bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of thyroid hormone on action potential and repolarizing currents in rat ventricular myocytes
Authors: Sun Zhuo-Qian , Ojamaa Kaie , Coetzee William A. , Artman Michael , Klein Irwin
Published: December 2017

Thyroid hormones play an important role in cardiac electrophysiology through both genomic and nongenomic mechanisms of action. The effects of triiodothyronine (T3) on the electrophysiological properties of ventricular myocytes isolated from euthyroid and hypothyroid rats were studied using whole cell patch clamp techniques. Hypothyroid ventricular myocytes showed significantly prolonged action potential duration (APD90) compared with euthyroid myocytes, APD90 of 151 ± 5 vs. 51 ± 8 ms, respectively. Treatment of hypothyroid ventricular myocytes with T3 (0.1 μM) for 5 min significantly shortened APD by 24% to 115 ± 10 ms. T3 similarly shortened APD in euthyroid ventricular myocytes, but only in the presence of 4-aminopyridine (4-AP), an inhibitor of the transient outward current ( I to), which prolonged the APD by threefold. Transient outward current ( I to) was not affected by the acute application of T3 to either euthyroid or hypothyroid myocytes; however, I to density was significantly reduced in hypothyroid compared with euthyroid ventricular myocytes.
Metabolically active components of fat free mass and resting energy expenditure in nonobese adults
Authors: Illner Kirsten , Brinkmann Gisbert , Heller Martin , Bosy-Westphal Anja , Müller Manfred J.
Published: December 2017

Resting energy expenditure (REE) and components of fat-free mass (FFM) were assessed in 26 healthy nonobese adults (13 males, 13 females). Detailed body composition analyses were performed by the combined use of dual-energy X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), bioelectrical impedance analysis (BIA), and anthropometrics. We found close correlations between REE and FFMBIA ( r = 0.92), muscle massDEXA( r = 0.89), and sum of internal organsMRI( r = 0.90). In a multiple stepwise regression analysis, FFMBIA alone explained 85% of the variance in REE (standard error of the estimate 423 kJ/day). Including the sum of internal organsMRI into the model increased the r 2 to 0.89 with a standard error of 381 kJ/day. With respect to individual organs, only skeletal muscleDEXAand liver massMRI significantly contributed to REE. Prediction of REE based on 1) individual organ masses and 2) a constant metabolic rate per kilogram organ mass was very close to the measured REE, with a mean prediction error of 96 kJ/day. The very close agreement between measured and predicted REE argues against significant variations in specific REEs of individual organs. In conclusion, the mass of internal organs contributes significantly to the variance in REE.
Utilization of very low density lipoprotein by rat heart: the effect of endotoxin
Authors: Bennett Mark J. , Hauton David , Hole David G. , Evans Rhys D.
Published: December 2017

The effect of endotoxin on myocardial utilization of very low density lipoprotein (VLDL) triacylglycerol (TAG) was studied. VLDL was prepared by rat liver perfusion and tested as substrate in the isolated working rat heart. Both liver and heart donor rats were pretreated in vivo with endotoxin or vehicle (control). VLDL-TAG synthesized by endotoxin-pretreated livers was assimilated and oxidized at an increased rate by hearts compared with control VLDL-TAG, regardless of the cardiac endotoxic status, with increased cardiac mechanical performance (cardiac output, hydraulic work). There was no change in incorporation of labeled VLDL lipids into myocardial tissue lipids. Lipoprotein lipase (LPL) activity was increased in endotoxin-pretreated hearts, and after perfusion with “endotoxic” VLDL, there was a tendency for translocation of LPL from tissue-residual to heparin-releasable compartments, but these changes were modest. Analysis of the VLDL composition showed that endotoxin-pretreated livers produced apolipoprotein (apo)-B48 VLDL with decreased particle size (and hence TAG content), but apo-B100 VLDL was unchanged. Oleate content of VLDL was increased, but there was no difference in apo-C or apo-E content. These results suggest that VLDL-TAG produced during sepsis/endotoxinemia may be destined for utilization by the heart as energy substrate. However, the mechanism for its increased efficacy is uncertain.
Osteoblast-like cells of the hypophysectomized rat: a model of aberrant osteoblast development
Authors: Evans Jodi F. , Yeh James K. , Aloia John F.
Published: December 2017

In a previous work, we demonstrated that the osteoprogenitors derived from the marrow stroma of the hypophysectomized (HX) rat demonstrate enhanced proliferative and differentiation capacities when placed in an optimal microenvironment. In this study, we sought to investigate the potential of the trabecular osteoblast-like cells of the HX rat. These cells represent a more mature pool of osteoblasts than the progenitors derived from the marrow stroma. We examined all three stages of osteoblast development using trabecular osteoblast-like cells derived from age-matched intact rats as a control. Using thymidine incorporation and cell number as indicators of proliferation, we found that these cells, like the osteoprogenitors derived from the HX rat, demonstrate augmented proliferation when placed in culture. Additionally, type I collagen expression remained at significant levels past the end stages of proliferation, at which point it is expected to be downregulated. Matrix maturation markers, such as alkaline phosphatase activity and bone sialoprotein expression, however, were significantly lower than in the controls. Mineralization potential, as measured by mineralized nodule formation, Ca2+ content, and OPN and OCN expression, was also significantly reduced. Our results have uncovered an aberrant model of osteoblast development in which proliferation is deregulated, resulting in a minimal capacity of these cells to develop into fully differentiated mineralizing osteoblasts.
Inverse relationship between protein intake and plasma free amino acids in healthy men at physical exercise
Authors: Forslund Anders H. , Hambræus Leif , van Beurden Hugo , Holmbäck Ulf , El-Khoury Antoine E. , Hjorth Gunilla , Olsson Roger , Stridsberg Mats , Wide Leif , Åkerfeldt Torbjörn , Regan Meredith , Young Vernon R.
Published: December 2017

The effect of a “normal” ( n = 8) and “high” ( n = 6) protein intake (1 and 2.5 g ⋅ kg−1⋅ day−1, respectively) and of exercise on plasma amino acid (AA) concentrations, insulin, and glucagon concentrations was followed throughout a continuous 24-h period in adult male subjects at energy balance after six days on a standardized diet and exercise program. Subjects were fasting from 2100 on day 6 to 1200 on day 7 and then fed 10 identical meals hourly until 2100. Physical exercise was performed (46% maximal oxygen uptake) between 0830 and 1000 (fasting) and in a fed state (1600–1730) on each day. The normal-protein group showed fasting plasma AA concentrations that were higher ( P < 0.05) than those for the high-protein group, except for leucine, methionine, and tyrosine. Glutamine, glycine, alanine, taurine, and threonine concentrations were distinctly higher (∼30% or greater) throughout the 24-h period in subjects consuming the normal- vs. the high-protein diets. Exercise appeared to increase, although not profoundly, the plasma concentrations of amino acids except for glutamate, histidine, ornithine, and tryptophan. The profound diet-related differences in plasma AA concentrations are only partially explained by differences in the renal clearance of the amino acids. We speculate on the possible metabolic basis for these findings.
Direct evidence of fiber type-dependent GLUT-4 expression in human skeletal muscle
Authors: Gaster M. , Poulsen P. , Handberg A. , Schrøder H. D. , Beck-Nielsen H.
Published: December 2017

GLUT-4 expression in individual fibers of human skeletal muscles in younger and older adults was studied. Furthermore, the dependency of insulin-stimulated glucose uptake on fiber type distribution was investigated. Fiber type distribution was determined in cryosections of muscle biopsies from 8 younger (29 yr) and 8 older (64 yr) healthy subjects, and estimates of GLUT-4 expression in individual fibers were obtained by combining immunohistochemistry and stereology. GLUT-4 was more abundantly expressed in slow compared with fast muscle fibers in both younger ( P < 0.007) and older ( P < 0.001) subjects. A 25% reduction of GLUT-4 density in fast fibers ( P < 0.001) and an unchanged GLUT-4 density in slow fibers were demonstrated in older compared with younger subjects. Insulin-stimulated glucose uptake rates measured by hyperinsulinemic, euglycemic clamp were not correlated with the fraction of slow fibers in the young ( r = −0.45, P > 0.25) or in the elderly ( r = 0.11, P > 0.75) subjects. In conclusion, in human skeletal muscle, GLUT-4 expression is fiber type dependent and decreases with age, particularly in fast muscle fibers.
Exercise attenuates the fasting-induced transcriptional activation of metabolic genes in skeletal muscle
Authors: Hildebrandt Audrey L. , Neufer P. Darrell
Published: December 2017

Fasting elicits a progressive increase in lipid metabolism within skeletal muscle. To determine the effects of fasting on the transcriptional regulation of genes important for metabolic control in skeletal muscle composed of different fiber types, nuclei from control and fasted (24 and 72 h) rats were subjected to nuclear run-on analysis using an RT-PCR-based technique. Fasting increased ( P < 0.05) transcription rate of the muscle-specific uncoupling protein-3 gene (UCP3) 14.3- to 21.1-fold in white gastrocnemius (WG; fast-twitch glycolytic) and 5.5- to 7.5-fold in red gastrocnemius (RG; fast-twitch oxidative) and plantaris (PL; mixed) muscles. No change occurred in soleus (slow-twitch oxidative) muscle. Fasting also increased transcription rate of the lipoprotein lipase (LPL), muscle carnitine palmitoyltransferase I (CPT I), and long-chain acyl-CoA dehydrogenase (LCAD) genes 1.7- to 3.7-fold in WG, RG, and PL muscles. Transcription rate responses were similar after 24 and 72 h of fasting. Surprisingly, increasing metabolic demand during the initial 8 h of starvation (two 2-h bouts of treadmill running) attenuated the 24-h fasting-induced transcriptional activation of UCP3, LPL, CPT I, and LCAD in RG and PL muscles, suggesting the presence of opposing regulatory mechanisms. These data demonstrate that fasting elicits a fiber type-specific coordinate increase in the transcription rate of several genes involved in and/or required for lipid metabolism and indicate that exercise may attenuate the fasting-induced transcriptional activation of specific metabolic genes.
Trafficking of dietary oleic, linolenic, and stearic acids in fasted or fed lean rats
Authors: Bessesen Daniel H. , Vensor S. Holly , Jackman Matthew R.
Published: December 2017

Increasing evidence supports the notion that there are significant differences in the health effects of diets enriched in saturated, as opposed to monounsaturated or polyunsaturated fat. However, the current understanding of how these types of fat differ in their handling by relevant tissues is incomplete. To examine the effects of fat type and nutritional status on the metabolic fate of dietary fat, we administered14C-labeled oleic, linolenic, or stearic acid with a small liquid meal to male Sprague-Dawley rats previously fasted for 15 h (fasted) or previously fed ad libitum (fed).14CO2production was measured for 8 h after tracer administration. The14C content of gastrointestinal tract, serum, liver, skeletal muscle (soleus, lateral, and medial gastrocnemius), and adipose tissue (omental, retroperitoneal, and epididymal) was measured at six time points (2, 4, 8, 24, and 48 h and 10 days) after tracer administration. Plasma levels of glucose, insulin, and triglyceride were also measured. Oxidation of stearic acid was significantly less than that of either linolenic or oleic acid in both the fed and fasted states. This reduction was in part explained by a greater retention of stearic acid within skeletal muscle and liver. Oxidation of oleate and stearate were significantly lower in the fed state than in the fasted state. In the fasted state, liver and skeletal muscle were quantitatively more important than adipose tissue in the uptake of dietary fat tracers during the immediate postprandial period. In contrast, adipose tissue was quantitatively more important than skeletal muscle or liver in the fed state. The movement of carbons derived from dietary fat between tissues is a complex time-dependent process, which varies in response to the type of fat ingested and the metabolic state of the organism.
Summation of behavioral and immunological stress: metabolic consequences to the growing mouse
Authors: Laugero Kevin D. , Moberg Gary P.
Published: December 2017

To address the hypothesis that multiple stressors can have cumulative effects on the individual, we determined the effects of restraint (R) stress (4 h/day for 7 days), immunological (L) stress [lipopolysaccharide (LPS) injection, 0.45 μg/g body wt on days 6 and 7], and R + L (RL) on the growth and energetics of C57Bl/6 male mice. R and L each repeatedly increased ( P < 0.05) circulating corticosterone (>8 times), but RL caused even greater (>250%, P < 0.05) concentrations of circulating corticosterone than did either stressor alone. Only L and RL increased ( P < 0.05) circulating interleukin-1β. Although R, L, and RL impaired growth (>75% below controls, P < 0.05), RL reduced growth to a greater extent. All stressors inhibited ( P < 0.05) lean (>33% below controls) and fat (>120% below controls) energy deposition, and like the effects on growth, combined RL stress inhibited lean and fat energy deposition to a greater extent than did either stressor acting alone. These results demonstrated that the summation of multiple stress results in a cumulative cost to the growing animal.
Effect of high-fat diet, surrounding temperature, and enterostatin on uncoupling protein gene expression
Authors: Rippe Catarina , Berger Karin , Böiers Charlotta , Ricquier Daniel , Erlanson-Albertsson Charlotte
Published: December 2017

Nonshivering thermogenesis induced in brown adipose tissue (BAT) during high-fat feeding is mediated through uncoupling protein 1 (UCP1). UCP2 is a recently identified homologue found in many tissues. To determine the role of UCP1 and UCP2 in thermoregulation and energy balance, we investigated the long-term effect of high-fat feeding on mRNA levels in mice at two different ambient temperatures. We also treated mice with the anorectic peptide enterostatin and compared mRNA levels in BAT, white adipose tissue (WAT), stomach, and duodenum. Here, we report that high-fat feeding at 23°C increased UCP1 and UCP2 levels in BAT four- and threefold, respectively, and increased UCP2 levels fourfold in WAT. However, at 29°C, UCP1 decreased, whereas UCP2 remained unchanged in BAT and increased twofold in WAT. Enterostatin increased UCP1 and decreased UCP2 mRNA in BAT. In stomach and duodenum, high-fat feeding decreased UCP2 mRNA, whereas enterostatin increased it. Our results suggest that the regulation of uncoupling protein mRNA levels by high-fat feeding is dependent on ambient temperature and that enterostatin is able to modulate it.
Evidence of UCP1-independent regulation of norepinephrine-induced thermogenesis in brown fat
Authors: Ribeiro Miriam O. , Lebrun Fabiana L. A. S. , Christoffolete Marcelo A. , Branco Marcelo , Crescenzi Alessandra , Carvalho Suzy D. , Negrão Núbio , Bianco Antonio C.
Published: December 2017

To study the thermal response of interscapular brown fat (IBF) to norepinephrine (NE), urethan-anesthetized rats (1.2 g/kg ip) maintained at 28–30°C received a constant venous infusion of NE (0–2 × 104pmol/min) over a period of 60 min. IBF temperatures (TIBF) were recorded with a small thermistor fixed under the IBF pad. Data were plotted against time and expressed as maximal variation (Δ t°C). Saline-injected rats showed a decrease in TIBFof ∼0.6°C. NE infusion increased TIBFby a maximum of ∼3.0°C at a dose of 104pmol · min−1· 100 g body wt−1. Surgically thyroidectomized (Tx) rats kept on 0.05% methimazole showed a flat response to NE. Treatment with thyroxine (T4, 0.8 μg · 100 g−1· day−1) for 2–15 days normalized mitochondrial UCP1 (Western blotting) and IBF thermal response to NE, whereas iopanoic acid (5 mg · 100 g body wt−1· day−1) blocked the effects of T4. Treatment with 3,5,3′-triiodothyronine (T3, 0.6 μg · 100 g body wt−1· day−1) for up to 15 days did not normalize UCP1 levels. However, these animals showed a normal IBF thermal response to NE. Cold exposure for 5 days or feeding a cafeteria diet for 20 days increased UCP1 levels by ∼3.5-fold. Nevertheless, the IBF thermal response was only greater than that of controls when maximal doses of NE (2 × 104pmol/min and higher) were used. Conclusions: 1) hypothyroidism is associated with a blunted IBF thermal response to NE; 2) two- to fourfold changes in mitochondrial UCP1 concentration are not necessarily translated into heat production during NE infusion.
Meal fatty acid uptake in human adipose tissue: technical and experimental design issues
Authors: Romanski S. A. , Nelson Rita M. , Jensen Michael D.
Published: December 2017

The adipose tissue uptake of dietary fat has been studied using fatty acid radiotracers incorporated into a meal, followed by adipose tissue biopsies. A number of experimental design issues, including the use of isotopic tracers to measure meal fatty acid oxidation and plasma appearance of tracer, as well as the heterogeneity of adipose tissue fatty acid uptake, have been addressed. We examined these questions in a study of 24 volunteers (12 men and 12 women) who consumed a meal containing [3H]triolein and [14C]triolein. Slight differences in the purity of [3H]triolein vs. [14C]triolein were found, which could affect the apparent adipose tissue uptake of meal fatty acids. The adipose tissue triglyceride specific activity from bilateral biopsy sites agreed well, implying that a unilateral biopsy is satisfactory for measuring tracer uptake. Meal fatty acid oxidation measured using [3H]triolein and [14C]triolein was well correlated ( r = 0.79, P < 0.0001). The peak tracer appearance in plasma chylomicrons occurred 1 h after the ingestion of a second, unlabeled meal. Our findings have implications for the experimental design of future meal fatty acid tracer/adipose tissue biopsy studies.
Hypertrophied rat hearts are less responsive to the metabolic and functional effects of insulin
Authors: Allard Michael F. , Wambolt Richard B. , Longnus Sarah L. , Grist Mark , Lydell Carmen P. , Parsons Hannah L. , Rodrigues Brian , Hall Jennifer L. , Stanley William C. , Bondy Gregory P.
Published: December 2017

We determined the effect of insulin on the fate of glucose and contractile function in isolated working hypertrophied hearts from rats with an aortic constriction ( n = 27) and control hearts from sham-operated rats ( n = 27). Insulin increased glycolysis and glycogen in control and hypertrophied hearts. The change in glycogen was brought about by increased glycogen synthesis and decreased glycogenolysis in both groups. However, the magnitude of change in glycolysis, glycogen synthesis, and glycogenolysis caused by insulin was lower in hypertrophied hearts than in control hearts. Insulin also increased glucose oxidation and contractile function in control hearts but not in hypertrophied hearts. Protein content of glucose transporters, protein kinase B, and phosphatidylinositol 3-kinase was not different between the two groups. Thus hypertrophied hearts are less responsive to the metabolic and functional effects of insulin. The reduced responsiveness involves multiple aspects of glucose metabolism, including glycolysis, glucose oxidation, and glycogen metabolism. The absence of changes in content of key regulatory molecules indicates that other sites, pathways, or factors regulating glucose utilization are responsible for these findings.
Overnight inhibition of insulin secretion restores pulsatility and proinsulin/insulin ratio in type 2 diabetes
Authors: Laedtke Thomas , Kjems Lise , Pørksen Niels , Schmitz Ole , Veldhuis Johannes , Kao Pai C. , Butler Peter C.
Published: December 2017

Impaired insulin secretion in type 2 diabetes is characterized by decreased first-phase insulin secretion, an increased proinsulin-to-insulin molar ratio in plasma, abnormal pulsatile insulin release, and heightened disorderliness of insulin concentration profiles. In the present study, we tested the hypothesis that these abnormalities are at least partly reversed by a period of overnight suspension of β-cell secretory activity achieved by somatostatin infusion. Eleven patients with type 2 diabetes were studied twice after a randomly ordered overnight infusion of either somatostatin or saline with the plasma glucose concentration clamped at ∼8 mmol/l. Controls were studied twice after overnight saline infusions and then at a plasma glucose concentration of either 4 or 8 mmol/l. We report that in patients with type 2 diabetes, 1) as in nondiabetic humans, insulin is secreted in discrete insulin secretory bursts; 2) the frequency of pulsatile insulin secretion is normal; 3) the insulin pulse mass is diminished, leading to decreased insulin secretion, but this defect can be overcome acutely by β-cell rest with somatostatin; 4) the reported loss of orderliness of insulin secretion, attenuated first-phase insulin secretion, and elevated proinsulin-to-insulin molar ratio also respond favorably to overnight inhibition by somatostatin. The results of these clinical experiments suggest the conclusion that multiple parameters of abnormal insulin secretion in patients with type 2 diabetes mechanistically reflect cellular depletion of immediately secretable insulin that can be overcome by β-cell rest.
Role of glucose in the regulation of glutamine metabolism in health and in type 1 insulin-dependent diabetes
Authors: Hankard Régis G. , Haymond Morey W. , Darmaun Dominique
Published: December 2017

To determine the effect of glucose availability on glutamine metabolism, glutamine kinetics were assessed under conditions of hyperglycemia resulting from 1) intravenous infusion of 7.5% dextrose in healthy adults and 2) insulin deficiency in young adults with insulin-dependent diabetes mellitus (IDDM). Eight healthy adults and five young adults with IDDM were studied in the postabsorptive state by use of a primed continuous infusion ofd-[U-14C]glucose,l-[5,5,5-2H3]leucine, andl-[3,4-13C]glutamine. Whether resulting from insulin deficiency or dextrose infusion, the rise in plasma glucose was associated with increased glucose turnover (23.5 ± 0.7 vs. 12.9 ± 0.3 μmol · kg−1 · min−1, P < 0.01 and 20.9 ± 2.5 vs. 12.8 ± 0.4 μmol · kg−1 · min−1, P = 0.03, in health and IDDM, respectively). In both cases, high blood glucose failed to alter glutamine appearance rate (Ra) into plasma [298 ± 9 vs. 312 ± 14 μmol · kg−1 · h−1, not significant (NS) and 309 ± 23 vs 296 ± 26 μmol · kg−1 · h−1, NS, in health and IDDM, respectively] and the estimated fraction of glutamine Ra arising from de novo synthesis (210 ± 7 vs. 217 ± 10 μmol · kg−1 · h−1, NS and 210 ± 16 vs. 207 ± 21 μmol · kg−1 · h−1, NS, in health and IDDM, respectively). When compared with the euglycemic day, the apparent contribution of glucose to glutamine carbon skeleton increased when high plasma glucose resulted from intravenous dextrose infusion in healthy volunteers (10 ± 0.8 vs. 4.8 ± 0.3%, P < 0.01) but failed to do so when hyperglycemia resulted from insulin deficiency in IDDM. We conclude that 1) the contribution of glucose to the estimated rate of glutamine de novo synthesis does not increase when elevation of plasma glucose results from insulin deficiency, and 2) the transfer of carbon from glucose to glutamine may depend on insulin availability.
Inhibition of lipolysis causes suppression of endogenous glucose production independent of changes in insulin
Authors: Mittelman Steven D. , Bergman Richard N.
Published: December 2017

We have shown that insulin controls endogenous glucose production (EGP) indirectly, via suppression of adipocyte lipolysis. Free fatty acids (FFA) and EGP are suppressed proportionately, and when the decline in FFA is prevented during insulin infusion, suppression of EGP is also prevented. The present study tested the hypothesis that suppression of lipolysis under conditions of constant insulin would yield a suppression of EGP. N6-cyclohexyladenosine (CHA) was used to selectively suppress adipocyte lipolysis during euglycemic clamps in conscious male dogs. FFA suppression by CHA caused suppression of EGP. Liposyn control experiments, which maintained FFA levels above basal during CHA infusion, completely prevented the decline in EGP, whereas glycerol control experiments, which maintained glycerol levels close to basal, did not prevent a decline in EGP. These controls suggest that the EGP suppression was secondary to the suppression of FFA levels specifically. A difference in the sensitivity of FFA and EGP suppression (FFA were suppressed ∼85% whereas EGP only declined ∼40%) was possibly caused by confounding effects of CHA, including an increase in catecholamine and glucagons levels during CHA infusion. Thus suppression of lipolysis under constant insulin causes suppression of EGP, despite a significant rise in catecholamines.
A statistical model of the human core-temperature circadian rhythm
Authors: Brown Emery N. , Choe Yong , Luithardt Harry , Czeisler Charles A.
Published: December 2017

We formulate a statistical model of the human core-temperature circadian rhythm in which the circadian signal is modeled as a van der Pol oscillator, the thermoregulatory response is represented as a first-order autoregressive process, and the evoked effect of activity is modeled with a function specific for each circadian protocol. The new model directly links differential equation-based simulation models and harmonic regression analysis methods and permits statistical analysis of both static and dynamical properties of the circadian pacemaker from experimental data. We estimate the model parameters by using numerically efficient maximum likelihood algorithms and analyze human core-temperature data from forced desynchrony, free-run, and constant-routine protocols. By representing explicitly the dynamical effects of ambient light input to the human circadian pacemaker, the new model can estimate with high precision the correct intrinsic period of this oscillator (∼24 h) from both free-run and forced desynchrony studies. Although the van der Pol model approximates well the dynamical features of the circadian pacemaker, the optimal dynamical model of the human biological clock may have a harmonic structure different from that of the van der Pol oscillator.
Effects of acute hypotensive stimuli on arginine vasopressin gene transcription in the rat hypothalamus
Authors: Kakiya Satoshi , Arima Hiroshi , Yokoi Hisashi , Murase Takashi , Yambe Yuko , Oiso Yutaka
Published: December 2017

We investigated the baroregulation of arginine vasopressin (AVP) gene transcription in the supraoptic (SON) and paraventricular nuclei (PVN) in conscious rats by use of intronic in situ hybridization. Hemorrhage of 16 ml/kg body wt decreased mean arterial pressure (MAP) by 57% and increased both plasma AVP (control, 1.2 ± 0.3 pg/ml; 16 ml/kg body wt, 38.9 ± 3.2 pg/ml) at 10 min and AVP heteronuclear (hn)RNA levels (SON, 150%; PVN, 140% of control values) at 20 min. On the other hand, hemorrhage of 7 ml/kg body wt had no significant effect on MAP, plasma AVP, or the AVP hnRNA levels. To better understand the baroregulation, we also examined the effects of sodium nitroprusside (SNP), which induces hypotension without a change in blood volume. The subcutaneous injection of 2 mg/kg body wt SNP, which decreased the MAP by 60%, increased both plasma AVP (control, 1.6 ± 0.4 pg/ml; 2 mg/kg body wt, 8.1 ± 0.4 pg/ml) at 10 min and AVP hnRNA levels (SON, 150%; PVN, 140% of control values) at 30 min. The injection of 0.1 mg/kg body wt SNP, which reduced the MAP by 10%, failed to increase either the plasma AVP or AVP hnRNA levels. These results indicate that AVP gene transcription increases rapidly after both hypotensive hemorrhage and normovolemic hypotension. In addition, it is suggested that the set point for AVP synthesis in the baroregulation is similar to that for AVP release.
Alterations in basal glucose metabolism during late pregnancy in the conscious dog
Authors: Connolly Cynthia C. , Holste Linda C. , Aglione Lisa N. , Neal Doss W. , Lacy D. Brooks , Smith Marta S. , Diamond Michael P. , Cherrington Alan D. , Chiasson Jean-Louis
Published: December 2017

We assessed basal glucose metabolism in 16 female nonpregnant (NP) and 16 late-pregnant (P) conscious, 18-h-fasted dogs that had catheters inserted into the hepatic and portal veins and femoral artery ∼17 days before the experiment. Pregnancy resulted in lower arterial plasma insulin (11 ± 1 and 4 ± 1 μU/ml in NP and P, respectively, P < 0.05), but plasma glucose (5.9 ± 0.1 and 5.6 ± 0.1 mg/dl in NP and P, respectively) and glucagon (39 ± 3 and 36 ± 2 pg/ml in NP and P, respectively) were not different. Net hepatic glucose output was greater in pregnancy (42.1 ± 3.1 and 56.7 ± 4.0 μmol · 100 g liver−1· min−1in NP and P, respectively, P < 0.05). Total net hepatic gluconeogenic substrate uptake (lactate, alanine, glycerol, and amino acids), a close estimate of the gluconeogenic rate, was not different between the groups (20.6 ± 2.8 and 21.2 ± 1.8 μmol · 100 g liver−1· min−1in NP and P, respectively), indicating that the increment in net hepatic glucose output resulted from an increase in the contribution of glycogenolytically derived glucose. However, total glycogenolysis was not altered in pregnancy. Ketogenesis was enhanced nearly threefold by pregnancy (6.9 ± 1.2 and 18.2 ± 3.4 μmol · 100 g liver−1· min−1in NP and P, respectively), despite equivalent net hepatic nonesterified fatty acid uptake. Thus late pregnancy in the dog is not accompanied by changes in the absolute rates of gluconeogenesis or glycogenolysis. Rather, repartitioning of the glucose released from glycogen is responsible for the increase in hepatic glucose production.
Induction of GLUT-1 protein in adult human skeletal muscle fibers
Authors: Gaster M. , Franch J. , Staehr P. , Beck-Nielsen H. , Smith T. , Schrøder H. D.
Published: December 2017

Prompted by our recent observations that GLUT-1 is expressed in fetal muscles, but not in adult muscle fibers, we decided to investigate whether GLUT-1 expression could be reactivated. We studied different stimuli concerning their ability to induce GLUT-1 expression in mature human skeletal muscle fibers. Metabolic stress (obesity, non-insulin-dependent diabetes mellitus), contractile activity (training), and conditions of de- and reinnervation (amyotrophic lateral sclerosis) could not induce GLUT-1 expression in human muscle fibers. However, regenerating muscle fibers in polymyositis expressed GLUT-1. In contrast to GLUT-1, GLUT-4 was expressed in all investigated muscle fibers. Although the significance of GLUT-1 in adult human muscle fibers appears limited, GLUT-1 may be of importance for the glucose supplies in immature and regenerating muscle.
Muscle glycogen content affects insulin-stimulated glucose transport and protein kinase B activity
Authors: Derave W. , Hansen B. F. , Lund S. , Kristiansen S. , Richter E. A.
Published: December 2017

We investigated the possible regulatory role of glycogen in insulin-stimulated glucose transport and insulin signaling in skeletal muscle. Rats were preconditioned to obtain low (LG), normal, or high (HG) muscle glycogen content, and perfused isolated hindlimbs were exposed to 0, 100, or 10,000 μU/ml insulin. In the fast-twitch white gastrocnemius, insulin-stimulated glucose transport was significantly higher in LG compared with HG. This difference was less pronounced in the mixed-fiber red gastrocnemius and was absent in the slow-twitch soleus. In the white gastrocnemius, insulin activation of insulin receptor tyrosine kinase and phosphoinositide 3-kinase was unaffected by glycogen levels, whereas protein kinase B activity was significantly higher in LG compared with HG. In additional incubation experiments on fast-twitch epitrochlearis muscles, insulin-stimulated cell surface GLUT-4 content was significantly higher in LG compared with HG. The data indicate that, in fast-twitch muscle, the effect of insulin on glucose transport and cell surface GLUT-4 content is modulated by glycogen content, which does not involve initial but possibly more downstream signaling events.
A new method for the study of chylomicron kinetics in vivo
Authors: Park Yongsoon , Grellner Wayne J. , Harris William S. , Miles John M.
Published: December 2017

Our understanding of the metabolism of chylomicrons, the lipoprotein that transports dietary fat from the intestine to peripheral tissues, is incomplete. The present studies were conducted to determine whether a labeled intravenous lipid emulsion could be used to estimate chylomicron triglyceride (TG) rate of appearance (Ra) and thereby quantify the rate of intestinal fat absorption. After an overnight fast, healthy volunteers ( n = 6) sipped a3H-labeled drink over 6.5 h at a rate of 175 mg fat · kg−1· h−1. Beginning at hour 5, an HPLC-purified,14C-labeled lipid emulsion was infused intravenously for 90 min. During the study, plasma total and chylomicron TG concentrations increased from 100 ± 21 to 237 ± 40 mg/dl and from undetectable to steady-state levels of 35 ± 13 mg/dl, respectively. After a minor correction for VLDL contamination, tracer-determined chylomicron TG Rawas 175 ± 30 mg · kg−1· h−1, equal to the presumed ingestion rate. In summary, a radiolabeled intravenous lipid emulsion is able to accurately estimate chylomicron TG Raand therefore can be used to measure in vivo fat absorption rates.
Dehydration-induced vasopressin secretion in humans: involvement of the histaminergic system
Authors: Kjær Andreas , Knigge Ulrich , Jørgensen Henrik , Warberg Jørgen
Published: December 2017

In rats, the hypothalamic neurotransmitter histamine participates in regulation of vasopressin secretion and seems to be of physiological importance, because blockade of the histaminergic system reduces dehydration-induced vasopressin secretion. We investigated whether histamine is also involved in regulation of vasopressin secretion during dehydration in humans. We found that 40 h of dehydration gradually increased plasma osmolality by 10 mosmol/kg and induced a fourfold increase in vasopressin levels. Pretreatment with the H2-receptor antagonists cimetidine or ranitidine significantly reduced the dehydration-induced increase in vasopressin levels ∼40% after 34 and 37 h of dehydration, whereas this was not the case with the H1-receptor antagonist mepyramine. Dehydration reduced aldosterone secretion by ∼50%. This effect of dehydration was reduced by both H1- and H2-receptor blockade after 16 and/or 34 h of dehydration. We conclude that vasopressin secretion in response to dehydration in humans is under the regulatory influence of histamine and that the effect seems to be mediated via H2-receptors. In addition, the regulation of aldosterone secretion during dehydration also seems to involve the histaminergic system via H1 and H2 receptors.
Direct effects of growth hormone on production and secretion of apolipoprotein B from rat hepatocytes
Authors: Lindén Daniel , Sjöberg Anders , Asp Lennart , Carlsson Linda , Oscarsson Jan
Published: December 2017

The aim of this study was to investigate the direct effects of growth hormone (GH) on production and secretion of apolipoprotein B (apoB)-containing lipoproteins from hepatocytes. Bovine GH (5–500 ng/ml) was given for 1 or 3 days to rat hepatocytes cultured on laminin-rich matrigel in serum-free medium. The effects of GH were compared with those of 3 nM insulin and 500 μM oleic acid. GH increased the editing of apoB mRNA, and the proportion of newly synthesized apoB-48 (of total apoB) in the cells and secreted into the medium changed in parallel. GH increased total secretion of apoB-48 (+30%) and apoB-48 in very low density lipoproteins (VLDL) more than twofold. Total apoB-100 secretion decreased 63%, but apoB-100-VLDL secretion was unaffected by GH. Pulse-chase studies indicated that GH increased intracellular early degradation of apoB-100 but not apoB-48. GH had no effect on apoB mRNA or LDL receptor mRNA levels. The triglyceride synthesis, the mass of triglycerides in the cells, and the VLDL fraction of the medium increased after GH incubation. Three days of insulin incubation had effects similar to those of GH. Combined incubation with oleic acid and GH had additive effects on apoB mRNA editing and apoB-48-VLDL secretion. In summary, GH has direct effects on production and secretion of apoB-containing lipoproteins, which may add to the effects of hyperinsulinemia and increased flux of fatty acids to the liver during GH treatment in vivo.
Ethanol stimulates glucose uptake and translocation of GLUT-4 in H9c2 myotubes via a Ca2+-dependent mechanism
Authors: Yu Bo , Schroeder Adrienne , Nagy Laura E.
Published: December 2017

Short-term exposure to ethanol impairs glucose homeostasis, but the effects of ethanol on individual components of the glucose disposal pathway are not known. To understand the mechanisms by which ethanol disrupts glucose homeostasis, we have investigated the direct effects of ethanol on glucose uptake and translocation of GLUT-4 in H9c2 myotubes. Short-term treatment with 12.5–50 mM ethanol increased uptake of 2-deoxyglucose by 1.8-fold in differentiated myotubes. Pretreatment of H9c2 myotubes with 100 nM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, had no effect on ethanol-induced increases in 2-deoxyglucose uptake. In contrast, preincubation with 25 μM dantrolene, an inhibitor of Ca2+release from the sarcoplasmic reticulum, blocked the stimulation of 2-deoxyglucose uptake by ethanol. Increased 2-deoxyglucose uptake after ethanol treatment was associated with a decrease in small intracellular GLUT-4 vesicles and an increase in GLUT-4 localized at the cell surface. In contrast, ethanol had no effect on the quantity of GLUT-1 and GLUT-3 at the plasma membrane. These data demonstrate that physiologically relevant concentrations of ethanol disrupt the trafficking of GLUT-4 in H9c2 myotubes resulting in translocation of GLUT-4 to the plasma membrane and increased glucose uptake.
Vitamin C suppresses oxidative lipid damage in vivo, even in the presence of iron overload
Authors: Chen Kent , Suh Jung , Carr Anitra C. , Morrow Jason D. , Zeind John , Frei Balz
Published: December 2017

Ascorbate is a strong antioxidant; however, it can also act as a prooxidant in vitro by reducing transition metals. To investigate the in vivo relevance of this prooxidant activity, we performed a study using guinea pigs fed high or low ascorbate doses with or without prior loading with iron dextran. Iron-loaded animals gained less weight and exhibited increased plasma β- N-acetyl-d-glucosaminidase activity, a marker of tissue lysosomal membrane damage, compared with control animals. The iron-loaded animals fed the low ascorbate dose had decreased plasma α-tocopherol levels and increased plasma levels of triglycerides and F2-isoprostanes, specific and sensitive markers of in vivo lipid peroxidation. In contrast, the two groups of animals fed the high ascorbate dose had significantly lower hepatic F2-isoprostane levels than the groups fed the low ascorbate dose, irrespective of iron load. These data indicate that 1) ascorbate acts as an antioxidant toward lipids in vivo , even in the presence of iron overload; 2) iron loading per se does not cause oxidative lipid damage but is associated with growth retardation and tissue damage, both of which are not affected by vitamin C; and 3) the combination of iron loading with a low ascorbate status causes additional pathophysiological changes, in particular, increased plasma triglycerides.
PACAP-(1–38) as neurotransmitter in the porcine adrenal glands
Authors: Tornøe Karen , Hannibal Jens , Jensen Tine Børglum , Georg Birgitte , Rickelt Lars Fledelius , Andreasen Malene Bolding , Fahrenkrug Jan , Holst Jens Juul
Published: December 2017

The concentration of pituitary adenylyl cyclase-activating polypeptide [PACAP-(1–38)] in porcine adrenal glands amounted to 14 ± 3 pmol/g tissue. PACAP immunoreactive (PACAP-IR) fibers innervated adrenal chromaffin cells (often co-localized with choline acetyltransferase). Subcapsular fibers traversed the cortex-innervating endocrine cells and blood vessels [some co-storing mainly calcitonin gene-related peptide but also vasoactive intestinal polypeptide (VIP)]. PACAP-IR fibers were demonstrated in the splanchnic nerves, whereas IR adrenal nerve cell bodies were absent. In isolated, vascularly perfused adrenal gland, splanchnic nerve stimulation (16 Hz) and capsaicin (10−5 M) increased PACAP-(1–38) release (1.6-fold and 6-fold respectively, P = 0.02). PACAP-(1–38) dose-dependently stimulated cortisol (2 × 10−10 M; 24-fold increase, P = 0.02) and chromogranin A fragment (2 × 10−9 M; 15-fold increase, P = 0.05) secretion. Both were strongly inhibited by the PAC1/VPAC2 receptor antagonist PACAP-(6–38) (10−7 M). PACAP-(6–38) also inhibited splanchnic nerve (10 Hz)-induced cortisol secretion but lacked any effect on splanchnic nerve-induced pancreastatin secretion. PACAP-(1–38) (2 × 10−10 M) decreased vascular resistance from 5.5 ± 0.6 to 4.6 ± 0.4 mmHg · min · ml−1. PACAP-(6–38) had no effect on this response. We conclude that PACAP-(1–38) may play a role in splanchnic nerve-induced adrenal secretion and in afferent reflex pathways.
Melatonin secretion occurs at a constant rate in both young and older men and women
Authors: Fourtillan J. B. , Brisson A. M. , Fourtillan M. , Ingrand I. , Decourt J. P. , Girault J.
Published: December 2017

The magnitude and duration of melatonin (MLT) secretion were measured over a period of 25 h with pharmacokinetic studies employing administration of D7MLT at midday and at midnight in two separate studies and two groups of subjects, 12 young and 11 older men and women. Plasma levels of endogenous MLT and D7MLT were quantified separately by use of a specific and sensitive method (gas chromatography-mass spectrometry) previously developed in our laboratory, enabling us to measure endogenous and exogenous MLT levels down to 0.5 pg/ml in plasma. In the two groups of subjects, MLT secretion occurred only at night: onset time of secretion was from 1915 to 2205 (Greenwich mean time), and offset was from 0305 to 0545. No MLT peak was observed in individual nocturnal MLT profiles that were similar to curves obtained for a rate-constant infusion. Modelization demonstrated the superimposition of observed data and simulated curves. MLT concentrations decreasing from the offset of secretion might correspond to the elimination of MLT present in the body at the end of nocturnal secretion. By use of the MLT clearance given by pharmacokinetics, the amount of secreted MLT was found to be 35.7 and 21.6 μg for men and women, respectively, and the rate of secretion was 4.6 and 2.8 μg/h, respectively. No significant gender difference was observed for these two parameters when normalized to body weight. No significant gender difference was observed for onset times of secretion or duration of secretion (7.6–8.6 h) within the two groups, or between young and older subjects.
Gluconeogenesis in moderately and severely hyperglycemic patients with type 2 diabetes mellitus
Authors: Boden Guenther , Chen Xinhua , Stein T. Peter
Published: December 2017

We tested the generally accepted concept that increased gluconeogenesis (GNG) and endogenous glucose production (EGP) are the main reasons for postabsorptive hyperglycemia in patients with type 2 diabetes mellitus (T2DM). GNG was measured with the 2H2O method by use of both the C5-to-C2 ratio (C5/C2, with gas chromatography-mass spectrometry) and the C5-to-2H2O ratio (C5/2H2O, with isotope ratio mass spectrometry), and EGP was measured with 3-[3H]glucose in 27 patients with T2DM [13 with fasting plasma glucose (FPG) >10 mM and 14 with FPG <10 mM] and in 7 weight- and age-matched nondiabetic controls. The results showed 1) that GNG could be determined accurately with 2H2O by using either C5/C2 or C5/2H2O; 2) that whereas after an overnight fast of 16 h, GNG was higher in the entire group of patients with T2DM than in controls (6.4 vs. 5.0 μmol · kg−1 · min−1 or 60.4 vs. 51.4% of EGP, P < 0.02), GNG was within normal limits (less than the mean ± 2 SD of controls or <65.3%) in 11/14 (79%) patients with mild to moderate hyperglycemia (FPG <10 mM) and in 5/13 (38%) of patients with severe hyperglycemia (FPG 10–20 mM); 3) that elevated GNG in T2DM was associated with a 43% decrease in prehepatic insulin secretion, i.e., with hepatic insulin deficiency; and 4) that FPG correlated significantly with glucose clearance (insulin resistance) ( r = 0.70) and with GNG ( r = 0.50) or EGP ( r = 0.45). We conclude 1) that peripheral insulin resistance is at least as important as GNG (and EGP) as a cause of postabsorptive hyperglycemia in T2DM and 2) that GNG and EGP in T2DM are increased under conditions of significant hepatic insulin deficiency and thus probably represent a late event in the course of T2DM.
The putative β4-adrenergic receptor is a novel state of the β1-adrenergic receptor
Authors: Granneman James G.
Published: December 2017

The atypical β3-adrenergic receptor (AR) agonist CGP-12177 has been used to define a novel atypical β-AR subtype, the putative β4-AR. Recent evaluation of recombinant β-AR subtypes and β-AR-deficient mice, however, has established the identity of the pharmacological β4-AR as a novel state of the β1-AR protein. The ability of aryloxypropanolamine ligands like CGP-12177 to independently interact with agonist and antagonist states of the β1-AR has important implications regarding receptor classification and the potential development of tissue-specific β-AR agonists.
DAG accumulation from saturated fatty acids desensitizes insulin stimulation of glucose uptake in muscle cells
Authors: Montell Eulàlia , Turini Marco , Marotta Mario , Roberts Matthew , Noé Véronique , Ciudad Carlos J. , Macé Katherine , Gómez-Foix Anna M.
Published: December 2017

The increased availability of saturated lipids has been correlated with development of insulin resistance, although the basis for this impairment is not defined. This work examined the interaction of saturated and unsaturated fatty acids (FA) with insulin stimulation of glucose uptake and its relation to the FA incorporation into different lipid pools in cultured human muscle. It is shown that basal or insulin-stimulated 2-deoxyglucose uptake was unaltered in cells preincubated with oleate, whereas basal glucose uptake was increased and insulin response was impaired in palmitate- and stearate-loaded cells. Analysis of the incorporation of FA into different lipid pools showed that palmitate, stearate, and oleate were similarly incorporated into phospholipids (PL) and did not modify the FA profile. In contrast, differences were observed in the total incorporation of FA into triacylglycerides (TAG): unsaturated FA were readily diverted toward TAG, whereas saturated FA could accumulate as diacylglycerol (DAG). Treatment with palmitate increased the activity of membrane-associated protein kinase C, whereas oleate had no effect. Mixture of palmitate with oleate diverted the saturated FA toward TAG and abolished its effect on glucose uptake. In conclusion, our data indicate that saturated FA-promoted changes in basal glucose uptake and insulin response were not correlated to a modification of the FA profile in PL or TAG accumulation. In contrast, these changes were related to saturated FA being accumulated as DAG and activating protein kinase C. Therefore, our results suggest that accumulation of DAG may be a molecular link between an increased availability of saturated FA and the induction of insulin resistance.