and 9% of the appearance rate of plasma lysine. With ileal microbial lysine enrichment, the contribution of microbial lysine to plasma lysine appearance was 44%. This amounts to a gross microbial lysine contribution to whole body plasma lysine turnover of between 11 and 130 mg ⋅ kg−1⋅ day−1, depending on the [15N]lysine precursor used. However, insofar as microbial amino acid synthesis is accompanied by microbial breakdown of endogenous amino acids or their oxidation by intestinal tissues, this may not reflect a net increase in lysine absorption. Thus we cannot reliably estimate the quantitative contribution of microbial lysine to host lysine homeostasis with the present paradigm. However, the results confirm the significant presence of lysine of microbial origin in the plasma free lysine pool.
Glycyrrhetinic acid-induced apoptosis in thymocytes: impact of 11β-hydroxysteroid dehydrogenase inhibition
Authors: Horigome Hiroshi , Horigome Atsushi , Homma Masato , Hirano Toshihiko , Oka Kitaro
Published: December 2017

It has been proposed that glycyrrhetinic acid (GA) enhances endogenous glucocorticoid (GC) action by suppressing the metabolism of the steroid. We show here that marked involution of the thymus occurred within 24 h of a single intraperitoneal administration of GA in mice. Thymocytes from mice treated with GA exhibited DNA cleavage and mitochondrial transmembrane potential disruption, as demonstrated with agarose gel electrophoresis and flow cytometric analysis. Immunocytochemical staining revealed that CD4+CD8+double positive cells markedly decreased after GA treatment. In contrast to GA in vivo, GA in vitro did not induce apoptosis of cultured thymocytes. These findings suggest that the apoptosis-inducing effect of GA on thymocytes is due to its indirect action. Because GA has been known to inhibit 11β-hydroxysteroid dehydrogenase (11β-HSD), we measured the enzyme activity in major organs and endogenous corticosterone concentration after GA treatment. The results showed a significant decrease of 11β-HSD activity ( P < 0.0001) and an increase in serum corticosterone concentration ( P< 0.005). We concluded that the inhibition of hepatic 11β-HSD activity by GA has a serious effect on GC metabolism, which results in a significant elevation of systemic GC levels. Apoptosis of thymocytes occurred as a consequence of the elevation in the level of endogenous corticosterone.
Sympathetic inhibition, leptin, and uncoupling protein subtype expression in normal fasting rats
Authors: Sivitz W. I. , Fink B. D. , Morgan D. A. , Fox J. M. , Donohoue P. A. , Haynes W. G.
Published: December 2017

To further investigate neural effects on leptin and uncoupling proteins (UCPs), we studied in vivo perturbations intended to block adrenergic input to peripheral tissues. We examined plasma leptin, leptin mRNA, and adipose and muscle UCP subtype mRNA in rats treated with α-methyl- p-tyrosine methyl ester (AMPT-ME), which inhibits catecholamine synthesis and 6-hydroxydopamine (6HDA), which is toxic to catecholinergic nerve terminals but, unlike AMPT-ME, does not enter the central nervous system. Intraperitoneal AMPT-ME, 250 mg/kg, was administered at 1800 and 0700 the following day, and rats were killed at 1200–1400. All rats were fasted with free access to water during this time. Intraperitoneal AMPT-ME increased plasma leptin by 15-fold, increased interscapular brown adipose tissue (IBAT) and epididymal fat leptin mRNA by 2- to 2.5-fold, and also increased plasma insulin and glucose concentrations. Intraperitoneal AMPT-ME decreased IBAT UCP-3 mRNA to 40% of control, while it increased epididymal adipose UCP-3 mRNA approximately twofold. Intravenous AMPT-ME, 250 mg/kg, administered to conscious rats for 5 h decreased lumbar sympathetic nerve activity, increased plasma leptin (5.89 ± 1.43 compared with 2.75 ± 0.31 ng/ml in vehicle-treated rats, n = 7, P < 0.05), and decreased cardiac rate with no sustained change in blood pressure. Intraperitoneal 6HDA, 100 mg/kg, as a single dose at 1800, increased plasma leptin approximately twofold after 18–20 h, increased IBAT (but not epididymal fat) leptin mRNA by two- to threefold, and decreased IBAT UCP-3 mRNA to 30–40% of control. Neither AMPT-ME nor 6HDA significantly altered mRNA encoding gastrocnemius muscle UCP-3, IBAT UCP-1, or IBAT and epididymal UCP-2. In summary, AMPT-ME and 6HDA increased plasma leptin and upregulated leptin mRNA expression. AMPT-ME also resulted in complex tissue and subtype-specific modulation of adipose UCP mRNA. These data are consistent with interaction between leptin and sympathetic nerve activity (SNA) in regulation of fat cell energy utilization. However, the in vivo modulation of leptin and UCPs appears complex and, beyond a causal effect of SNA per se, may depend on concurrent changes in plasma insulin, glucose, and circulatory hemodynamics.
A selective increase in circulating inhibin and inhibin pro-αC at the time of ovulation in the mare
Authors: Nagaoka Kentaro , Nambo Yasuo , Nagamine Natsuko , Nagata Shun-Ichi , Tanaka Yumiko , Shinbo Hiromi , Tsunoda Nobuo , Taniyama Hiroyuki , Watanabe Gen , Groome Nigel P. , Taya Kazuyoshi
Published: December 2017

The relationship between a selective increase in circulating immunoreactive (ir)-inhibin and the time of ovulation was investigated in mares. Concentrations of plasma ir-inhibin were measured every 4 h during the periovulatory period. Inhibin pro-αC, a precursor protein of the inhibin α-subunit, was also measured. The changes in ir-inhibin and inhibin pro-αC in circulation were parallel. Concentrations of both ir-inhibin and inhibin pro-αC in the plasma increased at the same time when ovulatory follicles ruptured, and the peak levels of circulating ir-inhibin and inhibin pro-αC were maintained for 4–8 h. There was no selective increase in plasma concentrations of estradiol-17β during the process of ovulation. These results suggest that the selective increase in ir-inhibin and inhibin pro-αC was caused by the absorption of follicular fluid after the rupture of ovulatory follicles. These results also suggest that the measuring of plasma concentrations of ir-inhibin or inhibin pro-αC in mares might be a useful method for detecting the time of ovulation.
Parathyroid hormone-parathyroid hormone-related peptide receptor expression and function in otosclerosis
Authors: Grayeli Alexis Bozorg , Sterkers Olivier , Roulleau Pierre , Elbaz Pierre , Ferrary Evelyne , Silve Caroline
Published: December 2017

The aim of this study was to investigate the possibility that an abnormality related to parathyroid hormone (PTH) action is involved in the increased bone turnover observed in otosclerosis. To do so, expression and function of the PTH-PTH-related peptide (PTHrP) receptor were studied in the involved tissue (stapes) and compared with that in control bone sample obtained from the external auditory canal (EAC) in the same patient in 10 cases of otosclerosis and in 1 case of osteogenesis imperfecta. PTH-PTHrP receptor expression was studied by RT-PCR of RNA prepared from cultured cells in three patients and RNA directly extracted from bone samples in four patients. PTH-PTHrP receptor function was assessed by measuring the stimulation of cAMP production by 0.8, 8, and 80 nM PTH in bone cell cultures in seven cases. Results showed that PTH-PTHrP receptor mRNA expression in the otosclerotic stapes was lower than that in EAC samples ( P < 0.05), whereas it was higher in stapes than that in EAC in the case of osteogenesis imperfecta. cAMP production after PTH stimulation was lower in bone cells cultured from otosclerotic stapes compared with that in cells cultured from EAC (range of increase in stimulation: 0.8–4.5 and 1.5–7 in stapes and EAC bone cells, respectively, P < 0.05). In contrast, the stimulation of cAMP production by forskolin was not significantly different in otosclerotic stapes and EAC bone cells (range of increase in stimulation: 20.7–83.1 and 4.9–99.8 in stapes and EAC, respectively, P > 0.05). These results show a lower stimulation of cAMP production in response to PTH associated with a lower PTH-PTHrP receptor mRNA expression in pathological stapes from patients with otosclerosis compared with that in control EAC samples. This difference supports the hypothesis that an abnormal cellular response to PTH contributes to the abnormal bone turnover in otosclerosis.
Pancreatic innervation is not essential for exercise-induced changes in glucagon and insulin or glucose kinetics
Authors: Coker Robert H. , Koyama Yoshiharu , Lacy D. Brooks , Williams Phillip E. , Rhèaume Nathalie , Wasserman David H.
Published: December 2017

The purpose of this study was to determine the role of pancreatic innervation in mediating exercise-induced changes in pancreatic hormone secretion and glucose kinetics. Dogs underwent surgery >16 days before an experiment, at which time flow probes were implanted on the portal vein and the hepatic artery, and Silastic catheters were inserted in the carotid artery, portal vein, and hepatic vein for sampling. In one group of dogs (DP) all nerves and plexuses to the pancreas were sectioned during surgery. A second group of dogs underwent sham denervation (SHAM). Pancreatic tissue norepinephrine was reduced by >98% in DP dogs. Each study consisted of basal (−30 to 0 min) and moderate exercise (0 to 150 min, 100 m/min, 12% grade) periods. Isotope ([3-3H]glucose) dilution and arteriovenous differences were used to assess hepatic function. Arterial and portal vein glucagon and insulin concentrations and the rate of net extrahepatic splanchnic glucagon release (NESGR) were similar in DP and SHAM during the basal period. Arterial and portal vein glucagon and NESGR increased similarly in DP and SHAM during exercise. Arterial and portal vein insulin were similar during exercise. Arterial glucose, tracer-determined endogenous glucose production, and net hepatic glucose output were similar in DP and SHAM during the basal and exercise periods. These results demonstrate that pancreatic nerves are not essential to pancreatic hormone secretion or glucose homeostasis during rest or moderate exercise.
Effects of parathyroid hormone-related protein on human mesangial cells in culture
Authors: Bosch Ricardo J. , Rojo-Linares Pilar , Torrecillas-Casamayor Guadalupe , Iglesias-Cruz M. Carmen , Rodríguez-Puyol Diego , Rodríguez-Puyol Manuel
Published: December 2017

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) produce similar biological effects through the PTH/PTHrP receptor. Because PTHrP exhibits vasodilatory properties, we evaluated the hypothesis that this hormone interacts with human mesangial cells (HMC). The PTHrP prevented both the expected reduction in the planar cell surface area and the increase in myosin light-chain phosphorylation induced by platelet-activating factor (PAF) on HMC, in a dose-dependent manner. This effect was completely blocked by pertussis toxin and dideoxyadenosine, suggesting that a G protein-coupled receptor and cAMP are important in the PTHrP transduction mechanism. Moreover, PTHrP increased cAMP synthesis and thymidine incorporation in HMC. However, whereas RT-PCR and Southern and Northern blot analyses demonstrated the expression of human PTH/PTHrP receptor in human kidney cortex, no expression could be demonstrated in HMC. These results show that PTH and PTHrP directly interact with mesangial cells. These effects might be mediated by a receptor different from the PTH/PTHrP receptor.
Bioavailability of starch and postprandial changes in splanchnic glucose metabolism in pigs
Authors: Noah Lionel , Krempf Michel , Lecannu Gérard , Maugère Pascale , Champ Martine
Published: December 2017

Changes in splanchnic metabolism in pigs were assessed after meals containing slowly or rapidly digested starch. The pigs were fed a mixed meal containing a “slow” native ( n = 5) or a “rapid” pregelatinized ( n = 5) cornstarch naturally enriched with [13C]glucose. Absorption of [13C]glucose was monitored by the arteriovenous difference technique, and infusion ofd-[6,6-2H2]glucose in the jugular vein was used to calculate the systemic appearance of [13C]glucose. Arteriovenous balance data obtained during a 12-h study period showed that the fraction of ingested glucose equivalent appearing as glucose in the portal vein was 49.7 ± 7.2% for the slow starch and 48.2 ± 7.5% for the rapid starch ( P = 0.86). These values, corrected for the gut extraction of circulating [13C]glucose, became 66.4 ± 5.6 and 65.3 ± 5.6%, respectively ( P = 0.35). Isotope dilution data indicated that systemic appearance of exogenous [13C]glucose represented 62.9 ± 7.6 and 67.4 ± 3.0% of the oral load for slow and rapid starch, respectively ( P = 0.68). Arterial glucose utilization by the gut increased from 7.3 ± 0.9 μmol ⋅ kg− 1 ⋅ min− 1before the meal to 8.5 ± 1.6 μmol ⋅ kg− 1 ⋅ min− 1during absorption, independently of the nature of the starch. Thus splanchnic glucose metabolism was unaffected by the nature of starch ingested.
Tyrosine requirements in children with classical PKU determined by indicator amino acid oxidation
Authors: Bross Rachelle , Ball Ronald O. , Clarke Joe T. R. , Pencharz Paul B.
Published: December 2017

Tyrosine (Tyr) is an essential amino acid in phenylketonuria (PKU) because of the limited hydroxylation of phenylalanine (Phe) to Tyr. The recommended intakes for Tyr in PKU are at least five times the recommended phenylalanine intakes. This suggests that Phe and Tyr contribute ∼20 and 80%, respectively, of the aromatic amino acid (AAA) requirement (REQ). In animals and normal humans, dietary Tyr was shown to spare 40–50% of the Phe requirement, proportions that reflect dietary and tissue protein composition. We tested the hypothesis that the Tyr REQ in PKU would account for 45% of the total AAA REQ by indicator amino acid oxidation (IAAO). Tyr REQ was determined in five children with PKU by examining the effect of varying dietary Tyr intake on lysine oxidation and the appearance of13CO2in breath (F13CO2) under dietary conditions of adequate energy, protein (1.5 g ⋅ kg−1⋅ day−1), and phenylalanine (25 mg ⋅ kg−1⋅ day−1). Lysine oxidation and F13CO2were determined using a primed 4-h oral equal-dose infusion ofl-[1-13C]lysine. Lysine oxidation and F13CO2decreased linearly as Tyr intake increased, to a break point that was interpreted as the mean dietary Tyr requirement (16.3 and 19.2 mg ⋅ kg−1⋅ day−1, respectively). At Tyr intakes of >16.3 and 19.2 mg ⋅ kg−1⋅ day−1, lysine oxidation and F13CO2, respectively, were low and constant. This represents 40.4 and 44.4%, respectively, of the total AAA intake. The current recommendations for Tyr intake in PKU patients appear to be overestimated by a factor of ∼5. This study is the first application of the IAAO technique in a pediatric population and in humans with an inborn error of metabolism.
17β-Estradiol and ICI-182780 regulate the hair follicle cycle in mice through an estrogen receptor-α pathway
Authors: Chanda Sanjay , Robinette C. Lee , Couse John F. , Smart Robert C.
Published: December 2017

Estradiol (E2) applied topically twice weekly to mouse skin at doses as low as 1 nmol inhibited hair growth by blocking the transition of the hair follicle from the resting phase (telogen) to the growth phase (anagen). In contrast, application of ≤10 nmol of other steroids produced limited inhibition. Topical treatment with the estrogen receptor (ER) antagonist ICI-182780 reversed the effects of E2, and when applied alone, ICI-182780 caused a telogen-to-anagen transition. Both E2and ICI-182780 were highly effective at their site of application but not at distant sites, indicating the direct rather than secondary systemic nature of their effects. Western analysis detected a 65-kDa ER-α immunoreactive dermal protein, and Northern analysis revealed the presence of a 6.7-kb ER-α mRNA. A ribonuclease protection assay confirmed the presence of ER-α transcripts but failed to detect ER-β transcripts. These findings implicate a skin-specific ER-α pathway in the regulation of the hair follicle cycle.
Endurance training increases gluconeogenesis during rest and exercise in men
Authors: Bergman Bryan C. , Horning Michael A. , Casazza Gretchen A. , Wolfel Eugene E. , Butterfield Gail E. , Brooks George A.
Published: December 2017

The hypothesis that endurance training increases gluconeogenesis (GNG) during rest and exercise was evaluated. We determined glucose turnover with [6,6-2H]glucose and lactate incorporation into glucose by use of [3-13C]lactate during 1 h of cycle ergometry at two intensities [45 and 65% peak O2consumption (V˙o2 peak)] before and after training [65% pretrainingV˙o2 peak], same absolute workload (ABT), and 65% posttrainingV˙o2 peak, same relative intensity (RLT). Nine males (178.1 ± 2.5 cm, 81.8 ± 3.3 kg, 27.4 ± 2.0 yr) trained for 9 wk on a cycle ergometer 5 times/wk for 1 h at 75%V˙o2 peak. The power output that elicited 66.0 ± 1.1% ofV˙o2 peakpretraining elicited 54.0 ± 1.7% posttraining. Rest and exercise arterial glucose concentrations were similar before and after training, regardless of exercise intensity. Arterial lactate concentration during exercise was significantly greater than at rest before and after training. Compared with 65% pretraining, arterial lactate concentration decreased at ABT (4.75 ± 0.4 mM, 65% pretraining; 2.78 ± 0.3 mM, ABT) and RLT (3.76 ± 0.46 mM) ( P < 0.05). At rest after training, the percentage of glucose rate of appearance (Ra) from GNG more than doubled (1.98 ± 0.5% pretraining; 5.45 ± 1.3% posttraining), as did the rate of GNG (0.11 ± 0.03 mg ⋅ kg−1⋅ min−1pretraining, 0.24 ± 0.06 mg ⋅ kg−1⋅ min−1posttraining). During exercise after training, %glucose Rafrom GNG increased significantly at ABT (2.3 ± 0.8% at 65% pre- vs. 7.6 ± 2.1% posttraining) and RLT (6.1 ± 1.5%), whereas GNG increased almost threefold ( P < 0.05) at ABT (0.24 ± 0.08 mg ⋅ kg−1⋅ min−165% pre-, and 0.71 ± 0.18 mg ⋅ kg−1⋅ min−1posttraining) and RLT (0.75 ± 0.26 mg ⋅ kg−1⋅ min−1). We conclude that endurance training increases gluconeogenesis twofold at rest and threefold during exercise at given absolute and relative exercise intensities.
Leptin production during early starvation in lean and obese women
Authors: Klein Samuel , Horowitz Jeffrey F. , Landt Michael , Goodrick Stephen J. , Mohamed-Ali Vidya , Coppack Simon W.
Published: December 2017

We evaluated abdominal adipose tissue leptin production during short-term fasting in nine lean [body mass index (BMI) 21 ± 1 kg/m2] and nine upper body obese (BMI 36 ± 1 kg/m2) women. Leptin kinetics were determined by arteriovenous balance across abdominal subcutaneous adipose tissue at 14 and 22 h of fasting. At 14 h of fasting, net leptin release from abdominal adipose tissue in obese subjects (10.9 ± 1.9 ng ⋅ 100 g tissue ⋅ − 1 ⋅ min− 1) was not significantly greater than the values observed in the lean group (7.6 ± 2.1 ng ⋅ 100 g− 1 ⋅ min− 1). Estimated whole body leptin production was approximately fivefold greater in obese (6.97 ± 1.18 μg/min) than lean subjects (1.25 ± 0.28 μg/min) ( P < 0.005). At 22 h of fasting, leptin production rates decreased in both lean and obese groups (to 3.10 ± 1.31 and 10.5 ± 2.3 ng ⋅ 100 g adipose tissue− 1 ⋅ min− 1, respectively). However, the relative declines in both arterial leptin concentration and local leptin production in obese women (arterial concentration 13.8 ± 4.4%, local production 10.0 ± 12.3%) were less ( P < 0.05 for both) than the relative decline in lean women (arterial concentration 39.0 ± 5.5%, local production 56.9 ± 13.0%). This study demonstrates that decreased leptin production accounts for the decline in plasma leptin concentration observed after fasting. However, compared with lean women, the fasting-induced decline in leptin production is blunted in women with upper body obesity. Differences in leptin production during fasting may be responsible for differences in the neuroendocrine response to fasting previously observed in lean and obese women.