bluuebunny/crossref_metadata_2025 huggingface dataset:
Osmotic threshold and sensitivity for vasopressin release and Fos expression by hypertonic NaCl in ovine fetus
Authors: Xu Zhice , Glenda Calvario , Day Linda , Yao Jiaming , Ross Michael G.
Published: December 2017

In adults, hyperosmolality stimulates central osmoreceptors, resulting in arginine vasopressin (AVP) secretion. Near-term fetal sheep have also developed mechanisms to respond to intravascular hypertonicity with stimulation of in utero AVP release. However, prior studies demonstrating fetal AVP secretion have utilized plasma tonicity changes greater than those required for adult osmotically induced AVP stimulation. We sought to examine near-term fetal plasma osmolality threshold and sensitivity for stimulation of AVP secretion and to correlate plasma hormone levels with central neuronal responsiveness. Chronically instrumented ovine fetuses (130 ± 2 days) and maternal ewes simultaneously received either isotonic or hypertonic intravascular NaCl infusions. Maternal and fetal plasma AVP and angiotensin II (ANG II) levels were examined at progressively increasing levels of plasma hypertonicity. Intravenous hypertonic NaCl gradually elevated plasma osmolality and sodium levels. Both maternal and fetal plasma AVP increased during hypertonicity, whereas ANG II levels were not changed. Maternal AVP levels significantly increased with a 3% increase in plasma osmolality, whereas fetal plasma AVP significantly increased only at higher plasma osmolality levels (over 6%). Thus the slope of the regression of AVP vs. osmolality was greater for ewes than for fetuses (0.232 vs. 0.064), despite similar maternal and fetal plasma osmolality thresholds for AVP secretion (302 vs. 304 mosmol/kg). Hyperosmolality induced Fos immunoreactivity (FOS-ir) in the circumventricular organs of the fetal brain. FOS-ir was also demonstrated in the fetal supraoptic and paraventricular nuclei (SON and PVN), and double labeling demonstrated that AVP-containing neurons in the SON and PVN expressed Fos in response to intravenous NaCl. These results demonstrate that, in the ovine fetus at 130 days of gestation, neuroendocrine responses to cellular dehydration are functional, although they evidence a relatively reduced sensitivity for AVP secretion compared with the adult.
Effects of prolactin on osteoblast alkaline phosphatase and bone formation in the developing rat
Authors: Coss Djurdjica , Yang Lili , Kuo Chiaoyun Benson , Xu Xiaolei , Luben Richard A. , Walker Ameae M.
Published: December 2017

The purpose of the current study was to determine whether maternal prolactin (PRL) had any effects on bone formation in the developing rat pup. Because the most prevalent forms of PRL in rats are unmodified and phosphorylated PRL, both recombinant PRL and a molecular mimic of phosphorylated PRL (PP-PRL) were administered to pregnant animals. Blood samples from the dams showed normal estrogen and progesterone and no effect of extra PRL on parathyroid hormone (PTH), calcium, or alkaline phosphatase (AP). In newborn pups, however, there was a 30% decrease in blood AP in both PRL-treated groups, whereas PTH and calcium levels were not different from controls. When primary rat osteoblasts were exposed to both PRLs, AP activity was reduced, with PP-PRL being the more potent form of the hormone. Histological examination of pup bone formation showed reduced calvarial bone and reduced endochondral ossification in pups exposed to PP-PRL. These results are the first to show a direct inhibitory effect of PRL on osteoblast function.
Tissue-specific regulation of erythropoietin production in the murine kidney, brain, and uterus
Authors: Chikuma Mariko , Masuda Seiji , Kobayashi Toshihiro , Nagao Masaya , Sasaki Ryuzo
Published: December 2017

Erythropoietin (Epo) produced by the kidney regulates erythropoiesis. Recent evidence suggests that Epo in the cerebrum prevents neuron death and Epo in the uterus induces estrogen (E2)-dependent uterine angiogenesis. To elucidate how Epo expression is regulated in these tissues, ovariectomized mice were given E2and/or exposed to hypoxia, and the temporal patterns of Epo mRNA levels were examined. Epo mRNA levels in the kidney and cerebrum were elevated markedly within 4 h after exposure to hypoxia. Although the elevated level of Epo mRNA in the kidney decreased markedly within 8 h despite continuous hypoxia, the high level in the cerebrum was sustained for ≥24 h, indicating that downregulation operates in the kidney but not in the brain. E2transiently induced Epo mRNA in the uterus but not in the kidney and cerebrum. Interestingly, the uterine Epo mRNA was hypoxia inducible only in the presence of E2. Thus Epo expression appears to be regulated in a tissue-specific manner, endorsing the tissue-specific functions of Epo.
Calorigenic actions of leptin are additive to, but not dependent on, those of thyroid hormones
Authors: Wang Jin-Lin , Chinookoswong Narumol , Yin Songmei , Shi Zhi-Qing
Published: December 2017

We examined a possible mechanistic interaction between leptin and thyroid hormones in rats with hypothyroidism induced by thyroidectomy (TX) and propylthiouracil administration. In study 1, the TX rats were treated by vehicle (V, n = 9) or by recombinant murine leptin (L, 0.3 mg · kg−1 · day−1, n = 9) or were pair-fed (PF, n = 9) against L. In study 2, the TX rats were all given 3,3′5′-triiodo-l-thyronine (T3) replacement (T, 5 μg · kg−1 · day−1) to correct hypothyroidism. They were then subdivided into three groups, namely, vehicle (T+V, n = 9), leptin (T+L, n = 10), and pair-feeding (T+PF, n = 9), similar to study 1 except for T3 (T). Reduced food consumption and weight gain in the TX rats were reversed by T3 replacement. Leptin suppressed food intake in the TX rats regardless of T3 replacement. O2consumption (V˙o 2) and CO2production (V˙co 2) were reduced in TX rats ( P < 0.05 vs. normal) but were normalized by either T3 or leptin treatment. T+L additively increasedV˙o 2 andV˙co 2 ( P < 0.05 vs. TX, T3, and L). The respiratory exchange ratio was unaltered in TX rats, with and without T3, but was significantly reduced by L or T+L treatments. These results indicate that the metabolic actions of leptin are not dependent on a normal thyroid status and that the effects of leptin and T3 on oxidative metabolism are additive.
Development of leptin resistance in rat soleus muscle in response to high-fat diets
Authors: Steinberg Greg R. , Dyck David J.
Published: December 2017

Direct evidence for leptin resistance in peripheral tissues such as skeletal muscle does not exist. Therefore, we investigated the effects of different high-fat diets on lipid metabolism in isolated rat soleus muscle and specifically explored whether leptin's stimulatory effects on muscle lipid metabolism would be reduced after exposure to high-fat diets. Control (Cont, 12% kcal fat) and high-fat [60% kcal safflower oil (n-6) (HF-Saff); 48% kcal safflower oil plus 12% fish oil (n-3)] diets were fed to rats for 4 wk. After the dietary treatments, muscle lipid turnover and oxidation in the presence and absence of leptin was measured using pulse-chase procedures in incubated resting soleus muscle. In the absence of leptin, phospholipid, diacylglycerol, and triacylglycerol (TG) turnover were unaffected by the high-fat diets, but exogenous palmitate oxidation was significantly increased in the HF-Saff group. In Cont rats, leptin increased exogenous palmitate oxidation (21.4 ± 5.7 vs. 11.9 ± 1.61 nmol/g, P = 0.019) and TG breakdown (39.8 ± 5.6 vs. 27.0 ± 5.2 nmol/g, P = 0.043) and decreased TG esterification (132.5 ± 14.6 vs. 177.7 ± 29.6 nmol/g, P = 0.043). However, in both high-fat groups, the stimulatory effect of leptin on muscle lipid oxidation and hydrolysis was eliminated. Partial substitution of fish oil resulted only in the restoration of leptin's inhibition of TG esterification. Thus we hypothesize that, during the development of obesity, skeletal muscle becomes resistant to the effects of leptin, resulting in the accumulation of intramuscular TG. This may be an important initiating step in the development of insulin resistance common in obesity.
Pubertal alterations in growth and body composition. V. Energy expenditure, adiposity, and fat distribution
Authors: Roemmich James N. , Clark Pamela A. , Walter Kim , Patrie James , Weltman Arthur , Rogol A. D.
Published: December 2017

We determined whether activity energy expenditure (AEE, from doubly labeled water and indirect calorimetry) or physical activity [7-day physical activity recall (PAR)] was more related to adiposity and the validity of PAR estimated total energy expenditure (TEEPAR) in prepubertal and pubertal boys ( n = 14 and 15) and girls ( n = 13 and 18). AEE, but not physical activity hours, was inversely related to fat mass (FM) after accounting for the fat-free mass, maturation, and age (partial r = −0.35, P ≤ 0.01). From forward stepwise regression, pubertal maturation, AEE, and gender predicted FM ( r2= 0.36). Abdominal visceral fat and subcutaneous fat were not related to AEE or activity hours after partial correlation with FM, maturation, and age. When assuming one metabolic equivalent (MET) equals 1 kcal · kg body wt−1· h−1, TEEPARunderestimated TEE from doubly labeled water (TEE bias) by 555 kcal/day ± 2 SD limits of agreement of 913 kcal/day. The measured basal metabolic rate (BMR) was >1 kcal · kg body wt−1· h−1and remained so until 16 yr of age. TEE bias was reduced when setting 1 MET equal to the measured (bias = 60 ± 51 kcal/day) or predicted (bias = 53 ± 50 kcal/day) BMR but was not consistent for an individual child (± 2 SD limits of agreement of 784 and 764 kcal/day, respectively) or across all maturation groups. After BMR was corrected, TEE bias remained greatest in the prepubertal girls. In conclusion, in children and adolescents, FM is more strongly related to AEE than activity time, and AEE, pubertal maturation, and gender explain 36% of the variance in FM. PAR should not be used to determine TEE of individual children and adolescents in a research setting but may have utility in large population-based pediatric studies, if an appropriate MET value is used to convert physical activity data to TEE data.
pH dependence of bone resorption: mouse calvarial osteoclasts are activated by acidosis
Authors: Meghji Sajeda , Morrison Matthew S. , Henderson Brian , Arnett Timothy R.
Published: December 2017

We examined the effects of HCO3−and CO2acidosis on osteoclast-mediated Ca2+release from 3-day cultures of neonatal mouse calvaria. Ca2+release was minimal above pH 7.2 in control cultures but was stimulated strongly by the addition of small amounts of H+to culture medium (HCO3−acidosis). For example, addition of 4 meq/l H+reduced pH from 7.12 to 7.03 and increased Ca2+release 3.8-fold. The largest stimulatory effects (8- to 11-fold), observed with 15–16 meq/l added H+, were comparable to the maximal Ca2+release elicited by 1,25-dihydroxyvitamin D3[1,25(OH)2D3; 10 nM], parathyroid hormone (10 nM), or prostaglandin E2(1 μM); the action of these osteolytic agents was attenuated strongly when ambient pH was increased from ∼7.1 to ∼7.3. CO2acidosis was a less effective stimulator of Ca2+release than HCO3−acidosis over a similar pH range. Ca2+release stimulated by HCO3−acidosis was almost completely blocked by salmon calcitonin (20 ng/ml), implying osteoclast involvement. In whole mount preparations of control half-calvaria, ∼400 inactive osteoclast-like multinucleate cells were present; in calvaria exposed to HCO3−acidosis and to the other osteolytic agents studied, extensive osteoclastic resorption, with perforation of bones, was visible. HCO3−acidosis, however, reduced numbers of osteoclast-like cells by ∼50%, whereas 1,25(OH)2D3treatment caused increases of ∼75%. The results suggest that HCO3−acidosis stimulates resorption by activating mature osteoclasts already present in calvarial bones, rather than by inducing formation of new osteoclasts, and provide further support for the critical role of acid-base balance in controlling osteoclast function.
Effects of hyperprolactinemia on rat prostate growth: evidence of androgeno-dependence
Authors: Van Coppenolle Fabien , Slomianny Christian , Carpentier Françoise , Le Bourhis Xuefen , Ahidouch Ahmed , Croix Dominique , Legrand Guillaume , Dewailly Etienne , Fournier Sarah , Cousse Henri , Authie Dominique , Raynaud Jean-Pierre , Beauvillain Jean-Claude , Dupouy Jean-Paul , Prevarskaya Natalia
Published: December 2017

The effects of the polypeptide hormone prolactin (PRL) in the development and regulation of benign prostate hyperplasia (BPH) and also in prostate cancer are not very well characterized. This study examines the action of PRL, either alone or in association with androgens [testosterone (T) or dihydrotestosterone (DHT)], in the rat prostate gland. The effects of PRL and androgens were investigated after 30 and 60 days in control, castrated, castrated with a substitutive implant of T or DHT, and sham-operated Wistar rats. To enhance PRL release, we induced hyperprolactinemia by administering chronic injections of sulpiride (40 mg · kg−1 · day−1). Chronic hyperprolactinemia induces enlargement and inflammation of the lateral rat prostate without any histological changes on ventral and dorsal lobes. We also demonstrate that hyperprolactinemia induces Bcl-2 overexpression in the lateral rat prostate and that this could inhibit the level of apoptosis. The in vivo model established here is a useful in vivo approach for studying the hormonal regulation of normal and pathological prostate development.
Fat depot origin affects fatty acid handling in cultured rat and human preadipocytes
Authors: Caserta Frank , Tchkonia Tamara , Civelek Vildan N. , Prentki Marc , Brown Nicholas F. , McGarry J. Denis , Forse R. Armour , Corkey Barbara E. , Hamilton James A. , Kirkland James L.
Published: December 2017

Regional differences in free fatty acid (FFA) handling contribute to diseases associated with particular fat distributions. As cultured rat preadipocytes became differentiated, FFA transfer into preadipocytes increased and was more rapid in single perirenal than in epididymal cells matched for lipid content. Uptake by human omental preadipocytes was greater than uptake by abdominal subcutaneous preadipocytes. Adipose-specific fatty acid binding protein (aP2) and keratinocyte lipid binding protein abundance was higher in differentiated rat perirenal than in epididymal preadipocytes. This interdepot difference in preadipocyte aP2 expression was reflected in fat tissue in older animals. Carnitine palmitoyltransferase 1 activity increased during differentiation and was higher in perirenal than in epididymal preadipocytes, particularly the muscle isoform. Long-chain acyl-CoA levels were higher in perirenal than in epididymal preadipocytes and isolated fat cells. These data are consistent with interdepot differences in fatty acid flux ensuing from differences in fatty acid binding proteins and enzymes of fat metabolism. Heterogeneity among depots results, in part, from distinct intrinsic characteristics of adipose cells. Different depots are effectively separate miniorgans.
Involvement of the suprachiasmatic nucleus in diurnal ACTH and corticosterone responsiveness to stress
Authors: Sage Dominique , Maurel Daniel , Bosler Olivier
Published: December 2017

We explored the contribution of the suprachiasmatic nucleus (SCN) in ACTH and corticosterone (CORT) diurnal responsiveness of the rat to restraint stress applied either in the morning (AM) or in the evening (PM). Ablation of the SCN caused the diurnal rhythmicity of the CORT response to disappear but had no effects on AM vs. PM differences in the ACTH response. Stress-response curves in SCN-lesioned rats that had prestress levels of CORT either in the AM range or in the PM range, when compared with those obtained for AM and PM controls, showed that the SCN differentially regulates the stress response depending on the underlying secretory activity of the adrenal cortex. When basal CORT secretion is at its lowest, the SCN inhibits CORT responsiveness to stress by controlling pituitary corticotrophs; but when it is at its highest, it has a permissive action that will bypass the hypophysis and reach the adrenals to adjust the response of the gland to ACTH.
Unreliable use of standard muscle hydration value in obesity
Authors: Mingrone G. , Bertuzzi A. , Capristo E. , Greco A. V. , Manco M. , Pietrobelli A. , Salinari S. , Heymsfield S. B.
Published: December 2017

Intramuscular water content is assumed to be constant in humans independent of their anthropometric characteristics. To verify whether this assumption is correct, intramuscular water, proteins, glycogen, and both total and intramyocytic triglycerides were measured in 51 samples of rectus abdominis muscle obtained from 16 lean and 35 overweight and obese subjects (body mass index cutoff 24.9 kg/m2). Data (referred to as wet tissue) were analyzed by means of a composition model at the cellular level of the skeletal muscle (SM). The average SM water content was 76.3 ± 3.3% in normal-weight individuals and 65.7 ± 5.8% in obese subjects ( P < 0.0001). Total triglycerides were 5.5 ± 2.3% in controls and 19.0 ± 7.0% in obese subjects ( P < 0.0001). The intramyocytic triglyceride fraction was also increased in obese subjects. The composition model provides an explanation for the negative correlation between total triglycerides and intramuscular water, and some of the model parameters were determined from the experimental data. In conclusion, although the hydration of fat-free SM mass may be unchanged in obese subjects, the hydration of in toto muscle mass decreases as its lipid content increases.
A stochastic differential equation model of diurnal cortisol patterns
Authors: Brown Emery N. , Meehan Patricia M. , Dempster Arthur P.
Published: December 2017

Circadian modulation of episodic bursts is recognized as the normal physiological pattern of diurnal variation in plasma cortisol levels. The primary physiological factors underlying these diurnal patterns are the ultradian timing of secretory events, circadian modulation of the amplitude of secretory events, infusion of the hormone from the adrenal gland into the plasma, and clearance of the hormone from the plasma by the liver. Each measured plasma cortisol level has an error arising from the cortisol immunoassay. We demonstrate that all of these three physiological principles can be succinctly summarized in a single stochastic differential equation plus measurement error model and show that physiologically consistent ranges of the model parameters can be determined from published reports. We summarize the model parameters in terms of the multivariate Gaussian probability density and establish the plausibility of the model with a series of simulation studies. Our framework makes possible a sensitivity analysis in which all model parameters are allowed to vary simultaneously. The model offers an approach for simultaneously representing cortisol's ultradian, circadian, and kinetic properties. Our modeling paradigm provides a framework for simulation studies and data analysis that should be readily adaptable to the analysis of other endocrine hormone systems.
Generation of growth hormone pulsatility in women: evidence against somatostatin withdrawal as pulse initiator
Authors: Dimaraki Eleni V. , Jaffe Craig A. , Demott-Friberg Roberta , Russell-Aulet Mary , Bowers Cyril Y. , Marbach Peter , Barkan Ariel L.
Published: December 2017

To test whether endogenous hypothalamic somatostatin (SRIH) fluctuations are playing a role in the generation of growth hormone (GH) pulses, continuous subcutaneous octreotide infusion (16 μg/h) was used to create constant supraphysiological somatostatinergic tone. Six healthy postmenopausal women (age 67 ± 3 yr, body mass index 24.7 ± 1.2 kg/m2) were studied during normal saline and octreotide infusion providing stable plasma octreotide levels of 2,567 ± 37 pg/ml. Blood samples were obtained every 10 min for 24 h, and plasma GH was measured with a sensitive chemiluminometric assay. Octreotide infusion suppressed 24-h mean GH by 84 ± 3% ( P = 0.00026), GH pulse amplitude by 90 ± 3% ( P = 0.00031), and trough GH by 54 ± 5% ( P = 0.0012), whereas GH pulse frequency remained unchanged. The response of GH to GH-releasing hormone (GHRH) was not suppressed, and the GH response to GH-releasing peptide-6 (GHRP-6) was unaffected. We conclude that, in women, periodic declines in hypothalamic SRIH secretion are not the driving force of endogenous GH pulses, which are most likely due to episodic release of GHRH and/or the endogenous GHRP-like ligand.
Increased bone turnover is associated with protein and energy metabolism in adolescents with sickle cell anemia
Authors: Buchowski Maciej S. , de la Fuente F. Alexander , Flakoll Paul J. , Chen Kong Y. , Turner Ernest A.
Published: December 2017

Contribution of bone turnover to the hypercatabolic state observed in sickle cell anemia is unknown. We examined the association between markers of bone turnover and basal rates of whole body protein turnover and energy expenditure in 28 adolescents with homozygous sickle cell anemia (HbSS) and in 26 matched controls with normal phenotype (HbAA). Whole body protein breakdown and synthesis were measured using a stable isotope of [15N]glycine, resting energy expenditure was measured by whole room indirect calorimetry, and the rate of pyridinoline cross-link (PYD) excretion in urine and fasting serum levels of the type I procollagen carboxy-terminal propeptide (PICP) were measured with commercial kits. Urinary PYD and serum PICP were significantly elevated in HbSS patients. The increase in procollagen synthesis, indicated by high levels of PICP, was significantly correlated with increased whole body protein synthesis. The increase in type I collagen degradation, indicated by high PYD excretion, was significantly correlated with increased protein breakdown. We conclude that increased rates of bone turnover contribute to the increased rates of protein turnover and energy expenditure observed in adolescents with homozygous sickle cell anemia.
AMP-activated protein kinase activity and glucose uptake in rat skeletal muscle
Authors: Musi Nicolas , Hayashi Tatsuya , Fujii Nobuharu , Hirshman Michael F. , Witters Lee A. , Goodyear Laurie J.
Published: December 2017

The AMP-activated protein kinase (AMPK) has been hypothesized to mediate contraction and 5-aminoimidazole-4-carboxamide 1-β-d-ribonucleoside (AICAR)-induced increases in glucose uptake in skeletal muscle. The purpose of the current study was to determine whether treadmill exercise and isolated muscle contractions in rat skeletal muscle increase the activity of the AMPKα1 and AMPKα2 catalytic subunits in a dose-dependent manner and to evaluate the effects of the putative AMPK inhibitors adenine 9-β-d-arabinofuranoside (ara-A), 8-bromo-AMP, and iodotubercidin on AMPK activity and 3- O-methyl-d-glucose (3-MG) uptake. There were dose-dependent increases in AMPKα2 activity and 3-MG uptake in rat epitrochlearis muscles with treadmill running exercise but no effect of exercise on AMPKα1 activity. Tetanic contractions of isolated epitrochlearis muscles in vitro significantly increased the activity of both AMPK isoforms in a dose-dependent manner and at a similar rate compared with increases in 3-MG uptake. In isolated muscles, the putative AMPK inhibitors ara-A, 8-bromo-AMP, and iodotubercidin fully inhibited AICAR-stimulated AMPKα2 activity and 3-MG uptake but had little effect on AMPKα1 activity. In contrast, these compounds had absent or minimal effects on contraction-stimulated AMPKα1 and -α2 activity and 3-MG uptake. Although the AMPKα1 and -α2 isoforms are activated during tetanic muscle contractions in vitro, in fast-glycolytic fibers, the activation of AMPKα2-containing complexes may be more important in regulating exercise-mediated skeletal muscle metabolism in vivo. Development of new compounds will be required to study contraction regulation of AMPK by pharmacological inhibition.
Physiological hyperinsulinemia impairs insulin-stimulated glycogen synthase activity and glycogen synthesis
Authors: Iozzo Patricia , Pratipanawatr Thonchai , Pijl Hanno , Vogt Christoph , Kumar Vineeta , Pipek Ruben , Matsuda Masafumi , Mandarino Lawrence J. , Cusi Kenneth J. , DeFronzo Ralph A.
Published: December 2017

Although chronic hyperinsulinemia has been shown to induce insulin resistance, the basic cellular mechanisms responsible for this phenomenon are unknown. The present study was performed 1) to determine the time-related effect of physiological hyperinsulinemia on glycogen synthase (GS) activity, hexokinase II (HKII) activity and mRNA content, and GLUT-4 protein in muscle from healthy subjects, and 2) to relate hyperinsulinemia-induced alterations in these parameters to changes in glucose metabolism in vivo. Twenty healthy subjects had a 240-min euglycemic insulin clamp study with muscle biopsies and then received a low-dose insulin infusion for 24 ( n = 6) or 72 h ( n = 14) (plasma insulin concentration = 121 ± 9 or 143 ± 25 pmol/l, respectively). During the baseline insulin clamp, GS fractional velocity (0.075 ± 0.008 to 0.229 ± 0.02, P < 0.01), HKII mRNA content (0.179 ± 0.034 to 0.354 ± 0.087, P < 0.05), and HKII activity (2.41 ± 0.63 to 3.35 ± 0.54 pmol · min−1· ng−1, P < 0.05), as well as whole body glucose disposal and nonoxidative glucose disposal, increased. During the insulin clamp performed after 24 and 72 h of sustained physiological hyperinsulinemia, the ability of insulin to increase muscle GS fractional velocity, total body glucose disposal, and nonoxidative glucose disposal was impaired (all P < 0.01), whereas the effect of insulin on muscle HKII mRNA, HKII activity, GLUT-4 protein content, and whole body rates of glucose oxidation and glycolysis remained unchanged. Muscle glycogen concentration did not change [116 ± 28 vs. 126 ± 29 μmol/kg muscle, P = nonsignificant (NS)] and was not correlated with the change in nonoxidative glucose disposal ( r = 0.074, P = NS). In summary, modest chronic hyperinsulinemia may contribute directly (independent of change in muscle glycogen concentration) to the development of insulin resistance by its impact on the GS pathway.
Adipose tissue tumor necrosis factor and interleukin-6 expression in human obesity and insulin resistance
Authors: Kern Philip A. , Ranganathan Subramanian , Li Chunling , Wood Linda , Ranganathan Gouri
Published: December 2017

Adipose tissue expresses tumor necrosis factor (TNF) and interleukin (IL)-6, which may cause obesity-related insulin resistance. We measured TNF and IL-6 expression in the adipose tissue of 50 lean and obese subjects without diabetes. Insulin sensitivity (SI) was determined by an intravenous glucose tolerance test with minimal-model analysis. When lean [body mass index (BMI) <25 kg/m2] and obese (BMI 30–40 kg/m2) subjects were compared, there was a 7.5-fold increase in TNF secretion ( P < 0.05) from adipose tissue, and the TNF secretion was inversely related to SI( r = −0.42, P < 0.02). IL-6 was abundantly expressed by adipose tissue. In contrast to TNF, plasma (rather than adipose) IL-6 demonstrated the strongest relationship with obesity and insulin resistance. Plasma IL-6 was significantly higher in obese subjects and demonstrated a highly significant inverse relationship with SI ( r = −0.71, P < 0.001). To separate the effects of BMI from SI, subjects who were discordant for SI were matched for BMI, age, and gender. By use of this approach, subjects with low SI demonstrated a 3.0-fold increased level of TNF secretion from adipose tissue and a 2.3-fold higher plasma IL-6 level ( P < 0.05) compared with matched subjects with a high SI. Plasma IL-6 was significantly associated with plasma nonesterified fatty acid levels ( r = 0.49, P < 0.002). Thus the local expression of TNF and plasma IL-6 are higher in subjects with obesity-related insulin resistance.
High-fat hypocaloric diet modifies carbohydrate utilization of obese rats during weight loss
Authors: Cha Ming C. , Johnson Julia A. , Hsu Chang-Yun , Boozer Carol N.
Published: December 2017

The effects of fat content in the hypocaloric diet on whole body glucose oxidation and adipocyte glucose transport were investigated in two animal-feeding experiments. Diet-induced obese rats were food restricted to 75% of their previous energy intakes with either a high (45% by calorie) or a low (12% by calorie) corn oil diet for 9 wk ( experiment 1) or 10 days ( experiment 2). The losses of body weight ( P< 0.05) and adipose depot weight ( P < 0.05) were less in the 45% compared with the 12% fat group. During the dynamic phase of weight loss ( day 10 of food restriction), plasma glucose and insulin concentrations were higher ( P < 0.05) in the 45% than those in the 12% fat group. Whole body carbohydrate oxidation rate in response to an oral load of glucose was increased ( P < 0.001) by food restriction in both dietary groups; however, carbohydrate oxidation rates were lower ( P < 0.01) in the 45% than in the 12% fat-fed rats during the weight loss period. Adipocyte glucose transport was greater ( P < 0.02) in the 45% than in the 12% fat group in an intra-abdominal adipose depot but not in subcutaneous fat. These data suggest that dietary fat content modifies whole body glucose oxidation and intra-abdominal adipocyte glucose uptake during weight loss.
Systemic and regional free fatty acid metabolism in type 2 diabetes
Authors: Basu Ananda , Basu Rita , Shah Pankaj , Vella Adrian , Rizza Robert A. , Jensen Michael D.
Published: December 2017

To determine whether type 2 diabetes mellitus alters systemic and regional free fatty acid ([3H]palmitate) metabolism, 14 nondiabetic (ND) and 14 type 2 diabetic (D) subjects underwent hyperinsulinemic-hyperglycemic (∼9.3 mM) clamps. The subjects were matched for age, body mass index, percent body fat, and fat-free mass. D subjects had more ( P < 0.05) visceral fat than ND. During somatostatin, replacement growth hormone, and glucagon infusions, insulin was infused to achieve moderate (∼75 pmol/l) and high (∼150 pmol/l) physiological insulin levels. D subjects had greater ( P < 0.02) systemic and regional (splanchnic and leg) palmitate release than ND subjects during both insulin infusion intervals. The relative contributions of splanchnic, leg, and nonsplanchnic upper body regions to systemic palmitate release did not differ between groups, although the last contributed the most (∼75%) to systemic palmitate release. Visceral fat area correlated with systemic palmitate flux ( r = 0.45, P < 0.03) during both insulin infusions. We conclude that type 2 diabetes is associated with a generalized impairment in insulin suppression of lipolysis compared with equally obese ND individuals.
ATP production and efficiency of human skeletal muscle during intense exercise: effect of previous exercise
Authors: Bangsbo Jens , Krustrup Peter , González-Alonso José , Saltin Bengt
Published: December 2017

The aim of the present study was to examine whether ATP production increases and mechanical efficiency decreases during intense exercise and to evaluate how previous exercise affects ATP turnover during intense exercise. Six subjects performed two (EX1 and EX2) 3-min one-legged knee-extensor exercise bouts [66.2 ± 3.9 and 66.1 ± 3.9 (±SE) W] separated by a 6-min rest period. Anaerobic ATP production, estimated from net changes in and release of metabolites from the active muscle, was 3.5 ± 1.2, 2.4 ± 0.6, and 1.4 ± 0.2 mmol ATP · kg dry wt−1· s−1during the first 5, next 10, and remaining 165 s of EX1, respectively. The corresponding aerobic ATP production, determined from muscle oxygen uptake, was 0.7 ± 0.1, 1.4 ± 0.2, and 4.7 ± 0.4 mmol ATP · kg dry wt−1· s−1, respectively. The mean rate of ATP production during the first 5 s and next 10 s was lower ( P < 0.05) than during the rest of the exercise (4.2 ± 1.2 and 3.8 ± 0.7 vs. 6.1 ± 0.3 mmol ATP · kg dry wt−1· s−1). Thus mechanical efficiency, expressed as work per ATP produced, was lowered ( P < 0.05) in the last phase of exercise (39.6 ± 6.1 and 40.7 ± 5.8 vs. 25.0 ± 1.3 J/mmol ATP). The anaerobic ATP production was lower ( P < 0.05) in EX2 than in EX1, but the aerobic ATP turnover was higher ( P < 0.05) in EX2 than in EX1, resulting in the same muscle ATP production in EX1 and EX2. The present data suggest that the rate of ATP turnover increases during intense exercise at a constant work rate. Thus mechanical efficiency declines as intense exercise is continued. Furthermore, when intense exercise is repeated, there is a shift toward greater aerobic energy contribution, but the total ATP turnover is not significantly altered.
Postexercise nutrient intake timing in humans is critical to recovery of leg glucose and protein homeostasis
Authors: Levenhagen Deanna K. , Gresham Jennifer D. , Carlson Michael G. , Maron David J. , Borel Myfanwy J. , Flakoll Paul J.
Published: December 2017

Although the importance of postexercise nutrient ingestion timing has been investigated for glycogen metabolism, little is known about similar effects for protein dynamics. Each subject ( n = 10) was studied twice, with the same oral supplement (10 g protein, 8 g carbohydrate, 3 g fat) being administered either immediately (EARLY) or 3 h (LATE) after 60 min of moderate-intensity exercise. Leg blood flow and circulating concentrations of glucose, amino acids, and insulin were similar for EARLY and LATE. Leg glucose uptake and whole body glucose utilization (d-[6,6-2H2]glucose) were stimulated threefold and 44%, respectively, for EARLY vs. LATE. Although essential and nonessential amino acids were taken up by the leg in EARLY, they were released in LATE. Although proteolysis was unaffected, leg (l-[ ring-2H5]phenylalanine) and whole body (l-[1-13C]leucine) protein synthesis were elevated threefold and 12%, respectively, for EARLY vs. LATE, resulting in a net gain of leg and whole body protein. Therefore, similar to carbohydrate homeostasis, EARLY postexercise ingestion of a nutrient supplement enhances accretion of whole body and leg protein, suggesting a common mechanism of exercise-induced insulin action.
A mathematical model of compartmentalized neurotransmitter metabolism in the human brain
Authors: Gruetter Rolf , Seaquist Elizabeth R. , Ugurbil Kâmil
Published: December 2017

After administration of enriched [1-13C]glucose, the rate of13C label incorporation into glutamate C4, C3, and C2, glutamine C4, C3, and C2, and aspartate C2 and C3 was simultaneously measured in six normal subjects by13C NMR at 4 Tesla in 45-ml volumes encompassing the visual cortex. The resulting eight time courses were simultaneously fitted to a mathematical model. The rate of (neuronal) tricarboxylic acid cycle flux ( VPDH), 0.57 ± 0.06 μmol · g−1· min−1, was comparable to the exchange rate between (mitochondrial) 2-oxoglutarate and (cytosolic) glutamate ( Vx, 0.57 ± 0.19 μmol · g−1· min−1), which may reflect to a large extent malate-aspartate shuttle activity. At rest, oxidative glucose consumption [CMRGlc(ox)] was 0.41 ± 0.03 μmol · g−1· min−1, and (glial) pyruvate carboxylation ( VPC) was 0.09 ± 0.02 μmol · g−1· min−1. The flux through glutamine synthetase ( Vsyn) was 0.26 ± 0.06 μmol · g−1· min−1. A fraction of Vsynwas attributed to be from (neuronal) glutamate, and the corresponding rate of apparent glutamatergic neurotransmission ( VNT) was 0.17 ± 0.05 μmol · g−1· min−1. The ratio [ VNT/CMRGlc(ox)] was 0.41 ± 0.14 and thus clearly different from a 1:1 stoichiometry, consistent with a significant fraction (∼90%) of ATP generated in astrocytes being oxidative. The study underlines the importance of assumptions made in modeling13C labeling data in brain.
Increased IGFR activity and glucose transport in cultured skeletal muscle from insulin receptor null mice
Authors: Shefi-Friedman Liat , Wertheimer Efrat , Shen Shlomzion , Bak Asia , Accili Domenico , Sampson Sanford R.
Published: December 2017

We have studied the role of the insulin receptor (IR) in metabolic and growth-promoting effects of insulin on primary cultures of skeletal muscle derived from the limb muscle of IR null mice. Cultures of IR null skeletal muscle displayed normal morphology and spontaneous contractile activity. Expression of muscle-differentiating proteins was slightly reduced in myoblasts and myotubes of the IR null skeletal muscle cells, whereas that of the Na+/K+pump appeared to be unchanged. Insulin-like growth factor receptor (IGFR) expression was higher in myoblasts from IR knockout (IRKO) than from IR wild-type (IRWT) mice but was essentially unchanged in myotubes. Expression of the GLUT-1 and GLUT-4 transporters appeared to be higher in IRKO than in IRWT myoblasts and was significantly greater in myotubes from IRKO than from IRWT cultures. Consistent with GLUT expression, both basal and insulin or insulin-like growth factor I (IGF-I)-stimulated glucose uptakes were higher in IR null skeletal myotubes than in wild-type skeletal myotubes. Interestingly, autophosphorylation of IGFR induced by insulin and IGF-I was markedly increased in IR null skeletal myotubes. These results indicate that, in the absence of IR, there is a compensatory increase in basal as well as in insulin- and IGF-I-induced glucose transport, the former being mediated via increased activation of the IGF-I receptor.
Glucose uptake and metabolism by cultured human skeletal muscle cells: rate-limiting steps
Authors: Perriott Laureta M. , Kono Tetsuro , Whitesell Richard R. , Knobel Susan M. , Piston David W. , Granner Daryl K. , Powers Alvin C. , May James M.
Published: December 2017

To use primary cultures of human skeletal muscle cells to establish defects in glucose metabolism that underlie clinical insulin resistance, it is necessary to define the rate-determining steps in glucose metabolism and to improve the insulin response attained in previous studies. We modified experimental conditions to achieve an insulin effect on 3- O-methylglucose transport that was more than twofold over basal. Glucose phosphorylation by hexokinase limits glucose metabolism in these cells, because the apparent Michaelis-Menten constant of coupled glucose transport and phosphorylation is intermediate between that of transport and that of the hexokinase and because rates of 2-deoxyglucose uptake and phosphorylation are less than those of glucose. The latter reflects a preference of hexokinase for glucose over 2-deoxyglucose. Cellular NAD(P)H autofluorescence, measured using two-photon excitation microscopy, is both sensitive to insulin and indicative of additional distal control steps in glucose metabolism. Whereas the predominant effect of insulin in human skeletal muscle cells is to enhance glucose transport, phosphorylation, and steps beyond, it also determines the overall rate of glucose metabolism.
Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise
Authors: Tipton Kevin D. , Rasmussen Blake B. , Miller Sharon L. , Wolf Steven E. , Owens-Stovall Sharla K. , Petrini Bart E. , Wolfe Robert R.
Published: December 2017

The present study was designed to determine whether consumption of an oral essential amino acid-carbohydrate supplement (EAC) before exercise results in a greater anabolic response than supplementation after resistance exercise. Six healthy human subjects participated in two trials in random order, PRE (EAC consumed immediately before exercise), and POST (EAC consumed immediately after exercise). A primed, continuous infusion ofl-[ ring-2H5]phenylalanine, femoral arteriovenous catheterization, and muscle biopsies from the vastus lateralis were used to determine phenylalanine concentrations, enrichments, and net uptake across the leg. Blood and muscle phenylalanine concentrations were increased by ∼130% after drink consumption in both trials. Amino acid delivery to the leg was increased during exercise and remained elevated for the 2 h after exercise in both trials. Delivery of amino acids (amino acid concentration times blood flow) was significantly greater in PRE than in POST during the exercise bout and in the 1st h after exercise ( P < 0.05). Total net phenylalanine uptake across the leg was greater ( P = 0.0002) during PRE (209 ± 42 mg) than during POST (81 ± 19). Phenylalanine disappearance rate, an indicator of muscle protein synthesis from blood amino acids, increased after EAC consumption in both trials. These results indicate that the response of net muscle protein synthesis to consumption of an EAC solution immediately before resistance exercise is greater than that when the solution is consumed after exercise, primarily because of an increase in muscle protein synthesis as a result of increased delivery of amino acids to the leg.
Lack of hepatic “interregulation” during inhibition of glycogenolysis in a canine model
Authors: Fosgerau K. , Mittelman S. D. , Sunehag A. , Dea M. K. , Lundgren K. , Bergman R. N.
Published: December 2017

It has been proposed that the glycogenolytic and gluconeogenic pathways contributing to endogenous glucose production are interrelated. Thus a change in one source of glucose 6-phosphate might be compensated for by an inverse change in the other pathway. We therefore investigated the effects of 1,4-dideoxy-1,4-imino-d-arabinitol (DAB), a potent glycogen phosphorylase inhibitor, on glucose production in fasted conscious dogs. When dogs were treated acutely with high glucagon, glucose production rose from 1.93 ± 0.14 to 3.07 ± 0.37 mg · kg−1· min−1( P < 0.01). When dogs were treated acutely with DAB in addition to high glucagon infusion, the stimulation of the glycogenolytic rate was completely suppressed. Glucose production rose from 1.85 ± 0.20 to 2.41 ± 0.17 mg · kg−1· min−1( P < 0.05), which was due to the increase in gluconeogenesis from 0.93 ± 0.09 to 1.54 ± 0.08 mg · kg−1· min−1( P < 0.001). In conclusion, infusion of DAB inhibited glycogenolysis; however, the absolute contribution of gluconeogenesis to glucose production was not affected. These results suggest that inhibition of glycogenolysis could be an effective antidiabetic treatment.
Efficacy of bright light and sleep/darkness scheduling in alleviating circadian maladaptation to night work
Authors: Horowitz Todd S. , Cade Brian E. , Wolfe Jeremy M. , Czeisler Charles A.
Published: December 2017

We tested the hypothesis that circadian adaptation to night work is best achieved by combining bright light during the night shift and scheduled sleep in darkness. Fifty-four subjects participated in a shift work simulation of 4 day and 3 night shifts followed by a 38-h constant routine (CR). Subjects received 2,500 lux ( Bright Light) or 150 lux ( Room Light) during night shifts and were scheduled to sleep (at home in darkened bedrooms) from 0800 to 1600 ( Fixed Sleep) or ad libitum ( Free Sleep). Dim light melatonin onset (DLMO) was measured before and after the night shifts. Both Fixed Sleepand Bright Light conditions significantly phase delayed DLMO. Treatments combined additively, with light leading to larger phase shifts. Free Sleep subjects who spontaneously adopted consistent sleep schedules adapted better than those who did not. Neither properly timed bright light nor fixed sleep schedules were consistently sufficient to shift the melatonin rhythm completely into the sleep episode. Scheduling of sleep/darkness should play a major role in prescriptions for overcoming shift work-related phase misalignment.
Renal clearance of endogenous leptin in hypertensive humans with or without renal artery stenosis
Authors: Fogteloo A. J. , Meinders A. E. , Pijl H. , Kroon A. A. , Frölich M. , De Leeuw P. W.
Published: December 2017

In humans, the kidney is involved in leptin clearance from the body. The present study was performed to assess the renal extraction of leptin in hypertensive patients with or without renal artery stenosis. Sixty-five hypertensive subjects (39 males and 26 females) underwent catheterization of the renal artery and both renal veins with blood sampling for measuring leptin levels. Blood flow to both kidneys was measured by the xenon washout technique. From these data, renal leptin uptake and renal fractional extraction of leptin were calculated. Endogenous creatinine clearance ranged from 24 to 191 ml/min in the males and from 20 to 149 ml/min in the females. In 25 patients, radiological signs of renal artery stenosis were present. Total renal leptin uptake by both kidneys averaged 141 ± 47 ng · min−1· 100 g−1. No differences in leptin uptake were found between males and females or between patients with or without renal artery stenosis. The average renal extraction fraction of leptin was 6 ± 2%. Renal leptin uptake and renal extraction fraction of leptin did not correlate with arterial leptin concentrations or with blood pressure, endogenous creatinine clearance, or the presence or absence of renal artery stenosis. In hypertensive patients with or without renal artery stenosis, the kidney removes only a small fraction of circulating leptin from the body within one passage. This fraction remains relatively constant despite wide variations in renal function or circulating leptin.
Effects of antecedent hypoglycemia, hyperinsulinemia, and excess corticosterone on hypoglycemic counterregulation
Authors: Shum Kathy , Inouye Karen , Chan Owen , Mathoo Julian , Bilinski Debra , Matthews Stephen G. , Vranic Mladen
Published: December 2017

This study aimed to differentiate the effects of repeated antecedent hypoglycemia, antecedent marked hyperinsulinemia, and antecedent increases in corticosterone on counterregulation to subsequent hypoglycemia in normal rats. Specifically, we examined whether exposure to hyperinsulinemia or elevated corticosterone per se could impair subsequent counterregulation. Four groups of male Sprague-Dawley rats were used: 1) normal controls (N) had 4 days of sham antecedent treatment; 2) an antecedent hypoglycemia group (AH) had 7 episodes of hyperinsulinemic hypoglycemia over 4 days; 3) an antecedent hyperinsulinemia group (AE) had 7 episodes of hyperinsulinemic euglycemia; and 4) an antecedent corticosterone group (AC) had 7 episodes of intravenous corticosterone to simulate the hypoglycemic corticosterone levels in AH rats. On day 5, hyperinsulinemic euglycemic-hypoglycemic clamps were performed. Epinephrine responses to hypoglycemia were impaired ( P< 0.05 vs. N) after antecedent hypoglycemia and hyperinsulinemia. This correlated with diminished ( P < 0.05 vs. N) absolute glucose production responses in AH rats and diminished incremental glucose production responses in AE rats. Paradoxically, norepinephrine responses were increased ( P < 0.05 vs. N) after antecedent hypoglycemia. Glucagon and corticosterone responses were unaffected by antecedent hypoglycemia and hyperinsulinemia. In AC rats, incremental but not absolute glucose production responses were decreased ( P < 0.05 vs. N). However, neuroendocrine counterregulation was unaltered. We conclude that both antecedent hypoglycemia and hyperinsulinemia impair epinephrine and glucose production responses to subsequent hypoglycemia, suggesting that severe recurrent hyperinsulinemia may contribute to the development of hypoglycemia-associated autonomic failure.
ATP from glycolysis is required for normal sodium homeostasis in resting fast-twitch rodent skeletal muscle
Authors: Okamoto Ken , Wang Weiyang , Rounds Jan , Chambers Elizabeth A. , Jacobs Danny O.
Published: December 2017

Myocellular sodium homeostasis is commonly disrupted during critical illness for unknown reasons. Recent data suggest that changes in intracellular sodium content and the amount of ATP provided by glycolysis are closely related. The role of glycolysis and oxidative phosphorylation in providing fuel to the Na+-K+pump was investigated in resting rat extensor digitorum longus muscles incubated at 30°C for 1 h. Oxidative inhibition with carbonyl cyanide m-chlorophenylhydrazone, known as CCCP (0.2 μM), or by hypooxygenation did not alter myocellular sodium or potassium content ([Na+]i, [K+]i, respectively), whereas treatment with iodoacetic acid (0.3 mM), which effectively blocked glycolysis, dramatically increased [Na+]iand the [Na+]i/[K+]iratio. Experiments using ouabain and measurements of myocellular high-energy phosphates indicate that Na+-K+-ATPase activity is only impaired when glycolysis is inhibited. The data suggest that normal glycolysis is required to regulate intracellular sodium in fast-twitch skeletal muscles, because it is the predominant source of the fuel for the Na+-K+-ATPase.