The transient receptor potential type V1 channel (vanilloid receptor 1, TRPV1) is a Ca 2ϩ -permeable nonspecific cation channel activated by various painful stimuli including ischemia. We hypothesized that TRPV1 is expressed in the arterioles and is involved in the regulation of microvascular tone. We found that TRPV1 stimulation by capsaicin (intra-arterial administration) of the isolated, perfused right hind limb of the rat increased vascular resistance (by 98 Ϯ 21 mm Hg at 10 g) in association with decreased skeletal muscle perfusion and elevation of skin perfusion (detected by dual-channel laser Doppler flowmetry). Denervation of the hind limb did not affect capsaicin-evoked changes in vascular resistance and tissue perfusion in the hind limb but reduced the elevation of perfusion in the skin. In isolated, pressurized skeletal (musculus gracilis) muscle arterioles (diameter, 147 Ϯ 35 m), capsaicin had biphasic effects: at lower concentrations, capsaicin (up to 10 nM) evoked dilations (maximum, 32 Ϯ 13%), whereas higher concentrations (0.1-1 M) elicited substantial constrictions (maximum, 66 Ϯ 7%). Endothelium removal or inhibition of nitric-oxide synthase abolished capsaicin-induced dilations but did not affect arteriolar constriction. Expression of TRPV1 was detected by reverse transcriptase-polymerase chain reaction in the aorta and in cultured rat aortic vascular smooth muscle cells (A7r5). Immunohistochemistry revealed expression primarily in the smooth muscle layers of the gracilis arteriole. These data demonstrate the functional expression of TRPV1 in vascular smooth muscle cells mediating vasoconstriction of the resistance arteries. Because of the dual effects of TRPV1 stimulation on the arteriolar diameter (dilation in skin, constriction in skeletal muscle), we propose that TRPV1 ligands represent drug candidates for tissue-specific modulation of blood distribution.The transient receptor potential type V1 channel (vanilloid receptor-1, TRPV1) is a nonselective cation channel, structurally belonging to the transient receptor potential family of ion channels. TRPV1 is found in sensory C and A-␦ fibers (Caterina et al., 1997) and functions as a ligand-, proton-, and heat-activated molecular integrator of nociceptive stimuli in the periphery (Szallasi and Blumberg, 1999;

Abstract-Based on findings of experimental models of diabetes mellitus (DM) showing increased expression of vascular cyclooxygenase-2 (COX-2), we hypothesized that in patients with DM changes in COX-2-dependent prostaglandin synthesis affect vasomotor responses of coronary arterioles. Arterioles were dissected from the right atrial appendages obtained at the time of cardiac surgery of patient with DM(ϩ) or without documented diabetes DM(Ϫ). Isolated arterioles (89Ϯ15 m in diameter) were cannulated and pressurized (at 80 mm Hg), and changes in diameter were measured with video microscopy. After spontaneous tone developed [DM(Ϫ): 32Ϯ7%; DM(ϩ): 37Ϯ5%; PϭNS], arteriolar responses to bradykinin were investigated. Dilations to bradykinin (0.1 nmol/L to 1 mol/L) were significantly (PϽ0.05) greater in DM(ϩ) than DM(Ϫ) patients (10 nmol/L: 77Ϯ10% versus 38Ϯ14%). In both groups, dilations were similar to the NO-donor, sodium nitroprusside. In arterioles of DM(ϩ), but not those of DM(Ϫ), patients' bradykinin-induced dilations were reduced by the nonselective COX inhibitor indomethacin or by the selective COX-2 inhibitor NS-398 (DM(ϩ) at 10 nmol/L: to 20Ϯ4% and 29Ϯ7%, respectively). Correspondingly, a marked COX-2 immunostaining was detected in coronary arterioles of DM(ϩ), but not in those of DM(Ϫ) patients. We conclude that in coronary arterioles of diabetic patients bradykinin induces enhanced COX-2-derived prostaglandin-mediated dilation. These findings are the first to show that in humans diabetes mellitus increases COX-2 expression and dilator prostaglandin synthesis in coronary arterioles, which may serve to increase dilator capacity and maintain adequate perfusion of cardiac tissues. (Circ Res. 2006;99:e12-e17.)

Erdei, Nóra, Attila Tóth, Enikő T. Pásztor, Zoltán Papp, István É des, Akos Koller, and Zsolt Bagi. High-fat diet-induced reduction in nitric oxide-dependent arteriolar dilation in rats: role of xanthine oxidase-derived superoxide anion. Am J Physiol Heart Circ Physiol 291: H2107-H2115, 2006. First published June 23, 2006 doi:10.1152/ajpheart.00389.2006.-Obesity frequently leads to the development of hypertension. We hypothesized that high-fat diet (HFD)-induced obesity impairs the endothelium-dependent dilation of arterioles. Male Wistar rats were fed with normal (control) or HFD (60% of saturated fat, for 10 wk). In rats with HFD, body weight, mean arterial blood pressure, and serum insulin, cholesterol, and glucose were elevated. In isolated gracilis muscle arterioles (diameter: ϳ160 m) of HFD, rat dilations to ACh (at 1 M, maximum: 83 Ϯ 3%) and histamine (at 10 M, maximum: 16 Ϯ 4%) were significantly (P Ͻ 0.05) decreased compared with those of control responses (maximum: 90 Ϯ 2 and 46 Ϯ 4%, respectively). Dilations to the NO donor sodium nitroprusside were similar in the two groups. Inhibition of NO synthesis by N -nitro-L-arginine methyl ester reduced AChand histamine-induced dilations in control arterioles but had no effect on microvessels of HFD rats. The superoxide dismutase mimetic Tiron or xanthine oxidase inhibitor allopurinol enhanced ACh (maximum: 90 Ϯ 2 and 93 Ϯ 2%, respectively)-and histamine (maximum: 30 Ϯ 7 and 37 Ϯ 8%, respectively)-induced dilations in HFD arterioles, whereas the NAD(P)H oxidase inhibitor apocynin had no significant effect. Correspondingly, in carotid arteries of HFD rats, an enhanced superoxide production was shown by lucigenin-enhanced chemiluminescence, in association with an increased xanthine oxidase, but not NAD(P)H oxidase activity. In addition, a marked xanthine oxidase immunostaining was detected in the endothelial layer of the gracilis arterioles of HFD, but not in control rats. These findings suggest that, in obese rats, NO mediation of endotheliumdependent dilation of skeletal muscle arterioles is reduced because of an enhanced xanthine oxidase-derived superoxide production. These alterations demonstrate substantial dysregulation of arteriolar tone by the endothelium in HFD-induced obesity, which may contribute to disturbed tissue blood flow and development of increased peripheral resistance. metabolic syndrome; high-fat diet; microvessel; endothelium; nitric oxide; superoxide; xanthine oxidase; allopurinol THE METABOLIC SYNDROME is commonly defined as a group of risk factors or abnormalities closely associated with obesity and insulin resistance that markedly increase the risk for both cardiovascular disease and diabetes mellitus. Population-based studies suggest that obesity is the driving force behind the high prevalence of metabolic syndrome (38). In the past decade, the prevalence of obesity increased dramatically (17) in association with a continuous rise of cardiovascular diseases, such as hypertension (15). Despite the intensive investigations, the mechani...

The impact of obesity on nitric oxide (NO)-mediated coronary microvascular responses is poorly understood. Thus NO-mediated vasomotor responses were investigated in pressurized coronary arterioles ( approximately 100 microm) isolated from lean (on normal diet) and obese (fed with 60% of saturated fat) rats. We found that dilations to acetylcholine (ACh) were not significantly different in obese and lean rats (lean, 83 +/- 4%; and obese, 85 +/- 3% at 1 microM), yet the inhibition of NO synthesis with N(omega)-nitro-l-arginine methyl ester reduced ACh-induced dilations only in vessels of lean controls. The presence of the soluble guanylate cyclase (sGC) inhibitor oxadiazolo-quinoxaline (ODQ) elicited a similar reduction in ACh-induced dilations in the two groups of vessels (lean, 60 +/- 11%; and obese, 57 +/- 3%). Dilations to NO donors, sodium nitroprusside (SNP), and diethylenetriamine (DETA)-NONOate were enhanced in coronary arterioles of obese compared with lean control rats (lean, 63 +/- 6% and 51 +/- 5%; and obese, 78 +/- 5% and 70 +/- 5%, respectively, at 1 microM), whereas dilations to 8-bromo-cGMP were not different in the two groups. In the presence of ODQ, both SNP and DETA-NONOate-induced dilations were reduced to a similar level in lean and obese rats. Moreover, SNP-stimulated cGMP immunoreactivity in coronary arterioles and also cGMP levels in carotid arteries were enhanced in obese rats, whereas the protein expression of endothelial NOS and the sGC beta1-subunit were not different in the two groups. Collectively, these findings suggest that in coronary arterioles of obese rats, the increased activity of sGC leads to an enhanced sensitivity to NO, which may contribute to the maintenance of NO-mediated dilations and coronary perfusion in obesity.

We characterized the vasoactive effects of OR‐1896, the long‐lived metabolite of the inodilator levosimendan, in coronary and skeletal muscle microvessels. The effect of OR‐1896 on isolated, pressurized (80 mmHg) rat coronary and gracilis muscle arteriole (∼150 μm) diameters was investigated by videomicroscopy. OR‐1896 elicited concentration‐dependent (1 nM–10 μM) dilations in coronary (maximal dilation: 66±6%, relative to that in Ca2+‐free solutions; pD2: 7.16±0.42) and gracilis muscle arterioles (maximal dilation: 73±4%; pD2: 6.71±0.42), these dilations proving comparable to those induced by levosimendan (1 nM–10 μM) in coronary (maximal dilation: 83±6%; pD2: 7.06±0.14) and gracilis muscle arterioles (maximal dilation: 73±12%; pD2: 7.05±0.1). The maximal dilations in response to OR‐1896 were significantly (P<0.05) attenuated by the nonselective K+ channel inhibitor tetraethylammonium (1 mM) in coronary (to 34±9%) and gracilis muscle arterioles (to 28±6%). Glibenclamide (5 or 10 μM), a selective ATP‐sensitive K+ channel (KATP) blocker, elicited a greater reduction of OR‐1896‐induced dilations in skeletal muscle arterioles than in coronary microvessels. Conversely, the selective inhibition of the large conductance Ca2+‐activated K+ channels (BKCa) with iberiotoxin (100 nM) significantly reduced the OR‐1896‐induced maximal dilation in coronary arterioles (to 21±6%), but was ineffective in skeletal muscle arterioles (72±8%). Accordingly, OR‐1896 elicits a substantial vasodilation in coronary and skeletal muscle arterioles, by activating primarily BKCa and KATP channels, respectively, and it is suggested that OR‐1896 contributes to the long‐term hemodynamic effects of levosimendan. British Journal of Pharmacology (2006) 148, 696–702. doi:

Objective-Type 2 diabetes mellitus (T2-DM) is frequently associated with vascular dysfunction and elevated blood pressure, yet the underlying mechanisms are not completely understood. We hypothesized that in T2-DM, the regulation of peripheral vascular resistance is altered because of changes in local vasomotor mechanisms. ). In isolated, pressurized gracilis muscle arterioles (diameter Ϸ80 m) from db/db mice, stepwise increases in intraluminal pressure (from 20 to 120 mm Hg) elicited a greater reduction in diameter than in control vessels at each pressure step (at 80 mm Hg, db/db, 66Ϯ4% versus control, 79Ϯ3%). The passive diameters of arterioles (obtained in Ca 2ϩ -free solution) and the calculated myogenic index were not significantly different in the 2 groups. The presence of the prostaglandin H 2 /thromboxane A 2 receptor antagonist SQ29548 did not affect arteriolar diameters of control mice but reduced the enhanced arteriolar tone of db/db mice back to control levels (at 80 mm Hg, 80Ϯ4%). The inhibitor of cyclooxygenase-1 (COX-1), SC-560, did not affect the basal tone of arterioles, whereas NS-398, an inhibitor of COX-2, caused a significant shift in the arteriolar pressure-diameter curve of vessels from db/db mice (at 80 mm Hg, 76Ϯ3%) but not in those of control mice. Also, in aortas of db/db mice, expression of COX-2 was enhanced compared with controls. Conclusions-Collectively, these findings suggest that in mice with T2-DM, the basal tone of skeletal muscle arterioles is increased because of an enhanced COX-2-dependent production of constrictor prostaglandins. These alterations in microvascular prostaglandin synthesis may contribute to the increase in peripheral resistance and blood pressure in

Our previous study showed that arteriolar tone is enhanced in Type 2 diabetes mellitus (T2-DM) due to an increased level of constrictor prostaglandins. We hypothesized that, in mice with T2-DM, hydrogen peroxide (H2O2) is involved in the increased synthesis of constrictor prostaglandins, hence enhanced basal tone in skeletal muscle arterioles. Isolated, pressurized gracilis muscle arterioles (∼100 μm in diameter) of mice with T2-DM (C57BL/KsJ- db−/ db−) exhibited greater basal tone to increases in intraluminal pressure (20–120 mmHg) than that of control vessels (at 80 mmHg, control: 25 ± 5%; db/ db: 34 ± 4%, P < 0.05), which was reduced back to control level by catalase ( db/ db: 24 ± 4%). Correspondingly, in carotid arteries of db/ db mice, the level of dichlorofluorescein-detectable and catalase-sensitive H2O2 was significantly greater. In control arterioles, exogenous H2O2 (0.1–100 μmol/l) elicited dilations (maximum, 58 ± 10%), whereas in arterioles of db/ db mice H2O2 caused constrictions (−28 ± 8%), which were converted to dilations (maximum, 16 ± 5%) by the thromboxane A2/prostaglandin H2 (TP) receptor antagonist SQ-29548. In addition, arteriolar constrictions in response to the TP receptor agonist U-46619 were not different between the two groups of vessels. Endothelium denudation did not significantly affect basal tone and H2O2-induced arteriolar responses in either control or db/ db mice. Also, in arterioles of db/ db mice, but not in controls, 3-nitrotyrosine staining was detected in the endothelial layer of vessels. Thus we propose that, in mice with T2-DM, arteriolar production of H2O2 is enhanced, which leads to increased synthesis of the constrictor prostaglandins thromboxane A2/prostaglandin H2 in the smooth muscle cells, which enhance basal arteriolar tone. These alterations may contribute to disturbed regulation of skeletal muscle blood flow in Type 2 diabetes mellitus.

Objectives-We hypothesized that simultaneous presence of obesity and hypertension activates adaptive vascular mechanisms affecting dilations of human coronary arterioles. Methods and Results-Agonist-induced dilations were assessed in isolated pressurized coronary arterioles from patients (nϭ38) who underwent cardiac surgery. Among normotensives we found that dilations to bradykinin (BK) and the NO-donor, sodium-nitroprusside (SNP) were reduced in obese subjects (BK, 10 Ϫ7 mol/L, lean:90Ϯ4%, obese:64Ϯ7%; SNP, 10 Ϫ6 mol/L, lean:89Ϯ7%, obese:76Ϯ5%). However, among hypertensives, both BK-and SNP-induced dilations were significantly enhanced in obese patients, when compared with lean individuals (BK, lean:71Ϯ7%, obese:85Ϯ3%; SNP, lean:60Ϯ6%, obese:83Ϯ2%). Correspondingly, in hypertensive patients, but not in those of normotensives, a positive correlation was found between body mass index (BMI) and BK-induced (Pϭ0.036, rϭ0.46), and also SNP-evoked (Pϭ0.031, rϭ0.44) coronary dilations. Moreover, in additional 55 hypertensive patients flow-mediated (FMD) and nitroglycerin (NTG)-induced dilations of the brachial artery were assessed. In obese hypertensive individuals, FMD-and NTG-induced dilations were greater (FMD:6.2Ϯ0.7%, NTG:17.2Ϯ0.9%), than in lean hypertensive patients (FMD:3.7Ϯ0.6%, NTG:13.6Ϯ1.1%). Correspondingly, FMD-and NTG-induced dilations were positively correlated with BMI (Pϭ0.020, rϭ0.31 and Pϭ0.033, rϭ0.29, respectively). Conclusions-These findings are the first to suggest that obesity may lead to activation of adaptive vascular mechanisms to enhance the dilator function of coronary and peripheral arterial vessels in hypertensive patients. (Arterioscler Thromb Vasc