Normal Wistar Research Articles

Antioxidant property of Grewia serrulata DC and its hypoglycemic effect on normal and hyperglycemic rats

AimThe present study was aimed to evaluate the antioxidant property and hypoglycemic activity of aqueous and ethanolic extracts of aerial parts of Grewia serrulata DC (AEGS & EEGS) in normal and hyperglycemic male Wistar Albino rats. MethodsThe antioxidant property was evaluated both in vitro and in vivo model using standard procedures. The hypoglycemic activity was evaluated by normal glucose and oral glucose tolerance test (NG-OGTT) method and by acute administration of AEGS and EEGS extracts at doses 200 and 400 mg/kg body wt p.o in Streptozotocin (STZ) induced hyperglycemic rats. ResultsThe ethanolic extract of Grewia serrulata DC exhibited strong free radical scavenging activity as evidenced by their low IC50 values in DPPH (1,1-diphenyl-2-picryl-hydrazyl) (9.16 ± 1.05 μg/ml), Superoxide (35.59 ± 1.6805 μg/ml) and nitric oxide (151.80 ± 1.79 μg/ml) methods. In in vivo study, treatment with ethanolic extract at both doses shows a significant dose dependent increase (p < 0.05 to p < 0.001) in the levels of superoxide dismutase (SOD) and Catalase (CAT) and a significant decrease (p < 0.05 to p < 0.001) in the levels of Thiobarbituric acid reactive substances (TBARS), when compared to CCl4 treated control in both liver and kidney. In NG-OGTT method EEGS shows reduction in glucose levels in normal rats and glucose loaded hyperglycemic rats and in STZ-induced hyperglycemic rats. ConclusionEEGS was found to possess strong antioxidant activity and good hypoglycemic activity compared to that of AEGS.

Effects of Ethanol Extract of Sida acuta Leaves on Some Organ Function Parameters and Physiologically Important Electrolytes in Normal Wistar Albino Rats

Effects of Ethanol Extract of Sida acuta Leaves on Some Organ Function Parameters and Physiologically Important Electrolytes in Normal Wistar Albino Rats

Methylglyoxal chronic administration promotes diabetes-like cardiac ischaemia disease in Wistar normal rats

Background and aimsThe influence of lifestyle is well documented, especially the diet regime, in the development of type 2 diabetes (T2D) and associated cardiovascular diseases. Diabetic patients have increased risk of suffering cardiac ischemia and impaired response to such accidents. Methylglyoxal (MG) circulates at high concentration in diabetics' blood and is linked to the development of diabetes chronic complications. We propose that besides promoting the cardiovascular disease, MG may also negatively regulate the endogenous cardioprotection pathways after ischemia. Methods and resultsWe performed a comparative study between three animal groups: normal Wistar (W), type 2 diabetic non-obese Goto-Kakizaki (GK) and normal rats submitted to MG chronic administration (3months) with gradually enhanced concentration, up to 75 mg/Kg (WMG). Hearts were submitted to different experimental conditions: control, ischemia and ischemia-reperfusion. Levels of oxidative stress markers, advanced glycation end-products (AGEs) and their receptors (RAGEs) were evaluated. The serine/threonine protein kinase Akt (Akt), crucial for cardiomyocytes recovery after ischemia, and apoptosis markers were also assessed.Levels of MG, systemic and cardiac oxidative stress markers, AGEs and RAGEs were similar in GK and WMG groups. Akt protein was negatively regulated by MG, leading to impaired apoptotic markers. ConclusionChronic MG administration to normal rodents mimicked most diabetic alterations, being associated with the development of cardiovascular disease and the impairment of survival pathways. Our results demonstrate the negative effect of MG rich diet in healthy animals and suggest the potential of methylglyoxal as a therapeutic target in diabetes.

Effects of whey proteins on glucose metabolism in normal Wistar rats and Zucker diabetic fatty (ZDF) rats.

Beneficial effects of milk protein on glucose metabolism have been reported. We hypothesized that dietary supplementation with specific milk protein fractions could prevent diabetes and differentially alter tissue gene expression. Therefore, we studied the effects of supplementing the diet with whey isolate, whey hydrolysate, Α-lactalbumin, and casein proteins in Zucker Diabetic Fatty rats (ZDF) and normal Wistar rats. A chow diet was included as well. Six week old male ZDF (n = 60) and Wistar rats (n = 44) were used in a 13 week study. P-glucose, p-insulin, p-glucagon, HbA1c, total-cholesterol, HDL-cholesterol, and triglycerides were measured. An oral glucose tolerance test (OGTT) was performed. Liver, muscle, and adipose samples were used for RT-PCR. One-way ANOVA and multiple comparison tests were performed. HbA1c increased during intervention, and was significantly lower for all milk protein fractions compared to chow in the ZDF rats (p < 0.05). At week 18, iAUCs during OGTT in the ZDF rats were similar for all milk protein-treated groups and significantly lower than in the chow fed group (p < 0.01). In the chow-fed group of ZDF rats, p-glucagon increased significantly compared to all milk protein fed animals. Total and HDL cholesterol were increased in the milk protein-treated ZDF rats compared with the control group. Expression of liver GYS2 and SREBP-2 were downregulated in the milk protein-fed ZDF groups compared with chow. We conclude that milk protein fractions improve glycemic indices in diabetic rats. No major differences were seen between the milk protein fractions. However, the fractions had a differential impact on tissue gene expression, most pronounced in ZDF rats.

Oxidative stress in streptozocin-diabetic rats: Amelioration by mulberry (Morus Indica L.) leaves.

OBJECTIVE: To investigate amelioration of oxidative stress by mulberry (Morus indica L.) leaves in streptozocin (STZ)-diabetic rats, as the leaves of mulberry (Morus indica L.) of Moraceae, are reported to be rich in a number of bioactive principles, i.e. antioxidant vitamins, flavonoids and moracins that can fight against oxidative stress in diabetes. METHOD: Normal wistar albino rats and STZ-diabetic rats were treated with dried mulberry leaf powder at 25% in the diet for a period of 8 weeks. The antioxidant role of mulberry was assessed by determining the effect of the leaves on hepatic lipid peroxidation, a marker of oxidative stress and the activity of hepatic antioxidant enzymes and serum antioxidant vitamins in comparison with untreated normal and diabetic rats. RESULTS: Increased oxidative stress as shown by increased lipid peroxidation and increased activity of catalase (CAT) in hepatic tissue, decreased serum ascorbic acid (vitamin C) and tocopherol (vitamin E) in diabetic rats were countered by mulberry leaves. In addition, decreased activities of hepatic antioxidant enzymes, i.e. glucose-6-phosphate dehydrogenase (G6PDH), glutathione peroxidase (GPx), glutathinone-S-tranferase (GST) and superoxide dismutase (SOD) were significantly increased by 34%, 61%, 19% and 53% respectively in mulberry leaves-treated diabetic rats as compared with diabetic control rats. CONCLUSION: Treatment with mulberry leaves protected STZ-diabetic rats from lipid peroxidation and elevated the activities of defense enzymes. This study reveals ameliorating effect of mulberry leaves on oxidative stress in diabetic rats by the synergistic action of a number of bioactive compounds present in mulberry leaves.

Pharmacokinetics of salsalate and salicylic acid in normal and diabetic rats

The pharmacokinetics (PK) of salsalate (SS) and salicylic acid (SA) was assessed in normal Wistar and diabetic Goto-Kakizaki rats. Three PK studies were conducted: (1) PK of SA in normal rats after intravenous dosing of SA at 20, 40, 80 mg/kg. (2) PK of SS and SA in normal rats after oral dosing of SS at 28, 56, 112 mg/kg. (3) PK during 4 months feeding of SS-containing diet in both normal and diabetic rats. The disposition of SS and SA were evaluated simultaneously using a pharmacokinetic model comprising several transit absorption steps and linear and nonlinear dual elimination pathways for SA. The results indicated that the nonlinear elimination pathway of SA only accounted for a small fraction of the total clearance (< 12%) at therapeutic concentrations. A flat profile of SA was observed after oral dosing of SS, particularly at a high dose. The possible reasons for this flat profile were posed. During the SS-diet feeding, the diabetic rats achieved lower blood concentrations of SA than normal rats with a higher apparent clearance (CL/F), possibly due to incomplete (47%) bioavailability. Such CL/F decreased with age in both diabetic and normal rats. The effect of diabetes on SA pharmacokinetics may necessitate increased dosing in the future usage of SS in diabetes.

The effects of Nigella sativa L. ethanolic extract on thyroid function in normal and alloxan-induced diabetic rats

Context: Nigella sativa, (black cumin seeds) compounds display a remarkable array of biochemical, immunological, and pharmacological actions, including bronchodilatory, antibacterial, hypotensive, immunopotentiating, hypoglycemic, and antitumor activity. Aims : The aim of the present study was to evaluate effects of Nigella sativa L. ethanolic extract (NSE) on the thyroid function test in normal and alloxan-induced diabetic Wistar albino rats. Settings and Design: Experimental study. Materials and Methods: Alloxan monohydrate was injected intraperitoneally at single dose of 150 mg/kg body weight to induce diabetes. Twenty Wistar albino rats were divided into four groups: NSE-treated normal, diabetic, NSE-treated diabetic, and control. NSE was administered daily orally by gavage at a dose of 1 g/kg body weight for 14 days. Serum concentration of TSH, T 4 , T 3 were measured by radioimmunoassay on day 7 th and 14 th . Statistical Analysis Used: Data are expressed as the mean ± S.E.M. For statistical analysis, ANOVA was used. Results: NSE induced a significant increase in the T 3 serum concentration on both day 7 th and 14 th in the diabetic rats and increase T 4 serum concentration on day 14 th in the normal rats. Conclusions: The results revealed that daily oral administration of Nigella sativa L. ethanolic extract (1 g/kg Bwt.) for 14 days significantly increased the serum concentration of T 4 in the normal Wistar albino rats. On the other hand the results revealed that treatment returned the serum concentration of T 3 to the normal level in the Alloxan-induced diabetic rats. Further work is suggested for evaluating the effect of Nigella sativa L. on the serum concentration of thyroid hormones to elucidate the possible mode of action.

Pioglitazone Attenuates Vascular Fibrosis in Spontaneously Hypertensive Rats

Objective. We sought to investigate whether the peroxisome proliferator-activated receptor-γ (PPAR-γ) ligand pioglitazone can attenuate vascular fibrosis in spontaneously hypertensive rats (SHRs) and explore the possible molecular mechanisms. Methods. SHRs (8-week-old males) were randomly divided into 3 groups (n = 8 each) for treatment: pioglitazone (10 mg/kg/day), hydralazine (25 mg/kg/day), or saline. Normal male Wistar Kyoto (WKY) rats (n = 8) served as normal controls. Twelve weeks later, we evaluated the effect of pioglitazone on vascular fibrosis by Masson's trichrome and immunohistochemical staining of collagen III and real-time RT-PCR analysis of collagen I, III and fibronectin mRNA.Vascular expression of PPAR-γ and connective tissue growth factor (CTGF) and transforming growth factor-β (TGF-β) expression were evaluated by immunohistochemical staining, western blot analysis, and real-time RT-PCR. Results. Pioglitazone and hydralazine treatment significantly decreased systolic blood pressure in SHRs. Masson's trichrome staining for collagen III and real-time RT-PCR analysis of collagen I, III and fibronectin mRNA indicated that pioglitazone significantly inhibited extracellular matrix production in the aorta. Compared with Wistar Kyoto rats, SHRs showed significantly increased vascular CTGF expression. Pioglitazone treatment significantly increased PPAR-γ expression and inhibited CTGF expression but had no effect on TGF-β expression. Conclusions. The results indicate that pioglitazone attenuated vascular fibrosis in SHRs by inhibiting CTGF expression in a TGF-β-independent mechanism.

Losartan improves aortic endothelium-dependent relaxation via proline-rich tyrosine kinase 2/Src/Akt pathway in type 2 diabetic Goto-Kakizaki rats

In diabetic states, endothelial dysfunction is related to vascular complications. We hypothesized that insulin-induced relaxation and the associated proline-rich tyrosine kinase 2 (Pyk2)/Src/Akt pathway would be abnormal in aortas from the Goto-Kakizaki (GK) type 2 diabetic rat, which exhibits hyperglycemia/insulin resistance, and that losartan treatment of such rats (25 mg·kg(-1)·day(-1) for 2 wk) would correct these abnormalities. Endothelium-dependent relaxation was by measuring isometric force in helical strips of aortas from four groups, each of 30 rats: normal Wistar (control), GK (diabetic), losartan-treated normal, and losartan-treated GK. Pyk2, Src, and Akt/endothelial nitric oxide synthase (eNOS) signaling-pathway protein levels and activities were assayed mainly by Western blotting and partly by immunohistochemistry. In GK (vs. age-matched control) aortas, various insulin-stimulated levels [nitric oxide production and the phosphorylations of eNOS at Ser(1177), of Akt at Thr(308), of phosphoinositide-dependent kinase-1 (PDK1) at Ser(241), of Src at Tyr(416), and of Pyk2 at Tyr(579)] were all significantly decreased and unaffected by either Src inhibitor (PP2) or Pyk2 inhibitor (AG17), while the insulin-stimulated levels of insulin receptor substrate (IRS)-1 phosphorylation at Ser(307), total-eNOS, and total-Akt were significantly increased. Losartan treatment normalized these altered levels. The insulin-stimulated phosphorylation levels of Src/PDK1/Akt/eNOS, but not of Pyk2, were decreased by PP2 in control and losartan-treated GK, but not in GK, aortas. These results suggest that in the GK diabetic aorta increased phospho-IRS-1 (at Ser(307)) and decreased Pyk2/Src activity inhibit insulin-induced stimulation of the PDK/Akt/eNOS pathway. The observed increase in phospho-IRS-1 (at Ser(307)) may result from increased angiotensin II activity.

Evaluation of the Hepatoprotective and Antioxidant Activities of an Indigenous Triherbal Formulation from South Eastern Nigeria using Wistar Albino Rats

A triherbal formulation prepared from a mixture of the leaves of Gongronema latifolium Benth., Ocimum gratissimum L. and Vernonia amygdalina Delile (GOV) was evaluated for hepato-nephro protective and antioxidant properties against D-galactosamine-induced hepatic and renal toxicity in Wistar albino rats. Normal Wistar albino rats were divided into seven groups of seven animals each. Two control experiments were setup which included normal rats treated with D-galactosamine and normal rats that received only distilled water. Three groups were treated with different doses of GOV extract (2000, 4000 and 8000mg kg-1 b. wt) and some standard hepatoprotective drugs such as Liv 52 and silymarin for 13 days prior to intoxication with D-galactosamine. The activities of serum liver enzymes, concentrations of some biochemical analytes, effect on heamatologic parameters and antioxidant status were monitored. The results showed that rats treated with GOV dose dependently exhibited significant (p<0.05) decrease in levels of ALP, ALT, AST, GGT, LDH, cholesterol, creatinine, triglycerides, urea and MDA and subsequently significantly (p<0.05) increased the albumin, total protein, catalase, GPx, GSH, GST and SOD levels when compared to the toxin control rats. The data from this study suggest that the triherbal formulation possess hepato- and nephro-protective potential against D-galactosamine induced hepatotoxicity in rats, thus providing scientific rationale for its use in traditional medicine for the treatment of liver diseases.

Characterization of Oxidative Stress Status during Diabetic Bone Healing

Early events associated with bone healing in patients with type 2 diabetes mellitus appear to be delayed. Hyperglycaemia and an associated increase in oxidative stress are cited as potential factors leading to a change in cellular behaviour. Using an in vivo model monitoring bone formation around implants placed into rat mandibles, we have previously identified that the onset of cell proliferation and osteoblast differentiation are delayed and subsequently prolonged compared with normal bone. This study used the same implant model to characterize oxidative stress biomarkers and primary antioxidant enzyme profiles during diabetic bone healing in vivo. Implants were placed into the sockets of incisors extracted from the mandibles of normal Wistar and diabetic Goto-Kakizaki rats for 3 and 9 weeks after implant insertion. Histochemical analysis confirmed a delay in bone healing around implants in diabetic animals. Immunohistochemical localization of peri-cellular staining for protein carbonyl groups, as a biomarker of oxidized protein content, was slightly higher in diabetic granulation tissue compared with normal tissue. However, no differences were observed in the staining patterns of advanced glycation end products. Minimal differences were observed in the number of cells positive for cytoplasmic superoxide dismutase (SOD)1 or mitochondrial SOD2. Significantly, catalase was absent in diabetic tissues. The results suggest that the oxidative environment in healing bone is differentially affected by hyperglycaemia, particularly in relation to catalase. The significance of these observations for diabetic bone healing is discussed.

Effects of catechin-rich oil palm leaf extract on normal and hypertensive rats’ kidney and liver

Catechin-rich oil palm (Elaeis guineensis) leaf extract (OPLE) possesses good ex vivo vasodilation, antioxidant and cardiovascular properties. This study evaluated the beneficial or toxic effects of OPLE on the liver and kidneys of normal and hypertensive rats. The OPLE (500mg/kg body weight) were administered orally to normal Wistar Kyoto rats, spontaneously hypertensive rats (SHR) and N-ω-nitro-l-arginine methyl ester (l-NAME)-induced NO-deficient hypertensive rats. The OPLE reduced hypertension in NO-deficient rats, but not in SHR. Hepatocytes or glomeruli injury and oxidative markers were high in hypertensive rats compared to normal rats, and they were reduced (p<0.05) by OPLE supplementation, even when there was no blood pressure reduction. Unlike the hypertensive drug captopril, the OPLE showed no toxicity to normal rats. The dose reported is equivalent 0.5g of catechins/day for humans or 2.5cups of tea. The catechins are from an abundant alternative source for potential use as functional food.

Delayed osteoblast differentiation and altered inflammatory response around implants placed in incisor sockets of type 2 diabetic rats

Central to the process of osseointegration is the recruitment of mesenchymal progenitor cells to the healing site, their proliferation and differentiation to bone synthesising osteoblasts. The process is under the control of pro-inflammatory cytokines and growth factors. The aim of this study was to monitor these key stages of osseointegration and the signalling milieu during bone healing around implants placed in healthy and diabetic bone. Implants were placed into the sockets of incisors extracted from the mandibles of normal Wistar and diabetic Goto-Kakizaki rats. Mandibles 1-12 weeks post-insertion of the implant were examined by histochemistry and immunocytochemistry to localise the presence of Stro-1- positive mesenchymal progenitor cells, proliferating cellular nuclear antigen proliferative cells, osteopontin and osteocalcin, macrophages, pro-inflammatory cytokines interleukin (IL)-1β, IL-6, tumour necrosis factor (TNF)-α and tumour growth factor (TGF)-β1. Image analysis provided a semi-quantification of positively expressing cells. Histological staining identified a delay in the formation of mineralised bone around implants placed in diabetic animals. Within the diabetic bone, the migration of Stro-1 mesenchymal cells in the healing tissue appeared to be unaffected. However, in the diabetic healing bone, the onset of cell proliferation and osteoblast differentiation were delayed and subsequently prolonged compared with normal bone. Similar patterns of change were observed in diabetic bone for the presence of IL-1β, TNF-α, macrophages and TGF-β1. The observed alterations in the extracellular presence of pro-inflammatory cytokines, macrophages and growth factors within diabetic tissues that correlate to changes in the signalling milieu, may affect the proliferation and differentiation of mesenchymal progenitor cells in the osseointegration process.

Haematopoietic activity of the seed aqueous extract of Hunteria umbellata (K. Schum) Hallier f. in experimental anaemia.

This study evaluates the haematopoietic and immunostimulatory activity of the seed aqueous extract of Hunteria umbellata (K. Schum) Hallier f. (HU) in normal and cyclophosphamide-induced pancytopaenic Wistar albino rats for 28 days. Results showed that oral pre-treatment with 50-200 mg/kg/day HU cause significant (p<0.05, p<0.01) dose related increases in haemoglobin (Hb), packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin concentration (MCHC), total leucocyte count (TLC) and lymphocyte differential (%lymp) in normal rats. Also, HU significantly (p<0.05, p<0.01, p<0.001) attenuated the cytotoxic effect of cyclophosphamide on the measured haematological parameters in the cyclophosphamide-treated rats, with 200 mg/kg/day HU offering the greatest protection. Thus, results obtained in this study suggest that HU possesses haematopoietic and immunostimulatory activity mediated possibly by promoting haematopoiesis through enhanced DNA synthesis/repair.

Eletrophysiological study of the caudal nerve on developing rats

To non-invasively study the sensory nerve conduction of the caudal nerve of normal developing rats. Twenty normal Wistar male rats served as subjects. Caudal nerve conduction studies were performed at 60 days from birth and weekly at end of six consecutive weeks. The caudal nerve was stimulated distally and nerve potentials were recorded proximally on the animal's tail using common 'alligator' clips as surface electrodes. The amplitude and the conduction velocity of the caudal nerve sensory action potential increased linearly from 29+/-6 microV to 85+/-13 microV and from 34+/-3 m/s to 44+/-4 m/s, respectively, between the 8th and the 15th week of life. The equations of linear regressions were as followed: Amplitude (microV) = 8.1 x weeks - 34 (R(2) = 0.99) and NCV (m/s) = 1.2 x weeks + 25 (R(2) = 0.86). It was possible to study non-invasively the sensitive conduction of the caudal nerve of normal developing rats and describe reference values. The technique and data may be used as animal model in physiological and pathological studies.

Orexin-1 Receptor Co-Localizes with Pancreatic Hormones in Islet Cells and Modulates the Outcome of Streptozotocin-Induced Diabetes Mellitus

Recent studies have shown that orexins play a critical role in the regulation of sleep/wake states, feeding behaviour, and reward processes. The exocrine and endocrine pancreas are involved in the regulation of food metabolism and energy balance. This function is deranged in diabetes mellitus. This study examined the pattern of distribution of orexin-1 receptor (OX1R) in the endocrine cells of the pancreas of normal and diabetic Wistar (a model of type 1 diabetes), Goto-Kakizaki (GK, a model of type 2 diabetes) rats and in orexin-deficient (OX−/−) and wild type mice. Diabetes mellitus (DM) was induced in Wistar rats and mice by streptozotocin (STZ). At different time points (12 h, 24 h, 4 weeks, 8 months and 15 months) after the induction of DM, pancreatic fragments of normal and diabetic rats were processed for immunohistochemistry and Western blotting. OX1R-immunoreactive nerves were observed in the pancreas of normal and diabetic Wistar rats. OX1R was also discernible in the pancreatic islets of normal and diabetic Wistar and GK rats, and wild type mice. OX1R co-localized with insulin (INS) and glucagon (GLU) in the pancreas of Wistar and GK rats. The number of OX1R-positive cells in the islets increased markedly (p<0.0001) after the onset of DM. The increase in the number of OX1R-positive cells is associated with a high degree of co-localization with GLU. The number of GLU- positive cells expressing OX1R was significantly (p<0.0001) higher after the onset of DM. The tissue level of OX1R protein increased with the duration of DM especially in type 1 diabetes where it co-localized with cleaved caspase 3 in islet cells. In comparison to STZ-treated wild type mice, STZ-treated OX−/− animals exhibited reduced hyperglycemia and handled glucose more efficiently in glucose tolerance test. The findings suggest an important role for the OX-OX1R pathway in STZ-induced experimental diabetes.

Application of Pulsed Magnetic Stimulation for Recovery from Muscle Fatigue in Hypokalemic and Normal Wistar Rats

Application of Pulsed Magnetic Stimulation for Recovery from Muscle Fatigue in Hypokalemic and Normal Wistar Rats

In vitro effect of vanadate on content, secretion and biosynthesis of insulin in isolated islets of normal Wistar rats.

In in vitro experiments the effect of (Na-ortho)vanadate (1-50 mumol/l) on content, secretion and biosynthesis of insulin was investigated in isolated islets of normal Wistar rats. Compared with controls insulin content is unchanged, but insulin secretion and biosynthesis rate are significantly reduced; secretion is significantly more reduced in the basal than in the stimulating glucose medium. Our results support the view that vanadate exhibits its influence on insulin metabolism in the beta cell already.

Insulin Resistance Induced by Glucosamine in Fructose-fed Rats

Glucosamine has been widely used to treat osteoporosis in clinic and it shows an effect on hexosamine biosynthetic pathway in glucose-induced insulin resistance. However, glucosamine and chronic hyperglycemia is not correlative. Thus, we used C (2)C (12) cell line to carry out the uptake assay of 2-[14C]-deoxy-d-glucose and [3H]-glucosamine. Glucosamine inhibited the in vitro glucose uptake in a concentration-dependent manner. The glucose transporter GLUT4 prepared for [3H]-glucosamine uptake showed a concentration-dependent competition between glucose and glucosamine uptake. The effects of glucosamine on glucose tolerance and homeostasis model assessment (HOMA) were also determined in normal Wistar and fructose-fed rats. Both plasma glucose levels and/or HOMA index were not changed in normal rats treated with glucosamine as compared with the saline-treated control. However, we found that glucosamine exhibited an effect on the expression of farnesoid X receptor in liver to exacerbate the values of HOMA and accelerate the development of insulin resistance in fructose-fed rats. Thus, glucosamine should be applied with caution in type-2 diabetic patients.

Effect of acidosis on the mechanism(s) of insulin-induced vasorelaxation in normal Wistar–Kyoto (WKY) rat aorta

The effect of acidosis on insulin-induced relaxation was studied in thoracic aortic rings (from Wistar–Kyoto (WKY) rats) with (+ ED) or without (− ED) endothelium. The rings were mounted in normal (pH 7.4) or acidotic (pH 7.2) Krebs solution for isometric tension recording. Phenylephrine (PE, 3.0 µM)-contracted tissues were exposed to insulin in the presence or absence of various inhibitors. Insulin exerted similar concentration-dependent relaxation of + ED tissues in normal and acidotic pH. Endothelium denudation, significantly ( p < 0.05) reduced insulin effect in normal, but not acidotic pH. Under normal pH, treatment with L-NAME or methylene blue significantly ( p < 0.05) reduced insulin responses in the + ED (but not the − ED) tissues. The insulin effect was also significantly ( p < 0.05) inhibited by tetraethylammonium (TEA; BK Ca blocker), 4-Aminopyridine (4-AP; K V channel blocker), combined treatments (L-NAME + 4-AP + TEA, in + ED tissues) or (4-AP + TEA, in − ED tissues). In either + ED or − ED tissues, indomethacin (cyclo-oxygenase inhibitor), glibenclamide (K ATP channel blocker), barium chloride (K ir channel blocker) or Ouabain (a Na +/K +-ATPase inhibitor) had no effect. Except for methylene blue (effect on + ED tissues), none of the drug treatments inhibited insulin vasodilator effect in acidosis (+ ED or − ED tissues). These data indicate that insulin exerts an endothelium-dependent and -independent vasodilatation in rat aorta which in normal pH is mediated via BK Ca and K v channels, including the EDNO-cGMP cascade. Acidosis abolishes the endothelium-dependent relaxation mechanism unraveling a novel mechanism that is as efficacious and is cGMP-, but not EDNO-, BK Ca- or K v-mediated.