bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of exercise intensity and training on lipid metabolism in young women
Authors: Friedlander Anne L. , Casazza Gretchen A. , Horning Michael A. , Buddinger Thomas F. , Brooks George A.
Published: December 2017

We examined the effects of exercise intensity and training [12 wk, 5 days/wk, 1 h, 75% peak oxygen consumption (V˙o 2 peak)] on lipolysis and plasma free fatty acid (FFA) flux in women ( n = 8; 24.3 ± 1.6 yr). Two pretraining trials (45 and 65% ofV˙o 2 peak) and two posttraining trials [same absolute workload (65% of oldV˙o 2 peak; ABT) and same relative workload (65% of newV˙o 2 peak; RLT)] were performed using infusions of [1,1,2,3,3-2H]glycerol and [1-13C]palmitate. Pretraining rates of FFA appearance (Ra), disappearance (Rd), and oxidation (Rox p) were similar between the 65% (6.8 ± 0.6, 6.2 ± 0.7, 3.1 ± 0.3 μmol ⋅ kg−1 ⋅ min−1, respectively) and the 45% ofV˙o 2 peaktrials. At ABT and RLT training increased FFA Ra to 8.4 ± 1.0 and 9.7 ± 1.1 μmol ⋅ kg−1 ⋅ min−1, Rd to 8.3 ± 1.0 and 9.5 ± 1.1 μmol ⋅ kg−1 ⋅ min−1, and Rox p to 4.8 ± 0.4 and 6.7 ± 0.7 μmol ⋅ kg−1 ⋅ min−1, respectively ( P ≤ 0.05). Total FFA oxidation from respiratory exchange ratio was also elevated after training at ABT and RLT, with all of the increase attributed to plasma FFA sources. Pretraining, glycerol Ra was higher during exercise at 65 than 45% of V˙o 2 peak(6.9 ± 0.9 vs. 4.7 ± 0.6 μmol ⋅ kg−1 ⋅ min−1) but was not changed by training. In young women 1) plasma FFA kinetics and oxidation are not linearly related to exercise intensity before training, 2) training increases FFA Ra, Rd, and Rox p whether measured at given absolute or relative exercise intensities, 3) whole body lipolysis (glycerol Ra) during exercise is not significantly impacted by training, and 4) training-induced increases in plasma FFA oxidation are the main contributor to elevated total FFA oxidation during exercise exertion after training.
Genesis of the ultradian rhythm of GH secretion: a new model unifying experimental observations in rats
Authors: Wagner Clemens , Caplan S. Roy , Tannenbaum Gloria S.
Published: December 2017

Growth hormone (GH) induces growth in animals and humans and also has important metabolic functions. The GH neuroendocrine axis consists of a signaling cascade from the hypothalamus to the pituitary, the liver, and peripheral tissues, including two major feedback mechanisms. GH is secreted from the pituitary into the circulating blood according to the effect on the somatotrophs of two hypothalamic peptides, GH-releasing hormone (GHRH) and its antagonist, somatostatin (SRIF). The typical GH profile in the male rat shows secretory episodes every 3.3 h, which are subdivided into two peaks. Focusing on the mechanisms for generation of this ultradian GH rhythm, we simulated the time course of GH secretion under a variety of conditions. The model that we propose is based on feedback of GH on its own release mediated both by GH receptors on SRIF neurons in the brain and by a delayed SRIF release into both the brain and portal blood. SRIF, with a resultant periodicity of 3.3 h, affects both the somatotroph cells in the pituitary and the GHRH neurons in the hypothalamus. The secretion of GHRH is postulated to occur in an ∼1-h rhythm modulated by the level of SRIF in the hypothalamus. The model predicts a possible mechanism for the feminization of the male GH rhythm by sex steroids and vice versa, and suggests experiments that might reveal the proposed intrinsic 1-h GHRH rhythm.
Adrenal-dependent modulation of the catalytic subunit isoforms of the Na+-K+-ATPase in aorta
Authors: Michea Luis , Valenzuela Viviana , Bravo Ignacio , Schuster Andrés , Marusic Elisa T.
Published: December 2017

Na+-K+-ATPase gene expression and activity were studied in aortas from adrenalectomized (ADX) rats and ADX rats with deoxycorticosterone supplement (ADX-DOCA). Northern analysis of RNA from ADX rats revealed a significant decrease in α2-mRNA levels (38.5 ± 8.3% of control, P < 0.01) that was prevented by DOCA ( P < 0.05). A decrease to 55.8 ± 7.7% in α2-isoform protein was observed 8 days after adrenal removal ( P < 0.05); DOCA reversed this effect (90.8 ± 10.5%). Adrenalectomy induced a decrease of 68.5 ± 4.5% in β1-mRNA ( P < 0.01) and 52.7 ± 8.3% in ADX-DOCA rats ( P < 0.01). Also, a reduction in β1-isoform protein that was not prevented by DOCA was detected after adrenalectomy (47.1 ± 11%, P < 0.01). In contrast, no differences in α1-mRNA or -protein levels were observed. Vascular sodium pump activity was reduced to 59.8 ± 4.6% of control values after adrenalectomy ( P < 0.01); this reduction was reversed by DOCA. Our data indicate that corticosteroids regulate Na+-K+-ATPase isoform expression and activity in vascular tissue in vivo, suggesting a mineralocorticoid-dependent modulation of α2-Na+-K+-ATPase gene expression in aorta, with β1-isoform expression dependent on the presence of glucocorticoids.
Glucose-stimulated insulin secretion is not obligatorily linked to an increase in O2consumption in βHC9 cells
Authors: Papas Klearchos K. , Jarema Mary Ann C.
Published: December 2017

We investigated the effects of glucose on the rates of oxygen consumption (OCR) and insulin secretion (ISR) by βHC9 cells derived from mouse pancreatic islets with β-cell hyperplasia. Our results demonstrate that the OCR by βHC9 cells incubated in nutrient-rich DMEM is unaffected by glucose (0–25 mM), is dissociated from the ISR (which increases with the addition of glucose), and is always higher than that measured in PBS. Glucose (25 mM) increases both the OCR and ISR when added to nutrient-free PBS. On the basis of results presented here, we suggest that, contrary to the current consensus, the observed increases in the OCR by β-cells upon addition of glucose to nutrient-free buffers may be unrelated to the process of glucose-stimulated insulin secretion (GSIS) and, instead, related to nutrient starvation. We believe that a reevaluation of the implication of changes in OCR upon glucose stimulation in the process of GSIS is warranted and that OCR and ISR measurements should be performed in more physiological media to avoid nutrient starvation artifacts.
Glucose-induced desensitization of the pancreatic β-cell is species dependent
Authors: Zawalich Walter S. , Bonnet-Eymard Marc , Zawalich Kathleen C.
Published: December 2017

The capacity of 20 mM glucose to desensitize insulin release was determined. A prior exposure to 20 mM glucose impaired the response of rat islets to subsequent restimulation. Compared with control islets, insulin secretory rates measured 25–30 min after the onset of 20 mM glucose stimulation were reduced by 75%. Restimulation of glucose-desensitized islets with 20 mM glucose plus 500 nM forskolin resulted in a dramatic enhancement of both phases of secretion. In contrast to the desensitization of rat islets induced by prior 20 mM glucose exposure, mouse islets were immune to this adverse effect of the hexose. Prior exposure to 20 mM glucose had no adverse effect on glucose usage rates. The activation of phospholipase C in glucose-desensitized rat islets was compromised when compared with control islets. The impairment could not be accounted for by a decrease in immunoreactive content of several major phospholipase C isozymes (β1 or δ1) or their partitioning between the membrane and cytosolic compartments. In contrast to rat islets, prior exposure of mouse islets to 20 mM glucose for 180 min had no effect on inositol phosphate accumulation. These observations document an additional difference between rat and mouse islets and suggest that the evolution of desensitization is a consequence of the impaired activation of phospholipase C in rat islets.
Endothelium removal induces iNOS in rat aorta in organ culture, leading to tissue damage
Authors: Binko J. , Meachem S. , Majewski H.
Published: December 2017

After endothelial damage in vivo, there is an induction of nitric oxide synthase (NOS) in the underlying smooth muscle cells. We hypothesized that intrinsic factors could induce NOS independently of blood elements. This was tested using an in vitro organ culture technique. Rat aortas with endothelium removed before 24-h organ culture (ERB) failed to constrict to phenylephrine after culture, whereas with endothelium removal after culture there was a normal constrictor response. Constrictor activity in ERB aortas was restored by the concomitant treatment with either the protein synthesis inhibitor cycloheximide (1 μM) or the NOS inhibitorl- N 5-(1-iminoethyl)ornithine hydrochloride (l-NIO, 100 μM). The ERB aortas also had an elevated NOS activity and induced NOS (iNOS) immunoreactivity. The constrictor response to phenylephrine in ERB aortas was only partially restored by acute application ofl-NIO subsequent to the 24-h organ culture, which suggests that other effects during culture contributed to the diminished tissue response. When ERB aortas were treated with reduced glutathione (GSH, 3 mM for 24 h), acute application of l-NIO then fully restored the constrictor effect. This suggests that peroxynitrite produced during culture may in part be responsible for loss of constrictor effects, and this was substantiated by the presence of nitrated tyrosine residues in aortic proteins and also widespread DNA damage, which was prevented by bothl-NIO and GSH. Thus some of the immediate (24-h) effects of endothelium removal involve intrinsic mechanisms resulting in iNOS synthesis, which leads to both nitric oxide and peroxynitrite generation, with resultant tissue damage and loss of contractile function.
Signal transduction pathways involved in fluid flow-induced PGE2production by cultured osteocytes
Authors: Ajubi N. E. , Klein-Nulend J. , Alblas M. J. , Burger E. H. , Nijweide P. J.
Published: December 2017

To maintain its structural competence, the skeleton adapts to changes in its mechanical environment. Osteocytes are generally considered the bone mechanosensory cells that translate mechanical signals into biochemical, bone metabolism-regulating stimuli necessary for the adaptive process. Prostaglandins are an important part of this mechanobiochemical signaling. We investigated the signal transduction pathways in osteocytes through which mechanical stress generates an acute release of prostaglandin E2(PGE2). Isolated chicken osteocytes were subjected to 10 min of pulsating fluid flow (PFF; 0.7 ± 0.03 Pa at 5 Hz), and PGE2release was measured. Blockers of Ca2+entry into the cell or Ca2+release from internal stores markedly inhibited the PFF-induced PGE2release, as did disruption of the actin cytoskeleton by cytochalasin B. Specific inhibitors of Ca2+-activated phospholipase C, protein kinase C, and phospholipase A2also decreased PFF-induced PGE2release. These results are consistent with the hypothesis that PFF raises intracellular Ca2+by an enhanced entry through mechanosensitive ion channels in combination with Ca2+- and inositol trisphosphate (the product of phospholipase C)-induced Ca2+release from intracellular stores. Ca2+and protein kinase C then stimulate phospholipase A2activity, arachidonic acid production, and ultimately PGE2release.
The anabolic effect of PGE2in rat bone marrow cultures is mediated via the EP4receptor subtype
Authors: Weinreb M. , Grosskopf A. , Shir N.
Published: December 2017

Prostaglandin E2(PGE2) is an anabolic agent in vivo that stimulates bone formation by recruiting osteoblasts from bone marrow precursors. To understand which of the known PGE2receptors (EP1–4) is involved in this process, we tested the effect of PGE2and various EP agonists and/or antagonists on osteoblastic differentiation in cultures of bone marrow cells by counting bone nodules and measuring alkaline phosphatase activity. PGE2increased both parameters, peaking at 100 nM, an effect that was mimicked by forskolin and was abolished by 2′,3′-dideoxyadenosine (an adenylate cyclase inhibitor) and was thus cAMP dependent, pointing to the involvement of EP2or EP4. Consistently, 17-phenyl-ω-trinor PGE2(EP1agonist) and sulprostone (EP3/EP1agonist) lacked any anabolic activity. Furthermore, butaprost (EP2agonist) was inactive, 11-deoxy-PGE1(EP4/EP2agonist) was as effective as PGE2, and the PGE2effect was abolished dose dependently by the selective EP4antagonist AH-23848B, suggesting the involvement of EP4. We also found that PGE2increased nodule formation and AP activity when added for the initial attachment period of 24 h only. Thus this study shows that PGE2stimulates osteoblastic differentiation in bone marrow cultures, probably by activating the EP4receptor, and that this effect may involve recruitment of noncommitted (nonadherent) osteogenic precursors, in agreement with its suggested mode of operation in vivo.
Pre-β-HDL stimulates placental lactogen release from human trophoblast cells
Authors: Handwerger Stuart , Datta Geeta , Richardson Brian , Schmidt Carrie M. , Siddiqi Tariq , Turzai Lisa , Anantharamaiah G. M.
Published: December 2017

To examine whether pre-β-high-density lipoprotein (HDL) may be involved in regulation of human placental lactogen (hPL) release, pre-β-HDL was isolated from term pregnancy serum, and the effect of purified pre-β-HDL on hPL release from trophoblast cells was examined after 1 h of exposure. Pre-β-HDL stimulated a dose-dependent increase in hPL release with half-maximal stimulation at a dose of 300–400 μg/ml, which is within the normal physiological range during pregnancy. Analysis of pre-β-HDL and α-HDL in serum from pregnant women at different stages of gestation (determined by Western blot analysis) indicated that the pre-β-HDL-to-α-HDL ratio increased linearly after the 10th week of gestation ( r = 0.88, P < 0.001), reaching a maximum sixfold greater than that of nonpregnant women. The increase in serum pre-β-HDL during pregnancy paralleled that of plasma hPL concentrations ( r = 0.93, P < 0.001). Two-dimensional electrophoresis indicated that the increase in pre-β-HDL was due primarily to an increase in pre-β1-HDL and pre-β2-HDL, two of the three forms of pre-β-HDL present in blood. These results suggest a role for pre-β-HDL in the regulation of hPL expression during pregnancy.
Isolation and characterization of plasmin-generated bioactive fragments of IGFBP-3
Authors: Booth Barbara A. , Boes Mary , Dake Brian L. , Bar Robert S.
Published: December 2017

Insulin-like growth factor-binding protein-3 (IGFBP-3) was digested with plasmin, and the proteolytic fragments were isolated by HPLC and tested for bioactivity as measured by stimulation of glucose uptake in microvessel endothelial cells. Two of the pooled fractions of the digest stimulated glucose uptake. The major bioactive pool, at an estimated protein concentration <50 ng/ml, stimulated glucose uptake to 150% of control with greater stimulation and 220% of control at ∼250 ng/ml. Two fragments were present in the bioactive fraction, the dominant one migrating at ∼20,000 and the other at ∼8,000. Both fragments bound125I-labeled insulin-like growth factor and [3H]heparin. NH2-terminal amino acid analysis of the bioactive peak yielded two sequences. One, representing the majority of the material, had an NH2-terminal sequence identical to IGFBP-3; the second fragment began at amino acid 202 of IGFBP-3. In contrast to the bioactive fragments, intact IGFBP-3, at concentrations up to 130 μg/ml, had no bioactivity. These findings demonstrate that IGFBP-3 can be degraded into fragments that have potent bioactivities that are not present in the intact IGFBP-3 molecule.
Contributions of net hepatic glycogenolysis and gluconeogenesis to glucose production in cirrhosis
Authors: Petersen Kitt Falk , Krssak Martin , Navarro Victor , Chandramouli Visvanathan , Hundal Ripudaman , Schumann William C. , Landau Bernard R. , Shulman Gerald I.
Published: December 2017

Net hepatic glycogenolysis and gluconeogenesis were examined in normal ( n = 4) and cirrhotic ( n = 8) subjects using two independent methods [13C nuclear magnetic resonance spectroscopy (NMR) and a2H2O method]. Rates of net hepatic glycogenolysis were calculated by the change in hepatic glycogen content before (∼11:00 PM) and after (∼7:00 AM) an overnight fast using13C NMR and magnetic resonance imaging. Gluconeogenesis was calculated as the difference between the rates of glucose production determined with an infusion of [6,6-2H2]glucose and net hepatic glycogenolysis. In addition, the contribution of gluconeogenesis to glucose production was determined by the2H enrichment in C-5/C-2 of blood glucose after intake of2H2O (5 ml/kg body water). Plasma levels of total and free insulin-like growth factor I (IGF-I) and IGF-I binding proteins-1 and -3 were significantly decreased in the cirrhotic subjects ( P < 0.01 vs. controls). Postprandial hepatic glycogen concentrations were 34% lower in the cirrhotic subjects ( P = 0.007). Rates of glucose production were similar between the cirrhotic and healthy subjects [9.0 ± 0.9 and 10.0 ± 0.8 μmol ⋅ kg body wt−1⋅ min−1, respectively]. Net hepatic glycogenolysis was 3.5-fold lower in the cirrhotic subjects ( P = 0.01) and accounted for only 13 ± 6% of glucose production compared with 40 ± 10% ( P = 0.03) in the control subjects. Gluconeogenesis was markedly increased in the cirrhotic subjects and accounted for 87 ± 6% of glucose production vs. controls: 60 ± 10% ( P = 0.03). Gluconeogenesis in the cirrhotic subjects, as determined from the2H enrichment in glucose C-5/C-2, was also increased and accounted for 68 ± 3% of glucose production compared with 54 ± 2% ( P = 0.02) in the control subjects. In conclusion, cirrhotic subjects have increased rates of gluconeogenesis and decreased rates of net hepatic glycogenolysis compared with control subjects. These alterations are likely important contributing factors to their altered carbohydrate metabolism.
Kinetic impairment of nitrogen and muscle glutamine metabolisms in old glucocorticoid-treated rats
Authors: Minet-Quinard Regine , Moinard Christophe , Villie Françoise , Walrand Stephane , Vasson Marie-Paule , Chopineau Jean , Cynober Luc
Published: December 2017

Aged rats are more sensitive to injury, possibly through an impairment of nitrogen and glutamine (Gln) metabolisms mediated by glucocorticoids. We studied the metabolic kinetic response of adult and old rats during glucocorticoid treatment. The male Sprague-Dawley rats were 24 or 3 mo old. Both adult and old rats were divided into 7 groups. Groups labeled G3, G5, and G7 received, by intraperitoneal injection, 1.50 mg/kg of dexamethasone (Dex) for 3, 5, and 7 days, respectively. Groups labeled G3PF, G5PF, and G7PF were pair fed to the G3, G5, or G7 groups and were injected with an isovolumic solution of NaCl. One control group comprised healthy rats fed ad libitum. The response to aggression induced specifically by Dex (i.e., allowing for variations in pair-fed controls) appeared later in the aged rats (decrease in nitrogen balance from day 1 in adults but only from day 4 in old rats). The adult rats rapidly adapted to Dex treatment, whereas the catabolic state worsened until the end of treatment in the old rats. Gln homeostasis was not maintained in the aged rats; despite an early increase in muscular Gln synthetase activity, the Gln pool was depleted. These results suggest a kinetic impairment of both nitrogen and muscle Gln metabolisms in response to Dex with aging.
GH insensitivity induced by endotoxin injection is associated with decreased liver GH receptors
Authors: Defalque Dominique , Brandt Nathalie , Ketelslegers Jean-Marie , Thissen Jean-Paul
Published: December 2017

Sepsis induces a state of growth hormone (GH) resistance associated with a decrease of circulating insulin-like growth factor (IGF) I, a GH-dependent anabolic hormone mainly produced by the liver. To address the mechanisms that might trigger GH insensitivity in sepsis, we investigated the regulation of liver GH receptor (GHR) and its gene expression by endotoxin. Endotoxin injection in rats decreased serum IGF-I and liver GH-binding sites after 10 h. In contrast to liver GHR, circulating GH-binding protein (GHBP) levels were not significantly reduced after endotoxin injection. The parallel decrease in IGF-I and GHR and in their corresponding liver mRNAs suggests that decreased serum IGF-I and liver GHR were likely to result from decreased liver synthesis. Although GH administration in control animals significantly enhanced serum IGF-I, it did fail to prevent the decline in serum IGF-I and liver GH-binding sites in endotoxemic rats. In this study, we showed that endotoxin injection induces a state of GH insensitivity associated with decreased liver GHR. This decline in GHR, which cannot be prevented by exogenous GH, might contribute to the GH insensitivity observed in sepsis.
Effects of arginine vasopressin on cell volume regulation in brain astrocyte in culture
Authors: Sarfaraz Darya , Fraser Cosmo L.
Published: December 2017

Astrocytes initially swell when exposed to hypotonic medium but rapidly return to normal volume by the process of regulatory volume decrease (RVD). The role that arginine vasopressin (AVP) plays in hypotonically mediated RVD in astrocytes is unknown. This study was therefore designed to determine whether AVP might play a role in astrocyte RVD. With the use of 3- O-[3H]methyl-d-glucose to determine water space, AVP treatment resulted in significantly increased 3- O-methyl-d-glucose water space within 30 s of hypotonic exposure ( P = 0.0001) and remained significantly elevated above baseline (1.75 μl/mg protein) at 5 min ( P < 0.021). In contrast, in untreated cells, complete RVD was achieved by 5 min. At 30 s, cell volume with AVP treatment was 37% greater than in cells that received no treatment (2.9 vs. 2.26 μl/mg protein, respectively; P < 0.006). The rate of cell volume increase (dV/d t) over 30 s was highly significant (0.038 vs. 0.019 μl ⋅ mg protein−1⋅ s−1in the AVP-treated vs. untreated group; P = 0.0004 by regression analysis). Additionally, the rate of cell volume decrease over the next 4.5 min was also significantly greater with vasopressin treatment (−dV/d t = 0.0027 vs. 0.0013 μl ⋅ mg protein−1⋅ s−1; P = 0.0306). The effect of AVP was concentration dependent with EC50= 3.5 nM. To determine whether AVP action was receptor mediated, we performed RVD studies in the presence of the V1-receptor antagonists benzamil and ethylisopropryl amiloride and the V2-receptor agonist 1-desamino-8-d-arginine vasopressin (DDAVP). Both V1-receptor antagonists significantly inhibited AVP-mediated volume increase by 40–47% ( P < 0.005), whereas DDAVP had no stimulatory effects above control. Taken together, these data suggest that AVP treatment of brain astrocytes in culture appears to increase 3- O-methyl-d-glucose water space during RVD through V1receptor-mediated mechanisms. The significance of these findings is presently unclear.
Expression of 25(OH)D324-hydroxylase in distal nephron: coordinate regulation by 1,25(OH)2D3and cAMP or PTH
Authors: Yang Wen , Friedman Peter A. , Kumar Rajiv , Omdahl John L. , May Brian K. , Siu-Caldera Mei-Ling , Reddy G. Satyanarayana , Christakos Sylvia
Published: December 2017

Previous studies using microdissected nephron segments reported that the exclusive site of renal 25-hydroxyvitamin D3-24-hydroxylase (24OHase) activity is the renal proximal convoluted tubule (PCT). We now report the presence of 24OHase mRNA, protein, and activity in cells that are devoid of markers of proximal tubules but express characteristics highly specific for the distal tubule. 24OHase mRNA was undetectable in vehicle-treated mouse distal convoluted tubule (DCT) cells but was markedly induced when DCT cells were treated with 1,25 dihydroxyvitamin D3[1,25(OH)2D3]. 24OHase protein and activity were also identified in DCT cells by Western blot analysis and HPLC, respectively. 8-Bromo-cAMP (1 mM) or parathyroid hormone [PTH-(1—34); 10 nM] was found to potentiate the effect of 1,25(OH)2D3on 24OHase mRNA. The stimulatory effect of cAMP or PTH on 24OHase expression in DCT cells suggests differential regulation of 24OHase expression in the PCT and DCT. In the presence of cAMP and 1,25(OH)2D3, a four- to sixfold induction in vitamin D receptor (VDR) mRNA was observed. VDR protein, as determined by Western blot analysis, was also enhanced in the presence of cAMP. Transient transfection analysis in DCT cells with rat 24OHase promoter deletion constructs demonstrated that cAMP enhanced 1,25(OH)2D3-induced 24OHase transcription but this enhancement was not mediated by cAMP response elements (CREs) in the 24OHase promoter. We conclude that 1) although the PCT is the major site of localization of 24OHase, 24OHase mRNA and activity can also be localized in the distal nephron; 2) both PTH and cAMP modulate the induction of 24OHase expression by 1,25(OH)2D3in DCT cells in a manner different from that reported in the PCT; and 3) in DCT cells, upregulation of VDR levels by cAMP, and not an effect on CREs in the 24OHase promoter, is one mechanism involved in the cAMP-mediated modulation of 24OHase transcription.
Prior streptozotocin treatment does not inhibit pancreas regeneration after 90% pancreatectomy in rats
Authors: Finegood Diane T. , Weir Gordon C. , Bonner-Weir Susan
Published: December 2017

The effects of residual β-cell mass and glycemia on regeneration of endocrine pancreas after 90% pancreatectomy were investigated. Streptozotocin or buffer alone was injected into 4-wk-old male Lewis rats ( day 0). On day 7, varying numbers of syngeneic islets were transplanted under the kidney capsule to achieve varying degrees of glucose normalization. On day 14, a 90% pancreatectomy or sham pancreatectomy was performed. On day 19, rats were killed and the pancreas was fixed for quantitative morphometric determination of β-cell mass. Focal areas of regenerating pancreas were observed in all animals that underwent partial pancreatectomy. The percentage of remnant pancreas classified as foci was unaffected by streptozotocin treatment or by plasma glucose. Moderate to severe hyperglycemia did not promote regeneration of the pancreatic β-cell mass; rather the total endocrine cell mass was inversely related to the plasma glucose level ( r = −0.5, P < 0.01). These data suggest that the precursor population for both endocrine and exocrine tissue is not susceptible to damage by streptozotocin and that local effects of residual β-cell mass are not important to regeneration after a 90% pancreatectomy.
Decreased insulin-stimulated GLUT-4 translocation in glycogen-supercompensated muscles of exercised rats
Authors: Kawanaka Kentaro , Han Dong-Ho , Nolte Lorraine A. , Hansen Polly A. , Nakatani Akira , Holloszy John O.
Published: December 2017

It was recently found that the effect of an exercise-induced increase in muscle GLUT-4 on insulin-stimulated glucose transport is masked by a decreased responsiveness to insulin in glycogen-supercompensated muscle. We evaluated the role of hexosamines in this decrease in insulin responsiveness and found that UDP- N-acetyl hexosamine concentrations were not higher in glycogen-supercompensated muscles than in control muscles with a low glycogen content. We determined whether the smaller increase in glucose transport is due to translocation of fewer GLUT-4 to the cell surface with the 2- N-4-(1-azi-2,2,2-trifluroethyl)-benzoyl-1,3-bis(d-mannose-4-yloxy)-2-propylamine (ATB-[2-3H]BMPA) photolabeling technique. The insulin-induced increase in GLUT-4 at the cell surface was no greater in glycogen-supercompensated exercised muscle than in muscles of sedentary controls and only 50% as great as in exercised muscles with a low glycogen content. We conclude that the decreased insulin responsiveness of glucose transport in glycogen-supercompensated muscle is not due to increased accumulation of hexosamine biosynthetic pathway end products and that the smaller increase in glucose transport is mediated by translocation of fewer GLUT-4 to the cell surface.
Undermodeling affects minimal model indexes: insights from a two-compartment model
Authors: Caumo Andrea , Vicini Paolo , Zachwieja Jeffrey J. , Avogaro Angelo , Yarasheski Kevin , Bier Dennis M. , Cobelli Claudio
Published: December 2017

The classic (hereafter cold) and the labeled (hereafter hot) minimal models are powerful tools to investigate glucose metabolism. The cold model provides, from intravenous glucose tolerance test (IVGTT) data, indexes of glucose effectiveness (SG) and insulin sensitivity (SI) that measure the effect of glucose and insulin, respectively, to enhance glucose disappearance and inhibit endogenous glucose production. The hot model provides, from hot IVGTT data, indexes of glucose effectiveness ([Formula: see text]) and insulin sensitivity ([Formula: see text]) that, respectively, measure the effects of glucose and insulin on glucose disappearance only. Recent reports call for a reexamination of some of the assumptions of the minimal models. We have previously pointed out the criticality of the single-compartment description of glucose kinetics on which both the minimal models are founded. In this paper we evaluate the impact of single-compartment undermodeling on SG, SI,[Formula: see text], and[Formula: see text] by using a two-compartment model to describe the glucose system. The relationships of the minimal model indexes to the analogous indexes measured with the glucose clamp technique are also examined. Theoretical analysis and simulation studies indicate that cold indexes are more affected than hot indexes by undermodeling. In particular, care must be exercised in the physiological interpretation of SG, because this index is a local descriptor of events taking place in the initial portion of the IVGTT. As a consequence, SG not only reflects glucose effect on glucose uptake and production but also the rapid exchange of glucose between the accessible and nonaccessible glucose pools that occurs in the early part of the test.
A critical evaluation of mass isotopomer distribution analysis of gluconeogenesis in vivo
Authors: Previs Stephen F. , Cline Gary W. , Shulman Gerald I.
Published: December 2017

There are conflicting reports concerning the reliability of mass isotopomer distribution analysis (MIDA) for estimating the contribution of gluconeogenesis to total glucose production (f) during [13C]glycerol infusion.1We have evaluated substrate-induced effects on rate of appearance (Ra) of glycerol and glucose and f during [2-13C]glycerol infusion in vivo. Five groups of mice were fasted for 30 h and then infused with [2-13C]glycerol at variable rates and variable13C enrichments ( group I: 20 μmol ⋅ kg−1⋅ min−1, 99%13C; group II: 60 μmol ⋅ kg−1⋅ min−1, 60%13C; group III: 60 μmol ⋅ kg−1⋅ min−1, 99%13C; group IV: 120 μmol ⋅ kg−1⋅ min−1, 40%13C; or group V: 120 μmol ⋅ kg−1⋅ min−1, 99%13C). The total glycerol Raincreased from ∼104 to ∼157 and to ∼210 μmol ⋅ kg−1⋅ min−1as the infusion of [2-13C]glycerol increased from 20 to 60 and to 120 μmol ⋅ kg− 1⋅ min−1, respectively. As the amount of 99% enriched [2-13C]glycerol increased from 20 to 60 and to 120 μmol ⋅ kg−1⋅ min−1( groups I, III, and V, respectively), plasma glycerol enrichment increased from ∼21 to ∼42 and to ∼57% and the calculated f increased from ∼27 to ∼56 and to ∼87%, respectively. Similar plasma glycerol enrichments were observed in groups I, II, and IV (i.e., ∼21–24%), yet f increased from ∼27 to ∼57 and to ∼86% in groups II and IV, respectively. Estimates of absolute gluconeogenesis increased from ∼14 to ∼33 and ∼86 μmol ⋅ kg−1⋅ min−1as the infusion of [2-13C]glycerol increased from 20 to 60 and 120 μmol ⋅ kg−1⋅ min−1. Plausible estimates of f were obtained only under conditions that increased total glycerol Ra∼2-fold ( P < 0.001) and increased glucose Ra∼1.5-fold ( P < 0.01) above basal. We conclude that in 30-h fasted mice, 1) estimates of f by MIDA with low infusion rates of [2-13C]glycerol yield erroneous results and 2) reasonable estimates of f are obtained at glycerol infusion rates that perturb glycerol and glucose metabolism.
Lung surfactant kinetics in conscious pigs
Authors: Martini Wenjun Z. , Chinkes David L. , Barrow Robert E. , Murphey E. D. , Wolfe Robert R.
Published: December 2017

The primary goal of this study was to determine the contributions of plasma free fatty acids (FFA) and de novo synthesized fatty acids (FA) to lung surfactant phosphatidylcholine (PC) synthesis. A new stable isotope tracer model was developed in which [1,2-13C2]acetate and uniformly labeled [U-13C16]palmitate were infused in nine normal overnight fasted pigs to quantify surfactant kinetics in the basal state and during low-dose glucose infusion (2 mg ⋅ kg−1⋅ min−1). There was no effect of glucose; therefore, all data were pooled. The surfactant PC-bound palmitate incorporation rate from plasma palmitate was 20.9 ± 1.9 nmol palmitate ⋅ h−1⋅ g wet lung−1, compared with the rate of 2.1 ± 0.3 nmol palmitate ⋅ h−1⋅ g wet lung−1from de novo synthesized palmitate. The PC-bound palmitate secretion rate from the lamellar body pool to the alveolar surface pool was 239 ± 26 nmol palmitate ⋅ h−1⋅ g wet lung−1. Approximately 90% of the secreted PC recycled back to the lamellar bodies for reutilization. We conclude that plasma is the primary contributor of FA for surfactant PC synthesis under the conditions of this experiment.
Characterization of receptors mediating AVP- and OT-induced glucagon release from the rat pancreas
Authors: Yibchok-Anun Sirintorn , Cheng Henrique , Heine Patricia A. , Hsu Walter H.
Published: December 2017

We characterized the receptors that mediate arginine vasopressin (AVP)- and oxytocin (OT)-induced glucagon release by use of a number of antagonists in the perfused rat pancreas and the fluorescence imaging of the receptors. AVP and OT (3 pM-3 nM) increased glucagon release in a concentration-dependent manner. The antagonist with potent V1breceptor-blocking activity, CL-4–84 (10 nM), abolished AVP (30 pM)-induced glucagon release but did not alter OT (30 pM)-induced glucagon release. d(CH2)5[Tyr(Me)2]AVP (10 nM), a V1areceptor antagonist, and L-366,948 (10 nM), a highly specific OT-receptor antagonist, failed to inhibit AVP-induced glucagon release. In contrast, L-366,948 (10 nM) abolished OT (30 pM)-induced glucagon release but did not change the effect of AVP. Fluorescent microscopy of rat pancreatic sections showed that fluorescence-labeled AVP and OT bound to their receptors in the islets of Langerhans and that the bindings were inhibited by 1 μM of Cl-4–84 and L-366,948, respectively. Because AVP and OT at physiological concentrations (3–30 pM) increased glucagon release, we conclude that AVP and OT increase glucagon release under the physiological condition through the activation of V1band OT receptors, respectively.
Decreased visceral adiposity accounts for leptin effect on hepatic but not peripheral insulin action
Authors: Barzilai Nir , She Li , Liu Lisen , Wang Jiali , Hu Meizu , Vuguin Patricia , Rossetti Luciano
Published: December 2017

Leptin decreases visceral fat (VF) and increases peripheral and hepatic insulin action. Here, we generated similar decreases in VF using leptin (Lep), β3-adrenoreceptor agonism (β3), or food restriction (FR) and asked whether insulin action would be equally improved. For 8 days before the in vivo study, Sprague-Dawley rats ( n = 24) were either fed ad libitum [control (Con)], treated with Lep or β3 (CL-316,243) by implanted osmotic mini-pumps, or treated with FR. Total VF was similarly decreased in the latter three groups (Lep, 3.11 ± 0.96 g; β3, 2.87 ± 0.48 g; and FR, 3.54 ± 0.77 g compared with 6.91 ± 1.41 g in Con; P < 0.001) independent of total fat mass (by3H2O) and food intake. Insulin (3 mU ⋅ kg−1⋅ min−1) clamp studies were performed to assess hepatic and peripheral insulin sensitivity. Decreased VF resulted in similar and marked improvements in insulin action on glucose production (GP) (Lep, 1.19 ± 0.51; β3, 1.46 ± 0.68; FR, 2.27 ±0.71 compared with 6.06 ± 0.70 mg ⋅ kg−1⋅ min−1in Con; P < 0.001). By contrast, reduction in VF by β3 and FR failed to reproduce the stimulation of insulin-mediated glucose uptake (∼60%), glycogen synthesis (∼80%), and glycolysis (∼25%) observed with Lep. We conclude that 1) a moderate decrease in VF uniformly leads to a marked increase in hepatic insulin action, but 2) the effects of leptin on peripheral insulin action are not due to the associated changes in VF or β3 activation.
A unique mechanism of desensitization to lipolysis mediated by β3-adrenoceptor in rats with thermal injury
Authors: Ikezu Tsuneya , Yasuhara Shingo , Granneman James G. , Kraemer Fredric B. , Okamoto Takashi , Tompkins Ronald G. , Martyn Jeevendra A. J.
Published: December 2017

Thermal injury causes a hypermetabolic state associated with increased levels of catabolic hormones, but the molecular bases for the metabolic abnormalities are poorly understood. We investigated the lipolytic responses after β3-adrenoceptor (β3-AR) agonists and evaluated the associated changes in β-AR and its downstream signaling molecules in adipocytes isolated from rats with thermal injury. Maximal lipolytic responses to a specific β3-AR agonist, BRL-37344, were significantly attenuated at post burn days (PBD) 3 and 7. Despite significant reduction of the cell surface β3-AR number and its mRNA at PBD 3 and 7, BRL-37344 and forskolin-stimulated cAMP levels were not decreased. Glycerol production in response to dibutyryl cAMP, a direct stimulant of hormone-sensitive lipase (HSL) via protein kinase A (PKA), was significantly attenuated. Although immunoblot analysis indicated no differences in the expression and activity of PKA or in the expression of HSL, HSL activity showed significant reductions. Finally, β3-AR-induced insulin secretion was indeed attenuated in vivo. These studies indicate that the β3-AR system is desensitized after burns, both in the adipocytes and in β3-AR-induced secretion of insulin. Furthermore, these data suggest a complex and unique mechanism underlying the altered signaling of lipolysis at the level of HSL in animals after burns.
Alterations in the early steps of the insulin-signaling system in skeletal muscle of GH-transgenic mice
Authors: Dominici Fernando P. , Cifone Debora , Bartke Andrzej , Turyn Daniel
Published: December 2017

Growth hormone (GH) excess is associated with insulin resistance, but the molecular mechanisms of this association are poorly understood. In the current work, we have examined the consequences of exposure to high GH levels on the early steps of the insulin-signaling system in the muscle of bovine (b) GH-transgenic mice. The protein content and the tyrosine phosphorylation state of the insulin receptor (IR), the IR substrate-1 (IRS-1), the association between IRS-1 and the p85 subunit of phosphatidylinositol (PI) 3-kinase, and the phosphotyrosine-derived PI 3-kinase activity in this tissue were studied. We found that in skeletal muscle of bGH-transgenic mice, exposure to high circulating GH levels results in 1) reduced IR abundance, 2) reduced IR tyrosine phosphorylation, 3) reduced efficiency of IRS-1 tyrosine phosphorylation, and 4) defective activation of PI 3-kinase by insulin. These alterations may be related to the insulin resistance exhibited by these animals.
Pharmacokinetics of insulin-like growth factor I in hypopituitarism: correlation with binding proteins
Authors: Mauras Nelly , Quarmby Valerie , Bloedow Duane C.
Published: December 2017

We investigated the pharmacokinetics of recombinant human insulin-like growth factor I (rhIGF-I) in growth hormone deficiency (GHD). Nine GHD adults [age 25 ± 3 (SE) yr] received rhIGF-I (60 μg/kg sc) twice, 10 h apart, and blood was sampled over 24 h. IGF-I and free IGF-I concentrations increased, whereas IGF binding protein 3 (IGFBP-3) and acid labile subunit (ALS) were unchanged during treatment. There was no correlation between absorption or terminal half-life of IGF-I and IGFBP-3 or ALS, but negative correlations with IGF-I clearance (CL/F) and volume of distribution (V/F). Positive correlations between both IGFBP-3 and ALS and IGF-I maximal concentration (Cmax) and time of Cmax( T max) were observed. Compared with normal individuals studied similarly (using 80 μg/kg), GHD subjects showed a normal absorption half-life, a faster elimination half-life, lower Cmax, yet normal T maxand V/F. In conclusion, GHD is associated with normal absorption and distribution of IGF-I yet faster elimination kinetics. Additionally, IGFBP-3 and ALS concentrations modulate the peak concentrations of IGF-I achieved and correlate reciprocally with its V/F and CL/F, underscoring the critical importance of binding proteins in modulating the bioavailability of IGF-I in vivo in humans.
4-Hydroxyisoleucine: experimental evidence of its insulinotropic and antidiabetic properties
Authors: Broca Christophe , Gross René , Petit Pierre , Sauvaire Yves , Manteghetti Michèle , Tournier Michel , Masiello Pellegrino , Gomis Ramon , Ribes Gérard
Published: December 2017

We have recently shown in vitro that 4-hydroxyisoleucine (4-OH-Ile), an amino acid extracted from fenugreek seeds, potentiates insulin secretion in a glucose-dependent manner. The present study was designed to investigate whether 4-OH-Ile could exert in vivo insulinotropic and antidiabetic properties. For this purpose, intravenous or oral glucose tolerance tests (IVGTTs and OGTTs, respectively) were performed not only in normal animals but also in a type II diabetes rat model. During IVGTT in normal rats or OGTT in normal dogs, 4-OH-Ile (18 mg/kg) improved glucose tolerance. The lactonic form of 4-OH-Ile was ineffective in normal rats. In non-insulin-dependent diabetic (NIDD) rats, a single intravenous administration of 4-OH-Ile (50 mg/kg) partially restored glucose-induced insulin response without affecting glucose tolerance; a 6-day subchronic administration of 4-OH-Ile (50 mg/kg, daily) reduced basal hyperglycemia, decreased basal insulinemia, and slightly, but significantly, improved glucose tolerance. In vitro, 4-OH-Ile (200 μM) potentiated glucose (16.7 mM)-induced insulin release from NIDD rat-isolated islets. So, the antidiabetic effects of 4-OH-Ile on NIDD rats result, at least in part, from a direct pancreatic B cell stimulation.
Entry of CART into brain is rapid but not inhibited by excess CART or leptin
Authors: Kastin Abba J. , Akerstrom Victoria
Published: December 2017

Cocaine- and amphetamine-regulated transcript (CART) is a new anorectic peptide found in the brain and periphery. It is closely associated with leptin, an anorectic agent saturably transported across the blood-brain barrier (BBB). Using multiple time-regression analysis, we found that CART has a rapid rate of entry into brain from blood. However, there was no self-inhibition with CART, even when perfused in blood-free buffer or in fasted mice, showing a lack of saturation. HPLC showed that at least 58% of the injected CART reached brain tissue in intact form, and capillary depletion with and without washout showed that the CART was not bound to endothelial cells or adherent to vascular components. There was no evidence for an efflux system out of the brain for CART. Thus CART can cross the BBB from blood to brain, but its rapid rate of entry is not inhibited by excess CART or leptin.
Hypothyroidism induces Fos-like immunoreactivity in ventral medullary neurons that synthesize TRH
Authors: Yuan Pu-Qing , Yang Hong
Published: December 2017

Altered thyroid statuses are associated with autonomic disorders. Thyrotropin-releasing hormone (TRH) in medullary nuclei regulates vagal efferent activity. Induction of Fos-like immunoreactivity (IR) in medullary TRH-synthesizing neurons was investigated in 24-h fasted rats with different thyroid statuses. Hypo- and hyperthyroidism were induced by 6- N-propyl-2-thiouracil (PTU) in drinking water and a daily intraperitoneal injection of thyroxine (T4; 10 μg ⋅ 100 g−1⋅ day−1), respectively, for 1–4 wk. The numbers of Fos-like IR positive neurons in the raphe pallidus, raphe obscurus, and parapyramidal regions, which were low in euthyroid rats (0–2/section), increased remarkably as the hypothyroidism progressed and were negatively correlated with serum T4levels. At the 4th wk, Fos-like IR positive neurons were 10- to 70-fold higher compared with euthyroid controls. Simultaneous T4replacement (2 μg ⋅ 100 g−1⋅ day−1) prevented the increases of Fos-like IR in PTU-treated rats. Hyperthyroidism did not change the number of Fos-like IR neurons in the raphe nuclei but reduced it in the parapyramidal regions. Double immunostaining revealed that most of the Fos-like IR induced by hypothyroidism was located in the prepro-TRH IR positive neurons. The selective and sustained induction of Fos-like IR in TRH-synthesizing neurons in ventral medullary nuclei by hypothyroidism indicates that these neurons play a role in the autonomic disorders observed in altered thyroid statuses.
Functional vagal input to chemically identified neurons in pancreatic ganglia as revealed by Fos expression
Authors: Wang Jiulin , Zheng Huiyuan , Berthoud Hans-Rudolf
Published: December 2017

The importance of neural elements in the control of both endocrine and exocrine pancreatic secretory functions and their coordination with gastrointestinal, hepatic, and general homeostatic functions is increasingly recognized. To better characterize the vagal efferent input to the pancreas, the capacity of electrical vagal stimulation to induce expression of c-Fos in neurochemically identified neurons of intrapancreatic ganglia was investigated. At optimal stimulation parameters, unilateral stimulation of either the left or right cervical vagus induced Fos expression in ∼30% of neurons in the head and 10–20% of neurons in the body and tail of the pancreas. There was no Fos expression if no stimulation or stimulation with a distally cut vagus was applied. Large proportions of neurons contained nitric oxide synthase as assessed with NADPH diaphorase histochemistry (88%) and choline acetyltransferase. The proportion of nitrergic and nonnitrergic neurons receiving vagal input was not different. It is concluded that a significant proportion of pancreatic neurons receives excitatory synaptic input from vagal preganglionic axons and that many of these vagal postganglionic neurons can produce nitric oxide and acetylcholine.
Zonation of acetate labeling across the liver: implications for studies of lipogenesis by MIDA
Authors: Puchowicz Michelle A. , Bederman Ilya R. , Comte Blandine , Yang Dawei , David France , Stone Eric , Jabbour Kareem , Wasserman David H. , Brunengraber Henri
Published: December 2017

Measurement of fractional lipogenesis by mass isotopomer distribution analysis (MIDA) of fatty acids or cholesterol labeled from [13C]acetate assumes constant enrichment of lipogenic acetyl-CoA in all hepatocytes. This would not be the case if uptake and release of acetate by the liver resulted in transhepatic gradients of acetyl-CoA enrichment. Conscious dogs, prefitted with transhepatic catheters, were infused with glucose and [1,2-13C2]acetate. Stable concentrations and enrichments of acetate were measured in artery (17 μM, 36%), portal vein (61 μM, 5.4%), and hepatic vein (17 μM, 1.0%) and were computed for mixed blood entering the liver (53 μM, 7.4%). We also measured balances of propionate and butyrate across gut and liver. All gut release of propionate and butyrate is taken up by the liver. The threefold decrease in acetate concentration and the sevenfold decrease in acetate enrichment across the liver strongly suggest that the enrichment of lipogenic acetyl-CoA decreases across the liver. Thus fractional hepatic lipogenesis measured in vivo by MIDA may be underestimated.