bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerobic metabolism of human quadriceps muscle: in vivo data parallel measurements on isolated mitochondria
Authors: Rasmussen Ulla F. , Rasmussen Hans N. , Krustrup Peter , Quistorff Bjørn , Saltin Bengt , Bangsbo Jens
Published: December 2017

The aim of the present study was to examine whether parameters of isolated mitochondria could account for the in vivo maximum oxygen uptake (V˙o 2 max) of human skeletal muscle.V˙o 2 max and work performance of the quadriceps muscle of six volunteers were measured in the knee extensor model (range 10–18 mmol O2 · min−1 · kg−1at work rates of 22–32 W/kg). Mitochondria were isolated from the same muscle at rest. Strong correlations were obtained betweenV˙o 2 max and a number of mitochondrial parameters (mitochondrial protein, cytochrome aa 3, citrate synthase, and respiratory activities). The activities of citrate synthase, succinate dehydrogenase, and pyruvate dehydrogenase, measured in isolated mitochondria, corresponded to, respectively, 15, 3, and 1.1 times the rates calculated from V˙o 2 max. The respiratory chain activity also appeared sufficient. Fully coupled in vitro respiration, which is limited by the rate of ATP synthesis, could account for, at most, 60% of theV˙o 2 max. This might be due to systematic errors or to loose coupling of the mitochondrial respiration under intense exercise.
The digestion rate of protein is an independent regulating factor of postprandial protein retention
Authors: Dangin Martial , Boirie Yves , Garcia-Rodenas Clara , Gachon Pierre , Fauquant Jacques , Callier Philippe , Ballèvre Olivier , Beaufrère Bernard
Published: December 2017

To evaluate the importance of protein digestion rate on protein deposition, we characterized leucine kinetics after ingestion of “protein” meals of identical amino acid composition and nitrogen contents but of different digestion rates. Four groups of five or six young men received anl-[1-13C]leucine infusion and one of the following 30-g protein meals: a single meal of slowly digested casein (CAS), a single meal of free amino acid mimicking casein composition (AA), a single meal of rapidly digested whey proteins (WP), or repeated meals of whey proteins (RPT-WP) mimicking slow digestion rate. Comparisons were made between “fast” (AA, WP) and “slow” (CAS, RPT-WP) meals of identical amino acid composition (AA vs. CAS, and WP vs. RPT-WP). The fast meals induced a strong, rapid, and transient increase of aminoacidemia, leucine flux, and oxidation. After slow meals, these parameters increased moderately but durably. Postprandial leucine balance over 7 h was higher after the slow than after the fast meals (CAS: 38 ± 13 vs. AA: −12 ± 11, P < 0.01; RPT-WP: 87 ± 25 vs. WP: 6 ± 19 μmol/kg, P< 0.05). Protein digestion rate is an independent factor modulating postprandial protein deposition.
Regulation of the leptin content of obese human adipose tissue
Authors: Russell C. D. , Ricci M. R. , Brolin R. E. , Magill E. , Fried S. K.
Published: December 2017

The objective of this study was to determine whether obese human adipose tissue contains preformed stores of leptin and their relationship to secreted leptin. Detergent increased detectable leptin by about twofold, suggesting that leptin is stored in a membrane-bound location. Subcutaneous tissue leptin was ∼1.6-fold higher than omental, paralleling known differences in leptin secretion and expression. The amount of leptin secreted during a 3-h incubation was similar to that of extractable tissue leptin. Tissue leptin levels were maintained over the incubation. Inhibition of protein synthesis decreased tissue leptin content but did not decrease leptin secretion until after 3 h of incubation. Culture of adipose tissue for 2 days with the combination of insulin and dexamethasone, but not with either hormone alone, increased tissue leptin content about twofold in both depots. Although insulin did not affect tissue leptin content, it potentiated leptin secretion (as a % of tissue stores). These data suggest that adipose tissue leptin storage and secretion per se are regulated. Regulation of the release of preformed leptin may modulate serum leptin levels in obese humans.
Local inhibition of nitric oxide temporarily stimulates aldosterone secretion in conscious sheep in vivo
Authors: Salemi Renato , McDougall John G. , Hardy Kenneth J. , Wintour E. Marelyn
Published: December 2017

The effect of localized blockage of endogenous nitric oxide (NO) on basal aldosterone secretion was studied in conscious sheep with autotransplanted adrenal glands. We have shown that infusion of the NO synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME; 130 μg/l blood flow) significantly stimulated basal aldosterone secretion rate (ASR). This stimulatory effect was seen up to 4 h of infusion. Beyond this time point, however, the elevated ASR level was not sustained, and it was seen to drop markedly to lower than control values at 5 h. l-NAME had no effect on cortisol secretion rate (FSR) during the first 4 h of infusion, but a significant reduction in FSR was seen by the 8-h time point. Adrenal blood flow was consistently decreased in association with long l-NAME infusion. Additionally, l-NAME was shown to have no effect on aldosterone secretion when infused systemically. We conclude that the relationship between NO and aldosterone secretion is an inhibitory one, in which NO seems to have a negative effect on basal aldosterone secretion.
Acetylcholine increases intracellular Ca2+in the rat pituitary folliculostellate cells in primary culture
Authors: Nakajima Yusaku , Uchiyama Maki , Shirai Yasumasa , Sakuma Yasuo , Kato Masakatsu
Published: December 2017

Pituitary folliculostellate cells (FSCs) are thought to partially inhibit pituitary hormone secretion through a paracrine mechanism. In this process, one of the important questions is what factors regulate the function of FSCs. Because ACh is synthesized in and possibly released from the corticotrophs and lactotrophs, we examined whether FSCs respond to ACh by the method of Ca2+imaging in primary cultured FSCs from male Wistar rats. ACh (30 nM-3 μM) increased intracellular calcium concentration ([Ca2+]i) of FSCs in a concentration-dependent manner, with an initial rapid rise followed by a relatively sustained increase. The complete block of the response by atropine and pirenzepine suggests involvement of muscarinic receptors. Depletion of the stored Ca2+by thapsigargin blocked the response completely. Blockers of phospholipase C, U-73122 and neomycin, suppressed significantly the rise of [Ca2+]i. These results suggest that ACh increases [Ca2+]iin FSCs by activating phospholipase C, presumably through activation of M1receptors. The rise in [Ca2+]icould trigger a variety of Ca2+-dependent cellular processes, including the synthesis and release of bioactive substances, which in turn act on endocrine cells.
Cortisol and GH secretory dynamics, and their interrelationships, in healthy aged women and men
Authors: Gusenoff Jeffrey A. , Harman S. Mitchell , Veldhuis Johannes D. , Jayme Jocelyn J. , St. Clair Carol , Münzer Thomas , Christmas Colleen , O'Connor Kieran G. , Stevens Thomas E. , Bellantoni Michele F. , Pabst Katherine , Blackman Marc R.
Published: December 2017

We studied 130 healthy aged women (n = 57) and men (n = 73), age 65–88 yr, with age-related reductions in insulin-like growth factor I and gonadal steroid levels to assess the interrelationships between cortisol and growth hormone (GH) secretion and whether these relationships differ by sex. Blood was sampled every 20 min from 8:00 PM to 8:00 AM; cortisol was measured by RIA and GH by immunoradiometric assay, followed by deconvolution analyses of hormone secretory parameters and assessment of approximate entropy (ApEn) and cross-ApEn. Cortisol mass/burst, cortisol production rate, and mean and integrated serum cortisol concentrations (P < 0.0005), and overnight basal GH secretion (P < 0.05), were elevated in women vs. men. Integrated cortisol concentrations were directly related to most measures of GH secretion in women (P < 0.01) and with mean and integrated GH concentrations in men (P < 0.05). Integrated GH concentrations were directly related to mean and integrated cortisol levels in women (P < 0.005) and men (P < 0.05), with no sex differences. There were no sex differences in cortisol or GH ApEn values; however, the cross-ApEn score was greater in women (P < 0.05), indicating reduced GH-cortisol pattern synchrony in aged women vs. men. There were no significant relationships of integrated cortisol secretion with GH ApEn, or vice versa, in either sex. Thus postmenopausal women appear to maintain elevated cortisol production in patterns that are relatively uncoupled from those of GH, whereas mean hormone outputs remain correlated.
Cysteine regulates expression of cysteine dioxygenase and γ-glutamylcysteine synthetase in cultured rat hepatocytes
Authors: Kwon Young Hye , Stipanuk Martha H.
Published: December 2017

Rat hepatocytes cultured for 3 days in basal medium expressed low levels of cysteine dioxygenase (CDO) and high levels of γ-glutamylcysteine synthetase (GCS). When the medium was supplemented with 2 mmol/l methionine or cysteine, CDO activity and CDO protein increased by >10-fold and CDO mRNA increased by 1.5- or 3.2-fold. In contrast, GCS activity decreased to 51 or 29% of basal, GCS heavy subunit (GCS-HS) protein decreased to 89 or 58% of basal, and GCS mRNA decreased to 79 or 37% of basal for methionine or cysteine supplementation, respectively. Supplementation with cysteine consistently yielded responses of greater magnitude than did supplementation with an equimolar amount of methionine. Addition of propargylglycine to inhibit cystathionine γ-lyase activity and, hence, cysteine formation from methionine prevented the effects of methionine, but not those of cysteine, on CDO and GCS expression. Addition of buthionine sulfoximine to inhibit GCS, and thus block glutathione synthesis from cysteine, did not alter the ability of methionine or cysteine to increase CDO. GSH concentration was not correlated with changes in either CDO or GCS-HS expression. The effectiveness of cysteine was equivalent to or greater than that of its precursors ( S-adenosylmethionine, cystathionine, homocysteine) or metabolites (taurine, sulfate). Taken together, these results suggest that cysteine itself is an important cellular signal for upregulation of CDO and downregulation of GCS.
Effects of antecedent prolonged exercise on subsequent counterregulatory responses to hypoglycemia
Authors: Galassetti Pietro , Mann Stephnie , Tate Donna , Neill Ray A. , Costa Fernando , Wasserman David H. , Davis Stephen N.
Published: December 2017

In the present study the hypothesis tested was that prior exercise may blunt counterregulatory responses to subsequent hypoglycemia. Healthy subjects [15 females (f)/15 males (m), age 27 ± 1 yr, body mass index 22 ± 1 kg/m2, hemoglobin AIc5.6 ± 0.5%] were studied during 2-day experiments. Day 1 involved either 90-min morning and afternoon cycle exercise at 50% maximal O2uptake (V˙o2 max) (priorEXE, n = 16, 8 m/8 f) or equivalent rest periods (priorREST, n = 14, 7 m/7 f). Day 2 consisted of a 2-h hypoglycemic clamp in all subjects. Endogenous glucose production (EGP) was measured using [3-3H]glucose. Muscle sympathetic nerve activity (MSNA) was measured using microneurography. Day 2 insulin (87 ± 6 μU/ml) and plasma glucose levels (54 ± 2 mg/dl) were equivalent after priorEXE and priorREST. Significant blunting ( P < 0.01) of day 2 norepinephrine (−30 ± 4%), epinephrine (−37 ± 6%), glucagon (−60 ± 4%), growth hormone (−61 ± 5%), pancreatic polypeptide (−47 ± 4%), and MSNA (−90 ± 8%) responses to hypoglycemia occurred after priorEXE vs. priorREST. EGP during day 2 hypoglycemia was also suppressed significantly ( P < 0.01) after priorEXE compared with priorREST. In summary, two bouts of exercise (90 min at 50%V˙o2 max) significantly reduced glucagon, catecholamines, growth hormone, pancreatic polypeptide, and EGP responses to subsequent hypoglycemia. We conclude that, in normal humans, antecedent prolonged moderate exercise blunts neuroendocrine and metabolic counterregulatory responses to subsequent hypoglycemia.
Exendin-4 reduces fasting and postprandial glucose and decreases energy intake in healthy volunteers
Authors: Edwards C. Mark B. , Stanley Sarah A. , Davis Rachel , Brynes Audrey E. , Frost Gary S. , Seal Leighton J. , Ghatei Mohammad A. , Bloom Stephen R.
Published: December 2017

Exendin-4 is a long-acting potent agonist of the glucagon-like peptide 1 (GLP-1) receptor and may be useful in the treatment of type 2 diabetes and obesity. We examined the effects of an intravenous infusion of exendin-4 (0.05 pmol · kg−1· min−1) compared with a control saline infusion in healthy volunteers. Exendin-4 reduced fasting plasma glucose levels and reduced the peak change of postprandial glucose from baseline (exendin-4, 1.5 ± 0.3 vs. saline, 2.2 ± 0.3 mmol/l, P < 0.05). Gastric emptying was delayed, as measured by the paracetamol absorption method. Volunteers consumed 19% fewer calories at a free-choice buffet lunch with exendin-4 (exendin-4, 867 ± 79 vs. saline 1,075 ± 93 kcal, P = 0.012), without reported side effects. Thus our results are in accord with the possibility that exendin-4 may be a potential treatment for type 2 diabetes, particularly for obese patients, because it acts to reduce plasma glucose at least partly by a delay in gastric emptying, as well as by reducing calorie intake.
Interrelationship between signal transduction pathways and 1,25(OH)2D3in UMR106 osteoblastic cells
Authors: Yang Wen , Hyllner Sven Johan , Christakos Sylvia
Published: December 2017

In this study, the interrelationship between signal transduction pathways and 1,25-dihydroxyvitamin D3[1,25(OH)2D3] action was examined in UMR106 osteoblastic cells. Treatment of these cells with 8-bromo-cAMP (1 mM) resulted in an upregulation of the vitamin D receptor (VDR) and an augmentation in the induction by 1,25(OH)2D3of 25(OH)D324-hydroxylase [24(OH)ase] and osteopontin (OPN) mRNAs as well as gene transcription. Transfection with constructs containing the vitamin D response element devoid of other promoter regulatory elements did not alter the cAMP-mediated potentiation, suggesting that cAMP-enhanced transcription is due, at least in part, to upregulation of VDR. Treatment with phorbol ester [12- O-tetradecanoyl-phorbol-13-acetate (TPA) 100 nM], an activator of protein kinase C, significantly enhanced 1,25(OH)2D3-induced OPN mRNA and transcription but had no effect on VDR or on 24(OH)ase mRNA or transcription. Studies using OPN promoter constructs indicate that TPA-enhanced OPN transcription is mediated by an effect on the OPN promoter separate from an effect on VDR. Thus interactions with signal transduction pathways can enhance 1,25(OH)2D3induction of 24(OH)ase and OPN gene expression, and, through different mechanisms, changes in cellular phosphorylation may play a significant role in determining the effectiveness of 1,25(OH)2D3on transcriptional control in cells expressing skeletal phenotypic properties.
Prevention of skeletal muscle insulin resistance by dietary cod protein in high fat-fed rats
Authors: Lavigne Charles , Tremblay Frédéric , Asselin Geneviève , Jacques Hélène , Marette André
Published: December 2017

In the present study, we tested the hypothesis that fish protein may represent a key constituent of fish with glucoregulatory activity. Three groups of rats were fed a high-fat diet in which the protein source was casein, fish (cod) protein, or soy protein; these groups were compared with a group of chow-fed controls. High-fat feeding led to severe whole body and skeletal muscle insulin resistance in casein- or soy protein-fed rats, as assessed by the euglycemic clamp technique coupled with measurements of 2-deoxy-d-[3H]glucose uptake rates by individual tissues. However, feeding cod protein fully prevented the development of insulin resistance in high fat-fed rats. These animals exhibited higher rates of insulin-mediated muscle glucose disposal that were comparable to those of chow-fed rats. The beneficial effects of cod protein occurred without any reductions in body weight gain, adipose tissue accretion, or expression of tumor necrosis factor-α in fat and muscle. Moreover, L6 myocytes exposed to cod protein-derived amino acids showed greater rates of insulin-stimulated glucose uptake compared with cells incubated with casein- or soy protein-derived amino acids. These data demonstrate that feeding cod protein prevents obesity-induced muscle insulin resistance in high fat-fed obese rats at least in part through a direct action of amino acids on insulin-stimulated glucose uptake in skeletal muscle cells.
Energy nutrients modulate the splanchnic sequestration of dietary nitrogen in humans: a compartmental analysis
Authors: Fouillet H. , Gaudichon C. , Mariotti F. , Bos C. , Huneau J. F. , Tomé D.
Published: December 2017

We used a previously developed compartmental model to assess the postprandial distribution and metabolism of dietary nitrogen (N) in the splanchnic and peripheral areas after the ingestion of a single meal containing milk protein either alone (MP) or with additional sucrose (SMP) or fat (FMP). The addition of fat was predicted to enhance splanchnic dietary N anabolism only transiently, without significantly affecting the global kinetics of splanchnic retention and peripheral uptake. In contrast, the addition of sucrose, which induced hyperinsulinemia, was predicted to enhance dietary N retention and anabolism in the splanchnic bed, thus leading to reduced peripheral dietary amino acid availability and anabolism. The incorporation of dietary N into splanchnic proteins was thus predicted to reach 18, 24, and 35% of ingested N 8 h after MP, FMP, and SMP, respectively. Such a model provides insight into the dynamics of the system in the nonsteady postprandial state and constitutes a useful, explanatory tool to determine the region-specific utilization of dietary N under different nutritional conditions.
Destabilization of TNF-α mRNA by retinoic acid in hepatic macrophages: implications for alcoholic liver disease
Authors: Motomura Kenta , Ohata Mitsuru , Satre Michael , Tsukamoto Hidekazu
Published: December 2017

Retinoic acid (RA) inhibits hepatic macrophage (HM) cytokine expression, and retinoids are depleted in alcoholic liver disease (ALD). However, neither the causal link between the two nor the mechanism underlying RA-mediated HM inhibition is known. The aim of the present study was to determine the mechanism of RA-induced inhibition of HM tumor necrosis factor (TNF)-α expression and the relevance of this regulation to ALD. Treatment with all- trans RA (500 nM) caused a 50% inhibition in lipopolysaccharide (LPS)-stimulated TNF-α expression by cultured normal rat HM. The mRNA levels for inducible nitric oxide synthase, interleukin (IL)-6, IL-1α, and IL-1β were also reduced, whereas those for transforming growth factor-β1, MMP-9, and membrane cofactor protein-1 were unaffected. The inhibitory effect on TNF-α expression was reproduced by LG268, a retinoid X receptor (RXR)-specific ligand, but not by TTNPB, an RA receptor (RAR)-specific ligand. RA did not alter LPS-stimulated NF-kB and activation protein-1 binding but significantly decreased TNF-α mRNA stability in HM. HM isolated from the ALD model showed significant decreases in all- trans RA (−48%) and 9- cis RA (−61%) contents, RA response element (RARE) binding, and mRNA levels for RARβ, RXRα, and cytosolic retinol binding protein-1, whereas TNF-α mRNA expression was induced. TNF-α mRNA stability was increased in these cells, and an ex vivo treatment with all- trans RA normalized both RARβ and TNF-α mRNA levels. These results demonstrate the RA-induced destabilization of TNF-α mRNA by cultured HM and the association of RA depletion with increased TNF-α mRNA stability in HM from experimental ALD. These findings suggest that RA depletion primes HM for proinflammatory cytokine expression in ALD, at least in part, via posttranscriptional regulation.
Effects of vitamin D receptor inactivation on the expression of calbindins and calcium metabolism
Authors: Li Yan Chun , Bolt Merry J. G. , Cao Li-Ping , Sitrin Michael D.
Published: December 2017

Hypocalcemia, rickets, and osteomalacia are major phenotypic abnormalities in vitamin D receptor (VDR)-null mice. In an attempt to understand the abnormal regulation of calcium metabolism in these animals, we examined the expression of calbindins (CaBP) as well as calcium handling in the intestine and kidney of VDR null mice. In adult VDR-null mice, intestinal and renal CaBP-D9k expression was reduced by 50 and 90%, respectively, at both the mRNA and protein levels compared with wild-type littermates, whereas renal CaBP-D28k expression was not significantly changed. Intestinal calcium absorption was measured by the rate of45Ca disappearance from the intestine after an oral dose of the isotope.45Ca absorption was similar in VDR-null and wild-type mice, but the amount of45Ca accumulated in the serum and bone was 3–4 times higher in wild-type mice than in VDR-null mice. Despite the hypocalcemia, the urinary excretion of calcium in VDR-null mice was not different from that in wild-type mice. Moreover, 1 wk of a high-calcium diet treatment that normalized the serum ionized calcium level of VDR-null mice increased the urinary calcium level of these mutant mice to twofold higher than that of wild-type mice on the same diet, suggesting impaired renal calcium conservation in VDR-null mice. These data demonstrate that renal CaBP-D9k, but not CaBP-D28k, is highly regulated by the VDR-mediated action of 1,25-dihydroxyvitamin D3. Furthermore, the results also suggest that impaired calcium conservation in the kidney may be the most important factor contributing to the development of hypocalcemia in VDR-null mice, and CaBP-D9k may be an important mediator of calcium reabsorption in the kidney.
Tissue-specific and isoform-specific changes in MCT1 and MCT4 in heart and soleus muscle during a 1-yr period
Authors: Hatta Hideo , Tonouchi Mio , Miskovic Dragana , Wang Yuxiang , Heikkila John J. , Bonen Arend
Published: December 2017

We examined the postnatal changes ( days 10, 36, 84, 160, 365) of monocarboxylate transporters (MCT)1 and MCT4 in rat heart and soleus muscle. In the heart, MCT1 protein and mRNA remained unaltered from day 10 until 1 yr of age. Both MCT4 protein and mRNA in the heart were detected at 10 days of age, but the MCT4 protein and transcript were not detected thereafter. In the soleus muscle, MCT1 protein (+38%) and mRNA (+136%) increased during the first 84 days and remained stable until 1 yr of age. In contrast, soleus MCT4 protein decreased by 90% over the course of 1 yr, with the most rapid decrease (−60%) occurring by day 84 ( P < 0.05). At the same time, MCT4 mRNA was increased by 74% from days 10to 84 ( P < 0.05), remaining stable thereafter. In conclusion, developmental changes in MCT transport proteins are tissue specific and isoform specific. Furthermore, it appears that MCT1 expression in the heart and MCT1 and MCT4 expression in the soleus are regulated by pretranslational processes, whereas posttranscriptional processes regulate MCT4 expression in the soleus muscle.
Thyroid hormone induces cerebellar astrocytes and C6 glioma cells to secrete mitogenic growth factors
Authors: Trentin A. G. , Alvarez-Silva M. , Moura Neto V.
Published: December 2017

In this study, the effect of thyroid hormone (triiodothyronine, T3) on the secretion of mitogenic growth factors in astrocytes and C6 glioma cells was examined. The proliferating activity of T3could be due, at least in part, to the astrocyte secretion of acidic and basic fibroblast growth factor (aFGF and bFGF), tumor necrosis factor-β, and transforming growth factor-β. In contrast, the conditioned medium (CM) of T3-treated C6 cells was mitogenic to this cell line only after hyaluronidase digestion, suggesting the impairment of growth factor mitogenic activity by hyaluronic acid. Furthermore, the presence of bFGF was significantly greater in the CM of both T3-treated astrocytes and T3-treated C6 cells than in the corresponding control CM. These data show that T3induces cerebellar astrocytes to secrete mitogenic growth factors, predominantly bFGF, that could influence astrocyte and neuronal proliferation via autocrine and paracrine pathways.
Methylation demand and homocysteine metabolism: effects of dietary provision of creatine and guanidinoacetate
Authors: Stead Lori M. , Au Keegan P. , Jacobs René L. , Brosnan Margaret E. , Brosnan John T.
Published: December 2017

S-adenosylmethionine, formed by the adenylation of methionine via S-adenosylmethionine synthase, is the methyl donor in virtually all known biological methylations. These methylation reactions produce a methylated substrate and S-adenosylhomocysteine, which is subsequently metabolized to homocysteine. The methylation of guanidinoacetate to form creatine consumes more methyl groups than all other methylation reactions combined. Therefore, we examined the effects of increased or decreased methyl demand by these physiological substrates on plasma homocysteine by feeding rats guanidinoacetate- or creatine-supplemented diets for 2 wk. Plasma homocysteine was significantly increased (∼50%) in rats maintained on guanidinoacetate-supplemented diets, whereas rats maintained on creatine-supplemented diets exhibited a significantly lower (∼25%) plasma homocysteine level. Plasma creatine and muscle total creatine were significantly increased in rats fed the creatine-supplemented or guanidinoacetate-supplemented diets. The activity of kidney l-arginine:glycine amidinotransferase, the enzyme catalyzing the synthesis of guanidinoacetate, was significantly decreased in both supplementation groups. To examine the role of the liver in mediating these changes in plasma homocysteine, isolated rat hepatocytes were incubated with methionine in the presence and absence of guanidinoacetate and creatine, and homocysteine export was measured. Homocysteine export was significantly increased in the presence of guanidinoacetate. Creatine, however, was without effect. These results suggest that homocysteine metabolism is sensitive to methylation demand imposed by physiological substrates.
Inverse relationship between peripheral insulin removal and action: studies with metformin
Authors: Zhang Z. , Radziuk J.
Published: December 2017

The interaction of insulin with metformin on muscle glucose metabolism was examined in the perfused rat hindquarter. Glucose, lactate, and insulin were measured at the inflow to and outflow from the hindquarter, which was perfused with human erythrocytes suspended in a Kreb's-Ringer albumin buffer for 120 min. Perfusions were performed with no additions (I) and with insulin infusions targeted to concentrations of 175 (II) and 350 pmol/l (III) as well as infusions targeted to levels of 0 (IV), 70 (V), and 175 pmol/l (VI) but in the presence of metformin (90 μg/ml). In the presence of metformin, identical infusion rates of insulin yielded higher insulin concentrations, namely 283 ± 19 vs. 202 ± 31 pmol/l for VI and II, respectively ( P < 0.05). Glucose uptake (GU) increased correspondingly to 79.8 ± 0.8 in VI from 60.8 ± 2.1 for IV and 50.1 ± 1.3 for II and 46.1 ± 2.7 mg/120 min for I ( P < 0.05). This enhanced GU was matched by increasing insulin levels using only a higher rate of its infusion (III): GU of 70.2 ± 2.4 mg/120 min with insulin of 334 ± 26 pmol/l ( P > 0.05). The simple concurrent presence of metformin and insulin [matching insulin concentrations in II rather than infusion rates (IV)] demonstrated no additonal effect on GU above that of metformin. The synergistic effects of metformin and insulin could thus be explained by a metformin-mediated decrease in the extraction of insulin by the hindquarter (4.8 ± 0.4% vs. 8.6 ± 0.9%, P< 0.05). This increases interstitial insulin (and, in a closed system, perfusate insulin), which acts on cell surface receptors to increase glucose uptake. The results demonstrate that the extracellular insulin concentration, rather than insulin internalization and degradation, is the primary determinant of insulin action on GU in muscle and that changes in tissue insulin extraction may alter local concentrations and, therefore, systemic insulin sensitivity. This provides both a physiological mechanism and a possible therapeutic target for improving insulin sensitivity.
Evidence against high glucose as a mediator of ERK1/2 or p38 MAPK phosphorylation in rat skeletal muscle
Authors: Kawano Yuichi , Ryder Jeffrey W. , Rincon Jorge , Zierath Juleen R. , Krook Anna , Wallberg-Henriksson Harriet
Published: December 2017

Hyperglycemia leads to multiple changes in insulin signaling in skeletal muscle from people with type 2 diabetes. We hypothesized that mitogen-activated protein kinase (MAPK) signaling cascades may be directly activated by an acute exposure to high extracellular glucose concentrations. We determined whether an elevation in the extracellular glucose concentration would induce signal transduction in skeletal muscle via MAPK cascades. Epitrochlearis muscles were incubated in the presence of 5 or 25 mM glucose. Exposure of muscle to either hyperosmosis (600 mM mannitol) or insulin (6 nM) led to a marked increase in extracellular signal-regulated protein kinase (ERK)1/2 phosphorylation. Hyperosmosis elicited a 5.2-fold increase in p38 phosphorylation ( P < 0.05), whereas insulin was without effect. ERK1/2 phosphorylation was not increased by high glucose exposure. After a 20-min exposure to 25 mM glucose, a tendency toward repressed (23%) p38 phosphorylation was observed ( P = 0.06). No effect of high glucose was noted on signal transduction to signal transducer and activator of transcription 3 and Akt. In conclusion, short-term exposure of skeletal muscle to high levels of glucose does not appear to alter ERK1/2 or p38 MAPK phosphorylation.
Effects of growth hormone on renal tubular handling of sodium in healthy humans
Authors: Hansen Troels Krarup , Møller Jens , Thomsen Klaus , Frandsen Erik , Dall Rolf , Jørgensen Jens Otto , Christiansen Jens Sandahl
Published: December 2017

To investigate the mechanisms behind the water- and sodium-retaining effects of growth hormone (GH), we studied the effect of GH on 1) water and sodium homeostasis, 2) the renin-angiotensin-aldosterone system (RAAS), and 3) lithium clearance (CLi) with and without concomitant prostaglandin (PG) synthesis inhibition with ibuprofen. GH administration for 6 days induced a significant increase in plasma renin, which was abolished by coadministration of ibuprofen (mU · l−1 · 24 h−1: control: 22.4 ± 4.3; GH: 37.7 ± 8.8; ibuprofen: 15.2 ± 3.0; GH + ibuprofen: 19.7 ± 2.5; ANOVA: P < 0.01). Comparable increments in extracellular volume were seen after 6-day treatment with GH alone and in combination with ibuprofen [liters: control, 19.57 ± 0.92; GH, 20.80 ± 1.00 (ANOVA: P< 0.0005); ibuprofen, 19.38 ± 0.90; GH + ibuprofen, 21.63 ± 1.37 (ANOVA: P < 0.0005)]. Treatment with GH increased CLi and changed the tubular handling of sodium and water. The absolute distal sodium reabsorption was increased, and this was only partially counterbalanced by decreased reabsorption in the proximal tubules. The data demonstrate that GH-induced activation of the RAAS can be blocked by concomitant PG synthesis inhibition and that the tubular effects of GH include increased distal nephron sodium and water reabsorption.
Body-size dependence of resting energy expenditure can be attributed to nonenergetic homogeneity of fat-free mass
Authors: Heymsfield Steven B. , Gallagher Dympna , Kotler Donald P. , Wang Zimian , Allison David B. , Heshka Stanley
Published: December 2017

An enduring enigma is why the ratio of resting energy expenditure (REE) to metabolically active tissue mass, expressed as the REE/fat-free mass (FFM) ratio, is greater in magnitude in subjects with a small FFM than it is in subjects with a large FFM. This study tested the hypothesis that a higher REE/FFM ratio in subjects with a small body mass and FFM can be explained by a larger proportion of FFM as high-metabolic-rate tissues compared with that observed in heavier subjects. REE was measured by indirect calorimetry, FFM by dual-energy X-ray absorptiometry (DEXA), and tissue/organ contributions to FFM by whole body magnetic resonance imaging (MRI) in healthy adults. Four tissue heat-producing contributions to FFM were evaluated, low-metabolic-rate fat-free adipose tissue (18.8 kJ/kg), skeletal muscle (54.4 kJ/kg), and bone (9.6 kJ/kg); and high-metabolic-rate residual mass (225.9 kJ/kg). Initial evaluations in 130 men and 159 women provided strong support for two key, developed models, one linking DEXA FFM with MRI FFM estimates and the other linking REE predicted from the four MRI-derived components with measured REE. There was an inverse association observed between measured REE/FFM and FFM ( r2= 0.17, P < 0.001). Allometric models revealed a similar pattern of tissue change relative to body mass across males and females with greater proportional increases in fat-free adipose tissue and skeletal muscle than in FFM and a smaller proportional increase in residual mass than in FFM. When examined as a function of FFM, positive slopes were observed for skeletal muscle/FFM and pooled low-metabolic-rate components, and a negative slope for residual mass. Our linked REE-body composition models and associations strongly support the hypothesis that FFM varies systematically in the proportion of thermogenic components as a function of body mass and FFM. These observations have important implications for the interpretation of between-individual differences in REE expressed relative to metabolically active tissue mass.
NOS expression is increased in endothelial cells exposed to plasma from women with preeclampsia
Authors: Davidge S. T. , Baker P. N. , Roberts J. M.
Published: December 2017

Endothelial cell function is proposed to be altered by a factor(s) in the maternal circulation of women with the pregnancy disorder preeclampsia. Our initial hypothesis was that in preeclampsia, such factor(s) would reduce synthesis of nitric oxide (NO) by endothelial cells. However, we previously observed increased NO synthase activity in endothelial cells exposed to plasma from preeclamptic women. This study tested whether exposing cells to plasma from preeclamptic women increased transcription and/or translation of endothelial NO synthase. Cultured bovine coronary microvascular endothelial cells were exposed to 2% plasma from patients with preeclampsia and patients with uncomplicated pregnancies. Nitrite production was greater in endothelial cells exposed to plasma from preeclamptic women (8.97 +/- 0.54 vs. 6.39 +/- 0.59 nmol nitrites.10(6) cells-1 x 24 h-1; P < 0.05). Similarly, endothelial NO synthase mass as measured by Western immunoblotting was significantly increased (20,980 +/- 1,406 vs. 15,047 +/- 1,003 absorbancy units; P < 0.02). There was no detectable difference in mRNA for endothelial NO synthase. However, actinomycin (3 micrograms/ml), a transcription inhibitor, significantly decreased nitrite production only in cells exposed to plasma from preeclamptic women (5.28 +/- 0.52 vs. 3.56 +/- 0.36 nmol.10(6) cells-1 x 24 h-1, P < 0.05). These findings indicate a regulation of the "constitutive" isoform of NO synthase by factor(s) in the blood of preeclamptic women, which may have significance in this pathological condition of pregnancy.
Double-exponential curve fitting of isometric relaxation: a new measure for myocardial lusitropism
Authors: Tamiya Kouichi , Beppu Toshiyuki , Ishihara Kazuaki
Published: December 2017

Pages H393–H406: Kouichi Tamiya, Toshiyuki Beppu, and Kazuaki Ishihara. “Double-exponential curve fitting of isometric relaxation: a new measure for myocardial lusitropism.” Page H402: Figure 10 should appear as the following.

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High muscle blood flows are not attenuated by recruitment of additional muscle mass
Authors: Richardson R. S. , Kennedy B. , Knight D. R. , Wagner P. D.
Published: December 2017

Recent studies have demonstrated that single-leg knee extensor (KE) exercise elicits high mass-specific blood flow (Q) which, if incremented toward maximum, in the presence of additional muscle recruitment would soon outstrip the heart's pumping capacity and blood pressure would fall. Thus incremental KE exercise provides the opportunity to determine the intensity at which, if at all, quadriceps muscle hemodynamics are altered during incremental exercise that involves a substantially greater muscle mass. Leg Q was measured during incremental KE exercise and again with superimposed incremental two-legged knee extensor exercise with incremental arm cranking (A+L) in trained subjects (n = 5). Leg Q and vascular conductance (VC) increased with work rate (WR) to reach high levels [Q = 385.7 +/- 26 and 342.3 +/- 15 ml.min-1.100 g-1 for KE and A+L exercise, respectively; VC at 90% of maximum WR (WRmax) = 79 +/- 5 and 75 +/- 6 ml.min-1. mmHg-1 for KE and A+L exercise, respectively], but the Q/WR and VC/WR relationships in KE and A+L exercise were not different. Maximum O2 consumption (VO2max) and the VO2max/WR relationship of the quadriceps were also unaffected by the additional muscle mass recruited. Despite a significantly greater net femoral venous norepinephrine (NE) outflow at both 90 and 100% of WRmax in A+L exercise (WRmax = 4,216 +/- 1,601 and 901 +/- 99 ng/ml for A+L and KE exercise, respectively; P < 0.05), leg Q continued to rise linearly with WR.(ABSTRACT TRUNCATED AT 250 WORDS)
cGMP elevation does not mediate muscarinic agonist-induced negative inotropy in rat ventricular cardiomyocytes
Authors: MacDonell K. L. , Tibbits G. F. , Diamond J.
Published: December 2017

Guanosine 3',5'-cyclic monophosphate (cGMP) has been suggested to be involved in the negative inotropic effects of muscarinic receptor agonists in beta-adrenergic receptor agonist-stimulated ventricular preparations. To test this hypothesis, changes in contractility induced by acetylcholine or carbachol, or the nitrovasodilator sodium nitroprusside (SNP), in the presence of 1 nM isoproterenol were measured in electrically stimulated rat ventricular cardiomyocytes. In parallel experiments, cardiomyocytes were treated with the same agonists, and cGMP and adenosine 3',5'-cyclic monophosphate (cAMP) levels were estimated. After 2 min, isoproterenol increased the magnitude of cell shortening by 60% and accelerated contraction and relaxation rates. Carbachol (1 and 10 microM) and acetylcholine (1 and 10 microM) inhibited the positive inotropic effects of isoproterenol, whereas SNP (10 and 100 microM) had no inotropic effect. All three agents increased cGMP levels but had no effect on isoproterenol-stimulated cAMP levels. SNP caused the largest elevations in cGMP. These results suggest that the negative inotropic effects of muscarinic agonists observed in isoproterenol-stimulated rat ventricular cardiomyocytes are not mediated by alterations in cGMP and/or cAMP levels.
Transfer function analysis of vagal control of heart rate during synchronized vagal stimulation
Authors: Mokrane A. , LeBlanc A. R. , Nadeau R.
Published: December 2017

Synchronized electrical stimulation was used to study the heart rate (HR) response to fluctuations in parasympathetic input to the sinus node in anesthetized dogs. This was obtained by varying the time interval (interpulse interval) between stimulatory vagal pulses. Spectral methods were used to estimate transfer functions between the excitatory signal and the resulting HR response for different intensities of vagal stimulation. The intensity of vagal stimulation was proportional to the number of pulses delivered in each cardiac cycle. From the estimated transfer functions, and based on a mathematical model of the time course of ACh concentration at the sinus node, filter models were derived by using a system identification approach. HR response was characterized by a combination of two different filter behaviors: a low-pass filter behavior of mean cut-off frequency of 0.065 Hz and an all-pass filter behavior. The magnitude of the low-pass filter gain decreased with increasing intensity of vagal stimulation. The magnitude of the all-pass filter gain increased and then decreased with increasing intensity of vagal stimulation. The all-pass filter characteristics of HR response during synchronized stimulation of the vagus nerves are specific to this mode of stimulation, because they were not observed in nonsynchronized modes of vagal stimulation. We can conclude that, during synchronized vagal stimulation, the HR response exhibits both a slow dynamic component and a fast component related to beat-to-beat variations.
Microvascular distensibility in two different vascular beds in idiopathic dilated cardiomyopathy
Authors: Wroblewski H. , Norgaard T. , Haunso S. , Kastrup J.
Published: December 2017

The local isotope-washout technique allows discrimination between blood flow in skin and muscle. Arteriolar constriction, mediated by the sympathetic nervous system, is abolished in a papaverine-histamine-relaxed vascular bed. Microvascular distensibility of relaxed resistance vessels was measured in skeletal muscle and skin of the lower limb in patients with congestive heart failure (CHF) secondary to idiopathic dilated cardiomyopathy and in healthy subjects. Vascular transmural pressure was elevated 40 mmHg by head-up tilt and caused muscle blood flow to increase by 11 +/- 9% in 20 CHF patients compared with 44 +/- 20% in 11 control subjects (P < 0.0003). Also the increase in skin blood flow was significantly reduced: 31 +/- 18% in 42 CHF patients compared with 62 +/- 29% in 25 control subjects (P < 0.001). Regression analysis demonstrated a significant association between microvascular distensibility in skin and skeletal muscle tissue (P = 0.003, r = 0.51, n = 31). Structure of terminal arterioles was determined in skin biopsies, and structural microangiopathy was found in 32 of 42 CHF patients. Multiple regression analysis demonstrated the degree of microangiopathy to be the only parameter significantly associated with microvascular distensibility (P = 0.005, r = 0.42). (There was no association to NY Heart Association functional class, left ventricular ejection fraction, duration of CHF, age of subject, or mean arterial blood pressure.) We conclude that patients with idiopathic dilated cardiomyopathy have similar decreased microvascular distensibility in skeletal muscle and skin. Furthermore, structural alterations in terminal arterioles seem to be associated with decreased distensibility and increased stiffness of the cutaneous microvascular bed.
Increased ACE and chymase-like activity in cardiac tissue of dogs with chronic mitral regurgitation
Authors: Dell'Italia L. J. , Meng Q. C. , Balcells E. , Straeter-Knowlen I. M. , Hankes G. H. , Dillon R. , Cartee R. E. , Orr R. , Bishop S. P. , Oparil S. , et al.
Published: December 2017

The current study was designed to test the hypothesis that intracardiac angiotensin-converting enzyme (ACE) activity, chymase-like activity, and angiotensin (ANG) peptide levels are increased and are positively related to wall stress estimates in response to the chronic low pressure volume overload of mitral regurgitation produced by percutaneous chordal rupture in the dog. Chronic mitral regurgitation (MR) resulted in an increase in left ventricular (LV) end-diastolic volume [59 +/- 11 (SD) to 103 +/- 32 ml, P < 0.001], LV mass (96 +/- 17 to 114 +/- 23 g, P < 0.001), and a decrease in the LV mass-to-end-diastolic volume ratio (1.64 +/- 0.22 to 1.16 +/- 0.23 g/ml, P < 0.001) measured by magnetic resonance imaging. In vitro studies of heart tissue extracts demonstrated that the majority of ANG II-forming activity was from chymase-like activity rather than from ACE activity in five normal (83.5 +/- 7.5 vs. 6.04 +/- 5.2%) and seven MR hearts (86 +/- 3.9 vs. 2.6 +/- 1.7%). ACE activity (1.22 +/- 0.22 vs. 3.55 +/- 0.62 mU/g, P < 0.05) and chymase-like activity (9.42 +/- 4.64 vs. 20.60 +/- 8.41 nmol.g-1.min-1, P < 0.05) were increased in MR compared with normal hearts. ACE activity correlated with the LV mass-to-volume ratio (r = -0.93, P < 0.001) and LV diastolic wall stress ( r = 0.71, P < 0.05); however, chymase-like activity did not correlate with any hemodynamic parameter. ANG II levels were significantly higher in the midwall of the left ventricle in MR hearts than in normal controls (85 +/- 39 vs. 27 +/- 16 pg/g, P < 0.01). Our results demonstrate a positive correlation between LV diastolic wall stress and increased ACE activity with increased ANG II stores, suggesting that mechanical wall stress activated intracardiac ACE. Although chymase accounted for most ANG II formation in vitro in extracts of both normal and MR dog hearts, the significance of this enzyme in vivo remains unclear
Role of ATP-sensitive K+ channels in cGMP-mediated pial artery vasodilation
Authors: Armstead W. M.
Published: December 2017

The present study was designed to investigate the role of ATP-sensitive K+ channels in guanosine 3',5'-cyclic monophosphate (cGMP)-mediated pial artery vasodilation in newborn pigs equipped with a closed cranial window. Sodium nitroprusside (SNP) (10(-8), 10(-6) M), a nitrovasodilator, elicited pial artery dilation that was attenuated by the ATP-sensitive K+ channel antagonist glibenclamide (10(-6) M). On a percentage basis, these responses were 25 +/- 1% for the presence of SNP (10(-6) M) alone, whereas 15 +/- 1% dilation was observed for SNP (10(-6) M) in the presence of glibenclamide (n = 5 pigs). Dilation produced by the cGMP analogue, 8-BrcGMP (10(-8), 10(-6) M), was similarly attenuated by glibenclamide. SNP-induced pial dilation was accompanied by increased cortical periarachnoid cerebrospinal fluid (CSF) cGMP levels, and these biochemical changes were blocked by the soluble guanylate cyclase inhibitor, LY-83583 (10(-5) M). SNP (10(-6) M) alone increased CSF cGMP concentration from 407 +/- 14 to 956 +/- 41 fmol/ml, whereas SNP in the presence of LY-83583 yielded a CSF cGMP concentration of 340 +/- 13, which was no different from the control value of 335 +/- 23 fmol/ml (n = 5 pigs). SNP-induced pial dilation was blunted by LY-83583, whereas 8-BrcGMP-induced dilation was unchanged. Cromakalim (10(-8), 10(-6) M), an ATP-sensitive K+ channel agonist, produced dilation that was blocked by glibenclamide (24 +/- 1 vs. 5 +/- 1% for cromakalim 10(-6) M, in the absence and presence of glibenclamide, respectively, n = 5). These data indicate that activation of ATP-sensitive K+ channels contribute to cGMP-mediated pial artery dilation.
Transients in myocardial O2 consumption after abrupt changes in perfusion pressure in goats
Authors: Dankelman J. , Van der Ploeg C. P. , Spaan J. A.
Published: December 2017

The dynamic oxygen content differences were analyzed in the present study. The left main coronary artery of the anesthetized, open-chest goat was perfused at constant pressure (Pp). Pp(t), arterial flow [Qa(t)], and the arteriovenous oxygen content difference [a-vO2(t)] were averaged per beat. The a-vO2 signal was corrected for mixing processes in the capillaries and transport time from capillaries to the venous measuring site [a-vO2(t)]. A change in Pp of 20 mmHg induced a temporary change in MVO2, referred to as the dynamic Gregg effect. With an increase in Pp, the maximal change of myocardial oxygen consumption [MVO2(t) = Qa(t).a-vO2(t)] was 15.0 +/- 3.6% (means +/- SE) during control and 31.3 +/- 2.3% with glibenclamide. With a decrease in Pp these changes were 16.3 +/- 2.9 and 21.0 +/- 1.1%. During control, the half-time for the rate of return of the MVO2 response was 4.2 +/- 0.8 s for an increase and 4.0 +/- 1.0 s for a decrease in Pp. With glibenclamide these values were 16.9 +/- 2.2 and 22.6 +/- 2.0 s. This study confirms that during steady state the Pp-induced MVO2 (steady-state Gregg effect) is diminished by autoregulation. However, it is concluded that during transients following abrupt changes in Pp, large changes in MVO2 occur depending on the rate of regulation (dynamic Gregg effect).