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1.
Neurochem Res ; 49(3): 684-691, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38017313

RESUMO

In the spinal cord, attenuation of the inhibitory action of glycine is related to an increase in both inflammatory and diabetic neuropathic pain; however, the glycine receptor involvement in diabetic neuropathy has not been reported. We determined the expression of the glycine receptor subunits (α1-α3 and ß) in streptozotocin-induced diabetic Long-Evans rats by qPCR and Western blot. The total mRNA and protein expression (whole spinal cord homogenate) of the α1, α3, and ß subunits did not change during diabetes; however, the α2 subunit mRNA, but not the protein, was overexpressed 45 days after diabetes induction. By contrast, the synaptic expression of the α1 and α2 subunits decreased in all the studied stages of diabetes, but that of the α3 subunit increased on day 45 after diabetes induction. Intradermal capsaicin produced higher paw-licking behavior in the streptozotocin-induced diabetic rats than in the control animals. In addition, the nocifensive response was higher at 45 days than at 20 days. During diabetes, the expression of the glycine receptor was altered in the spinal cord, which strongly suggests its involvement in diabetic neuropathy.


Assuntos
Diabetes Mellitus Experimental , Neuropatias Diabéticas , Ratos , Animais , Glicina/metabolismo , Receptores de Glicina/genética , Receptores de Glicina/metabolismo , Estreptozocina/toxicidade , Neuropatias Diabéticas/metabolismo , Diabetes Mellitus Experimental/induzido quimicamente , Diabetes Mellitus Experimental/metabolismo , Ratos Long-Evans , Medula Espinal/metabolismo , RNA Mensageiro/metabolismo
2.
Neurochem Int ; 145: 105007, 2021 05.
Artigo em Inglês | MEDLINE | ID: mdl-33675841

RESUMO

Diabetic retinopathy is the most common cause of vision loss among diabetic patients. Although hyperglycemia produces retinal oxidative stress in long-standing diabetes, the pathogenesis mechanism is unknown. The Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a central role in cell responses against oxidative damage. We used adult Long Evans rats where diabetes was induced by streptozotocin. Normal and treated rats were sacrificed at 7, 20, and 45 days after streptozotocin injection. We analyzed Nrf2 and Keap1 expression in retinal homogenates, cytoplasmic, and nuclear retinal fractions. Normal retina showed Nrf2 expression in all retina nuclear layers. We found a transitory decrease of Nrf2 mRNA and protein expression at 7 and 20 days after the streptozotocin injection that recovered later on: moreover, the protein level increased after 45 days. Keap1 immunoprecipitation revealed similar levels as Nrf2 in normal and diabetic rat retinas, indicating that the diabetic condition did not lead to dissociation of the Keap1-Nrf2 complex. Indeed, glutathione levels and superoxide dismutase activity were not altered in the treated rat retinas. These results do not support oxidative stress in the retina shortly after diabetes induction.


Assuntos
Diabetes Mellitus Experimental/metabolismo , Retinopatia Diabética/metabolismo , Fator 2 Relacionado a NF-E2/biossíntese , Retina/metabolismo , Animais , Diabetes Mellitus Experimental/induzido quimicamente , Diabetes Mellitus Experimental/genética , Retinopatia Diabética/induzido quimicamente , Retinopatia Diabética/genética , Feminino , Expressão Gênica , Fator 2 Relacionado a NF-E2/genética , Ratos , Ratos Long-Evans , Retina/efeitos dos fármacos , Estreptozocina
3.
Mitochondrion ; 52: 212-217, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32283307

RESUMO

Diabetic retinopathy is thought to be trigger by glucose- induced oxidative stress which leads to an increase of the mitochondrial permeability through opening the permeability transition pore (MTP). In several cell types, hexokinases interact with the mitochondria regulating MTP opening, avoiding cytochrome c release. We studied HK I mitochondrial proportion in control and streptozotocin-induced diabetic rat retinas. In the normal retina, 50% of HK I was linked to mitochondria, proportion that did not change up to 60 days of diabetes. Mitochondria from normal and diabetic rat retinas showed a limited swelling, and similar cytochrome c levels. G-6-P and glycogen content increased 3-6-fold in diabetic rat retinas, while lactate content did not vary. Results suggest that mitochondrial bound HK produce G-6-P and drove it to glycogen synthesis, controlling ROS production and lactate toxicity.


Assuntos
Diabetes Mellitus/induzido quimicamente , Retinopatia Diabética/metabolismo , Hexoquinase/metabolismo , Retina/metabolismo , Animais , Citocromos c/metabolismo , Diabetes Mellitus/metabolismo , Modelos Animais de Doenças , Feminino , Glucose-6-Fosfato/metabolismo , Mitocôndrias/metabolismo , Ratos , Estreptozocina
4.
Neurosci Lett ; 712: 134506, 2019 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-31541724

RESUMO

Diabetes mellitus is a metabolic disease that leads to several complications which include retinopathy. Neuronal abnormalities have been reported to appear before microvasculature alterations. We analyzed the expression levels of GlyR subunits in the retina at 7, 20, and 45 days after streptozotocin-induced diabetes to gain insight into the pathogenesis of diabetic retinopathy. We determined the mRNA and protein expression by qPCR and western blot, respectively. The mRNA and protein expression of the α1 subunit was not altered over the study period; however, they were slightly reduced in α2 yet statistically significant. While protein expression of α3 subunit was only reduced at 45 days diabetes. The mRNA and protein expression of the α4 subunit was remarkably decreased since day 7 of diabetes, remaining only ∼20% on day 45 of diabetes. Surprisingly, the mRNA of the ß subunit was highly increased, while its protein levels were not changed. The decrease in GlyR α subunits expression in the retina from diabetic animals suggest a perturbation in the inhibitory glycine signaling pathway, which might be related to the visual alterations observed in diabetes.


Assuntos
Diabetes Mellitus Experimental/metabolismo , Receptores de Glicina/metabolismo , Retina/metabolismo , Animais , Progressão da Doença , Feminino , Regulação da Expressão Gênica , Neurônios/metabolismo , Ratos , Ratos Long-Evans , Receptores de Glicina/genética , Transmissão Sináptica/fisiologia
5.
J Cereb Blood Flow Metab ; 39(5): 808-821, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-29047291

RESUMO

Moderate recurrent hypoglycemia (RH) is frequent in Type 1 diabetes mellitus (TIDM) patients who are under intensive insulin therapy increasing the risk for severe hypoglycemia (SH). The consequences of RH are not well understood and its repercussions on neuronal damage and cognitive function after a subsequent episode of SH have been poorly investigated. In the current study, we have addressed this question and observed that previous RH during seven consecutive days exacerbated oxidative damage and neuronal death induced by a subsequent episode of SH accompanied by a short period of coma, in the parietal cortex, the striatum and mainly in the hippocampus. These changes correlated with a severe decrease in reduced glutathione content (GSH), and a significant spatial and contextual memory deficit. Administration of the antioxidant, N-acetyl-L-cysteine, (NAC) reduced neuronal death and prevented cognitive impairment. These results demonstrate that previous RH enhances brain vulnerability to acute hypoglycemia and suggests that this effect is mediated by the decline in the antioxidant defense and oxidative damage. The present results highlight the importance of an adequate control of moderate hypoglycemic episodes in TIDM.


Assuntos
Disfunção Cognitiva/etiologia , Coma/complicações , Hipoglicemia/complicações , Estresse Oxidativo , Animais , Glicemia/metabolismo , Morte Celular , Disfunção Cognitiva/metabolismo , Disfunção Cognitiva/patologia , Coma/metabolismo , Coma/patologia , Glutationa/metabolismo , Humanos , Hipoglicemia/metabolismo , Hipoglicemia/patologia , Masculino , Neurônios/metabolismo , Neurônios/patologia , Ratos Wistar
6.
Cell Physiol Biochem ; 42(6): 2353-2363, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28848155

RESUMO

BACKGROUND/AIMS: Nitric oxide is a multifunctional molecule that can modify proteins via nitrosylation; it can also initiate signaling cascades through the activation of soluble guanylate cyclase. Diabetic retinopathy is the leading cause of blindness, but its pathogenesis is unknown. Multiple mechanisms including oxidative-nitrosative stress have been implicated. Our main goal was to find significant changes in nitric oxide (NO) levels and determine their association with nitrosative stress in the rat retina at the onset of diabetes. METHODS: Diabetes was induced by a single intraperitoneal administration of streptozotocin. The possible nitric oxide effects on the rat retina were evaluated by the presence of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), a specific marker for NO-producing neurons, detected by histochemistry performed on whole retinas and retina sections. Immunohistochemistry was also performed on retina sections for iNOS, 3-nitrotyrosine (3-NT) and glial fibrillary acidic protein (GFAP). Retinal nitric oxide levels were assessed by measuring total nitrate/nitrite concentrations. Retinal cGMP levels were determined by radioimmunoassay. Western blots for nitrotyrosine (3-NT) and oxidized proteins were performed. RESULTS: In the present study, we found increased activity of NADPH-diaphorase and iNOS immunoreactivity in the rat retina at the onset of diabetes; this increase correlated with a remarkable increase in NO levels as early as 7 days after the onset of diabetes. However, cGMP levels were not modified by diabetes, suggesting that NO did not activate its signaling cascade. Even so, Western blots revealed a progressive increase in nitrated proteins at 7 days after diabetes induction. Likewise, positive nitrotyrosine immunolabeling was observed in the photoreceptor layer, ganglion cell layer, inner nuclear layer and some Müller cell processes in the retinas of diabetic rats. In addition, levels of oxidized proteins were increased in the retina early after diabetes induction; these levels were reduced by the administration of L-NAME. In addition, stress in Müller cells was determined by immunoreactivity to the glial fibrillary acidic protein. CONCLUSIONS: Our findings indicated the occurrence of nitrosative stress at the onset of diabetes in the rat retina and emphasized the role of NO in retinal function and the pathogenesis of retinopathy.


Assuntos
Diabetes Mellitus Experimental/patologia , Óxido Nítrico/metabolismo , Estresse Oxidativo , Retina/metabolismo , Animais , GMP Cíclico/metabolismo , Diabetes Mellitus Experimental/induzido quimicamente , Diabetes Mellitus Experimental/metabolismo , Proteína Glial Fibrilar Ácida/metabolismo , Imuno-Histoquímica , Microscopia de Fluorescência , NADPH Desidrogenase/metabolismo , NG-Nitroarginina Metil Éster/farmacologia , Óxido Nítrico Sintase Tipo II/metabolismo , Estresse Oxidativo/efeitos dos fármacos , Carbonilação Proteica/efeitos dos fármacos , Ratos , Ratos Long-Evans , Retina/efeitos dos fármacos , Retina/patologia , Estreptozocina/toxicidade , Tirosina/análogos & derivados , Tirosina/metabolismo
7.
Neurochem Int ; 108: 177-182, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28343890

RESUMO

BACKGROUND AND METHODS: Glycine receptor (GlyR) consists of two α (1-4) and three ß subunits. Considerable evidence indicates that the adult retina expresses the four types of α subunits; however, the proportion of these subunits in adult and immature retina is almost unknown. In this report we have studied mRNA and the protein expression of GlyR subunits in the retina during postnatal rat development by Real-Time qRT-PCR and western blot. RESULTS: mRNA and protein expression indicated a gradual increase of the α1, α3, α4 and ß GlyR subunits during postnatal ages tested. The mRNA ß subunit showed higher expression levels (∼3 fold) than those observed for the α1 and α3 subunits. Very interestingly, the α2 GlyR subunit had the highest expression in the retina, even in the adult. CONCLUSIONS: These results revealed the expression of GlyR at early postnatal ages, supporting its role in retina development. In addition, our results indicated that the adult retina expressed a high proportion of the α2 subunit, suggesting the expression of monomeric and/or heteromeric receptors. A variety of studies are needed to further characterize the role of the specific subunits in both adult and immature retina.


Assuntos
Subunidades Proteicas/biossíntese , Receptores de Glicina/biossíntese , Retina/crescimento & desenvolvimento , Retina/metabolismo , Fatores Etários , Animais , Animais Recém-Nascidos , Expressão Gênica , Subunidades Proteicas/genética , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Ratos , Ratos Long-Evans , Receptores de Glicina/genética
8.
Neurochem Res ; 41(5): 1098-106, 2016 May.
Artigo em Inglês | MEDLINE | ID: mdl-26721508

RESUMO

Diabetes mellitus is a metabolic disease that leads to several complications which include retinopathy. Multiple biochemical abnormalities have been proposed to explain the development of retinopathy, including oxidative stress. Although the existence of oxidative stress has been established in the retina from long standing diabetic animals, pathogenesis and progression of retinopathy remain unclear. In order to gain insight into the pathogenesis of diabetic retinopathy, we analyzed the levels of different oxidative stress biomarkers in the retina at early stages during the progress of streptozotocin-induced diabetes. No significant changes in glutathione content, expression of NADPH-oxidase, levels of lipid peroxidation, nor production of free radicals were observed in the retina up to 45 days of diabetes induction. Likewise, a transient decrease in aconitase activity, parallel to an increase in the superoxide dismutase activity was observed at 20 days of hyperglycemia, suggesting a high capacity of retina to maintain its redox homeostasis, at least at early stages of diabetes. Nonetheless, we found an early and time-dependent increase in the levels of oxidized proteins, which was not affected by the administration of the antioxidant quercetin. Also, positive immunoreactivity to the reticulum stress protein CHOP was found in glial Müller cells of diabetic rat retinas. These findings suggest the occurrence of endoplasmic reticulum stress as a primary event in retina pathogenesis in diabetes.


Assuntos
Retinopatia Diabética/metabolismo , Estresse do Retículo Endoplasmático , Aconitato Hidratase/metabolismo , Animais , Biomarcadores/metabolismo , Células Ependimogliais/metabolismo , Radicais Livres/metabolismo , Glutationa/metabolismo , Peroxidação de Lipídeos , NADPH Oxidases/metabolismo , Estresse Oxidativo , Ratos Long-Evans , Retina/metabolismo , Fator de Transcrição CHOP/metabolismo
9.
PLoS One ; 7(2): e30822, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22363495

RESUMO

Retinal tissue is exceptional because it shows a high level of energy metabolism. Glycogen content represents the only energy reserve in retina, but its levels are limited. Therefore, elucidation of the mechanisms controlling glycogen content in retina will allow us to understand retina response under local energy demands that can occur under normal and pathological conditions. Thus, we studied retina glycogen levels under different experimental conditions and correlated them with glucose-6-phosphate (G-6-P) content and glycogen synthase (GS) activity. Glycogen and G-6-P content were studied in ex vivo retinas from normal, fasted, streptozotocin-treated, and insulin-induced hypoglycemic rats. Expression levels of GS and its phosphorylated form were also analyzed. Ex vivo retina from normal rats showed low G-6-P (14±2 pmol/mg protein) and glycogen levels (43±3 nmol glycosyl residues/mg protein), which were increased 6 and 3 times, respectively, in streptozotocin diabetic rats. While no changes in phosphorylated GS levels were observed in any condition tested, a positive correlation was found between G-6-P levels with GS activity and glycogen content. The results indicated that in vivo, retina glycogen may act as an immediately accessible energy reserve and that its content was controlled primarily by G-6-P allosteric activation of GS. Therefore, under hypoglycemic situations retina energy supply is strongly compromised and could lead to the alterations observed in type 1 diabetes.


Assuntos
Glicogênio Sintase/metabolismo , Glicogênio/metabolismo , Retina/enzimologia , Regulação Alostérica/efeitos dos fármacos , Animais , Glicemia/efeitos dos fármacos , Glicemia/metabolismo , Glucose-6-Fosfato/metabolismo , Glicogênio Fosforilase/metabolismo , Humanos , Insulina/administração & dosagem , Insulina/farmacologia , Fosforilação/efeitos dos fármacos , Ratos , Ratos Long-Evans , Retina/efeitos dos fármacos
10.
PLoS One ; 7(12): e52959, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-23285235

RESUMO

The vertebrate retina is a very metabolically active tissue whose energy demands are normally met through the uptake of glucose and oxygen. Glucose metabolism in this tissue relies upon adequate glucose delivery from the systemic circulation. Therefore, glucose transport depends on the expression of glucose transporters. Here, we show retinal expression of the Glut 4 glucose transporter in frog and rat retinas. Immunohistochemistry and in situ hybridization studies showed Glut 4 expression in the three nuclear layers of the retina: the photoreceptor, inner nuclear and ganglionar cell layers. In the rat retina immunoprecipitation and Western blot analysis revealed a protein with an apparent molecular mass of 45 kDa. ¹4C-glucose accumulation by isolated rat retinas was significantly enhanced by physiological concentrations of insulin, an effect blocked by inhibitors of phosphatidyl-inositol 3-kinase (PI3K), a key enzyme in the insulin-signaling pathway in other tissues. Also, we observed an increase in ³H-cytochalasin binding sites in the presence of insulin, suggesting an increase in transporter recruitment at the cell surface. Besides, insulin induced phosphorylation of Akt, an effect also blocked by PI3K inhibition. Expression of Glut 4 was not modified in retinas of a type 1 diabetic rat model. To our knowledge, our results provide the first evidence of Glut4 expression in the retina, suggesting it as an insulin- responsive tissue.


Assuntos
Proteínas de Ligação a DNA/genética , Insulina/farmacologia , Retina/efeitos dos fármacos , Retina/metabolismo , Fatores de Transcrição/genética , Animais , Citocalasina B/metabolismo , Proteínas de Ligação a DNA/metabolismo , Diabetes Mellitus Experimental/induzido quimicamente , Diabetes Mellitus Experimental/genética , Diabetes Mellitus Experimental/metabolismo , Diabetes Mellitus Experimental/patologia , Regulação da Expressão Gênica/efeitos dos fármacos , Glucose/farmacocinética , Proteína Oncogênica v-akt/metabolismo , Fosforilação/efeitos dos fármacos , Ligação Proteica , Rana pipiens , Ratos , Ratos Long-Evans , Fatores de Transcrição/metabolismo
11.
Diabetes ; 60(5): 1632-6, 2011 May.
Artigo em Inglês | MEDLINE | ID: mdl-21464442

RESUMO

OBJECTIVE: Type 2 diabetes is the most common form of diabetes worldwide. Some of its complications, such as retinopathy and neuropathy, are long-term and protracted, with an unclear etiology. Given this problem, genetic model systems, such as in flies where type 2 diabetes can be modeled and studied, offer distinct advantages. RESEARCH DESIGN AND METHODS: We used individual flies in experiments: control and mutant individuals with partial loss-of-function insulin pathway genes. We measured wing size and tested body weight for growth phenotypes, the latter by means of a microbalance. We studied total lipid and carbohydrate content, lipids by a reaction in single fly homogenates with vanillin-phosphoric acid, and carbohydrates with an anthrone-sulfuric acid reaction. Cholinesterase activity was measured using the Ellman method in head homogenates from pooled fly heads, and electroretinograms with glass capillary microelectrodes to assess performance of central brain activity and retinal function. RESULTS: Flies with partial loss-of-function of insulin pathway genes have significantly reduced body weight, higher total lipid content, and sometimes elevated carbohydrate levels. Brain function is impaired, as is retinal function, but no clear correlation can be drawn from nervous system function and metabolic state. CONCLUSIONS: These studies show that flies can be models of type 2 diabetes. They weigh less but have significant lipid gains (obese); some also have carbohydrate gains and compromised brain and retinal functions. This is significant because flies have an open circulatory system without microvasculature and can be studied without the complications of vascular defects.


Assuntos
Insulina/farmacologia , Animais , Peso Corporal/genética , Peso Corporal/fisiologia , Encéfalo , Drosophila , Eletrorretinografia , Metabolismo dos Lipídeos/efeitos dos fármacos , Metabolismo dos Lipídeos/genética , Mutação , Receptor de Insulina/genética , Receptor de Insulina/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética
12.
Chronobiol Int ; 27(1): 34-51, 2010 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-20205556

RESUMO

Previous studies suggested the retina could be a putative locus of daily crustacean hyperglycemic hormone (CHH) secretion, as it possesses its own metabolic machinery and is independent of the well-known CHH eyestalk locus responsible for the circadian secretion of this peptide. However, it has been proposed that hemolymph glucose and lactate concentrations play a dual role in the regulation of CHH in crayfish. To elucidate the temporal relationship between these two different CHH production loci and to examine their relationship with glucose regulation, we investigated the expression of CHH daily and circadian rhythms in the eyestalk and retina of crayfish using biochemical methods and time series analysis. We wanted to determine whether (1) putative retina and eyestalk CHH rhythmic expressions are correlated and if the oscillations of the two metabolic products of lactate and glucose in the blood due to CHH action on the target tissue correlate, and (2) retina CHH (RCHH) and the possible retinal substrate glycogen and its product glucose are temporally correlated. We found a negative correlation between daily and circadian changes of relative CHH abundance in the retina and eyestalk. This correlation and the cross-correlation values found between eyestalk CHH and hemolymph and glucose confirm that CHH produced by the X-organ sinus gland complex is under the previously proposed dual feedback control system over the 24 h time period. However, the presence of both glycogen and glucose in the retina, the cross-correlation values found between these parameters and hemolymph lactate and glucose, as well as RCHH and hemolymph and retina metabolic markers suggest RCHH is not under the same temporal metabolic control as eyestalk CHH. Nonetheless, their expression may be linked to common rhythms-generating processes.


Assuntos
Astacoidea/metabolismo , Ritmo Circadiano/fisiologia , Hormônios de Invertebrado/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Animais , Proteínas de Artrópodes , Olho/metabolismo , Retroalimentação Fisiológica , Glucose/metabolismo , Glicogênio/metabolismo , Hemolinfa/metabolismo , Ácido Láctico/metabolismo , Fotoperíodo , Retina/metabolismo
13.
Neuroreport ; 19(13): 1295-9, 2008 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-18695510

RESUMO

The amino acid glycine is an inhibitory neurotransmitter in the spinal cord, brain stem, and vertebrate retina. The effective synaptic concentrations of glycine are regulated by at least two transporters: glycine transporter 1 and glycine transporter 2. Here, we show retinal expression of glycine transporter 1 by in-situ hybridization and of glycine transporter 2 by reverse transcriptase-PCR and in-situ hybridization. In-situ hybridization signals were observed in the ganglionar and inner nuclear layer as well as in the outer nuclear layer of the frog and rat retinas. In addition, accumulation of H-glycine was observed in isolated photoreceptor cells. The expression of these transporters in nonglycinergic cells suggests that they may also modulate electrical signals.


Assuntos
Perfilação da Expressão Gênica , Proteínas da Membrana Plasmática de Transporte de Glicina/genética , Retina/metabolismo , Células Ganglionares da Retina/metabolismo , Animais , Proteínas da Membrana Plasmática de Transporte de Glicina/metabolismo , Hibridização In Situ , Neurônios/citologia , Neurônios/metabolismo , Células Fotorreceptoras de Vertebrados/citologia , Células Fotorreceptoras de Vertebrados/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Rana pipiens , Ratos , Ratos Long-Evans , Células Ganglionares da Retina/citologia , Reação em Cadeia da Polimerase Via Transcriptase Reversa
14.
Neurochem Res ; 33(8): 1541-5, 2008 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-18351463

RESUMO

Diabetes-induced increase in oxidative stress is postulated as playing a significant role in the development of retinopathy. The retinal pigment epithelium (RPE) which forms part of the retinal blood barrier has been reported to be affected in diabetes. Besides functioning as a neurotransmitter, the radical nitric oxide (NO) can act as a cytotoxic agent. NO is synthesized by nitric oxide synthase (NOS) that oxidizes arginine to citrulline producing NO. Given that intracellular concentration of arginine depends mainly on its transport, we studied arginine transport in RPE and retina from normal and streptozotocin-induced diabetic rats. Retina and RPE take up arginine by a saturable system with an apparent K(M) of 70-80 microM. Tissue incubation in the presence of insulin or high glucose concentrations significantly increased arginine transport in RPE but not in retina from control rats. Similarly, arginine uptake was enhanced in RPE, but not in the retina from streptozotocin-induced diabetic rats. However, NO content was two-fold higher in diabetic retina and RPE compared to that in the control rats. Such findings may suggest that diabetes induced an increase in NO levels in RPE, which may have brought about alterations in its functioning and in turn manifestations of diabetic retinopathy.


Assuntos
Arginina/metabolismo , Retinopatia Diabética/metabolismo , Óxido Nítrico/metabolismo , Epitélio Pigmentado Ocular/metabolismo , Retina/metabolismo , Animais , Diabetes Mellitus Experimental , Nitratos/metabolismo , Nitritos/metabolismo , Epitélio Pigmentado Ocular/citologia , Epitélio Pigmentado Ocular/fisiopatologia , Ratos , Ratos Long-Evans , Retina/citologia , Retina/fisiopatologia
15.
Neurochem Res ; 33(7): 1301-8, 2008 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-18274898

RESUMO

Glucose is the main fuel for energy metabolism in retina. The regulatory mechanisms that maintain glucose homeostasis in retina could include hormonal action. Retinopathy is one of the chemical manifestations of long-standing diabetes mellitus. In order to better understand the effect of hyperglycemia in retina, we studied glycogen content as well as glycogen synthase and phosphorylase activities in both normal and streptozotocin-induced diabetic rat retina and compared them with other tissues. Glycogen levels in normal rat retina are low (46 +/- 4.0 nmol glucosyl residues/mg protein). However, high specific activity of glycogen synthase was found in retina, indicating a substantial capacity for glycogen synthesis. In diabetic rats, glycogen synthase activity increased between 50% and 100% in retina, brain cortex and liver of diabetic rats, but only retina exhibited an increase in glycogen content. Although, total and phosphorylated glycogen synthase levels were similar in normal and diabetic retina, activation of glycogen synthase by glucose-6-P was remarkable increased. Glycogen phosphorylase activity decreased 50% in the liver of diabetic animals; it was not modified in the other tissues examined. We conclude that the increase in glycogen levels in diabetic retina was due to alterations in glycogen synthase regulation.


Assuntos
Diabetes Mellitus Experimental/metabolismo , Glicogênio/metabolismo , Retina/metabolismo , Animais , Glicemia/metabolismo , Córtex Cerebral/enzimologia , Eletroforese em Gel de Poliacrilamida , Glicogênio Fosforilase/metabolismo , Glicogênio Sintase/metabolismo , Fígado/enzimologia , Epitélio Pigmentado Ocular/enzimologia , Ratos , Ratos Long-Evans , Retina/enzimologia
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