bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of troglitazone on substrate storage and utilization in insulin-resistant rats
Authors: Sreenan Seamus , Keck Sara , Fuller Timothy , Cockburn Brian , Burant Charles F.
Published: December 2017

Elevated serum and tissue lipid stores are associated with skeletal muscle insulin resistance and diminished glucose-stimulated insulin secretion, the hallmarks of type 2 diabetes. We studied the effects of 6-wk treatment with the insulin sensitizer troglitazone on substrate storage and utilization in lean control and Zucker diabetic fatty (ZDF) rats. Troglitazone prevented development of diabetes and lowered serum triglycerides (TG) in ZDF rats. Soleus muscle glycogen and TG content were elevated twofold in untreated ZDF rats, and both were normalized by troglitazone to lean control levels ( P < 0.05). Troglitazone also normalized insulin-stimulated glucose uptake as well as basal and insulin-stimulated glycogen synthesis, implying increased skeletal muscle glycogen turnover. The proportion of active pyruvate dehydrogenase (PDH) in soleus muscle was reduced in ZDF relative to lean control rat muscle (16 ± 2 vs. 21 ± 2%) but was restored by troglitazone treatment (30 ± 3%). Increased PDH activation was associated with a 70% increase in glucose oxidation. Muscle lipoprotein lipase activity was decreased by 35% in ZDF compared with lean control rats and was increased twofold by troglitazone. Palmitate oxidation and incorporation into TG were higher in ZDF relative to lean control rats but were unaffected by troglitazone treatment. Troglitazone decreased the incorporation of glucose into the acyl group of TG by 60% in ZDF rats. In summary, ZDF rats demonstrate increased skeletal muscle glycogen and TG stores, both of which were reduced by troglitazone treatment. Troglitazone appears to increase both glycogen and TG turnover in skeletal muscle. Normalization of PDH activity and decreased glucose incorporation into acyl TG may underlie the improvements in intracellular substrate utilization and energy stores, which lead to decreased serum TG and glucose.
Endurance exercise training does not alter lipolytic or adipose tissue blood flow sensitivity to epinephrine
Authors: Horowitz Jeffrey F. , Braudy Renata J. , Martin Wade H. , Klein Samuel
Published: December 2017

We evaluated the relationship between lipolysis and adipose tissue blood flow (ATBF) in response to epinephrine and the effect of endurance exercise training on these responses. Five healthy untrained men underwent a four-stage incremental epinephrine infusion (0.00125, 0.005, 0.0125, and 0.025 μg ⋅ kg fat free mass−1 ⋅ min−1) plus hormonal clamp before and after 16 wk of cycle ergometry exercise training. Whole body glycerol and free fatty acid (FFA) rates of appearance (Ra) in plasma were determined by stable isotope methodology, and ATBF was assessed by133Xe clearance. After each training session, subjects were fed the approximate number of calories expended during exercise to prevent changes in body weight. Glycerol Ra, FFA Ra, and ATBF increased when plasma epinephrine concentration reached 0.8 nM, but at plasma epinephrine concentrations >1.6 nM ATBF plateaued, whereas lipolysis continued to increase. Exercise training increased peak oxygen uptake by 24 ± 7% (2.9 ± 0.2 vs. 3.6 ± 0.1 l/min; P < 0.05) but did not alter body weight [70.5 ± 3.8 vs. 72.0 ± 3.8 kg; P = nonsignificant (NS)] or percent body fat (18.4 ± 1.6 vs. 17.8 ± 1.9%; P = NS). Lipolytic and ATBF responses to epinephrine were also the same before and after training. We conclude that the lipolytic and ATBF responses to epinephrine are coordinated when plasma epinephrine concentration is ≤1.6 nM, but that at higher epinephrine concentrations, lipolysis continues to increase while ATBF remains constant. Endurance exercise training does not change lipolytic or ATBF sensitivity to epinephrine infusion in vivo during resting conditions.
Calories and aging alter gene expression for gluconeogenic, glycolytic, and nitrogen-metabolizing enzymes
Authors: Dhahbi Joseph M. , Mote Patricia L. , Wingo John , Tillman John B. , Walford Roy L. , Spindler Stephen R.
Published: December 2017

We characterized the effects of calorie restriction (CR) on the expression of key glycolytic, gluconeogenic, and nitrogen-metabolizing enzymes in mice. Of the gluconeogenic enzymes investigated, liver glucose-6-phosphatase mRNA increased 1.7- and 2.3-fold in young and old CR mice. Phospho enolpyruvate carboxykinase mRNA and activity increased 2.5- and 1.7-fold in old CR mice. Of the key glycolytic enzymes, pyruvate kinase mRNA and activity decreased ∼60% in CR mice. Hepatic phosphofructokinase-1 and pyruvate dehydrogenase mRNA decreased 10–20% in CR mice. Of the genes that detoxify ammonia generated from protein catabolism, hepatic glutaminase, carbamyl phosphate synthase I, and tyrosine aminotransferase mRNAs increased 2.4-, 1.8-, and 1.8-fold with CR, respectively. Muscle glutamine synthetase mRNA increased 1.3- and 2.1-fold in young and old CR mice. Hepatic glutamine synthetase mRNA and activity each decreased 38% in CR mice. These CR-induced changes are consistent with other studies suggesting that CR may decrease enzymatic capacity for glycolysis and increase the enzymatic capacity for hepatic gluconeogenesis and the disposal of byproducts of muscle protein catabolism.
Acute exercise increases nitric oxide synthase activity in skeletal muscle
Authors: Roberts Christian K. , Barnard R. James , Jasman Arnie , Balon Thomas W.
Published: December 2017

This study examined the effects of acute exercise on skeletal muscle nitric oxide synthase (NOS) activity. Female Sprague-Dawley rats were divided into three groups: control, exercise, and exercise + N G-nitro-l-arginine methyl ester (l-NAME). In the exercise + l-NAME group, l-NAME was administered in the drinking water (1 mg/ml) for 2 days and subsequently the exercise and exercise + l-NAME groups underwent a 45-min bout of exhaustive treadmill running after which NOS activity and muscle glycogen were measured. In the control and exercise groups, 1-amino- S-methylisothiourea (AMITU), a selective neuronal NOS inhibitor, with and without additional nonselective NOS blockade [with N G-monomethyl-l-arginine (l-NMMA)], was used in vitro to assess the contribution of nNOS to total NOS activity. The exercise bout increased NOS activity by 37% in exercise compared with control groups, and both groups had significantly greater NOS activity compared with exercise + l-NAME. AMITU decreased total NOS activity in the control and exercise groups by 31.8 and 30.2%, respectively, and these activities were significantly greater than AMITU +l-NMMA in both control and exercise groups. We conclude that 1) there is basal neuronal NOS and endothelial NOS activity in skeletal muscle, 2) an acute exercise bout increases NOS activity in skeletal muscle, and 3) glycogen depletion during exercise occurs irrespective of NOS activity.
Estimating gluconeogenesis with [U-13C]glucose: molecular condensation requires a molecular approach
Authors: Kelleher Joanne K.
Published: December 2017

Recently three equations for estimating gluconeogenesis in vivo have been proposed, two by J. A. Tayek and J. Katz [ Am. J. Physiol. 270 ( Endocrinol. Metab. 33): E709–E717, 1996, and Am. J. Physiol. 272 ( Endocrinol. Metab. 35): E476–E484, 1997] and one by B. R. Landau, J. Wahren, K. Ekberg, S. F. Previs, D. Yang, and H. Brunengraber [ Am. J. Physiol.274 ( Endocrinol. Metab. 37): E954–E961, 1998]. Both groups estimate gluconeogenesis from cycling of [U-13C]glucose to lactate and back to glucose, detected by mass spectrometry. Landau’s approach is based on analysis of labeled molecules, whereas Tayek and Katz’s is based on labeling of carbon atoms by use of the concept of “molar enrichment,” which weights each mass isotopomer by the number of labeled carbons. We derived an equation very similar to Landau’s using binomial probability. Our analysis demonstrates that the molecular-based approach is correct. Additionally, equations appropriate for 14C studies are not appropriate for 13C studies, because the method used to detect14C, decay of atoms, differs from13C mass isotopomers detected as labeled molecules. We conclude that the molar enrichment carbon-based approach is not useful in the derivation of equations for the polymerization of molecules detected by mass spectrometry of molecules, and we confirm the findings of Landau et al.
Calcium influx and intracellular stores in angiotensin II stimulation of normal and hyperplastic pituitary cells
Authors: Iglesias Arturo Gonzalez , Diaz-Torga Graciela , Lux-Lantos Victoria , Libertun Carlos , Becu-Villalobos Damasia
Published: December 2017

In rat pituitary cells from estrogen-induced hyperplasia, angiotensin II (ANG II) does not evoke a clear spike elevation of intracellular Ca2+concentration ([Ca2+]i) but induces a plateau increase. The present work was undertaken to establish whether this difference was related to a differential participation of intracellular and/or plasma membrane Ca2+channels. We first tested the effect of 10 nM ANG II on [Ca2+]iin the absence of extracellular Ca2+in cells depolarized with 25 mM K+or in the presence of blockers of L-type voltage-sensitive Ca2+channels (VSCC). These treatments did not alter spike elevation in [Ca2+]iin controls but reduced plateau levels in hyperplastic cells. Intracellular Ca2+stores were similar in both groups, as assessed by thapsigargin treatment, but this drug abolished spike increase in controls and scarcely modified plateau levels in hyperplastic cells. Finally, inositol trisphosphate (InsP3) production in response to ANG II was significantly higher in control cells. We conclude that the observed plateau rise in hyperplastic cells results mainly from Ca2+influx through VSCC. In contrast, in control cells, the ANG II-induced spike increase in [Ca2+]iresults from mobilization of Ca2+from thapsigargin-sensitive internal channels, activated by higher inositol 1,4,5-trisphosphate generation.
Effect of nutrition on tumor necrosis factor receptors in weight-gaining and -losing rats
Authors: Raina Nilima , Lamarre Jonathan , Liew Choong-Ching , Lofti Amir H. , Jeejeebhoy Khursheed N.
Published: December 2017

Previous studies showed that weight-gaining rats had greater retention and reduced turnover of125I-labeled tumor necrosis factor (TNF)-α in the circulation compared with weight-losing animals. We therefore tested the hypothesis that protein-energy restriction with weight loss reduces the levels of soluble TNF-α receptor (sTNFR) and membrane TNFR (mTNFR) and the cellular expression of TNF-α mRNA. Twenty-six male rats weighing 200–220 g were fed a liquid formula diet for 10 days and divided equally into weight-gaining rats meeting all nutritional requirements (WG rats) and weight-losing rats with protein-energy restriction (WL rats).125I-TNF-α binding was demonstrated in plasma and plasma membrane to proteins of molecular masses of 92 and 243 kDa, a finding identical to that seen with purified human p55. Excess unlabeled TNF-α displaced the binding showing its specificity. The degree of binding to plasma protein and liver plasma membrane was markedly reduced in WL rats. Northern analysis showed that the expression of p55 mRNA was increased in the lungs and reduced in kidneys of WL compared with WG rats. The expression of p75 mRNA was not influenced by the nutritional status. We conclude that levels of sTNFR and mTNFR were reduced in WL rats. Reduced sTNFR and liver mTNFR are not due to a reduction in the expression of either p55 or p75 mRNA in WL rats. Reduced mTNFR, together with reduced shedding of soluble receptors, may have a protective role in WL rats.
Oral amino acids stimulate muscle protein anabolism in the elderly despite higher first-pass splanchnic extraction
Authors: Volpi Elena , Mittendorfer Bettina , Wolf Steven E. , Wolfe Robert R.
Published: December 2017

Muscle protein synthesis and breakdown and amino acid transport were measured in 7 healthy young (30 ± 2 yr) and 8 healthy elderly (71 ± 2 yr) volunteers in the postabsorptive state and during the oral administration of an amino acid mixture withl-[ ring-2H5]phenylalanine infusion, femoral artery and vein catheterization, and muscle biopsies. Phenylalanine first-pass splanchnic extraction was measured by addingl-[ ring-13C6]phenylalanine to the mixture. In the postabsorptive state, no differences in muscle amino acid kinetics were detected between young and elderly volunteers. Phenylalanine first-pass splanchnic extraction was significantly higher in the elderly ( P < 0.003) during ingestion of amino acids, but the delivery to the leg increased to the same extent in both groups. Phenylalanine transport into the muscle, muscle protein synthesis, and net balance increased significantly ( P < 0.01) and similarly in both the young and the elderly. We conclude that, despite an increased splanchnic first-pass extraction, muscle protein anabolism can be stimulated by oral amino acids in the elderly as well as in the young.
Neural contribution to the effect of glucagon-like peptide-1-(7—36) amide on arterial blood pressure in rats
Authors: Barragán José Manuel , Eng John , Rodríguez Raquel , Blázquez Enrique
Published: December 2017

This study was designed to determine the contribution of the central nervous system (CNS) to the effects of glucagon-like peptide-1-(7—36) amide (tGLP-1) on arterial blood pressure and heart rate in rats. Accordingly, intracerebroventricular administration of the peptide produced an increase in cardiovascular parameters, which was blocked by previous administration of exendin-(9—39) through the same route, but not when it was intravenously injected. Intravenous administration of tGLP-1 produced a significant increase in arterial blood pressure and heart rate, which was blocked by the previous intracerebroventricular or intravenous administration of exendin-(9—39). Bilateral vagotomy blocked the stimulating effect of intracerebroventricular tGLP-1 administration on arterial blood pressure and heart rate. Also, bilateral vagotomy prevented the blocking effect of intracerebroventricular but not of intravenous exendin-(9—39) on cardiovascular parameters after intravenous administration of tGLP-1. These findings suggest that the action of tGLP-1 on cardiovascular parameters is under a dual control generated in the CNS and in peripheral structures and that the neural information emerging in the brain is transmitted to the periphery through the vagus nerve.
Genetic variability in plasma melatonin in sheep is due to pineal weight, not to variations in enzyme activities
Authors: Coon Steven L. , Zarazaga Luis A. , Malpaux Benoît , Ravault Jean-Paul , Bodin Loys , Voisin Pierre , Weller Joan L. , Klein David C. , Chemineau Philippe
Published: December 2017

This study was conducted to determine the origin of the high variability in the mean nocturnal plasma melatonin concentration (MC) in sheep. Two extreme groups of 25 lambs each [low (L) and high (H)] were obtained by calculating their genetic value on the basis of the MC of their parents. The MC of lambs was significantly higher in the H group than in the L group (L: 189.7 ± 24.4 vs. H: 344.1 ± 33.0 pg/ml, P < 0.001). Within each group, 13 lambs were slaughtered during the day (D) and 12 lambs during the night (N). Pineal weight was significantly higher in the H group than in the L group (L: 83.5 ± 6.7 vs. H: 119.1 ± 9.2 mg, P < 0.01) but did not differ between D and N. The amount of melatonin released in vitro per milligram of pineal gland, the arylalkylamine N-acetyltransferase (AANAT) activity, the AANAT protein content, and the level of AANAT mRNA differed significantly between D and N but not with genetic group. Hydroxyindole O-methyltransferase activity did not differ significantly between D and N or between genetic groups. Therefore, the genetic difference in MC between the two groups of lambs was attributed to a difference in pineal size, not in enzymatic activity of the pinealocytes.
Changes in cardiac protein kinase C activities and isozymes in streptozotocin-induced diabetes
Authors: Liu Xueliang , Wang Jingwei , Takeda Nobuakira , Binaglia Luciano , Panagia Vincenzo , Dhalla Naranjan S.
Published: December 2017

To understand cardiac dysfunction in diabetes, the activity of protein kinase C (PKC) and protein contents of its isozymes (PKC-α, -β, -ε, and -ζ) were examined in diabetic rats upon injection of streptozotocin (65 mg/kg iv). The hearts were removed at 1, 2, 4, and 8 wk, and some of the 6-wk diabetic animals had been injected with insulin (3 U/day) for 2 wk. The Ca2+-dependent PKC activity was increased by 43 and 51% in the homogenate fraction and 31 and 70% in the cytosolic fraction from the 4- and 8-wk diabetic hearts, respectively, in comparison with control values. The Ca2+-independent PKC activity was increased by 24 and 32% in the homogenate fraction and 52 and 89% in the cytosolic fraction from the 4- and 8-wk diabetic hearts, respectively, in comparison with control values. The relative protein contents of PKC-α, -β, -ε, and -ζ isozymes were increased by 43, 31, 48, and 38%, respectively, in the homogenate fraction and by 126, 119, 148, and 129%, respectively, in the cytosolic fraction of the 8-wk diabetic heart. The observed changes in heart homogenate and cytosolic fractions were partially reversible upon treatment of the diabetic rats with insulin. The results suggest that the increased myocardial PKC activity and increased protein contents of the cytosolic PKC isozymes are associated with subcellular alterations and cardiac dysfunction in the diabetic heart.
Effect of guanethidine-induced adrenergic blockade on the different proteolytic systems in rat skeletal muscle
Authors: Navegantes Luiz Carlos C. , Resano Neusa M. Z. , Migliorini Renato H. , Kettelhut Isis C.
Published: December 2017

Overall proteolysis and the activity of skeletal muscle proteolytic systems were investigated in rats submitted to guanethidine-induced adrenergic blockade for 4 days. In soleus, overall proteolysis increased by 15–20% during the first 2 days of guanethidine treatment but decreased to levels below control values after 4 days. Extensor digitorum longus (EDL) did not show the initial increase in total proteolysis, which was already reduced after 2 days of guanethidine treatment. The initial rise in the rate of protein degradation in soleus was accompanied by an increased activity of the Ca2+-dependent proteolytic pathway. In both soleus and EDL, the reduction in overall proteolysis was paralleled by decreased activities of the Ca2+-dependent and ATP-dependent proteolytic processes. No change was observed in the activity of the lysosomal proteolytic system. Overall proteolysis in soleus and EDL from nontreated rats was partially inhibited by isoproterenol, in vitro. The data suggest an acute inhibitory control of skeletal muscle proteolysis by the adrenergic system, well evident in the oxidative muscle, with an important participation of the Ca2+-dependent pathway.
Hormone pulsatility discrimination via coarse and short time sampling
Authors: Pincus Steven M. , Hartman Mark L. , Roelfsema Ferdinand , Thorner Michael O. , Veldhuis Johannes D.
Published: December 2017

Pulsatile hormonal secretion is a ubiquitous finding in endocrinology. However, typical protocols employed to generate data sets suitable for “pulsatility analysis” have required 60–300 samples, rendering such studies largely research methodologies, due primarily to considerable assay expense. One successful mathematical strategy in calibrating changes in pulsatility modalities is approximate entropy (ApEn), a quantification of sequential irregularity. Given the degree of differences between ApEn values in pathophysiological subjects vs. healthy controls reported in several recent studies, we queried to what extent coarser (less frequent) and shorter duration time sampling would still retain significant ApEn differences between clinically distinct cohorts. Accordingly, we reanalyzed data from two studies of 24-h profiles of healthy vs. tumoral hormone secretion: 1) growth hormone comparisons of normal subjects vs. acromegalics, originally sampled every 5 min; and 2) ACTH and cortisol comparisons of normal subjects vs. Cushing's disease patients, originally sampled every 10 min. By multiple statistical analyses, we consistently and highly significantly ( P < 0.0001) established that serum concentration patterns in tumor patients are more irregular than those of controls, with high sensitivity and specificity, even at very coarse (e.g., 60 min) sampling regimens and over relatively short (2–4 h) time intervals. The consistency of these findings suggests a broadly based utility of such shorter and/or coarser sampling methodologies. Substantial reduction in sampling requirements holds the potential to move analysis of pulsatile hormone release from a primarily research tool to a clinically applicable protocol, in appropriate diagnostic and therapeutic contexts.
Aspirin inhibits androgen response to chorionic gonadotropin in humans
Authors: Conte Domenico , Romanelli Francesco , Fillo Silvia , Guidetti Laura , Isidori Aldo , Franceschi Francesco , Latini Maurizio , di Luigi Luigi
Published: December 2017

Eicosanoids play an important role in the regulation of the hypothalamic-pituitary axis; less clear is their role in testicular steroidogenesis. To evaluate the involvement of cyclooxygenase metabolites, such as prostaglandins, in the regulation of human testicular steroidogenesis, we examined the effects of a prostaglandin-blocker, aspirin, on plasma testosterone, pregnenolone, progesterone, 17OH-progesterone, androstenedione, dehydroepiandrosterone, and 17β-estradiol response to human chorionic gonadotropin (hCG) in normal male volunteers in a placebo-controlled, single-blinded study. To test the efficacy of aspirin, seminal prostaglandin E2 levels were also determined. hCG stimulation increased peripheral levels of testosterone, 17OH-progesterone, androstenedione, dehydroepiandrosterone, and 17β-estradiol, without affecting circulating pregnenolone and progesterone values. Aspirin significantly lowered seminal prostaglandin E2levels, whereas it did not modify steroid concentrations not exposed to exogenous hCG. Moreover, the drug significantly reduced the response of testosterone, 17OH-progesterone, androstenedione, and dehydroepiandrosterone to hCG, as assessed by the mean integrated area under the curve, whereas it did not influence 17β-estradiol response. In conclusion, aspirin treatment inhibits androgen response to chorionic gonadotropin stimulation in normal humans. The action of aspirin is probably mediated via an effective arachidonate cyclooxygenase block.
Muscle lipid accumulation and protein kinase C activation in the insulin-resistant chronically glucose-infused rat
Authors: Laybutt D. Ross , Schmitz-Peiffer Carsten , Saha Asish K. , Ruderman Neil B. , Biden Trevor J. , Kraegen Edward W.
Published: December 2017

Chronic glucose infusion results in hyperinsulinemia and causes lipid accumulation and insulin resistance in rat muscle. To examine possible mechanisms for the insulin resistance, alterations in malonyl-CoA and long-chain acyl-CoA (LCA-CoA) concentration and the distribution of protein kinase C (PKC) isozymes, putative links between muscle lipids and insulin resistance, were determined. Cannulated rats were infused with glucose (40 mg ⋅ kg−1⋅ min−1) for 1 or 4 days. This increased red quadriceps muscle LCA-CoA content (sum of 6 species) by 1.3-fold at 1 day and 1.4-fold at 4 days vs. saline-infused controls (both P < 0.001 vs. control). The concentration of malonyl-CoA was also increased (1.7-fold at 1 day, P < 0.01, and 2.2-fold at 4 days, P < 0.001 vs. control), suggesting an even greater increase in cytosolic LCA-CoA. The ratio of membrane to cytosolic PKC-ε was increased twofold in the red gastrocnemius after both 1 and 4 days, suggesting chronic activation. No changes were observed for PKC-α, -δ, and -θ. We conclude that LCA-CoAs accumulate in muscle during chronic glucose infusion, consistent with a malonyl-CoA-induced inhibition of fatty acid oxidation (reverse glucose-fatty acid cycle). Accumulation of LCA-CoAs could play a role in the generation of muscle insulin resistance by glucose oversupply, either directly or via chronic activation of PKC-ε.
l-2-[13C]oxothiazolidine-4-carboxylic acid: a probe for precursor mobilization for glutathione synthesis
Authors: Fukagawa Naomi K. , Hercules Eswin , Ajami Alfred M.
Published: December 2017

l-2-Oxothiazolidine-4-carboxylic acid (OTZ), a 5-oxoproline analog, is metabolized by 5-oxoprolinase and converted to cysteine, the rate-limiting amino acid for GSH synthesis, with the release of CO2. [13C]OTZ (1.5 mg/kg) was used in 12 healthy men and women (ages 23–73 yr) to indirectly assess precursor mobilization for GSH synthesis when stores were reduced by 2 g acetaminophen. Expired breath samples were analyzed for13CO2, and results were analyzed using noncompartmental and two-compartment open minimal models. Results show an increase in13C excretion (higher OTZ hydrolysis) when GSH stores were reduced and 5-oxoprolinase substrate utilization patterns, consequently, were altered ( P < 0.01). A metabolic rate index (MRI) of the OTZ probe was found to be significantly higher after reduction of GSH content by acetaminophen ( P < 0.05). The difference in adaptive capacity (difference between control and postacetaminophen metabolic rate indexes) was two times as large in the young than the old subjects ( P < 0.01). These data support the use of [13C]OTZ as a probe to identify individuals who may be at risk for low GSH stores or who have an impaired capacity to synthesize GSH.
Analysis of the vasopressin system and water regulation in genetically polydipsic mice
Authors: Yambe Yuko , Watanabe-Tomita Yasuko , Kakiya Satoshi , Yokoi Hisashi , Nagasaki Hiroshi , Arima Hiroshi , Murase Takashi , Yuasa Hiromitsu , Kondo Kunikazu , Yamashita Hiroshi , Oiso Yutaka
Published: December 2017

Polydipsic mice, STR/N, which show extreme polydipsia and polyuria, were discovered in 1958. In the STR/N, urine outputs are much higher than in control mice. The possibility of an abnormal regulation of the arginine vasopressin (AVP) system, or an abnormality in the renal susceptibility to AVP, should be considered. In this study we investigated the AVP system and water regulation in STR/N. We sequenced the AVP and the AVP V2-receptor genes of the STR/N by direct sequencing. No mutation was found in either of them. AVP gene expression examined by in situ hybridization and plasma sodium in 8-wk-old STR/N was significantly lower than in control mice, whereas it was significantly higher at 20 wk. Renal sensitivity to injected AVP was attenuated in 20-wk-old STR/N. The suppression of AVP synthesis due to excessive water retention in 8-wk-old STR/N suggests that polydipsia may be the primary cause in this strain. The 20-wk-old STR/N became dehydrated with the acceleration of AVP synthesis, which might have resulted from secondary desensitization to AVP.
Induction of tissue plasminogen activator secretion from rat heart microvascular cells by fM 1,25(OH)2D3
Authors: Puri Sanjeev , Bansal Devi D. , Uskoković Milan R. , MacGregor Ronal R.
Published: December 2017

We investigated the effects of 1,25-dihydroxyvitamin D3[25(OH)2D3] on tissue plasminogen activator (tPA) secretion from primary cultures of rat heart microvascular cells. After an initial 5-day culture period, cells were treated for 24 h with 1,25(OH)2D3and several of its analogs. The results showed that 1,25(OH)2D3induced tPA secretion at 10−10to 10−16M. A less calcemic analog, Ro-25–8272, and an analog that binds the vitamin D receptor but is ineffective at perturbing Ca2+channels, Ro-24–5531, were ∼10% as active as 1,25(OH)2D3. An analog that binds the vitamin D receptor poorly but is an effective Ca2+channel agonist, Ro-24–2287, required ∼10−13M to induce tPA secretion. Combinations of Ro-24–5531 and Ro-24–2287 were approximately as potent as 1,25(OH)2D3. Treatment of the cells with BAY K 8644 or thapsigargin also increased tPA secretion, suggesting that increased cytosolic calcium concentration ([Ca2+]) induces tPA secretion. The results suggested that the sensitivity of the tPA secretory response of microvascular cells to 1,25(OH)2D3was due in part to generation of a vitamin D-depleted state in vitro and in part to synergistic effects of 1,25(OH)2D3on two different induction pathways of tPA release.
Effect of induced metabolic alkalosis on human skeletal muscle metabolism during exercise
Authors: Hollidge-Horvat M. G. , Parolin M. L. , Wong D. , Jones N. L. , Heigenhauser G. J. F.
Published: December 2017

The purpose of the study was to examine the roles of active pyruvate dehydrogenase (PDHa), glycogen phosphorylase (Phos), and their regulators in lactate (Lac−) metabolism during incremental exercise after ingestion of 0.3 g/kg of either NaHCO3[metabolic alkalosis (ALK)] or CaCO3[control (CON)]. Subjects ( n = 8) were studied at rest, rest postingestion, and during constant rate cycling at three stages (15 min each): 30, 60, 75% of maximal O2uptake (V˙o2 max). Radial artery and femoral venous blood samples, leg blood flow, and biopsies of the vastus lateralis were obtained during each power output. ALK resulted in significantly ( P < 0.05) higher intramuscular Lac−concentration ([Lac−]; ALK 72.8 vs. CON 65.2 mmol/kg dry wt), arterial whole blood [Lac−] (ALK 8.7 vs. CON 7.0 mmol/l), and leg Lac−efflux (ALK 10.0 vs. CON 4.2 mmol/min) at 75%V˙o2 max. The increased intramuscular [Lac−] resulted from increased pyruvate production due to stimulation of glycogenolysis at the level of Phos a and phosphofructokinase due to allosteric regulation mediated by increased free ADP (ADPf), free AMP (AMPf), and free Piconcentrations. PDHaincreased with ALK at 60%V˙o2 maxbut was similar to CON at 75%V˙o2 max. The increased PDHamay have resulted from alterations in the acetyl-CoA, ADPf, pyruvate, NADH, and H+concentrations leading to a lower relative activity of PDH kinase, whereas the similar values at 75% V˙o2 maxmay have reflected maximal activation. The results demonstrate that imposed metabolic alkalosis in skeletal muscle results in acceleration of glycogenolysis at the level of Phos relative to maximal PDH activation, resulting in a mismatch between the rates of pyruvate production and oxidation resulting in an increase in Lac−production.
Thyroid hormones differentially modulate enolase isozymes during rat skeletal and cardiac muscle development
Authors: Merkulova Tatyana , Keller Angélica , Oliviero Patricia , Marotte Françoise , Samuel Jane-Lyse , Rappaport Lydie , Lamandé Noël , Lucas Marguerite
Published: December 2017

During muscle development, an isozymic transition of the glycolytic enzyme enolase occurs from the embryonic and ubiquitous αα-isoform to the muscle-specific ββ-isoform. Here, we demonstrate a stimulatory role of thyroid hormones on these two enolase genes during rat development in hindlimb muscles and an inhibitory effect on the muscle-specific enolase gene in cardiac muscle. In hindlimb muscles the ubiquitous α-transcript level is diminished by hypothyroidism, starting at birth. On the contrary, the more abundant muscle-specific β-transcript is insensitive to hypothyroidism before establishment of the functional diversification of fibers and is greatly decreased thereafter. Our data support the hypothesis of a role of thyroid hormones in coordinating the expressions of contractile proteins and metabolic enzymes during muscle development. The subcellular localization of isoenolases, established here, is not modified by hypothyroidism. Our results underline the specificity of action of thyroid hormones, which modulate differentially two isozymes in the same muscle and regulate, in opposite directions, the expression of the same gene in two different muscles.
Measurement of interstitial albumin in human skeletal muscle and adipose tissue by open-flow microperfusion
Authors: Ellmerer Martin , Schaupp Lukas , Brunner Gernot A. , Sendlhofer Gerald , Wutte Andrea , Wach Paul , Pieber Thomas R.
Published: December 2017

The absolute concentration of albumin was measured in the interstitial fluid of subcutaneous adipose tissue and skeletal muscle in six healthy volunteers by combining the method of open-flow microperfusion and the no-net-flux calibration technique. By use of open-flow microperfusion, four macroscopically perforated double lumen catheters were inserted into the tissue regions of interest and constantly perfused. Across the macroscopic perforations of the catheters interstitial fluid was partially recovered in the perfusion fluid. Catheters were perfused with five solutions, each containing different concentrations of albumin. Absolute interstitial albumin concentrations were calculated by applying linear regression analysis to perfusate vs. sampled albumin concentration (no-net-flux calibration technique). Interstitial albumin concentrations were significantly lower ( P < 0.0001) in adipose tissue (7.36 g/l; r = 0.99, P < 0.0003; range: 4.3–10.7 g/l) and in skeletal muscle (13.25 g/l; r = 0.99, P < 0.0012; range: 9.7 to 15.7 g/l) compared with the serum concentration (48.9 ± 0.7 g/l, mean ± SE, n = 6; range: 46.4–50.4 g/l). Furthermore, interstitial albumin concentrations were significantly higher in skeletal muscle compared with adipose tissue ( P < 0.01). The study indicates that open-flow microperfusion allows stable sampling of macromolecules from the interstitial space of peripheral tissue compartments. Moreover, the present data report for the first time in healthy humans in vivo the true albumin concentrations of interstitial fluid of adipose tissue and skeletal muscle.
Differential action of hepatic sympathetic neuropeptides: metabolic action of galanin, vascular action of NPY
Authors: Mundinger Thomas O. , Taborsky Gerald J.
Published: December 2017

Activation of hepatic nerves increases both hepatic glucose production (HGP) and hepatic arterial vasoconstriction, the latter best described by a decrease of hepatic arterial conductance (HAC). Because activation of canine hepatic nerves releases the neuropeptides galanin and neuropeptide Y (NPY) as well as the classical neurotransmitter norepinephrine (NE), we sought to determine the relative role of these neuropeptides vs. norepinephrine in mediating metabolic and vascular responses of the liver. We studied the effects of local exogenous infusions of galanin and NPY on HGP and HAC to predict the metabolic and vascular function of endogenously released neuropeptide. Galanin ( n = 8) or NPY ( n = 4) was infused with and without NE directly into the common hepatic artery of halothane-anesthetized dogs, and we measured changes in HGP and HAC. A low dose of exogenous galanin infused directly into the hepatic artery potentiated the HGP response to NE yet had little effect on HGP when infused alone. The same dose of galanin infused into a peripheral vein ( n = 8) did not potentiate the HGP response to NE, suggesting that the locally infused galanin acted directly on the liver to modulate NE's metabolic action. In contrast, a large dose of exogenous NPY failed to influence HGP when infused either alone or in combination with NE. Finally, NPY, but not galanin, tended to decrease HAC when infused alone; neither neuropeptide potentiated the HAC response to NE. Therefore, both hepatic neuropeptides may contribute to the action of sympathetic nerves on liver metabolism and blood flow. It is likely that endogenous hepatic galanin acts directly on the liver to selectively modulate norepinephrine's metabolic action, whereas endogenous hepatic NPY acts independently of NE to cause vasoconstriction.
Somatotropin increases protein balance by lowering body protein degradation in fed, growing pigs
Authors: Vann Rhonda C. , Nguyen Hanh V. , Reeds Peter J. , Burrin Douglas G. , Fiorotto Marta L. , Steele Norman C. , Deaver Daniel R. , Davis Teresa A.
Published: December 2017

Somatotropin (ST) administration enhances protein deposition in well-nourished, growing animals. To determine whether the anabolic effect is due to an increase in protein synthesis or a decrease in proteolysis, pair-fed, weight-matched (∼20 kg) growing swine were treated with porcine ST (150 μg ⋅ kg−1⋅ day−1, n = 6) or diluent ( n = 6) for 7 days. Whole body leucine appearance (Ra), nonoxidative leucine disposal (NOLD), urea production, and leucine oxidation, as well as tissue protein synthesis (Ks), were determined in the fed steady state using primed continuous infusions of [13C]leucine, [13C]bicarbonate, and [15N2]urea. ST treatment increased the efficiency with which the diet was used for growth. ST treatment also increased plasma insulin-like growth factor I (+100%) and insulin (+125%) concentrations and decreased plasma urea nitrogen concentrations (−53%). ST-treated pigs had lower leucine Ra(−33%), leucine oxidation (−63%), and urea production (−70%). However, ST treatment altered neither NOLD nor Ksin the longissimus dorsi, semitendinosus, or gastrocnemius muscles, liver, or jejunum. The results suggest that in the fed state, ST treatment of growing swine increases protein deposition primarily through a suppression of protein degradation and amino acid catabolism rather than a stimulation of protein synthesis.
Cod and soy proteins compared with casein improve glucose tolerance and insulin sensitivity in rats
Authors: Lavigne Charles , Marette André , Jacques Hélène
Published: December 2017

The aim of the present study was to determine the effects of feeding various dietary proteins on insulin sensitivity and glucose tolerance in rats. Male Wistar rats were fed for 28 days with isoenergetic diets containing either casein, soy protein, or cod protein. Cod protein-fed and soy protein-fed rats had lower fasting plasma glucose and insulin concentrations compared with casein-fed animals. After intravenous glucose bolus, cod protein- and soy protein-fed rats induced lower incremental areas under glucose curves compared with casein-fed animals. Improved peripheral insulin sensitivity was confirmed by higher glucose disposal rates in cod protein- and soy protein-fed rats (15.2 ± 0.3 and 13.9 ± 0.6 mg ⋅ kg−1⋅ min−1, respectively) compared with casein-fed animals (6.5 ± 0.7 mg ⋅ kg−1⋅ min−1, P < 0.05). Moreover, test meal experiments revealed that, in the postprandial state, the lower plasma insulin concentrations in cod protein- and soy protein-fed animals could be also due to decreased pancreatic insulin release and increased hepatic insulin removal. In conclusion, the metabolic responses to three common dietary proteins indicate that cod and soy proteins, when compared with casein, improve fasting glucose tolerance and peripheral insulin sensitivity in rats.
Roles of insulin resistance and obesity in regulation of plasma insulin concentrations
Authors: Jones Clare N. O. , Abbasi Fahim , Carantoni Marcello , Polonsky Kenneth S. , Reaven Gerald M.
Published: December 2017

Plasma glucose, insulin, and C-peptide concentrations were determined in response to graded infusions of glucose, and insulin secretion rates were calculated over each sampling period. Measurements were also made of insulin clearance, resistance to insulin-mediated glucose, uptake, and the plasma glucose, insulin, and C-peptide concentrations at hourly intervals from 8:00 AM to 4:00 PM in response to breakfast and lunch. Plasma glucose, insulin, and C-peptide concentrations were significantly ( P < 0.01) higher in obese women in response to the graded intravenous glucose infusion, associated with a 40% ( P < 0.005) greater insulin secretory response. Degree of insulin resistance correlated positively ( P < 0.05) with the increase in insulin secretion rate in both nonobese ( r = 0.52) and obese ( r = 0.58) groups and inversely ( P < 0.05) with the decrease in insulin clearance in obese ( r = −0.46) and nonobese ( r = −0.39) individuals. Weight loss was associated with significantly lower plasma glucose, insulin, and C-peptide concentrations in response to graded glucose infusions and in day-long insulin concentrations. Neither insulin resistance nor the insulin secretory response changed after weight loss, whereas there was a significant increase in the rate of insulin clearance during the glucose infusion. It is concluded that 1) obesity is associated with a shift to the left in the glucose-stimulated insulin secretory dose-response curve as well as a decrease in insulin clearance and 2) changes in insulin secretion and insulin clearance in obese women are more a function of insulin resistance than obesity.
Cortisol inhibits hepatocyte growth factor/scatter factor expression and induces c-met transcripts in osteoblasts
Authors: Blanquaert Frederic , Pereira Renata C. , Canalis Ernesto
Published: December 2017

Hepatocyte growth factor/scatter factor (HGF/SF) is expressed by osteoblasts and has important effects on repair and bone remodeling. Because glucocorticoids regulate these two functions, we tested the effects of cortisol on the expression of HGF/SF and c-met, the protooncogene encoding the HGF/SF receptor, in cultures of osteoblast-enriched cells from 22-day fetal rat calvariae (Ob cells). Cortisol decreased HGF/SF mRNA levels and diminished the induction of HGF/SF transcripts by fibroblast growth factor-2 (FGF-2) and platelet-derived growth factor BB (PDGF BB). Cortisol also decreased FGF-2 and PDGF BB-induced HGF/SF mRNA and polypeptide levels in MC3T3 cells. In contrast, cortisol enhanced the expression of c-met transcripts in Ob cells. Cortisol did not modify the half-life of HGF/SF or of c-met mRNA in transcriptionally arrested cells, and it increased the rate of transcription of c-met. In conclusion, cortisol decreases HGF/SF transcripts in Ob cells and enhances c-met expression transcriptionally. The effects of cortisol on HGF/SF could be relevant to its inhibitory actions on bone formation and repair.
Endurance training, expression, and physiology of LDH, MCT1, and MCT4 in human skeletal muscle
Authors: Dubouchaud Hervé , Butterfield Gail E. , Wolfel Eugene E. , Bergman Bryan C. , Brooks George A.
Published: December 2017

To evaluate the effects of endurance training on the expression of monocarboxylate transporters (MCT) in human vastus lateralis muscle, we compared the amounts of MCT1 and MCT4 in total muscle preparations (MU) and sarcolemma-enriched (SL) and mitochondria-enriched (MI) fractions before and after training. To determine if changes in muscle lactate release and oxidation were associated with training-induced changes in MCT expression, we correlated band densities in Western blots to lactate kinetics determined in vivo. Nine weeks of leg cycle endurance training [75% peak oxygen consumption (V˙o2 peak)] increased muscle citrate synthase activity (+75%, P < 0.05) and percentage of type I myosin heavy chain (+50%, P < 0.05); percentage of MU lactate dehydrogenase-5 (M4) isozyme decreased (−12%, P < 0.05). MCT1 was detected in SL and MI fractions, and MCT4 was localized to the SL. Muscle MCT1 contents were consistent among subjects both before and after training; in contrast, MCT4 contents showed large interindividual variations. MCT1 amounts significantly increased in MU, SL, and MI after training (+90%, +60%, and +78%, respectively), whereas SL but not MU MCT4 content increased after training (+47%, P < 0.05). Mitochondrial MCT1 content was negatively correlated to net leg lactate release at rest ( r = −0.85, P < 0.02). Sarcolemmal MCT1 and MCT4 contents correlated positively to net leg lactate release at 5 min of exercise at 65%V˙o2 peak( r = 0.76, P < 0.03 and r = 0.86, P < 0.01, respectively). Results support the conclusions that 1) endurance training increases expression of MCT1 in muscle because of insertion of MCT1 into both sarcolemmal and mitochondrial membranes, 2) training has variable effects on sarcolemmal MCT4, and 3) both MCT1 and MCT4 participate in the cell-cell lactate shuttle, whereas MCT1 facilitates operation of the intracellular lactate shuttle.
Endurance training increases FFA oxidation and reduces triacylglycerol utilization in contracting rat soleus
Authors: Dyck D. J. , Miskovic D. , Code L. , Luiken J. J. F. P. , Bonen A.
Published: December 2017

We examined the effects of 8 wk of intense endurance training on free fatty acid (FFA) transporters and metabolism in resting and contracting soleus muscle using pulse-chase procedures. Endurance training increased maximal citrate synthase activity in red muscles (+54 to +91%; P ≤ 0.05) but failed to increase cytosolic fatty acid binding protein content, mRNA for fatty acyl-CoA synthase, and the putative FFA transporters or transport of palmitic acid into giant sarcolemmal vesicles. At rest, only triacylglycerol (TG) synthesis was significantly increased by training (+100.9 ± 8.7 vs. +66.6 ± 6.7 nmol/g wet wt; P ≤ 0.05). Muscle contraction increased TG synthesis (+46%; P ≤ 0.05) and palmitate oxidation (+115%; P ≤ 0.05) in untrained rats. Endurance training further enhanced synthesis of monoacylglycerol (MG), diacylglycerol (DG) and TG during contraction (+36, +69 and +71%, respectively; P ≤ 0.05), as well as exogenous palmitate oxidation (+41%; P ≤ 0.05) relative to untrained rats. Compared with those in untrained rats, TG breakdown and oxidation during contraction were reduced after training by 49 and 30%, respectively ( P ≤ 0.05). In conclusion, endurance training 1) increases FFA oxidation and incorporation into endogenous lipid pools during contraction and 2) reduces the rate of intramuscular TG utilization during contraction when exogenous FFA availability is adequate. The enhanced FFA uptake subsequent to training appears to be independent of altered maximal transport rates of FFA into the muscle cell.
Induction of growth hormone (GH) mRNA by pulsatile GH-releasing hormone in rats is pattern specific
Authors: Borski Russell J. , Tsai Wellington , Demott-Friberg Roberta , Barkan Ariel L.
Published: December 2017

Growth hormone-releasing hormone (GHRH) is a main inducer of growth hormone (GH) pulses in most species studied to date. There is no information regarding the pattern of GHRH secretion as a regulator of GH gene expression. We investigated the roles of the parameters of exogenous GHRH administration (frequency, amplitude, and total amount) upon induction of pituitary GH mRNA, GH content, and somatic growth in the female rat. Continuous GHRH infusions were ineffective in altering GH mRNA levels, GH stores, or weight gain. Changing GHRH pulse amplitude between 4, 8, and 16 μg/kg at a constant frequency (Q3.0 h) was only moderately effective in augmenting GH mRNA levels, whereas the 8 μg/kg and 16 μg/kg dosages stimulated weight gain by as much as 60%. When given at a 1.5-h frequency, GHRH doubled the amount of GH mRNA, elevated pituitary GH stores, and stimulated body weight gain. In the rat model, pulsatile but not continuous GHRH administration is effective in inducing pituitary GH mRNA and GH content as well as somatic growth. These studies suggest that the greater growth rate, pituitary mRNA levels, and GH stores seen in male compared with female rats are likely mediated, in part, by the endogenous episodic GHRH secretory pattern present in males.