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S Dufour

Publications and source records attributed to S Dufour.

At least 37 records · Page 2Linked to original sources
PubMed2000

13C/31P NMR assessment of mitochondrial energy coupling in skeletal muscle of awake fed and fasted rats. Relationship with uncoupling protein 3 expression.

To examine the relationship between mitochondrial energy coupling in skeletal muscle and change in uncoupling protein 3 (UCP3) expression during the transition from the fed to fasted state, we used a novel noninvasive (31)P/(13)C NMR spectroscopic approach to measure the degree of mitochondrial energy coupling in the hind limb muscles of awake rats before and after a 48-h fast. Compared with fed levels, UCP3 mRNA and protein levels in the gastrocnemius increased 1.7- (p < 0.01) and 2.9-fold (p < 0.001), respectively, following a 48-h fast. Tricarboxylic acid cycle flux measured using (13)C NMR as an index of mitochondrial substrate oxidation was 212 +/- 23 and 173 +/- 25 nmol/g/min (p not significant) in the fed and 48-h fasted groups, respectively. Unidirectional ATP synthesis flux measured using (31)P NMR was 79 +/- 15 and 57 +/- 9 nmol/g/s (p not significant) in the fed and 48-h fasted groups, respectively. Mitochondrial energy coupling as expressed by the ratio of ATP synthesis to tricarboxylic acid cycle flux was not different between the fed and fasted states. To test the hypothesis that UCP3 may be involved in the translocation of long chain free fatty acids (FFA) into the mitochondrial matrix under conditions of elevated FFA availability, [U-(13)C]palmitate/albumin was administered in a separate group of rats with (+) or without (-) etomoxir (an inhibitor of carnitine palmitoyltransferase I). The ratio of glutamate enrichment ((+) etomoxir/(-) etomoxir) in the hind limb muscles was the same between groups, indicating that UCP3 does not appear to function as a translocator for long chain FFA in skeletal muscle following a 48-h fast. In summary, these data demonstrate that despite a 2-3-fold increase in UCP3 mRNA and protein expression in skeletal muscle during the transition from the fed to fasted state, mitochondrial energy coupling does not change. Furthermore, UCP3 does not appear to have a major role in FFA translocation into the mitochondria. The physiological role of UCP3 following a 48-h fast in skeletal muscle remains to be elucidated.

Adenosine Triphosphate↗
PubMed2000

Assessment of mitochondrial energy coupling in vivo by 13C/31P NMR.

The recently cloned uncoupling protein homolog UCP3 is expressed primarily in muscle and therefore may play a significant role in the regulation of energy expenditure and body weight. However, investigation into the regulation of uncoupling protein has been hampered by the inability to assess its activity in vivo. In this report, we demonstrate the use of a noninvasive NMR technique to assess mitochondrial energy uncoupling in skeletal muscle of awake rats by combining (13)C NMR to measure rates of mitochondrial substrate oxidation with (31)P NMR to assess unidirectional ATP synthesis flux. These combined (31)P/(13)C NMR measurements were performed in control, 10-day triiodo-l-thyronine (T(3))-treated (model of increased UCP3 expression), and acute 2,4-dinitrophenol (DNP)-treated (protonophore and mitochondrial uncoupler) rats. UCP3 mRNA and protein levels increased 8.1-fold (+/- 1.1) and 2.8-fold (+/- 0.8), respectively, in the T(3)-treated vs. control rat gastrocnemius muscle. (13)C NMR measurements of tricarboxylic acid cycle flux as an index of mitochondrial substrate oxidation were 61 +/- 21, 148 +/- 25, and 310 +/- 48 nmol/g per min in the control, T(3), and DNP groups, respectively. (31)P NMR saturation transfer measurements of unidirectional ATP synthesis flux were 83 +/- 14, 84 +/- 14, and 73 +/- 7 nmol/g per s in the control, T(3), and DNP groups, respectively. Together, these flux measurements, when normalized to the control group, suggest that acute administration of DNP (mitochondrial uncoupler) and chronic administration of T(3) decrease energy coupling by approximately 80% and approximately 60%, respectively, and that the latter treatment correlates with an increase in UCP3 mRNA and protein expression. This NMR approach could prove useful for exploring the regulation of uncoupling protein activity in vivo and elucidating its role in energy metabolism and obesity.

Adenosine Triphosphate↗
PubMed2000

Distribution of the mRNA encoding the four dopamine D(1) receptor subtypes in the brain of the european eel (Anguilla anguilla): comparative approach to the function of D(1) receptors in vertebrates.

Four subtypes of D(1) dopamine receptors are expressed in the brain of the European eel (Anguilla anguilla), an elopomorph teleost. To correlate this molecular multiplicity with specific localisation and functions, the distribution of the D(1) receptor transcripts was analysed by in situ hybridisation. The four D(1) receptor transcripts exhibit largely overlapping expression territories. In telencephalon, they are found in the olfactory bulb and the dorsal telencephalon (except its lateral part) but are most abundant in the subpallial areas. More caudally, the entopeduncular nucleus, preoptic nuclei, preglomerular nuclear complex, ventral thalamus, periventricular hypothalamus, optic tectum and cerebellum, all contain various amounts of D(1) receptor transcripts. Finally, D(1) receptor mRNAs are present in nuclei associated with the cranial nerves. The two D(1A) receptor subtypes are generally the most abundant and present a different distribution in several areas. The D(1B) mRNA, although present in fewer areas than D(1A) transcripts, is the most abundant in ventrolateral telencephalon and torus semicircularis. The D(1C) receptor transcript, which has not been found in mammals, is restricted to diencephalon and cerebellum. In view of the expression territories of D(1) receptor transcripts and previous data, some areas of the everted telencephalon of teleost may be homologous to regions of the tetrapod brain. In particular, D(1) expression territories of the ventral telencephalon are likely to be equivalent to striatal areas. These observations suggest an evolutionary scenario in which the D(1A) receptor subtype was highly conserved after the first gene duplication during the evolution of craniates, whereas D(1B) and D(1C), and their associated specific characteristics, appeared later, probably in the gnathostome lineage.

Anguilla↗
PubMed2000

Molecular evolution of the growth hormone-releasing hormone/pituitary adenylate cyclase-activating polypeptide gene family. Functional implication in the regulation of growth hormone secretion.

Growth hormone-releasing hormone (GHRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) belong to the same superfamily of regulatory neuropeptides and have both been characterized on the basis of their hypophysiotropic activities. This review describes the molecular evolution of the GHRH/PACAP gene family from urochordates to mammals and presents the hypothesis that the respective roles of GHRH and PACAP in the control of GH secretion are totally inverted in phylogenetically distant groups of vertebrates. In mammals, GHRH and PACAP originate from distinct precursors whereas, in all submammalian taxa investigated so far, including birds, amphibians and fish, a single precursor encompasses a GHRH-like peptide and PACAP. In mammals, GHRH-containing neurons are confined to the infundibular and dorsomedial nuclei of the hypothalamus while PACAP-producing neurons are widely distributed in hypothalamic and extrahypothalamic areas. In fish, both GHRH- and PACAP-immunoreactive neurons are restricted to the diencephalon and directly innervate the adenohypophysis. In mammals and birds, GHRH plays a predominant role in the control of GH secretion. In amphibians, both GHRH and PACAP are potent stimulators of GH release. In fish, PACAP strongly activates GH release whereas GHRH has little or no effect on GH secretion. The GHRH/PACAP family of peptides thus provides a unique model in which to investigate the structural and functional facets of evolution.

Amino Acid Sequence↗
PubMed2000

Mechanism by which metformin reduces glucose production in type 2 diabetes.

To examine the mechanism by which metformin lowers endogenous glucose production in type 2 diabetic patients, we studied seven type 2 diabetic subjects, with fasting hyperglycemia (15.5 +/- 1.3 mmol/l), before and after 3 months of metformin treatment. Seven healthy subjects, matched for sex, age, and BMI, served as control subjects. Rates of net hepatic glycogenolysis, estimated by 13C nuclear magnetic resonance spectroscopy, were combined with estimates of contributions to glucose production of gluconeogenesis and glycogenolysis, measured by labeling of blood glucose by 2H from ingested 2H2O. Glucose production was measured using [6,6-2H2]glucose. The rate of glucose production was twice as high in the diabetic subjects as in control subjects (0.70 +/- 0.05 vs. 0.36 +/- 0.03 mmol x m(-2) min(-1), P < 0.0001). Metformin reduced that rate by 24% (to 0.53 +/- 0.03 mmol x m(-2) x min(-1), P = 0.0009) and fasting plasma glucose concentration by 30% (to 10.8 +/- 0.9 mmol/l, P = 0.0002). The rate of gluconeogenesis was three times higher in the diabetic subjects than in the control subjects (0.59 +/- 0.03 vs. 0.18 +/- 0.03 mmol x m(-2) min(-1) and metformin reduced that rate by 36% (to 0.38 +/- 0.03 mmol x m(-2) x min(-1), P = 0.01). By the 2H2O method, there was a twofold increase in rates of gluconeogenesis in diabetic subjects (0.42 +/- 0.04 mmol m(-2) x min(-1), which decreased by 33% after metformin treatment (0.28 +/- 0.03 mmol x m(-2) x min(-1), P = 0.0002). There was no glycogen cycling in the control subjects, but in the diabetic subjects, glycogen cycling contributed to 25% of glucose production and explains the differences between the two methods used. In conclusion, patients with poorly controlled type 2 diabetes have increased rates of endogenous glucose production, which can be attributed to increased rates of gluconeogenesis. Metformin lowered the rate of glucose production in these patients through a reduction in gluconeogenesis.

Calorimetry, Indirect↗
PubMed2000

Mechanism of troglitazone action in type 2 diabetes.

To examine the metabolic pathways by which troglitazone improves insulin responsiveness in patients with type 2 diabetes, the rate of muscle glycogen synthesis was measured by 13C-nuclear magnetic resonance (NMR) spectroscopy. The rate-controlling steps of insulin-stimulated muscle glucose metabolism were assessed using 31P-NMR spectroscopic measurement of intramuscular glucose-6-phosphate (G-6-P) combined with a novel 13C-NMR method to assess intracellular glucose concentrations. Seven healthy nonsmoking subjects with type 2 diabetes were studied before and after completion of 3 months of troglitazone (400 mg/day) therapy. After troglitazone treatment, rates of insulin-stimulated whole-body glucose uptake increased by 58+/-11%, from 629+/-82 to 987+/-156 micromol x m(-2) x min(-1) (P = 0.008), which was associated with an approximately 3-fold increase in rates of insulin-stimulated glucose oxidation (from 119+/-41 to 424+/-70 micromol x m(-2) x min(-1); P = 0.018) and muscle glycogen synthesis (26+/-17 vs. 83+/-35 micromol x l(-1) muscle x min(-1); P = 0.025). After treatment, muscle G-6-P concentrations increased by 0.083+/-0.019 mmol/l (P = 0.008 vs. pretreatment) during the hyperglycemic-hyperinsulinemic clamp, compared with no significant changes in intramuscular G-6-P concentrations in the pretreatment study, reflecting an improvement in glucose transport and/or hexokinase activity. The concentrations of intracellular free glucose did not differ between the pre- and posttreatment studies and remained >50-fold lower in concentration (<0.1 mmol/l) than what would be expected if hexokinase activity was rate-controlling. These results indicate that troglitazone improves insulin responsiveness in skeletal muscle of patients with type 2 diabetes by facilitating glucose transport activity, which thereby leads to increased rates of muscle glycogen synthesis and glucose oxidation.

Body Composition↗
PubMed1999

Differential function of N-cadherin and cadherin-7 in the control of embryonic cell motility.

Similar amounts of N-cadherin and cadherin-7, the prototypes of type I and type II cadherin, induced cell-cell adhesion in murine sarcoma 180 transfectants, Ncad-1 and cad7-29, respectively. However, in the initial phase of aggregation, Ncad-1 cells aggregated more rapidly than cad7-29 cells. Isolated Ncad-1 and cad7-29 cells adhered and spread in a similar manner on fibronectin (FN), whereas aggregated cad7-29 cells were more motile and dispersed than aggregated Ncad-1 cells. cad7-29 cells established transient contacts with their neighbors which were stabilized if FN-cell interactions were perturbed. In contrast, Ncad-1 cells remained in close contact when they migrated on FN. Both beta-catenin and cadherin were more rapidly downregulated in cad7-29 than in Ncad-1 cells treated with cycloheximide, suggesting a higher turnover rate for cadherin-7-mediated cell-cell contacts than for those mediated by N-cadherin. The extent of FN-dependent focal adhesion kinase phosphorylation was much lower if the cells had initiated N-cadherin-mediated rather than cadherin-7-mediated cell adhesion before plating. On grafting into the embryo, Ncad-1 cells did not migrate and remained at or close to the graft site, even after 48 h, whereas grafted cad7-29 cells dispersed efficiently into embryonic structures. Thus, the adhesive phenotype of cadherin-7-expressing cells is regulated by the nature of the extracellular matrix environment which also controls the migratory behavior of the cells. In addition, adhesions mediated by different cadherins differentially regulate FN-dependent signaling. The transient contacts specifically observed in cadherin- 7-expressing cells may also be important in the control of cell motility.

Animals↗
PubMed1999

A novel model to study the dorsolateral migration of melanoblasts.

Melanocytes derived from pluripotent neural crest cells migrate initially in the dorsolateral pathway between the ectoderm and dermomyotome. To understand the role of specific proteins involved in this cell migration, we looked for a cellular model that mimics the in vivo behavior of melanoblasts, and that allows functional studies of their migration. We report here that wild-type embryonic stem (ES) cells are able to follow the ventral and dorsolateral neural crest pathways after being grafted into chicken embryos. By contrast, a mutant ES cell line deficient for beta1 integrin subunits, proteins involved in cell-extracellular interactions, had a severely impaired migratory behavior. Interestingly, ES cells deficient for Kit, the tyrosine kinase receptor for the stem cell factor (SCF), behaved similarly to wild-type ES cells. Thus, grafting mouse ES cells into chicken embryos provides a new cellular system that allows both in vitro and in vivo studies of the molecular mechanisms controlling dorsolateral migration.

Animals↗
PubMed1999

Evidence that corticotropin-releasing hormone acts as a growth hormone-releasing factor in a primitive teleost, the European eel (Anguilla anguilla).

The inhibitory control of growth hormone (GH) release by somatostatin (SRIH) has been conserved throughout vertebrate evolution. In contrast, the neuropeptides involved in the stimulatory control of GH vary according to species and/or physiological situations. We investigated the direct pituitary regulation of GH release in a primitive teleost, the European eel (Anguilla anguilla L.) at the juvenile stage. Short-term serum-free primary cultures of dispersed pituitary cells were used, and GH release was measured by an homologous radioimmunoassay. Whereas growth hormone-releasing hormone (GHRH), gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), neuropeptide Y (NPY) and cholecystokinin (CCK) failed to induce any change in GH release, corticotropin-releasing hormone (CRH) dose-dependently stimulated GH release with a significant effect at 1 nM and a maximal effect (> or =400% of controls at 24 h) at 100 nM. In agreement with our previous studies, PACAP also stimulated GH release but its maximal effect was lower than that of CRH. Proopiomelanocortin (POMC)-peptides, corticotropin (ACTH), melanotropin (alpha-MSH), beta-endorphin) had no effect on GH release, at any dose tested (0.1-1000 nM), indicating that the stimulatory effect of CRH on GH release by somatotrophs was not mediated by CRH-induced release of POMC-peptides from corticotrophs and melanotrophs. The CRH antagonist, alpha-helical CRH(9-41), significantly inhibited the stimulatory effect of CRH on GH release, suggesting the implication of specific CRH receptors related to mammalian ones. The stimulatory effect of CRH on GH release was reduced after 24 h of incubation, indicating a desensitization. In contrast, no desensitization to the inhibitory effect of SRIH was observed. SRIH inhibited CRH action in a dose-dependent manner. The effect of SRIH was overriding, 1 nM SRIH being able to abolish the effect of 1000 nM CRH. In conclusion, in the eel, CRH stimulates GH release directly at the pituitary cell level. GH and cortisol secretions could interact in controlling several physiological functions such as metabolism and ion exchange. This study suggests that CRH may have played an important early role in vertebrates co-ordinating the activation of various endocrine axes involved in metamorphosis, osmoregulation, stress and fasting. The stimulatory role of CRH on GH release may have been partially conserved during evolution, as it is found in some human physio-pathological situations such as stress, fasting and depression.

Adrenocorticotropic Hormone↗
PubMed1999

Effects of free fatty acids on glucose transport and IRS-1-associated phosphatidylinositol 3-kinase activity.

To examine the mechanism by which free fatty acids (FFA) induce insulin resistance in human skeletal muscle, glycogen, glucose-6-phosphate, and intracellular glucose concentrations were measured using carbon-13 and phosphorous-31 nuclear magnetic resonance spectroscopy in seven healthy subjects before and after a hyperinsulinemic-euglycemic clamp following a five-hour infusion of either lipid/heparin or glycerol/heparin. IRS-1-associated phosphatidylinositol 3-kinase (PI 3-kinase) activity was also measured in muscle biopsy samples obtained from seven additional subjects before and after an identical protocol. Rates of insulin stimulated whole-body glucose uptake. Glucose oxidation and muscle glycogen synthesis were 50%-60% lower following the lipid infusion compared with the glycerol infusion and were associated with a approximately 90% decrease in the increment in intramuscular glucose-6-phosphate concentration, implying diminished glucose transport or phosphorylation activity. To distinguish between these two possibilities, intracellular glucose concentration was measured and found to be significantly lower in the lipid infusion studies, implying that glucose transport is the rate-controlling step. Insulin stimulation, during the glycerol infusion, resulted in a fourfold increase in PI 3-kinase activity over basal that was abolished during the lipid infusion. Taken together, these data suggest that increased concentrations of plasma FFA induce insulin resistance in humans through inhibition of glucose transport activity; this may be a consequence of decreased IRS-1-associated PI 3-kinase activity.

Adolescent↗
PubMed1999

Cortisol selectively stimulates pituitary gonadotropin beta-subunit in a primitive teleost, Anguilla anguilla.

It has been suggested that in mammals, glucocorticoids, beside their stress-related inhibitory effects on reproductive function, may also play a stimulatory role at the onset of puberty. Using the juvenile female eel as a model, we investigated the potential stimulatory role of cortisol (F) on pituitary gonadotropin (GtH-II). GtH-II levels were measured by RIA, and messenger RNA (mRNA) levels for alpha- and GtH-II beta-subunits were determined by dot blot using homologous probes. F treatment increased eel pituitary GtH-II content in vivo and in vitro. Using a long term, serum-free primary culture of pituitary cells, we studied the direct effect of F on GtH-II production. F increased the GtH-II cellular content in vitro in a dose- and time-dependent manner. The relative potencies of various corticosteroids on GtH-II were: triamcinolone acetonide > dexamethasone > F >> cortisone and aldosterone, indicating a glucocorticoid-specific receptor (GR). F stimulated GtH-II production through a selective increase in mRNA levels for GtH-II beta-subunit; no significant effect was observed on alpha-subunit mRNA levels. This stimulatory effect of F on GtH-II beta, played out directly at the pituitary cell level, recalls that of F on FSHbeta in the rat. The present study, performed in a primitive teleost at the juvenile stage, suggests that the role of F in the positive regulation of gonadotropins at puberty may have arisen early in vertebrate evolution.

Analysis of Variance↗
PubMed1998

Mitochondrial permeability transition during hypothermic to normothermic reperfusion in rat liver demonstrated by the protective effect of cyclosporin A.

The purpose of this study was to test the hypothesis that mitochondrial permeability transition might be implicated in mitochondrial and intact organ dysfunctions associated with damage induced by reperfusion after cold ischaemia. Energetic metabolism was assessed continuously by 31P-NMR on a model system of isolated perfused rat liver; mitochondria were extracted from the livers and studied by using top-down control analysis. During the temperature transition from hypothermic to normothermic perfusion (from 4 to 37 degrees C) the ATP content of the perfused organ fell rapidly, and top-down metabolic control analysis of damaged mitochondria revealed a specific control pattern characterized by a dysfunction of the phosphorylation subsystem leading to a decreased response to cellular ATP demand. Both dysfunctions were fully prevented by cyclosporin A, a specific inhibitor of the mitochondrial transition pore (MTP). These results strongly suggest the involvement of the opening of MTP in vivo during the transition to normothermia on rat liver mitochondrial function and organ energetics.

Animals↗
PubMed1998

Characterization and localization of two forms of gonadotropin-releasing hormone (GnRH) in the spinal cord of the frog Rana ridibunda.

Two molecular variants of gonadotropin-releasing hormone (GnRH) have been previously characterized in the brain of amphibians, i.e., mammalian GnRH (mGnRH) and chicken GnRH-II (cGnRH-II). The aim of the present study was to identify the molecular forms of gonadotropin-releasing hormone and to localize gonadotropin-releasing hormone-containing elements in the spinal cord of the frog Rana ridibunda using highly specific antisera against mGnRH and cGnRH-II. High-performance liquid chromatography (HPLC) analysis combined with radioimmunoassay (RIA) detection revealed that frog spinal cord extracts contained both mGnRH and cGnRH-II. Immunohistochemical labeling revealed that the frog spinal cord was devoid of GnRH-containing cell bodies. In contrast, numerous GnRH-immunoreactive fibers were observed throughout the entire length of the cord. mGnRH immunoreactivity was only detected in the rostral region of the cord and consisted of varicose processes located in the vicinity of the central canal. cGnRH-II-positive fibers were found throughout the spinal cord, the density of immunoreactive processes decreasing gradually toward the caudal region. Two main cGnRH-II-positive fiber tracts with a rostrocaudal orientation were observed: a relatively dense fiber bundle surrounding the central canal, and a more diffuse plexus in the white matter. In addition, short, varicose cGnRH-II-positive processes with a radial orientation were present throughout the gray matter. These fibers were particularly abundant ventromedially and formed a diffuse network that ramified laterally to end in the vicinity of motoneurons. Taken together, these data indicate that the frog spinal cord, like the frog brain, contains two forms of GnRH. The presence of numerous cGnRH-II-immunoreactive fibers in the ventral horn suggests that cGnRH-II may influence the activity of a subpopulation of motoneurons.

Animals↗
PubMed1998

Tyrosine hydroxylase in the european eel (Anguilla anguilla): cDNA cloning, brain distribution, and phylogenetic analysis.

We report the isolation of a full-length eel tyrosine hydroxylase (TH) cDNA that is characterized by a long 3' untranslated region and by a diversity restricted to the 3' end owing to the differential use of three polyadenylation signals. The longest eel TH mRNA was distinctive in the presence of four pentameric elements (AUUUA) in the AU-rich 3' noncoding region. Such a diversity could provide the basis of posttranscriptional or translational regulation of eel TH gene expression. Comparison of the eel TH sequence with those of other aromatic amino acid hydroxylases (TH, tryptophan hydroxylase, and phenylalanine hydroxylase) and phylogenetic analysis confirmed that the N-terminal regulatory domain is highly divergent, contrasting with the conservation of the catalytic core of the enzyme. Molecular phylogenies including the available sequences of the three hydroxylase genes suggested that the duplication of their common ancestor occurred before the emergence of arthropods. The regional expression of the eel TH mRNA was studied by semiquantitative PCR, northern blots, and in situ hybridization and compared with the immunocytochemical localization of TH protein. The data showed that TH mRNA is mostly expressed in the olfactory and hypothalamic areas, whereas sparse TH-expressing cell bodies are present in the telencephalic region and brainstem. No labeling was detected in the mesencephalic area, in striking contrast with that found in amphibians and amniotes.

Amino Acid Sequence↗
PubMed1998

RGDS glycosylated peptides as inhibitors of cell-attachment and platelet aggregation.

Glycopeptides derived from the GRGDS sequence were synthesized to study the effect of the sugar residue on the activity of these peptides. The peptides were tested as inhibitors of cell adhesion to fibronectin and of platelet aggregation. The sugar moiety was found to reduce the biological activity of the parent compounds except for the cyclic derivatives P37 and P38 where the inhibition of platelet aggregation was increased. Some interesting differences were observed between the peptides bearing sugar residues with free hydroxyl groups and those with peracetylated sugars.

Blood Platelets↗