bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of 1-mo bolus subcutaneous administration of exendin-4 in type 2 diabetes
Authors: Egan Josephine M. , Meneilly Graydon S. , Elahi Dariush
Published: March 2015

A gut insulinotropic peptide, glucagon-like peptide-1 (GLP-1), when given continuously subcutaneously, has been shown to be an effective agent to treat type 2 diabetes. Because of inactivation by dipeptidyl peptidase IV (DPP IV), it has a very short half-life (90–120 s), hence the need for continuous administration. Exendin-4 is an agonist of the GLP-1 receptor. It is not a substrate for DPP IV, and we previously demonstrated that intravenous administration has potent insulinotropic properties in type 2 diabetic volunteers. We evaluated the efficacy of bolus subcutaneous exendin-4 in insulin-naive type 2 diabetic volunteers. Ten patients aged 44–72 yr with mean fasting glucose levels of 11.4 ± 0.9 mmol/l were enrolled, and daily or twice-daily bolus subcutaneous exendin-4 was self-administered for 1 mo. Glycosylated hemoglobin, multiple daily capillary blood glucose, β-cell sensitivity to glucose, and peripheral tissue sensitivity to insulin were compared before and after treatment. The greatest decline in capillary blood glucose was seen before bed, with a drop from 15.5 to 9.2 mmol/l ( P < 0.0001). Glycosylated hemoglobin improved significantly with treatment, from 9.1 to 8.3% ( P = 0.009). β-Cell sensitivity to glucose was improved, as assessed by C-peptide levels during a hyperglycemic clamp. No significant adverse effects were noted or reported. Our data suggest that, even with this short duration of therapy, exendin-4 treatment had a significant effect on glucose homeostasis.
Chronic inflammation and the effect of IGF-I on muscle strength and power in older persons
Authors: Barbieri Michelangela , Ferrucci Luigi , Ragno Emilia , Corsi Annamaria , Bandinelli Stefania , Bonafè Massimiliano , Olivieri Fabiola , Giovagnetti Simona , Franceschi Claudio , Guralnik Jack M. , Paolisso Giuseppe
Published: March 2015

Deregulation of the inflammatory response plays a major role in the age-related decline of physical performance. The causal pathway leading from inflammation to disability has not been fully clarified, but several researches suggest that interleukin-6 (IL-6) causes a reduction of physical performance in elderly through its effect on muscle function. In vitro studies demonstrated that IL-6 inhibits the secretion of insulin-like growth factor I (IGF-I) and its biological activity, suggesting that the negative effect of IL-6 on muscle function might be mediated through IGF-I. We evaluated the joint effect of IGF-I and IL-6 on muscle function in a population-based sample of 526 persons with a wide age range (20–102 yr). After adjusting for potential confounders, such as age, sex, body mass index, IL-6 receptor, and IL-6 promoter polymorphism, IL-6, IGF-I, and their interaction were significant predictors of handgrip and muscle power. In analyses stratified by IL-6 tertiles, IGF-I was an independent predictor of muscle function only in subjects in the lowest IL-6 tertile, suggesting that the effect of IGF-I on muscle function depends on IL-6 levels. This mechanism may explain why IL-6 is a strong risk factor for disability.
Improved β-cell function after standardized weight reduction in severely obese subjects
Authors: Guldstrand Marie , Ahrén Bo , Adamson Ulf
Published: March 2015

Islet function was examined in 13 severely obese women [body mass index 46.4 ± 5.5 (SD) kg/m2] before and after standardized 15 and 25% weight reduction (WR) instituted by bariatric surgery. The insulin response to arginine at fasting (AIR1), at 14 mmol/l, and at >25 mmol/l glucose was reduced by 37–50% after 15 and 25% WR ( P ≤ 0.05). Insulin sensitivity was determined as the amount of glucose infused to reach 14 mmol/l divided by the insulin level (M/I), a measure showing a linear correlation with insulin sensitivity during euglycemic hyperinsulinemic clamps ( r = 0.74, P < 0.001) and a hyperbolic relation to AIR1 ( r = −0.63, P < 0.001) in 169 healthy subjects. M/I was increased by 318 ± 182% after 15% ( P = 0.004) and by 489 ± 276% after 25% WR ( P = 0.007). The reduction in insulin secretion was not as large as anticipated from the increased insulin sensitivity, which resulted in an increased disposition index (DI; AIR1 × M/I). Thus DI increased by 95 ± 24% after 15% ( P = 0.018) and by 176 ± 35% after 25% WR ( P = 0.011). This improved β-cell function correlated independently with reduced glucose, triglycerides, and leptin and increased adiponectin levels and was associated with a reduced proinsulin-to-insulin ratio. In contrast, glucagon secretion was not significantly affected by WR. We conclude that WR results in improved β-cell function when related to insulin sensitivity.
Pulsatile and nocturnal growth hormone secretions in men do not require periodic declines of somatostatin
Authors: Dimaraki Eleni V. , Jaffe Craig A. , Bowers Cyril Y. , Marbach Peter , Barkan Ariel L.
Published: March 2015

Using a continuous subcutaneous octreotide infusion to create constant supraphysiological somatostatinergic tone, we have previously shown that growth hormone (GH) pulse generation in women is independent of endogenous somatostatin (SRIH) declines. Generalization of these results to men is problematic, because GH regulation is sexually dimorphic. We have therefore studied nine healthy young men (age 26 ± 6 yr, body mass index 23.3 ± 1.2 kg/m2) during normal saline and octreotide infusion (8.4 μg/h) that provided stable plasma octreotide levels (764.5 ± 11.6 pg/ml). GH was measured in blood samples obtained every 10 min for 24 h. Octreotide suppressed 24-h mean GH by 52 ± 13% ( P = 0.016), GH pulse amplitude by 47 ± 12% ( P = 0.012), and trough GH by 39 ± 12% ( P = 0.030), whereas GH pulse frequency and the diurnal rhythm of GH secretion remained essentially unchanged. The response of GH to GH-releasing hormone (GHRH) was suppressed by 38 ± 15% ( P = 0.012), but the GH response to GH-releasing peptide-2 was unaffected. We conclude that, in men as in women, declines in hypothalamic SRIH secretion are not required for pulse generation and are not the cause of the nocturnal augmentation of GH secretion. We propose that GH pulses are driven primarily by GHRH, whereas ghrelin might be responsible for the diurnal rhythm of GH.
Altered energetic properties in skeletal muscle of men with well-controlled insulin-dependent (type 1) diabetes
Authors: Crowther Gregory J. , Milstein Jerrold M. , Jubrias Sharon A. , Kushmerick Martin J. , Gronka Rodney K. , Conley Kevin E.
Published: March 2015

This study asked whether the energetic properties of muscles are changed by insulin-dependent diabetes mellitus (or type 1 diabetes), as occurs in obesity and type 2 diabetes. We used 31P magnetic resonance spectroscopy to measure glycolytic flux, oxidative flux, and contractile cost in the ankle dorsiflexor muscles of 10 men with well-managed type 1 diabetes and 10 age- and activity-matched control subjects. Each subject performed sustained isometric muscle contractions lasting 30 and 120 s while attempting to maintain 70–75% of maximal voluntary contraction force. An altered glycolytic flux in type 1 diabetic subjects relative to control subjects was apparent from significant differences in pH in muscle at rest and at the end of the 120-s bout. Glycolytic flux during exercise began earlier and reached a higher peak rate in diabetic patients than in control subjects. A reduced oxidative capacity in the diabetic patients' muscles was evident from a significantly slower phosphocreatine recovery from a 30-s exercise bout. Our findings represent the first characterization of the energetic properties of muscle from type 1 diabetic patients. The observed changes in glycolytic and oxidative fluxes suggest a diabetes-induced shift in the metabolic profile of muscle, consistent with studies of obesity and type 2 diabetes that point to common muscle adaptations in these diseases.
Chronic intracerebroventricular infusion of MCH causes obesity in mice
Authors: Gomori Akira , Ishihara Akane , Ito Masahiko , Mashiko Satoshi , Matsushita Hiroko , Yumoto Mariko , Ito Makoto , Tanaka Takeshi , Tokita Shigeru , Moriya Minoru , Iwaasa Hisashi , Kanatani Akio
Published: March 2015

Melanin-concentrating hormone (MCH) is a cyclic amino acid neuropeptide localized in the lateral hypothalamus. Although MCH is thought to be an important regulator of feeding behavior, the involvement of this peptide in body weight control has been unclear. To examine the role of MCH in the development of obesity, we assessed the effect of chronic intracerebroventricular infusion of MCH in C57BL/6J mice that were fed with regular or moderately high-fat (MHF) diets. Intracerebroventricular infusion of MCH (10 μg/day for 14 days) caused a slight but significant increase in body weight in mice maintained on the regular diet. In the MHF diet-fed mice, MCH more clearly increased the body weight accompanied by a sustained hyperphagia and significant increase in fat and liver weights. Plasma glucose, insulin, and leptin levels were also increased in the MCH-treated mice fed the MHF diet. These results suggest that chronic stimulation of the brain MCH system causes obesity in mice and imply that MCH may have a major role in energy homeostasis.
Effect of thiazolidinediones and metformin on LDL oxidation and aortic endothelium relaxation in diabetic GK rats
Authors: Iida Kaoruko Tada , Kawakami Yasushi , Suzuki Masatsune , Shimano Hitoshi , Toyoshima Hideo , Sone Hirohito , Shimada Kazunori , Iwama Yoshitaka , Watanabe Yoshiro , Mokuno Hiroshi , Kamata Katsuo , Yamada Nobuhiro
Published: March 2015

In this study, using GK diabetic rats, we compared the effects of three insulin sensitizers on lipid oxidation and the aortic relaxation response. Eight-week-old rats were treated for 4 wk with either troglitazone or pioglitazone, both of which are thiazolidinediones, or with metformin. Despite the fact that only troglitazone has a similarity in structure to α-tocopherol, a potent antioxidant, the level of thiobarbituric acid-reactive substance was lower, and the lag time of the conjugated dienes was longer, in the blood samples from the rats in both troglitazone- and pioglitazone-treated groups. In contrast, another insulin sensitizer, metformin, failed to inhibit the oxidation of blood samples. The aortic vasorelaxation response was increased in both troglitazone- and metformin-treated groups compared with the untreated group. These findings suggest that thiazolidinediones have a beneficial effect on lipid oxidation irrespective of the drug's structural similarity to α-tocopherol. It is also suggested that the thiazolidinediones and metformin improve vascular function in diabetes. These effects may play a role in the prevention of atherosclerosis in diabetic patients.
Glucocorticoid-induced skeletal muscle atrophy is associated with upregulation of myostatin gene expression
Authors: Ma Kun , Mallidis Con , Bhasin Shalender , Mahabadi Vahid , Artaza Jorge , Gonzalez-Cadavid Nestor , Arias Jose , Salehian Behrouz
Published: March 2015

The mechanisms by which excessive glucocorticoids cause muscular atrophy remain unclear. We previously demonstrated that dexamethasone increases the expression of myostatin, a negative regulator of skeletal muscle mass, in vitro. In the present study, we tested the hypothesis that dexamethasone-induced muscle loss is associated with increased myostatin expression in vivo. Daily administration (60, 600, 1,200 μg/kg body wt) of dexamethasone for 5 days resulted in rapid, dose-dependent loss of body weight (-4.0, -13.4, -17.2%, respectively, P < 0.05 for each comparison), and muscle atrophy (6.3, 15.0, 16.6% below controls, respectively). These changes were associated with dose-dependent, marked induction of intramuscular myostatin mRNA (66.3, 450, 527.6% increase above controls, P < 0.05 for each comparison) and protein expression (0.0, 260.5, 318.4% increase above controls, P < 0.05). We found that the effect of dexamethasone on body weight and muscle loss and upregulation of intramuscular myostatin expression was time dependent. When dexamethasone treatment (600 μg · kg-1 · day-1) was extended from 5 to 10 days, the rate of body weight loss was markedly reduced to ∼2% within this extended period. The concentrations of intramuscular myosin heavy chain type II in dexamethasone-treated rats were significantly lower (-43% after 5-day treatment, -14% after 10-day treatment) than their respective corresponding controls. The intramuscular myostatin concentration in rats treated with dexamethasone for 10 days returned to basal level. Concurrent treatment with RU-486 blocked dexamethasone-induced myostatin expression and significantly attenuated body loss and muscle atrophy. We propose that dexamethasone-induced muscle loss is mediated, at least in part, by the upregulation of myostatin expression through a glucocorticoid receptor-mediated pathway.
Seasonal variation in sleeping metabolic rate, thyroid activity, and leptin
Authors: Plasqui Guy , Kester Arnold D. M. , Westerterp Klaas R.
Published: March 2015

We investigated seasonal variation in sleeping metabolic rate (SMR) and the possible relation to body composition, thyroid activity, and leptin. Twenty-five healthy volunteers were examined four times during the year: in spring (April, May), summer (July, August), autumn (October, November), and winter (January, February). Body composition was determined using a three-compartment model based on underwater weighing and the deuterium dilution method. SMR was measured during an overnight stay in a respiration chamber. A blood sample was taken for the analysis of free and total thyroxine, TSH, and leptin. SMR showed a significant seasonal variation ( P < 0.01) with a maximum in winter (4.54 kJ/min) and a minimum in summer (4.34 kJ/min). The amplitude was 0.10 ± 0.02 kJ/min, and the phase was November 5th. Season explained 17% of the intraindividual variation in SMR. The circannual rhythm in SMR could not be explained by changes in body composition, thyroid activity, or leptin. Interindividual variation in SMR was explained by fat-free mass ( P < 0.001) and leptin ( P < 0.001).
Calcium-sensing receptor stimulates PTHrP release by pathways dependent on PKC, p38 MAPK, JNK, and ERK1/2 in H-500 cells
Authors: Tfelt-Hansen J. , MacLeod R. J. , Chattopadhyay N. , Yano S. , Quinn S. , Ren X. , Terwilliger E. F. , Schwarz P. , Brown E. M.
Published: March 2015

Elevated extracellular calcium ([Ca2+]o) and other agonists potentially acting via the calcium-sensing receptor (CaR) increase parathyroid hormone-related peptide (PTHrP) release from H-500 Leydig cells. Here, we provide strong evidence for the CaR's involvement by using a dominant negative CaR that attenuates high [Ca2+]o-induced PTHrP release. This effect is likely transcriptional, because high [Ca2+]oupregulates the PTHrP transcript, an effect that is abolished by actinomycin D. Regulation of PTHrP release by the CaR involves activation of PKC as well as ERK1/2, p38 MAPK, and JNK pathways. However, we show for the first time that high [Ca2+]o-induced activation of the stress-activated protein kinase SEK1 is PKC independent, because there is an additive effect of a PKC inhibitor in combination with the JNK inhibitor on [Ca2+]o-stimulated PTHrP release. Furthermore, high [Ca2+]o, in a PKC-independent fashion, induces phosphorylation of ERK1/2, SEK1, p38 MAPK, and its downstream transcription factor ATF-2. We conclude that CaR regulation of PTHrP release in H-500 cells involves activation of PKC as well as the ERK1/2, p38 MAPK, and JNK pathways.
NPY ablation in C57BL/6 mice leads to mild obesity and to an impaired refeeding response to fasting
Authors: Segal-Lieberman Gabriella , Trombly Daniel J. , Juthani Viral , Wang Xiaomei , Maratos-Flier Eleftheria
Published: March 2015

Neuropeptide Y (NPY) is an orexigenic (appetite-stimulating) peptide that plays an important role in regulating energy balance. When administered directly into the central nervous system, animals exhibit an immediate increase in feeding behavior, and repetitive injections or chronic infusions lead to obesity. Surprisingly, initial studies of Npy−/− mice on a mixed genetic background did not reveal deficits in energy balance, with the exception of an attenuation in obesity seen in ob/ob mice in which the NPY gene was also deleted. Here, we show that, on a C57BL/6 background, NPY ablation is associated with an increase in body weight and adiposity and a significant defect in refeeding after a fast. This impaired refeeding response in Npy−/− mice resulted in a deficit in weight gain in these animals after 24 h of refeeding. These data indicate that genetic background must be taken into account when the biological role of NPY is evaluated. When examined on a C57BL/6 background, NPY is important for the normal refeeding response after starvation, and its absence promotes mild obesity.
Carbon monoxide stimulates insulin release and propagates Ca2+signals between pancreatic β-cells
Authors: Lundquist Ingmar , Alm Per , Salehi Albert , Henningsson Ragnar , Grapengiesser Eva , Hellman Bo
Published: March 2015

A key question for understanding the mechanisms of pulsatile insulin release is how the underlying β-cell oscillations of the cytoplasmic Ca2+concentration ([Ca2+]i) are synchronized within and among the islets in the pancreas. Nitric oxide has been proposed to coordinate the activity of the β-cells by precipitating transients of [Ca2+]i. Comparing ob/ ob mice and lean controls, we have now studied the action of carbon monoxide (CO), another neurotransmitter with stimulatory effects on cGMP production. A strong immunoreactivity for the CO-producing constitutive heme oxygenase (HO-2) was found in ganglionic cells located in the periphery of the islets and in almost all islet endocrine cells. Islets from ob/ ob mice had sixfold higher generation of CO (1 nmol · min–1· mg protein–1) than the lean controls. This is 100-fold the rate for their constitutive production of NO. Moreover, islets from ob/ ob mice showed a threefold increase in HO-2 expression and expressed inducible HO (HO-1). The presence of an excessive islet production of CO in the ob/ ob mouse had its counterpart in a pronounced suppression of the glucose-stimulated insulin release from islets exposed to the HO inhibitor Zn-protoporhyrin (10 μM) and in a 16 times higher frequency of [Ca2+]itransients in their β-cells. Hemin (0.1 and 1.0 μM), the natural substrate for HO, promoted the appearance of [Ca2+]itransients, and 10 μM of the HO inhibitors Zn-protoporphyrin and Cr-mesoporphyrin had a suppressive action both on the firing of transients and their synchronization. It is concluded that the increased islet production of CO contributes to the hyperinsulinemia in ob/ ob mice. In addition to serving as a positive modulator of glucose-stimulated insulin release, CO acts as a messenger propagating Ca2+signals with coordinating effects on the β-cell rhythmicity.
Glucose-dependent insulinotropic peptide stimulates thymidine incorporation in endothelial cells: role of endothelin-1
Authors: Ding Ke-Hong , Zhong Qing , Isales Carlos M.
Published: March 2015

We have previously characterized the receptor for glucose-dependent insulinotropic polypeptide (GIPR) in vascular endothelial cells (EC). Different EC types were found to contain distinct GIPR splice variants. To determine whether activation of the GIPR splice variants resulted in different cellular responses, we examined GIP effects on human umbilical vein endothelial cells (HUVEC), which contain two GIPR splice variants, and compared them with a spontaneously transformed human umbilical vein EC line, ECV 304, which contains four GIPR splice variants. GIP dose-dependently stimulated HUVEC and ECV 304 proliferation as measured by [3H]thymidine incorporation. GIP increased endothelin-1 (ET-1) secretion from HUVEC but not from ECV 304. Use of the endothelin B receptor blocker BQ-788 resulted in an inhibition of [3H]thymidine incorporation in HUVEC but not in ECV 304. These findings suggest that, although GIP increases [3H]thymidine incorporation in both HUVEC and ECV 304, this proliferative response is mediated by ET-1 only in HUVEC. These differences in cellular response to GIP may be related to differences in activation of GIPR splice variants.
Growth hormone secretion pattern is an independent regulator of growth hormone actions in humans
Authors: Jaffe Craig A. , Turgeon D. Kim , Lown Kenneth , Demott-Friberg Roberta , Watkins Paul B.
Published: March 2015

The importance of gender-specific growth hormone (GH) secretion pattern in the regulation of growth and metabolism has been demonstrated clearly in rodents. We recently showed that GH secretion in humans is also sexually dimorphic. Whether GH secretion pattern regulates the metabolic effects of GH in humans is largely unknown. To address this question, we administered the same daily intravenous dose of GH (0.5 mg · m−2 · day−1) for 8 days in different patterns to nine GH-deficient adults. Each subject was studied on four occasions: protocol 1 (no treatment), protocol 2 (80% daily dose at 0100 and 10% daily dose at 0900 and 1700), protocol 3 (8 equal boluses every 3 h), and protocol 4 (continuous GH infusion). The effects of GH pattern on serum IGF-I, IGF-binding protein (IGFBP)-3, osteocalcin, and urine deoxypyridinoline were measured. Hepatic CYP1A2 and CYP3A4 activities were assessed by the caffeine and erythromycin breath tests, respectively. Protocols 3 and 4 were the most effective in increasing serum IGF-I and IGFBP-3, whereas protocols administering pulsatile GH had the greatest effects on markers of bone formation and resorption. All GH treatments decreased CYP1A2 activity, and the effect was greatest for pulsatile GH. Pulsatile GH decreased, whereas continuous GH infusion increased, CYP3A4 activity. These data demonstrate that GH pulse pattern is an independent parameter of GH action in humans. Gender differences in drug metabolism and, potentially, gender differences in growth rate may be explained by sex-specific GH secretion patterns.
Effect of heart failure on the regulation of skeletal muscle protein synthesis, breakdown, and apoptosis
Authors: Persinger Rebecca , Janssen-Heininger Yvonne , Wing Simon S. , Matthews Dwight E. , LeWinter Martin M. , Toth Michael J.
Published: March 2015

Heart failure is often characterized by skeletal muscle atrophy. The mechanisms underlying muscle wasting, however, are not fully understood. We studied 30 Dahl salt-sensitive rats (10 male, 20 female) fed either a high-salt (HS; n = 15) or a low-salt (LS; n = 15) diet. This strain develops cardiac hypertrophy and failure when fed a HS diet. LS controls were matched to HS rats for gender and duration of diet. Body mass, food intake, and muscle mass and composition were measured. Skeletal muscle protein synthesis was measured by isotope dilution. An additional group of 27 rats (HS, n = 16; LS; n = 11) were assessed for expression of genes regulating protein breakdown and apoptosis. Gastrocnemius and plantaris muscles weighed less (16 and 22%, respectively) in HS than in LS rats ( P < 0.01). No differences in soleus or tibialis anterior weights were found. Differences in muscle mass were abolished after data were expressed relative to body size, because HS rats tended ( P = 0.094) to weigh less. Lower body mass in HS rats was related to a 16% reduction ( P < 0.01) in food intake. No differences in muscle protein or DNA content, the protein-to-DNA ratio, or muscle protein synthesis were found. Finally, no differences in skeletal muscle gene expression were found to suggest increased protein breakdown or apoptosis in HS rats. Our results suggest that muscle wasting in this model of heart failure is not associated with alterations in skeletal muscle metabolism. Instead, muscle atrophy was related to reduced body weight secondary to decreased food intake. These findings argue against the notion that heart failure is characterized by a skeletal muscle myopathy that predisposes to atrophy.
Glucose-induced suppression of endogenous glucose production: dynamic response to differing glucose profiles
Authors: Vella A. , Reed A. S. , Charkoudian N. , Shah P. , Basu R. , Basu A. , Joyner M. J. , Rizza R. A.
Published: March 2015

To determine whether, in the presence of constant insulin concentrations, a change in glucose concentrations results in a reciprocal change in endogenous glucose production (EGP), glucagon (∼130 ng/l) and insulin (∼65 pmol/l) were maintained at constant “basal” concentrations while glucose was clamped at ∼5.3 mM (euglycemia), ∼7.0 mM (sustained hyperglycemia; n = 10), or varied to create a “postprandial” profile (profile; n = 11). EGP fell slowly over the 6 h of the euglycemia study. In contrast, an increase in glucose to 7.13 ± 0.3 mmol/l resulted in prompt and sustained suppression of EGP to 9.65 ± 1.21 μmol·kg-1· min-1. On the profile study day, glucose increased to a peak of 11.2 ± 0.5 mmol/l, and EGP decreased to a nadir of 6.79 ± 2.54 μmol · kg-1· min-1by 60 min. Thereafter, the fall in glucose was accompanied by a reciprocal rise in EGP to rates that did not differ from those observed on the euglycemic study day (11.31 ± 2.45 vs. 12.11 ± 3.21 μmol · kg-1· min-1). Although the pattern of change of glucose differed markedly on the sustained hyperglycemia and profile study days, by design the area above basal did not. This resulted in equivalent suppression of EGP below basal (-1,952 ± 204 vs. -1,922 ± 246 mmol · kg-1· 6 h-1). These data demonstrate that, in the presence of a constant basal insulin concentration, changes in glucose within the physiological range rapidly and reciprocally regulate EGP.
Effect of training on the GH/IGF-I axis during exercise in middle-aged men: relationship to glucose homeostasis
Authors: Manetta Jérôme , Brun Jean Frederic , Maimoun Laurent , Callis Albert , Préfaut Christian , Mercier Jacques
Published: March 2015

The aim of this study was to compare circulating levels of growth hormone (GH), IGF-I, and IGF-binding protein (IGFBP)-1 and IGFBP-3 in response to a long-duration endurance exercise in trained vs. sedentary middle-aged males and to determine whether a relationship with glucose homeostasis exists. Seven trained men (Tr) were compared with seven age-matched sedentary men (Sed) during two trials of 60 min of cycling exercise performed below (−VT) and above (+VT) the ventilatory threshold. Insulin sensitivity (SI) was higher in Tr than in Sed ( P < 0.001). Basal GH, IGF-I, and IGFBP-1 and -3 were higher in Tr ( P < 0.05). During +VT, Tr had a threefold higher GH response, whereas their blood glucose level was better maintained ( P < 0.05). Basal IGFBP-1 was correlated with SI ( P < 0.01). These data indicate that endurance training in middle-aged men increased the activity of the GH/IGF-I system and improved glucoregulation both at rest and during high-intensity endurance exercise.
Smoking impairs muscle recovery from exercise
Authors: Price Thomas B. , Krishnan-Sarin Suchitra , Rothman Douglas L.
Published: March 2015

Cigarette smoking is a leading cause of many adverse health consequences. Chronic nicotine exposure leads to insulin resistance and may increase the risk of developing non-insulin-dependent diabetes mellitus in young otherwise healthy smokers. To evaluate smoking-induced effects on carbohydrate metabolism, we studied muscle glycogen recovery from exercise in a young healthy population of smokers. The study used 31P-13C NMR spectroscopy to compare muscle glycogen and glucose 6-phosphate levels during recovery in exercised gastrocnemius muscles of randomized cohorts of healthy male smokers (S) and controls (C). Data for the two groups were as follows: S, ≥20 cigarettes/day ( n = 8), 24 ± 2 yr, 173 ± 3 cm, 70 ± 4 kg and age- and weight-matched nonsmoking C ( n = 10), 23 ± 1 yr, 175 ± 3 cm, 67 ± 3 kg. Subjects performed single-leg toe raises to deplete glycogen to ∼20 mmol/l, and glycogen resynthesis was measured during the first 4 h of recovery. Plasma samples were assayed for glucose and insulin at rest and during recovery. Test subjects were recruited from the general community surrounding Yale University. Glycogen was depleted to similar levels in the two groups [23.5 ± 1.2 (S) and 19.1 ± 1.3 (C) mmol/l]. During the 1st h of recovery, glycogen synthesis rates were similar [13.8 ± 1.1 (S) and 15.3 ± 1.3 (C) mmol·l-1·h-1]. Between hours 1 and 4, glycogen synthesis was impaired in smokers [0.8 ± 0.2 (S) and 4.5 ± 0.5 (C) mmol·l-1·h-1, P = 0.0002] compared with controls. Glucose 6-phosphate was reduced in smokers during hours 1–4 [0.105 ± 0.006 (S) and 0.217 ± 0.019 (C) mmol/l, P = 0.0212]. We conclude that cigarette smoking impairs the insulin-dependent portion of muscle recovery from glycogen-depleting exercise. This impairment likely results from a reduction in glucose uptake.
Effects of dexamethasone and colostrum intake on the somatotropic axis in neonatal calves
Authors: Sauter Stephanie N. , Ontsouka Edgar , Roffler Bettina , Zbinden Yolande , Philipona Chantal , Pfaffl Michael , Breier Bernhard H. , Blum Jürg W. , Hammon Harald M.
Published: March 2015

Glucocorticoids and colostrum feeding influence postnatal maturation of the somatotropic axis. We have tested the hypothesis that dexamethasone (Dexa) affects the somatotropic axis in neonatal calves dependent on colostrum intake. Calves were fed either with colostrum or with a milk-based formula ( n = 14/group), and, in each feeding group, one-half of the calves were treated with Dexa (30 μg · kg body wt-1 · day-1). Pre- and postprandial blood samples were taken on days 1, 2, 4, and 5, and liver samples were taken on day 5 of life. Dexa increased insulin-like growth factor (IGF)-I, but decreased growth hormone (GH) and IGF-binding protein (IGFBP)-1 and -2 plasma concentrations and increased GH receptor (GHR) mRNA levels in liver. Dexa increased IGF-I mRNA levels only in formula-fed calves and increased hepatic GHR binding capacity, but only in colostrum-fed calves. Colostrum feeding decreased IGFBP-1 and -2 plasma concentrations and hepatic IGFBP-2 and -3 mRNA levels. In conclusion, Dexa and colostrum feeding promoted maturation of the somatotropic axis. Dexa effects partly depended on whether colostrum was fed or not.
Role of endothelium-derived relaxing factors in the renal response to vasoactive agents in hypothyroid rats
Authors: Moreno Juan Manuel , Wangensteen Rosemary , Sainz Juan , Rodríguez-Gomez Isabel , Chamorro Virginia , Osuna Antonio , Vargas Félix
Published: March 2015

This study analyzed the role of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in the abnormal renal vascular reactivity of hypothyroid rats. Renal responses to vasoconstrictors [VC: phenylephrine (PHE) and ANG II] and vasodilators [VD: ACh, sodium nitroprusside (SNP), and papaverine (PV)] were studied in kidneys from control and hypothyroid rats under normal conditions and after NO or EDHF blockade. NO was blocked by the administration of Nω-nitro-l-arginine methyl ester (l-NAME) and EDHF by the administration of tetraethylammonium (TEA) or by an increased extracellular K+. The response to VC was also evaluated after endothelium removal. Hypothyroid kidneys showed reduced responsiveness to PHE and a normal response to ANG II. l-NAME and TEA administration produced an increased sensitivity to PHE and to ANG II in control preparations. l-NAME also increased the response to PHE in hypothyroid kidneys, but the differences between control and hypothyroid kidneys were maintained. TEA administration did not change the response to either VC in hypothyroid preparations. In endothelium-removed preparations, TEA was unable to increase pressor responsiveness to VC. Hypothyroid kidneys showed reduced responsiveness to ACh and SNP and normal response to PV. The differences between hypothyroid and control preparations in the responses to ACh and SNP were maintained after l-NAME or increased K+. In conclusion, this study shows that 1) the attenuated response to PHE in hypothyroidism is not related to an increased production of endothelium-derived relaxing factors NO and EDHF; 2) the response to VC in hypothyroid preparations is insensitive to EDHF blockade; and 3) hypothyroid preparations have a reduced reactivity to the NO donor, and NO-independent vasodilatation remains unaffected.
Acute inflammation increases selective uptake of HDL cholesteryl esters into adrenals of mice overexpressing human sPLA2
Authors: Tietge Uwe J. F. , Maugeais Cyrille , Cain Willliam , Rader Daniel J.
Published: March 2015

The acute-phase protein secretory phospholipase A2 (sPLA2) influences the metabolism of high-density lipoproteins (HDL). The adrenals are known to utilize HDL cholesterol as a source of sterols. The aim of the present study was to test the hypothesis that sPLA2enhances the selective uptake of HDL into the adrenals in response to acute inflammation as a possible physiological role for the sPLA2-HDL interaction. Human sPLA2-transgenic mice, in which sPLA2expression is upregulated by inflammatory stimuli, were used. Ten hours after induction of the acute-phase response (APR) by injection of bacterial lipopolysaccharide (LPS), plasma levels of HDL cholesterol decreased significantly in sPLA2-transgenic mice (-18%, P < 0.05) but remained unchanged in wild-type mice. The fractional catabolic rates of both125I-labeled tyraminecellobiose (TC)-HDL and [3H]cholesteryl ether increased significantly in the sPLA2-transgenic mice after induction of the APR (0.18 ± 0.01 vs. 0.21 ± 0.01 pool/h, P < 0.05, and 0.31 ± 0.02 vs. 0.42 ± 0.05 pool/h, P < 0.05, respectively) but remained unchanged in the wild-type mice (0.10 ± 0.01 vs. 0.22 ± 0.02 pool/h, respectively). After induction of the APR, in both groups HDL holoparticle uptake by the liver was increased ( P < 0.001). sPLA2-transgenic mice had 2.4-fold higher selective uptake into the adrenals after induction of the APR than wild-type mice (156 ± 6 vs. 65 ± 5%/μg tissue protein, P < 0.001). In summary, upregulation of sPLA2expression during the APR specifically increases the selective uptake of HDL cholesteryl ester into the adrenals. These data suggest a novel metabolic role for sPLA2: modification of HDL during the APR to promote increased adrenal uptake of HDL cholesteryl ester to serve as source for steroid hormone synthesis.
Models of gastric hyperalgesia in the rat
Authors: Ozaki Noriyuki , Bielefeldt Klaus , Sengupta J. N. , Gebhart G. F.
Published: March 2015

Despite the prevalence of dyspepsia, nonhuman models for study of gastric hyperalgesia are limited. We thus characterized responses to gastric distension (GD) in the absence of and after two different gastric insults. A balloon was surgically placed into the stomach, and electromyographic responses to GD were recorded from the acromiotrapezius muscle at various times after balloon placement. Rats received either 20% acetic acid (HAc) or saline injections into the stomach wall or 0.1% iodoacetamide (IA) in drinking water. Responses to GD were monotonic with increasing distending pressure (10–80 mmHg) and were reproducible from days 3–14 after balloon implantation. Both HAc injection and IA ingestion led to increased responses to GD (i.e., gastric hyperalgesia), which, in the case of HAc, persisted for 60 days after HAc treatment. HAc injection produced ulcers in all treated animals; IA ingestion produced no lesions. Myeloperoxidase activity significantly increased after HAc but not saline injection or IA ingestion. In the awake, unrestrained rat, visceromotor responses to GD are quantifiable, reliable, and reproducible. Significantly enhanced responses to GD were apparent in two models of gastric insult, both of which may be useful for the study of the mechanisms of gastric hyperalgesia.
α-Lipoic acid preconditioning reduces ischemia-reperfusion injury of the rat liver via the PI3-kinase/Akt pathway
Authors: Müller Christian , Dünschede Friedrich , Koch Elke , Vollmar Angelika M. , Kiemer Alexandra K.
Published: March 2015

In liver resection and transplantation ischemia-reperfusion injury (IRI) is one of the main causes of organ dys- or nonfunction. The aim of the present study was to determine whether α-lipoic acid (LA) is able to attenuate IRI. Rat livers were perfused with Krebs-Henseleit buffer with or without LA (±wortmannin), followed by ischemia (1 h, 37°C) and reperfusion (90 min). Efflux of lactate dehydrogenase (LDH) and purine nucleoside phosphorylase (PNP) and hepatic ATP content were determined enzymatically. Activation of NF-κB and activating protein 1 (AP-1) was examined by EMSA, and protein phosphorylation was examined by Western blot. Caspase-3-like activity served as an indicator for apoptotic processes. Animals treated intravenously with 500 μmol LA were subjected to 90 min of partial no-flow ischemia followed by reperfusion for up to 7 days. Preconditioning with LA significantly reduced LDH and PNP efflux during reperfusion in isolated perfused rat livers. ATP content was significantly increased in LA-treated livers. Postischemic activation of NF-κB and AP-1 was significantly reduced in LA-pretreated organs. Preconditioning with LA significantly enhanced Akt phosphorylation. It showed neither effect on endothelial nitric oxide synthase nor on Bad phosphorylation. Importantly, simultaneous administration of wortmannin, an inhibitor of the phosphatidylinositol (PI)3-kinase/Akt pathway, blocked the protective effect of LA on IRI, demonstrating a causal relationship between Akt activation and hepatoprotection by LA. Interestingly, despite activation of Akt, LA did not reduce postischemic apoptotic cell death. The efficacy of LA treatment in vivo was shown by reduced GST plasma levels and improved liver histology of animals pretreated with LA. This study shows for the first time that the PI3-kinase/Akt pathway plays a central protective role in IRI of the rat liver and that LA administration attenuates IRI via this pathway.
Measurement of hepatic and intestinal CYP3A4 and PGP activity by combined po + iv [14C]erythromycin breath and urine test
Authors: Lemahieu W. P. D. , Maes B. D. , Ghoos Y. , Rutgeerts P. , Verbeke K. , Vanrenterghem Y.
Published: March 2015

The aim of the present study was to develop a test for measuring hepatic and intestinal removal of cytochrome P-450 3A4 (CYP3A4)- and P-glycoprotein (PGP)-dependent xenobiotics that would be applicable for clinical use in humans. Orally and intravenously administered [ N-methyl-14C]erythromycin was used for evaluation of 14C-labeled excretion dynamics in breath and urine. Simultaneous breath and urine test measurements were performed in 32 healthy volunteers and in 23 renal transplant recipients. Mathematical analysis of the excretion rate of labeled CO2 in breath and labeled carbon in urine resulted in 1) separation of both CYP3A4 and PGP activity in the liver and the intestinal mucosa and 2) numerical calculation of the dynamics of the different processes. The test was sufficiently sensitive to detect theoretically predicted process-specific pharmacological modulations by different drugs in healthy volunteers and after recent renal transplantation. It is concluded that the combined oral and intravenous erythromycin breath and urine test is a reliable and noninvasive test to measure phenotypic intestinal and hepatic CYP3A4 and PGP activity and may be a promising tool for prediction of drug interactions and dose adjustment of many pharmacotherapeutics in clinical practice, e.g., immunosuppressive agents after renal transplantation.
Developmental expression of eNOS in postnatal swine mesenteric artery
Authors: Reber Kristina M. , Su Baogen Y. , Clark K. Reed , Pohlman Dana L. , Miller Charles E. , Nowicki Philip T.
Published: March 2015

Developmental changes in the expression of endothelial nitric oxide synthase (eNOS) within the mesenteric artery of swine were studied in fetal (110 days postconception/117 days total gestation) and on postnatal days 1, 3, 10, and 30. Subjects in the 1-day-old group were subdivided into fed and nonfed. Transcription of eNOS was determined by real-time PCR, protein expression was evaluated by Western blotting, and hemodynamic and oxygenation parameters were measured within in situ gut loops before and after the administration of NG-monomethyl-l-arginine (l-NMMA). The abundance of eNOS mRNA remained steady throughout all ages. In contrast, expression of eNOS protein was twofold greater in the 1-day-old fed subjects compared with fetal or 1-day-old nonfed subjects. eNOS protein expression remained elevated on day 3, increased on day 10, and then declined to a level similar to the day 1 nonfed group by postnatal day 30. Intestinal vascular resistance was 31% lower in the day 1 fed group when compared to the day 1 nonfed group; resistance continued to decline through day 10 but then significantly increased on day 30. We conclude that the expression of eNOS changes within the mesenteric artery during early postnatal development at a posttranscriptional level.
Cytokines induce HIF-1 DNA binding and the expression of HIF-1-dependent genes in cultured rat enterocytes
Authors: Scharte Marion , Han Xiaonan , Bertges Daniel J. , Fink Mitchell P. , Delude Russell L.
Published: March 2015

Cellular adaptation to hypoxia depends, in part, on the transcription factor hypoxia-inducible factor-1 (HIF-1). Normoxic cells exposed to an inflammatory milieu often manifest phenotypic changes, such as increased glycolysis, that are reminiscent of those observed in hypoxic cells. Accordingly, we investigated the effects of cytomix, a mixture containing IFN-γ, TNF, and IL-1β on the expression of HIF-1-dependent proteins under normoxic and hypoxic conditions. Incubation of intestine-derived epithelial cells (IEC-6) under 1% O2increased HIF-1 DNA binding and expression of aldolase A, enolase-1, and VEGF mRNA. Incubation of normoxic cells with cytomix for 48 h also markedly increased HIF-1 DNA binding and expression of mRNAs for these proteins. Incubation of hypoxic cells with cytomix did not inhibit HIF-1 DNA binding or upregulation of HIF-1-dependent genes in response to hypoxia. Neither cytomix nor hypoxia increased steady-state levels of HIF-1α mRNA. Incubation of IEC-6 cells with cytomix induced nitric oxide (NO·) biosynthesis, which was blocked if the cultures containedl- NG-(1-iminoethyl)lysine hydrochloride (l-NIL). Treatment with l-NIL, however, failed to significantly alter aldolase A, enolase-1, and VEGF mRNA levels in normoxic cytomix-treated cells. Proinflammatory cytokines activate the HIF-1 pathway and increase expression of glycolytic genes in nontransformed rat intestinal epithelial cells, largely through an NO·-independent mechanism.
Baclofen blocks LES relaxation and crural diaphragm inhibition by esophageal and gastric distension in cats
Authors: Liu Jianmin , Pehlivanov Nonko , Mittal Ravinder K.
Published: March 2015

Esophageal distension and transient lower esophageal sphincter (LES) relaxation (TLESR) are accompanied by simultaneous relaxation of the LES and inhibition of crural diaphragm. Recent studies indicate that baclofen decreases the frequency of TLESR; however, its effect on the crural diaphragm is not known. We evaluated the effects of baclofen on LES relaxation and crural diaphragm inhibition induced by gastric distension and esophageal distension in cats. Five adult cats underwent surgical implantation of wire electrodes into the crural and costal diaphragm for measurement of their EMG activity, respectively. One week after the surgery, animals were lightly sedated and recordings were performed using a manometry catheter equipped with a 2.5-cm balloon. The effects of baclofen (10 μmol/kg iv) on the graded esophageal distension and gastric distension-induced LES and crural diaphragm responses were studied. Distension of the esophagus and stomach induces relaxation of the LES and inhibition of the crural diaphragm, simultaneously. Baclofen blocks both the esophageal and the gastric distension-induced relaxation of the LES and inhibition of the crural diaphragm. The magnitude of response to baclofen was significantly larger for the crural diaphragm inhibition than for the LES relaxation. Baclofen, a GABABreceptor agonist, blocks the reflex inhibitory pathway to the LES and crural diaphragm. The reflex inhibitory pathway to the crural diaphragm is more sensitive to blockade by baclofen than the reflex LES inhibitory pathway.
Poly(ADP-ribose) polymerase triggers the microvascular mechanisms of hepatic ischemia-reperfusion injury
Authors: Khandoga Andrej , Enders Georg , Biberthaler Peter , Krombach Fritz
Published: March 2015

Activation of poly(ADP-ribose) polymerase (PARP) mediates oxidative stress-induced cell injury. We tested the hypothesis that PARP contributes to ischemia-reperfusion (I/R) damage of the liver by triggering the mechanisms of microcirculatory failure. Leukocyte- and platelet-endothelial cell interactions as well as sinusoidal perfusion were analyzed by intravital fluorescence microscopy after lobar hepatic I/R (90 min/30 min) in C57BL/6 × 129/Sv wild-type (PARP+/+) and PARP-deficient (PARP−/−) mice. Hepatic I/R induced leukocyte/platelet-endothelial cell interactions and tissue injury in PARP+/+ mice, as indicated by impaired sinusoidal perfusion and increased alanine aminotransferase (ALT)/aspartate aminotransferase (AST) serum activities. In PARP−/− mice, however, the postischemic increase in the numbers of rolling/adherent leukocytes and platelets was significantly lower. In addition, I/R-induced translocation of CD62P as well as mRNA expression of CD62E, CD54, and CD106 were attenuated. The degree of perfusion failure was reduced and the increase in the ALT/AST activities was lower in PARP−/− mice compared with PARP+/+ mice. We conclude that PARP contributes to hepatic microvascular injury by triggering the expression/translocation of adhesion molecules and modulating leukocyte/platelet-endothelial cell interactions.
I. Shiga toxin B-subunit system: retrograde transport, intracellular vectorization, and more
Authors: Johannes Ludger
Published: March 2015

Many intracellular transport routes are still little explored. This is particularly true for retrograde transport between the plasma membrane and the endoplasmic reticulum. Shiga toxin B subunit has become a powerful tool to study this pathway, and recent advances on the molecular mechanisms of transport in the retrograde route and on its physiological function(s) are summarized. Furthermore, it is discussed how the study of retrograde transport of Shiga toxin B subunit allows one to design new methods for the intracellular delivery of therapeutic compounds.
Acidomucin goblet cell expansion induced by parenteral nutrition in the small intestine of piglets
Authors: Conour J. E. , Ganessunker D. , Tappenden K. A. , Donovan S. M. , Gaskins H. R.
Published: March 2015

Total parenteral nutrition (TPN) impairs small intestine development and is associated with barrier failure, inflammation, and acidomucin goblet cell expansion in neonatal piglets. We examined the relationship between intestinal goblet cell expansion and molecular and cellular indices of inflammation in neonatal piglets receiving TPN, 80% parenteral + 20% enteral nutrition (PEN), or 100% enteral nutrition (control) for 3 or 7 days. Epithelial permeability, T cell numbers, TNF-α and IFN-γ mRNA expression, and epithelial proliferation and apoptosis were compared with goblet cell numbers over time. Epithelial permeability was similar to control in the TPN and PEN jejunum at day 3 but increased in the TPN jejunum by day 7. By day 3, intestinal T cell numbers were increased in TPN but not in PEN piglets. However, goblet cell expansion was established by day 3 in both the TPN and PEN ileum. Neither TNF-α nor IFN-γ mRNA expression in the TPN and PEN ileum correlated with goblet cell expansion. Thus goblet cell expansion occurred independently of overt inflammation but in association with parenteral feeding. These data support the hypothesis that goblet cell expansion represents an initial defense triggered by reduced epithelial renewal to prevent intestinal barrier failure.