bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistance exercise training increases mixed muscle protein synthesis rate in frail women and men ≥76 yr old
Authors: Yarasheski Kevin E. , Pak-Loduca Jina , Hasten Debbie L. , Obert Kathleen A. , Brown Mary Beth , Sinacore David R.
Published: December 2017

Muscle atrophy (sarcopenia) in the elderly is associated with a reduced rate of muscle protein synthesis. The purpose of this study was to determine if weight-lifting exercise increases the rate of muscle protein synthesis in physically frail 76- to 92-yr-old women and men. Eight women and 4 men with mild to moderate physical frailty were enrolled in a 3-mo physical therapy program that was followed by 3 mo of supervised weight-lifting exercise. Supervised weight-lifting exercise was performed 3 days/wk at 65–100% of initial 1-repetition maximum on five upper and three lower body exercises. Compared with before resistance training, the in vivo incorporation rate of [13C]leucine into vastus lateralis muscle protein was increased after resistance training in women and men ( P < 0.01), although it was unchanged in five 82 ± 2-yr-old control subjects studied two times in 3 mo. Maximum voluntary knee extensor muscle torque production increased in the supervised resistance exercise group. These findings suggest that muscle contractile protein synthetic pathways in physically frail 76- to 92-yr-old women and men respond and adapt to the increased contractile activity associated with progressive resistance exercise training.
Hepatic denervation does not affect plasma vasopressin response to intragastric hypertonic saline in conscious rats
Authors: Carlson Scott H. , Wyss J. Michael
Published: December 2017

Peripheral osmoreceptors monitor dietary NaCl and modify central nervous system and renal sympathetic nervous system activity accordingly. Experimental evidence suggests that these responses are dependent on the hepatic nerves. Peripheral osmoreceptors also modify arginine vasopressin (AVP) secretion. However, although hepatic denervation reportedly blunts activation of both supraoptic and paraventricular hypothalamic neurons after intraportal NaCl infusion, the role of the hepatic nerves in the AVP release has not been directly examined. The present study tests the hypothesis that the hepatic nerves modify AVP release in response to intragastric NaCl infusion. Wistar-Kyoto rats (WKY) received either hepatic denervation or a sham operation. Intragastric NaCl infusion significantly elevated plasma AVP in both sham-operated WKY and hepatic-denervated WKY, and the responses were not different between these groups. Second, previous studies suggest that both AVP secretion and baroreflexes are blunted in spontaneously hypertensive rats (SHR), deficits that contribute to the observed hypertension in SHR. We hypothesized that SHR also have a blunted peripheral osmoreceptor reflex and that this contributes to NaCl-sensitive hypertension. In contrast to our prediction, in SHR intragastric NaCl infusion induced an increase in plasma AVP that was similar to that in the WKY groups. Thus, although hepatic osmoreceptors are important for chronic regulation of arterial pressure, renal sympathetic nervous system activity, and the activity of hypothalamic neurons, they do not appear to influence plasma AVP concentration in response to intragastric NaCl.
Impact of lack of suppression of glucagon on glucose tolerance in humans
Authors: Shah Pankaj , Basu Ananda , Basu Rita , Rizza Robert
Published: December 2017

People with type 2 diabetes have defects in both α- and β-cell function. To determine whether lack of suppression of glucagon causes hyperglycemia when insulin secretion is impaired but not when insulin secretion is intact, twenty nondiabetic subjects were studied on two occasions. On both occasions, a “prandial” glucose infusion was given over 5 h while endogenous hormone secretion was inhibited. Insulin was infused so as to mimic either a nondiabetic ( n = 10) or diabetic ( n = 10) postprandial profile. Glucagon was infused at a rate of 1.25 ng ⋅ kg−1⋅ min−1, beginning either at time zero to prevent a fall in glucagon (nonsuppressed study day) or at 2 h to create a transient fall in glucagon (suppressed study day). During the “diabetic” insulin profile, lack of glucagon suppression resulted in a marked increase ( P < 0.002) in both the peak glucose concentration (11.9 ± 0.4 vs. 8.9 ± 0.4 mmol/l) and the area above basal of glucose (927 ± 77 vs. 546 ± 112 mmol ⋅ l−1⋅ 6 h) because of impaired ( P < 0.001) suppression of glucose production. In contrast, during the “nondiabetic” insulin profile, lack of suppression of glucagon resulted in only a slight increase ( P< 0.02) in the peak glucose concentration (9.1 ± 0.4 vs. 8.4 ± 0.3 mmol/l) and the area above basal of glucose (654 ± 146 vs. 488 ± 118 mmol ⋅ l−1⋅ 6 h). Of interest, when glucagon was suppressed, glucose concentrations differed only minimally during the nondiabetic and diabetic insulin profiles. These data indicate that lack of suppression of glucagon can cause substantial hyperglycemia when insulin availability is limited, therefore implying that inhibitors of glucagon secretion and/or glucagon action are likely to be useful therapeutic agents in such individuals.
Monoclonal antibodies to growth hormone (GH) prolong liver GH binding and GH-induced IGF-I/IGFBP-3 synthesis
Authors: Beauloye V. , Muaku S. M. , Lause P. , Portetelle D. , Renaville R. , Robert A. R. , Ketelslegers J. M. , Maiter D.
Published: December 2017

This time-course study further explored the mechanisms whereby monoclonal antibodies (MAbs) may enhance growth hormone (GH) effects. Hypophysectomized rats were killed 0, 1, 3, 6, 12, 24, and 48 h after a single injection of bovine (b) GH alone or complexed with an anti-bGH MAb. Serum insulin-like growth factor I (IGF-I) concentrations were increased more and for a longer period after MAb-GH complexes (peak at 24 h: 295 ± 24 ng/ml) than after bGH alone (peak at 12 h: 219 ± 37 ng/ml; P < 0.01), whereas liver IGF-I mRNA was similar at 12 h in both groups but remained higher at 24 h (by 65%, P < 0.001) and 48 h (by 64%, P < 0.001) in the presence of the MAb. Induction of serum insulin-like growth factor-binding protein (IGFBP)-3 and liver IGFBP-3 mRNA by bGH also was markedly amplified by the MAb (3.6- and 2-fold at 24 h, respectively; P < 0.01). GH receptors (GHR) remained occupied for a longer period after MAb-GH injection (36 ± 16 and 35 ± 8% at 6 and 12 h, respectively) compared with bGH alone (0 ± 28 and −15 ± 11%), whereas total liver GH-binding sites and GHR mRNA levels were not affected by the MAb. We conclude that MAbs against GH amplify and prolong the serum IGF-I response to GH, which may result from both a prolongation of liver IGF-I synthesis and an enhanced induction of IGFBP-3. These two effects may in turn be the consequences of sustained GH binding to its liver receptors in the presence of MAb.
Insulin regulation of glucose transport and phosphorylation in skeletal muscle assessed by PET
Authors: Kelley David E. , Williams Katherine V. , Price Julie C.
Published: December 2017

The current study examined in vivo insulin regulation of glucose transport and phosphorylation in skeletal muscle of healthy, lean volunteers. Positron emission tomography (PET) imaging and compartmental modeling of the time course of skeletal muscle uptake and utilization after a bolus injection of 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG) was performed during metabolic steady-state conditions at four rates of euglycemic insulin infusion. Leg glucose uptake (LGU) was determined by arteriovenous limb balance assessments. The metabolism of [18F]FDG strongly correlated with skeletal muscle LGU ( r= 0.72, P < 0.01). On the basis of compartmental modeling, the fraction of glucose undergoing phosphorylation (PF) increased in a dose-responsive manner from 11% during basal conditions to 74% at the highest insulin infusion rate ( P < 0.001). The PF and LGU were highly correlated ( r = 0.73, P < 0.001). Insulin also increased the volume of distribution of nonphosphorylated [18F]FDG ( P < 0.05). In step-wise regression analysis, the volume of distribution of nonphosphorylated [18F]FDG and the rate constant for glucose phosphorylation accounted for most of the variance in LGU ( r = 0.91, P < 0.001). These findings indicate an important interaction between transport and phosphorylation in the control of insulin-stimulated glucose metabolism in skeletal muscle.
d-Glucose and insulin stimulate migration and tubular formation of human endothelial cells in vitro
Authors: Shigematsu Satoshi , Yamauchi Keishi , Nakajima Kohji , Iijima Sachiko , Aizawa Toru , Hashizume Kiyoshi
Published: December 2017

Effects of highd-glucose and insulin on the endothelial cell migration and tubular formation were investigated with the use of ECV304 cells, a clonal human umbilical cord endothelial cell line. Exposure of the cells to highd-glucose resulted in a marked increase in the migration, which was blocked by inhibitors of protein kinase C such as H7 (10 μM) and GF109203X (200 nM). Furthermore, a protein kinase C agonist, phorbol 12-myristate 13-acetate, had an effect similar to that of glucose on ECV304 cells. Glucose stimulation of the migration was additively enhanced by 100 nM insulin, and the insulin effect was found to be unaffected by either PD-98059 or wortmannin, a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase inhibitor and a phosphatidylinositol 3-kinase inhibitor, respectively. Neither did H7 inhibit insulin stimulation of the migration. In contrast, a combination of high d-glucose and insulin, rather than either one alone, promoted tubular formation, which was inhibited by addition of 10 μM PD-98059. Stimulation of ECV304 cells by the combination of highd-glucose and insulin also caused an activation of MAPK, which was again obliterated by the same concentration of PD-98059. In conclusion, human endothelial cell migration and tubular formation are stimulated by highd-glucose and insulin in different ways. In the former reaction, either is effective, a combination of the two results in an additive effect, and activation of protein kinase C is involved. In contrast, tubular formation will only occur in the presence of a combination of highd-glucose and insulin, and MAPK plays an essential role.
Effect of induced metabolic acidosis on human skeletal muscle metabolism during exercise
Authors: Hollidge-Horvat M. G. , Parolin M. L. , Wong D. , Jones N. L. , Heigenhauser G. J. F.
Published: December 2017

The roles of pyruvate dehydrogenase (PDH), glycogen phosphorylase (Phos), and their regulators in lactate (Lac−) metabolism were examined during incremental exercise after ingestion of 0.3 g/kg of either NH4Cl [metabolic acidosis (ACID)] or CaCO3[control (CON)]. Subjects were studied at rest, at rest postingestion, and during continuous steady-state cycling at three stages (15 min each): 30, 60, and 75% of maximal oxygen uptake. Radial artery and femoral venous blood samples, leg blood flow, and biopsies of the vastus lateralis were obtained during each power output. ACID resulted in significantly lower intramuscular concentration of [Lac−] (ACID 40.8 vs. CON 56.9 mmol/kg dry wt), arterial whole blood [Lac−] (ACID 4.7 vs. CON 6.5 mmol/l), and leg Lac−efflux (ACID 3.05 vs. CON 6.98 mmol ⋅ l−1⋅ min−1). The reduced intramuscular [Lac−] resulted from decreases in pyruvate production due to inhibition of glycogenolysis, at the level of Phos a, and phosphofructokinase, together with an increase in the amount of pyruvate oxidized relative to the total produced. The reduction in Phos a activity was mediated through decreases in transformation, decreases in free inorganic phosphate concentration, and decreases in the posttransformational allosteric regulator free AMP. Reduced PDH activity occurred with ACID and may have resulted from alterations in the concentrations of acetyl-CoA, free ADP, pyruvate, NADH, and H+, leading to greater relative activity of the kinase. The results demonstrate that imposed metabolic acidosis in skeletal muscle results in decreased Lac−production due to inhibition of glycogenolysis at the level of Phos and increased pyruvate oxidation at PDH.
Oligomycin sensitivity of mitochondrial F1F0-ATPase in diabetes-prone BHE/Cdb rats
Authors: Kim Sook-Bae , Berdanier Carolyn D.
Published: December 2017

BHE/Cdb and Sprague-Dawley rats differ in their mitochondrial DNA sequence for the ATPase 6 (“subunit a”) gene. Base substitutions in this sequence result in the substitution of asparagine for aspartate at position 101 and the substitution of serine for leucine at position 129. Differences in sensitivity to oligomycin were observed. When the isolated F1F0-ATPase complex was studied and ATPase activity was assessed, that which was isolated from the BHE/Cdb rats was less sensitive to oligomycin inhibition than that which was isolated from the Sprague-Dawley rats. In contrast, when oxygen consumption was measured [oxygen phosphorylation (OXPHOS)] and a dose-response curve was generated with isolated mitochondria from these two strains, there was a shift to the left for the BHE/Cdb rat mitochondria. These mitochondria were more sensitive to oligomycin inhibition of OXPHOS than were mitochondria isolated from Sprague-Dawley rats. The OXPHOS results are consistent with those from human fibroblasts having either a normal or mutated ATPase 6 gene.
Glucocorticoids reverse leptin effects on food intake and body fat in mice without increasing NPY mRNA
Authors: Solano Joel M. , Jacobson Lauren
Published: December 2017

Glucocorticoid stimulation of appetite and leptin expression conflicts with leptin inhibition of food intake and suggests that glucocorticoids reduce sensitivity to leptin. To determine if glucocorticoids impair feeding and metabolic responses to leptin, we measured leptin-induced changes in food intake, body weight, hormones, carcass fat, and hypothalamic neuropeptide Y (NPY) mRNA in adrenalectomized mice with and without corticosterone replacement. Leptin infusion (0.5 μg/h) significantly decreased food intake and body weight in adrenalectomized mice. Corticosterone replacement approximating normal 24-h mean levels restored food intake but did not permit weight gain equivalent to PBS-infused controls. Corticosterone levels comparable to stress-induced production completely reversed leptin-induced reductions in weight gain and body fat, despite significant attenuation by leptin of corticosterone-induced increases in plasma insulin levels. Glucocorticoid replacement increased food intake without reversing leptin inhibition of hypothalamic NPY mRNA levels. We conclude that glucocorticoid levels within the physiological range can interfere with leptin action and that glucocorticoid effects are at least partly independent of NPY.
Origins of the hydrogen bound to carbon 1 of glucose in fasting: significance in gluconeogenesis quantitation
Authors: Chandramouli Visvanathan , Ekberg Karin , Schumann William C. , Wahren John , Landau Bernard R.
Published: December 2017

Healthy subjects ingested2H2O.2H enriched the hydrogen bound to carbon 1 of blood glucose 1.3 to 1.8 times more than the hydrogens bound to carbon 6. Enrichment at carbon 1 was more than at carbon 5 after 14 h, but not after 42 h, of fasting. After overnight fasting, when [2,3-3H]succinate was infused, 34 times as much3H was bound to carbon 6 as to carbon 1. On [1-2H,1-3H,1-14C]galactose infusion, the ratios of2H to14C and of3H to14C in blood glucose were 30% less than in the galactose.3H at carbon 6 was 1% of that at carbon 1 of the glucose. Thus, although the two hydrogens bound to carbon 1 and the two bound to carbon 6 of fructose 6-phosphate ( p) during gluconeogenesis are equally enriched in2H via pyruvate’s equilibration with alanine, one of each is further enriched via hydration of fumarate that is converted to glucose. That hydrogen at carbon 1 of fructose 6-phosphate ( P) is also enriched in fructose 6- P’s equilibration with mannose 6- P.2H from2H2O at carbon 1 to carbon 2 of blood glucose cannot then quantitate gluconeogenesis because of [1-2H]glucose formation during glycogenolysis. Triose-P cycling has a minimal effect on quantitation.2H recovery in glucose from [1-2H]galactose does not quantitate galactose conversion via UDP-glucose to glycogen.
Exercise and insulin cause GLUT-4 translocation in human skeletal muscle
Authors: Thorell Anders , Hirshman Michael F. , Nygren Jonas , Jorfeldt Lennart , Wojtaszewski Jørgen F. P. , Dufresne Scott D. , Horton Edward S. , Ljungqvist Olle , Goodyear Laurie J.
Published: December 2017

Studies in rodents have established that GLUT-4 translocation is the major mechanism by which insulin and exercise increase glucose uptake in skeletal muscle. In contrast, much less is known about the translocation phenomenon in human skeletal muscle. In the current study, nine healthy volunteers were studied on two different days. On one day, biopsies of vastus lateralis muscle were taken before and after a 2-h euglycemic-hyperinsulinemic clamp (0.8 mU ⋅ kg−1 ⋅ min−1). On another day, subjects exercised for 60 min at 70% of maximal oxygen consumption (V˙o 2 max), a biopsy was obtained, and the same clamp and biopsy procedure was performed as that during the previous experiment. Compared with insulin treatment alone, glucose infusion rates were significantly increased during the postexercise clamp for the periods 0–30 min, 30–60 min, and 60–90 min, but not during the last 30 min of the clamp. Plasma membrane GLUT-4 content was significantly increased in response to physiological hyperinsulinemia (32% above rest), exercise (35%), and the combination of exercise plus insulin (44%). Phosphorylation of Akt, a putative signaling intermediary for GLUT-4 translocation, was increased in response to insulin (640% above rest), exercise (280%), and exercise plus insulin (1,000%). These data demonstrate that two normal physiological conditions, moderate intensity exercise and physiological hyperinsulinemia ∼56 μU/ml, cause GLUT-4 translocation and Akt phosphorylation in human skeletal muscle.
Effects of a physiological GH pulse on interstitial glycerol in abdominal and femoral adipose tissue
Authors: Gravholt Claus Højbjerg , Schmitz Ole , Simonsen Lene , Bülow Jens , Christiansen Jens Sandahl , Møller Niels
Published: December 2017

Physiologically, growth hormone (GH) is secreted in pulses with episodic bursts shortly after the onset of sleep and postprandially. Such pulses increase circulating levels of free fatty acid and glycerol. We tested whether small GH pulses have detectable effects on intercellular glycerol concentrations in adipose tissue, and whether there would be regional differences between femoral and abdominal subcutaneous fat, by employing microdialysis for 6 h after administration of GH (200 μg) or saline intravenously. Subcutaneous adipose tissue blood flow (ATBF) was measured by the local Xenon washout method. Baseline of interstitial glycerol was higher in adipose tissue than in blood [220 ± 12 (abdominal) vs. 38 ± 2 (blood) μmol/l, P < 0.0005; 149 ± 9 (femoral) vs. 38 ± 2 (blood) μmol/l, P < 0.0005] and higher in abdominal adipose tissue compared with femoral adipose tissue ( P < 0.0005). Administration of GH induced an increase in interstitial glycerol in both abdominal and femoral adipose tissue (ANOVA: abdominal, P = 0.04; femoral, P = 0.03). There was no overall difference in the response to GH in the two regions during the study period as a whole (ANOVA: P = 0.5), but during peak stimulation of lipolysis abdominal adipose tissue was, in absolute but not in relative terms, stimulated more markedly than femoral adipose tissue (ANOVA: P = 0.03 from 45 to 225 min). Peak interstitial glycerol values of 253 ± 37 and 336 ± 74 μmol/l were seen after 135 and 165 min in femoral and abdominal adipose tissue, respectively. ATBF was not statistically different in the two situations (ANOVA: P = 0.7). In conclusion, we have shown that a physiological pulse of GH increases interstitial glycerol concentrations in both femoral and abdominal adipose tissue, indicating activated lipolysis. The peak glycerol increments after GH were higher in abdominal adipose tissue, perhaps due to a higher basal rate of lipolysis in this region.
Leptin response to carbohydrate or fat meal and association with subsequent satiety and energy intake
Authors: Romon M. , Lebel P. , Velly C. , Marecaux N. , Fruchart J. C. , Dallongeville J.
Published: December 2017

To assess the impact of the macronutrient content of a meal on the postprandial leptin response and its relationship with postprandial satiety, 22 young healthy subjects (11 men and 11 women) were given, in a randomized order, an isoenergetic meal [carbohydrate (81%) or fat (79%)] or remained fasting. Blood sampling and hunger and satiety scores were collected hourly during 9 h after the meal. Spontaneous intake was measured at a buffet meal at 9 h postprandially. In both genders, leptin response was higher after the carbohydrate meal than after the fat meal and while fasting. In women, leptin levels were higher after the fat meal than while fasting. Leptin response was significantly correlated to insulin response ( r = 0.51, P < 0.0001). Hunger and satiety ratings and subsequent energy intake were not different after carbohydrate or fat intake. In conclusion, a carbohydrate meal induces higher postprandial leptin levels than an isoenergetic fat meal. Short-term regulation of postprandial satiety and food intake is not influenced by circulating leptin.
Endothelin-1 stimulates heat shock protein 27 induction in osteoblasts: involvement of p38 MAP kinase
Authors: Kawamura Hidenori , Otsuka Takanobu , Matsuno Hiroyuki , Niwa Masayuki , Matsui Nobuo , Kato Kanefusa , Uematsu Toshihiko , Kozawa Osamu
Published: December 2017

We previously reported that endothelin-1 (ET-1) activates p42/p44 mitogen-activated protein (MAP) kinase in osteoblast-like MC3T3-E1 cells and consequently induces synthesis of interleukin-6. In the present study, we investigated the effect of ET-1 on the induction of heat shock protein 27 (HSP 27) in MC3T3-E1 cells. ET-1 time and dose dependently stimulated HSP 27 accumulation. ET-1 induced an increase in the levels of mRNA for HSP 27. Both staurosporine and calphostin C, inhibitors of protein kinase C (PKC), suppressed the ET-1-induced HSP 27 accumulation. 12- O-tetradecanoylphorbol 13-acetate (TPA), a PKC activator, induced the HSP 27 accumulation and the expression of mRNA for HSP 27. The ET-1-stimulated HSP 27 accumulation was reduced in PKC-downregulated MC3T3-E1 cells. The HSP 27 accumulation by ET-1 was not suppressed by PD-98059, an inhibitor of the upstream kinase that activates p42/p44 MAP kinase. ET-1 or TPA induced the phosphorylation of p38 MAP kinase. SB-203580, an inhibitor of p38 MAP kinase, reduced the ET-1-stimulated HSP 27 accumulation. Calphostin C and U-73122, a phospholipase C inhibitor, suppressed the ET-1-induced phosphorylation of p38 MAP kinase. U-73122 and propranolol, a phosphatidic acid phosphohydrolase inhibitor, reduced the ET-1-stimulated HSP 27 accumulation. SB-203580 suppressed the ET-1-stimulated increase in the mRNA levels for HSP 27. These results strongly suggest that ET-1 stimulates HSP 27 induction in osteoblasts and that p38 MAP kinase activation is involved in the HSP 27 induction.
Cyclosporin-induced dyslipoproteinemia is associated with selective activation of SREBP-2
Authors: Wu Jinmei , Zhu Yong Hong , Patel Shailendra B.
Published: December 2017

The use of cyclosporin A has contributed greatly to the success of organ transplantation. However, cyclosporin-associated side effects of hypertension, nephrotoxicity, and dyslipoproteinemia have tempered these benefits. Cyclosporin-induced dyslipoproteinemia may be an important risk factor for the accelerated atherosclerosis observed posttransplantation. Using a mouse model, we treated Swiss-Webster mice for 6 days with a daily dose of 20 μg/g body wt of cyclosporin and observed significant elevations of plasma cholesterol, triglyceride, and apolipoprotein B (apoB) levels relative to vehicle-alone treated control animals. Measurement of the rate of secretion of very low-density lipoprotein (VLDL) by the liver in vivo showed that cyclosporin treatment led to a significant increase in the rate of hepatic VLDL triglyceride secretion. Total apoB secretion was unaffected. Northern analysis showed that cyclosporin A treatment increased the abundance of hepatic mRNA levels for a number of key genes involved in cholesterol biosynthesis relative to vehicle-alone treated animals. Two key transcriptional factors, sterol regulatory element-binding protein (SREBP)-1 and SREBP-2, also showed differential expression; SREBP-2 expression was increased at the mRNA level, and there was an increase in the active nuclear form, whereas the mRNA and the nuclear form of SREBP-1 were reduced. These results show that the molecular mechanisms by which cyclosporin causes dyslipoproteinemia may, in part, be mediated by selective activation of SREBP-2, leading to enhanced expression of lipid metabolism genes and hepatic secretion of VLDL triglyceride.
Insulin resistance and glucose transporter expression during the euglycemic hyperinsulinemic clamp in the lamb
Authors: Gelardi Nancy L. , Rapoza Robert E. , Renzulli Joseph F. , Cowett Richard M.
Published: December 2017

Three- to six-day-old lambs infused with 100 mU ⋅ kg−1 ⋅ min−1insulin required greater amounts of glucose to maintain euglycemia during a euglycemic hyperinsulinemic clamp compared with 31- to 35-day-old insulin-infused lambs (15.87 ± 3.47 vs. 4.30 ± 1.11 mg ⋅ kg−1 ⋅ min−1, P < 0.05, respectively). Endogenous glucose production persisted in both groups; however, the percent decrease compared with age-matched lambs receiving no insulin was greater in the younger group compared with the older group (53%, P < 0.001, vs. 34%, P < 0.01). The younger animals showed greater glucose utilization compared with the older animals (215 vs. 96%, respectively, P < 0.01). No effect of insulin was noted on GLUT-4 protein expression in either group. GLUT-2 expression was increased in older vs. younger lambs. Older insulin-infused lambs showed lower GLUT-2 expression than older 0 insulin-infused lambs [0.94 ± 0.07 vs. 1.64 ± 0.10 (OD) units, P < 0.005]. Increased sensitivity to insulin in the younger animals was not related to acute changes in GLUT-4 expression. Increased GLUT-2 expression with age, as well as decreased expression with hyperinsulinemia, is consistent with the development of an insulin-resistant state in the adult.
Effects of glutamine supplementation, GH, and IGF-I on glutamine metabolism in critically ill patients
Authors: Jackson N. C. , Carroll P. V. , Russell-Jones D. L. , Sönksen P. H. , Treacher D. F. , Umpleby A. M.
Published: December 2017

During critical illness glutamine deficiency may develop. Glutamine supplementation can restore plasma concentration to normal, but the effect on glutamine metabolism is unknown. The use of growth hormone (GH) and insulin-like growth factor I (IGF-I) to prevent protein catabolism in these patients may exacerbate the glutamine deficiency. We have investigated, in critically ill patients, the effects of 72 h of treatment with standard parenteral nutrition (TPN; n = 6), TPN supplemented with glutamine (TPNGLN; 0.4 g ⋅ kg− 1 ⋅ day− 1, n = 6), or TPNGLN with combined GH (0.2 IU ⋅ kg− 1 ⋅ day− 1) and IGF-I (160 μg ⋅ kg− 1 ⋅ day− 1) (TPNGLN+GH/IGF-I; n = 5) on glutamine metabolism using [2-15N]glutamine. In patients receiving TPNGLN and TPNGLN+GH/IGF-I, plasma glutamine concentration was increased (338 ± 22 vs. 461 ± 24 μmol/l, P < 0.001, and 307 ± 65 vs. 524 ± 71 μmol/l, P < 0.05, respectively) and glutamine uptake was increased (5.2 ± 0.5 vs. 7.4 ± 0.7 μmol ⋅ kg− 1 ⋅ min− 1, P < 0.05 and 5.2 ± 1.1 vs. 7.6 ± 0.8 μmol ⋅ kg− 1 ⋅ min− 1, P < 0.05). Glutamine production and metabolic clearance rates were not altered by the three treatments. These results suggest that there is an increased requirement for glutamine in critically ill patients. Combined GH/IGF-I treatment with TPNGLN did not have adverse effects on glutamine metabolism.
A mathematical model quantifying GnRH-induced LH secretion from gonadotropes
Authors: Blum J. Joseph , Reed Michael C. , Janovick Jo Ann , Conn P. Michael
Published: December 2017

A mathematical model is developed to investigate the rate of release of luteinizing hormone (LH) from pituitary gonadotropes in response to short pulses of gonadotropin-releasing hormone (GnRH). The model includes binding of the hormone to its receptor, dimerization, interaction with a G protein, production of inositol 1,4,5-trisphosphate, release of Ca2+from the endoplasmic reticulum, entrance of Ca2+into the cytosol via voltage-gated membrane channels, pumping of Ca2+out of the cytosol via membrane and endoplasmic reticulum pumps, and release of LH. Cytosolic Ca2+dynamics are simplified (i.e., oscillations are not included in the model), and it is assumed that there is only one pool of releasable LH. Despite these and other simplifications, the model explains the qualitative features of LH release in response to GnRH pulses of various durations and different concentrations in the presence and absence of external Ca2+.
Novel salmon cardiac peptide hormone is released from the ventricle by regulated secretory pathway
Authors: Kokkonen Kati , Vierimaa Heidi , Bergström Sari , Tervonen Virpi , Arjamaa Olli , Ruskoaho Heikki , Järvilehto Matti , Vuolteenaho Olli
Published: December 2017

We used the secretion of the novel salmon cardiac peptide (sCP) as a model to examine the mechanisms of ventricular hormone release. Mechanical load increased dose dependently the secretion of immunoreactive sCP from isolated perfused salmon ventricle, with 3.3-fold increase when a load of 13 cmH2O was applied. Endothelin-1 (5 nmol/l) was also able to rapidly increase the secretion of sCP. The released peptide corresponded to the biologically active sCP-29, whereas the large ventricular storage consisted of pro-sCP-sized material. With the use of immunoelectron microscopy, a large number of granules containing immunoreactive sCP could be detected in salmon ventricle. As judged by RNA blot analysis, there was very active basal expression of the sCP gene in the ventricle, which was not increased by mechanical load of up to 2-h duration. Our results show that the ventricle actively expresses the gene of sCP, stores the prohormone in secretory granules, and releases the peptide in response to mechanical load and endothelin-1. Thus the salmon ventricle uses the regulated pathway to produce and release a hormone structurally related to the mammalian natriuretic peptides.
No limiting role for glycogenin in determining maximal attainable glycogen levels in rat skeletal muscle
Authors: Hansen Bo Falck , Derave Wim , Jensen Pia , Richter Erik A.
Published: December 2017

We examined whether the protein level and/or activity of glycogenin, the protein core upon which glycogen is synthesized, is limiting for maximal attainable glycogen levels in rat skeletal muscle. Glycogenin activity was 27.5 ± 1.4, 34.7 ± 1.7, and 39.7 ± 1.3 mU/mg protein in white gastrocnemius, red gastrocnemius, and soleus muscles, respectively. A similar fiber type dependency of glycogenin protein levels was seen. Neither glycogenin protein level nor the activity of glycogenin correlated with previously determined maximal attainable glycogen levels, which were 69.3 ± 5.8, 137.4 ± 10.1, and 80.0 ± 5.4 μmol/g wet wt in white gastrocnemius, red gastrocnemius, and soleus muscles, respectively. In additional experiments, rats were exercise trained by swimming, which resulted in a significant increase in the maximal attainable glycogen levels in soleus muscles (∼25%). This increase in maximal glycogen levels was not accompanied by an increase in glycogenin protein level or activity. Furthermore, even in the presence of very high glycogen levels (∼170 μmol/g wet wt), ∼30% of the total glycogen pool continued to be present as unsaturated glycogen molecules (proglycogen). Therefore, it is concluded that glycogenin plays no limiting role for maximal attainable glycogen levels in rat skeletal muscle.
In vivo rates of erythrocyte glutathione synthesis in children with severe protein-energy malnutrition
Authors: Reid Marvin , Badaloo Asha , Forrester Terrence , Morlese John F. , Frazer Margaret , Heird William C. , Jahoor Farook
Published: December 2017

Although the compromised GSH status of children with edematous protein-energy malnutrition (PEM) has been documented, the in vivo kinetic mechanism(s) responsible for this is not known. To determine if decreased synthesis contributes to the alteration of GSH homeostasis, the fractional and absolute rates of synthesis of erythrocyte GSH were determined shortly after admission ( study 1), ∼9 days postadmission ( study 2), and at recovery ( study 3) in seven children with edematous PEM and seven children with nonedematous PEM. Children with edematous PEM had significantly lower erythrocyte GSH and slower absolute rates of GSH synthesis than children with nonedematous PEM both shortly after admission, when they were both malnourished and infected, and ∼9 days later, when the infection had resolved but they were still malnourished. At these times, the edematous group also had significantly lower erythrocyte GSH concentrations and absolute rates of synthesis than at recovery. Plasma and erythrocyte-free cysteine concentrations of the edematous group were significantly lower at studies 1 and 2 than at recovery. In contrast, erythrocyte GSH concentrations, rates of GSH synthesis, and plasma and erythrocyte free cysteine concentrations of the nonedematous group were similar at all three time points and greater at studies 1 and 2 than in the edematous group. These results confirm that GSH deficiency is characteristic of edematous PEM and suggest that this is due to a reduced rate of synthesis secondary to a shortage in cysteine.
Correction of diet-induced hyperglycemia, hyperinsulinemia, and skeletal muscle insulin resistance by moderate hyperleptinemia
Authors: Buettner Roland , Newgard Christopher B. , Rhodes Christopher J. , O'Doherty Robert M.
Published: December 2017

Human obesity and high fat feeding in rats are associated with the development of insulin resistance and perturbed carbohydrate and lipid metabolism. It has been proposed that these metabolic abnormalities may be reversible by interventions that increase plasma leptin. Up to now, studies in nongenetic animal models of obesity and in human obesity have concentrated on multiple injection therapy with mixed results. Our study sought to determine whether a sustained, moderate increase in plasma leptin, achieved by administration of a recombinant adenovirus containing the leptin cDNA (AdCMV-leptin) would be effective in reversing the metabolic abnormalities of the obese phenotype. Wistar rats fed a high-fat diet (HF) were heavier ( P< 0.05), had increased fat mass and intramuscular triglycerides (mTG), and had elevated plasma glucose, insulin, triglyceride, and free fatty acids compared with standard chow-fed (SC) control animals (all P < 0.01). HF rats also had impaired glucose tolerance and were markedly insulin resistant, as demonstrated by a 40% reduction in insulin-stimulated muscle glucose uptake ( P < 0.001). Increasing plasma leptin levels to 29.0 ± 1.5 ng/ml (from 7.0 ± 1.4 ng/ml, P < 0.001) for a period of 6 days decreased adipose mass by 40% and normalized plasma glucose and insulin levels. In addition, insulin-stimulated skeletal muscle glucose uptake was normalized in hyperleptinemic rats, an effect that correlated closely with a 60% ( P < 0.001) decrease in mTG. Importantly, HF rats that received a control adenovirus containing the β-galactosidase cDNA and were calorically matched to AdCMV-leptin-treated animals remained hyperglycemic, hyperinsulinemic, insulin resistant, and maintained elevated mTG. We conclude that a gene-therapeutic intervention that elevates plasma leptin moderately for a sustained period reverses diet-induced hyperglycemia, hyperinsulinemia, and skeletal muscle insulin resistance, and that these improvements are tightly linked to leptin-induced reductions in mTG.
Deactivation of TSH receptor signaling in filter-cultured pig thyroid epithelial cells
Authors: Ericson Lars E. , Nilsson Mikael
Published: December 2017

Thyrotropin [thyroid-stimulating hormone (TSH)] receptor on-off signaling was studied in polarized monolayers of pig thyrocytes cultured on permeable support. Transepithelial resistance (R) and potential difference (PD) were used as parameters to monitor the effect of altered TSH concentrations on vectorial electrolyte transport. TSH induced rapid but long-lasting changes in R (decrease) and PD (increase) that were cAMP-dependent and related to enhanced transcellular conductance of sodium and chloride. Withdrawal of TSH from cultures prestimulated with TSH (0.1 mU/ml) for 48 h resulted in restitution of R to control level within 30 min. Such deactivation was markedly accelerated by mild trypsinization, which degraded receptor-bound ligand without affecting TSH receptor responsiveness or ion transporting capacity. Small alterations in the TSH concentration (0.01–0.1 mU/ml) were followed almost instantaneously by adjustments of R. In contrast, the reversal of R after acute TSH stimulation (30 min) and subsequent TSH washout was delayed for several hours independently of cell surface trypsinization. The observations indicate that, during continuous exposure to physiological concentrations, TSH exerts a close minute-to-minute surveillance of thyroid function and the rate-limiting step of deactivation is the dissociation of ligand from the TSH receptor at the cell surface. TSH-deprived cells briefly exposed to TSH are refractory to rapid deactivation, probably because of altered metabolism downstream of TSH receptor signal transduction.
Protein kinase C-β mediates lipoprotein-induced generation of PAI-1 from vascular endothelial cells
Authors: Ren Song , Shatadal Shalini , Shen Garry X.
Published: December 2017

Elevated levels of low-density lipoproteins (LDL) and lipoprotein(a) [Lp(a)] have been considered strong risk factors for atherosclerotic cardiovascular disease. Increased production of plasminogen activator inhibitor-1 (PAI-1) has been implicated in the development of thrombosis and atherosclerosis. Previous studies by our group and others demonstrated that oxidation enhances LDL- and Lp(a)-induced production of PAI-1 in human umbilical vein endothelial cells (HUVEC). The present study examined the involvement of protein kinase C (PKC) and its isoform in vascular endothelial cells (EC) induced by native or oxidized LDL and Lp(a). Treatment with Lp(a) or LDL transiently increased PKC activity at 15 min and 5.5 h after the start of lipoprotein treatment in EC. Copper-oxidized LDL and Lp(a) induced greater PKC activation in EC compared with comparable forms of those lipoproteins. Additions of 1 μM calphostin C, a PKC-specific inhibitor, at the beginning or ≥5 h, but not ≥9 h, after the initiation of lipoprotein treatment, blocked native and oxidized LDL- or Lp(a)-induced increases in PKC activity and PAI-1 production. Treatment of LDL, Lp(a), or their oxidized forms was induced in translocation of PKC-β1 from cytosol to membrane in HUVEC. Treatments with 60 nM 379196, a PKC-β-specific inhibitor, effectively prevented PAI-1 production induced by LDL, Lp(a), or their oxidized forms in HUVEC and human coronary artery EC. The results suggest that activation of PKC-β may mediate the production of PAI-1 in cultured arterial and venous EC induced by LDL, Lp(a), or their oxidized forms.
Thyroid hormone-induced stimulation of the sarcoplasmic reticulum Ca2+ATPase gene is inhibited by LIF and IL-6
Authors: Gloss Bernd , Villegas Sonia , Villarreal Francisco J. , Moriscot Anselmo , Dillmann Wolfgang H.
Published: December 2017

We investigated the effects of the leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) on 3,3′, 5-triiodo-l-thyronine, or thyroid hormone (T3)-stimulated sarcoplasmic reticulum Ca2+ATPase (SERCA2) gene expression on cultured neonatal rat cardiac myocytes. A reduction of T3induced increases in SERCA2 mRNA levels after co-treatment with LIF or IL-6. To investigate for the molecular mechanism(s) responsible for the blunted gene expression, a 3.2-kb SERCA2 promoter construct containing a reporter gene was transfected into cardiac myocytes. T3treatment stimulated transcriptional activity twofold, whereas co-treatment with T3and either of the cytokines caused an inhibition of T3-induced SERCA2 transcriptional activity. A T3-responsive 0.6-kb SERCA2 construct also showed a similar inhibition by cytokines. Cytokine inhibition of SERCA2 transcriptional activity was also evident when a 0.6-kb SERCA2 mutant, T3-unresponsive promoter construct was used. Treatment with T3and cytokines showed a significant decrease in transcription when a reporter construct was used that was comprised of direct repeats of SERCA2 thyroid response element I. These data provide evidence for cytokine-mediated inhibitory effects on the SERCA2 promoter that may be mediated by interfering with T3action.
Single exposure to testosterone in adulthood rapidly induces regularity in the growth hormone release process
Authors: Painson Jean-Claude , Veldhuis Johannes D. , Tannenbaum Gloria S.
Published: December 2017

The neonatal gonadal steroid milieu is known to be important in imprinting the striking sexual dimorphism of growth hormone (GH) secretion; however, the influence of the sex steroids on GH control in adult life and their mechanism/site of action are largely unknown. In the present study, we tested the hypothesis that testosterone (T) subserves the gender-specific regularity of the GH release process in adulthood. The approximate entropy statistic (ApEn) was used to quantify the degree of regularity of GH release patterns over time. Eighteen hours after a single subcutaneous injection of 1 mg T, both sham-operated and ovariectomized (OVX) female adult rats displayed plasma GH profiles that were strikingly similar to the regular male-like ultradian rhythm of GH secretion. The highest ApEn values, denoting greater disorderliness of GH secretion, were observed in the ovary-intact group, and T injection significantly ( P < 0.001) reduced this irregularity whether or not the ovaries were present. Serial intravenous injections of GH-releasing hormone (GHRH) caused a similar increase in plasma GH levels in sham-operated females independently of time of administration. In contrast, female rats administered T exhibited a male-like intermittent pattern of GH responsiveness to GHRH, the latter known to be due to the cyclic release of endogenous somatostatin. These results demonstrate that acute exposure to T during adult life can rapidly and profoundly “masculinize” GH pulse-generating circuits in the female rat. Our findings suggest that the enhanced orderliness characteristic of the GH release process in males, compared with females, is regulated by T. We postulate that this T-induced regularity is mediated at the level of the hypothalamus by inducing regularity in somatostatin secretion, which in turn governs overall GH periodicity.
Abundance and subcellular distribution of MCT1 and MCT4 in heart and fast-twitch skeletal muscles
Authors: Bonen Arend , Miskovic Dragana , Tonouchi Mio , Lemieux Kathleen , Wilson Marieangela C. , Marette André , Halestrap Andrew P.
Published: December 2017

The expression of two monocarboxylate transporters (MCTs) was examined in muscle and heart. MCT1 and MCT4 proteins are coexpressed in rat skeletal muscles, but only MCT1 is expressed in rat hearts. Among six rat fast-twitch muscles (red and white gastrocnemius, plantaris, extensor digitorum longus, red and white tibialis anterior) there was an inverse relationship between MCT1 and MCT4 ( r = −0.94). MCT1 protein was correlated with MCT1 mRNA ( r = 0.94). There was no relationship between MCT4 mRNA and MCT4 protein. MCT1 ( r = −0.97) and MCT4 ( r = 0.88) protein contents were correlated with percent fast-twitch glycolytic fiber. When normalized for their mRNAs, MCT1 but not MCT4 was still correlated with the percent fast-twitch glycolytic fiber composition of rat muscles ( r = −0.98). MCT1 and MCT4 were also measured in plasma membranes (PM), triads (TR), T tubules (TT), sarcoplasmic reticulum (SR), and intracellular membranes (IM). There was an intracellular pool of MCT4 but not of MCT1. The MCT1 subcellular distribution was as follows: PM (100%) > TR (31.6%) > SR (15%) = TT (14%) > IM (1.7%). The MCT4 subcellular distribution was considerably different [PM (100%) > TR (66.5%) > TT (36%) = SR (43%) > IM (24%)]. These studies have shown that 1) the mechanisms regulating the expression of MCT1 (transcriptional and posttranscriptional) and MCT4 (posttranscriptional) are different and 2) differences in MCT1 and MCT4 expression among muscles, as well as in their subcellular locations, suggest that they may have different roles in muscle.
Compartmental modeling of postprandial dietary nitrogen distribution in humans
Authors: Fouillet H. , Gaudichon C. , Mariotti F. , Mahé S. , Lescoat P. , Huneau J. F. , Tomé D.
Published: December 2017

A linear 11-compartment model was developed to describe and simulate the postprandial distribution of dietary nitrogen. The values of its 15 constant diffusion coefficients were estimated from the experimental measurement of 15N nitrogen kinetics in the intestine, blood, and urine after the oral administration of15N-labeled milk protein in humans. Model structure development, parameter estimation, and sensibility analysis were achieved using SAAM II and SIMUSOLV softwares. The model was validated at each stage of its development by testing successively its a priori and a posteriori identifiability. The model predicted that, 8 h after a meal, the dietary nitrogen retained in the body comprised 28% free amino acids and 72% protein, ∼30% being recovered in the splanchnic bed vs. 70% in the peripheral area. Twelve hours after the meal, these values had decreased to 18 and 23% for the free amino acid fraction and splanchnic nitrogen, respectively. Such a model constitutes a useful, explanatory tool to describe the processes involved in the metabolic utilization of dietary proteins.
β-Cell adaptation in 60% pancreatectomy rats that preserves normoinsulinemia and normoglycemia
Authors: Liu Ye Qi , Nevin Peter W. , Leahy Jack L.
Published: December 2017

Islet β-cells are the regulatory element of the glucose homeostasis system. When functioning normally, they precisely counterbalance changes in insulin sensitivity or β-cell mass to preserve normoglycemia. This understanding seems counter to the dogma that β-cells are regulated by glycemia. We studied 60% pancreatectomy rats (Px) 4 wk postsurgery to elucidate the β-cell adaptive mechanisms. Nonfasting glycemia and insulinemia were identical in Px and sham-operated controls. There was partial regeneration of the excised β-cells in the Px rats, but it was limited in scope, with the pancreas β-cell mass reaching 55% of the shams (40% increase from the time of surgery). More consequential was a heightened glucose responsiveness of Px islets so that glucose utilization and insulin secretion per milligram of islet protein were both 80% augmented at normal levels of glycemia. Investigation of the biochemical basis showed a doubled glucokinase maximal velocity in Px islets, with no change in the glucokinase protein concentration after adjustment for the different β-cell mass in Px and sham islets. Hexokinase activity measured in islet extracts was also minimally increased, but the glucose 6-phosphate concentration and basal glucose usage of Px islets were not different from those in islets from sham-operated rats. The dominant β-cell adaptive response in the 60% Px rats was an increased catalytic activity of glucokinase. The remaining β-cells thus sense, and respond to, perceived hyperglycemia despite glycemia actually being normal. β-Cell mass and insulin secretion are both augmented so that whole pancreas insulin output, and consequently glycemia, are maintained at normal levels.