Impaired endothelial alpha-2 adrenergic receptor-mediated vascular relaxation in the fructose-fed rat

Silencing of GPR82 with Interference RNA Improved Metabolic Profiles in Rats with High Fructose Intake

Metabolic syndrome (MS) is a clinical condition, constituted by alterations that lead to the onset of type II diabetes and cardiovascular disease. It has been reported that orphan G-protein-coupled receptor 82 (GPR82) participates in metabolic processes. The aim of this study was to evaluate the function of GPR82 in MS using a small interfering RNA (siRNA) against this receptor. We used Wistar rats of 10-12 weeks of age fed with a high-fructose solution (70%) for 9 weeks to induce MS. Subsequently, the rats were treated with an intrajugular dose of an siRNA against GPR82 and the effects were evaluated on day 3 and 7 after administration. On day 3 the siRNA had a transient effect on decreasing blood pressure and triglycerides and increasing high-density lipoprotein cholesterol, which recovered to the MS control on day 7. Decreased gene expressions of GPR82 mRNA in the aorta and heart were observed on day 3; moreover, decreased gene expression was maintained in the aorta on day 7. Therefore, we conclude that the orphan receptor GPR82 participates in the development of MS induced by fructose and the silencing of this receptor could ameliorate metabolic components.

Effect of infliximab and tocilizumab on fructose-induced hyperinsulinemia and hypertension in rats

Fructose administration can induce hypertension, insulin resistance and hypertriglyceridemia. Here, we investigated the possible protective effect of infliximab (IFX), a tumor necrosis factor alpha (TNF-α) inhibitor, or tocilizumab (TOC), an interleukin-6 (IL6) inhibitor, on fructose-induced increase in blood pressure, insulin resistance and hyperlipidemia in rats. The animals were fed a 60% fructose diet in the absence or presence of IFX (5 mg/kg, i.p., once weekly) or TOC (8 mg/kg, i.p., once every two weeks). Fructose significantly increased blood pressure, heart rate and homeostatic model assessment of insulin resistance (HOMA-IR). Fructose also significantly raised the concentrations of fasting plasma insulin, triglycerides, total cholesterol, uric acid, tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), malondialdhyde (MDA) and nitric oxide. Fructose also significantly decreased plasma superoxide dismutase (SOD) and catalase activities. In addition, fructose significantly increased aortic endothelin and nitric oxide concentrations. Both IFX and TOC attenuated the fructose-induced increase in blood pressure, insulin resistance, and the concentrations of uric acid, MDA and IL-6. TOC significantly reduced fructose-induced increase in triglycerides and cholesterol. In addition, IFX increased plasma SOD and catalase activities. Our results showed that both IFX and TOC were partially successful in reversing fructose - induced changes.

Health implications of high-fructose intake and current research

Although fructose consumption has dramatically increased and is suspected to be causally linked to metabolic abnormalities, the mechanisms involved are still only partially understood. We discuss the available data and investigate the effects of dietary fructose on risk factors associated with metabolic disorders. The evidence suggests that fructose may be a predisposing cause in the development of insulin resistance in association with the induction of hypertriglyceridemia. Experiments in animals have shown this relation when they are fed diets very high in fructose or sucrose, and human studies also show this relation, although with conflicting results due to the heterogeneity of the studies. The link between increased fructose consumption and increases in uric acid also has been confirmed as a potential risk factor for metabolic syndrome, and insulin resistance/hyperinsulinemia may be causally related to the development of hypertension. Collectively, these results suggest a link between high fructose intake and insulin resistance, although future studies must be of reasonable duration, use defined populations, and improve comparisons regarding the effects of relevant doses of nutrients on specific endpoints to fully understand the effect of fructose intake in the absence of potential confounding factors.

α-Tocopherol Improves Microcirculatory Dysfunction on Fructose Fed Hamsters

Fructose, an everyday component of western diet associated to chronic hyperglycemia and enhanced free radical production, impairs endothelial function and supplementation with antioxidants might improve it. In this study we investigated if vitamin E could reverse the microvascular damage elicited by fructose. Male Syrian golden hamsters drank either 10% fructose solution (F) or filtered water (C), combined with three concentrations of vitamin E in their chows [zero, normal (VE) or 5X (5XVE)] during 60 days. Microvascular reactivity in response to topical application of acetylcholine (Ach; endothelium-dependent vasodilator) or sodium nitroprusside (SNP; endothelium-independent vasodilator) and macromolecular permeability increase induced by either 30 min ischemia followed by reperfusion (I/R) or topical application of histamine (5 μM) were assessed using the cheek pouch preparation. Compared to controls (drinking filtered water), fructose-drinking animals showed decreased vasodilatation to acetylcholine in all concentrations tested (-56.2% for 10^-9M, -53.9% for 10^-7M and -43.7% for 10^-5M). On the other hand, vitamin E supplementation resulted in increased responses for both water and fructose drinking groups (177.4% for F vs. F/5XVE and 241.6% for C vs. C/5XVE for 10^-5M Ach). Endothelial-independent vasodilatation explored by topical application of SNP was restored and even enhanced with the supplementation of 5X vitamin E in both groups (80.1% for F vs. F/5XVE; 144.2% for C vs. C/5XVE; 3.4% of difference for C/5XVE vs. F/5XVE on 10^-5M SNP). The number of leaky sites after I/R and histamine stimuli in vitamin E supplemented animals decreased (-25.1% and -15.3% for F vs. F/5XVE; and -21.7% and -16% of leaky sites comparing C vs. C/5XVE, respectively for I/R and histamine stimuli) pointing to tightening of the endothelial barrier for macromolecular permeability. Our results strongly suggest that vitamin E could improve the endothelial function and permeability barrier and also reverse impairments elicited by sugar overload.

The effects of phentolamine on fructose-fed rats

Metabolic syndrome (MS) is a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. MS is associated with obesity, increased blood pressure, hyperlipidemia, and hyperglycemia. This study was designed to investigate the pharmacological profile of phentolamine, a nonselective α adrenergic receptor antagonist, in the prevention of increased blood pressure in fructose-fed rats. Phentolamine prevented the fructose-induced increase in systolic blood pressure without affecting insulin sensitivity and major metabolic parameters. The levels of plasma noradrenaline and angiotensin II, 2 proposed contributors to the development of fructose-induced elevated blood pressure, were examined. Neither noradrenaline nor angiotensin II levels were affected by phentolamine treatment. Since overproduction of nitric oxide has been shown to lead to an elevation in peroxynitrite, the role of oxidative stress, a proposed mechanism of fructose-induced elevated blood pressure and insulin resistance, was examined by measuring plasma levels of total nitrate/nitrite. Plasma nitrate/nitrite was significantly elevated in all fructose-fed animals, regardless of treatment with phentolamine. Another proposed contributor toward fructose-induced MS is an elevation in uric acid levels. In this experiment, plasma levels of uric acid were found to be increased by dietary fructose and were unaffected by phentolamine treatment.

Simvastatin-induced cardiac autonomic control improvement in fructose-fed female rats

OBJECTIVE

Because autonomic dysfunction has been found to lead to cardiometabolic disorders and because studies have reported that simvastatin treatment has neuroprotective effects, the objective of the present study was to investigate the effects of simvastatin treatment on cardiovascular and autonomic changes in fructose-fed female rats.

METHODS

Female Wistar rats were divided into three groups: controls (n = 8), fructose (n = 8), and fructose+ simvastatin (n = 8). Fructose overload was induced by supplementing the drinking water with fructose (100 mg/L, 18 wks). Simvastatin treatment (5 mg/kg/day for 2 wks) was performed by gavage. The arterial pressure was recorded using a data acquisition system. Autonomic control was evaluated by pharmacological blockade.

RESULTS

Fructose overload induced an increase in the fasting blood glucose and triglyceride levels and insulin resistance. The constant rate of glucose disappearance during the insulin intolerance test was reduced in the fructose group (3.4 ± 0.32%/min) relative to that in the control group (4.4 ± 0.29%/min). Fructose + simvastatin rats exhibited increased insulin sensitivity (5.4 ± 0.66%/min). The fructose and fructose + simvastatin groups demonstrated an increase in the mean arterial pressure compared with controls rats (fructose: 124 ± 2 mmHg and fructose+simvastatin: 126 ± 3 mmHg vs. controls: 112 ± 2 mmHg). The sympathetic effect was enhanced in the fructose group (73 ± 7 bpm) compared with that in the control (48 ± 7 bpm) and fructose+simvastatin groups (31 ± 8 bpm). The vagal effect was increased in fructose + simvastatin animals (84 ± 7 bpm) compared with that in control (49 ± 9 bpm) and fructose animals (46 ± 5 bpm).

CONCLUSION

Simvastatin treatment improved insulin sensitivity and cardiac autonomic control in an experimental model of metabolic syndrome in female rats. These effects were independent of the improvements in the classical plasma lipid profile and of reductions in arterial pressure. These results support the hypothesis that statins reduce the cardiometabolic risk in females with metabolic syndrome.

Sugary drinks in the pathogenesis of obesity and cardiovascular diseases

Soft drink overconsumption is now considered to be a major public health concern with implications for cardiovascular diseases. This follows a number of studies performed in animals suggesting that chronic consumption of refined sugars can contribute to metabolic and cardiovascular dysregulation. In particular, the monosaccharide fructose has been attracting increasing attention as the more harmful sugar component in terms of weight gain and metabolic disturbances. High-fructose corn syrup is gradually replacing sucrose as the main sweetener in soft drinks and has been blamed as a potential contributor to the current high prevalence of obesity. There is also considerable evidence that fructose, rather than glucose, is the more damaging sugar component in terms of cardiovascular risk. This review focuses on the potential role of sugar drinks, particularly the fructose component, in the pathogenesis of obesity and cardiovascular diseases.

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.

Role of hyperglycaemia in the pathogenesis of hypotension observed in type-1 diabetic rats

The role of hyperglycaemia in the pathogenesis of hypotension in diabetic disorders was investigated using the changes in cardiac M(2)-muscarinic receptor (M(2)-mAChR) gene expression in type-1-like diabetic rats and cultured cardiomyocytes. Blood pressure was markedly decreased in diabetic rats following the intravenous injection of streptozotocin (STZ) for 8 weeks. Also, the baroreflex sensitivity (Delta HR/Delta BP), as measured by the changes in heart rate (Delta HR) and mean blood pressure (Delta BP) 1 min after the intravenous injection of phenylephrine (10 microg/kg), was significantly increased. Arecaidine propargyl ester (APE), a M(2)-mAChR agonist produced a marked reduction in heart rate in these diabetic rats. Normalization of plasma glucose in diabetic rats using insulin (0.5 IU) or phlorizin (1 mg/kg) injection attenuated the blood pressure reduction and reversed the mRNA and protein levels of cardiac M(2)-mAChR. A high concentration of glucose (20 mmol/l) directly influenced the increase in gene expression of M(2)-mAChR in the H9c2 cardiac cell line. Hyperglycaemia induced an increase in cardiac M(2)-mAChR gene expression, suggesting a role in the pathogenesis of hypotension in diabetic disorders.

Increase of cardiac M2-muscarinic receptor gene expression in type-1 but not in type-2 diabetic rats

Changes of cardiac M2-muscarinic receptor (M2-mAChR) gene expression was investigated in type-1 like diabetic rats induced by intravenous injection of streptozotocin (STZ) and type-2 like diabetic rats induced by fed with fructose-rich chow. Systolic blood pressure (SBP) in STZ-diabetic rats was significantly lower than that in age-matched non-diabetic rats, while the SBP in type-2 like diabetic rats was higher than in non-diabetic rats. Also, the mRNA or protein level of cardiac M2-mAChR in STZ-diabetic rats was markedly higher than non-diabetic rats, but it was not observed in type-2 like diabetic rats as compared to age-matched non-diabetic rats. Arecaidine propargyl ester (APE), the agonist of M2-mAChR, produced a marked reduction of heart rate in STZ-diabetic rats but made less influence on heart rate in fructose-fed rats or non-diabetic rats. The results suggest that cardiac M2-mAChR gene expression is raised in type-1 like diabetic rats but not in type-2 like diabetic rats, this difference mainly due to hyperglycemia, for the production of hypotension in diabetic disorders.

Noradrenaline and angiotensin II modify vascular prostanoid release in fructose-fed hypertensive rats

1 A fructose-enriched diet induces hypertension, metabolic alterations and insulin resistance in rats, resembling human metabolic syndrome. Previously, we found that prostanoid production was altered in fructose-fed rats. 2 This study analysed the effects of incubation with noradrenaline (NA) and angiotensin II (Ang II) on prostanoid release in mesenteric vascular beds from control and fructose-fed rats. Animals which received fructose solution (10% w/v) for 22 weeks showed higher systolic blood pressure and triglyceridaemia. 3 In controls, NA increased 6-keto-prostaglandin (PG) F(1)alpha (prostacyclin metabolite) and thromboxane (TX) production. Ang II increased only TX release. In fructose-fed animals, NA increased 6-keto-PG F(1)alpha and TX. PGF(2)alpha (vasoconstrictor) was also elevated. Ang II also increased PGF(2)alpha and PGE(2) levels. 4 In conclusion, in fructose rats Ang II in vitro stimulates a vasoconstrictor prostanoid not stimulated in controls. This could be related to the observed in vivo blood pressure increase. In fructose-fed animals, NA and Ang II also augment vasodilator prostanoids, suggesting a compensatory mechanism because of long-term hypertension.

Receptor-mediated activation of nitric oxide synthesis by arginine in endothelial cells

Arginine contains the guanidinium group and thus has structural similarity to ligands of imidazoline and alpha-2 adrenoceptors (alpha-2 AR). Therefore, we investigated the possibility that exogenous arginine may act as a ligand for these receptors in human umbilical vein endothelial cells and activate intracellular nitric oxide (NO) synthesis. Idazoxan, a mixed antagonist of imidazoline and alpha-2 adrenoceptors, partly inhibited L-arginine-initiated NO formation as measured by a Griess reaction. Rauwolscine, a highly specific antagonist of alpha-2 AR, at very low concentrations completely inhibited NO formation. Like L-arginine, agmatine (decarboxylated arginine) also activated NO synthesis, however, at much lower concentrations. We found that dexmedetomidine, a specific agonist of alpha-2 AR was very potent in activating cellular NO, thus indicating a possible role for alpha-2 AR in L-arginine-mediated NO synthesis. D-arginine also activated NO production and could be inhibited by imidazoline and alpha-2 AR antagonists, thus indicating nonsubstrate actions of arginine. Pertussis toxin, an inhibitor of G proteins, attenuated L-arginine-mediated NO synthesis, thus indicating mediation via G proteins. L-type Ca(2+) channel blocker nifedipine and phospholipase C inhibitor U73122 inhibited NO formation and thus implicated participation of a second messenger pathway. Finally, in isolated rat gracilis vessels, rauwolscine completely inhibited the L-arginine-initiated vessel relaxation. Taken together, these data provide evidence for binding of arginine to membrane receptor(s), leading to the activation of endothelial NO synthase (eNOS) NO production through a second messenger pathway. These findings provide a previously unrecognized mechanistic explanation for the beneficial effects of L-arginine in the cardiovascular system and thus provide new potential avenues for therapeutic development.

Dexmedetomidine-induced pulmonary alterations in sheep

Alpha(2) agonist-induced pulmonary oedema in sheep might be related to alterations in pulmonary haemodynamics and/or activation of inflammatory processes. In seven sevoflurane-anaesthetized sheep pulmonary haemodynamics, arterial oxygen tensions, nitric oxide and prostaglandin E(2) concentrations were determined before and after intravenous dexmedetomidine (2microg kg(-1)). In a second trial, lung tissue was sampled for histopathology and quantitative real-time PCR for IL-1beta and iNOS mRNA in a control sheep and 2, 10 and 30min after dexmedetomidine. Computer tomography of the lung under sevoflurane anaesthesia before and after dexmedetomidine was performed. Two minutes after dexmedetomidine mean pulmonary artery pressure, pulmonary arterial occlusion pressure and estimated capillary pressurewere significantly increased to 34.5mmHg, 22.2mmHg and 27.1mmHg, respectively. On computer tomography, lung density increased immediately after dexmedetomidine, with maximal density occurring between 9 and 12min. Histopathology was consistent with vascular congestion followed by protein and erythrocyte extravasation into alveoli. Increased iNOS mRNA levels were detected in sevoflurane anaesthetized animals only. An IL-1beta signal occurred after morphological changes had occurred in lung tissue. These findings support hydrostatic stress as the underlying cause of alpha(2) agonist-induced pulmonary oedema in sheep.

Vascular Angiotensin Type 1 Receptor Expression Is Associated with Vascular Dysfunction, Oxidative Stress and Inflammation in Fructose-Fed Rats

This study determined whether or not oxidative stress and vascular dysfunction in fructose-induced hyperinsulinemic rats are associated with activation of the vascular renin-angiotensin system (RAS). Four groups of rats were used. CONT rats were fed normal rat chow, CONT+CAP were fed normal rat chow and given 500 mg/L captopril in their drinking water, fructose-fed rats (FFR) were fed a high-fructose diet and FFR+CAP were fed the high-fructose diet plus captopril in water. After 8 weeks, the vascular reactivity of mesenteric artery segments was measured. Blood was analyzed for insulin, glucose, hydrogen peroxide and 8-isoprostane. Aortic and heart tissue were used for subjected to quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis. Systolic blood pressure was significantly higher in FFR (p<0.05), and captopril treatment inhibited the blood pressure increase. Mesenteric artery dose-response curves to acetylcholine were shifted to the right in FFR (p<0.05) and were normal in FFR+CAP. Plasma insulin (p<0.05), hydrogen peroxide (p<0.02) and 8-isoprostane (p<0.05) were increased in FFR. Captopril treatment reducd hydrogen peroxide and 8-isoprostane concentrations. Aortic tissue mRNA expression levels were increased for angiotensin-converting enzyme (ACE, p<0.05), angiotensin type 1 receptor (AT1R, p<0.02), NOX4 (p<0.02) and VCAM-1 (p<0.05) in FFR aortic samples. Captopril treatment reduced AT1R, NOX4 and VCAM-1 expression in FFR to levels not different from CONT. Similar changes in heart tissue mRNA expression for angiotensinogen, AT1R and NOX4 were also observed. These results demonstrate that vascular RAS is upregulated in FFR and support the hypothesis that vascular RAS mediates vascular dysfunction and vascular oxidative stress in FFR.

beta(1) Receptors protect the renal afferent arteriole of angiotensin-infused rabbits from norepinephrine-induced oxidative stress

Renal afferent arterioles (Aff) from angiotensin II (AngII)-infused rabbits have enhanced contractions to AngII that are normalized by tempol (superoxide dismutase mimetic), whereas contractions to norepinephrine (NE) are normal and unaffected by tempol. Tested was the hypothesis that beta-receptor stimulation with NE prevents enhanced reactivity and superoxide generation. Preconstricted Aff from AngII- or vehicle-infused rabbits were perfused at physiologic pressure. Aff from vehicle-infused rabbits had strong, endothelium-independent relaxations to dobutamine (beta(1)-receptor agonist; 78 +/- 6%; P < 0.0001; mean +/- SD) but only weak relaxations to salbutamol (beta(2)-receptor agonist; 13 +/- 3%; P < 0.05) or BRL-37,344 (beta(3)-receptor agonist; 14 +/- 3%; P < 0.05). Contractions to NE were similar in Aff from vehicle- and AngII-infused rabbits (-36 +/- 5 versus -34 +/- 3%; NS) and were unaffected by tempol (-32 +/- 4%; NS). In contrast, phenylephrine contractions (alpha(1) agonist) were enhanced in Aff from AngII-infused rabbits (-59 +/- 6 versus -46 +/- 4%; P < 0.05) and normalized by tempol. NE contractions in Aff from AngII-infused rabbits (-34 +/- 4%) were enhanced (P < 0.01) by propranolol (nonselective beta antagonist; -53 +/- 6%), CGP-20,712A (selective beta(1)-receptor antagonist; -61 +/- 9%), or Rp-cAMP (competitive inhibitor of cAMP; -56 +/- 4%); were normalized by tempol; but were unaffected by ICI-118,551 (selective beta(2)-receptor antagonist) or SR-59,230A (selective beta(3)-receptor antagonist). Superoxide generation in Aff from AngII-infused rabbits that were assessed from ethidium:dihydroethidium was enhanced by addition of CGP-20,712A to NE but was normalized by tempol. Aff have robust alpha(1)-receptor contraction and beta(1)-receptor dilation. NE elicits beta(1) signaling via cAMP that moderates oxidative stress and contractions in Aff from AngII-infused rabbits.

Alpha(2)-adrenergic receptor signalling in hypertension

Cardiovascular regulation by the sympathetic nervous system is mediated by activation of one or more of the nine known subtypes of the adrenergic receptor family; alpha(1A)-, alpha(1B)-, alpha(1D)-, alpha(2A)-, alpha(2B)-, alpha(2C)-, beta(1)-, beta(2)- and beta(3)-ARs (adrenoceptors). The role of the alpha(2)-AR family has long been known to include presynaptic inhibition of neurotransmitter release, diminished sympathetic efferent traffic, vasodilation and vasoconstriction. This complex response is mediated by one of three subtypes which all uniquely affect blood pressure and blood flow. All three subtypes are present in the brain, kidney, heart and vasculature. However, each differentially influences blood pressure and sympathetic transmission. Activation of alpha(2A)-ARs in cardiovascular control centres of the brain lowers blood pressure and decreases plasma noradrenaline (norepinephrine), activation of peripheral alpha(2B)-ARs causes sodium retention and vasoconstriction, whereas activation of peripheral alpha(2C)-ARs causes cold-induced vasoconstriction. In addition, non-selective agonists elicit endothelium-dependent vasodilation and presynaptic inhibition of noradrenaline release. The evidence that each of these receptor subtypes uniquely participates in cardiovascular control is discussed in this review.

Regulation of Skeletal Muscle Peroxisome Proliferator-Activated Receptor .GAMMA. Expression by Exercise and Angiotensin-Converting Enzyme Inhibition in Fructose-Fed Hypertensive Rats

The purpose of this study was to examine the effects of chronic exercise training and angiotensin-converting enzyme (ACE) inhibition on peroxisome proliferator-activated receptor gamma (PPAR gamma) expression in fat and skeletal muscle in fructose-fed spontaneously hypertensive rats (SHR). SHR were fed a fructose-rich diet over 16 weeks of either exercise training (Ex group: 20 m/min, 0% grade, 60 min/day, 5 days/week), ACE inhibitor administration (TM group: temocapril, 10 mg/kg/day), or a combination of both treatments (TM+Ex group). The systolic blood pressure was reduced exclusively in the temocapril-treated groups. Serum leptin level was positively correlated with the ratio of epididymal fat weight to body weight (p<0.001). Exercise training significantly upregulated the PPARgamma expression in all tissues, which was attenuated by temocapril. PPARgamma expression was significantly upregulated in skeletal muscles in the Ex group, and temocapril administration attenuated this effect in the Ex+TM group. The level of PPARgamma protein was significantly higher in the extensor digitorum longus muscle than in the soleus muscle. Both TM and Ex prevented the fructose diet-induced transitions of fiber type. These data suggested that PPARgamma expression is tissue-specific, and that alterations in PPARgamma expression in the skeletal muscle induced by either or both treatments may have contributed to reducing the fat mass via the regulation of metabolic homeostasis. Changes in muscle morphology were independent of PPARgamma expression, and the higher proportion of type I fiber might also explain some of the beneficial impact of exercise and ACE inhibition on energy metabolism.

Chronological changes of alpha-adrenoceptor-mediated vascular constriction in Otsuka-Long-Evans-Tokushima fatty rats

In recent years, it has been suggested that many factors are involved in the development of hypertension accompanying insulin resistance. Because changes in vascular reactivity could be one of these factors, we here investigated chronological changes of alpha-adrenoceptor (AR)-mediated peripheral arteriolar vasoconstriction in a rat model of type II diabetes. Otsuka-Long-Evans-Tokushima fatty (OLETF) rats that naturally develop insulin resistance at the age of 16 weeks and type II diabetes at the age of 30 weeks (DM group) and control rats (N group) were used. Arterioles with a diameter of approximately 100 microm were removed from the cremaster muscle of 8-, 16- and 40-week-old rats and their diameters were measured in a tissue bath. The concentration-response curve (CRC) was determined for phenylephrine and UK14,304 both with and without N(G)-monomethyl-L-arginine (LNMMA). Although there were no significant differences in the CRC for phenylephrine between the 8-week-old DM group and N group, a leftward shift was seen for the 16- and 40-week-old DM groups. There were no significant differences in the CRC for UK14,304 between the two groups at any age, but in the presence of LNMMA, a leftward shift was seen in the 8- and 16-week-old but not in the 40-week-old DM groups. One possible explanation for these results is that impaired endothelium-dependent dilatation may have offset the reduction in arteriolar smooth muscle contraction. In conclusion, in the OLETF rats, the sensitivity of alpha-AR-mediated arteriolar vasoconstriction increased after the onset of insulin resistance. The sensitivity of alpha2-AR-mediated arteriolar smooth muscle contraction and endothelium-dependent vascular relaxation were both presumed to be impaired after the onset of type II diabetes.

Impact of exercise and angiotensin converting enzyme inhibition on tumor necrosis factor-alpha and leptin in fructose-fed hypertensive rats

The aim of this study was to evaluate the effects of moderate-intensity regular exercise and/or an angiotensin converting enzyme (ACE) inhibition on tumor necrosis factor-alpha (TNF-alpha) and glucose and lipid metabolism parameters. Spontaneously hypertensive rats (SHRs) were fed a fructose-rich diet during 16 weeks of either exercise training (Ex group: 20 m/min, 0% grade, 60 min/day, 5 days/week), administration of an ACE inhibitor (TM group: temocapril, 10 mg/kg/day), or a combination of both (TM+Ex group). The systolic blood pressure was reduced exclusively in the TM and TM+Ex group. Epididymal fat pads (EPI) weighed less in the TM+Ex group than in the single-treatment (TM) group. The serum leptin level was significantly and directly correlated with the EPI weight (p < 0.001). The TNF-alpha content per gram of EPI was the highest in the TM+Ex group. In addition, the EPI TNF-alpha level was negatively correlated with both the EPI weight and the serum leptin level (p < 0.001, respectively). In contrast, the TNF-alpha level of skeletal muscles was identical among the groups. The extensor digitorum longus had a significantly higher abundance of TNF-alpha protein than the soleus muscle. These data indicate that the local TNF-alpha expression is tissue-specific, and that upregulation of TNF-alpha in EPI by exercise training and/or ACE inhibition may have contributed to the reduction in fat cell volume via the induction of apoptosis and/or the regulation of metabolic homeostasis.