Metaplastic carcinoma of the breast with chondroid differentiation (matrix-producing carcinoma): study of the diagnostic cost-effectiveness of fine-needle aspiration biopsy and needle core biopsy.

UNLABELLED: Metaplastic carcinoma with chondroid differentiation (MMPC) is a subtype of breast metaplastic carcinoma with mesenchymal differentiation. Although fine-needle aspiration (FNAB) and core-needle biopsy (CNB) are commonly used for the diagnosis of breast cancer, not enough studies proving the diagnostic cost-effectiveness of these techniques for the identification of MMPC have been published so far. The aim of this study was to investigate the concordance between the presurgical diagnosis using FNAB/CNB and the definitive diagnosis in the surgical specimen in pure MMPC. A case of MMPC is also reported. STUDY DESIGN: All cases of MMPC diagnosed in our institution from 1995 to 2011 were reviewed. The presence of chondroid differentiation in cytological studies or biopsies and the proportion of chondroid matrix in the surgical specimen were evaluated. RESULTS: A total of 13 cases of pure MMPC were collected. The diagnosis was suspected in 25% of FNABs and was rendered in 40% of CNBs. CONCLUSIONS: The chondroid component in MMPC is hard to identify by FNAB and CNB. The random distribution and proportion of the chondroid differentiation in the tumour and the expertise in performing the technique and in identifying the chondroid component may play an important role in the diagnosis of MMPC using these techniques.

Risk factors for lymphedema after breast surgery: A prospective cohort study in the era of sentinel lymph node biopsy.

INTRODUCTION: The Objective was to investigate the incidence of lymphedema after breast cancer treatment and to analyze the risk factors involved in a tertiary level hospital. METHODS: Prospective longitudinal observational study over 3 years post-breast surgery. 232 patients undergoing surgery for breast cancer at our institution between September 2013 and February 2018. Sentinel lymph node biopsy (SLNB) or axillary lymphadenectomy (ALND) were mandatory in this cohort. In total, 201 patients met the inclusion criteria and had a median follow-up of 31 months (range, 1-54 months). Lymphedema was diagnosed by circumferential measurements and truncated cone calculations. Patients and tumor characteristics, shoulder range of motion limitation and local and systemic therapies were analyzed as possible risk factors for lymphedema. RESULTS: Most cases of lymphedema appeared in the first 2 years. 13.9% of patients developed lymphedema: 31% after ALND and 4.6% after SLNB (p < 0.01), and 46.7% after mastectomy and 11.3% after breast-conserving surgery (p < 0.01). The lymphedema rate increased when axillary radiotherapy (RT) was added to radical surgery: 4.3% for SLNB alone, 6.7% for SLNB + RT, 17.6% for ALND alone, and 35.2% for ALND + RT (p < 0.01). In the multivariate analysis, the only risk factors associated with the development of lymphedema were ALND and mastectomy, which had hazard ratios (95% confidence intervals) of 7.28 (2.92-18.16) and 3.9 (1.60-9.49) respectively. CONCLUSIONS: The main risk factors for lymphedema were the more radical surgeries (ALND and mastectomy). The risk associated with these procedures appeared to be worsened by the addition of axillary radiotherapy. A follow-up protocol in patients with ALND lasting at least two years, in which special attention is paid to these risk factors, is necessary to guarantee a comprehensive control of lymphedema that provides early detection and treatment.

Relationship Between Stink Bug Populations in Winter Shelters and Atmospheric Variables in Soybean Growing Areas in Southern Brazil.

Stink bugs (Pentatomidae) are among the main entomological problems in the international farming. Their ability in using alternative plants (refuges) during the off-season is one of the reasons that led them to the status of key pests in several crops. Like other insect species, stink bugs are subject to atmospheric variations. Therefore, the objective of this experiment was to evaluate the abundance, the co-occurrence, and its variations according to the weather in the off-season. The work was conducted between 2014 and 2018, in the municipality of Cruz Alta, state of Rio Grande do Sul (RS), Brazil. Every year, refuges formed by Poaceae and located around the cropped area were evaluated in the second fortnight of June, corresponding to the beginning of the winter solstice. Atmospheric variables corresponding to the evaluation period were used to explain the variation in the populations. In short, our results demonstrated interannual variations in the population abundance of stink bugs in the evaluated refuges. We also found variations in the co-occurrence between species. Finally, we demonstrate the trend in the increase in these refuges in years with cold and dry off-seasons.

Regulation of System A amino-acid transport activity by phospholipase C and cAMP-inducing agents in skeletal muscle: modulation of insulin action.

The present study was designed to investigate the effect of phospholipase C and compounds known to promote synthesis of cAMP on System A transport activity under basal and insulin-stimulated conditions in the incubated muscle. In parallel, we also examined the effect of these agents on muscle glucose transport activity. Phospholipase C caused marked stimulation of alpha-(methyl)-aminoisobutyric acid (MeAIB--a System-A-specific analogue) uptake uptake and that of 3-O-methylglucose by the incubated muscle. In contrast, the activatory effect of insulin on System A was largely inhibited by phospholipase C. The effects of phospholipase C on transport processes differed from the effects provoked by phorbol esters (TPA), indicating that they are not just a consequence of TPA-sensitive protein kinase C activation. Agents such as isoproterenol, cholera toxin or forskolin, known cAMP inducers, caused glycogen depletion and stimulation of lactate production in the incubated muscle. However, these agents did not alter basal or insulin-stimulated MeAIB uptake. Isoproterenol and cholera toxin did not affect maximal stimulation of 3-O-methylglucose uptake caused by insulin. Our data indicate that System A transport is activated by phospholipase C in skeletal muscle, and that this effect is not due simply to activation of TPA-sensitive isoforms of protein kinase C. The effect of insulin on System A is reduced by either phospholipase C or TPA, which suggests the mediation of protein kinase C. On the basis of the lack of effect of cAMP-inducing agents on insulin-stimulated System A and glucose transport activities, we conclude that cAMP-dependent protein kinase does not cause any generalized blockade of insulin action in skeletal muscle, in contrast to what has been reported in other cell types.

GLUT1 glucose transporter gene transcription is repressed by Sp3. Evidence for a regulatory role of Sp3 during myogenesis.

GLUT1 glucose transporters are highly expressed in proliferating and transformed cells as well as in tissues during fetal life. However, the mechanisms that regulate GLUT1 gene expression remain largely unknown. Here, we demonstrate that Sp3 proteins bind to the GLUT1 proximal promoter gene and inhibit transcriptional activity in muscle and non-muscle cells. Two different Sp3 translational products (110 and 74 kDa) derived from differential translational initiation were detected in nuclear extracts from myoblast cells, and both Sp3 protein species inhibited GLUT1 gene transcriptional activity. The inhibitory effect of Sp3 was dominant over the stimulatory effect of Sp1 on transcriptional activity of GLUT1 gene. Furthermore, abolition of Sp3 binding to the proximal promoter of GLUT1 gene completely blocked the response to Sp3. We provide evidence that the expression of Sp3 protein is subject to regulation in muscle cells and that this is likely to control GLUT1. Thus, Sp3 protein was up-regulated in the absence of changes in Sp1 early after the induction of IGF-II-dependent myogenesis. Furthermore, forced over-expression of MyoD caused an enhancement in the cellular Sp3/Sp1 ratio which was concomitant to a reduced GLUT1 expression. Later during myogenesis, Sp3 expression was substantial whereas Sp1 was markedly down-regulated. In summary, we provide direct evidence that the transcription factor Sp3 represses gene expression in non-muscle and muscle cells and this is likely to operate in fetal heart by binding to the GLUT1 gene promoter. This is the first description of a repressor of GLUT1 gene transcription. Furthermore, we propose that variations in the ratio of Sp3 versus Sp1 regulate GLUT1 promoter activity and this is crucial in the down-regulation of GLUT1 associated to myogenesis.

[Simultaneous location of non-palpable breast neoplasms and sentinel node (SN) study by radioisotopic techniques]. / Localización simultánea de neoplasias de mama no palpables y estudio del ganglio centinela (GC) mediante técnicas radioisotópicas.

OBJECTIVE: To obtain correct location of non-palpable breast lesions, with high suspicion of malignancy and detection of SN by radiosotopic techniques. MATERIAL AND METHODS: Thirty-one patients whose ages ranged from 35 to 79 years, with non-palpable breast lesions detected by mammography and/or ultrasonography were studied. All the patients were diagnosed of breast cancer and treated with primary chemotherapy. All the patients underwent total axillary dissection. At 24 hours of the intervention, all patients received one dose of 37 MBq (1 mCi) of 99mTc labeled macroaggregated albumin (MAA) in the center of the lesion by ultrasonographic guide. Scintigraphic images were performed in anterior and lateral projections (in prone decubitus with hanging breast) to verify the correct location of the radiopharmaceutical. After, a study of the SN was performed by subdermal administration of an 18 MBq (0.5 mCi) dose of 99mTc labeled nanocolloid. The SN site was labeled on the skin with indelible ink. The intrasurgical site of the breast lesion and SN was performed using a gamma detector probe. Correct placement of the intralesional radiopharmaceutical, existence of disease free borders and histological study of SN were performed by the pathologist in the surgical act. The differed pathology study was performed with hematoxilin-eosin and immunohistochemistry. RESULT: In 29 of the 31 lesion sites, there was good placement of the radiotracer (93.5 %). There was 1 case of contamination of the needle pathway and another that did not coincide with the lesion, due to poor placement. Location of the SN was 96 % in the axilla and 4 % in axilla and internal mammary chain. The SN was located in surgery in 28/31 patients (90 %). CONCLUSION: Simultaneous radioguided location of the hidden breast lesions and sentinel node is a simple method, which is well tolerated by the patients and can be done in a single operation act.

Insulin resistance of skeletal muscle during pregnancy is not a consequence of intrinsic modifications of insulin receptor binding or kinase activities.

Insulin action in skeletal muscle is markedly depressed at late pregnancy. The purpose of this study was to investigate whether insulin resistance of skeletal muscle during pregnancy is associated to intrinsic alterations in the biological activities of insulin receptor. To that end, insulin receptors from mixed, red and white skeletal muscle from control and 19-20 days pregnant rats were partially purified and insulin binding and tyrosine kinase activities were evaluated. Muscle insulin receptors from diabetic rats were also studied provided that changes in receptor number and tyrosine kinase activities had been clearly substantiated. Total high affinity insulin binding sites expressed either per gram of tissue or per milligram of protein were similar in muscles from control and pregnant rats, in contrast to diabetic rats in which an increased high affinity receptor number was observed. No differences in affinity were detected for high affinity binding sites in any of the groups investigated. The integrity of the partially purified insulin receptors from control and pregnant groups was identical as determined by affinity cross-linking of [125I-TyrB26]insulin to the receptor and by beta-subunit phosphorylation. Autophosphorylation of the beta-subunit and the pattern of phosphopeptides obtained after digestion of phosphorylated beta-subunit with trypsin, elastase, and staphylococcal V8 protease were indistinguishable in control and pregnant groups. Tyrosine receptor kinase was also similar in receptor preparations from control and pregnant muscle. This is in contrast to diabetes in which a defective tyrosine kinase was confirmed. In order to detect possible differences due to the fiber type, further sets of experiments were performed in receptor preparations from red and white muscle. In keeping with previous data, tyrosine kinase activity of the insulin receptor was 2.5-fold greater in red muscle than white muscle; however, under these conditions, receptor kinase activity was unmodified in preparations from pregnant rats in red and white muscle fibers. Recent evidence has revealed the existence of an insulin binding inhibitor in muscle extracts. We detected the presence of such an inhibitor in the flow-through fraction after WGA chromatography. This inhibitory activity was found to be greater in muscle extracts obtained from pregnant rats as compared to fractions from control rats. We conclude that insulin resistance of skeletal muscle at late pregnancy is not explained by intrinsic modifications of insulin receptor binding or kinase activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of hexose transport by metformin in L6 muscle cells in culture.

L6 muscle cells grown in culture to the stage of fused myotubes were incubated with the oral hypoglycemic drug metformin to test the effects of this drug on glucose transport. Metformin increased the initial rate of uptake of 2-deoxyglucose and 3-O-methylglucose. The effect was time dependent, with half-maximal stimulation at 5-6 h and maximal stimulation by about 16 h. The stimulation of hexose uptake was not prevented by cycloheximide. In 15 mM glucose medium, the basal rate of transport was lower than in 5 mM glucose medium. The stimulation of hexose uptake by metformin was comparable in absolute units in both media; hence, relative to basal uptake, stimulation was greater in the high glucose medium than in the low glucose medium. In 5 mM glucose medium, half-maximal stimulation was obtained with 800 microM metformin when tested for 24 h. The stimulation of hexose transport by metformin was only detectable in fused myotubes and not in perfusion myoblasts. No significant changes were observed in glucose transporter levels in total cell membranes from L6 myotubes (measured as D-glucose-protectable binding sites for cytochalasin-B) or in the total levels of the immunoreactive glucose transporter isoforms GLUT4 or GLUT1. It is concluded that metformin stimulates hexose transport into differentiated muscle cells by acting at a posttranslational level. We speculate that this might also constitute the basis for the ability of the drug to lower glycemia in diabetic individuals.

Characterization of two distinct intracellular GLUT4 membrane populations in muscle fiber. Differential protein composition and sensitivity to insulin.

A major objective for the understanding of muscle glucose disposal is the elucidation of the intracellular trafficking pathway of GLUT4 glucose carriers in the muscle fiber. In this report, we provide functional and biochemical characterization of two distinct intracellular GLUT4 vesicle pools obtained from rat skeletal muscle. The two pools showed a differential response to insulin; thus, one showed a marked decrease in GLUT4 levels but the other did not. They also showed a markedly different protein composition as detected by quantitative vesicle immunoisolation analysis. The GLUT4 pool showing no response to insulin contained SCAMP proteins and the vSNARE proteins VAMP2 and cellubrevin, whereas only VAMP2 was found in the insulin-recruitable GLUT4 pool. SDS-PAGE and further silver staining of the immunoprecipitates revealed discrete polypeptide bands associated to the insulin-sensitive pool, and all these polypeptide bands were found in the insulin-insensitive population. Furthermore, some polypeptide bands were exclusive to the insulin-insensitive population. The presence of cellubrevin and SCAMP proteins, endosomal markers, suggest that the insulin-insensitive GLUT4 membrane population belongs to an endosomal compartment. In addition, we favor the view that the insulin-sensitive GLUT4 membrane pool is segregated from the endosomal GLUT4 population and is undergoes exocytosis to the cell surface in response to insulin. Intracellular GLUT4 membranes obtained from skeletal muscle contain cellubrevin, and VAMP2 and GLUT4-vesicles from cardiomyocytes also contain cellubrevin. This suggests that vSNARE proteins are key constituents of GLUT4 vesicles. The presence of the tSNARE protein SNAP25 in skeletal muscle membranes and SNAP25 and syntaxin 1A and syntaxin 1B in cardiomyocyte plasma membranes further suggest a role of the SNAREs in GLUT4 trafficking in muscle.

System A transport activity is stimulated in skeletal muscle in response to diabetes.

We have studied the activity of system A transport in skeletal muscle during experimental diabetes. Five days after streptozotocin injection, rats showed a marked hyperglycemia and a substantial decrease in the content of GLUT-4 protein in skeletal muscle and adipose tissue. Under these conditions, basal uptake of 2-(methyl)aminoisobutyric acid (MeAIB), an index of system A transport activity, was enhanced in extensor digitorum longus (EDL) muscles from diabetic rats compared to controls. Furthermore, insulin-stimulated MeAIB uptake by the incubated EDL and soleus muscles was markedly greater in diabetic than in control rats. The derepressive phase of adaptive regulation was partially blocked in the diabetic muscle, and incubation of muscles for 3 h in the absence of amino acids led to a lower stimulation of system A transport activity in muscles from diabetic groups compared to controls. We propose that the activated system A might participate in the enhanced alanine release from muscle cells that occurs in diabetes.

Regulation of glucose transport, and glucose transporters expression and trafficking in the heart: studies in cardiac myocytes.

Cardiac muscle is characterized by a high rate of glucose consumption. In the absence of insulin, glucose transport into cardiomyocytes limits the rate of glucose utilization and therefore it is important to understand the regulation of glucose transporters. Cardiac muscle cells express 2 distinct glucose transporters, GLUT4 and GLUT1; although GLUT4 is quantitatively the more important glucose transporter expressed in heart, GLUT1 is also expressed at a substantial level. In isolated rat cardiomyocytes, insulin acutely stimulates glucose transport and translocates both GLUT4 and GLUT1 from an intracellular site to the cell surface. Recent evidence indicates the existence of at least 2 distinct intracellular membrane populations enriched in GLUT4 with a different protein composition. Elucidation of the intracellular location of these 2 GLUT4 vesicle pools in cardiac myocytes, their role in GLUT4 trafficking, and their relation to insulin-induced GLUT4 translocation needs to be addressed.

Effect of benzyl succinate on insulin receptor function and insulin action in skeletal muscle: further evidence for a lack of spare high-affinity insulin receptors.

Benzyl succinate inhibited insulin binding and tyrosine receptor kinase in a concentration-dependent manner in the partially purified insulin receptor preparation from rat skeletal muscle. Benzyl succinate lowered the apparent number of high-affinity insulin binding sites. We have made use of the inhibitory effect of benzyl succinate to investigate the possible presence of spare high-affinity insulin receptors in muscle. Benzyl succinate inhibited the effect of a supramaximal concentration of insulin on 3-O-methylglucose uptake, 2-(methylamino)isobutyric acid uptake and lactate production by the incubated muscle. Furthermore, the inhibitory effect of benzyl succinate on insulin binding in vitro closely correlated with its inhibitory effect on insulin action in vivo. These findings suggest the absence of spare high-affinity insulin receptors in skeletal muscle. In contrast to data obtained in skeletal muscle, benzyl succinate did not affect the maximally insulin-stimulated glucose transport, although it caused a marked decrease in insulin sensitivity in isolated rat adipocytes, for which the existence of spare insulin receptors is well documented.

Benfluorex improves muscle insulin responsiveness in middle-aged rats previously subjected to long-term high-fat feeding.

It has been reported that benfluorex ameliorates the insulin resistance induced by high-fat feeding when its administration is initiated at the same time as the change in diet. Here we have examined whether benfluorex reverses insulin resistance when this is established in middle-aged rats chronically maintained on a high-fat diet. Untreated 12-month-old rats that had been subjected to a high-fat diet for the last 6 months showed markedly lower insulin-induced stimulation of 2-deoxyglucose uptake by strips of soleus muscle and a reduced expression of GLUT4 glucose carriers in skeletal muscle. However, animals subjected to the same protocol but treated with benfluorex during the last month of high-fat feeding showed marked improvement in insulin-stimulated glucose transport by soleus muscle. Benfluorex treatment caused a substantial increase in the content of GLUT4 protein in white muscle; however, GLUT4 levels in red muscle remained low. Our results indicate: (i) that benfluorex treatment in middle-aged rats reverses the insulin resistance induced by high-fat feeding in soleus muscle; (ii) benfluorex is active even when it is administered once the insulin-resistant state is already established; (iii) reversion of muscle insulin resistance by benfluorex can occur independently of modifications in GLUT4 protein expression.

Trafficking pathway of GLUT4 glucose transporters in muscle (review).

Skeletal muscle is a major glucose-utilizing tissue in the absorptive state and alterations in muscle insulin-stimulated glucose uptake lead to derangements in whole body glucose disposal. The major glucose transporter expressed in skeletal muscle is the GLUT4 isoform. In the muscle fiber, GLUT4 undergoes insulin-stimulated translocation to T-tubules and to sarcolemma and it represents a pharmacological target for the treatment of diabetes mellitus, insulin-resistant states or in cardiac dysfunction. We review recent studies describing the characterization of the cellular steps followed by GLUT4 in muscle and we propose several working models for an integrated structure of the GLUT4 trafficking pathway.

Inhibitors such as staurosporine, H-7 or polymyxin B cannot be used in skeletal muscle to prove the role of protein kinase C on insulin action.

The precise role of protein kinase C in insulin action in skeletal muscle is not well defined. Based on the fact that inhibitors of protein kinase C block some insulin effects, it has been concluded that some of the biological actions of insulin are mediated via protein kinase C. In this study, we present evidence that inhibitors of protein kinase C such as staurosporine, H-7 or polymyxin B cannot be used to ascertain the role of protein kinase C in skeletal muscle. This is based on the following experimental evidences: a) staurosporine, H-7 and polymyxin B markedly block in muscle the effect of insulin on System A transport activity; however, this effect of insulin is not mimicked in muscle by TPA-induced stimulation of protein kinase C, b) H-7 and polymyxin B block insulin action on System A transport activity in an additive manner to the inhibitory effect of phorbol esters, c) staurosporine, H-7 and polymyxin B block the effect of insulin on lactate production, a process that is activated by insulin and TPA in an additive fashion, and d) staurosporine completely blocks the tyrosine kinase activity of insulin receptors partially purified from rat skeletal muscle.

Sentinel node localization in patients with non-palpable breast cancer.

The aim of this study was to demonstrate that radionuclide sentinel node detection can be applied to patients with non-palpable breast cancer. One hundred and ten consecutive women with unilateral breast cancer were studied. Group 1 was made up of 80 patients with palpable breast cancer (mean age, 58 years) and group 2 of 30 patients with non-palpable breast cancer detected mammographically (mean age, 55 years). Tc-nanocolloid (111 MBq) was injected peritumorally in palpable tumours, and in the tumour area (ultrasound guided) in non-palpable tumours. At 2 h post-injection, anterior and lateral scintigrams were obtained from patients in the supine position. The location of the sentinel node was marked on the patient's skin. Patients with non-palpable tumours were moved to the surgery room 3 h later, and those with palpable tumours 24 h later. The histopathological study included three haematoxylineosin sections and immunochemistry. All patients underwent axillary lymphadenectomy. The sentinel node was detected in 67 cases (84%) in group 1 and in 28 cases (93%) in group 2. In four patients (5%) in group 1 and two patients (7%) in group 2, no axillary sentinel node was detected in the surgical bed, although it had been seen in scintigraphy. In nine patients (11%) in group 1, neither scintigraphic nor surgical detection was successful. Skip metastasis was seen in six cases (10%) of palpable tumours and in one case (4%) of non-palpable tumours. It can be concluded that non-palpable breast tumours cannot be considered an exclusion criterion for sentinel node localization and biopsy. Ultrasonography-guided injection, followed by scintigraphic and surgical detection of the sentinel node, may help in the management of patients with non-palpable breast tumours.

Subdermal re-injection: a method to increase surgical detection of the sentinel node in breast cancer without increasing the false-negative rate.

PURPOSE: The aim of this study was to evaluate in breast cancer whether subdermal (SB) re-injection improves surgical detection (SD) of the sentinel node (SN) in patients with negative lymphoscintigraphy on peritumoral (PT) injection, without increasing the false-negative (FN) rate. METHODS: Group I comprised 261 patients with invasive breast cancer >3 cm and clinically negative axilla treated with primary chemotherapy. Axillary lymphadenectomy was performed in all of these patients. Group IA comprised 201 patients with PT injection, while group IB comprised 60 patients with SB injection in the tumour quadrant. Group II comprised 652 patients with breast cancer <3 cm; in 73 of these patients with negative lymphoscintigraphy, SB re-injection was performed. For lymphoscintigraphy, 37-55 MBq (99m)Tc-albumin nanocolloid in 1 ml was used for PT injection, and 18 MBq in 0.2 ml for SB injection. Five-minute images were obtained 2 h p.i. for PT injection and 20-30 min p.i. for SB injection. SD was performed 4 or 24 h p.i. Lymphoscintigraphic (LD), surgical and internal mammary (IM) detection rates were calculated. In group I, FN, negative predictive value (NPV) and accuracy (A) were calculated. Statistical analysis was performed using the chi-square test. RESULTS: In percentages, results were as follows: Group IA: SD: 84.1, FN: 13.6, NPV: 88.9, A: 78.6, IM: 14.5*. Group IB: SD: 90, FN: 0, NPV: 100, A: 90, IM: 1.7* (*p<0.025). Group II: PT injection only: LD: 82.4, SD: 94; PT injection+SB re-injection: LD: 90, SD: 98.5. SD was 97.8** in patients with positive lymphoscintigraphy and 58.5** when lymphoscintigraphy was negative (**p<0.001). CONCLUSION: For correct staging, including extra-axillary drainage, peritumoural injection should first be performed. When the SN is not visualised, and only in those cases, SB re-injection should be performed, which increases the SD rate without increasing the FN rate.

Mechanisms regulating GLUT4 glucose transporter expression and glucose transport in skeletal muscle.

Skeletal muscle is a major glucose-utilizing tissue in the absorptive state and the major glucose transporter expressed in muscle in adulthood is GLUT4. GLUT4 expression is exquisitely regulated in muscle and this seems important in the regulation of insulin-stimulated glucose uptake by this tissues. Thus, muscle GLUT4 overexpression in transgenic animals ameliorates insulin resistance associated with obesity or diabetes. Recent information indicates that glut4 gene transcription is regulated by a number of factors in skeletal muscle that include MEF2, MyoD myogenic proteins, thyroid hormone receptors, Kruppel-like factor KLF15, NF1, Olf-1/Early B cell factor and GEF/HDBP1. In addition, studies in vivo indicate that under normal conditions the activity of the muscle-specific GLUT4 enhancer is low in adult skeletal muscle compared with the maximal potential activity that it can attain at high levels of the MRF transcription factors, MEF2, and TRalpha1. This finding indicates that glut4 transcription may be greatly up-regulated via activation of this enhancer through an increase in the levels of expression or activity of these transcription factors. Understanding the molecular basis of the expression of glut4 will be useful for the appropriate therapeutic design of treatments for insulin-resistant states. The nature of the intracellular signals that mediate the stimulation of glucose transport in response to insulin or exercise is also reviewed.

Insulin-stimulated alpha-(methyl)aminoisobutyric acid uptake in skeletal muscle. Evidence for a short-term activation of uptake independent of Na+ electrochemical gradient and protein synthesis.

1. The present study was designed to explore the mechanisms by which insulin stimulates system A of amino acid transport in extensor digitorum longus (EDL) muscles, by using a system A analogue, alpha-(methyl)aminoisobutyric acid (MeAIB). 2. Insulin stimulation of MeAIB uptake was noted after only 30 min of incubation and was maximal at 60 min. Kinetics of the insulin effect on MeAIB uptake were characterized by an increased Vmax. without modification of Km for MeAIB. 3. Incubation of EDL muscles with cycloheximide for 90 min did not modify MeAIB uptake in either the presence or the absence of insulin, indicating the independence of insulin action from protein synthesis de novo. Incubations for 180 min with cycloheximide caused a decrease in basal MeAIB uptake; however, the percentage stimulation of amino acid transport by insulin was unaltered. Basal MeAIB uptake was increased by incubation for 180 min, but under these conditions no change in the percentage effect of insulin was found. 4. Ouabain, gramicidin D, or both, markedly decreased basal MeAIB uptake by EDL muscle, but the percentage effect of insulin was unaltered. 5. We conclude that insulin action on amino acid transport through system A in muscle is rapid, is characterized by an increased Vmax., and is independent of protein synthesis de novo and the Na+ electrochemical gradient. Our data are compatible with insulin acting directly on the system A transporter.

Torsion of a wandering accessory spleen: CT findings.

Torsion of an accessory spleen is a rare entity that can have a variable clinical presentation. We report the computed tomographic (CT) findings of an acute torsion of an accessory spleen in a 13-year-old girl. CT disclosed a hypodense mesenteric mass with peripheral inflammatory changes.