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

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-fructose feeding impacts on the adrenergic control of renal haemodynamics in the rat

The present study explored the hypothesis that a prolonged 8 weeks exposure to a high fructose intake suppresses adrenergic and angiotensin II (Ang II)-mediated vasoconstriction and is associated with a higher contribution of α1D-adrenoceptors. A total of thirty-two Sprague–Dawley rats received either 20 % fructose solution (FFR) or tap water (control, C) to drink ad libitum for 8 weeks. Metabolic and haemodynamic parameters were assessed weekly. The renal cortical vasoconstrictor responses to noradrenaline (NA), phenylephrine (PE), methoxamine (ME) and Ang II were determined in the presence and absence of BMY7378 (α1D-adrenoceptor antagonist). FFR had increased blood pressure, plasma levels of glucose, TAG and insulin. FFR expressed reduced renal vascular responses to adrenergic agonists and Ang II (NA: 50 %, PE: 50 %, ME, 65 %, Ang II: 54 %). Furthermore in the C group, the magnitude of the renal cortical vasoconstriction to all agonists was blunted in the presence of the low or high dose of BMY7378 (NA: 30 and 31 %, PE: 23 and 33 %, ME: 19 and 44 %, Ang II: 53 and 77 %), respectively, while in the FFR, vasoconstriction was enhanced to adrenergic agonists and reduced to Ang II (NA: 8 and 83 %, PE: 55 %, ME, 2 and 177 %, Ang II: 61 and 31 %). Chronic high fructose intake blunts vascular sensitivity to adrenergic agonists and Ang II. Moreover, blocking of the α1D-adrenoceptor subtype results in enhancement of renal vasoconstriction to adrenergic agonists, suggesting an inhibitory action of α1D-adrenoceptors in the FFR. α1D-Adrenoceptors buffer the AT1-receptor response in the renal vasculature of normal rats and fructose feeding suppressed this interaction.

Vascular dysfunction in type 2 diabetic TallyHo mice: role for an increase in the contribution of PGH2/TxA2 receptor activation and cytochrome p450 products

In this study, we tested the hypothesis that spontaneously diabetic TallyHo (TH) mice, a novel polygenic model for type 2 diabetes, will exhibit endothelial dysfunction associated with an increased contribution from endothelium-derived contractile factors (EDCF). The cellular mechanisms underlying the increased contribution of EDCF were explored in 16 and 30-week-old male TH and age-matched male C57BL/6J mice (n=4-9). Blood glucose and serum lipid profiles were markedly increased in the TH mice. Superoxide generation, assessed with a lucigenin chemiluminescence assay, was markedly increased in the aortae of TH mice. Endothelium-dependent vascular relaxations and contractions to acetylcholine (ACh), but not endothelium-independent relaxations to sodium nitroprusside, were impaired and vascular contractions to phenylephrine were significantly enhanced in aortae from TH mice. Nomega-nitro-L-arginine methyl ester markedly increased the ACh-induced contractions in TH mice, whereas SQ29548, a thromboxane receptor antagonist, and cytochrome P450 (CYP) inhibitors 17-octadecynoic acid and sulfaphenazole, the latter being specific for CYP2C6 and 2C9, decreased and (or) normalized the contractile response to ACh in TH mice. The present study indicates that enhanced contribution of prostaglandin H2/thromboxane A2 receptor and CYP, likely CYP2C6 and 2C9, play a critical role in the pathogenesis of increased EDCF in the aortae of type 2 diabetic TH mice.

Altered role of smooth muscle endothelin receptors in coronary endothelin-1 and α1-adrenoceptor-mediated vasoconstriction in Type 2 diabetes

Regulation of vascular tone and blood flow involves interactions between numerous local and systemic vascular control signals, many of which are altered by Type 2 diabetes (T2D). Vascular responses to endothelin-1 (ET-1) are mediated by endothelin type A (ETA) and type B (ETB) receptors that have been implicated in cross talk with α1-adrenoceptors (α1-AR). ETAand ETBreceptor expression and plasma ET-1 levels are elevated in T2D; however, whether this influences coronary α1-AR function has not been examined. Therefore, we examined the effect of ETAand ETBreceptor inhibition on coronary vasoconstriction to ET-1 and α1-AR activation in a mouse model of T2D. Coronary vascular responses were examined in isolated mouse hearts from control and diet-induced T2D C57BL/6J mice. Responses to ET-1 and the selective α1-AR agonist phenylephrine (PE) were examined alone and in the presence of the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester (l-NAME) alone or in combination with selective ETAor ETBreceptor inhibitors BQ-123 and BQ-788, respectively. Vasoconstriction to ET-1 was enhanced, whereas ETB, but not ETA, receptor blockade reduced basal coronary tone in T2D hearts. In the presence of l-NAME, ETAreceptor inhibition attenuated ET-1 vasoconstriction in both groups, whereas ETBinhibition abolished this response only in control hearts. In addition, ETAinhibition enhanced α1-AR-mediated vasoconstriction in T2D, but not control, hearts following l-NAME treatment. Therefore, in this model, enhanced coronary ET-1 responsiveness is mediated primarily through smooth muscle ETBreceptors, whereas the interaction with α1-ARs is mediated solely through the ETAreceptor subtype.

Effect of cerivastatin on endothelial dysfunction and aortic CD36 expression in diabetic hyperlipidemic rats

A mutation of the CD36 gene that encodes a fatty acid transporter has been reported to play a role in insulin resistance in spontaneously hypertensive rat (SHR). Statins reduce circulating cholesterol and triglyceride concentrations. The objective of this study was to determine the role of CD36 and the significance of statin therapy in insulin-resistance syndromes. We determined the isometric relaxation induced by acetylcholine or lecithinized superoxide dismutase (SOD) in aortas obtained from Otsuka Long Evans Tokushima Fatty (OLETF) rats, a model of insulin resistance and dyslipidemia, and normal control (Long Evans Tokushima Otsuka; LETO) rats with or without cerivastatin treatment. We also determined the effect of cerivastatin on aortic expression of CD36 and PPARgamma. The CD36 genotype and microsatellite markers on chromosome 4 were also determined. The relaxation induced by acetylcholine and lecithinized SOD were attenuated in OLETF rats but restored by a low dose of cerivastatin without significant changes in serum cholesterol. These relaxations were also restored by a high dose of cerivastatin with significant reductions in serum cholesterol and triglyceride. Cerivastatin increased the aortic expression of CD36 and PPARgamma mRNA in both LETO and OLETF rats. However, the basal level of CD36 mRNA and the increase in CD36 mRNA in response to cerivastatin were significantly lower in OLETF rats than in LETO rats. Although the abnormal CD36 genotype reported in SHR was not found in OLETF rats, the microsatellite markers of D4Rat151 and D4Rat115 differed between OLETF and LETO rats. In conclusion, insulin resistance in OLETF rats may be partially due to an altered expression of CD36. Increased aortic expression of CD36 in response to cerivastatin could explain the reduction in serum triglyceride concentrations with statin therapy and may have pronounced beneficial effects in insulin-resistance syndromes.

[Magic of the physician's word]

OBJECTIVE

The aim of this work was to find obesity control method without rebound. In our previous studies, gymnemate extracted from Gymnema sylvestre, inhibited oleic acid absorption. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a genetic multifactor syndrome model, exhibits progressive overweight, hyperlipidemia and hyperglycemia. The effect of gymnemate on obesity in OLETF was investigated.

METHODS

Three groups were divided (n=4-8): (1) OLETF-gymnemate, gymnema water extract (containing gymnemate) diet (62.5 g/kg) and water (2.5 g/kg) were supplied 2 weeks from 26-28 weeks, following it general diet and water were fed 3 weeks to observe if it rebound, (2) OLETF-control and (3) the counterpart Long-Evans Tokushima Otsuka rats as normal-control.

RESULTS

With gymnemate treatment, the food and water intake were decreased about 1/3 and 2/3, along with body weight reduced 57.2+/- 6.4 and 75.5+/- 6.3 g during 1 and 2 weeks respectively. In the end of experiment (3 weeks after gymnemate withdrawal), the body weight was decreased to no significant difference with normal-control. The total cholesterol was decreased about 1/3, moreover LDL+VLDL (low-density and very-low-density lipoprotein) cholesterol decreased about 1/2. The proportion of HDL (high-density lipoprotein) cholesterol to the total cholesterol was increased. The serum triglyceride was decreased to the 1/4 of OLETF control. The level of serum cholesterol and triglyceride was no significant difference in gymnemate group with normal group.

CONCLUSION

Supplementation with gymnemate promoted weight loss by its ability to reduce hyperlipidemia, which was no withdrawal rebound: an important discovery. Supplementation with gymnemate is a novel therapeutic tool for weight management, especially in multifactor syndrome.