CD36 gene deletion reduces muscle insulin sensitivity in mice by up-regulating PTP1B expression / 南方医科大学学报

OBJECTIVE@#To investigate the effect CD36 deficiency on muscle insulin signaling in mice fed a normal-fat diet and explore the possible mechanism.@*METHODS@#Wild-type (WT) mice and systemic CD36 knockout (CD36-/-) mice with normal feeding for 14 weeks (n=12) were subjected to insulin tolerance test (ITT) after intraperitoneal injection with insulin (1 U/kg). Real-time PCR was used to detect the mRNA expressions of insulin receptor (IR), insulin receptor substrate 1/2 (IRS1/2) and protein tyrosine phosphatase 1B (PTP1B), and Western blotting was performed to detect the protein expressions of AKT, IR, IRS1/2 and PTP1B in the muscle tissues of the mice. Tyrosine phosphorylation of IR and IRS1 and histone acetylation of PTP1B promoter in muscle tissues were detected using co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation (ChIP), respectively.@*RESULTS@#CD36-/- mice showed significantly lowered insulin sensitivity with obviously decreased area under the insulin tolerance curve in comparison with the WT mice (P < 0.05). CD36-/- mice also had significantly higher serum insulin concentration and HOMA-IR than WT mice (P < 0.05). Western blotting showed that the p-AKT/AKT ratio in the muscle tissues was significantly decreased in CD36-/- mice as compared with the WT mice (P < 0.01). No significant differences were found in mRNA and protein levels of IR, IRS1 and IRS2 in the muscle tissues between WT and CD36-/- mice (P>0.05). In the muscle tissue of CD36-/- mice, tyrosine phosphorylation levels of IR and IRS1 were significantly decreased (P < 0.05), and the mRNA and protein levels of PTP1B (P < 0.05) and histone acetylation level of PTP1B promoters (P < 0.01) were significantly increased as compared with those in the WT mice. Intraperitoneal injection of claramine, a PTP1B inhibitor, effectively improved the impairment of insulin sensitivity in CD36-/- mice.@*CONCLUSION@#CD36 is essential for maintaining muscle insulin sensitivity under physiological conditions, and CD36 gene deletion in mice causes impaired insulin sensitivity by up-regulating muscle PTP1B expression, which results in detyrosine phosphorylation of IR and IRS1.

Soluble insulin receptor and metabolic syndrome

The metabolic syndrome describes a group of signs that increase the likelihood for developing type 2 diabetes mellitus, cardiovascular diseases and some types of cancer. The action of insulin depends on its binding to membrane receptors on its target cells. We wonder if blood insulin could travel bound to proteins and if, in the presence of hyperinsulinemia, a soluble insulin receptor might be generated. We used young adult Wistar rats (which have no predisposition to obesity or diabetes), whose drinking water was added 20 % of sugar and that were fed a standard diet ad libitum for two and six months. They were compared with control rats under the same conditions, but that had running water for consumption. At two months, the rats developed central obesity, moderate hypertension, high triglyceride levels, hyperinsulinemia, glucose intolerance and insulin resistance, i.e., metabolic syndrome. Electrophoresis of the rats’ plasma proteins was performed, followed by Western Blot (WB) for insulin and for the outer portion of the insulin receptor. The bands corresponding to insulin and to the receptor external part were at the same molecular weight level, 25-fold higher than that of free insulin. We demonstrated that insulin, both in control animals and in those with hyperinsulinemia, travels bound to the receptor outer portion (ectodomain), which we called soluble insulin receptor, and that is released al higher amounts in response to plasma insulin increase; in rats with metabolic syndrome and hyperinsulinemia, plasma levels are much higher than in controls. Soluble insulin receptor increase in blood might be an early sign of metabolic syndrome.

El esqueleto como órgano endocrino: funciones metabólicas de la osteocalcina / The skeleton as an endocrine organ: metabolic functions of osteocalcin

El esqueleto es uno de los sistemas más grandes de un vertebrado y, como tal, es razonable especular que no puede funcionar aislado del resto del organismo. De hecho, sabemos que existen sistemas complejos de regulación cruzada entre el esqueleto y muchos otros órganos. Hoy poseemos herramientas que nos permiten realizar supresión genética en células o tejidos específicos. Esto nos ha permitido comprender cómo los órganos se comunican entre sí y ha revitalizado el concepto de fisiología del organismo como un todo. Efectivamente, los últimos años han sido testigos del descubrimiento de funciones inesperadas que ejerce el esqueleto y que afectan al organismo en su totalidad. Una de tales funciones reconocidas recientemente es el control del metabolismo energético, a través de la secreción de osteocalcina. La osteocalcina es una hormona producida por los osteoblastos que regula la secreción de insulina, la sensibilidad a esta hormona y el metabolismo energético. Los hallazgos iniciales suscitaron varias preguntas fundamentales sobre la naturaleza de la acción de la insulina sobre el hueso. Pero esto solo fue la punta del iceberg. Efectivamente, más adelante se descubrió, mediante el análisis de ratones que carecen del receptor de insulina (Ins R) solamente en osteoblastos, que la acción de la insulina sobre estas células favorecía la homeostasis de la glucosa en todo el cuerpo. Es importante destacar que esta función de la insulina en los osteoblastos opera mediante la regulación negativa de la carboxilación y la biodisponibilidad de la osteocalcina. Más aún, se observó que las vías de señalización de la insulina en los osteoblastos regulan positivamente no solo la formación sino también la resorción del hueso. Curiosamente, parece que las vías de señalización de la insulina en osteoblastos pueden inducir la activación de la osteocalcina mediante la estimulación de la actividad de los osteoclastos. De hecho, el bajo pH generado durante la resorción ósea es suficiente para desencadenar la descarboxilación (y subsiguiente activación) de la osteocalcina. En breve discutiremos dos nuevas proposiciones: 1) los osteoblastos son un blanco utilizado por la insulina para controlar la homeostasis de la glucosa en todo el organismo y 2) la resorción ósea desempeña un papel fundamental en la regulación de la activación de la osteocalcina. (AU)

The skeleton is one of the biggest systems in a vertebrate animal and, as such, it is reasonable to speculate that it cannot function isolated from the rest of the organism. In fact, we know that complex systems exist for the cross-regulation between the skeleton and several other organs. Today, we have the tools that allow us to perform genetic suppression in specific cells or tissues. This has allow us understand the mechanisms by which the organs communicate with each other and has revitalized the concept of organismal physiology as a whole. Studies conducted in recent years have uncovered unexpected functions performed by the skeleton. One of these is the control of global energy metabolism, through the secretion of osteocalcin, a protein produced by osteoblasts that acts as a hormone regulating insulin secretion, insulin sensitivity and energy expenditure. The evidence comes from the analysis of mice lacking insulin receptor (InsR) exclusively in osteoblasts. These mice have a global metabolic phenotype demonstrating that the action of insulin in osteoblasts promotes the homeostasis of glucose throughout the body. This action of insulin in osteoblasts is mediated by the negative regulation of the carboxylation (and bioavailability) of osteocalcin. The decarboxylation (and activation) of osteocalcin, in turn, occurs in the osteoclastic resorption pit. Briefly: the osteoblast is a target used by insulin to control the homeostasis of glucose throughout the body and bone resorption is the mechanism that regulates the activation of osteocalcin. (AU)

A digital volumetric tomography (DVT) study in the mandibular molar region for miniscrew placement during mixed dentition

OBJECTIVE: To assess bone thickness for miniscrew placement in the mandible during mixed dentition by using digital volumetric tomograph (DVT). MATERIAL AND METHODS: A total of 15 healthy patients aged 8-10 years old, with early exfoliated mandibular second deciduous molar, were included. DVT images of one quadrant of the mandible were obtained using Kodak extraoral imaging systems and analyzed by Kodak dental imaging software. The error of the method (EM) was calculated using Dahlberg's formula. Mean and standard deviation were calculated at 6 and 8 mm from the cementoenamel junction (CEJ).Paired t-test was used to analyze the measurements. RESULTS: Buccal cortical bone thickness, mesiodistal width and buccolingual bone depth at 6 mm were found to be 1.73 + 0.41, 2.15 + 0.49 and 13.18 + 1.22 mm, respectively; while at 8 mm measurements were 2.42 + 0.34, 2.48 + 0.33 and 13.65 + 1.25 mm, respectively. EM for buccal cortical bone thickness, mesiodistal width and buccolingual bone depth was 0.58, 0.40 and 0.48, respectively. The difference in measurement at 6 and 8 mm for buccal cortical plate thickness (P < 0.05) and buccolingual bone thickness (P < 0.05) was found to be significant, whereas for mesiodistal width it was insignificant (P > 0.05). CONCLUSION: Bone thickness measurement has shown promising evidence for safe placement of miniscrews in the mandible during mixed dentition. The use of miniscrew is the best alternative, even in younger patients. .

OBJETIVO: avaliar, por meio de tomografia volumétrica digital (TVD), a espessura óssea necessária para a instalação de mini-implante na arcada inferior durante a fase de dentição mista. MÉTODOS: um total de 15 pacientes saudáveis, com idades entre 8 e 10 anos, com segundo molar inferior decíduo irrompido recentemente, foram incluídos no presente estudo. Imagens de TVD da hemiarcada inferior foram obtidas utilizando sistemas de imagens extrabucais Kodak. As imagens foram analisadas por meio do programa de imagens Kodak. O erro do método (EM) foi calculado utilizando a fórmula de Dahlberg. Médias e desvios-padrão foram calculados de 6 a 8mm aquém da junção amelocementária. O teste t foi utilizado para a análise das medidas. RESULTADOS: a espessura do osso cortical vestibular, largura mesiodistal e profundidade óssea vestibulolingual, a 6mm, foram de 1,73 + 0,41; 2,15 + 0,49; e 13,18 + 1,22 mm, respectivamente. Já a 8mm, os valores foram de 2,42 + 0,34; 2,48 + 0,33; e 13,65 + 1,25mm. O EM para a espessura do osso cortical vestibular, largura mesiodistal e profundidade óssea vestibulolingual foi de 0,58, 0,40 e 0,48mm, respectivamente. A diferença entre as medidas a 6 e 8mm para a espessura do osso cortical vestibular (p < 0,05) e a espessura óssea vestibulolingual (p < 0,05) foi significativa, embora não tenha sido significativa para a largura mesiodistal (p < 0,05). CONCLUSÃO: a mensuração da espessura óssea demonstra evidências promissoras para a segura instalação de mini-implantes na arcada inferior e na fase de dentição mista. O uso de mini-implantes tem se mostrado a melhor alternativa, mesmo nos casos de pacientes mais jovens. .

Insulin Signaling Network in Cancer.

The primary function of insulin is viewed as a hormone that controls blood glucose level. However, there is growing evidence that aberrant insulin level and insulin-mediated signaling can lead to cancer development and progression. The insulin-cancer relationship has stemmed from various observational and epidemiological studies, which linked higher incidence of cancer with central obesity, type II diabetes and other conditions associated with increased levels of circulating insulin, insulin resistance and hyperinsulinemic states. Increased risk of developing a range of cancers is also seen with a certain treatment options used to lower blood glucose level in diabetic patients. While metformin monotherapy has the lowest risk of developing cancer, in comparison, treatment with insulin or insulin secretagogues shows more likelihood to develop solid cancers. Cellular signaling initiated by insulin provides a clue regarding these diverse cellular outcomes. This review discusses how the insulin enacts such diverse physiological effects and the insulin-cancer relationship, with focus on the role of insulin signaling in cancer.

Insulin Receptor Expression in Clear Cell Renal Cell Carcinoma and Its Relation to Prognosis

PURPOSE: Both insulin and insulin-like growth factor (IGF)-1 signaling are key regulators of energy metabolism, cellular growth, proliferation, and survival. The IGF-1 receptor (IGF-1R) is overexpressed in most types of human cancers including renal cell carcinoma (RCC) with poor prognosis. Insulin receptor (IR) shares downstream effectors with IGF-1R; however, the expression and function of IR in the tumorigenesis of renal cancer remains elusive. Therefore, we examined the expression of IR and its prognostic significance in clear cell RCC (CCRCC). MATERIALS AND METHODS: Immunohistochemical staining for IR was performed on 126 formalin-fixed paraffin-embedded CCRCC tissue samples. Eight of these cases were utilized for western blot analysis. The results were compared with various clinico-pathologic parameters of CCRCC and patient survival. RESULTS: IR was expressed in the nuclei of CCRCC tumor cells in 109 cases (87.9%). Higher IR expression was significantly correlated with the presence of cystic change, lower Fuhrman nuclear grade, lower pathologic T stage, and lower TNM stage, although it wasn't significantly related to diabetes status and patient survival. Western blot analyses supported the results of the immunohistochemistry studies. CONCLUSION: IR expression in CCRCC may be associated with favorable prognostic factors.

Insulin Receptor Expression in Clear Cell Renal Cell Carcinoma and Its Relation to Prognosis

PURPOSE: Both insulin and insulin-like growth factor (IGF)-1 signaling are key regulators of energy metabolism, cellular growth, proliferation, and survival. The IGF-1 receptor (IGF-1R) is overexpressed in most types of human cancers including renal cell carcinoma (RCC) with poor prognosis. Insulin receptor (IR) shares downstream effectors with IGF-1R; however, the expression and function of IR in the tumorigenesis of renal cancer remains elusive. Therefore, we examined the expression of IR and its prognostic significance in clear cell RCC (CCRCC). MATERIALS AND METHODS: Immunohistochemical staining for IR was performed on 126 formalin-fixed paraffin-embedded CCRCC tissue samples. Eight of these cases were utilized for western blot analysis. The results were compared with various clinico-pathologic parameters of CCRCC and patient survival. RESULTS: IR was expressed in the nuclei of CCRCC tumor cells in 109 cases (87.9%). Higher IR expression was significantly correlated with the presence of cystic change, lower Fuhrman nuclear grade, lower pathologic T stage, and lower TNM stage, although it wasn't significantly related to diabetes status and patient survival. Western blot analyses supported the results of the immunohistochemistry studies. CONCLUSION: IR expression in CCRCC may be associated with favorable prognostic factors.

The role of gut-liver axis in the restriction of intrauterine growth in a model of experimental gastroschisis / O papel do eixo intestino-fígado na restrição de crescimento intra-uterino em um modelo de gastrosquise experimental

PURPOSE: To evaluate the intrauterine growth restriction (IUGR) by the expression of IR-β, IRS-1, IRS-2, IGF-IRβ and Ikappaβ in experimental model of gastroschisis. METHODS: Pregnant rats at 18.5 days of gestation were submitted to surgery to create experimental fetal gastroschisis (term = 22 days) were divided in three groups: gastroschisis (G), control (C) and sham (S). Fetuses were evaluated for body weight (BW), intestinal (IW), liver (LW) and their relations IW/BW and LW/BW. IR-β and IGF-IRβ receptors, IRS-1 and IRS-2 substrates and Ikappaβ protein were analyzed by western blotting. RESULTS: BW was lower in G, the IW and IW / BW were greater than C and S (p<0.05) groups. The liver showed no differences between groups. In fetuses with gastroschisis, compared with control fetuses, the expression of IGF-IRβ (p<0.001) and Ikappaβ (p<0.001) increased in the liver and intestine, as well as IR-β (p<0.001) which decreased in both. In contrast to the intestine, IRS-1 (p<0.001) increased in the liver and IRS-2 decreased (p<0.01). CONCLUSION: The axis of the intestine liver has an important role in inflammation, with consequent changes in the metabolic pathway of glucose can contribute to the IUGR in fetuses with gastroschisis.

OBJETIVO: Avaliar a restrição de crescimento intra-uterino (RCIU) pela expressão de IR-β, IRS-1, IRS-2, IGF-IRβ e a via inflamatória do Ikappaβ no modelo de gastrosquise experimental. MÉTODOS: Ratas grávidas com 18,5 dias de gestação foram submetidas a cirurgia experimental para criar gastrosquise fetal (termo = 22 dias) e os fetos foram divididos em três grupos: gastrosquise (G), controle (C) e sham (S). Os fetos foram avaliados quanto ao peso corporal (BW), intestinal (IW), fígado (LW) e suas relações IW/BW e LW/BW. Os receptores IR-β e IGF-IRβ, os substratos IRS-1 e IRS-2 e a proteína Ikappaβ foram analisados por western blotting. RESULTADOS: O BW de G foi menor, o IW e IW/BW foram superiores a C e S (p < 0.05). O fígado não apresentou diferenças entre os grupos. Nos fetos com gastrosquise, quando comparados com fetos controles, a expressão de IGF-IRβ (p<0.001) e Ikappaβ (p<0.001) aumentou no fígado e intestino, assim como IR-β (p<0.001) que diminuiu em ambos. Inversamente ao intestino, IRS-1 (p<0.001) aumentou no fígado e IRS-2 diminuiu (p<0.01). CONCLUSÃO: O eixo do intestino fígado tem um papel importante na inflamação, com consequentes alterações na via metabólica de glicose que pode contribuir para a RCIU em fetos com gastrosquise.

Factores de riesgo asociados a síndrome metabólico en pacientes atendidos en familia laboratorios clínicos, Valencia, Estado Carabobo, Venezuela, periodo diciembre 2011 marzo 2012 / Risk factors associated with metabolic syndrome in patients attending family clinical laboratory, Valencia, Carabobo State, Venezuela, period december 2011 march 2012

El Síndrome Metabólico (SM), se puede definir como una serie de síntomas clínicos y biaoquímicos que se presentan, tanto en individuos obesos como delgados, aparentemente sanos. La importancia de SM radica en que las personas que lo padecen tienen mayor riesgo de desarrollar Enfermedades Cardiovasculares o Diabetes Mellitus tipo II (DM2). Determinar la incidencia de Síndrome Metabólico, sus factores de riesgo predominantes y la ralación existente con la insulina basal y post prandial en los pacientes que acudieron al Laboratorio Clínico Familia. Se estudiaron 100 pacientes de ambos sexos con edades comprendidas entre 13 a 71 años, que acudieron a Familia Laboratorios Clínicos. El diagnostico para síndrome metabólico fue definido de acuerdo a los criterios de la National Cholesterol Education Program (NECP)/Adult Treatment Panel III (ATP III). En esta investigación se observó un 75% de pacientes con estado nutricional alterado (44% obesos y 31% con sobrepeso) siendo estadísticamente significativo para la presencia de sobrepeso u obesidad respecto al estado nutricional normal (p<0,01). Se determinó una prevalencia para síndrome metabólico de 28% siendo el criterio más resaltante la circunferencia abdominal 96,4%, seguido de HDL-C bajo con 75% y triglicéridos altos en un 67,9%. Se midió la insulina basal obteniendo una prevalencia del 14% por encima del valor normal, donde solo el 7% fue diagnosticado con SM, el 35% presentó insulina post prandial elevada. Con los datos obtenidos se pudo observar que los valores de insulina postprandial, tomando como limite 60 µUI/ml, no se alteraron con respecto al número de criterios de diagnostico para SM, como tampoco hubo relación con la circunferencia abdominal, no se evidenció estadísticamente significativa entre la presencia de circunferencia abdominal por encima del límite establecido para cada sexo y la elevación de la insulina postprandial de 2 horas superiore a 60 µUI/ml., (p>0,05)...

Metabolic Syndrome (MS) can be defined as a series of clinical and biochemical symptoms that occur both in obese and lean apparently healthy. The importance of the SM is that people with the condition are at increased risk od developing cardiovascular disease and type II diabetes mellitus (T2DM). To determine the incidence of metabolic syndrome prevalen risk factors and the relationship with basal insulin and postprandial in patients presenting to the Family Clinical Laboratory. We studied 100 patients of both sexes aged 13-71 years, who attented Family Clinical Laboratory. The diagnosis for metabolic syndrome was defined according to the criteria of the National Cholesterol Education Program (NECP)/Adult Treatment Panel III (ATP III). In this survery found 75% of patients with altered nutritional status (44% obese and 31% overweight) were statisfically significant for presence of overweight or obese compared to normal nutritional status (p<0.01). The sero prevalence for metabolic syndrome of 28% being the most salient criterion waist circumference 96.4%, followed by low HDL-C by 75% and triglycerides by 67.9%. Basal insulin was measured by obtaining a prevalence of 14% above the normal value, where only 7% were diagnosed with MS, 35% had elevated postprandial insulin values, taking as limit 60 mUL/ml, were not altered with respect to the number of diagnostic criteria for MS, as there was no relationship with waist cirscumference, no evidence statiscally significant association between the presence of abdominal circumference above the limit established for each sex and elevated postprandial insulin over 2 hours 60 mUL/ml (p<0.05). This study was correlational, cross and not experimental, which found that the predominant risk for factor was by the abdominal circumference and overweight and obesity over the range for both sexes. No association between postprandial insulin, the prevalence of risk factors and waist circumference.

Hepatic STAMP2 decreases hepatitis B virus X protein-associated metabolic deregulation

Six transmembrane protein of prostate 2 (STAMP2) plays a key role in linking inflammatory and diet-derived signals to systemic metabolism. STAMP2 is induced by nutrients/feeding as well as by cytokines such as TNFalpha, IL-1beta, and IL-6. Here, we demonstrated that STAMP2 protein physically interacts with and decreases the stability of hepatitis B virus X protein (HBx), thereby counteracting HBx-induced hepatic lipid accumulation and insulin resistance. STAMP2 suppressed the HBx-mediated transcription of lipogenic and adipogenic genes. Furthermore, STAMP2 prevented HBx-induced degradation of IRS1 protein, which mediates hepatic insulin signaling, as well as restored insulin-mediated inhibition of gluconeogenic enzyme expression, which are gluconeogenic genes. We also demonstrated reciprocal expression of HBx and STAMP2 in HBx transgenic mice. These results suggest that hepatic STAMP2 antagonizes HBx-mediated hepatocyte dysfunction, thereby protecting hepatocytes from HBV gene expression.

Molecular mechanism of insulin resistance.

Free fatty acids are known to play a key role in promoting loss of insulin sensitivity,thereby causing insulin resistance and type 2 diabetes.However,the underlying mechanism involved is still unclear.In searching for the cause of the mechanism,it has been found that palmitate inhibits insulin receptor (IR)gene expression,leading to a reduced amount of IR protein in insulin target cells. PDK1-independent phosphorylation of PKC(eta) causes this reduction in insulin receptor gene expression.One of the pathways through which fatty acid can induce insulin resistance in insulin target cells is suggested by these studies.We provide an overview of this important area,emphasizing the current status.

Orally active insulin mimics: where do we stand now?

The war against diabetes through the development of new drugs is an ongoing continuous process to counter the alarming global increase in the prevalence of diabetes and its complications, particularly in developing countries like India. Unfortunately, the speed with which our knowledge of diabetes and its effects is expanding is not matched by the availability of new drugs. Following the identification of the insulin receptor (IR), its intrinsic kinase activity and molecular cloning, many studies have looked at IR as an ideal drug target. This review summarizes in brief the latest advancements in this field with particular reference to the current situation in respect of the development of orally active insulin mimetics in the treatment of type 2 diabetes.

The regulatory mechanism of phosphatidylinositol 3-kinase by insulin in 3T3 L1 fibroblasts: phosphorylation-independent activation of phosphatidylinositol 3-kinase

Phosphatidylinositol (PI) 3-kinase plays an important role in transducing the signals of various growth factor receptors. However, the regulatory mechanism of PI3-kinase activity by these growth factor receptors is not completely understood. Therefore, we attempted to clarify the regulatory mechanism of PI3-kinase using insulin and 3T3 L1 fibroblasts. Our results showed that insulin stimulated PI3-kinase activity seven-fold and concomitantly phosphorylated a p85 subunit at the tyrosine residue. However, this tyrosine phosphorylation was not significant in the activation of PI3-kinase as the PI3-kinase pulled down by the overexpressed GST-p85 fusion protein showed as high an activity as the immunoprecipitated one. The p110 subunit was phosphorylated at both serine and tyrosine residues without insulin treatment. Since the phosphorylation state was not changed by insulin. The results suggested that phosphorylation of the p110 subunit does not control PI3-kinase activity. Finally, it was shown that the insulin receptor substrate-1 (IRS-1) binding to PI3-kinase was not sufficient for full activation because the amount of IRS-1 pulled down by the GST-p85 fusion protein reached almost maximum, after incubation with insulin-treated cell lysates for 20 min, whereas PI3-kinase activity reached its maximum only after incubation for 5 h. All results suggest that the phosphorylation of p85 subunit at tyrosine residues and phosphorylation of p110 subunit at tyrosine or serine residues are not functionally significant in the regulation of PI3-kinase activity. They also suggest that P13-kinase is needed to bind to other protein(s) as well as the insulin receptor substrate-1 for full activation.

Decreased basal and acute insulin-stimulated effect on the uptake of glucose and amino acid in vitro by thyroid glands from streptozotocin-diabetic rats

Since experimental diabetes in rats and mice is associated with impairment of several aspects of thyroid function, we determined glucose and amino acid uptake in vitro by isolated thyroid glands from normal and streptozotocin-diabetic rats. Adult male Wistar rats weighing 150-200 g were used. Diabetes was induced by intraperitoneal injection streptozotocin (STZ, 65 mg/kg body weight) and after five days only rats with blood glucose levels higher than 250 mg/dl were used. The thyroid glands were preincubated in Krebs-Ringer bicarbonate buffer in the presence or absence of insulin (0.7 nM to 7 muM) for 90 min and then incubated with the same concentration of the hormone or its vehicle plus 0.2 muCi of [l-l4C]-2-deoxy-D-glucose ([l4C]DG) or [l4C] methylaminoisobutyric acid ([l4C]MeAIB) for 15 to 180 min. The uptake of [l4C]DG or [l4C]MeAIB by the thyroid glands of normal rats increased as a function of incubation time, and the presence of insulin (7 muM) induced a significant increase of labelled DG from 3.30 ñ 0.11 to 4.16 ñ O.12 and of labelled MeAIB from 1.79 ñ 0.06 to 3.10 ñ 0.17 tissue/medium ratio (TIM) after 45 min of incubation. The lowest concentration of insulin that increased both [l4C]DG and [l4C]MeAIB transport was 7 nM. Thyroid glands from STZ rats exhibited lower basal values of [l4C]DG (4.03 ñ 0.11 T/M) or [l4C]MeAIB uptake (1.05 ñ 0.05 T/M) than glands from normal rats (4.62 ñ 0.13 and 1.70 ñ 0.O8 T/M, respectively). Insulin produced a stimulatory effect on the transport of both substrates in STZ rats. However, the maximals stimulating concentration of the hormone did not restore[l4C]DG and [l4C)MeAIB uptake to control values (4.89 + O.17 in STZ rats versus 5.44 ñ 0.17 T/M in controls for [l4C]DG, and 1.51 ñ 0.11 in STZ rats versus 2.19 ñ 0.10 T/M in controls for [l4C]MeAIB). These results indicate that insulin exerts a direct action on the thyroid gland, and its absence or reduction affects thyroid metabolism, contributing, at least in part, to the abnormality in thyroid function associated with diabetes mellitus.

Insulin and IGF-I stimulated RNA synthesis in primary cultures of neuronal cells: involvement of cyclic AMP and protein kinase-c

La insulina y el IGF-I promueven el crecimiento de las células neuronales de rata en cultivo primario. Con el objeto de investigar el mecanismo de transducción de señales hormonales en este sistema biológico, estudiamos el efecto de agonistas de AMP cíclico y un estimulador de la proteína kinasa-C sobre la síntesis de ARN basal e inducida por hormonas. Los agentes que aumentan los níveles de AMP cíclico endógenos (foraskolina, dibutiril-AMP cíclico, toxina colérica) bloquearon los efectos estimuladores de la insulina y el factor de crecimiento; el dibutiril AMP cíclico, sin embargo, no alteró la unión de las hormonas a sus receptores. Aunque a diferencia de los agentes antes mencionados, el ester de forbol elevó significativamente la síntesis de ARN basal; este, no obstante, inhibió la estimulación por la insulina. Este último efecto probablemente fue mediado por un incremento en los niveles de AMP cíclico, como se ha encontrado en otros tipos de células. La estaurosporina, un inhibidor de la proteína kinasa-C, también bloqueó los efectos de la insulina sobre la síntesis de RNA