RESUMEN

AIM: In hepatocytes, the peroxisome proliferator-activated receptor (PPAR)-α and insulin receptor (IR) are critical for transcriptional responses to fasting and feeding, respectively. The present report analyzes the effects of nutritional status (fasting vs feeding) on the expression of a large panel of hepatokines in hepatocyte-specific PPAR-α (Pparαhep-/-) and IR (IRhep-/-) null mice. METHODS: Pparαhep-/- and IRhep-/- mice, and their wild-type littermates, were subjected to fasting or feeding metabolic challenges, then analyzed for hepatokine gene expression. Experiments were conducted in mice of both genders. RESULTS: Our data confirmed that PPAR-α is essential for regulating fasting-induced Fgf21 and Angptl4 expression. In mice lacking PPAR-α, fasting led to increased Igfbp1 and Gdf15 gene expression. In the absence of hepatic IR, feeding induced overexpression of Igfbp1, follistatin (Fst) and adropin (Enho), and reduced activin E (Inhbe) expression. Gender had only a modest influence on hepatokine gene expression in the liver. CONCLUSION: The present results highlight the potential roles of hepatokines as a class of hormones that substantially influence nutritional regulation in both female and male mice.

Asunto(s)

Ingestión de Alimentos/fisiología , Ayuno/metabolismo , Hepatocitos/metabolismo , PPAR alfa/metabolismo , Receptor de Insulina/metabolismo , Transducción de Señal/fisiología , Proteína 4 Similar a la Angiopoyetina/genética , Proteína 4 Similar a la Angiopoyetina/metabolismo , Animales , Factores de Crecimiento de Fibroblastos/genética , Factores de Crecimiento de Fibroblastos/metabolismo , Expresión Génica , Insulina/metabolismo , Ratones , Ratones Noqueados , PPAR alfa/genética , Receptor de Insulina/genética

RESUMEN

A novel protein was cloned from a rat liver cDNA library by interaction with the liver glucokinase. This protein contained 339 residues and possessed a canonical consensus sequence for a dual specificity phosphatase. The recombinant protein was able to dephosphorylate phosphotyrosyl and phosphoseryl/threonyl substrates. We called this protein the glucokinase-associated phosphatase (GKAP). The GKAP partially dephosphorylated the recombinant glucokinase previously phosphorylated, in vitro, by protein kinase A. The GKAP fused with green fluorescent protein was located in the cytosol, where glucokinase phosphorylates glucose, and not in the nucleus where the glucokinase is retained inactive by the glucokinase regulatory protein. More importantly, the GKAP accelerated the glucokinase activity in a dose-dependent manner and with a stoichiometry compatible with a physiological mechanism. This strongly suggested that the interaction between GKAP and glucokinase had a functional significance. The cloning of this novel protein with a dual specificity phosphatase activity allows the description of a possible new regulatory step in controlling the glycolysis flux.

Asunto(s)

Glucoquinasa/metabolismo , Glucosa/metabolismo , Fosfoproteínas Fosfatasas/metabolismo , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Núcleo Celular/enzimología , Clonación Molecular , Citosol/enzimología , ADN Complementario/genética , Fosfatasas de Especificidad Dual , Glutatión Transferasa/metabolismo , Proteínas Fluorescentes Verdes , Cinética , Proteínas Luminiscentes/metabolismo , Datos de Secuencia Molecular , Fosfoproteínas Fosfatasas/química , Fosfoproteínas Fosfatasas/genética , Fosforilación , Ratas , Proteínas Recombinantes de Fusión/metabolismo , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Especificidad por Sustrato

RESUMEN

The molecular adapter Grb7 is likely to be implicated in the development of certain cancer types. In this study we show that Grb7 binds the insulin receptors, when they are activated and tyrosine phosphorylated. This interaction is documented by two-hybrid experiments, GST pull-down assays and in vivo coimmunoprecipitations. In addition, our results argue in favor of a preferential association between Grb7 and the insulin receptors when compared to other tyrosine kinase receptors like the EGF receptor, the FGF receptor and Ret. Interestingly, Grb7 is not a substrate of the insulin receptor tyrosine kinase activity. Grb7 binds the activated tyrosine kinase loop of the insulin receptors. Two domains of Grb7 are implicated in the insulin receptor binding: the SH2 domain and the PIR (phosphotyrosine interacting region). The role of these two domains in the interaction with the insulin receptor was already reported for Grb10 and Grb14, the other members of the Grb7 family of proteins. However, the relative importance of these domains varies, considering the receptor and the Grb protein. These differences should be a determinant of the specificity of the receptor tyrosine kinase-Grbs binding, and thus of the implication of Grb7/10/14 in signal transduction.

Asunto(s)

Proteínas/genética , Proteínas/metabolismo , Receptor de Insulina/metabolismo , Animales , Sitios de Unión , Células COS/metabolismo , Clonación Molecular , Femenino , Proteína Adaptadora GRB7 , Riñón/metabolismo , Hígado/metabolismo , Datos de Secuencia Molecular , Mutación , Fosforilación , Placenta/metabolismo , Embarazo , Proteínas/inmunología , Ratas , Receptor de Insulina/genética , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Técnicas del Sistema de Dos Híbridos , Levaduras/genética , Dominios Homologos src

RESUMEN

We cloned by interaction with the beta-subunit of the insulin receptor the rat variant of the human adapter Grb14 (rGrb14). rGrb14 is specifically expressed in rat insulin-sensitive tissues and in the brain. The binding of rGrb14 to insulin receptors is insulin-dependent in vivo in Chinese hamster ovary (CHO) cells overexpressing both proteins and importantly, in rat liver expressing physiological levels of proteins. However, rGrb14 is not a substrate of the tyrosine kinase of the receptor. In the two-hybrid system, two domains of rGrb14 can mediate the interaction with insulin receptors: the Src homology 2 (SH2) domain and a region between the PH and SH2 domains that we named PIR (for phosphorylated insulin receptor-interacting region). In vitro interaction assays using deletion mutants of rGrb14 show that the PIR, but not the SH2 domain, is able to coprecipitate insulin receptors, suggesting that the PIR is the major binding domain of rGrb14. The interaction between rGrb14 and the insulin receptors is almost abolished by mutating tyrosine residue Tyr1150 or Tyr1151 of the receptor. The overexpression of rGrb14 in CHO-IR cells decreases insulin stimulation of both DNA and glycogen synthesis. These effects are accompanied by a decrease in insulin-stimulated tyrosine phosphorylation of IRS-1, but insulin receptor autophosphorylation is unaltered. These findings suggest that rGrb14 could be a new downstream signaling component of the insulin-mediated pathways.

Asunto(s)

Insulina/metabolismo , Proteínas/química , Transducción de Señal/fisiología , Proteínas Adaptadoras Transductoras de Señales , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Sitios de Unión/fisiología , Células CHO , Clonación Molecular , Cricetinae , Hígado/metabolismo , Datos de Secuencia Molecular , Mutación/genética , Fosforilación , Fosfotirosina/análisis , ARN Mensajero/metabolismo , Ratas , Proteínas Tirosina Quinasas Receptoras/metabolismo , Receptor de Insulina/genética , Receptor de Insulina/metabolismo , Análisis de Secuencia de ADN , Homología de Secuencia , Dominios Homologos src/fisiología

RESUMEN

Insulin receptor substrate-1 (IRS-1) and Shc are two proteins implicated in intracellular signal transduction. They are activated by an increasing number of extracellular signals, mediated by receptor tyrosine kinases, cytokine receptors, and G protein-coupled receptors. In this study we demonstrate that Shc interacts directly with IRS-1, using the yeast two-hybrid system and an in vitro interaction assay. Deletion analysis of the proteins to map the domains implicated in this interaction shows that the phosphotyrosine binding domain of Shc binds to the region of IRS-1 comprising amino acids 583-661. An in vitro association assay, performed with or without activation of tyrosine kinases, gives evidence that tyrosine phosphorylation of IRS-1 and Shc drastically improves the interaction. Site-directed mutagenesis on IRS-1 583-693 shows that the asparagine, but not the tyrosine residue of the N625GDY628motif domain, is implicated in the IRS-1-Shc-phosphotyrosine binding interaction. Mutation of another tyrosine residue, Tyr608, also induced a 40% decrease in the interaction. This study, describing a phosphotyrosine-dependent interaction between IRS-1 and Shc, suggests that this association might be important in signal transduction.

Asunto(s)

Proteínas Adaptadoras Transductoras de Señales , Proteínas Adaptadoras del Transporte Vesicular , Fosfoproteínas/metabolismo , Proteínas/metabolismo , Transducción de Señal , Dominios Homologos src , Secuencia de Aminoácidos , Asparagina/metabolismo , Sitios de Unión , Humanos , Proteínas Sustrato del Receptor de Insulina , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Fosfoproteínas/genética , Fosforilación , Unión Proteica , Proteínas Recombinantes de Fusión/metabolismo , Proteínas Adaptadoras de la Señalización Shc , Proteína Transformadora 1 que Contiene Dominios de Homología 2 de Src , Tirosina/metabolismo

RESUMEN

The neurotransmitter serotonin mediates a wide variety of peripheral and central physiological effects through the binding to multiple receptor subtypes (Wilkinson, L. O., and Dourish, C. T. (1991) in Serotonin Receptor Subtypes: Basic and Clinical Aspects (Peroutka, S. J., ed) Vol. 15, pp.147-210, Wiley-Liss, New York). Among them, serotonin 5-HT2A receptors are known to activate the phospholipase C-beta second messenger pathway (Peroutka, S. J. (1995) Trends Neurosci. 18, 68-69). We identified and localized in rat skeletal muscle myoblasts a functional serotonin 5-HT2A receptor. This receptor was detected on the plasma membrane, in myoblasts, and at the level of T-tubules in contracting myotubes. Binding of serotonin to its receptor increases the expression of genes involved in myogenic differentiation. Unexpectedly, the 5-HT2A receptor is able to activate another signaling pathway; it triggers a rapid and transient tyrosine phosphorylation of Jak2 kinase in response to serotonin. Jak2 auto-phosphorylation is followed by the tyrosine phosphorylation of STAT3 (signal transducers and activators of transcription) and its translocation into the nucleus. We also find that the 5-HT2A receptor and STAT3 co-precipitate with Jak2, indicating that they are physically associated. We conclude that the serotonin 5-HT2A receptor identified in skeletal muscle myoblasts is able to activate the intracellular phosphorylation pathway used by cytokines. The presence of serotonin receptors in T-tubules suggests a role for serotonin in excitation-contraction coupling and (or) an effect in skeletal muscle fiber repairing.

Asunto(s)

Proteínas de Unión al ADN/metabolismo , Músculo Esquelético/metabolismo , Proteínas Tirosina Quinasas/metabolismo , Proteínas Proto-Oncogénicas , Receptores de Serotonina/metabolismo , Transactivadores/metabolismo , Animales , Secuencia de Bases , Membrana Celular/metabolismo , Membrana Celular/ultraestructura , Células Cultivadas , Feto , Transportador de Glucosa de Tipo 1 , Transportador de Glucosa de Tipo 2 , Janus Quinasa 2 , Datos de Secuencia Molecular , Proteínas de Transporte de Monosacáridos/biosíntesis , Músculo Esquelético/citología , Músculo Esquelético/efectos de los fármacos , Miogenina/biosíntesis , Fosforilación , Reacción en Cadena de la Polimerasa , Ratas , Receptor de Serotonina 5-HT2A , Receptores de Serotonina/análisis , Receptores de Serotonina/biosíntesis , Factor de Transcripción STAT3 , Serotonina/metabolismo , Serotonina/farmacología , Transducción de Señal , Transcripción Genética/efectos de los fármacos

RESUMEN

PCTAIRE-1 is a member of the cyclin-dependent kinase (cdk)-like class of proteins, and is localized mainly in the mammalian brain. Using the yeast two-hybrid system we screened a mouse brain cDNA library with PCTAIRE-1 as bait, and isolated several clones coding for the mouse homologs of the following proteins: p11 (also known as calpactin I light chain) and the eta, theta (also known as tau) and zeta isoforms of 14-3-3 proteins. We confirmed that these four proteins interact with PCTAIRE-1 by demonstrating the biochemical interactions using the pure recombinant proteins. The fact that 14-3-3 proteins are known to interact with many other intracellular proteins (such as C-kinase, Raf, Bcr, P13-kinase) and p11 with annexin II (a major pp60(v-src) and C-kinase substrate) suggests that PCTAIRE-1 might be part of multiple signal transduction cascades and cellular protein networks.

Asunto(s)

Anexina A2/metabolismo , Quinasas Ciclina-Dependientes , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas/metabolismo , Tirosina 3-Monooxigenasa , Proteínas 14-3-3 , Secuencia de Aminoácidos , Animales , Anexina A2/genética , Secuencia de Bases , Encéfalo/enzimología , Clonación Molecular , Ratones , Datos de Secuencia Molecular , Peso Molecular , Unión Proteica , Proteínas Serina-Treonina Quinasas/química , Proteínas Serina-Treonina Quinasas/genética , Proteínas/genética , ARN Mensajero/genética , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/metabolismo , Saccharomyces cerevisiae/genética

RESUMEN

The yeast U6 snRNA gene, SNR6, transcribed by RNA polymerase III or C, is shown to have a mixed promoter with upstream, intragenic and downstream elements. The distant downstream B block behaves as a typical enhancer element. Required in vivo, and for transcription of chromatin templates in vitro, it was also active in reversed orientation. As shown by footprinting and electron microscopy, the factor TFIIIC, or tau, bound the B block in an oriented manner and was able to induce DNA looping. The factor TFIIIC appeared to act via a weak A block located at position +21. This A block-related motif was essential in vivo and with chromatin templates. When changed into a consensus A block it favored DNA looping by TFIIIC firmly anchored on the B block, and activated a B block lacking gene in vivo and in vitro. The role of the TATA box at -30 was most apparent using a purified transcription system. With the A block, it appeared to contribute to start site selection. The results suggest a model where three weak promoter elements collaborate to assemble the transcription complex by DNA looping and synergistic protein-DNA interactions.

Asunto(s)

Elementos de Facilitación Genéticos , Regiones Promotoras Genéticas , ARN Nuclear Pequeño/genética , Saccharomyces cerevisiae/genética , Factores de Transcripción TFIII , Secuencia de Bases , ADN de Hongos/metabolismo , ADN de Hongos/ultraestructura , Genes Fúngicos , Datos de Secuencia Molecular , Mutación , ARN de Hongos/genética , Factores de Transcripción/metabolismo , Factores de Transcripción/ultraestructura , Transcripción Genética

RESUMEN

The U6 small nuclear (sn)RNA gene (SNR6) from the yeast Saccharomyces cerevisiae is transcribed by RNA polymerase III in vivo. This gene is unusual in having a TATA box at position -30, and an essential B-block element located downstream of the T-rich termination signal. The B block is one of the two intragenic promoter elements of transfer RNA genes that are recognized by transcription factor (TF)IIIC (ref. 4). But accurate in vitro transcription of yeast U6 snRNA gene by PolIII in a purified system requires only TFIIIB components, including the TATA-box binding protein TBP. Here we report that, after nucleosome reconstitution or chromatin assembly, U6 snRNA synthesis becomes dependent on TFIIIC and on the integrity of the B-block element. This observation resolves an apparent paradox between in vitro and in vivo results concerning the necessity of the downstream B-block element and sheds light on a new role of TFIIIC in gene activation.

Asunto(s)

Cromatina/fisiología , Genes Fúngicos , ARN Nuclear Pequeño/genética , Saccharomyces cerevisiae/genética , Factores de Transcripción TFIII , Factores de Transcripción/metabolismo , Transcripción Genética , Animales , Cromatina/efectos de los fármacos , Cromatografía de Afinidad , Regulación Fúngica de la Expresión Génica , Histonas/metabolismo , Histonas/farmacología , Mutagénesis Sitio-Dirigida , Oocitos/fisiología , Plásmidos , Reacción en Cadena de la Polimerasa/métodos , Mapeo Restrictivo , Saccharomyces cerevisiae/metabolismo , Eliminación de Secuencia , Factores de Transcripción/aislamiento & purificación , Factores de Transcripción/farmacología , Transcripción Genética/efectos de los fármacos , Activación Transcripcional , Xenopus

RESUMEN

The suckling period in the rat is characterized by a continuously low plasma insulin concentration and a physiological insulin resistance, particularly in the adipose tissue. This insulin resistance disappears after weaning on the high-carbohydrate adult diet. We have studied the number, structure, and function of adipose tissue insulin receptors during the suckling-weaning transition. The insulin receptor number determined either on intact adipocytes or after partial purification was higher during suckling (15 days), whereas the affinity was similar when compared with weaned rats (30 days). The molecular weight of the alpha- and beta-subunits were identical in both groups and, when analyzed in nonreducing conditions, the alpha 2 beta 2-form was the unique detectable form of the receptor. Neither the basal and insulin-stimulated autophosphorylation of the insulin receptor beta-subunit nor the tyrosine kinase activity toward a synthetic substrate was decreased during the suckling period. Thus, in the adipose tissue of the suckling rat, a marked insulin resistance is concomitant with a normal insulin receptor number and function.

Asunto(s)

Tejido Adiposo/metabolismo , Resistencia a la Insulina/fisiología , Insulina/farmacología , Proteínas Tirosina Quinasas/metabolismo , Receptor de Insulina/metabolismo , Tejido Adiposo/crecimiento & desarrollo , Envejecimiento , Animales , Células Cultivadas , Reactivos de Enlaces Cruzados/farmacología , Carbohidratos de la Dieta , Insulina/análogos & derivados , Insulina/metabolismo , Insulina/fisiología , Cinética , Sustancias Macromoleculares , Peso Molecular , Fosforilación , Ratas , Ratas Endogámicas , Receptor de Insulina/efectos de los fármacos , Receptor de Insulina/aislamiento & purificación , Succinimidas/farmacología , Tripsina/farmacología

RESUMEN

Early after lesion of the ventromedial hypothalamus nuclei (VMH), insulin-induced glucose utilization is increased in white adipose tissue (WAT), whereas oxidative and glycolytic muscles are, respectively, normoresponsive or resistant to insulin. Five weeks later, all of the muscles are resistant, whereas WAT returns to normal responsiveness. The aim of this study was to characterize the insulin receptor kinase activity in WAT and muscles 1 and 6 wk after lesion. The number and affinity of insulin receptors were not modified in any of the tissues studied. Autophosphorylation and phosphorylation of an exogenous substrate were similar in oxidative and glycolytic muscles of VMH and control rats both 1 and 6 wk after the lesion. Insulin receptors from WAT of 1-wk VMH rats exhibited a 2.5-fold increase in insulin-stimulated autophosphorylation and phosphorylation. Six weeks after the lesion, both autophosphorylation and phosphorylation returned to normal values. This suggests that insulin receptor tyrosine kinase activity does not play a significant role in the insulin resistance of skeletal muscles but has a crucial role in mediating the variations of insulin action on WAT observed during the development of VMH obesity.

Asunto(s)

Tejido Adiposo/metabolismo , Enfermedades Hipotalámicas/metabolismo , Músculos/metabolismo , Obesidad/metabolismo , Proteínas Tirosina Quinasas/metabolismo , Animales , Femenino , Hipotálamo Medio , Ratas , Ratas Endogámicas , Receptor de Insulina , Factores de Tiempo

RESUMEN

The mammary gland is a tissue that is extremely sensitive to insulin during lactation; during weaning, the effect of insulin is rapidly abolished. The purpose of this study was to characterize the mammary gland insulin receptors and their kinase activity in lactating and weaned mammary gland. The apparent molecular weight of the alpha-subunit was slightly lower in the mammary gland than in liver and white adipose tissue (127,000 vs. 134,000), but the apparent molecular weight of the beta-subunit was similar in the three tissues (95,000). Insulin induced a 10-fold increase in beta-subunit autophosphorylation, and the half-maximal effect was achieved at 2 nM insulin. After 24 h of weaning, the number of insulin receptors was decreased by 30%, but the kinase activity of the beta-subunit was unchanged. During the euglycemic hyperinsulinemic clamp, insulin entirely activated pyruvate dehydrogenase in lactating rat mammary gland, whereas after 24 h of weaning it was unable to increase the proportion of the enzyme in the active form. These results suggest that the site of alteration in the action of insulin on the mammary gland during weaning is distal to the receptor.

Asunto(s)

Lactancia/metabolismo , Glándulas Mamarias Animales/metabolismo , Receptor de Insulina/metabolismo , Tejido Adiposo/metabolismo , Animales , Femenino , Técnica de Clampeo de la Glucosa , Cinética , Hígado/metabolismo , Sustancias Macromoleculares , Glándulas Mamarias Animales/efectos de los fármacos , Microsomas/metabolismo , Peso Molecular , Fosforilación , Proteínas Tirosina Quinasas/metabolismo , Ratas , Ratas Endogámicas , Receptor de Insulina/aislamiento & purificación

RESUMEN

The expression of different glucose transporter isoforms was measured during the development and differentiation of the rat mammary gland. Before conception, when the mammary gland is mainly composed of adipocytes, Glut 4 and Glut 1 mRNAs and proteins were present. During pregnancy, the expression of Glut 4 decreased progressively, whereas that of Glut 1 increased. In the lactating mammary gland only Glut 1 was present, and was expressed at a high level. The absence of Glut 4 suggests that glucose transport is not regulated by insulin in the lactating rat mammary gland.

Asunto(s)

Lactancia , Glándulas Mamarias Animales/fisiología , Proteínas de Transporte de Monosacáridos/metabolismo , Animales , Northern Blotting , Western Blotting , Diferenciación Celular , Expresión Génica , Glándulas Mamarias Animales/crecimiento & desarrollo , Peso Molecular , Proteínas de Transporte de Monosacáridos/clasificación , Proteínas de Transporte de Monosacáridos/genética , ARN Mensajero/genética , Ratas , Ratas Endogámicas

RESUMEN

The mechanism responsible for the insulin resistance described in vivo in brown adipose tissue (BAT) of lactating rats was investigated. The effect of insulin on glucose metabolism was studied on isolated brown adipocytes of non-lactating and lactating rats. Insulin stimulation of total glucose metabolism is 50% less in brown adipocytes from lactating than from non-lactating rats. This reflects a decreased effect of insulin on glucose oxidation and lipogenesis. However, the effect of noradrenaline (8 microM) on glucose metabolism was preserved in brown adipocytes from lactating rats as compared with non-lactating rats. The number of insulin receptors is similar in BAT of lactating and non-lactating rats. The insulin-receptor tyrosine kinase activity is not altered during lactation, for receptor autophosphorylation as well as tyrosine kinase activity towards the synthetic peptide poly(Glu4-Tyr1). The defect in the action of insulin is thus localized at a post-receptor level. The insulin stimulation of pyruvate dehydrogenase activity during euglycaemic/hyperinsulinaemic clamps is 2-fold lower in BAT from lactating than from non-lactating rats. However, the percentage of active form of pyruvate dehydrogenase is similar in non-lactating and lactating rats (8.6% versus 8.9% in the basal state, and 37.0% versus 32.3% during the clamp). A decrease in the amount of pyruvate dehydrogenase is likely to be involved in the insulin resistance described in BAT during lactation.

Asunto(s)

Tejido Adiposo Pardo/metabolismo , Glucosa/metabolismo , Resistencia a la Insulina , Insulina/farmacología , Receptor de Insulina/metabolismo , Tejido Adiposo Pardo/efectos de los fármacos , Animales , Animales Lactantes , Células Cultivadas , Femenino , Técnica de Clampeo de la Glucosa , Cinética , Lactancia , Fosforilación , Embarazo , Proteínas Tirosina Quinasas/metabolismo , Complejo Piruvato Deshidrogenasa/metabolismo , Ratas , Ratas Endogámicas

RESUMEN

The effects of maternal hypoglycemia and/or hyperketonemia on glucose utilization by individual fetal rat tissues have been studied in vivo. To decrease blood glucose and to raise fetal blood ketone body concentrations, 19-day pregnant rats were submitted to 48 or 96 h of starvation. To differentiate between the effects of decreased blood glucose and increased ketone body concentrations, fed pregnant rats were infused for 2 h with DL-beta-hydroxybutyrate. After 96 h of maternal starvation, fetal 2-deoxy-D-glucose (2DG) uptake decreased from 13.6 +/- 0.5 to 8.6 +/- 1.15 micrograms.min-1.g-1. This was mainly due to a decrease in 2DG uptake by fetal hindlimb muscles and heart. By contrast, 2DG uptake in fetal liver and brain was not affected by maternal starvation. Acute hyperketonemia in fed pregnant rats induced a 23% decrease in 2DG uptake by the whole fetus mainly as the result of a lowered 2DG uptake in fetal hindlimb muscles. These data suggest that fetal 2DG uptake does not simply depend on lowered blood glucose level during maternal starvation but that other hormonal, cardiovascular, or metabolic adaptations are implicated. In the rat, most of the fetal tissues including brain are protected against maternal hypoglycemia.

Asunto(s)

Desoxiazúcares/metabolismo , Desoxiglucosa/metabolismo , Feto/metabolismo , Hidroxibutiratos/farmacología , Cuerpos Cetónicos/sangre , Intercambio Materno-Fetal , Inanición , Ácido 3-Hidroxibutírico , Animales , Glucemia/metabolismo , Ayuno , Femenino , Glucólisis , Insulina/sangre , Embarazo , Ratas , Ratas Endogámicas , Valores de Referencia

RESUMEN

Three phases of starvation have been described from changes in protein and lipid utilization in birds and mammals. In the present study, tissue glucose utilization was measured in vivo during these three phases, using a 2-deoxy-[1-3H]glucose technique in the anesthetized rat. According to this technique, the term glucose utilization therefore refers to transport and phosphorylation of glucose in tissues, ie, whatever is the fate of glucose. Whole-body glucose turnover rate, which was determined by a continuous infusion of [3-3H]glucose, decreased by 40% during the first two days of starvation (phase 1); it did not change thereafter, neither in the protein-sparing phase 2 nor in phase 3, which is marked by an increase in net protein breakdown. Two days of starvation caused a marked decrease in the glucose utilization in skeletal muscles; this decrease was higher in oxidative muscles (65% in diaphragm, 66% in soleus) than in glycolytic muscles (31% in extensor digitorum longus, 34% in epitrochlearis). Glucose utilization also decreased in heart atria (75%), heart ventricles (93%), and white adipose tissue (54%); by contrast, there was a two-fold increase in glucose utilization in brown adipose tissue and no change in brain and skin. No variations were observed in glucose utilization in any of the tissues from phase 1 to phase 2. However, phase 3 was marked by a decrease in glucose utilization in extensor digitorum longus (45%), brown adipose tissue (76%), brain (29%), and skin (40%), whereas there was a 2.3- and 3.4-fold increase in glucose utilization in diaphragm and heart ventricles, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

Glucosa/metabolismo , Inanición , Tejido Adiposo/metabolismo , Animales , Glucemia/metabolismo , Peso Corporal , Encéfalo/metabolismo , Radioisótopos de Carbono , Masculino , Músculos/metabolismo , Miocardio/metabolismo , Especificidad de Órganos , Ratas , Ratas Endogámicas , Valores de Referencia , Piel/metabolismo , Factores de Tiempo

RESUMEN

The effect of insulin on glucose metabolism in mammary gland was studied by the euglycaemic/hyperinsulinaemic-clamp technique. Measurement of metabolite concentrations and enzyme activities in the mammary gland suggests two sites of action of insulin: phosphofructokinase-1 and acetyl-coA carboxylase. The increase in phosphofructokinase-1 activity could be linked to the 2-fold increase in fructose 2,6-bisphosphate concentration, since no change in maximal activity and in sensitivity of the enzyme toward fructose 6-phosphate was detected in vitro.

Asunto(s)

Glucosa/metabolismo , Insulina/farmacología , Lactancia/metabolismo , Glándulas Mamarias Animales/metabolismo , Acetil-CoA Carboxilasa/metabolismo , Animales , Glucemia/metabolismo , Activación Enzimática/efectos de los fármacos , Inducción Enzimática/efectos de los fármacos , Femenino , Fructosadifosfatos/farmacología , Insulina/sangre , Isoenzimas/metabolismo , Fosfofructoquinasa-1/metabolismo , Embarazo , Ratas , Ratas Endogámicas

Asunto(s)

Glucosa/fisiología , Homeostasis , Lactancia/fisiología , Embarazo/fisiología , Femenino , Humanos , Insulina/sangre , Resistencia a la Insulina

RESUMEN

Glucose is an important fuel for rat brown adipose tissue in vivo and its utilization is highly sensitive to insulin. In this study, the different glucose metabolic pathways and their regulation by insulin and norepinephrine were examined in isolated rat brown adipocytes, using [6-14C]glucose as a tracer. Glucose utilization was stimulated for insulin concentrations in the range of 40-1000 microU/ml. Furthermore, the addition of adenosine deaminase (200 mU/ml) or adenosine (10 microM) did not alter insulin sensitivity of glucose metabolism. The major effect of insulin (1 mU/ml) was a respective 7-fold and 5-fold stimulation of lipogenesis and lactate synthesis, whereas glucose oxidation remained very low. The 5-fold stimulation of total glucose metabolism by 1 mU/ml of insulin was accompanied by an 8-fold increase in glucose transport. In the presence of norepinephrine (8 microM), total glucose metabolism was increased 2-fold. This was linked to a 7-fold increase of glucose oxidation, whereas lipogenesis was greatly inhibited (by 72%). In addition, norepinephrine alone did not modify glucose transport. The addition of insulin to adipocytes incubated with norepinephrine, induced a potentiation of glucose oxidation, while lipogenesis remained very low. In conclusion, in the presence of insulin and norepinephrine glucose is a oxidative substrate for brown adipose tissue. However the quantitative importance of glucose as oxidative fuel remains to be determined.

Asunto(s)

Tejido Adiposo Pardo/metabolismo , Glucosa/metabolismo , Insulina/farmacología , Norepinefrina/farmacología , Tejido Adiposo Pardo/efectos de los fármacos , Animales , Transporte Biológico Activo/efectos de los fármacos , Sinergismo Farmacológico , Femenino , Técnicas In Vitro , Cinética , Oxidación-Reducción , Ratas , Ratas Endogámicas

RESUMEN

Feeding a high fat diet during lactation should reduce the competition for glucose utilization between the mammary gland and the other maternal tissues, because dietary fat is directly utilized for milk lipid synthesis. Glucose homeostasis was studied in nonlactating and lactating rats fed a high fat diet and compared with that in rats fed a high carbohydrate diet. In nonlactating rats fed a high fat diet, blood glucose concentration was slightly higher, whereas plasma insulin concentration was lower than in nonlactating rats fed a high carbohydrate diet. In the postabsorptive state, plasma free fatty acids and blood ketone bodies were not modified by the nature of the diet consumed. Glucose turnover rate and glucose metabolic clearance rate in the postabsorptive state in nonlactating rats fed a high carbohydrate diet were not different from those in rats fed a high fat diet [9.5 +/- 1.4 vs. 8.8 +/- 0.8 mg/(min X kg) and 8.9 +/- 1.2 vs. 7.9 +/- 0.7 mL/(min X kg)]. In lactating rats, blood glucose and ketone bodies, plasma insulin and free fatty acid concentrations were not affected in the postabsorptive state by the composition of the diet consumed. The glucose metabolic clearance rate in lactating rats fed the high carbohydrate diet was higher than that in nonlactating rats fed the same diet. However, the glucose metabolic clearance rate in lactating rats fed the high fat diet was not different from that in nonlactating rats fed the same diet.

Asunto(s)

Grasas de la Dieta/administración & dosificación , Glucosa/metabolismo , Lactancia/metabolismo , Animales , Peso Corporal/efectos de los fármacos , Carbohidratos de la Dieta/administración & dosificación , Carbohidratos de la Dieta/metabolismo , Grasas de la Dieta/metabolismo , Ácidos Grasos no Esterificados/sangre , Femenino , Insulina/sangre , Cuerpos Cetónicos/sangre , Cinética , Embarazo , Ratas , Ratas Endogámicas