bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of fertility by metabolic cues
Authors: Wade G. N. , Schneider J. E. , Li H. Y.
Published: December 2017

In female mammals, reproduction is extremely sensitive to the availability of oxidizable metabolic fuels. When food intake is limited or when an inordinate fraction of the available energy is diverted to other uses such as exercise or fattening, reproductive attempts are suspended in favor of processes necessary for individual survival. Both reproductive physiology and sexual behaviors are influenced by food availability. Nutritional effects on reproductive physiology are mediated by changes in the activity of gonadotropin-releasing hormone (GnRH) neurons in the forebrain, whereas the suppression of sexual behaviors appears to be due, at least in part, to decreases in estrogen receptor in the ventromedial hypothalamus. Work using pharmacological inhibitors of glucose and fatty acid oxidation indicates that reproductive physiology and behavior respond to short-term (minute-to-minute or hour-to-hour) changes in metabolic fuel oxidation, rather than to any aspect of body size or composition (e.g., body fat content or fat-to-lean ratio). These metabolic cues seem to be detected in the viscera (most likely in the liver) and in the caudal hindbrain (probably in the area postrema). This metabolic information is then transmitted to the GnRH-secreting or estradiol-binding effector neurons in the forebrain. There is no evidence to date for direct detection of metabolic cues by these forebrain effector neurons. This metabolic fuels hypothesis is consistent with a large body of evidence and seems to account for the infertility that is seen in a number of situations, including famine, eating disorders, excessive exercise, cold exposure, lactation, some types of obesity, and poorly controlled diabetes mellitus.
Precision of DLW energy expenditure measurements: contribution of natural abundance variations
Authors: Ritz P. , Cole T. J. , Couet C. , Coward W. A.
Published: December 2017

Accuracy and precision of the the doubly labeled water (DLW) measurements of energy expenditure are commonly estimated with models that do not account for 2H and 18O natural abundance variation. A new and simple treatment that completes the ratio-product model is derived in the present study. It uses both linear regression of multipoint data with time and information on within-subject 2H and 18O natural abundance variation. Use of this treatment is demonstrated in a group of seven subjects in whom 2H and 18O natural abundance variation was assessed by collecting predose samples for 6-8 days before dosing. In this set of 16 measurements, the precision (coefficient of variation) of individual DLW estimates of CO2 production was 4.90 +/- 2.14%, of which 3.23 +/- 1.20% arose from natural abundance variation.
Plasma methionine and cysteine kinetics in response to an intravenous glutathione infusion in adult humans
Authors: Fukagawa N. K. , Ajami A. M. , Young V. R.
Published: December 2017

Glutathione (GSH), a tripeptide (gamma-glutamyl-cysteinyl-glycine), is thought to be both a storage and a transport form of cysteine (Cys). In a previous study (T. Hiramatsu, N.K. Fukagawa, J.S. Marchini, J. Cortiella, Y.-M. Yu, T.E. Chapman, and V.R. Young. Am. J. Clin. Nutr. 60: 525-533, 1994), the direct tracer-derived estimate of Cys flux was considerably higher than that predicted from estimates of protein turnover. To further examine the components of plasma Cys flux, seven normal-weight healthy adult men and women (26 +/- 2 yr) received stable isotope tracer infusions of L-[methyl-2H3;1-13C]methionine, L-[3,3-2H2]cysteine, and L-[methyl-2H3]leucine for 460 min. After a 3-h baseline period, GSH was administered at approximately 32 mumol.kg-1.h-1 until the end of the study. Expired breath and blood samples were obtained at timed intervals and analyzed for isotope enrichment using mass spectrometry. Leucine, alpha-ketoisocaproate, and methionine (carboxyl carbon, methyl moiety, remethylation, and transsulfuration) turnover were reduced during GSH administration (P < 0.01). In the final hour of GSH administration, Cys flux increased by 61% from 55.1 +/- 1.7 to 88.7 +/- 5.2 mumol.kg-1.h-1 (P < 0.01), which was essentially equivalent to the rate of exogenous GSH infusion. These data suggest that GSH breakdown accounts for approximately 50% of tracer-derived Cys flux basally and for all of the increase in measured Cys turnover during exogenous GSH infusion.
Effects of prolonged glucose infusion on insulin secretion, clearance, and action in normal subjects
Authors: Boden G. , Ruiz J. , Kim C. J. , Chen X.
Published: December 2017

It was the aim of this study to determine whether prolonged hyperglycemia can produce "glucose toxicity" in normal human subjects. To this end, plasma glucose was clamped at approximately 5, approximately 8.8, and approximately 12.6 mM for 68 h in healthy volunteers. Rates of insulin secretion (by deconvolution of plasma C-peptide) and rates of insulin clearance [area under curve (AUC) 24 h insulin secretion/AUC 24 h insulin] were determined. Pre- and posthyperglycemia glucose turnover was measured (with [6,6-2H2]glucose) during euglycemic-hyperinsulinemic clamping to assess peripheral (muscle) and hepatic insulin action. Hyperglycemia (approximately 12.6 mM) for 68 h was associated with significant reductions in rates of insulin secretion (-35%, P < 0.05), insulin clearance (-57%, P < 0.05), glucose infusion rates needed to maintain hyperglycemia (-36%, P < 0.05), and insulin-stimulated glucose uptake (-55%, P < 0.01). No significant changes were seen during approximately 8.8 mM hyperglycemia or during euglycemia. These data showed that 12.6 mM hyperglycemia, but not 8.8 mM hyperglycemia or euglycemia, was associated with reduced insulin secretion, insulin clearance, and peripheral (muscle) insulin action. We concluded that 1) in normal subjects, desensitization to glucose involving beta-cells and muscle developed at plasma glucose concentrations between approximately 9 and approximately 12 mM, and 2) these effects were partially compensated for by a decrease in insulin clearance.
Progressive effect of endurance training on metabolic adaptations in working skeletal muscle
Authors: Phillips S. M. , Green H. J. , Tarnopolsky M. A. , Heigenhauser G. J. , Grant S. M.
Published: December 2017

We investigated the hypothesis that a program of prolonged endurance training, previously shown to decrease metabolic perturbations to acute exercise within 5 days of training, would result in greater metabolic adaptations after a longer training duration. Seven healthy male volunteers [O2 consumption = 3.52 +/- 0.20 (SE) l/min] engaged in a training program consisting of 2 h of cycle exercise at 59% of pretraining peak O2 consumption (VO2peak) 5-6 times/wk. Responses to a 90-min submaximal exercise challenge were assessed pretraining (PRE) and after 5 and 31 days of training. On the basis of biopsies obtained from the vastus lateralis muscle, it was found that, after 5 days of training, muscle lactate concentration, phosphocreatine (PCr) hydrolysis, and glycogen depletion were reduced vs. PRE (all P < 0.01). Further training (26 days) showed that, at 31 days, the reduction in PCr and the accumulation of muscle lactate was even less than at 5 days (P < 0.01). Muscle oxidative potential, estimated from the maximal activity of succinate dehydrogenase, was increased only after 31 days of training (+41%; P < 0.01). In addition, VO2peak was only increased (10%) by 31 days (P < 0.05). The results show that a period of short-term training results in many characteristic training adaptations but that these adaptations occurred before increases in mitochondrial potential. However, a further period of training resulted in further adaptations in muscle metabolism and muscle phosphorylation potential, which were linked to the increase in muscle mitochondrial capacity.
Augmented insulin action on rates of protein synthesis after resistance exercise in rats
Authors: Fluckey J. D. , Vary T. C. , Jefferson L. S. , Farrell P. A.
Published: December 2017

This study investigated whether insulin has a modulatory effect on protein synthesis rates in skeletal muscle after four sessions of resistance exercise. Male rats engaged in resistance exercise (Acute) that required full extension of the hindlimbs with weights over the scapula or performed the standing movement with no additional weight (Nonex). Two separate studies were conducted. Rates of protein synthesis for study 1 (Acute, n = 6; Nonex, n = 6) were assessed 16 h postexercise by incorporation of [3H]phenylalanine ([3H]F) into muscle protein by use of an in vivo flooding dose protocol. Rates of protein synthesis in soleus of Acute (100 +/- 9 nmol F.g-1.h-1) were significantly higher than in Nonex (72 +/- 9 nmol F.g-1.h-1, P < 0.05). Rates of protein synthesis were significantly higher in gastrocnemius of Acute vs. Nonex (48 +/- 7 vs. 25 +/- 2 nmol F.g-1.h-1) but not in extensor digitorum longus (EDL). Assessment of protein synthesis rates for study 2 was conducted 16 h after resistance exercise with use of [3H]F incorporation into muscle protein during in situ bilateral hindlimb perfusion, with each leg perfused simultaneously but separately. Perfusion medium for one leg, but not the other, contained insulin (6.25 ng/ml). Soleus and gastrocnemius of Acute had higher protein synthesis rates than Nonex only in the leg that received insulin. For gastrocnemius, rates of protein synthesis in Acute without insulin were significantly lower than in Nonex with or without insulin. Insulin had no effect on protein synthesis rates for any muscle in Nonex rats. Neither exercise nor insulin affected protein synthesis rates in EDL. We conclude that insulin is a necessary component in elevated protein synthesis rates after resistance exercise in muscles composed of primarily slow-or fast-twitch fibers, and that a physiological perturbation (resistance exercise in this study) is required to observe such modulation, because rates of protein synthesis in Nonex muscles were not influenced by insulin.
Diverse signaling pathways in the cellular actions of insulin
Authors: Saltiel A. R.
Published: December 2017

Insulin is one of the most important regulators of glucose and lipid homeostasis. Many of its cellular actions are mediated by changes in protein phosphorylation. The consequences of these phosphorylation events extend from a series of different short-term metabolic actions to longer-term effects of the hormone on cellular growth and differentiation. Although the insulin receptor itself is a tyrosine kinase that is activated upon hormone binding, the ensuing changes in phosphorylation occur predominantly on serine and threonine residues. Moreover, insulin can simultaneously stimulate the phosphorylation of some proteins and the dephosphorylation of others. These paradoxical effects of insulin suggest that separate signal transduction pathways may emanate from the receptor itself to produce the pleiotropic actions of the hormone.
Metabolic responses of canine gracilis muscle during contraction with partial ischemia
Authors: Timmons J. A. , Poucher S. M. , Constantin-Teodosiu D. , Worrall V. , MacDonald I. A. , Greenhaff P. L.
Published: December 2017

The metabolic effects of partial ischemia on canine skeletal muscle were examined during 20 min of isometric contraction. A reduction in blood flow of approximately 75% resulted in an approximate 40% reduction in contractile function. Muscle lactate accumulation and phosphocreatine (PCr) hydrolysis were greater during ischemia, indicating a greater reliance on anaerobic ATP regeneration. Pyruvate dehydrogenase transformation to its active form (PDCa) during contraction was not affected by ischemia, such that PDCa did not appear to be a determinant of skeletal muscle fatigue. Acetylcarnitine concentration was greater during ischemic contraction and inversely correlated with PCr concentration (r = -0.79, P<0.01). Furthermore, acetylcarnitine accumulation and PCr degradation correlated with the degree of skeletal muscle fatigue (r = 0.56, P<0.05 and r = 0.70, P<0.01, respectively). Thus the greater the acetyl group oxidation, the lesser the contribution from anaerobic ATP provision and, subsequently, the smaller the degree of muscle fatigue observed. The metabolic characteristics of this model of ischemic muscle contraction are indistinguishable from the normal metabolic responses observed with increasing contractile intensity.
Effect of chronic hypoxia on myometrial responsiveness in the pregnant rat
Authors: Rhee J. W. , Longo L. D. , Pearce W. J. , Bae N. H. , Valenzuela G. J. , Ducsay C. A.
Published: December 2017

Mechanisms involving the timing of normal parturition are not well understood in most animal species. To gain a greater understanding of the mechanisms, we employed hypoxia to perturb the normal system of parturition. The present study was designed to investigate the effects of chronic hypoxia on myometrial contractility in the near-term pregnant rat. Rats were exposed to room air (control) or to continuous hypoxia (10.5% O2) either from experimental days 19 through 21 (2-day exposure) or from experimental days 15 through 21 (6-day exposure). On day 21, blood was collected for hormone assays, and the uterine horns were collected from each dam. One horn was snap-frozen in liquid nitrogen for oxytocin (OT) receptor analysis, and the other was used for in vitro assessment of myometrial contractile responses to cumulative doses of OT or arginine vasopressin (AVP). Hypoxic exposure resulted in approximately 60% reduction of the maximal myometrial contractile response to OT and a significant reduction in OT binding sites from 256.9 +/- 34.9 to 84.9 +/- 21.3 fmol/mg protein (P<0.01). In contrast, the contractile response to AVP was unaffected after exposure to chronic hypoxia (P> 0.05). Additionally, we observed no difference in the plasma concentrations of estrogen, progesterone, and corticosterone. We conclude that chronic hypoxia decreased the effectiveness of OT-specific contractile mechanisms, at least partially through a decrease in OT binding sites.
Perinatal energy stores and excessive fat deposition in genetically obese (fa/fa) rats
Authors: Meierfrankenfeld B. , Abelenda M. , Jauker H. , Klingenspor M. , Kershaw E. E. , Chua S. C. , Leibel R. L. , Schmidt I.
Published: December 2017

To find out whether perinatal differences in energy stores are essential for the phenotypic manifestation of the fa/fa genotype in 16-day-old rats, we investigated Zucker rats (13M) x Brown Norway (BN) hybrids. +/fa and fa/fa hybrids were identified by molecular polymorphisms approximately 1 cM from the fa locus. The fat content of all pups increased rapidly after birth, and differences between +/fa and fa/fa hybrid pups were significant in 7- and 16-day-old rats but not at 0, 1, and 4 days of age. For 16-day-old 13MBN hybrids as well as 13M Zucker rats, plots of carcass fat vs. body mass were closely fitted by parallel regression lines, with carcass fat similarily higher in fa/fa than +/fa pups of both strains. Fetal and neonatal plasma insulin concentration and hepatic glycogen in the 13MBN hybrid pups did not differ between +/fa and fa/fa litter-mates, nor did the hepatic and adipose tissue triglycerides in 24-h-old 13MBN hybrid pups. The manifest differences between fatty and lean 16-day-old pups thus do not depend on differences in perinatal energy stores.
An isotopic method for measurement of muscle protein fractional breakdown rate in vivo
Authors: Zhang X. J. , Chinkes D. L. , Sakurai Y. , Wolfe R. R.
Published: December 2017

We have developed a novel method to measure the fractional breakdown rate (FBR) of muscle protein. This method involves infusing isotope tracer to reach an isotopic equilibrium and then observing its decay in the arterial blood and muscle intracellular pool. The calculation of FBR is based on the rate at which tracee released from breakdown dilutes the intracellular enrichment using a modified precursor-product equation. To test this method, L-[1,2-13C2]leucine and L-[ring-13C6]phenylalanine were infused into six dogs for measurement of FBR and fractional synthesis rate (FSR), respectively. Leucine and phenylalanine kinetics in the hindlimb were measured simultaneously using the arteriovenous (A-V) balance method. The measured FBR (0.17 +/- 0.02%/h) and FSR (0.10 +/- 0.01%/h) were in agreement with the results from the A-V balance method. In conclusion, our new method provides a feasible approach for measurement of muscle protein FBR. This method can be combined with the tracer incorporation method to measure both breakdown and synthesis in the same infusion study.
Reduction of dietary obesity in aP2-Ucp transgenic mice: mechanism and adipose tissue morphology
Authors: Kopecky J. , Rossmeisl M. , Hodny Z. , Syrovy I. , Horakova M. , Kolarova P.
Published: December 2017

C57BL6/J mice with the expression of the mitochondrial uncoupling protein (UCP) gene from the fat-specific aP2 gene promoter were used to study the mechanism by which the aP2-Ucp transgene affects adiposity and reduces high-fat diet induced obesity. In the transgenic mice, UCP synthesized in white fat was inserted into mitochondria, and oxygen uptake by epididymal fat fragments indicated UCP-induced thermogenesis. The respirometry data, UCP content, cytochrome oxidase activity, and tissue morphology suggested functional involution of brown fat. Despite 25- to 50-fold lower mitochondrial cytochrome oxidase activity in white than in brown fat cells, total oxidative capacity in white and brown adipose tissue is comparable. Appearance of novel small cells in the gonadal fat of the transgenic mice was associated with a higher DNA content than that of the nontransgenic mice. The results prove a potential of transgenically altered mitochondria in white fat to modulate adiposity and energy expenditure and suggest the existence of a yet unidentified site-specific link between energy metabolism in adipocytes and cellularity.
Insulin resistance of skeletal muscle produced by hepatic parasympathetic interruption
Authors: Xie H. , Lautt W. W.
Published: December 2017

The objective was to determine the site of insulin resistance produced by intraportal atropine or surgical hepatic denervation. A modified euglycemic clamp was used in fasted cats to test the acute effect of insulin (100 mU/kg) on arteriovenous glucose gradients across the hindlimbs (mainly reflecting skeletal muscle), the guts (all organs draining into the portal vein), and the liver. Responses to insulin were determined before and after hepatic denervation and after 3 mg/kg intraportal atropine. The interventions were done in random order. Responses after either intervention were similar and were not potentiated by the combined treatment. Regional insulin resistance was assessed by comparing the change in glucose gradients in response to insulin before and after treatments. Hepatic and gut responses to insulin were unaltered, but hindlimb responses were significantly impaired after denervation or atropine. We speculate that the hepatic parasympathetic nerves regulate release of a liver-generated factor that selectively controls insulin effectiveness in skeletal muscle. This mechanism may be involved with insulin resistance in non-insulin-dependent diabetes and chronic liver disease.
Noninvasive probing of citric acid cycle intermediates in primate liver with phenylacetylglutamine
Authors: Yang D. , Previs S. F. , Fernandez C. A. , Dugelay S. , Soloviev M. V. , Hazey J. W. , Agarwal K. C. , Levine W. C. , David F. , Rinaldo P. , Beylot M. , Brunengraber H.
Published: December 2017

In human and primate liver, phenylacetate and glutamine form phenylacetylglutamine, which is excreted in urine. Probing noninvasively the labeling pattern of liver citric acid cycle intermediates with phenylacetylglutamine assumes that the labeling pattern of its glutamine moiety reflects that of liver alpha-ketoglutarate. To validate this probe, we infused monkeys with [U-13C3]lactate, [3-13C]lactate, [1, 2-13C2]acetate, [2-13C]acetate, [U-13C3]glycerol, or 2-[3-13C]ketoisocaproate and compared the labeling patterns of urinary phenylacetyl-glutamine with those of glutamate and glutamine in liver, plasma, muscle, and kidney and liver alpha-ketoglutarate. Only with [U-13C3]lactate or [3-13C]lactate does the labeling pattern of phenylacetylglutamine reflect patterns of liver alpha-ketoglutarate and glutamate. With [13C]acetate, muscle and kidney glutamate are more labeled than liver metabolites. This confirms that with [13C]acetate, the labeling pattern of liver metabolites is influenced by 13CO2 and [13C]glutamine made in peripheral tissues. Our data validate the use of phenylacetylglutamine labeled from [3-13C]lactate or [3-13C]pyruvate to probe noninvasively the pyruvate carboxylase-to-pyruvate dehydrogenase flux ratio in human subjects.
Nitric oxide is an early mediator of the increase in bone formation by mechanical stimulation
Authors: Fox S. W. , Chambers T. J. , Chow J. W.
Published: December 2017

We tested the ability of NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase (NOS), to suppress the osteogenic response in a recently developed model of mechanically induced osteogenesis. L-NMMA was given either as a single intraperitoneal dose, 15 min before the episode of mechanical stimulation, or as four doses every 6 h, commencing 2 h after loading. Administration of L-NMMA before loading completely prevented the increase in cancellous bone formation by mechanical stimulation. This suppression was largely lost when L-NMMA was administered after loading. Thus the response is likely to be due to activation of a preexistent constitutive NOS in bone cells during or very soon after mechanical stimulation. Suppression of the osteogenic response by L-NMMA was prevented by coadministration of L-arginine but not by the inactive isomer, D-arginine. These changes in cancellous bone were mirrored by similar changes on the corticoendosteal and periosteal bone surfaces. These data suggest that early release of NO is a key signal in the transduction of mechanical stimuli into subsequent bone formation.
Fasting and decreased B cell sensitivity: important role for fatty acid-induced inhibition of PDH activity
Authors: Zhou Y. P. , Priestman D. A. , Randle P. J. , Grill V. E.
Published: December 2017

Fasting inhibits glucose-induced insulin secretion. We investigated the role of a glucose fatty acid cycle for such inhibition and its molecular basis in pancreatic islets from 48-h fasted rats. The fasting-impaired insulin response to 27 mM glucose was restored by 41% with a carnitine palmitoyltransferase I inhibitor, etomoxir. Etomoxir also restored (by 50%) impaired glucose oxidation in islets from fasted rats and increased the ratio of oxidation to glycolytic flux from 33 to 43%. Fasting decreased total pyruvate dehydrogenase (PDH) activity (active, unphosphorylated plus inactive, phosphorylated form) by 29%, as well as the percentage of active form (54 +/- 5 vs. 79 +/- 2% in fed rats, P < 0.001). Fasting increased islet PDH kinase activity as follows: PDH-bound activity by 36% and free (not PDH bound) PDH kinase by 70%. Fasting failed to affect PDH kinase content when assayed by an enzyme-linked immunoabsorbent assay with antibodies raised against 45 kDa PDH kinase alpha-chain. We conclude that fasting impairs B cell function to a major extent through the operation of a glucose fatty acid cycle and that decreased PDH activity resulting from increased specific activity of PDH kinase constitutes an important molecular mechanism.
Response of phosphoenolpyruvate cycle activity to fasting and to hyperinsulinemia in human subjects
Authors: Wolfe R. R. , Chinkes D. , Baba H. , Rosenblatt J. , Zhang X. J.
Published: December 2017

We have used a new isotopic tracer technique to investigate the physiological role of the phosphoenolpyruvate (PEP) cycle in metabolic adaptation to fasting and to hyperinsulinemia. The forward direction of the PEP cycle is the conversion of oxaloacetate (OAA) to PEP, and the net flux of the cycle is the rate at which PEP from OAA goes on to form glucose or glycogen, as opposed to being recycled to pyruvate and then OAA. Normal volunteers (n = 6) were studied after an overnight fast and then again after 3 days of fasting, and five additional subjects were studied during a hyperinsulinemic clamp (insulin concentration = 568 +/- 25 microU/ml, glucose infusion = 14.2 +/- 0.55 mg.kg-1.min-1). After an overnight fast, 35.4 +/- 6.7% of PEP from OAA was recycled to pyruvate-lactate. Short-term fasting caused a significant increase in the conversion of OAA to PEP and also a drop in the percentage of PEP from OAA that went to pyruvate-lactate to 15.2 +/- 4.0%. The principal response to hyperinsulinemia was a decrease in the recycling of OAA to lactate, because there was no significant change in the conversion of OAA to PEP. We conclude that changes in both directions of the PEP cycle are important in regulating gluconeogenic-glyconeogenic flux.
Appetite regulation by carbohydrate: role of blood glucose and gastrointestinal hormones
Authors: Lavin J. H. , Wittert G. , Sun W. M. , Horowitz M. , Morley J. E. , Read N. W.
Published: December 2017

To investigate the mechanisms by which intestinal carbohydrate affects eating behavior, seven fasted, healthy male volunteers received intraduodenal infusions of glucose or saline over a 90-min period while blood glucose levels were matched by use of intravenous glucose and saline infusions. A second study examined the effect of intraduodenal glucose on eating behavior when the gastrointestinal hormone response was inhibited by intravenous octreotide. Intravenous glucose infusion did not affect hunger or satiety. In contrast, intraduodenal infusion of glucose suppressed hunger, increased fullness and satiety ratings, reduced energy intake, and resulted in higher plasma insulin responses compared with the intravenous glucose infusion. Octreotide abolished the plasma insulin response to intraduodenal glucose and reversed the changes in ratings and eating behavior. This study has shown that the effects of intestinal glucose on appetite are not mediated via an increase in blood glucose but are likely to reflect small intestinal stimulation of release of either insulin or intestinal incretins.
Increased PTHRP production by a tyrosine kinase oncogene, Tpr-Met: role of the Ras signaling pathway
Authors: Aklilu F. , Park M. , Goltzman D. , Rabbani S. A.
Published: December 2017

We have used the Tpr-Met oncogene as a model to examine signaling pathways of growth factors and tyrosine kinase oncogenes that can increase parathyroid hormone-related peptide (PTHRP) production. PTHRP production in Tpr-Met transfected cells, when assessed by Northern blot analysis and radioimmunoassay, was increased four- to eightfold. Treatment of these cells with the transcriptional inhibitor actinomycin D and nuclear run-off assays showed that the major cause of increased PTHRP mRNA was enhanced gene transcription. To analyze the intracellular signaling molecules involved in PTHRP production, stable cell lines expressing a Tyr489 Phe mutant of the Tpr-Met oncoprotein were examined. The mutant fails to activate phosphatidylinositol (PI)-3 kinase or associate with the Grb-2 adaptor protein and caused a significant reduction in PTHRP production. Treatment of wild-type Tpr-Met transfected cells with wortmannin, a PI-3 kinase inhibitor, had no effect on PTHRP production; however, treatment of these cells with lovastatin, an inhibitor of p21ran isoprenylation, significantly reduced PTHRP expression. These results show that PTHRP is a downsteam target of the Tpr-Met oncogene and indicate that the PTHRP stimulating activity is mediated via the Ras signaling pathway.
Interactions between 2H and 18O natural abundance variations and DLW measurements of energy expenditure
Authors: Ritz P. , Cole T. J. , Davies P. S. , Goldberg G. R. , Coward W. A.
Published: December 2017

Appropriate corrections for 2H and 18O natural abundance are necessary in energy expenditure measurements with the doubly labeled water (DLW) method. The contribution of natural abundance variations to errors in the method is generally ignored if an appropriate dose level is given. Calculation of the appropriate dose level assumes that 2H and 18O natural abundance values are covariant and have a fixed slope. This study has investigated the between- and within-subject natural abundance variations, the latter over periods of time similar to those used in DLW experiment. Although 2H and 18O natural abundance values are covariant between subjects, the slope of their relationship is different from that of the Meteoric Water Line. Within subjects there is no such demonstrable covariance. It is concluded that: 1) the determinants of 2H and 18O natural abundance are different within and between subjects; 2) the concept of an optimal ratio of doses is not valid, and a safer strategy is probably to use a ratio > 10; 3) natural abundance variations may contribute significantly to the magnitude of error in the DLW measurements of energy expenditure.
Levels of plasma C19 steroids and 5 alpha-reduced C19 steroid glucuronides in primates, rodents, and domestic animals
Authors: Guillemette C. , Hum D. W. , Belanger A.
Published: December 2017

In this study, a comparison of circulating levels of androsterone glucuronide and androstane-3 alpha, 17 beta-diol glucuronide in the male and female of several mammalian species was performed. Glucuronidated steroids were not detected in the circulation of the dog, bovine, swine, and rodent. High levels of circulating glucuronidated steroids were measured in the cynomolgus monkey and found to be 10-fold higher than in humans. The determination of tissue levels of unconjugated and conjugated C19 steroids was then performed in intact and castrated rats treated with androgens. Steroid glucuronides were not detected in the plasma, skin, prostate, or liver of either intact or treated rats, although the levels of unconjugated steroids in the plasma and tissues were increased after steroid treatments. Significant levels were detected in the bile, thus suggesting hepatic formation of steroid glucuronides in the rat. It is suggested that the monkey represents the best animal model to date to study the contribution of diphosphoglucuronosyltransferases present in steroid target peripheral tissues to circulating levels of steroid glucuronides.
Comparison of mass isotopomer dilution methods used to compute VLDL production in vivo
Authors: Chinkes D. L. , Aarsland A. , Rosenblatt J. , Wolfe R. R.
Published: December 2017

The recent development of mass isotopomer distribution methods represents an important new tool for quantifying synthetic rates. These methods allow precursor enrichment to be determined indirectly from the enrichment of the product, thus sidestepping the often difficult problem of measuring the precursor enrichment. Two different methods have been described to compute synthetic rates by this general approach in the laboratories of M. K. Hellerstein and J. K. Kelleher, and variations of these basic approaches have also been presented by W. N. Lee and by ourselves. A comparison between the different methods has never been reported. In this paper, we take a specific application, calculation of the fractional rate of incorporation of acetyl-CoA into very low density lipoprotein-bound palmitate, and compare the results obtained from all of the mass isotopomer methods using the same data set obtained in vivo in human subjects. We found that it is critical that the measured background isotopomer distribution of palmitate is used rather than the theoretical background isotopomer distribution. We also found that the different methods give comparable precursor enrichments and comparable fractional synthesis rates, provided that the enrichments in Kelleher's method are properly weighted. Thus the choice of method to use is a matter of personal preference.
Pig pancreatic acinar cells possess predominantly the CCK-B receptor subtype
Authors: Morisset J. , Levenez F. , Corring T. , Benrezzak O. , Pelletier G. , Calvo E.
Published: December 2017

Studies performed on pig indicated that its pancreas was insensitive to the gastrointestinal hormone cholecystokinin (CCK) and suggested that its secretions were rather under the control of the neurotransmitter acetylcholine. This study was performed to determine reasons for this insensitivity by comparing secretory responses to different secretagogues and establishing the dominant CCK receptor type. Pancreatic acini prepared from weaned piglets were evaluated for their sensitivity to carbamylcholine (Cch), caerulein, JMV-180, and secretin. RNA were extracted for CCK-A and CCK-B receptor expression using specific cRNA probes. Results indicate that pig pancreatic acini are sensitive to Cch and relatively insensitive to caerulein with no response to JMV-180, a CCKA agonist, or secretin; MK-329, a CCK-A receptor antagonist, significantly inhibited caerulein-induced enzyme secretion from 10(-8) M. The pig pancreas expresses few CCK-A mRNA receptors but a majority of CCK-B. These data demonstrate that the pig pancreas expresses a majority of CCK-B receptors. In conclusion, the pig pancreas possesses a large majority of CCK-B receptors responsible for their low sensitivity to CCK.
In vivo effects of dexamethasone and sucrose on glucose transport (GLUT-4) protein tissue distribution
Authors: Coderre L. , Vallega G. A. , Pilch P. F. , Chipkin S. R.
Published: December 2017

Tissue-specific changes in GLUT-4 were compared in the following three different rat models by inducing varying degrees of hyperinsulinemia with or without hyperglycemia and hypertriglyceridemia: 1) sucrose feeding (Suc), 2) subcutaneous dexamethasone administration (Dex), and 3) a combination of both treatments (Dex/Suc). Suc raised circulatory insulin and triglyceride levels without affecting plasma glucose, whereas both Dex and Dex/Suc induced significant hyperinsulinemia, hyperglycemia, and hypertriglyceridemia. In adipocytes and skeletal muscle, Suc feeding was not associated with any change in total cellular GLUT-4 levels. However, Suc induced a sevenfold increase in fat cell plasma membrane GLUT-4 levels in the basal state and inhibited GLUT-4 translocation in response to insulin. Administration of Dex or Dex/Suc diminished GLUT-4 expression in fat cells, increased it in skeletal muscle, but did not induce any change in heart. Similar to Suc feeding, Dex and Dex/Suc also increased the amount of GLUT-4 detected at the plasma membrane of adipocytes in the basal state and inhibited GLUT-4 translocation in response to insulin. These results emphasize the specific regulation of GLUT-4 in insulin-sensitive tissues.
Vagal hepatopancreatic reflex effect evoked by intraportal appearance of tGLP-1
Authors: Nakabayashi H. , Nishizawa M. , Nakagawa A. , Takeda R. , Niijima A.
Published: December 2017

Among proglucagon-derived peptides, the truncated form of glucagon-like peptide-1, GLP-1(7-36)amide (tGLP-1), is known as the most likely physiological humoral incretin. To examine whether there exists any relationship between tGLP-1 levels in the portal vein and activities of the hepatic and pancreatic vagal system, changes of the impulse discharge rate in the hepatic afferent vagus and the pancreatic efferent vagus upon intraportal tGLP-1 injection were measured in situ in rats anesthetized with urethan and chloralose. First, a 1-min bolus tGLP-1 injection at a periphysiological dose of 0.2 pmol or a pharmacological dose of 4.0 pmol, but not the vehicle injection, significantly facilitated the hepatic vagal afferents for > 90 min, showing weaker facilitation at the 0.05 pmol dose. Notably, the injection of noninsulinotropic full-length GLP-1 failed to facilitate the afferents at the 4.0 or 40.0 pmol dose. Second, the intraportal tGLP-1 injections at the 0.05 and 0.2 pmol dose facilitated marginally and significantly the pancreatic vagal efferents in normal rats, respectively, but had no effect on the hepatic vagotomized rats, even at the 40.0 pmol dose. The present results indicate that an intraportal appearance of tGLP-1 is specifically recognized by the hepatic vagal nerve, and this recognition further augments the pancreatic vagal efferent activity in a reflex way, suggesting another nature of tGLP-1 as neuroincretin in the enteroinsular axis.
Interaction of exercise training and clenbuterol on GLUT-4 protein in muscle of obese Zucker rats
Authors: Kuo C. H. , Ding Z. , Ivy J. L.
Published: December 2017

Chronic administration of clenbuterol, a beta 2-adrenergic agonist, attenuates the exercise training-induced improvement in muscle insulin resistance of the obese Zucker rat. The present study was conducted to determine whether clenbuterol also attenuates the increase in muscle GLUT-4 protein that occurs with exercise training and whether the action of clenbuterol is related to its ability to downregulate the beta-adrenergic receptors. Female obese Zucker rats were randomly assigned to one of the following four groups: control (CON, n = 7), clenbuterol (CL, n = 8), exercise training (TR, n = 8), and clenbuterol with exercise training (CL+TR, n = 8). Rats assigned to the training groups were run on a rodent motor-driven treadmill for 6-7 wk. Rats receiving clenbuterol were intubated with 0.8 mg/kg body weight 30 min before running each day. Red quadriceps (RQ) and white quadriceps (WQ) GLUT-4 protein concentrations of TR rats were significantly greater than those of CON and CL+TR rats. The RQ GLUT-4 protein concentration of the CL+TR rats was significantly greater than that of CON rats, but this difference did not occur in the WQ. GLUT-4 protein concentrations were not different between the CON and CL rats. The patterns of RQ and WQ GLUT-4 mRNA were similar to those of their respective GLUT-4 proteins. Rats receiving daily injections of propranolol (30 mg/kg body wt), a beta-adrenergic receptor antagonist, demonstrated no increase in GLUT-4 protein in RQ or WQ after 6 wk of exercise training. These results indicate that 1) clenbuterol can attenuate the increase in muscle GLUT-4 protein associated with exercise training and 2) this effect is likely mediated by a downregulation of the beta-adrenergic receptors.
Leptin is related to body fat content in male distance runners
Authors: Hickey M. S. , Considine R. V. , Israel R. G. , Mahar T. L. , McCammon M. R. , Tyndall G. L. , Houmard J. A. , Caro J. F.
Published: December 2017

Leptin, the product of the ob gene, has been reported to be related to body fat in humans (Considine et al. N. Engl. J. Med. 334: 292, 1996). However, little is known about the physiology of this putative satiety signal in humans. The purpose of the present study was to determine whether leptin is related to body fat content in relatively lean endurance-trained adults. In addition, the effect of acute exercise on circulating leptin concentration was studied. Thirteen male runners, whose mean age, height, weight, %fat, and maximal oxygen consumption (VO2max) were 32.2 +/- 2.5 yr, 176.2 +/- 1.6 cm, 71.9 +/- 6.9 kg, 9.7 +/- 0.9%, and 62.9 +/- 2.2 ml.kg-1.min-1, respectively, were studied. Blood samples were obtained after an overnight fast and again immediately after the completion of a 20-mile run at 70% VO2max under controlled environmental conditions. Serum leptin was closely related to fat mass (r = 0.92) in the runners. Acute exercise had no detectable effect on serum leptin levels (PRE = 2.19 +/- 0.32 ng/ml, POST = 2.14 +/- 0.36 ng/ml). These data indicate that, even at a biological extreme of body fat, circulating leptin concentration is closely related to fat content. Furthermore, the data suggest that, in trained individuals with low leptin concentrations, acute exhaustive exercise has no immediate effect on circulating leptin concentration.
Reconstitution and characterization of two forms of cyclic nucleotide-gated channels from skeletal muscle
Authors: Santy L. C. , Guidotti G.
Published: December 2017

A cyclic nucleotide-gated channel present in skeletal muscle plasma membrane has previously been identified as being responsible for insulin-activated sodium entry into muscle cells (J. E. M. McGeoch and G. Guidotti. J. Biol. Chem. 267:832-841, 1992). We have isolated this channel activity to further study and characterize it. The channel was solubilized from rabbit skeletal muscle sarcolemma and functionally reconstituted into phospholipid vesicles, as assayed by patch-clamp analysis of the reconstituted proteins. Channel activity was isolated by 8-bromo-guanosine 3',5'-cyclic monophosphate affinity chromatography, producing two distinct peaks of cyclic nucleotide-gated channel activity. These two types of channel activity differ in guanosine 3',5'-cyclic monophosphate affinity and in the ability to be opened by adenosine 3',5'-cyclic monophosphate. The cyclic nucleotide-gated channel from rod outer segments also forms two peaks of activity when purified in this manner. The presence of two forms of channel activity could have implications for the mechanism of insulin-activated sodium entry.
Glycerol production and utilization in humans: sites and quantitation
Authors: Landau B. R. , Wahren J. , Previs S. F. , Ekberg K. , Chandramouli V. , Brunengraber H.
Published: December 2017

Liver is assumed to be the major site of glycerol uptake and fatty acid reesterification. [U-13C]glycerol was infused into ten 60 h-fasted healthy subjects. Measured were 1) blood glycerol concentrations and 13C enrichments in brachial and pulmonary arteries and in hepatic, renal, superficial, and deep forearm veins; 2) glycerol appearance rates in systemic circulation; and 3) splanchnic bed and kidney glycerol uptakes with use of balance and tracer methodology. Glycerol concentrations were one-fifth in hepatic, one-half in renal, 40% more in superficial, and the same in deep vein and pulmonary artery as in brachial artery blood. Glycerol enrichments were one-fifth in hepatic, two-thirds to three-quarters in renal and superficial veins, and the same in pulmonary as in brachial artery blood. Splanchnic glycerol uptake was 29% and kidney glycerol uptake was 17% of glycerol's rate of appearance, 5.11 mumol.min-1.kg-1. Splanchnic fatty acid uptake was 25% of calculated fatty acid release. Glycerol contributed 15% to glucose production. Most of the [13C]glycerol uptake by splanchnic bed and kidneys was incorporated into glucose. Thus, in 60 h-fasted individuals, most glycerol uptake does not occur in liver, and the extent of fatty acid reesterification in liver is in doubt.
Glucose-6-phosphatase flux and the hepatic glucose balance model
Authors: Rognstad R.
Published: December 2017

Mice were studied with the euglycemic hyperinsulinemic and the hyperglycemic clamp techniques after a 6-h fast: 1) euglycemic (6.7 +/- 0.2 mM) hyperinsulinemia (approximately 800 microU/ml); 2) hyperglycemic (15.3 +/- 0.4 mM) hyperinsulinemia (approximately 800 microU/ml). All mice received an infusion of [3-3H]glucose and [U-14C]lactate. Basal hepatic glucose production (HGP) averaged approximately 170 mumol.kg-1.min-1 in both groups. During euglycemic and hyperglycemic hyperinsulinemia, HGP decreased by 53% (to 76.7 +/- 11.1 mumol.kg-1.min-1; P < 0.01) and 74% (to 43.3 +/- 7.2 mumol.kg-1.min-1; P < 0.01), respectively. Hyperglycemia increased glucose cycling (by 2.1-fold; P < 0.01) and the contribution of gluconeogenesis to HGP (88 vs. 43%; P < 0.01) while decreasing that of glycogenolysis (12 vs. 57%; P < 0.01). The percentage of neosynthetized hepatic glycogen formed via the direct pathway was markedly increased during hyperglycemia (53 +/- 2% vs. 23 +/- 3%; P < 0.01). These data indicate that the assessment of hepatic glucose fluxes can be accomplished in conscious unrestrained mice and that, in the presence of hyperinsulinemia, hyperglycemia causes 1) a further inhibition of HGP mainly via inhibition of glycogenolysis and increase in hepatic glucose cycling; and 2) about a fivefold stimulation in the direct pathway of hepatic glycogen formation.
Insulin-like growth factor I inhibits degradation and improves retention of protein in hindlimb muscle of lambs
Authors: Oddy V. H. , Owens P. C.
Published: December 2017

We infused recombinant human insulin-like growth factor I (IGF-I) for 4 h at 12.3 micrograms.h-1.kg live weight-1 directly into the left femoral artery and measured the rates of synthesis, degradation, and gain of protein by the treated and contralateral limbs of well-fed (n = 8), feed-restricted (n = 10), and fasted (n = 9) castrated male lambs. Reducing feed intake decreased net protein gain of hindlimb muscle, reduced hindlimb glucose uptake, and lowered arterial plasma concentrations of IGF-I, insulin, glucose, phenylalanine, tyrosine, and isoleucine. The effect of nutrition on IGF-binding proteins (IGFBP) was generally small; IGFBP-2 was more abundant in fasted lambs. Infusion of IGF-I into the left femoral artery increased plasma levels of IGF-I 2- to 4-fold in the left femoral vein and by 1.5- to 3-fold in the artery and right femoral vein. In the treated limb, IGF-I reduced protein degradation, increased protein gain, and increased glucose uptake without altering blood flow or oxygen uptake, regardless of feed intake. Systemically, IGF-I reduced plasma insulin, phenylalanine, tyrosine, isoleucine, and leucine in all nutrition groups. Plasma IGFBP-3 was increased by 4 h of IGF-I treatment in fasted but not in fed lambs. In fed but not fasted lambs, IGF-I increased blood glucose concentration. Effects of IGF-I on protein metabolism in the contralateral limb were affected by nutrition, generally more so in fasted than in unrestricted fed lambs.
Pancreatic islet blood flow in normal and obese-hyperglycemic (ob/ob) mice
Authors: Carlsson P. O. , Andersson A. , Jansson L.
Published: December 2017

The present study evaluated whether a microsphere technique could be used for islet blood flow measurements in anesthetized mice. When this was confirmed, we applied the technique in different strains of mice. Approximately 9 x 10(4) microspheres could be given without interfering with mean arterial blood pressure. Mixing of the microspheres with arterial blood was adequate, and the extraction of microspheres in capillary beds was nearly 100%. In NMRI mice whole pancreatic blood flow was estimated to be 0.54 +/- 0.11 ml.min-1.g pancreatic tissue-1 and islet blood flow to be 18 +/- 4 microliters.min-1.g pancreas-1 (n = 12 animals per experiment), whereas corresponding values in lean C57Bl/6 mice were twice as high. In C57Bl/6 mice glucose (3 g/kg iv) doubled islet blood flow without affecting whole pancreatic blood flow, whereas no effect was seen after an equimolar dose of 3-O-methylglucose. In obese-hyperglycemic C57Bl/6 mice, islet blood flow was more than five times higher than in the lean C57Bl/6 mice when expressed as blood flow per gram pancreas. However, when islet blood perfusion was corrected for islet weight, it was lower in the obese than in the lean mice, suggesting an impaired ability in obese mice to increase blood flow in concert with the increased islet mass. This may contribute to the insufficient insulin secretion and resulting hyperglycemia seen in these animals.