Attenuation of fructose-induced hypertension in rats by exercise training

Quality by design aided self-nano emulsifying drug delivery systems development for the oral delivery of Benidipine: Improvement of biopharmaceutical performance

The primary objective of the research effort is to establish efficient solid self-nanoemulsifying drug delivery systems (S-SNEDDS) for benidipine (BD) through the systematic application of a quality-by-design (QbD)-based paradigm. Utilizing Labrafil M 2125 CS, Kolliphor EL, and Transcutol P, the BD-S-SNEDDS were created. The central composite design was adopted to optimize numerous components. Zeta potential, drug concentration, resistance to dilution, pH, refractive index, viscosity, thermodynamic stability, and cloud point were further investigated in the most efficient formulation, BD14, which had a globule size of 156.20 ± 2.40 nm, PDI of 0.25, zeta potential of -17.36 ± 0.18 mV, self-emulsification time of 65.21 ± 1.95 s, % transmittance of 99.80 ± 0.70%, and drug release of 92.65 ± 1.70% at 15 min. S-SNEDDS were formulated using the adsorption process and investigated via Fourier transform infrared spectroscopy, Differential scanning calorimeter, Scanning electron microscopy, and powder X-ray diffraction. Optimized S-SNEDDS batch BD14 dramatically decreased blood pressure in rats in contrast to the pure drug and the commercial product, according to a pharmacodynamics investigation. Accelerated stability tests validated the product's stability. Therefore, the development of oral S-SNEDDS of BD may be advantageous for raising BD's water solubility and expanding their releasing capabilities, thereby boosting oral absorption.

Impacts of High Fructose Diet and Chronic Exercise on Nitric Oxide Synthase and Oxidative Stress in Rat Kidney

Chronic exercise (Ex) exerts antihypertensive and renoprotective effects in rats fed a high fructose diet (HFr). To elucidate the mechanisms, the impacts of an HFr and Ex on the nitric oxide (NO) system and oxidative stress in the kidney were examined. Rats were fed a control diet or an HFr, and a part of the HFr-fed rats underwent treadmill running for 12 weeks. The HFr did not affect nitrate/nitrite (NO_x) levels in plasma and urine, and Ex increased the NO_x levels. The HFr increased thiobarbituric acid reactive substance (TBARS) levels in plasma and urine, and Ex decreased the HFr-increased TBARS levels in plasma. The HFr increased the neuronal and endothelial NO synthase (nNOS and eNOS) expressions, and Ex enhanced the HFr-increased eNOS expression. The HFr inhibited the eNOS phosphorylation at serine 1177, and Ex restored the HFr-inhibited eNOS phosphorylation. The HFr increased xanthine oxidase and NADPH oxidase activities, and Ex restored the HFr-increased xanthine oxidase activity but enhanced the HFr-increased NADPH oxidase activity. The HFr increased the nitrotyrosine levels, and Ex attenuated the HFr-increased levels. These results indicate that although Ex enhances the HFr-increased eNOS expression and NADPH oxidase activity, an HFr inhibits renal eNOS phosphorylation and NO bioavailability, whereas Ex ameliorates them.

Exercise Training Prevents High Fructose-Induced Hypertension and Renal Damages in Male Dahl Salt-Sensitive Rats

INTRODUCTION

High-fructose diet (HFr) causes metabolic syndrome, and HFr-induced hypertension and renal damage are exaggerated in Dahl salt-sensitive (DS) rats. Exercise training (Ex) has antihypertensive and renal protective effects in rats fed HFr; however, there has been little discussion about the DS rats, which exhibit metabolic disturbances. This study thus examined the effects of Ex on DS rats fed HFr.

METHODS

Male DS rats were divided into three groups. The control group was fed a control diet, and both the HFr group and the HFr-Ex group were fed an HFr (60% fructose). The HFr-Ex group also underwent treadmill running (20 m·min -1 , 60 min·d -1 , 5 d·wk -1 ). After 12 wk, renal function, histology, and renin-angiotensin system were examined.

RESULTS

HFr increased blood pressure, urinary albumin, and creatinine clearance, and Ex inhibited these increases. HFr induced glomerular sclerosis, podocyte injury, afferent arteriole thickening, and renal interstitial fibrosis, and Ex ameliorated them. HFr reduced plasma renin activity, and Ex further reduced the activity. HFr also increased the expression of angiotensinogen, renin, angiotensin-converting enzyme (ACE), and angiotensin II type 1 receptor, and Ex restored the ACE expression to the control levels. HFr decreased the expression of ACE2, angiotensin II type 2 receptor, and Mas receptor, and Ex restored the ACE2 and Mas receptor expressions to the control levels and further decreased the angiotensin II type 2 receptor expression. HFr increased the ACE activity and decreased the ACE2 activity, and Ex restored these activities to the control levels.

CONCLUSIONS

Ex prevents HFr-induced hypertension and renal damages in DS rats. The changes in renal renin-angiotensin system may be involved in the mechanism of the antihypertensive and renal protective effects of Ex.

Fructose plus High-Salt Diet in Early Life Results in Salt-Sensitive Cardiovascular Changes in Mature Male Sprague Dawley Rats

Fructose and salt intake remain high, particularly in adolescents and young adults. The present studies were designed to evaluate the impact of high fructose and/or salt during pre- and early adolescence on salt sensitivity, blood pressure, arterial compliance, and left ventricular (LV) function in maturity. Male 5-week-old Sprague Dawley rats were studied over three 3-week phases (Phases I, II, and III). Two reference groups received either 20% glucose + 0.4% NaCl (GCS-GCS) or 20% fructose + 4% NaCl (FHS-FHS) throughout this study. The two test groups ingested fructose + 0.4% NaCl (FCS) or FHS during Phase I, then GCS in Phase II, and were then challenged with 20% glucose + 4% NaCl (GHS) in Phase III: FCS-GHS and FHS-GHS, respectively. Compared with GCS-GCS, systolic and mean pressures were significantly higher at the end of Phase III in all groups fed fructose during Phase I. Aortic pulse wave velocity (PWV) was elevated at the end of Phase I in FHS-GHS and FHS-FHS (vs. GCS-GCS). At the end of Phase III, PWV and renal resistive index were higher in FHS-GHS and FHS-FHS vs. GCS-GCS. Diastolic, but not systolic, LV function was impaired in the FHS-GHS and FHS-FHS but not FCS-FHS rats. Consumption of 20% fructose by male rats during adolescence results in salt-sensitive hypertension in maturity. When ingested with a high-salt diet during this early plastic phase, dietary fructose also predisposes to vascular stiffening and LV diastolic dysfunction in later life.

Sirt1 and Sirt3 Activation Improved Cardiac Function of Diabetic Rats via Modulation of Mitochondrial Function

In the present study, we aimed to evaluate the effect of Sirt1, Sirt3 and combined activation in high fructose diet-induced insulin resistance rat heart and assessed the cardiac function focusing on mitochondrial health and function. We administered the Sirt1 activator; SRT1720 (5 mg/kg, i.p.), Sirt3 activator; Oroxylin-A (10 mg/kg i.p.) and the combination; SRT1720 + Oroxylin-A (5 mg/kg and 10 mg/kg i.p.) daily from 12th week to 20th weeks of study. We observed significant perturbations of most of the cardiac structural and functional parameters in high fructose diet-fed animals. Administration of SRT1720 and Oroxylin-A improved perturbed cardiac structural and functional parameters by decreasing insulin resistance, oxidative stress, and improving mitochondrial function by enhancing mitochondrial biogenesis, OXPHOS expression and activity in high fructose diet-induced insulin-resistant rats. However, we could not observe the synergistic effect of SRT1720 and Oroxylin-A combination. Similar to in-vivo study, perturbed mitochondrial function and oxidative stress observed in insulin-resistant H9c2 cells were improved after activation of Sirt1 and Sirt3. We observed that Sirt1 activation enhances Sirt3 expression and mitochondrial biogenesis, and the opposite effects were observed after Sirt1 inhibition in cardiomyoblast cells. Taken together our results conclude that activation of Sirt1 alone could be a potential therapeutic target for diabetes-associated cardiovascular complications.

Low-intensity exercise diverts cardiac fatty acid metabolism from triacylglycerol synthesis to beta oxidation in fructose-fed rats

CONTEXT

Excessive fructose consumption causes ectopic lipid storage leading to metabolic disorders and cardiovascular diseases associated with defective substrate utilisation in the heart.

OBJECTIVE

Examining the preventive impact of low-intensity exercise on alterations related to fructose-rich diet (FRD) on cardiac fatty acid (FA) transport and metabolism.

MATERIALS AND METHODS

Male Wistar rats were divided into control and two groups that received 10% fructose for 9 weeks, one of which was additionally exposed to exercise.

RESULTS

FRD elevated plasma and cardiac TAG, FATP1 in plasma membrane, Lipin 1 in microsomes and HSL mRNA, while mitochondrial CPT1 was decreased. Exercise decreased plasma free FA level, raised CD36 in plasma membrane and FATP1 in lysate, mitochondrial CPT1 and decreased microsomal Lipin 1 in fructose-fed rats.

CONCLUSIONS

FRD changed plasma lipids and augmented partitioning of FA to TAG storage in the heart, whereas exercise in FRD rats switched metabolism of FA towards β-oxidation.

Chronic exercise provides renal-protective effects with upregulation of fatty acid oxidation in the kidney of high fructose-fed rats

Excessive fructose intake causes metabolic syndrome and lipid accumulation in the kidney and leads to renal dysfunction and damage. Exercise (Ex) improves lipids regulation, but the mechanisms are unclarified in the kidney. In the present study, male Sprague-Dawley rats were allocated to groups fed with control or high-fructose (HFr) diet. Part of rats in each group underwent aerobic treadmill Ex for 12 wk. Drug treatment was performed as the fenofibrate gavage during the last 4 wk on HFr diet-fed rats. Renal function, histological changes, and expression of regulators involved in fatty acid (FA) metabolism were assessed. In CON diet-fed groups, Ex did not affect renal function or histology and significantly increased renal expression of FA β-oxidation regulators including acyl-CoA dehydrogenases (CADs), acyl-CoA oxidase, peroxisome proliferator-activated receptor (PPAR)-α, and PPAR-γ coactivator (PGC)-1α and lipogenic factors including acetyl-CoA carboxylase (ACCα), FA synthase (FAS), and sterol regulatory element-binding protein 1c. HFr caused albuminuria, lipid accumulation, and renal pathohistological changes, which were attenuated by Ex but not by fenofibrate. HFr decreased renal expression of medium- and short-chain CADs and PPAR-α and increased renal expression of ACCα, FAS, and sterol regulatory element-binding protein 1c. Ex increased expression of CADs, carnitine palmitoyltransferase type I, acyl-CoA oxidase, PPAR-α, and PGC-1α and decreased renal expression of ACCα and FAS in HFr diet-fed rats. The Ex-induced FA metabolism alteration was similar to that in the fenofibrate-treated group. In conclusion, the present study indicates that Ex enhanced renal FA metabolism, which might protect the kidney in lipid dysregulation diseases.

Enhanced bioavailability and antihypertensive activity of nisoldipine loaded nanoemulsion: optimization, cytotoxicity and uptake across Caco-2 cell line, pharmacokinetic and pharmacodynamic studies

Objective: The present study explored the antihypertensive activity of nisoldipine in oil in water nanoemulsion to improve its oral bioavailability via intestinal lymphatic uptake.Methods: Nanoemulsion was prepared by ultrasonication technique using Peceol, Cremophor EL and Transcutol HP as oil, surfactant and cosurfactant respectively. Optimization was done employing 3² full factorial design. The developed formulation was assessed for in vitro,cell line, ex vivo and in vivo studies.Results: The experimental results indicated homogeneity of the nanoemulsion with globule size of 62.35 ± 2.55 nm and PDI value of 0.108 ± 0.01 with negative zeta potential (-26.2 ± 3.6 mV). Transmission electron microscopy showed spherical oil globules morphology. The in vitro diffusion study showed significant increase in drug release from NE formulations (98.51 ± 2.64%) as compared to plain drug dispersion (29.73 ± 2.15%) in 0.1 N HCl + 0.5% SLS medium. Moreover, higher quantitative and qualitative uptake of nanoemulsion via Caco-2 cells showed superior intestinal absorption and improved therapeutic activity of nisoldipine when compared to drug dispersion. Pharmacokinetic and pharmacodynamic study confirmed significantly (p ˂ 0.05) greater bioavailability and antihypertensive activity of nisoldipine nanoemulsion when compared to its dispersion. These results are visualized in abstract figure.Conclusion: Thus, prepared nanoemulsion showed potential as oral delivery system for nisoldipine with superior oral bioavailability and therapeutic efficacy over drug dispersion.

Voluntary exercise opposes insulin resistance of skeletal muscle glucose transport during liquid fructose ingestion in rats

We have recently reported that male rats given liquid fructose ingestion exhibit features of cardiometabolic abnormalities including non-obese insulin resistance with impaired insulin signaling transduction in skeletal muscle (Rattanavichit Y et al. Am J Physiol Regul Integr Comp Physiol 311: R1200-R1212, 2016). While exercise can attenuate obesity-related risks of cardiometabolic syndrome, the effectiveness and potential mechanism by which exercise modulates non-obese insulin resistance have not been fully studied. The present investigation evaluated whether regular exercise by voluntary wheel running (VWR) can reduce cardiometabolic risks induced by fructose ingestion. Moreover, the potential cellular adaptations following VWR on key signaling proteins known to influence insulin-induced glucose transport in skeletal muscle of fructose-ingested rats were investigated. Male Sprague-Dawley rats were given either water or liquid fructose (10% wt/vol) without or with access to running wheel for 6 weeks. We demonstrated that VWR restored insulin-stimulated glucose transport in the soleus muscle by improving the functionality of several signaling proteins, including insulin-stimulated IRβ Tyr¹¹⁵⁸/Tyr¹¹⁶²/Tyr¹¹⁶³ (82%), IRS-1 Tyr⁹⁸⁹ (112%), Akt Ser⁴⁷³ (56%), AS160 Thr⁶⁴² (76%), and AS160 Ser⁵⁸⁸ (82%). These effects were accompanied by lower insulin-stimulated phosphorylation of IRS-1 Ser³⁰⁷ (37%) and JNK Thr¹⁸³/Tyr¹⁸⁵ (49%), without significant changes in expression of proteins in the renin-angiotensin system. Intriguingly, multiple cardiometabolic abnormalities were not observed in fructose-ingested rats with access to VWR. Collectively, this study demonstrates that the development of cardiometabolic abnormalities as well as insulin resistance of skeletal muscle and defective signaling molecules in rats induced by fructose ingestion could be opposed by VWR.

Bilateral renal cryodenervation decreases arterial pressure and improves insulin sensitivity in fructose-fed Sprague-Dawley rats

Consumption of food high in fructose is prevalent in modern diets. One week of moderately high fructose intake combined with high salt diet has been shown to increase blood pressure and failed to suppress plasma renin activity (PRA). We tested the hypothesis that the hypertension and high PRA are consequences of elevated renal sympathetic nerve activity (RSNA). In protocol 1, we assessed RSNA by telemetry in conscious Sprague-Dawley rats given 20% fructose or 20% glucose in drinking water on a 0.4% NaCl diet (NS) for 1 wk and then transitioned to a 4% NaCl diet (HS). After an additional week, mean arterial pressure (MAP) and RSNA increased significantly in fructose-fed but not glucose-fed HS rats. In protocol 2, fructose (Fruc)- or glucose (Glu)-fed rats on NS or HS diet for 3 wk underwent sham denervation (shamDNX) or bilateral renal denervation using cryoablation (cryoDNX). MAP was higher in Fruc-HS rats compared with Glu-NS, Glu-HS, or Fruc-NS rats and decreased after cryoDNX ( P < 0.01). MAP did not change in Fruc-HS shamDNX rats. Renal norepinephrine content decreased by 85% in cryoDNX ( P < 0.01 vs. shamDNX). PRA significantly decreased after cryoDNX in both Fruc-NS and Fruc-HS rats. Nonfasting blood glucose levels were similar among the four groups. Glucose-to-insulin ratio significantly increased in Fruc-HS cryoDNX rats, consistent with greater insulin sensitivity. Taken together, these studies show that renal sympathoexcitation is, at least in part, responsible for salt-dependent increases in MAP, increased PRA, and decreased insulin sensitivity in rats fed a moderately high fructose diet for as little as 3 wk.

Voluntary Running Improves In Vivo Insulin Resistance in High-Salt Diet–Fed Rats

It is well known that exercise training, including voluntary running (VR), improves insulin resistance. However, the effect of VR on insulin resistance induced by high salt intake is unclear. The aim of this study was to determine whether VR would improve the glucose utilization in normal male Sprague-Dawley rats fed a high-salt diet (HSD) on 2-week early prevention and 1-week midway intervention protocols. In vivo glucose utilization was measured by euglycemic clamp technique. Further analyses of the possible changes in insulin signaling occurring in skeletal muscle were performed by Western blot and reverse transcription polymerase chain reaction (RT-PCR). The glucose infusion rates (GIRs) after 2 weeks of HSD feeding were decreased (HSD vs. control: 21.5 ± 0.8 vs. 27 ± 0.5 mg/kg body wt/min; P < 0.05), and improved by 2 weeks VR to 30.5 ± 1.5 mg/kg body wt/min. Additionally, the GIRs after 3 weeks of HSD feeding were decreased (HSD vs. control: 20.0 ± 0.3 vs. 26.5 ± 0.6 mg/kg body wt/min; P < 0.05), and they also improved by the third week of VR (28.5 ± 0.7 mg/ kg body wt/min vs. sedentary; P < 0.01). There were no differences in skeletal muscle for the total mass of insulin receptor-beta (IR-β), IR substrate-1 (IRS-1), Akt, and glucose transporter 4 (GLUT4) in any of the groups of 2 weeks of HSD loading control and VR. VR did not regulate the enhanced tyrosine phosphorylation of IR-β and IRS-1 by 2 weeks of HSD feeding. However, the enhanced serine phosphorylation of Akt and the tyrosine phosphorylation of GLUT4 were significantly inhibited by the early VR. HSD also impaired GLUT4 content in the plasma membrane and mRNA expression, but the decreases were improved by 2 weeks of VR. These results suggest that early voluntary exercise would prevent the development of insulin resistance induced by an HSD due in part by enhancing the impaired GLUT4 translocation and mRNA expression in skeletal muscle.

Renal Denervation

Resistant hypertension, defined as failure to reach blood pressure (BP) goals despite treatment with ≥3 antihypertensive agents, one of which is a diuretic, bears a significant risk of cardiovascular complications. Strong evidence exists, implicating the overactivation of the sympathetic nervous system (SNS) in the pathogenesis of resistant hypertension through complex neurohormonal interactions. Renal denervation is a novel attractive option to achieve adequate blockade of the sympathetic system, with subsequent BP reductions in patients with resistant hypertension. Data have shown promising results regarding the efficacy of the procedure, maintaining a favorable safety profile. As such, the paradigm of resistant hypertension has expanded in other conditions involving a hyperadrenergic state such as the metabolic syndrome, heart failure, arrhythmias, sleep apnea, and renal failure. This review focuses on the pathophysiological rationale of modifying SNS tone and the evidence of the benefits of such intervention beyond BP control.

Metabolic, hemodynamic and structural adjustments to low intensity exercise training in a metabolic syndrome model

Background

The increase in fructose consumption is paralleled by a higher incidence of metabolic syndrome, and consequently, cardiovascular disease mortality. We examined the effects of 8 weeks of low intensity exercise training (LET) on metabolic, hemodynamic, ventricular and vascular morphological changes induced by fructose drinking in male rats.

Methods

Male Wistar rats were divided into (n = 8 each) control (C), sedentary fructose (F) and ET fructose (FT) groups. Fructose-drinking rats received D-fructose (100 g/l). FT rats were assigned to a treadmill training protocol at low intensity (30% of maximal running speed) during 1 h/day, 5 days/week for 8 weeks. Measurements of triglyceride concentrations, white adipose tissue (WAT) and glycemia were carried out together with insulin tolerance test to evaluate metabolic profile. Arterial pressure (AP) signals were directly recorded. Baroreflex sensitivity (BS) was evaluated by the tachycardic and bradycardic responses. Right atria, left ventricle (LV) and ascending aorta were prepared to morphoquantitative analysis.

Results

LET reduced WAT (−37.7%), triglyceride levels (−33%), systolic AP (−6%), heart weight/body weight (−20.5%), LV (−36%) and aortic (−76%) collagen fibers, aortic intima-media thickness and circumferential wall tension in FT when compared to F rats. Additionally, FT group presented improve of BS, numerical density of atrial natriuretic peptide granules (+42%) and LV capillaries (+25%), as well as the number of elastic lamellae in aorta compared with F group.

Conclusions

Our data suggest that LET, a widely recommended practice, seems to be particularly effective for preventing metabolic, hemodynamic and morphological disorders triggered by MS.

Effect of bromocriptine on cardiovascular complications associated with metabolic syndrome in fructose fed rats

OBJECTIVE

The objective of the present study was to evaluate the effect of bromocriptine on cardiovascular complications associated with type-2 diabetes mellitus (DM).

MATERIALS AND METHODS

Metabolic syndrome or type 2 DM was induced by administration of fructose (66% solution, p.o.) in rats. Bromocriptine mesylate (10 mg/kg, i.p.) was given in fructose-treated rats for a period of 6 weeks after induction of diabetes. After drug treatment, the parameters such as body weight, food and water intake, serum glucose, triglycerides, cholesterol, insulin, and blood pressure (BP) were measured weekly and at the end of study. At the end of treatment, BP was determined by invasive method and vascular reactivity was tested with adrenaline (Adr), noradrenaline (NA), and phenylephrine (PE). Acetylcholine-induced vasorelaxation was tested on isolated rat aorta and histopathology of hearts was also done.

RESULTS

Fructose-fed rats showed significant weight gain, hyperglycemia, hyperlipidemia, hyperinsulinemia, and rise of BP. Administration of bromocriptine at a dose 10 mg/kg, i.p. significantly decreased weight gain, serum glucose, triglyceride, cholesterol and insulin levels in rats fed on fructose. Bromocriptine also significantly reduced elevated BP in fructose-fed hypertensive rats. Chronic treatment with bromocriptine significantly improved the relaxant response to acetylcholine on fructose-fed hyperinsulinemic rat aorta and also reduced the pressor response to Adr, NA, and PE. Bromocriptine also showed a protection from hypertrophy and degenerative changes in myocardium.

CONCLUSION

Bromocriptine has beneficial effect in reduction of cardiovascular complications associated with metabolic syndrome.

Preventive role of exercise training in autonomic, hemodynamic, and metabolic parameters in rats under high risk of metabolic syndrome development

High fructose consumption contributes to metabolic syndrome incidence, whereas exercise training promotes several beneficial adaptations. In this study, we demonstrated the preventive role of exercise training in the metabolic syndrome derangements in a rat model. Wistar rats receiving fructose overload in drinking water (100 g/l) were concomitantly trained on a treadmill (FT) or kept sedentary (F) for 10 wk. Control rats treated with normal water were also submitted to exercise training (CT) or sedentarism (C). Metabolic evaluations consisted of the Lee index and glycemia and insulin tolerance test (kITT). Blood pressure (BP) was directly measured, whereas heart rate (HR) and BP variabilities were evaluated in time and frequency domains. Renal sympathetic nerve activity was also recorded. F rats presented significant alterations compared with all the other groups in insulin resistance (in mg · dl(-1) · min(-1): F: 3.4 ± 0.2; C: 4.7 ± 0.2; CT: 5.0 ± 0.5 FT: 4.6 ± 0.4), mean BP (in mmHG: F: 117 ± 2; C: 100 ± 2; CT: 98 ± 2; FT: 105 ± 2), and Lee index (in g/mm: F = 0.31 ± 0.001; C = 0.29 ± 0.001; CT = 0.27 ± 0.002; FT = 0.28 ± 0.002), confirming the metabolic syndrome diagnosis. Exercise training blunted all these derangements. Additionally, FS group presented autonomic dysfunction in relation to the others, as seen by an ≈ 50% decrease in baroreflex sensitivity and 24% in HR variability, and increases in sympathovagal balance (140%) and in renal sympathetic nerve activity (45%). These impairments were not observed in FT group, as well as in C and CT. Correlation analysis showed that both Lee index and kITT were associated with vagal impairment caused by fructose. Therefore, exercise training plays a preventive role in both autonomic and hemodynamic alterations related to the excessive fructose consumption.

Low-volume exercise can prevent sucrose-induced weight gain but has limited impact on metabolic measures in rats

PURPOSE

Rats given sugar-sweetened drinks can develop glucose intolerance, insulin resistance and dyslipidaemia. The aim of this study was to investigate whether such metabolic disruptions and also possible weight gain induced by chronic sucrose consumption could be attenuated by low-volume exercise.

METHODS

Using a 2 × 2 factorial design, rats were given free access for 57 days to either a 10% sucrose solution (Suc and SucEx) or water only (Con and ConEx), while exercise rats (SucEx and ConEx) received 20-min treadmill training every 3 days. Caloric intake and body weight were measured throughout this dietary intervention. Oral glucose tolerance tests were performed on days 29 and 54. Plasma insulin, triglycerides and leptin were also measured, together with post-mortem measures of retroperitoneal fat pads and liver triglycerides.

RESULTS

In groups given sucrose, exercise reduced calorie consumption, reduced weight gain and decreased leptin relative to non-exercised controls. Exercise was found to improve glucose tolerance and insulin action at day 29, but not day 54.

CONCLUSIONS

Low-volume exercise can be effective in preventing weight gain in sucrose-fed rats, probably via reduction of subcutaneous fat, but prevention of the glucose intolerance and dyslipidaemia produced by sucrose consumption may be transient.

Evaluation of mechanism for antihypertensive action of Clerodendrum colebrookianum Walp., used by folklore healers in north-east India

ETHNOPHARMACOLOGICAL RELEVANCE

The present investigation was aimed to justify the pharmacological basis in traditional use of Clerodendrum colebrookianum as antihypertensive agent in north-east India.

MATERIALS AND METHODS

The aqueous extract (AECc), its aqueous, n-butanol (nBFCc), Ethyl-acetate (EtFCc) and Chloroform fractions of C. colebrookianum leaves were evaluated for antihypertensive potential by using fructose-induced hypertension model in rats and in isolated frog heart. The ex-vivo muscarinic action in isolated rat ileum, in-vitro assay for Rho-kinase (ROCK -II), phosphodiesterase-5 (PDE-5) and angiotension converting enzyme (ACE) were also carried out to establish the mechanism of action of samples. The total phenolic and flavonoied contents in test samples were estimated to establish phyto-pharmacological relationship.

RESULTS

The 100μg/mL test samples were showed calcium antagonism in rat ileum and at 50μg/mL and 75μg/mL doses exhibited ROCK-II and PDE-5 inhibition respectively where, EtFCc was caused maximum 68.62% (ROCK-II) and 52.28% (PDE-5) inhibition, but none of the sample was exhibit effect in ACE at 100μg/mL. The test samples also showed negative inotropic and chronotropic effect on isolated frog heart and significant (P<0.001) reduction in systolic blood pressure and heart rate in hypertensive rats compared to control. The total phenolic content maximum 80μg gallic acid equivalents in nBFCc and flavonoids content maximum 69.57μg Quercetin equivalent in AECc were estimated.

CONCLUSIONS

These observations established the traditional claim and thus C. colebrookianum could be a potent antihypertensive agent for use in future. The antihypertensive effect mediated by cholinergic action and following ROCK - II, PDE-5 inhibition of C. colebrookianum.

Exercise training prevents diastolic dysfunction induced by metabolic syndrome in rats

OBJECTIVE

High fructose consumption contributes to the incidence of metabolic syndrome and, consequently, to cardiovascular outcomes. We investigated whether exercise training prevents high fructose diet-induced metabolic and cardiac morphofunctional alterations.

METHODS

Wistar rats receiving fructose overload (F) in drinking water (100 g/l) were concomitantly trained on a treadmill (FT) for 10 weeks or kept sedentary. These rats were compared with a control group (C). Obesity was evaluated by the Lee index, and glycemia and insulin tolerance tests constituted the metabolic evaluation. Blood pressure was measured directly (Windaq, 2 kHz), and echocardiography was performed to determine left ventricular morphology and function. Statistical significance was determined by one-way ANOVA, with significance set at p<0.05.

RESULTS

Fructose overload induced a metabolic syndrome state, as confirmed by insulin resistance (F: 3.6 ± 0.2 vs. C: 4.5 ± 0.2 mg/dl/min), hypertension (mean blood pressure, F: 118 ± 3 vs. C: 104 ± 4 mmHg) and obesity (F: 0.31 ± 0.001 vs. C: 0.29 ± 0.001 g/mm). Interestingly, fructose overload rats also exhibited diastolic dysfunction. Exercise training performed during the period of high fructose intake eliminated all of these derangements. The improvements in metabolic parameters were correlated with the maintenance of diastolic function.

CONCLUSION

The role of exercise training in the prevention of metabolic and hemodynamic parameter alterations is of great importance in decreasing the cardiac morbidity and mortality related to metabolic syndrome.

The Relation between Fructose-Induced Metabolic Syndrome and Altered Renal Haemodynamic and Excretory Function in the Rat

This paper explores the possible relationships between dietary fructose and altered neurohumoral regulation of renal haemodynamic and excretory function in this model of metabolic syndrome. Fructose consumption induces hyperinsulinemia, hypertriglyceridaemia, insulin resistance, and hypertension. The pathogenesis of fructose-induced hypertension is dubious and involves numerous pathways acting both singly and together. In addition, hyperinsulinemia and hypertension contribute significantly to progressive renal disease in fructose-fed rats. Moreover, increased activity of the renin-angiotensin and sympathetic nervous systems leading to downregulation of receptors may be responsible for the blunted vascular sensitivity to angiotensin II and catecholamines, respectively. Various approaches have been suggested to prevent the development of fructose-induced hypertension and/or metabolic alteration. In this paper, we address the role played by the renin-angiotensin and sympathetic nervous systems in the haemodynamic alterations that occur due to prolonged consumption of fructose.

High dose astaxanthin lowers blood pressure and increases insulin sensitivity in rats: are these effects interdependent?

The present investigation in Sprague-Dawley rats (SD) was designed to examine effects of astaxanthin (Asta) at different doses on elevated blood pressure (BP) and glucose-insulin perturbations produced by heavy sucrose ingestion. We also examined effects of Asta on BP during restraint stress. SD were divided into six groups each containing eight rats. All SD ate a basic diet of ground regular rat chow with sucrose added at 30% w/w. The Control group received only the basic diet containing added sucrose, while the other five groups each received the same diet with added test material: captopril, (30 mg/Kg), pioglitazone (15.0 mg/Kg), low Asta (25 mg/Kg), medium Asta (50 mg/kg) or high Asta (100 mg/Kg). Many tests were carried out to examine the mechanisms behind the effects of Asta on BP (serum ACE activity, losartan challenge, and LNAME challenge) and the glucose-insulin system (glucose tolerance, HOMA measurement, and insulin challenge). In SD, a relatively low dose of Asta decreased SBP, but produced no major changes in the glucose-insulin system simulating results from a previous study using Zucker Fatty Rats. Increasing the dose of Asta resulted in both a lowering of elevated systolic BP and enhanced insulin sensitivity determined by many different estimations. BP lowering was consistent with changes in the renin-angiotensin (RAS) and nitric oxide (NO) systems. At the examined doses of each, captopril lowered BP in SD without influencing glucose-insulin metabolism, whereas pioglitazone favorably affected glucose-insulin metabolism while showing essentially no effects on BP. Accordingly, Asta beneficially affects both sucrose-induced elevations of BP and insulin resistance at relatively high doses in SD. Also, Asta at higher doses lessens restraint stress, whereas, captopril and pioglitazone did not at the doses examined, even though they influenced the BP and glucose-insulin systems respectively.

The fructose-fed rat: a review on the mechanisms of fructose-induced insulin resistance and hypertension

The metabolic syndrome is an important public health concern that predisposes individuals to the development of cardiovascular disease and/or Type 2 diabetes. The fructose-fed rat is an animal model of acquired systolic hypertension that displays numerous features of the metabolic syndrome. This animal model is used to study the relationship between insulin resistance/compensatory hyperinsulinemia and the development of hypertension. Several mechanisms have been proposed to mediate the link between insulin resistance and hypertension. In this review, we have addressed the role of sympathetic nervous system overactivation, increased production of vasoconstrictors, such as endothelin-1 and angiotensin II, and prostanoids in the development of hypertension in fructose-fed rats. The roles of nitric oxide, impaired endothelium-dependent relaxation and sex hormones in the pathogenesis of the fructose-fed induced hypertensive rats have also been highlighted. More recently, increased formation of reactive oxygen species and elevated levels of uric acid have been reported to contribute to fructose-induced hypertension.

Hemodynamic changes in postprandial state

Several experimental data suggest that single sugar intake may induce heart rate acceleration and blood pressure elevation as a result of sympathetic activation secondary to insulin response and from alterations in endothelial function due to activation of oxidative stress. These hemodynamic effects might be more marked in patients with arterial hypertension or metabolic disorders, in particular in hypertensive patients with diabetes. A high-fat load may also induce activation of oxidative stress and endothelial dysfunction. However, the long-term effect of repeated intake of single sugar and fat on blood pressure, oxidative stress, and endothelial function should be tested in controlled trials. On the contrary, a balanced mixed meal (50% carbohydrates) does not induce any significant blood pressure changes. Nevertheless, acarbose treatment is able to reduce hypertension incidence in patients with impaired glucose tolerance and to improve endothelial function. In elderly subjects, in particular with type 2 diabetes or with severe dysautonomia, sigle sugar intake may account for nonhypoglycemic postprandial dizziness.

Whole Cinnamon and Aqueous Extracts Ameliorate Sucrose-Induced Blood Pressure Elevations in Spontaneously Hypertensive Rats

OBJECTIVE

Many agents (nutrients, nutraceuticals, and drugs) that enhance insulin sensitivity and/or reduce circulating insulin concentrations lower blood pressure (BP). Recently, it was reported that cinnamon has the potential to favorably influence the glucose/insulin system. Accordingly, the purpose of the present study was to examine the effects of dietary cinnamon on systolic BP (SBP), and various glucose- and insulin-related parameters in spontaneously hypertensive rats (SHR).

METHODS

In a series of three experiments, treated SHR eating sucrose and non sucrose containing diets were given various amounts of cinnamon, cinnamon extracts, or chromium. Then various parameters such as: body weight, systolic blood pressure, hematology and blood chemistries were followed for three to four weeks.

RESULTS

Diets high in sucrose content are associated with insulin resistance and the elevation of SBP. Addition to diets of cinnamon (8% w/w) reduced the SBP of rats eating sucrose containing diets to virtually the same levels as SHR consuming non sucrose containing (only starch) diets. The presence of cinnamon in the diet also decreased the SBP of SHR consuming a non sucrose-containing diet, suggesting that cinnamon reduces more than just sucrose-induced SBP elevations--perhaps a genetic component(s) of the elevated BP as well. The effects of cinnamon on SBP tended to be dose-dependent. Cinnamon did not decrease the levels of blood glucose, but did lower circulating insulin concentrations. Aqueous extracts of cinnamon also decreased SBP and lowered the circulating levels of fructosamine.

CONCLUSIONS

Cinnamon is used for flavor and taste in food preparation, but cinnamon may have additional roles in glucose metabolism and BP regulation. Therefore, BP regulation may not only be influenced favorably by limiting the amounts of dietary substances that have negative effects on BP and insulin function but also by the addition of beneficial ones, such as cinnamon, that have positive effects.

Hypertension, single sugars and fatty acids

Macronutrients may induce various hemodynamic effects. In the fructose-fed rat blood pressure increase is associated with insulin resistance and enhanced sympathetic activity. In humans, oral glucose intake induces a slight and transient increase of blood pressure secondary to sympathetic activation. This increase may be higher in hypertensive subjects and followed by a significant fall in blood pressure in elderly subjects. Saturated fatty acid-enriched diet induces in male rats a significant increase in blood pressure related to sympathetic activation. Some observational and interventional studies suggest that n-3 polyunsaturated fatty-acids may reduce blood pressure in humans. Thus, both carbohydrates and fatty acid balance may contribute to blood pressure changes. The clinical relevance of these data should be evaluated in long-term trials, in particular in overweight and hypertensive subjects.

Renal Effects

Amylin bound to kidney cortex in a distinctive pattern. Binding appeared specific in that it was displaceable with amylin antagonists. It was associated with activation of cyclic AMP (cAMP), and was thereby likely to represent receptor binding and activation. Amylin's principal effects at the kidney included a stimulation of plasma renin activity, reflected in aldosterone increases at quasi-physiological amylin concentrations. It was unclear whether this was a local or a systemic effect. Other renal effects in rats included a diuretic effect and a natriuretic effect. The latter was mainly driven by the diuresis, since urinary sodium concentration did not change. Amylin had a transient effect to lower plasma potassium concentration. This effect was likely to be a consequence of activation of Na+/K+-ATPase, an action shared with insulin and catecholamines. Amylin lowered plasma calcium, particularly ionized calcium, likely due to an antiresorptive effect at osteoclasts. Immunoreactive amylin was detected in the developing kidney. It appeared to have a trophic effect in kidney, and its absence resulted in renal dysgenesis. Neurons in the subfornical organ (SFO), which has a role in fluid/electrolyte homeostasis, were potently activated by amylin. The dipsogenic and renal effects of amylin may be related to effects at the SFO.

Blockade of the renin???angiotensin system decreases adipocyte size with improvement in insulin sensitivity

OBJECTIVE

Based on results of in vitro studies, it has been hypothesized that blockade of the renin-angiotensin system (RAS) promotes the recruitment and differentiation of pre-adipocytes and that increased formation of small insulin-sensitive adipocytes counteracts ectopic deposition of lipids, thereby improving insulin sensitivity. We investigated the effect of RAS blockade on insulin sensitivity, adipocyte size, and intramuscular lipid content in fructose-fed rats (FFR) as a model of insulin-resistant hypertension.

DESIGN AND METHODS

Six-week-old male Sprague-Dawley rats were divided into two groups: those fed a standard chow (control) and those fed a fructose-rich chow for 6 weeks. FFR were treated with a vehicle or with 1 mg/kg per day of temocapril, an angiotensin-converting enzyme inhibitor, or 0.1 mg/kg per day of olmesartan, an angiotensin II type 1 receptor blocker, for the last 2 weeks. Insulin sensitivity (M value: mg/kg per min) was estimated by the euglycemic hyperinsulinemic glucose clamp method. Sizes of adipocytes derived from epididymal fat and triglyceride content in the soleus muscle were determined.

RESULTS

FFR had lower M value, higher blood pressure, larger adipocyte size, higher ratio of epididymal fat pads over body weight (%fat pads), and higher intramuscular triglyceride than did the control rats. Both temocapril and olmesartan significantly improved the M value and decreased blood pressure and adipocyte size without change in %fat pads in FFR. Adipocyte size was negatively correlated with the M value. Treatment for 2 weeks decreased, but not significantly, intramuscular triglyceride.

CONCLUSIONS

RAS blockade decreases adipocyte size without change in epididymal %fat pads accompanied by improvement in insulin sensitivity.

Insulin receptors and renal sodium handling in hypertensive fructose-fed rats

BACKGROUND

Insulin resistance and hypertension are present in Sprague-Dawley rats fed a fructose-enriched diet. In these rats, insulin might elevate blood pressure via an antinatriuretic action.

METHODS

To investigate the sodium-insulin interaction in fructose-fed rats, we compared insulin sensitivity, insulin receptor binding, and insulin receptor mRNA levels in the kidney and skeletal muscle of rats that were fed standard rat chow or a fructose-enriched diet (66%) with either low (0.07%), normal (0.3%), or high (7.5%) NaCl concentrations for 3 weeks.

RESULTS

Systolic blood pressure increased in the fructose-fed rats receiving the normal and high-salt diet, but not the low-salt diet. When the rats were fed the low-salt diet, the rate of glucose infusion required to maintain euglycemia during a hyperinsulinemic clamp and insulin receptor number and mRNA levels in skeletal muscle were lower in fructose-fed than control rats. High-salt diet decreased significantly the rate of glucose disposal during the clamp and muscular insulin receptor number and mRNA levels in control, but not fructose-fed rats. During the low-salt diet, renal insulin receptor number and mRNA levels were comparable in fructose-fed and control rats and hyperinsulinemia had comparable acute antinatriuretic effects in the two groups; when the rats were maintained on the high-salt diet, the expected decrease in renal insulin receptor number and mRNA levels occurred in control but not fructose-fed rats and, consistent with this finding, the antinatriuretic response to hyperinsulinemia was blunted only in controls. An inverse relationship between dietary NaCl content and renal insulin receptor mRNA levels was observed in control but not fructose-fed rats.

CONCLUSION

Fructose-fed rats appear to have lost the feedback mechanism that limits insulin-induced sodium retention through a down-regulation of the renal insulin receptor when the dietary NaCl content is increased. This abnormality might possibly contribute to the elevation of blood pressure in these rats.

Chinese medicine, Jiang-Tang-Ke-Li, improves insulin resistance by modulating muscle fiber composition and muscle tumor necrosis factor-alpha in fructose-fed rats

Insulin resistance and hyperinsulinemia are common findings in patients with essential hypertension. These impairments in glucose metabolism are commonly associated with diabetes mellitus, hypertension, and dyslipidemia, which are high risk factors of cardiovascular diseases, and recent evidence indicates that they may play a role in the development of coronary artery disease. The aim of this study was to determine the effect of Jiang-Tang-Ke-Li (JTKL), a traditional Chinese medicine used to treat diabetes mellitus in China, on insulin resistance and hypertension in fructose-fed rats (FFR). Systolic blood pressures in the FFR groups were significantly higher than that in the control group, although JTKL had no effect on systolic blood pressure for the last 2 weeks of treatment with the medicine. The average rate of glucose infusion during a glucose clamp, as an index of insulin sensitivity (M value), was significantly lower in the FFR than in the control rats, and treatment with JTKL for 2 weeks significantly increased the M value to that of the control. Treatment with Panax ginseng (PG), a component of JTKL, for 2 weeks also significantly increased the M value of FFR to the control level. The composite ratio of type I fibers in soleus muscle decreased significantly in the FFR compared to that in the control, and treatment with JTKL led to recovery of the composite ratio of type I fibers to the same level as that of the control group. The M value showed a significant positive correlation with the composite ratio of type I fibers and a significant negative correlation with the composite ratio of type II fibers. Tumor necrosis factor (TNF)-alpha levels were significantly higher in the soleus and extensor digitorum longus (EDL) muscles of the FFR than in those of the control rats. Treatment with JTKL for 2 weeks significantly lowered TNF-alpha levels to the control levels. M values showed a significant negative correlation with TNF-alpha in both the soleus and EDL muscles. The results suggest that the Chinese medicine JTKL, which contains PG as one of its valid components, improves insulin resistance by modulating muscle fiber composition and TNF-alpha in skeletal muscles in hypertensive and insulin-resistant FFR.

Effects of Exercise Training on Glomerular Structure in Fructose-Fed Spontaneously Hypertensive Rats

A high-fructose diet (HFD) has been shown to elevate blood pressure (BP) and to decrease insulin sensitivity in rats. Although running exercise can attenuate these phenomena, its effect on target organ protection is not clear. We investigated whether exercise training has renal protective effects in this model. Nine-week-old spontaneously hypertensive rats were allocated to groups that received HFD or a control diet (control group) for 15 weeks. At the age of 10 weeks, fructose-fed rats were allocated to groups that were given vehicle (FRU group), temocapril, an angiotensin converting enzyme inhibitor (TEM group), exercise training (EX group; treadmill running), or temocapril plus exercise training (TEM+EX group). BP was higher in the FRU group than in the control group. Exercise training tended to decrease BP and temocapril treatment decreased BP significantly. Proteinuria was similar in the five groups. Plasma leptin concentration and epididymal fat weight were lower in the EX and TEM+EX groups than in the FRU group. In the soleus muscle of the FRU group, the composite ratio of type I fiber was decreased and that of type IIa fiber was increased compared with those in the control group. Both temocapril and exercise training restored these ratios. The glomerular sclerosis index (GSI) was higher in the FRU group than in the control group. GSI was decreased equally in the TEM, EX, and TEM+EX groups and was positively correlated with plasma leptin concentration. The results suggest that exercise training ameliorates glomerular sclerosis through mechanisms other than a reduction in BP.

Low-dose dexamethasone in the rat: a model to study insulin resistance

The main aim of this study was to set up a new animal model to study insulin resistance. Wistar rats (6 or 7 per group) received the following for 4 wk in experiment 1: 1) vehicle, 2) 2 microg/day subcutaneous dexamethasone, 3) metformin (400 mg x kg(-1) x day(-1) os), and 4) dexamethasone plus metformin. In experiment 2 the rats received the following: 1) vehicle, 2) dexamethasone, 3) dexamethasone plus arginine (2%; as substrate of the nitric oxide synthase for nitric oxide production) in tap water, and 4) dexamethasone plus isosorbide dinitrate (70 mg/kg; as direct nitric oxide donor) in tap water. Insulin sensitivity was significantly reduced by dexamethasone already at week 1, before the increase in blood pressure (day 15) and without significant changes in body weight compared with vehicle. Dexamethasone-treated rats had significantly higher triglycerides, hematocrit, and insulin, whereas serum total nitrates/ nitrites were lower compared with vehicle. The concomitant treatment with metformin minimized all the described effects of dexamethasone. In experiment 2, only isosorbide dinitrate was able to prevent the observed dexamethasone-induced metabolic, hemodynamic, and insulin sensitivity changes. Chronic low-dose subcutaneous dexamethasone (2 microg/day) is a useful model to study the relationships between insulin resistance and blood pressure in the rat, and dexamethasone might decrease insulin sensitivity and increase blood pressure through an endothelium-mediated mechanism.

Modulation of insulin resistance and hypertension by voluntary exercise training in the TG(mREN2)27 rat

Hypertension is often accompanied by insulin resistance of skeletal muscle glucose transport. The male heterozygous TG(mREN2)27 rat, which harbors a mouse transgene for renin, displays local elevations in the renin-angiotensin system and exhibits markedly elevated systolic blood pressure (SBP). The present study was undertaken to characterize insulin-stimulated skeletal muscle glucose transport in male heterozygous TG(mREN2)27 rats and to evaluate the effect of voluntary exercise training on SBP and skeletal muscle glucose transport. Compared with normotensive Sprague-Dawley rats, TG(mREN2)27 rats displayed a 53% elevation (P < 0.05) in SBP, a twofold increase in plasma free fatty acid levels, and an exaggerated insulin response during an oral glucose tolerance test. Moreover, insulin-mediated glucose transport (2-deoxyglucose uptake) in isolated epitrochlearis and soleus muscles of TG(mREN2)27 animals was 33 and 43% less, respectively, than in Sprague-Dawley controls. TG(mREN2)27 rats ran voluntarily for 6 wk and achieved daily running distances of 6-7 km over the final 3 wk. Training caused a 36% increase in peak aerobic capacity and a 16% reduction in resting SBP. Fasting plasma insulin (21%) and free fatty acid (34%) levels were reduced in the trained TG(mREN2)27 rats. Whole body glucose tolerance was improved in the trained TG(mREN2)27 rats and was associated with increases of 39 and 50% in insulin-mediated glucose transport in epitrochlearis and soleus muscles, respectively. Whole muscle GLUT-4 protein was increased in the soleus (23%), but not in the epitrochlearis, of trained TG(mREN2)27 rats. These data indicate that the male heterozygous TG(mREN2)27 rat is a model of both hypertension and insulin resistance. Importantly, both of these defects can be beneficially modified by voluntary exercise training.

Effects of L-arginine on blood pressure and metabolic changes in fructose-hypertensive rats

In the present study, we examined the effects of chronic L-arginine treatment on plasma insulin levels and systolic blood pressure (SBP) in fructose-fed (F) rats. Fructose feeding resulted in hyperinsulinemia and elevated blood pressure when compared with that in controls (plasma insulin, 311.3+/-11.4 v control 164.4+/-11.8 pmol/L, P < .05; SBP, 135.4+/-4.2 v control 105.5+/-1.3 mm Hg, P < .05). L-arginine treatment of fructose-hypertensive rats prevented the development of hyperinsulinemia and hypertension (plasma insulin, 200.1+/-7.5 pmol/L; P < .05 compared with that in F rats; SBP, 108.0+/-0.9 mm Hg; P < .05 compared with F rats). However, treatment with L-arginine did not influence any of these parameters in control rats. Statistical analysis of the data of plasma insulin level and SBP, revealed a significant correlation between these two variables. On the other hand, L-arginine treatment of F rats prevented the increased glucose and insulin concentrations in response to oral glucose challenge. L-arginine treatment also prevented the decrease in insulin sensitivity of F rats. These results indicate that L-arginine treatment is able to prevent fructose-induced hypertension and hyperinsulinemia. Our data also suggest a strong relationship between hyperinsulinemia and hypertension in this hypertensive rat model. Therefore, the antihypertensive effect of L-arginine could be, at least in part, the result of the restoration of plasma insulin levels by its vasodilator ability to increase blood flow to insulin sensitive tissues.

Effects of the Chinese medicine Jiang-Tang-Ke-Li on insulin resistance in fructose-fed rats

The aim of this study was to determine the effect of Jiang-Tang-Ke-Li (JTKL), a Chinese medicine used to treat diabetes mellitus, on insulin resistance and hypertension in fructose-fed rats (FFR). Six-week-old male Sprague-Dawley rats were fed either normal rat chow (control) or a fructose-rich chow (FFR) for 6 weeks. For the last 2 weeks of the 6-week period of either diet, the rats were treated by gavage with gum arabic solution as a vehicle (control or FFR) or JTKL (3.24 g/kg/day; FFR+JT), and then an euglycemic hyperinsulinemic glucose clamp technique was performed to estimate insulin sensitivity. Systolic blood pressure was measured each week of the 6-week period. At the end of the glucose clamp, the soleus and extensor digitorum longus (EDL) muscles were dissected out for determination of the role of tumor necrosis factor (TNF)-alpha by an ELISA assay. Systolic blood pressures in the FFR groups were significantly higher than that in the control group, although there was no effect on systolic blood pressure for the last 2 weeks of treatment with JTKL. The average rate of glucose infusion during the glucose clamp, as an index of insulin sensitivity (M value), was significantly lower in the FFR than in the control rats, and treatment with JTKL for 2 weeks significantly increased the M value to that of control. TNF-alpha levels were significantly higher in the soleus and EDL muscles of the FFR (480+/-46 and 570+/-45 pg/g wet tissue in the soleus and EDL muscles, respectively) than in those of the control rats (177+/-34 and 206+/-33 pg/g wet tissue in the soleus and EDL muscles, respectively; p<0.01). Treatment with JTKL for 2 weeks significantly lowered TNF-alpha levels to the control levels (189+/-22 and 239+/-92 pg/g wet tissue in the soleus and EDL muscles, respectively). The results suggest that the Chinese medicine JTKL improves insulin resistance and modulates TNF-alpha in the soleus and EDL muscles in hypertensive and insulin-resistant fructose-fed rats.

The tissue renin-angiotensin system in rats with fructose-induced hypertension: overexpression of type 1 angiotensin II receptor in adipose tissue

OBJECTIVE

Fructose feeding induces hypertension, insulin-resistance and hypertriglyceridemia in Sprague-Dawley rats. The mechanisms of fructose-induced hypertension are as yet unknown. Here we investigate the effects of fructose feeding and of varying salt intake on blood pressure, glucose tolerance, plasma renin activity, and tissue angiotensinogen, renin, and AT1 receptor mRNA levels in this model of hypertension.

DESIGN AND METHODS

To investigate the role of the renin-angiotensin system in fructose-induced hypertension we measured angiotensinogen, renin and angiotensin II type 1 (AT1) receptor mRNA levels in tissues of Sprague-Dawley rats that were fed either standard rat chow or a diet containing 66% fructose.

RESULTS

Blood pressure (P < 0.05) and triglyceride (P < 0.01) levels were significantly greater in the fructose-fed animals. Plasma glucose and insulin responses to an oral glucose load were significantly greater (P< 0.05) in fructose-fed than control rats. Angiotensinogen mRNA levels in liver and fat, and renin mRNA levels in kidney did not differ between fructose-fed and control animals. Levels of AT1 receptor mRNA were significantly greater in the fat obtained from fructose-fed rats than in that from control rats (P< 0.05), but this was not so in the kidney. To determine whether fructose-induced hypertension is dependent on dietary salt content, rats were fed standard rat chow and a fructose-enriched diet with low and high sodium chloride concentrations. Blood pressure increased significantly (P< 0.05) only in the fructose-fed rats receiving the high-salt diet Similarly, increased AT1 receptor mRNA levels were observed only in the fructose-fed rats that were maintained on the high-salt diet

CONCLUSIONS

Fructose feeding induces hypertension in normal- or high-salt fed animals and it is associated with an increased expression of the AT1 receptor in adipose tissue. These findings suggest that AT1 receptors might play a role in the pathophysiology of metabolic and hemodynamic abnormalities induced by fructose feeding.

The effects of an angiotensin-converting enzyme inhibitor and an angiotensin II receptor antagonist on insulin resistance in fructose-fed rats

The aim of this study was to compare the effects of an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin II receptor (AT) antagonist on insulin resistance, especially on muscle fiber composition in fructose-induced insulin-resistant and hypertensive rats. Six-week-old male Sprague-Dawley rats were fed either normal rat chow (control) or a fructose-rich diet (FFR). For the last two weeks of a six-week period of either diet, the rats were treated with gum arabic solution as a vehicle (control or FFR), angiotensin-converting enzyme inhibitor (FFR+ACE), temocapril (1 mg/kg/ day) or an angiotensin II receptor antagonist (FFR+AT), CS-866 (0.3 mg/kg/day), by gavage, and then the euglycemic hyperinsulinemic glucose clamp technique was performed to evaluate insulin sensitivity. At the end of the glucose clamp, the soleus muscle was dissected for determination of the muscle fiber composition by ATPase methods. Blood pressure at the glucose clamp in the FFR group was significantly higher than that of the control group, and both temocapril and CS-866 significantly lowered the blood pressure of the FFR group. The average rate of glucose infusion during the glucose clamp, as a measure of insulin sensitivity (M value), was significantly lower in the FFR rats compared to the controls (15.4 +/- 0.4, 10.9 +/- 0.6 mg/kg/min, for control and FFR, respectively, P < .01). Both temocapril and CS-866 partially improved the M values compared to FFR (13.2 +/- 0.7, 12.8 +/- 0.5 mg/kg/min, for FFR+ACE, FFR+AT, respectively, P < .01 compared with FFR, P < .05 compared with control). The composite ratio of type I fibers of the soleus muscle was decreased significantly in the FFR rats compared with the controls (82% +/- 2%, 75% +/- 2%, for control and FFR, respectively, P < .01), and both temocapril and CS-866 restored a composite ratio of type I fibers to the same level as that of the controls (81% +/- 1%, 80% +/- 1% for FFR+ACE and FFR+AT, respectively). The M value was significantly correlated with the composition of type I and type II fibers. These results suggest that the fiber composition of skeletal muscle is correlated to insulin resistance, and that both ACE inhibitors and AT antagonists may modulate the muscle fiber composition in a hypertensive and insulin-resistant animal model, fructose-fed rats, to the same extent.

Metabolic effects of vanadyl sulfate in humans with non-insulin-dependent diabetes mellitus: in vivo and in vitro studies

To investigate the efficacy and mechanism of action of vanadium salts as oral hypoglycemic agents, 16 type 2 diabetic patients were studied before and after 6 weeks of vanadyl sulfate (VOSO4) treatment at three doses. Glucose metabolism during a euglycemic insulin clamp did not increase at 75 mg/d, but improved in 3 of 5 subjects receiving 150 mg VOSO4 and 4 of 8 subjects receiving 300 mg VOSO4. Basal hepatic glucose production (HGP) and suppression of HGP by insulin were unchanged at all doses. Fasting glucose and hemoglobin A1c (HbA1c) decreased significantly in the 150- and 300-mg VOSO4 groups. At the highest dose, total cholesterol decreased, associated with a decrease in high-density lipoprotein (HDL). There was no change in systolic, diastolic, or mean arterial blood pressure on 24-hour ambulatory monitors at any dose. There was no apparent correlation between the clinical response and peak serum level of vanadium. The 150- and 300-mg vanadyl doses caused some gastrointestinal intolerance but did not increase tissue oxidative stress as assessed by thiobarbituric acid-reactive substances (TBARS). In muscle obtained during clamp studies prior to vanadium therapy, insulin stimulated the tyrosine phosphorylation of the insulin receptor, insulin receptor substrate-1 (IRS-1), and Shc proteins by 2- to 3-fold, while phosphatidylinositol 3-kinase (PI 3-kinase) activity associated with IRS-1 increased 4.7-fold during insulin stimulation (P = .02). Following vanadium, there was a consistent trend for increased basal levels of insulin receptor, Shc, and IRS-1 protein tyrosine phosphorylation and IRS-1-associated PI 3-kinase, but no further increase with insulin. There was no discernible correlation between tyrosine phosphorylation patterns and glucose disposal responses to vanadyl. While glycogen synthase fractional activity increased 1.5-fold following insulin infusion, there was no change in basal or insulin-stimulated activity after vanadyl. There was no increase in the protein phosphatase activity of muscle homogenates to exogenous substrate after vanadyl. Vanadyl sulfate appears safe at these doses for 6 weeks, but at the tolerated doses, it does not dramatically improve insulin sensitivity or glycemic control. Vanadyl modifies proteins in human skeletal muscle involved in early insulin signaling, including basal insulin receptor and substrate tyrosine phosphorylation and activation of PI 3-kinase, and is not additive or synergistic with insulin at these steps. Vanadyl sulfate does not modify the action of insulin to stimulate glycogen synthesis. Since glucose utilization is improved in some patients, vanadyl must also act at other steps of insulin action.

Taurine attenuates hypertension and improves insulin sensitivity in the fructose-fed rat, an animal model of insulin resistance

Fructose feeding induces moderate increases in blood pressure levels in normal rats, which is associated with hyperinsulinemia, insulin resistance, and impaired glucose tolerance. Increased vascular resistance, sodium retention, and sympathetic overactivity have been proposed to contribute to the blood pressure elevation in this model. Taurine, a sulphur-containing amino acid, has been reported to have antihypertensive and sympatholytic actions. In the present study, the effects of taurine on blood pressure, plasma levels of glucose and insulin, glucose tolerance, and renal function were studied in fructose-fed rats. Fructose-fed rats had higher blood pressure and elevated plasma levels of insulin and glucose. The plasma glucose levels were higher in fructose-fed rats than in controls at 15, 30, and 60 min after the oral glucose load. Treatment with 2% taurine in drinking water prevented the blood pressure elevation and attenuated the hyperinsulinemia in fructose-fed rats. The exaggerated glucose levels in response to the oral glucose load was also prevented by taurine administration. Thus, taurine supplementation could be beneficial in circumventing metabolic alterations in insulin resistance.

Soluble dietary fibre improves insulin sensitivity by increasing muscle GLUT-4 content in stroke-prone spontaneously hypertensive rats

1. The effects of soluble dietary fibre (psyllium) on peripheral insulin sensitivity and skeletal muscle GLUT-4 protein expression were studied in 12 male stroke-prone spontaneously hypertensive rats (SHRSP) fed a high-caloric diet from 5 to 9 weeks of age. 2. In the psyllium-supplemented group, fasting plasma glucose was significantly reduced and glucose levels following an oral glucose tolerance test were significantly lower than in the cellulose-supplemented group at 30 (P < 0.05) and 60 min (P < 0.01). However, there was no difference in insulin secretion. 3. In the psyllium-supplemented group, skeletal muscle GLUT-4 content was significantly increased in the plasma membrane (P < 0.001), but not in the intracellular membrane. 4. No significant difference was found in phosphatidylinositol 3 (PI3)-kinase activity between cellulose and psyllium diet not only in the basal state but also when stimulated by insulin. 5. These results demonstrate that psyllium increases blood glucose disposal by increasing skeletal muscle plasma membrane GLUT-4 content without PI3-kinase activation.

Bezafibrate, an anti-hypertriglyceridemic drug, attenuates vascular hyperresponsiveness and elevated blood pressure in fructose-induced hypertensive rats

A high fructose diet induces hypertension, hyperinsulinemia - insulin resistance, and hypertriglyceridemia (syndrome X). In this study, we investigated the role of an abnormal lipid profile in mediating fructose-induced hypertension. We hypothesized that bezafibrate, a lipid-lowering drug, would reduce elevated blood pressure and inhibit increased vascular reactivity in fructose-fed rats. Male rats were placed on four different diets: group 1 was fed standard chow (n = 6); group 2 was fed 60% fructose (n = 5); group 3 was fed fructose plus bezafibrate (30 mg·kg-1·day-1; drinking water; n = 5); and group 4 was fed standard chow plus bezafibrate (n = 6). In addition, the direct effects of very low density lipoprotein (VLDL) on vascular reactivity were examined. Bezafibrate treatment lowered blood pressure, free fatty acids, and triglycerides in the fructose-fed group, suggesting that lipid abnormalities play a role in the elevation of blood pressure in the fructose-induced hypertensive rat. Aortae from fructose-fed rats were hyperresponsive to the calcium channel agonist Bay K 8644, which was normalized with bezafibrate treatment. Incubation of aortae in a VLDL medium resulted in increased responsiveness to Bay K 8644, lending further support to lipid abnormalities altering vascular reactivity. An altered lipid profile evidenced by elevated triglycerides and free fatty acids is causally related to the development of high blood pressure and increased vascular reactivity in the fructose-induced hypertensive rat.Key words: Sprague-Dawley rats, hypertriglyceridemia, free fatty acids, vascular reactivity, aortae.

Mechanisms of insulin resistance in rat models of hypertension and their relationships with salt sensitivity

Several lines of evidence suggest that insulin resistance and the resultant hyperinsulinaemia are causally related to hypertension. Insulin actions are initiated by binding to a high-affinity transmembrane protein receptor which is present in all mammalian cells. These effects are predominant in skeletal muscle, liver, and fat and involve a number of tissue-specific and biochemically diverse events. Less well known are effects of insulin occurring in tissues not usually considered as insulin targets, which are hypothetical contributors to the pro-hypertensive action of the hormone. These effects include activation of renal sodium reabsorption, stimulation of the sympathetic nervous system, growth-promoting activity on vascular smooth muscle cells, and modulation of transmembrane cation transport. Epidemiological investigations have implicated sodium intake in the pathogenesis of hypertension. Because of the sodium-retaining effects of insulin, it has been postulated that insulin resistance with associated hyperinsulinaemia may be critical for the pathogenesis of salt-sensitivity in essential hypertensive subjects. Insulin resistance is present also in strains of rats with genetic hypertension that can be utilized as models to study the molecular mechanisms of this abnormality. In the present article, we summarize the current knowledge of the mechanisms of insulin resistance in rat models of arterial hypertension in which decreased sensitivity to insulin occurs and propose a rationale hypothesis that links insulin resistance with salt-sensitivity and hypertension.

Insulin resistance and human disease: a short history

The notion that tissue resistance to insulin might play an important role in certain disease states is approximately 60 years old. However, recognition of its central role in this regard is a relatively recent phenomenon. In this review an effort has been made to trace a brief history of insulin resistance from its inception to its current position as the fundamental abnormality in both type 2 diabetes and Syndrome X.

Exogenous hyperinsulinemia causes insulin resistance, hyperendothelinemia, and subsequent hypertension in rats

In many clinical and animal studies, hypertension and insulin resistance coexist, but their mechanistic relationship is unclear. We explored the causal link between these two parameters in a rat model with chronic hyperinsulinemia induced with human insulin (1 U/d) released from subcutaneously implanted minipumps. Rats with saline minipumps served as a control. During the first experiment, plasma levels of insulin and glucose and the systolic blood pressure of the two groups were continuously monitored for 17 days. In the subsequent four experiments, rats were killed on days 10 and 13 to measure plasma endothelin-1 (ET-1) levels and the glucose transport into and insulin and ET-1 binding of isolated adipocytes. In one experiment, rats were tested for oral glucose tolerance on days 10 and 13. In another experiment, ET-1 binding to the aortic plasma membrane was also determined. The results showed that rats became hyperinsulinemic throughout the experimental period by the instillation of exogenous insulin. Hyperinsulinemic rats were consistently hypoglycemic during the first day, but they became euglycemic thereafter, indicating an insulin-resistant state. Glucose intolerance was obvious by day 10, but significant hypertension was not detected until the 11th day on insulin infusion. Compared with the saline controls, insulin-infused rats had an increase of plasma ET-1 levels but a decrease of both basal and insulin-stimulated glucose transport into adipocytes. ET-1 binding to adipocytes of the insulin-infused group was elevated significantly from day 10 through day 13. ET-1 binding to the aortic membranes, supposedly downregulated by the increased plasma ET-1 and hypertension, was similar to that found in the controls on day 13. These results imply that hyperinsulinemia in rats could lead to hypertension via the elevation of plasma ET-1 levels together with an unaltered vascular binding of ET-1, which was probably unrelated to the insulin resistance.