STZ-DM Rats Research Articles

Esculeoside A alleviates reproductive toxicity in streptozotocin-diabetic rats’ s model by activating Nrf2 signaling

This examination studied if Esculeoside A (ESA) alleviates reproductive toxicity in a type 1 diabetes mellitus (T1DM) rat model and if activating Nrf2 underlies this protection. T1DM was established by a single injection of STZ. Aged-matched adult control and STZ-DM rats were administered either the vehicle (5% carboxymethyl cellulose) or ESA (100 mg/kg). An additional group [STZ-DM + ESA (100 mg) + brusatol (2 m/kg] was added. All treatments were conducted for 16 weeks. ESA failed to attenuate weight loss, hyperglycemia, and hypoinsulinemia but significantly attenuated the associated dyslipidemia in STZ-DM rats. In parallel, ESA also enhanced total sperm count, motility, survival, reduced head and tail sperm abnormalities, increased circulatory concentrations of follicular stimulating hormone (FSH), testosterone, and Luteinizing hormone (LH), and stimulated the testicular expression of several steroidogenic enzymes (StAR, CYP11A1, CYP17A1, 3β-HSD1) in STZ-DM rats. These observations were associated with a higher testicular increase in the transcription, protein levels, and nuclear activities of Nrf2 that coincided with a reduction in the total levels of MDA and keap1 and a significant increase in the total levels of some antioxidants such as HO-1, SOD, and GSH. In concomitance, ESA reduced the testicular mRNA and nuclear concentrations of NF-κB and depressed the levels of TNF-α and IL-6. Brusatol prevented all these protective effects of ESA. In conclusion, activation of Nrf2 triggers the protective potential of ESA against reproductive toxicity in STZ-DM rats.

Differences in metabolic improvement after metabolic surgery are linked to the gut microbiota in non-obese diabetic rats.

Different metabolic/bariatric surgery approaches vary in their effect on weight loss and glucose levels, although the underlying mechanism is unclear. Studies have demonstrated that the gut microbiota might be an important mechanism of improved metabolism after metabolic/bariatric surgery. To investigate the relationship between the improvement in metabolic disturbances and the changes in gut microbiota after gastric or intestinal bypass. We performed sleeve gastrectomy (SG), distal small intestine bypass (DSIB) or sham surgery in nonobese rats with diabetes induced by 60 mg/kg streptozotocin (STZ-DM). The group comparisons revealed that both SG and DSIB induced a reduction in body weight and significant improvements in glucose and lipid metabolism in the STZ-DM rats. Furthermore, DSIB exhibited a stronger glucose-lowering and lipid-reducing effect on STZ-DM rats than SG. 16S ribosomal RNA gene sequencing revealed the gut abundance of some Lactobacillus spp. increased in both the SG and DSIB groups after surgery. However, the DSIB group exhibited a more pronounced increase in the gut abundance of Lactobacillus spp. compared to the SG group, with more Lactobacillus spp. types increased in the gut. The gut abundance of Lactobacillus was significantly correlated with the improvement in glycolipid metabolism and the change in serum fibroblast growth factor 21 levels.

In Vitro and In Vivo Antiglycation Effects of Connarus ruber Extract.

Accumulation of advanced glycation end products (AGEs) of the Maillard reaction has been implicated in the pathogenesis of diabetes and its complications. Connarus ruber has been used as a folk remedy for several diseases, including diabetes; however, its underlying mechanism has not yet been investigated. This study investigated the effects of C. ruber extract against glycation on collagen-linked AGEs in vitro and streptozotocin-induced diabetic rats (STZ-DM rats) in vivo. The antiglycation activities of C. ruber extract and aminoguanidine (AG) were examined using a collagen glycation assay kit. Nonfluorescent AGE, Nε-carboxymethyl lysine (CML), Nω-carboxymethyl arginine, and Nε-carboxyethyl lysine levels were measured via electrospray ionization-liquid chromatography-tandem mass spectrometry. The effect of the extract on the cytotoxicity of methylglyoxal (MG), a precursor of AGEs, was examined in HL60 cells. STZ-DM rats were treated with the extract for 4 wk, and the effect was assessed using biochemical markers in the serum and CML-positive cells in renal tissues. C. ruber extract dose-dependently inhibited the glycation of collagen and formation of nonfluorescent AGEs, which was comparable to AG, and it significantly attenuated MG-induced cytotoxicity in HL60 cells. Furthermore, the glycated albumin levels in STZ-DM rats decreased, the increase in serum lipid levels was reversed, and immunohistochemistry demonstrated that CML deposition in the glomerulus of STZ-DM rats significantly decreased. Although further studies are needed, C. ruber could be a potential therapeutic for preventing and progressing many pathological conditions, including diabetes.

Ellagic acid prevents streptozotocin-induced hippocampal damage and memory loss in rats by stimulating Nrf2 and nuclear factor-κB, and activating insulin receptor substrate/PI3K/Akt axis.

This study examined the protective effect of ellagic acid (EA) against streptozotocin (STZ)-induced hippocampal damage and memory loss and investigated some mechanisms of action. Adult male rats were divided into 4 groups (n = 12) as control, control + EA (50 mg/kg), STZ-DM, and STZ-DM + EA. Treatments were given orally and daily for 8 weeks. Memory function was assessed by the Morris water maze (MWM) and passive learning avoidance test. In addition, blood samples were used to measure glucose and insulin levels. Also, the hippocampus was used to measure markers of oxidative stress, inflammation, and insulin signaling. Associated with the improved memory, EA preserved the structure of the CA1 area of rats' hippocampus and suppressed the hippocampal expression of Bax and cleaved caspase 3. Concomitantly, EA increased rats' weekly weights gain and fasting plasma insulin levels and reduced the hippocampal levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) and plasma glucose levels in diabetic rats. In both the control and STZ-DM rats, EA significantly lowered the hippocampal levels of reactive oxygen species (ROS) and malondialdehyde (MDA) but significantly increased the hippocampal levels of glutathione (GSH) and manganese superoxide dismutase (MnSOD), as well as the nuclear levels of NF-κB and nuclear factor-erythroid 2-related factor (Nrf-2). Besides, and in the hippocampus of both groups, EA increased the phosphorylation of insulin receptor substrate (IRS), PI3K, Akt, GS3Kβ, and CREB, and increased levels of BDNF and Bcl-2. In conclusion, these data suggest that the neuroprotective effect of EA on rats' hippocampus and memory function is associated with upregulation of Nrf2 and Bcl-2, suppression of NF-κB, and activation of CREB and IRS/PI3K/Akt/ GS3Kβ axis.

Effects of renal denervation on cardiovascular, metabolic and renal functions in streptozotocin-induced diabetic rats

Diabetes promotes renal sympathetic hyperactivity, autonomic imbalance, and cardiovascular and renal dysfunction. Bilateral renal denervation (BRD) has emerged as a treatment for diabetes; however, the mechanisms that underlie the beneficial effects of BRD are unknown. AimsThe present study evaluated the effects of BRD on autonomic, cardiovascular, metabolic, and renal function in streptozotocin-diabetic rats. Main methodsWistar rats were separated into three experimental groups: control (CTR), diabetic (DM), and diabetic that underwent BRD (DM BRD). BRD was performed two weeks after STZ-diabetes induction, the experiments were performed four weeks after DM induction. This study evaluated sympathetic vasomotor nerve activity in different territories (renal, lumbar and splanchnic), arterial baroreceptor reflex, metabolic and renal function. Key findingsBRD significantly reduced glycemia, glycosuria, albuminuria, and SGLT2 gene expression in the kidney in DM rats. Renal sympathetic nerve activity (rSNA) was significantly increased and splanchnic sympathetic nerve activity (sSNA) was significantly decreased in DM rats, without changes in lumbar sympathetic nerve activity (lSNA). BRD was able to normalize sSNA and significantly increase lSNA in DM rats compared to control rats. Additionally, cardiac baroreceptor sensitivity was impaired in DM rats, and BRD significantly improved baroreflex sensitivity. SignificanceOur data suggest that renal nerves play an important role in autonomic, cardiovascular, and renal dysfunction in STZ-DM rats. Thus, sympathetic renal hyperactivity should be considered a possible therapeutic target in diabetic patients.

Изменения внеклеточно регистрируемых потенциалов действия изолированного сердца крысы при развитии стрептозотоцинового диабета

Left ventricles (LV) of isolated hearts of the control rats (n = 7) and rats injected with streptozotocin (STZ; n = 21) were studied on the four-week post-injection term using 5-µm tip (O.D.) glass extracellular microelectrodes. STZ-rats that maintained hyperglycemia by the time of the study (random glucose > 11 mM; n = 3) were designated as diabetic animals (diabetes mellitus group; STZ-DM). Remaining STZ-rats (n = 18) were designated as normoglycemic rats (STZ-NG group). In control and in STZ-rat hearts two main types of sinus rhythm action potentials (AP) of epicardial ventricular myocytes could be recorded: signals characterized by a single (AP1) or double negative peaks (AP2). Respective time parameters of AP1 (rise time, and 50% and 90% decay times (T50 and T90) not differed between studied groups of rats. However, T50 of AP2 of LV myocytes of STZ-NG and STZ-DM rats were statistically significantly longer than T50 of AP2 recorded in control rat hearts. Furthermore, in 28% of STZ-NG and in 67% of STZ-DM rat hearts additional type of AP (AP3) featuring a complex, multi-peak negative phase and prominent positive phase of after-hyperpolarization were recorded. Appearance of AP3 was associated with a proportional decrease in the relative frequency of AP2 recordings (from 80-85% to 55-60% of all recordings). Frequency of AP1 recordings remained stable, 15-20% in all experiments in all groups of rats. Tentatively, observed in this study modulation in electrical activity of ventricular myocytes of STZ-rat hearts results from structure-functional changes in organization of the T-system of these myocytes. Regardless of validity of this suggestion, it is important that changes in electrogenesis of cardiomyocytes develop fast (1 month) not only in STZ-DM rats, but also in hearts of STZ-rats with normal or moderately increased blood glucose levels, which may be considered as the state equivalent to the state of early prediabetes.

Effects Of Endurance Exercise Training On The Cardiac Function Quantification By Echocardiography In STZ-DM Rats

Many studies have demonstrated that diabetes mellitus (DM) is associated with cardiac dysfunction. Exercise training is beneficial for the treatment of chronic heart failure. PURPOSE: the aim of the present study was to evaluated effects of endurance exercise training (EX) on cardiac function quantification by echocardiography in DM rats. We also evaluated the levels of connexin 43 of the heart. METHODS: the Sprague-Dawley (SD) male rats were divided into 3 groups as two experimental groups and one control group. The first groups as a control group received adjuvant. The second and third groups were the DM groups, received 150 mg/kg STZ by intraperitoneal injection. After one week, EX was carried out in the third group (DM-EX group) for four weeks. The cardiac functions of those animals were evaluated by echocardiography method. The animals were sacrificed; the connexin 43 of heart was evaluated by western blot. The tissues of heart were stained by H&E or Masson’s trichrome stain. The morphology and fibrosis of cardiac cells were analyzed. RESULTS: the results show that the distances of interventricular septal and left ventricular (LV) posterior wall were shorter in DM and DM-EX groups than in control group (P<0.05). The LV diameter was longer in DM-EX group than in control group (P<0.05). The weights of rat’s body, heart and LV mass were lower in DM and DM-EX groups than in control group (P<0.05). The values of heart and LV mass weighted by body mass were higher in DM group than in control group (P<0.05). The heart connexin 43 was lowest in DM group than in control and DM-EX group (P<0.05). The length of cardiomyocyte diameter was longer in DM and DM-EX group than in control group (P<0.05). The percent of fibrotic area in heart tissue was highest in DM group than in others (P<0.05). The fibrotic area of heart was smaller in DM-EX group than in DM group (P<0.05). CONCLUSIONS: those results suggested that EX may decrease cardiac dysfunction from DM damage through connexin 43 increasing and lower myocardial fibrosis.

Antifibrogenic role of valproic acid in streptozotocin induced diabetic rat penis.

We investigated the therapeutic effects of valproic acid (VPA) on erectile dysfunction and reducing penile fibrosis in streptozocin (STZ)-induced diabetic rats. Eighteen male rats were divided into three experimental groups (Control, STZ-DM, STZ-DM plus VPA) and diabetes was induced by transperitoneal single dose STZ. Eight weeks after, VPA and placebo treatments were given according to groups for 15 days. All rats were anesthetised for the measurement of in vivo erectile response to cavernous nerve stimulation. Afterward penes were evaluated histologically in terms of immune labelling scores of endothelial nitric oxide synthase (eNOS), vascular endothelial growth factor (VEGF) and transforming growth factor-β1 (TGF-β1). Slides were also evaluated in terms of collagen/smooth muscle ratio and penile apoptosis. After the treatment with VPA, erectile responses were found as improved when compared with STZ-DM rats but not statistically meaningful. eNOS and VEGF immune expressions diminished in penile corpora of STZ-DM rats and improved with VPA treatment. VPA led to decrease in TGF-β1 expression and collagen content of diabetic rats' penes. Penile apoptosis was not diminished with VPA. In conclusion, VPA treatment seems to be effective for reducing penile fibrosis in diabetic rats and more prolonged treatment period may enhance erectile functions.

Effect of Jinmaitong capsule on inducible nitric oxide synthase and nitrotyrosine in diabetic rats

To observe the effect of Jinmaitong capsule (JMT), a compound traditional Chinese medicine, on expressions of inducible nitric oxide synthase (iNOS) and nitro tyrosine (NT) protein in streptozocin-induced diabetic (STZ-DM) rats. Intraperitoneal injection of streptozocin in rats to establish a model. STZ-DM rats were randomly divided into the model control group (distilled water), the small-dose JMT group (JMT at dose of 0.45 g x kg(-1) x d(-1)), the medium-dose JMT group (JMT at dose of 0.88 g x kg(-1) x d(-1)), the large-dose JMT group (JMT at dose of 1.75 g x kg(-1) x d(-1)) and Vitamin C group (VC at dose of 0.05 g x kg(-1) x d(-1)). Ten normal rats with matching weight and age were selected as the normal control group (distilled water). After intragastric administration for 16 weeks, the expressions of iNOS and NT in sciatic nerve were detected by the immunohistochemistry method. The expression levels of iNOS and NT protein in diabetic rats were higher than those in normal rats (P<0.05, P<0.01). Compared with the model group, the levels of iNOS and NT protein in JMT and VC groups were significantly decreased (P<0.05, P<0.01). Particularly, the medium-dose JMT group showed a better effect than the VC group (P<0.05, P<0.01). JMT could down-regulate the expressions of iNOS and NT protein of sciatic nerve in diabetic rats.

Opposing effects of NaCl restriction and carbohydrate loading on urine volume in diabetic rats

To test the effects of dietary NaCl and carbohydrate content on urine volume in diabetic rats. Streptozotocin-induced diabetic rats were subjected to NaCl restriction using either a NaCl-deficient carbohydrate-rich synthetic diet (Altromin C1036) supplemented to contain 0.16% NaCl (C1036 + lowNaCl) or a modified normal cereal-based diet (Altromin 1320) containing 0.086% NaCl (lowNaCl-1320). Normal diet contained 0.2683% NaCl. Using the C1036 + lowNaCl diet, earlier reported paradoxical increases in water intake and urine volume of diabetic rats were reproduced. However, water intake and urine volume also increased in diabetic rats offered the synthetic C1036 diet supplemented with NaCl to normal levels. Using the lowNaCl-1320 diet, water intake and urine volume were markedly reduced. Highly significant correlations between urine volume and both osmotic output and urinary glucose excretion were found in diabetic rats on normal diet, but these correlations were absent in diabetic rats on synthetic diet, which showed higher urine volumes than expected from the correlations. In contrast, urine volume was significantly correlated with carbohydrate intake in diabetic rats, irrespective of the diet. (i) The synthetic diet dramatically increases the urine volume in STZ-DM rats irrespectively of NaCl content. (ii) Rats with STZ-DM on a normal diet show reduced water intake and urine volume in response to dietary NaCl restriction. (iii) A shift to high carbohydrate diet induces polyuria in STZ-DM rats. (iv) Urine volume in all STZ-DM rats only shows correlation with dietary carbohydrate intake. (v) Glucose-driven osmotic diuresis is unlikely to explain the carbohydrate-induced polyuria.

Interstitial cells of Cajal, macrophages and mast cells in the gut musculature: morphology, distribution, spatial and possible functional interactions

Interstitial cells of Cajal (ICC) are recognized as pacemaker cells for gastrointestinal movement and are suggested to be mediators of neuromuscular transmission. Intestinal motility disturbances are often associated with a reduced number of ICC and/or ultrastructural damage, sometimes associated with immune cells. Macrophages and mast cells in the intestinal muscularis externa of rodents can be found in close spatial contact with ICC. Macrophages are a constant and regularly distributed cell population in the serosa and at the level of Auerbach’s plexus (AP). In human colon, ICC are in close contact with macrophages at the level of AP, suggesting functional interaction. It has therefore been proposed that ICC and macrophages interact. Macrophages and mast cells are considered to play important roles in the innate immune defence by producing pro-inflammatory mediators during classical activation, which may in itself result in damage to the tissue. They also take part in alternative activation which is associated with anti-inflammatory mediators, tissue remodelling and homeostasis, cancer, helminth infections and immunophenotype switch. ICC become damaged under various circumstances – surgical resection, possibly post-operative ileus in rodents – where innate activation takes place, and in helminth infections – where alternative activation takes place. During alternative activation the muscularis macrophage can switch phenotype resulting in up-regulation of F4/80 and the mannose receptor. In more chronic conditions such as Crohn’s disease and achalasia, ICC and mast cells develop close spatial contacts and piecemeal degranulation is possibly triggered.

Suppression of calcineurin signaling reduces PGC‐1α expression in a chronic model of muscle atrophy

Diabetes mellitus (DM) causes persistent skeletal muscle atrophy, which contributes to renal failure and a decreased quality of life. Contractile activity is known to blunt persistent muscle atrophy, suggesting that decreased calcium‐dependent signaling could contribute to the atrophy process. Therefore, we examined the calcineurin (Cn)/NFAT/MEF2 signaling pathway in a streptocotozin (STZ) –induced DM model of chronic muscle atrophy. Cn protein as well as NFAT and MEF2 transcription activity was decreased in 21d STZ‐DM rats. Additionally, PGC‐1α, a downstream target of Cn/NFAT/MEF2 signaling, was decreased. To determine whether reduced Cn signaling is directly responsible for the decrease in PGC‐1α, we utilized CnA‐isoform specific knockout mice. NFAT and MEF2 activity and PGC‐1α mRNA were decreased in muscle from CnAα−/− and CnAβ−/− mice. PGC‐1α is a transcriptional cofactor with roles in muscle MHCI fiber‐type specification and preservation of muscle mass. In 21d STZ‐DM rats, fiber‐type switching from MHCI to MHCII was observed and MHCII fibers atrophied to a greater extent. These results suggest that atrophy in systemic disease states may be sustained through suppression of Cn signaling and loss of PGC‐1α expression resulting in changes in functional capacity and fiber‐type switching.

Insulin has no effect on vascular endothelial growth factor expression in the retina of streptozotocin-induced diabetic rats

Objective To investigate if insulin can affect the expression of vascular endothelial growth factor (VEGF) in the retina of streptozotocin-induced diabetic rats. Methods A total of 60 male Sprague-Dawley rats were randomly divided into sodium citrate buffer control group (CIT-CON, n= 30) and STZ-induced diabetic group (STZ-DM, n=30). At the 16th week, 24 rats from CIT-CON group at random were randomly divided to group A (sodium citrate buffer control group, n = 12) and group B (sodium citrate buffer plus insulin group, n= 12). The remaining 6 rats from as CIT-CON group served as negative control. At the same time, 24 rats from STZ-DM group at random were randomly divided to group C (STZ-induced diabetic group, n= 12) and group D (STZ-induced diabetic plus insulin group, n= 12). The remaining 6 rats from STZ-DM group also served as negative control. 4 IU of insulin was injected subcutaneously to rats of group B and D. Immunohistochemistry, Western blot and Real-time polymerase chain reaction (RT-PCR) were used to measure the expression level of VEGF protein and mRNA respectively. RESULTS Insulin significantly increased the VEGF mRNA (7.71 ± 0.25 vs 5.36 ±0. 37, t test P 0. 05) and protein expression (0. 5152±0. 0109 vs 0. 5099±0. 0100, t test P>0.05). Conclusions Insulin had no effect on VEGF expression in the retina of STZ-DM rats. Key words: Insulin/ physiology, Diabetic retinopathy/ etiology; Vascular endothelial growth factors / analysis; Disease models, animal

Macula densa (pro)renin receptor abundance correlates with renal renin content

The (pro)renin receptor [(P)RR] has been localized to the basolateral membrane of the macula densa (MD), adjacent to (pro)renin (PR) producing granular cells. The PRR is a new exciting element of the renin‐angiotensin system (RAS). Patho(physiological) conditions, such as dietary salt, hypertension, and diabetes mellitus (DM), have well established effects on RAS and renal PR expression. We hypothesized that under these conditions (P)RR abundance in MD cells correlates with renal PR expression. First, (P)RR immunofluorescence was performed on kidney sections after rats were placed on normal salt (4% salt, NS), salt‐deficient (0.4% salt, SD), or high salt (8% salt, HS) diet for one week. Compared to NS, less cytosolic but very intense basolateral membrane labeling was observed in MD cells in response to LS, while HS greatly reduced MD (P)RR labeling. (P)RR immunoblotting using cultured mouse‐derived MD cells (MMDD1) treated with SD medium for 15‐75 minutes presented up‐regulation of (P)RR protein. Next, western blotting was performed with renal cortical homogenates from control and STZ‐DM rats against renin and (P)RR. Up‐regulation of both renin (2.6‐fold) and (P)RR (1.4‐fold) was confirmed in DM. In summary, MD (P)RR abundance correlates with renal cortical renin content, suggesting that either high/low renin states modulate MD function via the (P)RR, or the MD (P)RR regulates renal (pro)renin synthesis.

Diabetes‐related alterations in second messenger regulation of potassium channel activity in corporal smooth muscle cells

Corporal smooth muscle (CSM) relaxation mediates penile erection, and second messenger activation of the KCa and KATP channel subtypes plays a major role in this process. The goal of this study was to evaluate the potential role of altered second messenger activated hyperpolarizing K+ currents in CSM to diabetes (DM)‐related erectile dysfunction (ED). Corporal tissue was excised from the STZ‐DM rats following 2 months of DM. Whole cell currents were recorded from short‐term cultured CSM cells of DM and age‐matched control (AMC) rats; in the absence and presence of either cAMP (prostaglandin E1 (PGE1; 10 uM) or 8‐Br‐cAMP (1 mM)) or cGMP (sodium nitroprusside (SNP; 10 uM) or 8‐Br‐cGMP (1 mM)) activation. Holding potential was −70 mV, with I‐V curves constructed in 10 mV increments from −60 to +100 mV. Resting potentials were lower in DM (−44 ± 1.3 mV; n=40) than AMC (−56 ± 1.4 mV; n=40) (p&lt;0.05). Outward whole cell K+ currents were reduced in DM (206 ± 11 pA; n=40) relative to AMC (321 ± 16 pA; n=40) (p&lt;0.05). K+ currents induced by cGMP, SNP, cAMP and PGE1 were significantly diminished in DM relative to AMC. IBTX (100 nM) decreased cGMP‐activated K+ currents more than glibenclamide (GLIB; 10 uM) in AMC rats, but less than GLIB in DM rats. The data suggest that cGMP and cAMP‐mediated K+ currents are decreased in DM rats, and that altered regulation of the KCa and KATP channel subtypes might contribute to DM‐related ED in rats.

Skeletal muscle fiber type switching and atrophy in diabetes mellitus

This study demonstrates that switching of mammalian skeletal muscle fibers, identified as to Myosin Heavy Chain (MHC) type, from MHCI to MHCII occurs along with selective MHCII fiber atrophy in Diabetes Mellitus (DM). DM characterized by reduced plasma insulin level was induced by streptozotocin (40 mg/kg body wt STZ in buffer) injection of 6 wk old male Sprague‐Dawley rats; no exogenous insulin was administered. Rats, matched as to birth date and weight, were randomly assigned to test STZ‐DM or Control (injected with buffer only) group; after 3 wks the STZ‐DM (2) and Control rats (2) were sacrificed and their white gastrocnemius (GAST) and soleus (SOL) muscles excised. A 3–5 mm transverse section of each excised muscle was immediately cut and flash frozen (−80°C). The frozen tissue was cut into 12 μm cross‐sections in a cryostat; fibers in cross‐section were stained and identified as to type using 3 different MHC antibodies in serial cross‐sections. For each SOL and GAST cross‐section, 100 contiguous fibers were MHC typed. The proportions and CSA of combined MHCIIa, x/d,b and MHCI (nonhybrid) fibers were analyzed for GAST and SOL, comparing STZ‐DM to Control. MHCI to MHCII type switching in STZ‐DM was significant (p&lt;0.05) only for SOL, although it was evident in GAST. CSA of only the STZ‐DM MHCII fibers was significantly (p&lt;0.05) decreased in both SOL and GAST. Supported by Emory University (SKD) and R01 DK50740‐09 (SRP).

Insulin action in the brain contributes to glucose lowering during insulin treatment of diabetes

To investigate the role of brain insulin action in the pathogenesis and treatment of diabetes, we asked whether neuronal insulin signaling is required for glucose-lowering during insulin treatment of diabetes. Hypothalamic signaling via the insulin receptor substrate-phosphatidylinositol 3-kinase (IRS-PI3K) pathway, a key intracellular mediator of insulin action, was reduced in rats with uncontrolled diabetes induced by streptozotocin (STZ-DM). Further, infusion of a PI3K inhibitor into the third cerebral ventricle of STZ-DM rats prior to peripheral insulin injection attenuated insulin-induced glucose lowering by approximately 35%-40% in both acute and chronic insulin treatment paradigms. Conversely, increased PI3K signaling induced by hypothalamic overexpression of either IRS-2 or protein kinase B (PKB, a key downstream mediator of PI3K action) enhanced the glycemic response to insulin by approximately 2-fold in STZ-DM rats. We conclude that hypothalamic insulin signaling via the IRS-PI3K pathway is a key determinant of the response to insulin in the management of uncontrolled diabetes.

Galanin-Like Peptide mRNA Alterations in Arcuate Nucleus and Neural Lobe of Streptozotocin-Diabetic and Obese Zucker Rats

Galanin-like peptide (GALP) is a 60-amino-acid peptide with structural similarities to galanin and a high affinity for galanin receptors. GALP is expressed by a discrete population of neurons in the arcuate nucleus (ARC) and median eminence of the hypothalamus of several species, including the rat. GALP neurons express leptin receptors and GALP mRNA levels are decreased slightly in fasted rats and stimulated significantly by acute leptin treatment in combination with fasting. In studies to further explore the leptin dependence of GALP expression, we examined GALP mRNA levels in the hypothalamus of obese Zucker and streptozotocin-induced diabetic (STZ-DM) rats. In leptin receptor-deficient obese Zucker rats, with 75% higher body weight than lean littermates, GALP mRNA levels in the ARC were decreased by 75%, while neuropeptide Y (NPY) mRNA levels were increased 7-fold (n = 5, p < 0.001), consistent with earlier reports. In hypoleptinemic diabetic rats with 4.5-fold higher blood glucose and 15% lower body weight than controls, GALP mRNA levels in the ARC were decreased by 90%, while NPY mRNA levels were increased 9-fold (n = 5, p < 0.001). GALP is also expressed by pituicytes in the neural lobe of the rat pituitary gland and GALP expression is increased by osmotic stimulation such as dehydration and salt loading. Thus, in STZ-DM rats that are in a hyperosmotic state with elevated plasma vasopressin levels, GALP mRNA levels were increased by ∼20-fold in the neural lobe relative to control (n = 4, p < 0.001). The current findings are consistent with a strong tonic influence of leptin receptor signalling on hypothalamic GALP expression under normal conditions, and possible abnormalities in GALP neuronal signalling and their putative targets, thyrotropin-releasing hormone and gonadotropin hormone-releasing hormone neurons, under pathophysiological conditions such as diabetes and obesity. Our data in STZ-DM rats also clearly demonstrate that GALP gene expression is differentially regulated in neurons and pituicytes.

Nicorandil improves diabetes and rat islet beta-cell damage induced by streptozotocin in vivo and in vitro.

N-(2-hydroxyethyl)-nicotinamide nitrate (nicorandil) is a unique anti-anginal agent, reported to act as both an ATP-sensitive K(+) channel opener (PCO) and a nitric oxide donor. It also has an anti-oxidant action. We examined the effects of nicorandil on streptozotocin (STZ)-induced islet beta-cell damage both in vivo and in vitro. STZ-induced diabetic Brown Norway rats (STZ-DM) were fed with nicorandil-containing chow from day 2 (STZ-DM-N48), 3 (STZ-DM-N72), and 4 (STZ-DM-N96) to day 30. Body weight, blood glucose, and plasma insulin were measured every week. For the in vitro assay, neonatal rat islet-rich cultures were performed and cells were treated with nicorandil from 1 h before to 2 h after exposure to STZ for 30 min. Insulin secretion from islet cells was assayed after an additional 24 h of culture. We also observed the effect of nicorandil on the generation of reactive oxygen species (ROS) from rat inslinoma cells (RINm5F). Body weight loss and blood glucose levels of STZ-DM-N48 rats were significantly lower than those of STZ-DM rats. Immunohistochemical staining of insulin showed preservation of insulin-secreting islet beta-cells in STZ-DM-N48 rats. Nicorandil also dose-dependently recovered the insulin release from neonatal rat islet cells treated with STZ in in vitro experiments. Nicorandil did not act as a PCO on neonatal rat islet beta-cells or RINm5F cells, and did not show an inhibitory effect on poly(ADP-ribose) polymerase-1. However, the drug inhibited the production of ROS stimulated by high glucose (22.0 mmol/l) in RINm5F cells. These results suggested that nicorandil improves diabetes and rat islet beta-cell damage induced by STZ in vivo and in vitro. It protects islet beta-cells, at least partly, via a radical scavenging effect.

Effect of uncontrolled diabetes on plasma ghrelin concentrations and ghrelin-induced feeding.

Plasma levels of the orexigenic hormone, ghrelin, decrease rapidly on nutrient ingestion and yet are paradoxically elevated in rats with hyperphagia induced by streptozotocin-induced diabetes (STZ-DM). In the current work, we investigated the mechanisms underlying the relationships among uncontrolled diabetes, food intake, and plasma ghrelin concentrations in an effort to clarify whether increased ghrelin signaling contributes to diabetic hyperphagia. Whereas food intake did not increase until d 3 after STZ administration, plasma ghrelin levels were increased by more than 2-fold (P < 0.05) on d 1. As hyperphagia developed, however, plasma ghrelin levels declined steadily. Because this reduction of plasma ghrelin levels was reversed by matching food intake of STZ-DM rats to that of nondiabetic controls, our results demonstrated that the effect of uncontrolled diabetes to increase plasma ghrelin levels is partially offset by hyperphagic feeding. In addition, we found that although intragastric nutrient infusion rapidly and comparably decreased plasma ghrelin levels in both groups (by 46-49%; P < 0.05), this effect was short lived in STZ-DM rats relative to nondiabetic controls (60 min vs. 120 min; P < 0.05). We further demonstrated that in rats with STZ-DM, food intake increased by 357% (P < 0.05) in response to intracerebroventricular administration of ghrelin at a dose that was subthreshold for feeding effects in nondiabetic controls. Collectively, these findings demonstrate that uncontrolled diabetes increases both circulating ghrelin levels and behavioral sensitivity to ghrelin. Although plasma ghrelin levels fall in response to hyperphagic feeding, these findings support the hypothesis that increased ghrelin signaling contributes to the pathogenesis of diabetic hyperphagia.