Receptors In Diabetic Rats Research Articles

Involvement of γ-Aminobutyric acid and N-methyl-D-aspartate receptors in diabetic gastropathy in rats: possible beneficial effect of prolonged treatment with insulin and magnesium supplement

Gastrointestinal dysfunction is a severe and common complication in diabetic patients. Some evidence shows that gamma-aminobutyric acid (GABA) and glutamate contribute to diabetic gastrointestinal abnormalities. Hence, we examined the impact of prolonged treatment with insulin and magnesium supplement on the expression pattern of GABA type A (GABA-A), GABA-B and N-methyl-D-aspartate (NMDA) glutamate receptors as well as nitric oxide synthase 1 (NOS-1) in the stomach of type 2 diabetic rats. Twenty-four male Wistar rats were randomized to 4 groups (6 rats each): 1) control, 2) type 2 diabetes: rats fed with a high fat diet for 3 months + low dose of streptozotocin (35 mg/kg), 3) type 2 diabetes + magnesium, and 4) type 2 diabetes + insulin. The expression of NOS-1 as well as GABA-A, GABA-B, and NMDA receptors was detected using western blotting. NOS-1 expression was substantially diminished (p<0.01) while the expression of GABA-A (p<0.001), GABA-B (p<0.001), and NMDA (p<0.001) receptors was enhanced in the stomach of diabetic rats relative to control. Treatment with magnesium and insulin improved NOS-1 expression in diabetic rats, although this effect was greater in magnesium treatment alone. Magnesium also restored the expression of GABA-A and GABA-B receptors in diabetic rats to control values. Moreover, insulin treatment improved GABA-A receptor expression in diabetic rats (p<0.05). No considerable alterations were detected in NMDA receptor level in the treatment groups. The results suggest a significant role of magnesium and insulin in improving gastric motility and secretory disorders associated with diabetes through modifying the expression of GABAergic receptors.

Implication of lncRNA MSTRG.81401 in Hippocampal Pyroptosis Induced by P2X7 Receptor in Type 2 Diabetic Rats with Neuropathic Pain Combined with Depression.

Major depressive disorder (MDD) is a common complication of diabetes and is often observed alongside diabetic neuropathic pain (DNP) as a comorbidity in diabetic patients. Long non-coding RNA (lncRNA) plays an important role in various pathophysiological processes. The P2X7 receptor is responsible for triggering inflammatory responses, such as pyroptosis, linked to pain and depression. The aim of this study was to investigate the effect of lncRNA MSTRG.81401 on hippocampal pyroptosis induced by the P2X7 receptor in diabetic rats with DNP combined with MDD (DNP + MDD). Our results showed that the expression of lncRNA MSTRG.81401 was significantly elevated in the hippocampus of DNP + MDD rats compared with the control group. Following the administration of shRNA targeting lncRNA MSTRG.81401, a notable elevation in mechanical and thermal pain thresholds was observed in rats with comorbid DNP and MDD. Additionally, significant improvements in depression-like behaviors were evident in the open-field test (OFT), sucrose preference test (SPT), and forced swim test (FST). In the DNP + MDD rats, elevated levels in hippocampal P2X7 receptor mRNA and protein were observed, along with increased co-expression of P2X7 and the astrocytic marker glial fibrillary acidic protein (GFAP). Meanwhile, in DNP + MDD rats, the heightened mRNA expression of NOD-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein (ASC), pyroptosis-related protein Gasdermin D (GSDMD), caspase-1, IL-1β, IL-18, and TNF-α was detected, in addition to increased serum levels of IL-1β, IL-18 and TNF-α. After shRNA treatment with lncRNA MSTRG.81401, the above abnormal changes in indicators for pyroptosis and inflammation were improved. Therefore, our study demonstrates that shRNA of lncRNA MSTRG.81401 can alleviate the pain and depression-like behaviors in diabetic rats associated with the comorbidity of DNP and MDD by inhibiting the hippocampal P2X7 receptor-mediated pyroptosis pathway and pro-inflammatory responses. This suggests that the P2X7R/NLRP3/caspase-1 implicated pyroptosis and inflammatory scenario may serve as a potential target for the management of comorbid DNP and MDD in diabetes.

Schisandrin B Alleviates Diabetic Cardiac Autonomic neuropathy Induced by P2X7 Receptor in Superior Cervical Ganglion via NLRP3.

Diabetic cardiovascular autonomic neuropathy (DCAN) is a common complication of diabetes mellitus which brings about high mortality, high morbidity, and large economic burden to the society. Compensatory tachycardia after myocardial ischemia caused by DCAN can increase myocardial injury and result in more damage to the cardiac function. The inflammation induced by hyperglycemia can increase P2X7 receptor expression in the superior cervical ganglion (SCG), resulting in nerve damage. It is proved that inhibiting the expression of P2X7 receptor at the superior cervical ganglion can ameliorate the nociceptive signaling dysregulation induced by DCAN. However, the effective drug used for decreasing P2X7 receptor expression has not been found. Schisandrin B is a traditional Chinese medicine, which has anti-inflammatory and antioxidant effects. Whether Schisandrin B can decrease the expression of P2X7 receptor in diabetic rats to protect the cardiovascular system was investigated in this study. After diabetic model rats were made, Schisandrin B and shRNA of P2X7 receptor were given to different groups to verify the impact of Schisandrin B on the expression of P2X7 receptor. Pathological blood pressure, heart rate, heart rate variability, and sympathetic nerve discharge were ameliorated after administration of Schisandrin B. Moreover, the upregulated protein level of P2X7 receptor, NLRP3 inflammasomes, and interleukin-1β in diabetic rats were decreased after treatment, which indicates that Schisandrin B can alleviate the chronic inflammation caused by diabetes and decrease the expression levels of P2X7 via NLRP3. These findings suggest that Schisandrin B can be a potential therapeutical agent for DCAN.

Combination Therapy with GABA and MgSO4 Improves Insulin Sensitivity in Type 2 Diabetic Rat.

Background Gamma-aminobutyric acid (GABA) and magnesium sulfate (MgSO4) play a crucial role in glycemic control. Therefore, we studied the effect of combination therapy with GABA and MgSO4 to improve insulin sensitivity in diabetes induced by streptozotocin as well as high-fat diet in a diabetic rat model. Design and Methods. Forty randomly selected rats were assigned to four groups: nondiabetic control group was fed the normal diet, insulin-resistant diabetic rat model was induced by streptozotocin and high-fat diet, GABA + MgSO4 group received GABA and MgSO4, and insulin group was treated with insulin. Body weight, abdominal fat, blood glucose, serum insulin, and glucagon concentration were measured. The glucose clamp technique, glucose tolerance test, and insulin tolerance test were performed to study insulin sensitivity. Also, the expressions of glucose 6 phosphatase, glucagon receptor, and phosphoenolpyruvate carboxykinase genes in liver were assessed for the gluconeogenesis pathway. Protein translocation and glucose transporter 4 (Glut4) genes expression in muscle were also assessed. Results Combination of GABA + MgSO4 or insulin therapy enhanced insulin level, glycemic control, glucose and insulin tolerance test, some enzymes expression in the gluconeogenesis pathway, body fat, body weight, and glucagon receptor in diabetic rats. Moreover, an increase was observed in protein and gene expression of Glut4. Insulin sensitivity in combination therapy was more than the insulin group. Conclusions GABA and MgSO4 enhanced insulin sensitivity via increasing Glut4 and reducing the gluconeogenesis enzyme and glucagon receptor gene expressions.

Abscisic acid interplays with PPARγ receptors and ameliorates diabetes-induced cognitive deficits in rats.

This study intended to evaluate if central administration of abscisic acid (ABA) alone or in combination with GW9662, a peroxisome proliferator-activated receptor γ (PPAR-γ) antagonist, could modulate learning and memory as well as hippocampal synaptic plasticity in a rat model of streptozotocin (STZ)-induced diabetes. Intraperitonealinjectionof STZ (65 mg/kg) was used to induce diabetes. Diabetic rats were than treated with intracerebroventricular (i.c.v.) administration of ABA (10, 15 and 20 µg/rat), GW9662 (3 µg/rat) or GW9662 (3 µg/rat) plus ABA (20 µg/rat). Animals' spatial and passive avoidance learning and memory performances were assessed by Morris water maze (MWM) and shuttle box tasks, respectively. Further, in vivo electrophysiologicalfield recordings were assessed in the CA1 region. STZ diabetic rats showed diminished learning and memory in both MWM and shuttle box tasks. The STZ-induced memory deficits were attenuated by central infusion of ABA (10 and 20 µg/rat). Besides, STZ injection impaired long-term potentiationinduction in CA1 neurons that was attenuated by ABA at 20 μg/rat. Central administration of GW9662 (3 µg/rat) alone did not modify STZ-induced spatial and passive avoidance learning and memory performances of rats. Further, GW9662 prevented ABA capacity to restore learning and memory in behavioral and electrophysiology trials. Altogether, ABA ameliorates cognitive deficits in rats via activation of PPAR-γ receptor in diabetic rats.

Renal expression of sigma 1 receptors in diabetic rats

The purpose of this study was to determine the changes in the expression of sigma 1 receptors (σ1Rs) in the kidney of diabetic rats, which could indicate their possible role in the pathogenesis of diabetic nephropathy (DN). Sprague-Dawley rats were were given intraperitoneal injection of 55 mg/kg streptozotocin (STZ) in order to induce type I of diabetes (DM1). Control and diabetic rats were sacrificed 2 weeks or 2 months after DM1 induction. Expression of σ1Rs was determined in kidneys of the experimental rats, using immunohistochemistry.The most prominent expression of σ1Rs was found in distal tubuli (DT). Results have shown significant increase in renal σ1Rs section percentage area of rats 2 months after DM1 induction, compared to both control group at the same age and diabetic group 2 weeks after induction (P < 0.01 both). Similarly, a number of immunoreactive DT increased in diabetic group 2 months after induction, compared to DM1 group 2 weeks after induction (P < 0.001). We also found a decrease of a number of immunoreactive DT 2 weeks post DM1 induction (P < 0.01). However, the same was found during maturation of the control rats (P < 0.001). In addition, a strong co-expression of σ1R and proinflammatory factor TGFβ was seen in vacuolated DT.The results indicate to the potential role of σ1Rs in postnatal maturation of the rat kidneys and in distal tubular damage in the pathogenesis of the diabetic nephropathy. We conclude that σ1Rs could be potential target in treatment of the diabetic nephropathy.

Mitochondrial angiotensin II receptors regulate oxygen consumption in kidney mitochondria from healthy and type 1 diabetic rats.

Exaggerated activation of the renin-angiotensin-aldosterone system (RAAS) is a key feature in diseases such as hypertension, diabetes, and chronic kidney disease. Recently, an intracellular RAAS was demonstrated with angiotensin II (ANG II) type 1 (AT1) and type 2 (AT2) receptors expressed in nuclei and mitochondria. Diabetes is associated with both mitochondrial dysfunction and increased intracellular ANG II concentration in the kidney cortex. The present study investigated the role of ANG II signaling in kidney cortex mitochondria isolated from control and streptozotocin-induced diabetic rats. Mitochondrial oxygen consumption was evaluated after addition of ANG II alone or after preincubation with candesartan (AT1 receptor antagonist), PD-123319 (AT2 receptor antagonist), or the two in combination. ANG II binds to only mitochondrial AT2 receptors in control rats and both AT1 receptors and AT2 receptors in diabetic rats. ANG II decreased oxygen consumption in mitochondria from both control and diabetic rats. ANG II response was reversed to increased oxygen consumption by the nitric oxide synthase inhibitor N-nitro-l-arginine methyl ester. AT1 receptor inhibition did not affect the response to ANG II, whereas AT2 receptor inhibition abolished the response in mitochondria from control rats and reversed the response to increased oxygen consumption through superoxide-induced mitochondrial uncoupling in mitochondria from diabetic rats. ANG II decrease mitochondrial respiration via AT2 receptor-mediated nitric oxide release in both control and diabetic rats. AT1 receptors do not regulate mitochondria function in control rats, whereas ANG II via AT1 receptors increase mitochondria leak respiration in diabetic animals.

Effects of nano-curcumin on gene expression of insulin and insulin receptor

BackgroundThis study investigates the effects of nano-curcumin on gene expression of insulin and insulin receptor in diabetic rats. Forty female rats were divided into four groups (ten rats for each). The first group was non-diabetic rats acting as negative control and rats of the second group were rendered diabetic by STZ served as positive controls. The third one was induced diabetic and received oral Diamicron for 3 weeks. The fourth was rendered diabetic and administrated oral nano-curcumin for 3 weeks.ResultsA significant increase of blood glucose was showed in diabetic rats with significant reduction of insulin level compared to non-diabetic controls. The gene expression of insulin and insulin receptor were more significant in diabetic untreated rats compared to the control non-diabetic group. The induction of curcumin as well as Diamicron to diabetic rats normalized significantly their blood sugar level. Also, curcumin-treated rats indicated significant higher in gene expression of insulin and insulin receptor than positive and negative controls.ConclusionThe results suggest that nano-curcumin could be used as antidiabetic therapy, induced hypoglycemia, and increase the gene expression of insulin and insulin receptor in STZ-induced diabetic rats. More studies are needed to illustrate the definite mechanism of action of nano-curcumin concerning the upregulation of gene expression of the above-mentioned genes.

Effect of siglidine on glucose lipid metabolism and the expression of iNOS and GLP-1 receptors in diabetic rats.

Diabetic nephropathy (DN) has become the major complication of diabetes. The progression of the disease impedes the efficacy of DN treatment. Therefore, the strategies to inhibit or reverse kidney damage in DN patients are of critical importance. We aim to investigate the effect of sitagliptin on DN within rat model and analyze the associated metabolism and expression of iNOS/GLP-1 receptor. Diabetic model was generated by using Sprague-Dawley (SD) rats, which received an intra-peritoneal injection of 30 mg/kg streptozotocin. Rats were then treated with saline or 15 mg/(kg.d) sitagliptin by gavage. After 12 weeks, fasting blood glucose and insulin resistance were measured. Rat glucose and lipid metabolism were evaluated by high triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C). Western blot was used to measure expression of glucose-6-phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK), fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) related with glucose-lipid metabolism, and expression of iNOS and GLP-1 expression in kidney tissues. After 12 weeks of feeding, the levels of blood glucose and lipid in sitagliptin group were significantly decreased compared to those in control group (p<0.05), whilst insulin sensitivity was enhanced (p<0.05). Western blot showed that sitagliptin downregulated the expressions of glucose-lipid metabolism proteins such as G6Pase, PEPCK, ACC and FAS in rat livers, inhibited iNOS expression in kidneys and elevated GLP-1 receptor activity (p<0.05). Sitagliptin effectively stabilizes blood glucose and lipid levels in DN rats, significantly improves glucose-lipid metabolism and protects kidney and vascular endothelial cells during DN pathogenesis through inhibiting iNOS expression and elevating GLP-1 receptor activity.

Increase in renal erythropoietin receptors in diabetic rats is mainly mediated by hyperglycemia associated with the STAT3/GATA-1 signaling pathway

Erythropoietin (EPO) produces cytoprotection in many tissues by activating the EPO receptor (EPOR); these effects include anti-oxidative stress and the inhibition of apoptosis in renal tubular cells. Moreover, EPO is clinically used in diabetic patients who suffer from chronic renal disease. However, the effect of hyperglycemia on renal EPOR expression remains unknown. Therefore, we determined the changes in renal EPOR expression in diabetic rats and investigated the role of potential factors using cultured cells. Streptozotocin-induced hyperglycemic rats (STZ rats) treated with insulin or phloridzin to correct hyperglycemia were used to investigate treated with insulin or phloridzin to correct hyperglycemia were used to investigate the EPOR changes. Potential factors, including the transducer and activator of transcription 3 (STAT3) and GATA binding protein 1 (GATA1), were identified in cultured NRK-49F cells after incubation with high glucose (HG) levels to mimic diabetic animals. Renal EPOR expression was reduced by insulin and phloridzin in STZ rats, and hyperglycemia recovered. An increase in EPORs was also reproduced in hyperglycemia-exposed NRK-49F cells and HK-2 cells, which showed a higher expression of STAT3 or GATA1. Furthermore, the application of siRNA specific to STAT3 or GATA1 attenuated the higher expression of EPORs in HG-incubated NRK-49F cells. Moreover, stattic administered at a dose that was sufficient to inhibit STAT3 restored the level of renal EPORs in diabetic rats. Taken together, the expression of renal EPORs is increased by hyperglycemia via the STAT3/GATA1 pathway and has been characterized in both diabetic rats and cultured cells.

Characteristics of dendroaspis natriuretic peptide and its receptor in streptozotocin-induced diabetic rats.

Dendroaspis natriuretic peptide (DNP) shares a functionally important sequence homology with other natriuretic peptides. However, the characteristics of DNP and its receptor in the context of diabetes remafin to be fully elucidated. In the present study, alterations in the plasma levels and tissue contents of DNP and the properties of its receptor in diabetic rats, induced by streptozotocin (STZ) injection, were investigated. The plasma levels of DNP were 90.01 ± 4.12 and 196.68 ± 5.60 pg/ml in the control and STZ-induced diabetic rats, respectively. The tissue contents of DNP in the cardiac atrium, ventricle, renal cortex and inner medulla of the STZ-induced diabetic rats were also significantly increased compared with the control rats. Specific (125)I-DNP-binding sites were located predominantly in the glomeruli and inner medulla of the rat kidney. In the glomeruli of the kidney, the apparent dissociation constants (Kd) of (125)I-DNP in the control and STZ-induced diabetic rats were 0.41 ± 0.03 and 0.56 ± 0.06 nM, respectively. The maximum binding capacities (Bmax) of (125)I-DNP in control and STZ-induced diabetic rats were 2.98 ± 0.21 and 6.22 ± 1.06 fmol/mg protein, respectively. However, no differences were observed in the apparent Kd and Bmax of (125)I-DNP in the inner medulla of the kidney between the control and STZ-induced diabetic rats. In the glomerular and inner medullary kidney membranes, DNP stimulated the production of cyclic guanosine monophosphate (cGMP) in a dose-dependent manner. The magnitude of cGMP production in glomerular membranes was greater in the STZ-induced diabetic rats, whereas the magnitude of cGMP production in the inner medullary membranes was lower in the STZ-induced diabetic rats compared with the control rats. These results indicated that STZ-induced diabetes modulate DNP and its receptor, and also suggested that modulation of the DNP system is involved in the renal function of diabetic animals via the intracellular domain of the kidney NP receptor.

Effects of Low-Protein Diets Supplemented with Ketoacid on Expression of TGF-β and Its Receptors in Diabetic Rats.

TGF-β 1 has been recognized as a key mediator in DN. This study aimed to observe the effects of low-protein diets supplemented with ketoacid on mRNA and protein expression of TGF-β and TβRI and t TβRII receptors in the renal tissue of diabetic rats. A diabetes model was established in 72 male SD rats. They were then equally randomized to three groups: NPD group, LPD group, and LPD + KA group. Additional 24 male SD rats receiving normal protein diets were used as the control. Eight rats from each group were sacrificed at weeks 4, 8, and 12 after treatment, from which SCr, BUN, serum albumin, and 24 h urinary protein excretion were collected. The expressions of TGF-β 1, TβRI, and TβRII in LPD and LPD + KA groups were significantly lower than those in NPD group and lower in LPD + KA group than those in LPD group. Low-protein diets supplemented with ketoacid have been demonstrated to provide a protective effect on the renal function as represented by reduced SCr, BUN, and urinary protein excretion, probably through downregulating the gene expression of TGF-β 1 and its receptors in LPD + KA group.

Berberine regulates the expression of E-prostanoid receptors in diabetic rats with nephropathy

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetic patients. Effective therapies to prevent the development of this disease and to improve advanced kidney injury are required. Berberine (BBR) has preventive effects on diabetes and its complications. This study is to investigate the effects of BBR on the expression of E-prostanoid receptors (EPs) in rats with high-fat diet and streptozotocin (STZ)-induced DN and underlying molecular mechanisms of BBR on DN rats. DN model was induced in male Sprague-Dawley rats with high-fat diet and low dose of STZ injection. BBR (50, 100, 200mg/kg/d) were orally administered to rats after STZ injection and conducted for 8weeks. The levels of interleukin-6 (IL-6) and prostaglandin E2 (PGE2) in renal cortex were measured by enzyme-linked immunosorbent assay. Expression of EPs receptors (EP1-EP4) were determined by western blotting. Remarkable renal damage, hyperglycemia and hyperlipidemia were observed in DN rats. BBR could restore renal functional parameters, suppress alterations in histological and ultrastructural changes in the kidney tissues, improve glucose and lipid metabolism disorders, and increase cAMP levels compared with those of DN model group (Wang et al. in Mol Biol Rep 40:2405-2418, 2013). The level of IL-6 and PGE2 were significantly increased in DN model group compared with normal group, BBR could apparently reduced the level of IL-6 and PGE2. Furthermore, the expression of EP1 and EP3 were both increased and EP4 was lessened in the DN model group compared with normal group, BBR could down-regulate total protein expression of EP1 and EP3 of renal cortex in DN rats and up-regulate the expression of EP4, and there is no significant difference on the expression of EP2 among all groups. These studies demonstrate, for the first time, that BBR exerts renoprotection in high-fat diet and STZ-induced DN rats by modulating the proteins expression of EPs in EP-G protein-cAMP signaling pathway.

Reduced Number, G Protein Coupling, and Antinociceptive Efficacy of Spinal Mu-Opioid Receptors in Diabetic Rats Are Reversed by Nerve Growth Factor

This study investigated putative mechanisms of impaired spinal opioid antinociception such as a downregulation of mu-opioid receptor (MOR) number, coupling, and efficacy in rats with advanced (12 weeks) streptozotocin (STZ)-induced diabetes. Intravenous injection of STZ (45 mg/kg) in Wistar rats led to selective degeneration of insulin-producing pancreatic ß-cells, elevated blood glucose, and mechanical hyperalgesia. In these animals, dose-dependent and naloxone-reversible intrathecal fentanyl antinociception was significantly impaired and associated with a loss in MOR immunoreactivity of calcitonin gene-related peptide–immunoreactive (CGRP-IR) sensory nerve terminals, membrane-bound MOR binding sites, and MOR-stimulated G protein coupling within the dorsal horn of the spinal cord. Intrathecal delivery of nerve growth factor (NGF) in diabetic animals normalized spinal MOR number and G protein coupling and rescued spinal fentanyl-induced antinociception. These findings identify for the first time a loss in functional MOR on central terminals of sensory neurons as a contributing factor for the impaired spinal opioid responsiveness during advanced STZ-induced diabetes that can be reversed by NGF. Moreover, they support growing evidence of a distinct regulation of opioid responsiveness during various painful states of disease (eg, arthritis, cancer, neuropathy) and may give novel therapeutic incentives. PerspectiveIn diabetic neuropathy a loss in sensory neuron mu-opioid receptor number and coupling contributes to impaired spinal opioid antinociception that can be reversed by NGF. These findings support growing evidence of a distinct regulation of opioid responsiveness during various painful diseases and may give novel therapeutic incentives.

The Extracellular cAMP-Adenosine Pathway Regulates Expression of Renal D1 Dopamine Receptors in Diabetic Rats

Activation of D1 dopamine receptors expressed in the kidneys promotes the excretion of sodium and regulates sodium levels during increases in dietary sodium intake. A decrease in the expression or function of D1 receptors results in increased sodium retention which can potentially lead to the development of hypertension. Studies have shown that in the absence of functional D1 receptors, in null mice, the systolic, diastolic, and mean arterial pressures are higher. Previous studies have shown that the expression and function of D1 receptors in the kidneys are decreased in animal models of diabetes. The mechanisms that down-regulate the expression of renal D1 receptor gene in diabetes are not well understood. Using primary renal cells and acutely isolated kidneys from the streptozotocin-induced rat diabetic model, we demonstrate that the renal D1 receptor expression is down-regulated by the extracellular cAMP-adenosine pathway in vitro and in vivo. In cultures of primary renal cells, a 3 mm, 60-h cAMP treatment down-regulated the expression of D1 receptors. In vivo, we determined that the plasma and urine cAMP levels as well as the expression of 5'-ectonucleotidase, tissue-nonspecific alkaline phosphatase, and adenosine A2a receptors are significantly increased in diabetic rats. Inhibitors of 5'-ectonucleotidase and tissue-nonspecific alkaline phosphatase, α,β-methyleneadenosine 5'-diphosphate, and levamisole, respectively, blocked the down-regulation of D1 receptors in the primary renal cells and in the kidney of diabetic animals. The results suggest that inhibitors of the extracellular cAMP-adenosine pathway reverse the down-regulation of renal D1 receptor in diabetes.

Down regulation of cerebellar serotonergic receptors in streptozotocin induced diabetic rats: Effect of pyridoxine and Aegle marmelose

Oxidative stress plays an important role in cerebellar damage caused by diabetes, leading to deterioration in glucose homeostasis causing metabolic disorders. The present study was carried out to find the effects of Aegle marmelose leaf extract and insulin alone and in combination with pyridoxine on the cerebellar 5-HT through 5-HT 2A receptor subtype, gene expression studies on the status of antioxidants—superoxide dismutase (SOD), glutathione peroxidase (GPx), 5-HT 2A and 5-HT transporter (5-HTT) and immunohistochemical studies in streptozotocin induced diabetic rats. 5-HT and 5-HT 2A receptor binding parameters, B max and K d, showed a significant decrease ( p < 0.001) in the cerebellum of diabetic rats compared to control. Gene expression studies of SOD, GPx, 5-HT 2A and 5-HTT in cerebellum showed a significant down regulation ( p < 0.001) in diabetic rats compared to control. Pyridoxine treated alone and in combination with insulin, A. marmelose to diabetic rats reversed the B max, K d of 5-HT, 5-HT 2A and the gene expression of SOD, GPx, 5-HT 2A and 5-HTT in cerebellum to near control. The gene expression of 5-HT 2A and 5-HTT were confirmed by immunohistochemical studies. Also, the Rotarod test confirms the motor dysfunction and recovery by treatment. These data suggest the antioxidant and neuroprotective role of pyridoxine and A. marmelose through the up regulation of 5-HT through 5-HT 2A receptor in diabetic rats. Our results suggest that pyridoxine treated alone and in combination with insulin and A. marmelose has a role in the regulation of insulin synthesis and release, normalizing diabetic related oxidative stress and neurodegeneration affecting the motor ability of an individual by serotonergic receptors through 5-HT 2A function. This has clinical significance in the management of diabetes.

Differential effect of insulin treatment on decreased levels of beta-defensins and Toll-like receptors in diabetic rats

Many infections are associated with diabetes, as the ability of the body to fight pathogens is impaired. Recently, altered levels of defensins and polymorphism in Toll-like receptors (TLRs), two crucial components of the innate immune system, have been associated with diabetes. To study the functionality of the innate immune system during diabetes, we measured the expression levels of rat beta-defensin 1 (rBD-1), rBD-2, rTLR2, and rTLR4 in the kidney, lung, liver, and brain of streptozotocin-induced diabetic rats with and without insulin treatment. In the kidneys of diabetic rats, lower levels of rBD-1, rTLR2, and rTLR4 were found. These low levels could be restored with insulin treatment. In contrast, rBD-2 was highly induced in the lungs of diabetic rats, most likely, as a result of a pro-inflammatory response. In the liver and brain of diabetic rats, lower levels of TLRs and/or defensins could not be restored with insulin treatment. Our findings suggest for the first time that high blood glucose and/or insulin deficiency abrogates the expression level of the innate immune system components, defensins and TLRs, explaining the recurrent infections during diabetes. These findings may lay the grounds for future design of novel treatments that will induce defensins and TLRs and, as a result, bolster the immune system in diabetic patients.

Involvement of cholecystokinin in peripheral nociceptive sensitization during diabetes in rats as revealed by the formalin response

The possible pronociceptive role of peripheral cholecystokinin (CCK-8) as well as CCK A and CCK B receptors in diabetic rats was assessed. Subcutaneous injection of 0.5% formalin induced a greater nociceptive behavior in diabetic than in non-diabetic rats. Moreover, local peripheral injection of CCK-8 (0.1–100 μg) significantly increased 0.5% formalin-induced nociceptive activity in diabetic, but not in non-diabetic, rats. This effect was restricted to the formalin-injected paw as administration of CCK-8 into the contralateral paw was ineffective. Local peripheral administration of CCK-8, in the absence of formalin injection, produced a low level of, but significant increase in, flinching behavior in diabetic compared to non-diabetic rats. In addition, local peripheral administration of the non-selective CCK receptor antagonist proglumide (1–100 μg), CCK A receptor antagonist lorglumide (0.1–100 μg) or CCK B receptor antagonist CR-2945 (0.1–100 μg), but not vehicle or contralateral administration of CCK receptor antagonists, significantly reduced 0.5% formalin-induced flinching in diabetic rats. CR-2945 was the most effective drug in this condition. These effects were not observed in non-diabetic rats. The local peripheral pronociceptive effect of CCK-8 (100 μg) was significantly reduced by proglumide (100 μg), lorglumide (100 μg), and CR-2945 (100 μg). Results suggest that diabetes-induced peripheral sensitization could be due to a local peripheral release of CCK-8, which in turn would act on CCK B, mainly but also in CCK A, receptors located on the primary afferent neurons.

Effects of cholecystokinin octapeptide on the exocrine pancreas in a new rat model of type 2 diabetes

We investigated the effects of increasing concentrations of cholecystokinin octapeptide (CCK-8) on the exocrine pancreas of a new model of type 2 diabetic rats due to the partial protection exerted by nicotinamide against the β-cytotoxic effect of streptozotocin. CCK-8, administered for 8 successive days, exerted a biphasic action on the growth of the pancreas in non-diabetic and type 2 diabetic rats; however, the latter were less sensitive to CCK-8. Similar results were obtained in vitro by measuring the uptake of 5-bromo-2′-deoxyuridine (BrdU) in cultured isolated acinar cells. This effect was completely blocked by 3 S(−)( N′-2,3-dihydro-1-methyl-2-oxo5-phenyl-1 H-1,4-benzo-diazepin-3-yl)-1 H-indole-2-carboxamide (L 364,718; a CCK 1 receptor antagonist) but not by (3 R)-3[ N′-(3-methylphenyl)ureido]-1,3-dihydro-1-methyl-5-phenyl-2 H1,4-benzo-diazepin-2-one (L 365,260; a CCK 2 receptor antagonist), suggesting a direct effect via CCK 1 receptors. Binding studies showed that these effects were mediated by a single class of low-affinity CCK 1 receptors in diabetic rats and two classes of CCK-8 binding sites (with high and low affinity) in non-diabetic rats. Thus, in our new type 2 diabetes model, the loss of sensitivity of the pancreas to CCK-8 could be attributed to the loss of CCK 1 receptors of high affinity.

Myocardial angiotensin II (Ang II) receptors in diabetic rats.

Myocardial angiotensin II (Ang II) receptors in diabetic rats.