Grape-Derived Polyphenols Improve Aging-Related Endothelial Dysfunction in Rat Mesenteric Artery: Role of Oxidative Stress and the Angiotensin System

Aging is characterized by the development of an endothelial dysfunction, which affects both the nitric oxide (NO)- and the endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations, associated with vascular oxidative stress and the activation of the angiotensin system. This study investigated whether red wine polyphenols (RWPs), antioxidants and potent stimulators of NO- and EDHF-mediated relaxations improve aging-related endothelial dysfunction, and, if so, examined the underlying mechanism. Mesenteric artery reactivity was determined in organ chambers, vascular oxidative stress by dihydroethidine and MitoSOX staining, and expression of target proteins by immunohistochemical staining. Control young rats (16 weeks) received solvent (ethanol, 3% v/v), and middle-aged rats (46 weeks) either solvent or RWPs (100 mg/kg/day) in the drinking water. The acetylcholine-induced endothelium-dependent NO component was slightly reduced whereas the EDHF component was markedly blunted in rings of middle-aged rats compared to young rats. The endothelial dysfunction was associated with oxidative stress, an upregulation of angiotensin II and AT1 receptors and a down-regulation of SKCa, IKCa, and angiotensin converting enzyme. Intake of RWPs for either one or two weeks improved the NO and the EDHF components of the relaxation, and normalized oxidative stress, the expression of SKCa, IKCa and the components of the angiotensin system. The protective effect of the 2-week RWPs treatment persisted for one and two weeks following stopping intake of RWPs. Thus, intake of RWPs caused a persistent improvement of the endothelial function, particularly the EDHF component, in middle-aged rats and this effect seems to involve the normalization of the expression of SKCa, IKCa and the angiotensin system

Responses to endothelium-dependent agonists in subcutaneous arteries excised from hypercholesterolaemic men

1. Vasomotor function of the vascular endothelium was examined in human subcutaneous arteries excised from 8 hypercholesterolaemic and 7 normolipidaemic subjects. 2. Left gluteal skin biopsies were performed under local anaesthesia. Subcutaneous arteries were isolated and two vessels from each subject mounted in separate myographs. A 20 ml fasting blood sample was taken at the time of the biopsy. 3. Hypercholesterolaemic subjects had either never been treated with lipid lowering therapy or therapy had been stopped at least two weeks before the study (n=2). At the time of the study total plasma cholesterol levels (control: 4.6±0.3 vs hypercholesterolaemic: 8.3±0.6 mmol l(−1): P<0.01) were significantly elevated in hypercholesterolaemic subjects when compared with controls. 4. Full concentration-response curves to the vasoconstrictor noradrenaline and the vasodilators acetylcholine and substance P were constructed. A single point concentration-response to sodium nitroprusside (10 μM) was also obtained. Dilator responses were obtained in vessels pre-constricted with a submaximal concentration of noradrenaline. Vessels were then incubated for 30 min with either L- or D-arginine (10 μM) and the concentration-response curves to the three dilator agonists repeated in the presence of the amino acid. 5. Maximum relaxation responses to acetylcholine (control vs hypercholesterolaemic: 83.3±6.1% vs 47.4±13.5%; P<0.05), but not to substance P or sodium nitroprusside, were dampened in the hypercholesterolaemic group when compared with controls. 6. Neither incubation with L-arginine nor D-arginine had any effect on maximum relaxation responses to acetylcholine in either the control group (pre L-arginine vs plus L-arginine: 83.3±6.1 vs 82.3±5.5%, pre D-arginine vs plus D-arginine: 98.9±1.2 vs 98.2±1.1%) or the hypercholesterolaemic group (pre L-arginine vs plus L-arginine: 47.4±13.5 vs 55.3±14.3%, pre D-arginine vs plus D-argenine: 43.3±13.6 vs 65.4±12.3%). 7. When results from the two study groups were pooled, the strongest predictor of maximum relaxation obtained to acetylcholine was apolipoprotein A(1) (r=0.67; P=0.001). 8. In conclusion, relaxation responses mediated by the endothelium-dependent agonist acetylcholine, but not by substance P, are impaired in hypercholesterolaemic patients. L-Arginine did not improve the impaired relaxation responses to acetylcholine. We suggest that impaired endothelium-dependent relaxation is specific to acetylcholine and not to an abnormal L-arginine-nitric oxide pathway in subcutaneous arteries excised from this study group

AT(2) receptor-dependent vasodilation is mediated by activation of vascular kinin generation under flow conditions

1. Physiological roles of angiotensin II type 2 receptor (AT(2)) are not well defined. This study was designed to investigate the mechanisms of AT(2)-dependent vascular relaxation by studying vasodilation in pressurized and perfused rat mesenteric arterial segments. 2. Perfusion of angiotensin II in the presence of AT(1) antagonist elicited vascular relaxation, which was completely dependent on AT(2) receptors on endothelium. FR173657 (>1 μM), a bradykinin (BK) B(2)-specific antagonist, significantly suppressed AT(2)-dependent vasodilation (maximum inhibition: 68.5% at 10 μM). 3. Kininogen-deficient Brown Norway Katholiek rats showed a significant reduction in AT(2)-mediated vasodilatory response compared with normal wild-type Brown Norway rats. 4. Indomethacin (>1 μM), aprotinin (10 μM) and soybean trypsin inhibitor (10 μM) also reduced AT(2)-dependent vasodilation. 5. Our results demonstrated that stimulation of AT(2) receptors caused a significant vasodilation through local production of BK in resistant arteries of rat mesentery in a flow-dependent manner. Such vasodilation counterbalances AT(1)-dependent vasoconstriction to regulate the vascular tone

Differential effects of glucose on agonist-induced relaxations in human mesenteric and subcutaneous arteries

Background and purpose: Acute periods of hyperglycaemia are strongly associated with vascular disorder, yet the specific effects of high glucose on human blood vessel function are not fully understood. In this study we (1) characterized the endothelial-dependent relaxation of two similarly sized but anatomically distinct human arteries to two different agonists and (2) determined how these responses are modified by acute exposure to high glucose. Experimental approach: Ring segments of human mesenteric and subcutaneous arteries were mounted in a wire myograph. Relaxations to acetylcholine and bradykinin were determined in a control (5 mM) and high glucose (20 mM) environment over a 2 and 6 h incubation period. Key results: Bradykinin-induced relaxation in both sets of vessels was mediated entirely by EDHF whilst that generated by acetylcholine, though principally generated by EDHF, also had contribution from prostacyclin and possibly nitric oxide in mesenteric and subcutaneous vessels, respectively. A 2-h incubation of high glucose impaired bradykinin-induced relaxation of subcutaneous vessels whilst, in contrast, the relaxation generated by bradykinin in mesenteric vessels was enhanced at the same time point. High glucose significantly augmented the relaxation generated by acetylcholine in mesenteric and subcutaneous vessels at a 2 and 6 h incubation point, respectively. Conclusions and implications: Short periods of high glucose exert a variable influence on endothelial function in human isolated blood vessels that is dependent on factors of time, agonist-used and vessel studied. This has implications for how we view the effects of acute hyperglycaemia found in patients with diabetes mellitus as well as other conditions