bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic modeling of [18F]FDG in skeletal muscle by PET: a four-compartment five-rate-constant model
Authors: Bertoldo A. , Peltoniemi P. , Oikonen V. , Knuuti J. , Nuutila P. , Cobelli C.
Published: December 2017

Various modeling strategies have been developed to convert regional [18F]fluorodeoxyglucose ([18F]FDG) concentration measured by positron emission tomography (PET) to a measurement of physiological parameters. However, all the proposed models have been developed and tested mostly for brain studies. The purpose of the present study is to select the most accurate model for describing [18F]FDG kinetics in human skeletal muscle. The database consists of basal and hyperinsulinemic-euglycemic studies performed in normal subjects. PET data were first analyzed by an input-output modeling technique (often called spectral analysis). These results provided guidelines for developing a compartmental model. A new model with four compartments and five rate constants (5K model) emerged as the best. By accounting for plasma and extracellular and intracellular kinetics, this model allows, for the first time, PET assessment of the individual steps of [18F]FDG kinetics in human skeletal muscle, from plasma to extracellular space to transmembrane transport into the cell to intracellular phosphorylation. Insulin is shown to affect transport and phosphorylation but not extracellular kinetics, with the transport step becoming the main site of control. The 5K model also allows definition of the domain of validity of the classic three-compartment three- or four-rate-constant models. These models are candidates for an investigative tool to quantitatively assess insulin control on individual metabolic steps in human muscle in normal and physiopathological states.
Recovery of13CO2during rest and exercise after [1-13C]acetate, [2-13C]acetate, and NaH13CO3infusions
Authors: Trimmer Jeff K. , Casazza Gretchen A. , Horning Michael A. , Brooks George A.
Published: December 2017

For estimating the oxidation rates (Rox) of glucose and other substrates by use of13C-labeled tracers, we obtained correction factors to account for label dilution in endogenous bicarbonate pools and TCA cycle exchange reactions. Fractional recoveries of13C label in respiratory gases were determined during 225 min of rest and 90 min of leg cycle ergometry at 45 and 65% peak oxygen uptake (V˙o2 peak) after continuous infusions of [1-13C]acetate, [2-13C]acetate, or NaH13CO3. In parallel trials, [6,6-2H]glucose and [1-13C]glucose were given. Experiments were conducted after an overnight fast with exercise commencing 12 h after the last meal. During the transition from rest to exercise, CO2production increased ( P < 0.05) in an intensity-dependent manner. Significant differences were observed in the fractional recoveries of13C label as13CO2at rest (NaH13CO3, 77.5 ± 2.8%; [1-13C]acetate, 49.8 ± 2.4%; [2-13C]acetate, 26.1 ± 1.4%). During exercise, fractional recoveries of13C label from [1-13C]acetate, [2-13C]acetate, and NaH13CO3were increased compared with rest. Magnitudes of label recoveries during both exercise intensities were tracer specific (NaH13CO3, 93%; [1-13C]acetate, 80%; [2-13C]acetate, 65%). Use of an acetate-derived correction factor for estimating glucose oxidation resulted in Rox values in excess ( P< 0.05) of glucose rate of disappearance during hard exercise. We conclude that, after an overnight fast: 1) recovery of13C label as13CO2from [13C]acetate is decreased compared with bicarbonate; 2) the position of13C acetate label affects carbon dilution estimations; 3) recovery of13C label increases in the transition from rest to exercise in an isotope-dependent manner; and 4) application of an acetate correction factor in glucose oxidation measurements results in oxidation rates in excess of glucose disappearance during exercise at 65% of V˙o2 peak. Therefore, bicarbonate, not acetate, correction factors are advocated for estimating glucose oxidation from carbon tracers in exercising men.
Norepinephrine kinetics in freely moving rats
Authors: Maignan Emmanuelle , Legrand Monique , Aboulfath Ilham , Safar Michel , Cuche Jean-Louis
Published: December 2017

Norepinephrine (NE) kinetics were investigated in freely moving (FM) and minimally stressed (MS) rats with the isotope dilution technique. 1) The mean NE spillover rate (NE-SOR) was 79 ± 6 ng · kg−1· min−1, and the mean NE metabolic clearance rate (NE-MCR) 179 ± 9 ml · kg−1· min−1( n = 31). Thus the NE kinetics in FM and MS rats are much faster than in human beings, probably related to a higher sympathetic drive. 2) Whether the magnitude of NE-MCR is related to the level of plasma NE concentration was investigated. No significant correlation was calculated between plasma NE concentration and NE-MCR in 31 control rats. When plasma NE concentration was varied during either acute or chronic infusion of exogenous NE, NE-MCR remained unchanged as long as animal hemodynamics were not altered. When plasma NE concentration was high enough to increase mean arterial pressure (MAP), NE-MCR was decreased. However, when MAP was increased within comparable magnitude, NE-MCR was decreased during NE and increased during epinephrine (Epi) infusion. Thus the existence of an α-/β-adrenergic mechanism involved in the regulation of NE-MCR independent of known hemodynamic mechanisms is suggested. 3) The “epinephrine hypothesis” was revisited in FM and MS rats. At variance with humans, very high plasma Epi concentrations have to be induced to increase NE-SOR in resting rats. Furthermore, NE-MCR was also increased, accounting for the nonsignificant increase of plasma NE concentration. Within the range of Epi concentrations with no effect on NE-SOR, an increase of NE release was revealed when the presynaptic α2-adrenoreceptors were partially inhibited by yohimbine. This suggests the existence of a second epinephrine hypothesis.
Role of carotid bodies in control of the neuroendocrine response to exercise
Authors: Koyama Yoshiharu , Coker Robert H. , Denny Joshua C. , Lacy D. Brooks , Jabbour Kareem , Williams Phillip E. , Wasserman David H.
Published: December 2017

This study was aimed at assessing the role of carotid body function in neuroendocrine and glucoregulatory responses to exercise. The carotid bodies and associated nerves were removed (CBR, n = 6) or left intact (Sham, n = 6) in anesthetized dogs >16 days before experiments, and infusion and sampling catheters were implanted. Conscious dogs were studied at rest and during 150 min of exercise. Isotopic dilution was used to assess glucose production (Ra) and disappearance (Rd). Arterial glucagon was reduced in CBR compared with Sham at rest (29 ± 3 vs. 47 ± 3 pg/ml). During exercise, glucagon increased more in Sham than in CBR (47 ± 9 vs. 15 ± 2 pg/ml). Cortisol and epinephrine levels were similar in the two groups at rest and during exercise. Basal norepinephrine was similar in CBR and Sham. During exercise, norepinephrine increased by 432 ± 124 pg/ml in Sham, but by only 201 ± 28 pg/ml in CBR. Basal arterial plasma glucose was 108 ± 2 and 105 ± 2 mg/dl in CBR and Sham, respectively. Arterial glucose dropped by 10 ± 3 mg/dl at onset of exercise in CBR ( P < 0.01) but was unchanged in Sham (decrease of 3 ± 2 mg/dl, not significant). Basal glucose kinetics were equal in Sham and CBR. At onset of exercise, Raand Rdwere transiently uncoupled in CBR (i.e., Rd> Ra) but were closely matched in Sham. In steady-state exercise, Raand Rdwere closely matched in both groups. Insulin was equal in the basal period and decreased similarly during exercise. These studies suggest that input from the carotid bodies, or receptors anatomically close to them, 1) is important in control of basal glucagon and the exercise-induced increment in glucagon, 2) is involved in the sympathetic response to exercise, and 3) participates in the non-steady-state coupling of Rato Rd, but 4) is not essential to glucoregulation during sustained exercise.
Daily delivery of dietary nitrogen to the periphery is stable in rats adapted to increased protein intake
Authors: Morens Céline , Gaudichon Claire , Fromentin Gilles , Marsset-Baglieri Agnès , Bensaïd Ahmed , Larue-Achagiotis Christiane , Luengo Catherine , Tomé Daniel
Published: December 2017

Dietary nitrogen was traced in rats adapted to a 50% protein diet and given a meal containing 1.50 g15N-labeled protein (HP-50 group). This group was compared with rats usually consuming a 14% protein diet and fed a meal containing either 0.42 g (AP-14 group) or 1.50 g (AP-50 group) of15N-labeled protein. In the HP group, the muscle nonprotein nitrogen pool was doubled when compared with the AP group. The main adaptation was the enhancement of dietary nitrogen transferred to urea (2.2 ± 0.5 vs. 1.3 ± 0.1 mmol N/100 g body wt in the HP-50 and AP-50 groups, respectively). All amino acids reaching the periphery except arginine and the branched-chain amino acids were depressed. Consequently, dietary nitrogen incorporation into muscle protein was paradoxically reduced in the HP-50 group, whereas more dietary nitrogen was accumulated in the free nitrogen pool. These results underline the important role played by splanchnic catabolism in adaptation to a high-protein diet, in contrast to muscle tissue. Digestive kinetics and splanchnic anabolism participate to a lesser extent in the regulation processes.
Gut expression and regulation of FAT/CD36: possible role in fatty acid transport in rat enterocytes
Authors: Chen Min , Yang Yingkui , Braunstein Evan , Georgeson Keith E. , Harmon Carroll M.
Published: December 2017

Fatty acid translocase (FAT)/CD36 is one of several putative plasma membrane long-chain fatty acid (LCFA) transport proteins; however, its role in intestinal absorption of LCFA is unknown. We hypothesized that FAT/CD36 would be differentially expressed along the longitudinal axis of the gut and during intestinal development, suggesting specificity of function. We found that intestinal mucosal FAT/CD36 mRNA levels varied by anatomic location along the longitudinal gut axis: stomach 45 ± 7, duodenum 173 ± 29, jejunum 238 ± 17, ileum 117 ± 14, and colon 9 ± 1% (means ± SE with 18S mRNA as control). FAT/CD36 protein levels were also higher in proximal compared with distal intestinal mucosa. Mucosal FAT/CD36 mRNA was also regulated during intestinal maturation, with a fourfold increase from neonatal to adult animals. In addition, FAT/CD36 mRNA levels and enterocyte LCFA uptake were rapidly downregulated by intraduodenal oleate infusion. These findings suggest that FAT/CD36 plays a role in the uptake of LCFA by small intestinal enterocytes. This may have important implications in understanding fatty acid absorption in human physiological and pathophysiological conditions.
A nonlabeled method to evaluate cortisol production rate by modeling plasma CBG-free cortisol disposition
Authors: Picard-Hagen N. , Gayrard V. , Alvinerie M. , Smeyers H. , Ricou R. , Bousquet-Melou A. , Toutain P. L.
Published: December 2017

This study aimed to develop a nonlabeled method for the measurement of cortisol production rate to evaluate adrenal function. The cortisol production rate determination requires that of cortisol clearance, which is not a parameter but a variable resulting from the saturable binding of cortisol to corticosteroid-binding globulin (CBG). Our method is based on evaluation of the plasma clearance of the CBG-free cortisol fraction. This parameter was evaluated from a pharmacokinetic model of total plasma cortisol disposition that takes into account specific binding of the corticoid to CBG in the plasma. We have shown that the CBG-free cortisol kinetics and CBG-binding parameters thus evaluated are not statistically different from those obtained by the radioisotopic method and equilibrium dialysis, suggesting that the plasma CBG-free cortisol clearance is independent of the total plasma cortisol concentrations and represents the actual parameter of cortisol elimination. We validated this modeling approach by using it to calculate the in vivo entry rate of cortisol mimicked by the perfusion of cortisol at a known rate.
Testosterone dose-response relationships in healthy young men
Authors: Bhasin Shalender , Woodhouse Linda , Casaburi Richard , Singh Atam B. , Bhasin Dimple , Berman Nancy , Chen Xianghong , Yarasheski Kevin E. , Magliano Lynne , Dzekov Connie , Dzekov Jeanne , Bross Rachelle , Phillips Jeffrey , Sinha-Hikim Indrani , Shen Ruoquing , Storer Thomas W.
Published: December 2017

Testosterone increases muscle mass and strength and regulates other physiological processes, but we do not know whether testosterone effects are dose dependent and whether dose requirements for maintaining various androgen-dependent processes are similar. To determine the effects of graded doses of testosterone on body composition, muscle size, strength, power, sexual and cognitive functions, prostate-specific antigen (PSA), plasma lipids, hemoglobin, and insulin-like growth factor I (IGF-I) levels, 61 eugonadal men, 18–35 yr, were randomized to one of five groups to receive monthly injections of a long-acting gonadotropin-releasing hormone (GnRH) agonist, to suppress endogenous testosterone secretion, and weekly injections of 25, 50, 125, 300, or 600 mg of testosterone enanthate for 20 wk. Energy and protein intakes were standardized. The administration of the GnRH agonist plus graded doses of testosterone resulted in mean nadir testosterone concentrations of 253, 306, 542, 1,345, and 2,370 ng/dl at the 25-, 50-, 125-, 300-, and 600-mg doses, respectively. Fat-free mass increased dose dependently in men receiving 125, 300, or 600 mg of testosterone weekly (change +3.4, 5.2, and 7.9 kg, respectively). The changes in fat-free mass were highly dependent on testosterone dose ( P = 0.0001) and correlated with log testosterone concentrations ( r = 0.73, P = 0.0001). Changes in leg press strength, leg power, thigh and quadriceps muscle volumes, hemoglobin, and IGF-I were positively correlated with testosterone concentrations, whereas changes in fat mass and plasma high-density lipoprotein (HDL) cholesterol were negatively correlated. Sexual function, visual-spatial cognition and mood, and PSA levels did not change significantly at any dose. We conclude that changes in circulating testosterone concentrations, induced by GnRH agonist and testosterone administration, are associated with testosterone dose- and concentration-dependent changes in fat-free mass, muscle size, strength and power, fat mass, hemoglobin, HDL cholesterol, and IGF-I levels, in conformity with a single linear dose-response relationship. However, different androgen-dependent processes have different testosterone dose-response relationships.
Oral estrogen antagonizes the metabolic actions of growth hormone in growth hormone-deficient women
Authors: Wolthers Troels , Hoffman David M. , Nugent Ailish G. , Duncan Mark W , Umpleby Margot , Ho Ken K. Y.
Published: December 2017

We have determined whether oral estrogen reduces the biological effects of growth hormone (GH) in GH-deficient (GHD) women compared with transdermal estrogen treatment. In two separate studies, eight GHD women randomly received either oral or transdermal estrogen for 8 wk before crossing over to the alternate route of administration. The first study assessed the effects of incremental doses of GH (0.5, 1.0, 2.0 IU/day for 1 wk each) on insulin-like growth factor I (IGF-I) levels during each estrogen treatment phase. The second study assessed the effects of GH (2 IU/day) on lipid oxidation and on protein metabolism using the whole body leucine turnover technique. Mean IGF-I level was significantly lower during oral estrogen treatment ( P < 0.05) and rose dose dependently during GH administration by a lesser magnitude ( P < 0.05) compared with transdermal treatment. Postprandial lipid oxidation was significantly lower with oral estrogen treatment, both before ( P < 0.05) and during ( P < 0.05) GH administration, compared with transdermal treatment. Protein synthesis was lower during oral estrogen both before and during GH administration ( P < 0.05). Oral estrogen antagonizes several of the metabolic actions of GH. It may aggravate body composition abnormalities already present in GHD women and attenuate the beneficial effects of GH therapy. Estrogen replacement in GHD women should be administered by a nonoral route.
Threonine metabolism in isolated rat hepatocytes
Authors: House James D. , Hall Beatrice N. , Brosnan John T.
Published: December 2017

The removal of the 1-carbon of threonine can occur via threonine dehydrogenase or threonine aldolase, this carbon ending up in glycine to be liberated by the mitochondrial glycine cleavage system and producing CO2. Alternatively, in the threonine dehydratase pathway, the 1-carbon ends up in α-ketobutyrate, which is oxidized in the mitochondria to CO2. Rat hepatocytes, incubated in Krebs-Henseleit medium, were incubated with 0.5 mMl-[1-14C]threonine, and14CO2 production was measured. Added glycine (0.3 mM) marginally suppressed threonine oxidation. Cysteamine (0.5 mM), a potent inhibitor of the glycine cleavage system, reduced threonine oxidation to 65% of controls. However, α-cyanocinnamate (0.5 mM), a competitive inhibitor of mitochondrial α-keto acid uptake, reduced threonine oxidation to 35% of controls. These data provided strong evidence that ∼65% of threonine oxidation occurs through the glycine-independent threonine dehydratase pathway. Glucagon (10−7 M) increased threonine oxidation and stimulated threonine uptake by these cells. In summary, the majority of threonine oxidation occurs through the threonine dehydratase pathway in rat hepatocytes, and threonine oxidation is increased by glucagon, which also increases threonine's transport.
Chronic activation of AMP kinase results in NRF-1 activation and mitochondrial biogenesis
Authors: Bergeron Raynald , Ren Jian Ming , Cadman Kevin S. , Moore Irene K. , Perret Pascale , Pypaert Marc , Young Lawrence H. , Semenkovich Clay F. , Shulman Gerald I.
Published: December 2017

The underlying mechanism by which skeletal muscle adapts to exercise training or chronic energy deprivation is largely unknown. To examine this question, rats were fed for 9 wk either with or without β-guanadinopropionic acid (β-GPA; 1% enriched diet), a creatine analog that is known to induce muscle adaptations similar to those induced by exercise training. Muscle phosphocreatine, ATP, and ATP/AMP ratios were all markedly decreased and led to the activation of AMP-activated protein kinase (AMPK) in the β-GPA-fed rats compared with control rats. Under these conditions, nuclear respiratory factor-1 (NRF-1) binding activity, measured using a cDNA probe containing a sequence encoding for the promoter of δ-aminolevulinate (ALA) synthase, was increased by about eightfold in the muscle of β-GPA-fed rats compared with the control group. Concomitantly, muscle ALA synthase mRNA and cytochrome ccontent were also increased. Mitochondrial density in both extensor digitorum longus and epitrochlearis from β-GPA-fed rats was also increased by more than twofold compared with the control group. In conclusion, chronic phosphocreatine depletion during β-GPA supplementation led to the activation of muscle AMPK that was associated with increased NRF-1 binding activity, increased cytochrome c content, and increased muscle mitochondrial density. Our data suggest that AMPK may play an important role in muscle adaptations to chronic energy stress and that it promotes mitochondrial biogenesis and expression of respiratory proteins through activation of NRF-1.
A new perspective on adiposity in a naturally obese mammal
Authors: Ortiz Rudy M. , Noren Dawn P. , Litz Beate , Ortiz C. Leo
Published: December 2017

Many mammals seasonally reduce body fat due to inherent periods of fasting, which is associated with decreased leptin concentrations. However, no data exist on the correlation between fat mass (FM) and circulating leptin in marine mammals, which have evolved large fat stores as part of their adaptation to periods of prolonged fasting. Therefore, FM was estimated (by tritiated water dilution), and serum leptin and cortisol were measured in 40 northern elephant seal ( Mirounga angustirostris) pups early (<1 wk postweaning) and late (6–8 wk postweaning) during their natural, postweaning fast. Body mass (BM) and FM were reduced late; however, percent FM (early: 43.9 ± 0.5, late: 45.5 ± 0.5%) and leptin [early: 2.9 ± 0.1 ng/ml human equivalents (HE), late: 3.0 ± 0.1 ng/ml HE] did not change. Cortisol increased between early (9.2 ± 0.5 μg/dl) and late (16.3 ± 0.9 μg/dl) periods and was significantly and negatively correlated with BM ( r = 0.426; P < 0.0001) and FM ( r = 0.328; P = 0.003). FM and percent FM were not correlated ( P > 0.10) with leptin at either period. The present study suggests that these naturally obese mammals appear to possess a novel cascade for regulating body fat that includes cortisol. The lack of a correlation between leptin and FM may reflect the different functions of fat between terrestrial and marine mammals.
Lipid rafts and insulin signaling
Authors: Bickel Perry E.
Published: December 2017

Lipid rafts are domains within the plasma membrane that are enriched in cholesterol and lipids with saturated acyl chains. Specific proteins, including many signaling proteins, segregate into lipid rafts, and this process is important for certain signal transduction events in a variety of cell types. Within the past decade, data have emerged from many laboratories that implicate lipid rafts as critical for proper compartmentalization of insulin signaling in adipocytes. A subset of lipid rafts, caveolae, are coated with membrane proteins of the caveolin family. Direct interactions between resident raft proteins (caveolins and flotillin-1) and insulin-signaling molecules may organize these molecules in space and time to ensure faithful transduction of the insulin signal, at least with respect to the glucose-dependent actions of insulin in adipocytes. The in vivo relevance of this model remains to be determined.
Hemodialysis stimulates muscle and whole body protein loss and alters substrate oxidation
Authors: Ikizler T. Alp , Pupim Lara B. , Brouillette John R. , Levenhagen Deanna K. , Farmer Kali , Hakim Raymond M. , Flakoll Paul J.
Published: December 2017

The hemodialysis (HD) procedure has been implicated as a potential catabolic factor predisposing the chronic HD (CHD) patients to protein calorie malnutrition. To assess the potential effects of HD on protein and energy metabolism, we studied 11 CHD patients 2 h before, during, and 2 h after HD by use of primed constant infusion of l-[1-13C]leucine andl-[ ring-2H5]phenylalanine. Our results showed that HD led to increased whole body (10%) and muscle protein (133%) proteolysis. Simultaneously, whole body protein synthesis did not change, and forearm synthesis increased (120%). The net result was increased net whole body protein loss (96%) and net forearm protein loss (164%). During the 2-h post-HD period, the muscle protein breakdown trended toward baseline, whereas whole body protein breakdown increased further. Substrate oxidation during the post-HD was significantly altered, with diminished carbohydrate and accelerated lipid and amino acid oxidation. These data demonstrate that hemodialysis is an overall catabolic event, decreasing the circulating amino acids, accelerating rates of whole body and muscle proteolysis, stimulating muscle release of amino acids, and elevating net whole body and muscle protein loss.
Effect of basal lamina of ovarian follicle on T- and L-type Ca2+currents in differentiated granulosa cells
Authors: Asem Elikplimi K. , Qin Wuxuan , Rane Stanley G.
Published: December 2017

Patch clamp experiments were conducted to study the effects of basal lamina (basement membrane) of chicken ovarian follicle on membrane Ca2+currents in differentiated chicken granulosa cells in a homologous system. The whole cell patch clamp technique was used to simultaneously monitor membrane capacitance (an indirect measure of total cell surface area) and currents flowing through voltage-dependent Ca2+channels (using Ba2+as the charge carrier). Membrane capacitance was smaller in cells incubated on intact basal lamina than in control cells (incubated on tissue culture-treated plastic substratum). Granulosa cells expressed both T- and L-type Ca2+currents, and the amplitudes of the currents in cells incubated on intact basal lamina were significantly lower than those of control cells. Also, granulosa cells incubated on intact basal lamina were found to have significantly lower T- or L-type Ca2+current densities than control cells. Intact basal lamina that had been stored for 12 mo produced effects on T- and L-type Ca2+currents similar to those caused by freshly isolated basal lamina. The basal lamina was solubilized completely in one step and used to coat glass coverslips (uncoated glass coverslips served as controls). Granulosa cells incubated on coverslips precoated with solubilized basal lamina assumed spherical shape similar to those incubated on intact basal lamina. Similar to the observations made for intact basal lamina, the solubilized basal lamina suppressed T- and L-type Ca2+currents in the differentiated granulosa cells. Moreover, fibronectin, laminin, and type IV collagen, obtained from commercial sources, attenuated T- and L-type Ca2+currents in the differentiated granulosa cells. This interplay between basal lamina and Ca2+currents may be one mechanism that subserves the effects of the matrix material on metabolic functions of granulosa cells.
LDL receptor but not apolipoprotein E deficiency increases diet-induced obesity and diabetes in mice
Authors: Schreyer Sandra A. , Vick Cynthia , Lystig Theodore C. , Mystkowski Paul , LeBoeuf Renée C.
Published: December 2017

The aim of this study was to determine whether phenotypes associated with type 2 diabetes are altered in dyslipidemic obese mice. C57BL/6 wild-type, low-density lipoprotein (LDL) receptor-deficient (LDLR−/−), and apolipoprotein E-deficient (apoE−/−) mice were fed a high-fat, high-carbohydrate diet (diabetogenic diet), and the development of obesity, diabetes, and hypertriglyceridemia was examined. Wild-type mice became obese and developed hyperglycemia, but not hypertriglyceridemia, in response to this diet. LDLR−/− mice fed the diabetogenic diet became more obese than wild-type mice and developed severe hypertriglyceridemia and hyperleptinemia. Surprisingly, glucose levels were only modestly higher and insulin levels and insulin-to-glucose ratios were not strikingly different from those of wild-type mice. In contrast, diabetogenic diet-fed apoE−/− mice were resistant to changes in glucose and lipid homeostasis despite becoming obese. These data suggest that modifications in lipoprotein profiles associated with loss of the LDL receptor or apoE function have profound and unique consequences on susceptibility to diet-induced obesity and type 2 diabetic phenotypes.
Increased hepatic lipogenesis but decreased expression of lipogenic gene in adipose tissue in human obesity
Authors: Diraison Frédérique , Dusserre Eric , Vidal Hubert , Sothier Monique , Beylot Michel
Published: December 2017

To determine whether increased lipogenesis contributes to human obesity, we measured (postabsorptive state), in lean and obese subjects, lipid synthesis (deuterated water method) and the mRNA concentration (RT-competitive PCR) in subcutaneous adipose tissue of fatty acid synthase (FAS) and sterol regulatory element-binding protein (SREBP)-1c. Before energy restriction, obese subjects had an increased contribution of hepatic lipogenesis to the circulating triglyceride pool (14.5 ± 1.3 vs. 7.5 ± 1.9%, P < 0.01) without enhancement of cholesterol synthesis. This increased hepatic lipogenesis represented an excess of 2–5 g/day of triglycerides, which would represent 0.7–1.8 kg on a yearly basis. The lipogenic capacity of adipose tissue appeared, on the contrary, decreased with lower FAS mRNA levels ( P < 0.01) and a trend for decreased SREBP-1c mRNA ( P = 0.06). Energy restriction in obese patients decreased plama insulin ( P < 0.05) and leptin ( P < 0.05) and normalized hepatic lipogenesis. FAS mRNA levels were unchanged, whereas SREBP-1c increased. In conclusion, subjects with established obesity have an increased hepatic lipogenesis that could contribute to their excessive fat mass but no evidence for an increased lipogenic capacity of adipose tissue.
Nitric oxide does not mediate autoregulation of retinal blood flow in newborn pig
Authors: Gidday J. M. , Zhu Y.
Published: December 2017

Isoflurane-anesthetized newborn pigs were used to test the hypothesis that nitric oxide mediates autoregulatory dilations of retinal arterioles. Fundus images were monitored by videomicroscopy at x310, and stimulus-induced changes in retinal arteriolar diameter were measured by on-line image analysis. Dilatative responses to systemic hypoxia (arterial O2 tension 20-30 mmHg), hypotension (mean arterial blood pressure 40 mmHg), or hypercapnia (arterial CO2 tension 70-85 mmHg) were assessed after intravitreal microsuffusion of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) over the observed arterioles. Twenty-five nanomoles L-NMMA constricted arterioles by 24 +/- 2% (P < 0.01; n = 17 pigs); a significant constriction (14 +/- 2%) was still observed 80 min after drug administration (n = 5). Complete nitric oxide synthase inhibition at this dose was indicated by the findings that co-administration of 2.5 mumol L-arginine reversed this constriction within 17 +/- 2 min (n = 3), that L-NMMA, but not D-NMMA, completely inhibited the 20 +/- 3% P < 0.01) arteriolar dilation induced by intravitreal acetylcholine (7.5 nmol; n = 4), and that no additional constriction was evidenced after administration of a 10-fold greater concentration of L-NMMA (n = 8). However, despite the prominent arteriolar constriction induced by L-NMMA under baseline conditions, increases in retinal arteriolar diameter still occurred in response to hypoxia (n = 5), hypotension (n = 4), or hypercapnia (n = 5) in animals pretreated with 50 nmol L-NMMA; these responses did not differ significantly from arteriolar dilations observed in untreated control animals (n = 16) subjected to the same stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)
Spatiotemporal changes of Ca2+ during electrically evoked contractions in atrial and ventricular cells
Authors: Berlin J. R.
Published: December 2017

Spatial and temporal changes of intracellular calcium ion concentration ([Ca2+]i) during stimulated contractions were observed by confocal microscopy in rat ventricular and guinea pig atrial myocytes. Fluorescence intensity profiles in fluo 3-acetoxymethyl ester (fluo 3-AM)-loaded cells were collected from the entire cell, selected regions of the cell, or along a single scanned line across the cell. In rat ventricular myocytes, the increase of [Ca2+]i after a single stimulus from field electrodes occurred synchronously across the cell whether fluo 3 fluorescence was monitored in a narrow region aligned with the long axis of the cell or in line-scan images of a single z-line across the cell. However, during the onset of Ca2+ channel blockade by nifedipine (5 microM), electrical stimulation produced spatially nonuniform, focal increases of [Ca2+]i. In guinea pig atrial myocytes, stimulated increases of [Ca2+]i first appeared in focal regions at the cell periphery before spreading to the cell interior. Line-scan images showed the peripheral rise of [Ca2+]i led that at the center of the cell by 34 +/- 4 ms (mean +/- SE, n = 3). These data demonstrate that the t-tubular network ensures synchronous increases of [Ca2+]i throughout the cell during an action potential. In the absence of t tubules or when the number of sarcolemmal Ca2+ channels opened by membrane depolarization is greatly reduced, stimulated increases of [Ca2+]i can be observed to arise in focal regions of the cell.
Endothelial dysfunction in a model of hyperglycemia and hyperinsulinemia
Authors: Pieper G. M. , Meier D. A. , Hager S. R.
Published: December 2017

Insulinopenic diabetes is known to produce endothelial dysfunction. This dysfunction could arise from either hyperglycemia or inadequate insulin. It is not known whether endothelial dysfunction occurs when hyperglycemia is present with elevated insulin levels. In this study, we utilized an experimental model of hyperglycemia with hyperinsulinemia to investigate latent endothelial dysfunction. Rats were continuously infused with glucose or saline for 72 h to achieve peak plasma glucose concentrations of approximately 25 mM. Plasma insulin rose by 12-fold in glucose-infused rats. No significant differences in serum electrolyte concentration were noted between control and glucose-infused rats after 72 h. Blood pressure was not altered by this intervention. Aortic rings taken from control rats relaxed to the endothelium-dependent vasodilators, acetylcholine and A-23187, and to the endothelium-independent vasodilator, nitroglycerin. Relaxation to acetylcholine but not to A-23187 or nitroglycerin was impaired in glucose-infused rat aortic rings. Incubation in vitro with either indomethacin or superoxide dismutase did not restore the impaired relaxation to acetylcholine in rings taken from glucose-infused rats. Thus hyperglycemia with hyperinsulinemia selectively impairs receptor-dependent, endothelium-dependent relaxation. These studies suggest that elevated glucose may be a common pathway leading to endothelial dysfunction in insulin-dependent diabetes mellitus and hyperglycemia-induced insulin resistance.
Opioids contribute to hypoxia-induced pial artery dilation through activation of ATP-sensitive K+ channels
Authors: Shankar V. , Armstead W. M.
Published: December 2017

It has been previously observed that hypoxia increases cerebrospinal fluid (CSF) methionine enkephalin and leucine enkephalin levels, and these opioids contribute to hypoxia-induced pial artery vasodilation. The present study was designed to investigate whether the activation of ATP-sensitive K+ channels (KATP) mediates the contribution of opioids to the hypoxia-induced pial artery dilation. The closed-cranial window technique was used to measure pial diameter in newborn pigs. Glibenclamide (10(-6) M), a KATP inhibitor, attenuated the dilation resulting from moderate and severe hypoxia [23 +/- 1 and 33 +/- 2% vs. 7 +/- 1 and 18 +/- 2%, respectively, for moderate and severe hypoxia (arterial PO2 approximately 35 and 25 mmHg, respectively) in the absence vs. presence of glibenclamide]. In addition, glibenclamide attenuated the dilation produced by methionine enkephalin (10(-8) and 10(-6) M) (13 +/- 1 vs. 4 +/- 2% and 21 +/- 2 vs. 7 +/- 3%, respectively, for methionine enkephalin in the absence and presence of glibenclamide). Leucine enkephalin-induced dilation was similarly attenuated by glibenclamide. Cromakalim (10(-8) and 10(-6) M), a KATP agonist, produced dilation that was blocked by glibenclamide (12 +/- 1 and 25 +/- 1 vs. 3 +/- 1 and 5 +/- 1% before and after glibenclamide, respectively). These data show that activation of KATP contributes to methionine enkephalin- and leucine enkephalin-induced dilation. Furthermore, these observations suggest that opioids contribute to hypoxia-induced pial artery dilation via KATP activation.
Thoracic duct lymph flow responses to hemorrhage in the ovine fetus
Authors: Brace R. A.
Published: December 2017

Blood volume returns toward normal after hemorrhage much more rapidly in the fetus than in the adult due to a rapid entry of fluid and plasma proteins into the fetal circulation. One potential source of fetal fluids and plasma proteins is the lymphatic system, since basal lymph flow rate and interstitial protein concentration are high in the fetus. Furthermore, studies in adults suggest that lymph flow rate may increase following hemorrhage. To test the hypothesis that hemorrhage induces an increase in lymph flow in the fetus, 15 late-gestation ovine fetuses underwent left thoracic duct catheterization with low-resistance catheters and were studied 5 or more days after surgery at 134 +/- 1 (SE) days gestation. The protocol included three successive 30-min periods: control, hemorrhage, and recovery. During the first 5 min of the hemorrhagic period, 61 +/- 4 ml of fetal blood were removed. The blood was reinfused over the first 5 min of the recovery period. After the hemorrhage, fetal arterial pressure, venous pressure, and heart rate decreased (analysis of variance, P < 0.001). These variables significantly increased above basal levels following blood reinfusion. Fetal hematocrit (P < 0.001) and plasma protein concentration (P < 0.05) also decreased after the hemorrhage and returned to control values after the reinfusion. Fetal lymph flow rate was 0.55 +/- 0.06 (SE) ml/min before the hemorrhage and decreased by a maximum of 30.3 +/- 6.3% (P < 0.001) at 8 min after the end of the hemorrhage. Lymph flow rate was reduced by an average of 19.1 +/- 6.6% during the hemorrhagic period and returned to prehemorrhage levels following blood reinfusion.(ABSTRACT TRUNCATED AT 250 WORDS)
Inotropic effects of alpha 1-adrenergic agonists in myocardium from rats with postinfarction heart failure
Authors: Litwin S. E. , Vatner D. E. , Morgan J. P.
Published: December 2017

In clinical and experimental heart failure, the inotropic response to beta-adrenergic receptor stimulation is depressed. Therefore, non-beta-adrenergic mechanisms may assume increasing importance for summoning inotropic reserve in the failing heart. To test the integrity of the inotropic pathway mediated by alpha 1-adrenergic receptor stimulation in a model of chronic ischemic heart failure, we administered phenylephrine to noninfarcted left ventricular papillary muscles isolated from sham-operated rats (n = 10) and rats with large (> 40% left ventricular circumference) anterior myocardial infarctions (n = 9). Isometric force was monitored, and intracellular Ca2+ (Cai2+) transients were recorded with the bioluminescent protein aequorin. Compared with muscles from sham-operated rats, contractility of muscles from rats with postinfarction heart failure was depressed at extracellular Ca2+ concentrations between 0.5 and 3.0 mM. Phenylephrine produced comparable dose-dependent increases in developed tension (126 +/- 4 vs. 125 +/- 7% of baseline) and peak rate of tension rise (125 +/- 4 vs. 140 +/- 9% of baseline) in muscles from sham and infarcted rats, respectively. There was no significant change in the time course of the isometric twitch or in the time course or amplitude of the Cai2+ transient after phenylephrine administration in muscles from either group. No evidence of Cai2+ overload, as defined by spontaneous Ca2+ release, was observed during phenylephrine administration in muscles from normal or failing hearts. The density of alpha 1-adrenoceptors measured with [3H]prazosin binding in crude membranes isolated from noninfarcted left ventricular tissue was not different in control and infarcted hearts (48 +/- 5 vs. 53 +/- 4 fmol/mg protein). These data indicate that the positive inotropic effect of alpha-agonists may be preserved in chronic ischemic heart failure. In both normal and failing myocardium, the inotropic effects of alpha 1-adrenergic stimulation occurred with little or no increase in Cai2+ availability and no apparent adverse effects on myocardial relaxation. Therefore, agents that act by similar mechanisms may have certain therapeutic advantages over traditional inotropic agents in patients with heart failure.
Permissive role for nitric oxide in active thermoregulatory vasodilation in rabbit ear
Authors: Farrell D. M. , Bishop V. S.
Published: December 2017

The present study was designed to test the hypothesis that during whole body heating (WBH), nitric oxide (NO) synthesized in the endothelium acts synergistically with an unknown neurotransmitter to elicit active vasodilation. Rabbits were instrumented for the measurement of mean arterial pressure, heart rate, and ear blood flow (EBF) (Doppler ultrasound). During WBH, either N omega-nitro-L-arginine methyl ester (L-NAME, 10-40 mg over 10-15 min, n = 6 rabbits; group 1), a NO synthase inhibitor, or saponin (30-40 mg over 10-20 min, n = 6 rabbits; group 2), a detergent that denudes the endothelium, was given via a lingual artery catheter until thermoregulatory vasodilation was reversed. When EBF stabilized at the new reduced level, the NO donor, sodium nitroprusside (SNP), was infused (0.2-1.0 mg/ml, 0.01-0.05 ml/min, 2-5 min) via the lingual artery catheter. During WBH, EBF increased from 0.39 +/- 0.08 to 6.47 +/- 0.63 kHz in group 1, and from 0.69 +/- 0.18 to 5.72 +/- 0.49 kHz in group 2. Infusion of L-NAME decreased EBF in group 1 to 1.97 +/- 0.40 kHz. Infusion of saponin decreased EBF in group 2 to 1.23 +/- 0.40 kHz. Subsequent SNP infusion during hyperthermia returned EBF to 6.88 +/- 0.72 kHz in group 1 and 5.53 +/- 1.27 kHz in group 2 but had no effect when administered during normothermia. These results suggest that NO acts in conjunction with another substance, presumably the neurotransmitter released on WBH, to elicit thermoregulatory vasodilation.
VEGF gene expression is upregulated in electrically stimulated rat skeletal muscle
Authors: Hang J. , Kong L. , Gu J. W. , Adair T. H.
Published: December 2017

Vascular endothelial growth factor (VEGF; also called vascular permeability factor) is a secreted mitogen with distinct target cell specificity for vascular endothelial cells. Hypoxia upregulates VEGF expression, making it a likely mediator of the angiogenesis that occurs in poorly perfused tissues. The purpose of this study was to determine whether VEGF gene expression is upregulated in chronically stimulated skeletal muscles, where hypoxia is thought to trigger the growth of blood vessels. The right anterior tibialis and extensor digitorum longus muscles of 12 rats were stimulated electrically (10 Hz, 300 microseconds pulses) for up to 21 days by way of the peroneal motor nerve. The contralateral muscles served as control. Northern analysis showed that VEGF mRNA levels increased by approximately sixfold after 4 days of stimulation and then decreased gradually over the next several days. VEGF mRNA levels were still elevated by two- to threefold after 21 days of stimulation. Higher VEGF mRNA levels in the early stages of muscle stimulation and gradually decreasing levels in later stages are consistent with a metabolic hypothesis in which tissue oxygenation controls VEGF expression. These studies support the hypothesis that VEGF has a physiological role in promoting angiogenesis in stimulated skeletal muscle.
Nitric oxide is an important determinant of coronary flow at rest and during hypoxemic stress in fetal lambs
Authors: Reller M. D. , Burson M. A. , Lohr J. L. , Morton M. J. , Thornburg K. L.
Published: December 2017

Fourteen fetal lambs were instrumented with atrial, coronary sinus, and arterial catheters and a proximal left circumflex coronary artery Doppler probe and were studied at a mean gestational age of 130 +/- 3 (SD) days, 7 +/- 2 days after surgery. Myocardial blood flow was assessed using 15-microns microspheres and Doppler flow velocities. In 11 fetuses, the maximal myocardial flow response to left atrial adenosine infusion was 802 +/- 215 ml.min-1x 100 g-1, 3.5-fold greater than baseline flow. Acute fetal hypoxemia in six fetuses to an arterial PO2 of 8.8 +/- 0.8 mmHg and an arterial O2 content (CaO2) of 1.7 +/- 0.2 ml/dl was not associated with significant change in coronary perfusion pressure; yet left ventricular myocardial flow increased to 1,020 +/- 198 ml.min-1 x 100 g-1, a value significantly greater than that seen with adenosine (P < 0.05). Left atrial N omega-nitro-L-arginine (L-NNA), a competitive inhibitor of nitric oxide synthase (NOS), was infused at a dosage of approximately 1 mg.kg-1.min-1 for 60 min in 10 fetuses. Although L-NNA was associated with a significant increase in arterial pressure, left ventricular myocardial flow decreased (162 +/- 79 ml.min-1 x 100 g-1) as did myocardial O2 consumption (P < 0.05). Acute hypoxemia in five fetuses that received L-NNA was associated with significant further increases in systemic arterial pressure; however, left ventricular myocardial flow was only 771 +/- 237 ml.min-1 x 100 g-1, a value similar to that seen with adenosine and approximately 75% of that seen with acute hypoxemia alone. We conclude that nitric oxide plays an important role in the regulation of fetal myocardial flow during basal conditions as well as in the exuberant vasodilatory response associated with acute hypoxemic stress.
Substrate and inhibitor specificities of the monocarboxylate transporters of single rat heart cells
Authors: Wang X. , Levi A. J. , Halestrap A. P.
Published: December 2017

We have used the intracellular pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) to characterize the substrate and inhibitor specificity of monocarboxylate transport into isolated rat heart cells. Further evidence was obtained for the presence of two lactate carriers present in heart cells (Wang et al., Biochem. J. 290: 249-258, 1993) both distinct from the recently cloned monocarboxylate transporter isoform 1 (MCT-1) found in many other cell types. Only one isoform was potently inhibited by alpha-cyano-4-hydroxycinnamate [CHC; inhibitor constant (Ki) 190 microM] and the stilbene disulfonates 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (Ki 79 microM) and 4,4'-dinitrostilbene-2,2'-disulfonate (Ki of cis- and trans-isomers 38 and 171 microM, respectively; neither isomer inhibits MCT-1). The second carrier had a Ki of approximately 3 mM for CHC and 0.5-2 mM for the stilbene disulfonates. Thus, unlike in many other tissues, in rat heart cells these inhibitors are not effective at blocking lactate transport totally unless used at very high concentrations. Both carriers were inhibited by 3-isobutyl-1-methylxanthine (Ki 340 microM) and neither by 5-nitro-2-(3-phenylpropylamino)benzoate (a potent inhibitor of MCT-1). The overall Michaelis constant (Km) and maximum reaction rate (Vmax) for transport of a variety of substituted monocarboxylates (C2-C5) were determined, although it was not possible to elucidate the kinetic parameters of the two isoforms. Of physiological interest, the ketone bodies D-beta-hydroxybutyrate and acetoacetate had K(m) values of 10 and 5.4 mM, respectively. Vmax values were similar to those of L-lactate and pyruvate and indicate that transport could limit rates of utilization of ketone bodies. No stereoselectivity for L-over D-isomers of 2-chloro or 2-hydroxy acids was observed.
Effect of stepped hypoglycemia on regional cerebral blood flow response to physiological brain activation
Authors: Powers W. J. , Hirsch I. B. , Cryer P. E.
Published: December 2017

The effect of vasoactive stimuli on cerebral blood flow (CBF) has been variously reported as normal or impaired by hypoglycemia. We measured regional CBF (rCBF) in contralateral somato-sensory cortex at rest and during vibrotactile stimulation of one hand in four normal awake human volunteers during fasting euglycemia (5.1-5.2 mumol/ml) with 0.9% saline infusion, euglycemia (5.1-5.2 mumol/ml) with hyperinsulinemic clamp, mild hypoglycemia (3.2-3.6 mumol/ml) with hyperinsulinemic clamp, and moderate hypoglycemia (2.3-3.2 mumol/ml) with hyperinsulinemic clamp. No changes in mean arterial pressure, arterial PCO2, or arterial oxygen content occurred. There was no change in the magnitude of the normalized rCBF response to physiological brain stimulation with progressive arterial hypoglycemia (r = 0.10, P = 0.73). We interpret this to mean that there was a progressive reduction in cerebral glucose delivery to the area of physiological activation as arterial glucose concentrations fell. Therefore, the increase in rCBF during physiological brain activation is not regulated by a mechanism that matches local cerebral glucose supply to local cerebral glucose demand.