Responses In Diabetic Rats Research Articles

Diabetes induces changes in ILK, PINCH and components of related pathways in the spinal cord of rats

Recent work suggests that diabetes affects processing of peripheral, spinal and supraspinal signals in the spinal cord. However, there is little evidence for spinal cord lesions that would account for alterations in behavioral responses induced by experimental diabetes. Therefore, we assessed the expression of proteins that might affect neuronal cytoskeletal stability and thus promote dendritic and synaptic reorganization in diabetic rats. Expression of ILK, PINCH, PI3K, GSK-3β, tau, MAP2, synaptophysin and drebrin in the lumbar spinal cord of non-diabetic and streptozotocin-diabetic rats was assessed by Western-blot analysis and immunocytochemistry after 8 and 20 weeks of diabetes. The impact of diabetes on the proteins studied was duration-dependent with changes observed after 20 but not 8 weeks of diabetes. ILK and PINCH proteins levels were significantly decreased and both colocalized to neurons and oligodendrocytes. PI3K protein levels were also significantly decreased, while GSK-3β activity tended to be increased. Phosphorylation of tau and MAP2A/B protein expression were significantly increased, and expression of synaptophysin and drebrin were reduced in diabetic rats. Decreased ILK and PINCH as well as alterations of components of related signaling pathways are associated with tau hyperphosphorylation, MAP2 overexpression and reduction of synaptic proteins in the spinal cord of diabetic rats, suggesting that ILK and PINCH contribute to stabilization of axonal and dendritic structures. However, these changes are not likely the cause of altered behavioral responses in diabetic rats that occur after short-term diabetes, but may contribute to structural changes occurring in long-term diabetes.

The Effect of Low-Level Laser Therapy on Healing of Skin Incisions Made Using a Diode Laser in Diabetic Rats

To investigate the effect of low-level laser therapy (LLLT) on healing of skin incisions made using a diode laser in diabetic rats. Eighteen diabetic Wistar rats were used for this study. One incision was performed on the left side of the dorsum using a diode laser, and the other two incisions were made with a scalpel and diode laser on the right side of each rat. The wound on the left side of each rat received laser stimulation (10 J/cm(2)). The rats were assigned to three experimental groups. Group 1, scalpel (n = 18); Group 2, diode (n = 18); Group 3, diode + biostimulation (n = 18). Reepithelialization was fastest in Group 2 than Group 1 at day 10. The difference between Groups 1 and 3 was also statistically significant in reepithelialization at day 10. There was a significant difference between Groups 1 and 2 and between Groups 2 and 3 in inflammation at day 10. There was no difference between any of the groups in inflammation and reepithelialization at day 20. Scalpel incisions heal more slowly than diode and diode + biostimulation incisions in diabetic rats. We can suggest that diode + biostimulation may produce the least amount of tissue injury, with the fastest resolution of inflammatory response in diabetic rats. Diode laser incision (4 W) with 10-J/cm(2) LLLT seems to have a beneficial effect on skin incisions in diabetic rats.

SirT1 knockdown in liver decreases basal hepatic glucose production and increases hepatic insulin responsiveness in diabetic rats

Hepatic gluconeogenesis is a major contributing factor to hyperglycemia in the fasting and postprandial states in type 2 diabetes mellitus (T2DM). Because Sirtuin 1 (SirT1) induces hepatic gluconeogenesis during fasting through the induction of phosphoenolpyruvate carboxylase kinase (PEPCK), fructose-1,6-bisphosphatase (FBPase), and glucose-6-phosphatase (G6Pase) gene transcription, we hypothesized that reducing SirT1, by using an antisense oligonucleotide (ASO), would decrease fasting hyperglycemia in a rat model of T2DM. SirT1 ASO lowered both fasting glucose concentration and hepatic glucose production in the T2DM rat model. Whole body insulin sensitivity was also increased in the SirT1 ASO treated rats as reflected by a 25% increase in the glucose infusion rate required to maintain euglycemia during the hyperinsulinemic-euglycemic clamp and could entirely be attributed to increased suppression of hepatic glucose production by insulin. The reduction in basal and clamped rates of glucose production could in turn be attributed to decreased expression of PEPCK, FBPase, and G6Pase due to increased acetylation of signal transducer and activator of transcription 3 (STAT3), forkhead box O1 (FOXO1), and peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha), known substrates of SirT1. In addition to the effects on glucose metabolism, SirT1 ASO decreased plasma total cholesterol, which was attributed to increased cholesterol uptake and export from the liver. These results indicate that inhibition of hepatic SirT1 may be an attractive approach for treatment of T2DM.

Tocotrienol attenuates oxidative–nitrosative stress and inflammatory cascade in experimental model of diabetic neuropathy

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, is recognised as one of the most difficult types of pain to treat. The development of tolerance, inadequate relief and potential toxicity of classical antinociceptives warrant the investigation of the newer agents to relieve this pain. Reactive oxygen/nitrogen species, cytokines and apoptosis are implicated in the pathogenesis of diabetic neuropathy. The aim of the present study was to explore the effect of tocotrienol on thermal and mechanical hyperalgesia, allodynia, oxidative–nitrosative stress, inflammation and apoptosis in streptozotocin-induced experimental diabetes. Diabetic rats developed neuropathy which was evident from a marked hyperalgesia and allodynia associated with enhanced nitrosative stress, release of inflammatory mediators (TNF-α, IL-1β, TGF-1β) and caspase-3. Chronic treatment with tocotrienol (25, 50 and 100 mg/kg body weight; p.o.) for 4 weeks starting from the 4th week of streptozotocin injection significantly attenuated behavioral, biochemical and molecular changes associated with diabetic neuropathy. Moreover, diabetic rats treated with insulin–tocotrienol combination produced more pronounced beneficial effect as compared to their per se groups. The major finding of the study is that insulin alone corrected the hyperglycemia and partially reversed the pain response in diabetic rats. However, combination with tocotrienol not only attenuated the diabetic condition but also reversed neuropathic pain through modulation of oxidative–nitrosative stress, inflammatory cytokine release and caspase-3 in the diabetic rats and thus it may find clinical application to treat neuropathic pain in the diabetic patients.

Assessment of Anti-Diabetic Activity of Syzygium jambolanum Using In vitro Model

Problem statement: Poor glycemic control and oxidative stress is implicated as a common pathway in the development of diabetic neuropathy. Approach: In the present study, we investigated the protective effects of Enicostemma littorale Blume (EL) (2.5 g kg-1), a hypoglycemic and antioxidant herbal medicine in alloxan-induced diabetic neuropathy in male Charles foster rats. Results: Tail flick latency in hot immersion test and the formalin test were used to evaluate nociceptive responses in diabetic rats compared to non-diabetic rats. Preventive treatment of EL (for 45 days) and standard drug glibenclamide (Glib) significantly improved nociception in diabetic rats. The changes in lipid peroxidation status and anti-oxidant enzymes (super-oxide dismutase, glutathione peroxidase and catalase) levels observed in diabetic rats, were significantly restored by EL and glib treatment. Decrease in Na-K+ ATPase activity was also significantly restored by EL. Glibenclamide was used as standard drug in present study. Conclusion: This study provided experimental evidence to preventive effect of EL on nerve function and oxidative stress in animal model of diabetic neuropathy. Hence EL may be tried clinically for the treatment of diabetic neuropathy since it was used as folk medicine in diabetic patients.

Advanced Glycation End Products of DNA: Quantification of N2-(1-Carboxyethyl)-2′-deoxyguanosine in Biological Samples by Liquid Chromatography Electrospray Ionization Tandem Mass Spectrometry

Methylglyoxal (MG) and related alpha-oxoaldehydes react with proteins, lipids, and DNA to give rise to covalent adducts known as advanced glycation end products (AGEs). Elevated levels of AGEs have been implicated in the pathological complications of diabetes, uremia, Alzheimer's disease, and possibly cancer. There is therefore widespread interest in developing sensitive methods for the in vivo measurement of AGEs as prognostic biomarkers and for treatment monitoring. The two diastereomeric MG-DNA adducts of N(2)-(1-carboxyethyl)-2'-deoxyguanosine (CEdG) are the primary glycation products formed in DNA; however, accurate assessment of their distribution in vivo has not been possible since there is no readily available quantitative method for CEdG determination in biological samples. To address these issues, we have developed a sensitive and quantitative liquid chromatography electrospray ionization tandem mass spectrometry assay using the stable isotope dilution method with an (15)N(5)-CEdG standard. Methods for CEdG determination in urine or tissue extracted DNA are described. Changes in urinary CEdG in diabetic rats in response to oral administration of the AGE inhibitor LR-90 are used to demonstrate the potential utility of the method for treatment monitoring. Both stereoisomeric CEdG adducts were detected in a human breast tumor and normal adjacent tissue at levels of 3-12 adducts/10(7) dG, suggesting that this lesion may be widely distributed in vivo. Strategies for dealing with artifactual adduct formation due to oxoaldehyde generation during DNA isolation and enzymatic workup procedures are described.

Neutrophil response of anaerobic jump trained diabetic rats

This paper investigated the effect of jump training on blood biochemical parameters and neutrophil responses of diabetic rats. Male Wistar rats were divided into control, trained, diabetic and trained-diabetic groups. Diabetes was induced by i.v. injection of streptozotocin. Jump training consisted of six sets of ten jumps in water with overload of 50% of body mass with 1-min of resting, four times per week during 6 weeks. Plasma glucose, lactate, triacylglycerol and total cholesterol concentrations, differential leukocyte count, phagocytosis and anion superoxide production by neutrophils were evaluated. Diabetes caused hyperglycemia, hypertriacylglycerolemia, and body weight loss. Physical training reversed hypertriacylglycerolemia. Jump training increased phagocytosis and anion superoxide production by blood neutrophils from trained and trained-diabetic rats. Neutrophilia and lymphocytopenia occur in diabetic and trained-diabetic rats. Anaerobic jump training in diabetic rats reduced hypertriacylglycerolemia and increased neutrophil anion superoxide production. Phagocytosis was not altered in trained-diabetic rats.

Differential expression of liver proteins in streptozotocin-induced diabetic rats in response to hypoglycemic mushroom polysaccharides

We investigated the influence of hypoglycemic fungal extracellular polysaccharides (EPS) on the differential expression of liver proteins in streptozotocin (STZ)-induced diabetic rats. The results of diabetic study revealed that orally administrated EPS exhibited an excellent hypoglycemic effect, lowering the average plasma glucose level in EPS-fed rats to 55.1% with enhanced glucose tolerance. In the next step, we analyzed the differential expression patterns of rat liver proteins from each group to discover potent candidates for diabetes-associated proteins. 34 proteins were upregulated and 35 proteins were downregulated upon diabetes induction. Surprisingly, the altered levels of most proteins in the diabetic group were fully or partially restored to those of the non-diabetic control group by EPS treatment. Although the molecular basis of protein modulation after EPS administration in diabetic rats was not verified, the results of the proteomic analysis provide impetus for further studies to identify reliable biomarkers for diabetic therapy.

Submerged Culture Mycelium and Broth of Grifola frondosa Improve Glycemic Responses in Diabetic Rats

Grifola frondosa, an edible fungus with a large fruiting body and overlapping caps, has been demonstrated to be a natural source of health-promoting substances, mainly due to its polysaccharides beta-glucan. By using male Wistar rats injected with saline (normal rats) or nicotinamide plus streptozotocin (diabetic rats), we investigated the effects of an orally ingested placebo (CON and STZ groups), culture mycelium (CGM and SGM groups), broth (CGB and SGB groups), and mycelium plus broth (CGX and SGX groups) of Grifola frondosa on glycemic responses. During the experimental period (from day 0 to day 15), the STZ group had significantly lower body weight compared to the CON group (one-way ANOVA, p<0.05). Moreover, the STZ group had significantly higher blood glucose concentrations at 2 hour-postprandial periods on days 0, 7, and 14 and in an oral glucose tolerance test (OGTT) on day 10, as well as significantly higher serum fructosamine and triglyceride on day 15 compared to the CON group. These diabetes-induced increases were significantly attenuated by administrations of mycelium and/or broth, i.e., the SGM, SGB, and SGX groups. The results of repeated-measures analysis and three-way ANOVA indicated that diabetes mellitus significantly increases, and mycelium administration significantly decreases postprandial blood glucose; diabetes mellitus significantly increases, and mycelium and broth administrations significantly decrease serum triglyceride, fructosamine, and blood glucose concentrations; moreover, in the area under the curve in OGTT, p<0.05. Our results revealed that submerged-culture mycelia and broth of Grifola frondosa have bioactivities for improving glycemic responses.

Diabetes mellitus and responses of the urinary bladder to acetylcholine: an in vitro study

This study was prompted by the inconsistent reports and apparent controversies that exist in the biomedical literature on the responses of diabetic bladder strips to cholinergic nerve stimulation or exogenously-administered muscarinic agonists, especially acetylcholine (ACh). In the present study, acetylcholine-induced contractions of urinary bladders isolated from normoglycaemic (normal) and streptozotocin-treated, diabetic Wistar rats were examined under physiological conditions. Mechanical contractile changes of the isolated urinary bladders of STZ-treated, diabetic rats in response to bath-applied acetylcholine were compared with those obtained from isolated urinary bladders of normal, age-matched, control rats. Results obtained show that urinary bladders from diabetic rats were always more spontaneously active after mounting, than those of the age-matched normal, control rats. ACh (10(-8)-10(-4) M) provoked concentration-related, atropine-sensitive contractions of the isolated urinary bladders of both diabetic and age-matched normal, control rats. However, acetylcholine always induced more powerful and greater contractions of the diabetic bladders compared with bladders from the age-matched normal, control rats. The magnitude and/or intensity of the diabetic bladder enhanced contractile responses to ACh continued to increase as the diabetic state of the animals progressed.

Expression of Hypothalamic KiSS-1 System and Rescue of Defective Gonadotropic Responses by Kisspeptin in Streptozotocin-Induced Diabetic Male Rats

Hypogonadotropism is a common feature of uncontrolled diabetes, for which the ultimate mechanism remains to be elucidated. Kisspeptins, ligands of G protein-coupled receptor 54 (GPR54) encoded by the KiSS-1 gene, have recently emerged as major gatekeepers of the gonadotropic axis. Alteration in the hypothalamic KiSS-1 system has been reported in adverse metabolic conditions linked to suppressed gonadotropins, such as undernutrition. However, its potential contribution to defective gonadotropin secretion in diabetes has not been evaluated. We report herein analyses of luteinizing hormone (LH) responses to kisspeptin and hypothalamic expression of the KiSS-1 gene in streptozotocin (STZ)-induced diabetic male rats. In addition, functional studies involving kisspeptin replacement or continuous administration of leptin and insulin to diabetic male rats are presented. Kisspeptin administration evoked robust LH and testosterone bursts and enhanced postgonadectomy LH concentrations, despite prevailing attenuation of gonadotropic axis in diabetic animals. In addition, hypothalamic KiSS-1 mRNA levels were unambiguously decreased in diabetic male rats, and the postorchidectomy rise in KiSS-1 mRNA was severely blunted. Repeated administration of kisspeptin to diabetic rats evoked persistent LH and testosterone responses and partially rescued prostate and testis weights. In addition, central infusion of leptin, but not insulin, was sufficient to normalize hypothalamic KiSS-1 mRNA levels, as well as LH and testosterone concentrations. In summary, we provide evidence for altered expression of the hypothalamic KiSS-1 system in a model of uncontrolled diabetes. This observation, together with the ability of exogenous kisspeptin to rescue defective LH responses in diabetic rats, unravel the physiopathological implication, and potential therapeutic intervention, of the KiSS-1 system in altered gonadotropin secretion of type 1 diabetes.

A Rice Bran Oil Diet Increases LDL-Receptor and HMG-CoA Reductase mRNA Expressions and Insulin Sensitivity in Rats with Streptozotocin/Nicotinamide-Induced Type 2 Diabetes

A rice bran oil (RBO) diet can reduce plasma lipids; this was attributed to the specific components, gamma-oryzanol and gamma-tocotrienol, which individually were shown to be hypocholesterolemic; however, the mechanism of their effects on diabetic hyperlipidemia and the development of diabetes is not known. Rats with streptozotocin/nicotinamide-induced type 2 diabetes were divided into control, RO10, and RO15 groups, and fed cholesterol-free diets containing 0, 10, and 15 g RBO with 0, 352, and 528 g gamma-oryzanol and 0, 6.0 and 9.0 mg gamma-tocotrienol/100 g diet for 4 wk. Diabetic rats fed the RBO diet had greater insulin sensitivity (P = 0.02) than rats fed the control diet. Diabetic rats fed the RBO diet also had lower plasma triglyceride (P = 0.003), LDL cholesterol (P = 0.028), and hepatic triglyceride concentrations (P = 0.04), as well as greater fecal neutral sterol and bile acid excretion than those fed the control diet. After 4 wk, there was an approximately 100% (P < 0.001) increase in the abundance of hepatic cholesterol 7alpha-hydroxylase, an 89% (P < 0.001) increase in the hepatic LDL-receptor, and a 50% (P < 0.001) increase in hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA in rats fed the RBO diet compared with those fed the control diet. These findings support the conclusion that a rice bran oil-containing diet can significantly suppress hyperlipidemic and hyperinsulinemic responses in diabetic rats. The high contents of gamma-oryzanol and gamma-tocotrienol in RBO can lead to increased fecal neutral sterol and bile acid excretion, via upregulation of cholesterol synthesis and catabolism.

Edaravone attenuates hydroxyl radical stress and augmented angiotensin II response in diabetic rats

Reactive oxygen species (ROS) potentiate angiotensin II (Ang II) responses in diabetic vasculature. However, superoxide scavengers partially restore this effect, suggesting free radicals other than superoxide could be involved. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is an antioxidant, which primarily scavenges hydroxyl radicals and is approved for use in stroke patients. Hence, to evaluate the role of hydroxyl radical stress in diabetic vascular complications, we studied the effect of edaravone (3 mg kg −1, i.p., b.i.d.) treatment on Ang II responses in thoracic aorta isolated from streptozotocin (60 mg kg −1 i.p.) induced 8 weeks diabetic male Sprague–Dawley rats. Ang II (10 −10 to 10 −6 M), tert-butyl hydro peroxide (tBHP; 10 −6 to 10 −2 M) or hydrogen peroxide (H 2O 2; 10 −6 to 10 −3 M) induced contractile response was significantly enhanced in aortic strips from diabetic as compared to control rats. Lipid peroxidation was significantly enhanced while the superoxide dismutase (SOD) and catalase activity was significantly lower in aorta of diabetic rats as compared to control rats. Acute (in vitro) exposure of edaravone (10 −5 M) to aortic strips from diabetic rats in the organ bath restored the augmented Ang II but not tBHP or H 2O 2-induced contractile response. In vivo edaravone (3 mg kg −1, i.p., b.i.d.) treatment for 2 weeks selectively attenuated the augmented Ang II- but not tBHP- or H 2O 2-induced contractile response. The enhanced systolic pressure, lipid peroxidation and the reduced SOD and catalase activity were restored to control values following 2 weeks edaravone treatment. From our results we infer that hydroxyl radical stress augments Ang II response in diabetic rat thoracic aorta and edaravone could be an ideal antioxidant adjuvant in the therapy of diabetic vascular complications.

The effect of systemic leptin administration on aorta smooth muscle responses in diabetic rats

Leptin produces effects in central nervous system and peripheral tissues via its specific receptors. Leptin also stimulates nitric oxide release in a concentration-dependent manner. In this study, our aim was to test the hypothesis that whether leptin has a modulatory role on endothelium or smooth muscle function in streptozotocin (STZ)-induced diabetic rats. Wistar-Albino rats were divided into four groups: 1 -- Control, 2 -- Diabetic, 3 -- Control + leptin and 4 -- Diabetic + leptin. Experimental diabetes was produced by intraperitoneal injection of a single dose of STZ (55 mg/kg). Diabetes was determined by increased fasting blood glucose level on the 7th day of the experiment. Leptin (0.1 mg/kg/day) was administered intraperitoneally for 5 days. At the end of the 5th day, thoracic aortas were isolated and phenylephrine (Phe)-induced contractions and acetylcholine (ACh)-induced relaxations of each group were estimated. In diabetic rats, Phe-induced contractility was increased (p < 0.05). Leptin pre-treatment increased the Phe-induced contractility significantly in aortic rings obtained from diabetic rats (p < 0.05). In normal rats, leptin administration produced only a slight and non-significant increase in Phe-induced contractions. Although the relaxant responses were decreased in diabetic rats, leptin administration enhanced the ACh-induced relaxation in both normal and diabetic animals significantly. As a conclusion; chronic leptin pre-treatment caused a significant increase both in Phe-induced contractions and ACh-induced Endothelial-Derived Relaxing Factor (EDRF)/Nitric oxide-mediated relaxations in the aortic rings isolated from streptozotocin-induced diabetic rats. This peptide hormone caused a significant increase in the relaxations obtained by ACh while not inducing a significant alteration in the contractile effect of Phe in control rats.

Role of insulin on PGE 2 generation during LPS-induced lung inflammation in rats

Alterations in arachidonic acid (AA) metabolism have been reported to occur in diabetes mellitus. The present study was carried out to verify if these alterations are due to the relative lack of insulin or to high levels of blood glucose. Male Wistar rats were rendered diabetic by alloxan injection (42 mg/kg, i.v.), 10 or 30 days before the experiments. Some diabetic rats received a single dose (4 IU, s.c.) of NPH insulin 2 h before an intratracheal instillation of lipopolysaccharide (LPS, 750 μg) or saline. Six hours after LPS challenge, the following parameters were analysed: blood glucose levels, total and differential leukocyte counts in bronchoalveolar lavage (BAL) fluid; linoleic acid and AA content in blood neutrophils (HPLC), and levels of prostaglandin (PG)E 2 in BAL (ELISA). Relative to controls, a reduced number of neutrophils (18%) and decreased amounts of PGE 2 (40%) were observed in the BAL fluid of diabetic rats in response to LPS. A single dose of insulin was not able to reduce blood sugar levels to normal values, but instead resulted in the normalization of both leukocyte migration to the lungs and levels of PGE 2. Accordingly, these abnormalities might be primarily linked to a continuing insulin deficiency rather than to secondary hyperglycaemia occurring in the diabetic rat. In conclusion, data presented suggest that insulin might regulate neutrophil migration and generation of PGE 2 during the course of acute lung injury induced by LPS.

ORIGINAL RESEARCH—BASIC SCIENCE: Enhancement of Both EDHF and NO/cGMP Pathways Is Necessary to Reverse Erectile Dysfunction in Diabetic Rats

Phosphodiesterase 5 (PDE5) inhibitors are less effective in the treatment of erectile dysfunction (ED) in diabetic men than in nondiabetic patients. We have evaluated the effects of sildenafil, a PDE5 inhibitor that enhances the nitric oxide (NO)/cGMP pathway, calcium dobesilate (DOBE), which potentiates endothelium-derived hyperpolarizing factor (EDHF)-mediated responses and the combination of both on erectile responses elicited by cavernosal nerve electrical stimulation (CNES) in a rat model of ED after 8 weeks of streptozotocin-induced diabetes. After 8 weeks of diabetes, erectile responses to CNES were significantly decreased in diabetic animals compared with nondiabetic time controls. While intravenous administration of sildenafil (0.3 mg/kg) or DOBE (10 mg/kg), individually, enhanced erectile responses in nondiabetic rats (214.7 +/- 34.1% and 268.5 +/- 30.1% of control response at 1 Hz, respectively), each failed to significantly enhance erectile responses in diabetic rats. Only when administered in combination did DOBE and sildenafil markedly potentiate erectile responses in these animals (380.1 +/- 88.6% of control response at 1 Hz), completely restoring erectile function. These findings emphasize the importance of NO/cGMP and EDHF pathways for normal erectile function. They also give support to the in vitro observation that diabetes impairs NO and EDHF-dependent responses, precluding the complete recovery of erectile function with PDE5 inhibitors and explaining the relatively poor clinical response of diabetic men with ED to PDE5 inhibition. Finally, our study suggests that a pharmacological approach that combines enhancement of NO/cGMP and EDHF pathways could be necessary to treat ED in many diabetic men.

Exercise training modulates heat shock protein response in diabetic rats.

Strenuous exercise induces oxidative stress and modification of intracellular proteins. Exercise training, however, upregulates endogenous antioxidant defenses and heat shock protein (HSP) expression. In diabetes, perturbations in the endogenous antioxidant and HSP protection have been reported. The aim of this study was to examine the effect of 8 wk of endurance training on HSP expression and oxidative stress markers in the skeletal muscle, heart, and liver of streptozotocin-induced diabetic (SID) and nondiabetic control rats. Induction of diabetes decreased HSP72 expression in heart, liver, and vastus lateralis muscles. SID increased heme oxygenase-1, an oxidative stress-inducible HSP, in liver, red gastrocnemius muscle, and vastus lateralis muscle and glucose-regulated protein 75 in liver. SID increased HSP90 levels in the heart, but levels decreased in the liver. Diabetes induced oxidative stress marker protein carbonyl levels and tissue inflammation. Although endurance training increased the expression of HSP72 in all of the tissues examined, this induction was less pronounced in diabetic rats than in nondiabetic controls. Furthermore, endurance training induced the activation and expression of transcriptional regulator heat shock factor-1 only in nondiabetic control animals. In summary, diabetes may increase susceptibility to oxidative damage and impair HSP protection, but endurance training may offset some of the adverse effects of diabetes by upregulating tissue HSP expression. Our results suggest that diabetes impairs HSP protection, possibly via transcriptionally mediated mechanisms.

Antinociceptive action of a p38α MAPK inhibitor, SD-282, in a diabetic neuropathy model

Diabetes can induce a bewildering list of sensory changes, including alteration in pain sensitivity. Painful diabetic neuropathy is refractory to most common analgesics. This study examined the effect of a p38α MAPK inhibitor, SD-282, on mechanical allodynia, thermal hyperalgesia, and formalin-evoked nociception in streptozotocin-induced diabetic rats. Four-week diabetic rats exhibited mechanical allodynia, decreased mechanical thresholds, and C- and Aδ-fiber mediated thermal hyperalgesia. Mechanical and thermal responses were measured in diabetic rats following acute and repeated intraperitoneal administration of vehicle, 15 or 45 mg/kg SD-282. Mechanical allodynia was reversed by acute and repeated administration of 15 and 45 mg/kg SD-282. Repeated administration of 15 or 45 mg/kg SD-282 prevented the exacerbation of C-, but not Aδ-fiber, mediated thermal hyperalgesia. Repeated administration of 45 mg/kg SD-282 attenuated flinching behaviors during the quiescent period and the second phase of the formalin response in diabetic rats. Acute and repeated administration of 15 or 45 mg/kg SD-282 had no effect on mechanical, thermal or formalin responses in age-matched control rats. These results indicate a potential therapeutic value of p38α MAPK inhibitors in the treatment of aberrant pain sensitivity produced by diabetes.

Influence of exercise on dilatation of the basilar artery during diabetes mellitus

Our goal was to examine whether exercise training alleviates impaired nitric oxide synthase (NOS)-dependent dilatation of the basilar artery in Type 1 diabetic rats. To test this hypothesis, we measured in vivo diameter of the basilar artery in sedentary and exercised nondiabetic and diabetic rats in response to NOS-dependent (acetylcholine) and -independent (nitroglycerin) agonists. To determine the potential role for nitric oxide in vasodilatation in sedentary and exercised nondiabetic and diabetic rats, we examined responses after NG-monomethyl-l-arginine (l-NMMA). We found that acetylcholine produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic rats. Acetylcholine produced only minimal vasodilatation in sedentary diabetic rats. However, exercise alleviated impaired acetylcholine-induced vasodilatation in diabetic rats. Nitroglycerin produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic and diabetic rats. l-NMMA produced similar inhibition of acetylcholine-induced dilatation of the basilar artery in sedentary and exercised nondiabetic and diabetic rats. Finally, we found that endothelial NOS (eNOS) protein in the basilar artery was higher in diabetic compared with nondiabetic rats and that exercise increased eNOS protein in the basilar artery of nondiabetic and diabetic rats. We conclude that 1) exercise can alleviate impaired NOS-dependent dilatation of the basilar artery during diabetes mellitus, 2) the synthesis and release of nitric oxide accounts for dilatation of the basilar artery to acetylcholine in sedentary and exercised nondiabetic and diabetic rats, and 3) exercise may exert its affect on cerebrovascular reactivity during diabetes by altering levels of eNOS protein in the basilar artery.

Effect of combination endothelial nitric oxide synthase gene therapy and sildenafil on erectile function in diabetic rats.

Erectile dysfunction associated with diabetes mellitus is caused in part by disordered endothelial smooth muscle relaxation, neuropathy, and a decrease in cavernosal nitric oxide synthase (NOS) activity. The purpose of this study was to determine whether a combination of sildenafil and adenoviral gene transfer of endothelial NOS (eNOS) could enhance the erectile response in diabetic rats. Five groups of animals were utilized: (1) age-matched control rats, (2) streptozotocin (STZ)-induced diabetic rats (60 mg/kg i.p.), (3) STZ-rats + sildenafil (2 mg/kg i.v.), (4) STZ-rats transfected with AdCMVbetagal or AdCMVeNOS, and (5) STZ-rats transfected with AdCMVeNOS +sildenafil (2 mg/kg i.v.). At 2 months after i.p. injection of STZ, groups 4 and 5 were transfected with the adenoviruses and 1-2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Cyclic 3',5'-guanosine monophosphate (cGMP) levels were assessed in the cavernosal tissue. STZ-diabetic rats had a significant decrease in erectile function as determined by the peak intracavernosal pressure (ICP) and total ICP (area under the erectile curve; AUC) after CNS when compared to control rats. STZ-diabetic rats+AdCMVeNOS had a peak ICP and AUC, which were similar to control animals. STZ-diabetic rats administered sildenafil demonstrated a significant increase in peak ICP at the 5 and 7.5 V settings, while the AUC was significantly increased at all voltage (V) settings. The increase in both ICP and AUC of STZ-diabetic rats transfected with AdCMVeNOS at all V settings was greater than STZ-diabetic rats transfected with AdCMVbetagal. STZ-diabetic rats transfected with AdCMVeNOS and administered sildenafil had a significant increase in total ICP that was greater than eNOS gene therapy alone. Cavernosal cGMP levels were significantly decreased in STZ-diabetic rats, but were increased after transfection with AdCMVeNOS to values greater than control animals. In conclusion, overexpression of eNOS and cGMP in combination with sildenafil significantly increased both the peak ICP and total ICP to CNS in the STZ-diabetic rat, which was similar to the response observed in control rats. Moreover, the total erectile response was greater in STZ-diabetic rats receiving eNOS gene therapy plus sildenafil than STZ-rats receiving sildenafil or eNOS gene therapy alone.