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Reactive oxygen species (ROS), such as superoxide anions and hydrogen peroxide, are reported to contribute to the dynamic regulation of contractility in various arterial preparations, however, the situation in pressurized, myogenically active resistance arteries is much less clear. In the present study, we have utilized established pharmacological inhibitors of NADPH oxidase activity to examine the potential contribution of ROS to intrinsic myogenic contractility in adult Sprague–Dawley rat resistance arteries and responses to vasoactive agents acting via the endothelium (i.e., acetylcholine, SKA-31) or smooth muscle (i.e., sodium nitroprusside, phenylephrine). In cannulated and pressurized cremaster skeletal muscle and middle cerebral arteries, the NOX inhibitors 2-acetylphenothiazine (2-APT) and VAS2870, selective for NOX1 and NOX2, respectively, evoked concentration-dependent inhibition of basal myogenic tone in a reversible and irreversible manner, respectively, whereas the non-selective inhibitor apocynin augmented myogenic contractility. The vasodilatory actions of 2-APT and VAS2870 occurred primarily via the vascular endothelium and smooth muscle, respectively. Functional responses to established endothelium-dependent and –independent vasoactive agents were largely unaltered in the presence of either 2-APT or apocynin. In cremaster arteries from Type 2 Diabetic (T2D) Goto-Kakizaki rats with endothelial dysfunction, treatment with either 2-APT or apocynin did not modify stimulus-evoked vasoactive responses, but did affect basal myogenic tone. These same NOX inhibitors produced robust inhibition of total NADPH oxidase activity in aortic tissue homogenates from control and T2D rats, and NOX isozymes 1, 2 and 4, along with superoxide dismutase 1, were detected by qPCR in cremaster arteries and aorta from both species. Based on the diverse effects that we observed for established, chemically distinct NOX inhibitors, the functional contribution of vascular NADPH oxidase activity to stimulus-evoked vasoactive signaling in myogenically active, small resistance arteries remains unclear.

INTRODUCTION Exercise training has antiatherogenic effects on conduit and resistance artery function and structure in humans and induces angiogenic changes in skeletal muscle. However, training-induced adaptation in cutaneous microvessels is poorly understood, partly because of technological limitations. Optical coherence tomography (OCT) is a novel high-resolution imaging technique capable of visualizing cutaneous microvasculature at a resolution of ~30 μm. We utilized OCT to visualize the effects of training on cutaneous microvessels, alongside assessment of conduit artery flow-mediated dilation (FMD). METHODS We assessed brachial FMD and cutaneous microcirculatory responses at rest and in response to local heating and reactive hyperemia: pretraining and posttraining in eight healthy men compared with age-matched untrained controls (n = 8). Participants in the training group underwent supervised cycling at 80% maximal heart rate three times a week for 8 wk. RESULTS We found a significant interaction (P = 0.04) whereby an increase in FMD was observed after training (post 9.83% ± 3.27% vs pre 6.97% ± 1.77%, P = 0.01), with this posttraining value higher compared with the control group (6.9% ± 2.87%, P = 0.027). FMD was not altered in the controls (P = 0.894). There was a significant interaction for OCT-derived speed (P = 0.038) whereby a significant decrease in the local disk heating response was observed after training (post 98.6 ± 3.9 μm·s-1 vs pre 102 ± 5 μm·s-1, P = 0.012), whereas no changes were observed for OCT-derived speed in the control group (P = 0.877). Other OCT responses (diameter, flow rate, and density) to local heating and reactive hyperemia were unaffected by training. CONCLUSIONS Our findings suggest that vascular adaptation to exercise training is not uniform across all levels of the arterial tree; although exercise training improves larger artery function, this was not accompanied by unequivocal evidence for cutaneous microvascular adaptation in young healthy subjects.

Purpose While maximum blood flow influences one's maximum rate of oxygen consumption (V̇O2max), with so many indices of vascular function, it is still unclear if vascular function is related to V̇O2max in healthy, young adults. The purpose of this study was to determine if several common vascular tests of conduit artery and resistance artery function provide similar information about vascular function and the relationship between vascular function and V̇O2max. Methods Twenty‐two healthy adults completed multiple assessments of leg vascular function, including flow‐mediated dilation (FMD), reactive hyperemia (RH), passive leg movement (PLM), and rapid onset vasodilation (ROV). V̇O2max was assessed with a graded exercise test on a cycle ergometer. Results Indices associated with resistance artery function (e.g., peak flow during RH, PLM, and ROV) were generally related to each other (r = 0.47–77, p

Modulation of vascular function follows an exercise intensity-dependent pattern in young adults. This study aimed to investigate the potential intensity-dependent effects of an acute bout of exercise on conduit and resistance artery function in healthy older adults.Eleven healthy older adults (five males/six females, 66 ± 1 yr) completed 30 min of recumbent cycling at 50%-55% (low intensity) and 75%-80% (high intensity) of their age-predicted HRmax on two separate study visits. Doppler ultrasound measures of brachial artery flow-mediated dilation (FMD) and reactive hyperemia were taken at baseline, 10 min postexercise, and 1 h postexercise. In addition, cardiovascular hemodynamics and brachial shear rate were measured every 5 min during exercise.Brachial artery FMD was enhanced 10 min after high-intensity exercise (4.8% ± 0.2% to 9.1% ± 0.3%, P0.01), but not low-intensity (4.7% ± 0.2% to 6.2% ± 0.3%, P = 0.54) exercise. Peak and total (area under the curve) blood flow during reactive hyperemia (measures of resistance artery function) were enhanced 10 min postexercise for both intensities (peak low intensity, 372 ± 31 to 444 ± 37 mL·min; peak high intensity, 391 ± 30 to 455 ± 28 mL·min; total low intensity, 142 ± 16 to 205 ± 20 mL; total high intensity, 158 ± 14 to 240 ± 25 mL; main effect of time for both, P0.05). However, the magnitude of change in peak and the total blood flow were not different between exercise intensities (interaction effect; P = 0.56 and P = 0.97, respectively). Independent of exercise intensity, FMD returned to baseline 1 h after exercise (high, 5.9% ± 0.3%; low, 5.1% ± 0.1%; both P0.05).Our data indicate that high-intensity exercise acutely enhances conduit artery function in healthy older adults. In addition, an acute bout of exercise enhances resistance artery function independent of intensity.

We propose an integrated pathophysiological approach that we named “large/small artery cross-talk” in order to better explain how large and small artery changes interact in pressure wave transmission; increase central pressure pulsatility; exaggerate cardiac, brain, and kidney damage; and lead to cardiovascular and renal complications. The cross-talk between the micro- and the macrocirculation promotes a vicious circle, which can begin either from large vessels or at the site of small arteries. Sequentially, increased resistance in small arteries increases mean BP and then increases arterial stiffness in the large elastic arteries, which concomitantly with more pressure wave reflections increases central systolic blood pressure, ultimately leading to target organ damage. The increased central BP pulsatility is in turn a factor of small resistance artery damage. Lastly, the increase in the media-to-lumen ratio of small resistance arteries and the concomitant reduction in lumen diameter represent the most important part of the structural aspects of increased total peripheral resistance, leading to a rise in mean BP and thus prolonging the vicious circle.

Aims The relationship between resistance artery remodelling and endothelial function remains unknown. In this study, we assessed (i) the capacity of endothelial function and nitric oxide (NO) availability to provide more information on the severity of resistance artery remodelling than common cardiovascular risk factors in subjects at low or high cardiovascular risk; and (ii) differences between patterns of resistance artery remodelling associated with deficit of NO availability and with exposure to cardiovascular risk factors. Methods and results All analyses were conducted on the microvascular data set of the Italian Society for Arterial Hypertension (SIIA) that includes 356 patients with measures of small resistance arteries remodelling acquired with pressure or wire myography. Information on endothelial function and NO availability were also available in 116 patients. The European Heart Score (HS) was used to define the total cardiovascular risk of each patient. Endothelial function was inversely related with the severity of the resistance artery remodelling, and this association remained significant after adjustment for the HS. By contrast, the HS lost its significant association with the media-to-lumen (M/L) ratio and the media cross-sectional area after adjustment for endothelial function. The strength of these associations was similar in subjects at high and low cardiovascular risk. The addition of endothelial function and NO availability to the HS significantly improved the identification of subjects at more and less severe resistance artery remodelling. A severe deficit of NO availability was associated with hypertrophic remodelling, while a higher HS was more clearly associated with eutrophic remodelling. Conclusion Resistance artery endothelial function and NO availability might represent important factors involved in resistance artery remodelling, independently from cardiovascular risk factor exposure.

Background Endothelial dysfunction is an early pathogenic event in the progression of cardiovascular disease in patients with Type 2 Diabetes (T2D). Endothelial KCa2.3 and KCa3.1 K+ channels are important regulators of arterial diameter, and we thus hypothesized that SKA-31, a small molecule activator of KCa2.3 and KCa3.1, would positively influence agonist-evoked dilation in myogenically active resistance arteries in T2D. Methodology Arterial pressure myography was utilized to investigate endothelium-dependent vasodilation in isolated cremaster skeletal muscle resistance arteries from 22 to 24 week old T2D Goto-Kakizaki rats, age-matched Wistar controls, and small human intra-thoracic resistance arteries from T2D subjects. Agonist stimulated changes in cytosolic free Ca2+ in acutely isolated, single endothelial cells from Wistar and T2D Goto-Kakizaki cremaster and cerebral arteries were examined using Fura-2 fluorescence imaging. Main findings Endothelium-dependent vasodilation in response to acetylcholine (ACh) or bradykinin (BK) was significantly impaired in isolated cremaster arteries from T2D Goto-Kakizaki rats compared with Wistar controls, and similar results were observed in human intra-thoracic arteries. In contrast, inhibition of myogenic tone by sodium nitroprusside, a direct smooth muscle relaxant, was unaltered in both rat and human T2D arteries. Treatment with a threshold concentration of SKA-31 (0.3 μM) significantly enhanced vasodilatory responses to ACh and BK in arteries from T2D Goto-Kakizaki rats and human subjects, whereas only modest effects were observed in non-diabetic arteries of both species. Mechanistically, SKA-31 enhancement of evoked dilation was independent of vascular NO synthase and COX activities. Remarkably, SKA-31 treatment improved agonist-stimulated Ca2+ elevation in acutely isolated endothelial cells from T2D Goto-Kakizaki cremaster and cerebral arteries, but not from Wistar control vessels. In contrast, SKA-31 treatment did not affect intracellular Ca2+ release by the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor cyclopiazonic acid. Conclusions Collectively, our data demonstrate that KCa channel modulation can acutely restore endothelium-dependent vasodilatory responses in T2D resistance arteries from rats and humans, which appears to involve improved endothelial Ca2+ mobilization.

Matching oxygen supply to consumption across different tissues is a critical function of the vasculature. The remarkably wide range of metabolic demand between resting and active skeletal muscle renders control of blood flow to skeletal muscle tissues especially important and challenging. Mechanisms of exercise hyperemia are believed to be multifaceted and redundant, reflecting both the complexity of this response as well as its importance. We explored two candidate mechanisms of exercise hyperemia, examining ATP release from red blood cells and hemoglobin alpha in the endothelium of resistance arteries. We first studied the participation of Pannexin 1 in a red blood cell pathway reported to link hypoxia to elevated cyclic AMP and finally ATP release via Pannexin 1 to promote vasodilatory signaling in the endothelium. Our findings contradict previous claims that these components participate in the same signaling pathway. Furthermore, our work highlights a number of methodological considerations that we present as best practices for future in vitro work studying ATP release from red blood cells. Finally, we report exercise data that suggests more broadly a lack of significant role for Pannexin 1 in exercise performance. Subsequently, we hypothesized a novel role for endothelial hemoglobin alpha as a nitrite reductase during hypoxia. This mechanism has received significant attention in red blood cell hemoglobin, but has not previously been examined in the endothelium. Creating novel genetic models of Hba1 deletion, we demonstrated a reduction in exercise performance upon deletion of endothelial Hba1 in mice. These effects appear to be independent of the endothelial Hbα-eNOS interaction previously reported by our laboratory. Preliminary myography data shows impaired dilation of EC Hba1Δ/Δ skeletal muscle resistance arteries in response to hypoxia. We identify further experiments planned to clarify the mechanism underlying these results. Taken together, our findings point to a novel role for endothelial hemoglobin alpha as a critical regulator of skeletal muscle blood flow during exercise.

Chemical signals from perivascular adipose tissue (PVAT) modulate the structure and function of blood vessels. This may be partially under sympathetic neural control, however, little is known about the density of sympathetic innervation of PVAT. We hypothesized sympathetic nerve (SN) density in PVAT surrounding mesenteric resistance arteries (MRAs) is similar to that in the adventitia of the MRAs, and that high-fat feeding (HFF, 16 weeks) would decrease the density of SNs on MRAs and in PVAT. To test these hypotheses, we labeled SNs on MRAs and in PVAT with rabbit anti-tyrosine hydroxylase (TH) antibodies/AlexaFluor488-conjugated donkey-anti-rabbit antibodies, ex vivo. TH staining density (fraction occupied by TH-labeled structures) was computed from thresholded, background subtracted, maximum intensity z-projections of image stacks. TH staining density was higher at the surface of MRAs (0.21±0.03, n = 14) than within PVAT (0.013±0.003, n = 42, p16 fold lower. HFF does not affect SN density on MRAs or in PVAT. However, given the larger size of adipocytes in HFF rats, this may mean an increase in SN density/adipocyte. Nonetheless, the low density of SNs in mesenteric PVAT suggests limited direct SN control of PVAT function in the bulk of PVAT adipocytes.

The aorta has limited ability to accommodate increasing body size by remodeling. The dramatic rise in pediatric obesity threatens to overwhelm this intrinsic remodeling program and lead to abnormal aortic function. As hypothesized, pulse pressure, as an index of aortic function, has indeed risen dramatically in parallel with the rise of pediatric obesity, while at the same time mean arterial pressure, as an index of small resistance artery function, has fallen. These divergent large-artery-versus-small-artery indices may combine to explain the counterintuitive decrease in systolic blood pressure in children and adults during the global obesity pandemic. The pathophysiologic mechanisms underpinning these contrasting trends are not yet known.

The effect of intraluminal hyperglycaemia was investigated in the iliac artery of 11 anaesthetised pigs. Following isolation of a test segment, hyperglycaemic blood (40 mmol·L–1) caused a significant dilatation of the artery of 167 ± 208 μm (mean ± SD; n = 6, P = 0.031). Dilatations were reduced by N(G)-nitro-l-arginine methyl esther (250 μg·mL–1) from 145 ± 199 to 38 ± 5 μm), but this was not statistically significant (n = 6, P = 0.18). Intra-arterial infusions of d-glucose (20–40 mmol·L–1·min–1), during graded constrictions, caused statistically significant increases in blood flow (n = 11, P = 0.0013). Vasodilatation was confirmed by measurements of the ratio of immediate pressure steps to flow steps (∂P/∂F) during the graded obstruction experiments, showing a decrease in instantaneous vascular resistance from a control of 0.62 ± 0.30 to 0.33 ± 0.34 mm Hg·mL–1·min–1 (n = 7, P = 0.016). Autoregulation was assessed from the slopes of the plots of steady-state flow versus pressure. There were significant increases in the slope from 2.32 ± 1.03 to 5.88 ± 5.60 mL·min–1·(mm Hg)–1 (n = 7, P = 0.0078), indicating significant impairment of autoregulation. In conclusion, luminal hyperglycaemia relaxes both arterial and resistance vessel smooth muscle.

Hypertension is associated with altered structure of the resistance vessels, a process known as remodeling. This review summarizes current concepts concerning the structure of a subgroup of the resistance vessels, the small arteries, and the modes of remodeling, some of the determinants of remodeling, and some signaling pathways for remodeling. It is shown that the available evidence points to important roles for blood flow and growth factors, in addition to blood pressure, as causes of resistance artery remodeling. Finally, the relationship between vascular structure and blood pressure is discussed, in particular with regard to the effects of antihypertensive therapy. Here again, it appears that blood flow plays an important role in allowing the correction of the abnormal resistance vessel structure seen in hypertension.

Aims Prolonged P2Y-receptor signalling can cause vasoconstriction leading to hypertension, vascular smooth muscle hypertrophy, and hyperplasia. G protein-coupled receptor signalling is negatively regulated by G protein-coupled receptor kinases (GRKs) and arrestin proteins, preventing prolonged or inappropriate signalling. This study investigates whether GRKs and arrestins regulate uridine 5′-triphosphate (UTP)-stimulated contractile signalling in adult Wistar rat mesenteric arterial smooth muscle cells (MSMCs). Methods and results Mesenteric arteries contracted in response to UTP challenge: When an EC50 UTP concentration (30 µM, 5 min) was added 5 min before ( R 1) and after ( R 2) the addition of a maximal UTP concentration ( R max: 100 µM, 5 min), R 2 responses were decreased relative to R 1, indicating desensitization. UTP-induced P2Y-receptor desensitization of phospholipase C signalling was studied in isolated MSMCs transfected with an inositol 1,4,5-trisphosphate biosensor and/or loaded with Ca2+-sensitive dyes. A similar protocol ( R 1/ R 2 = 10 µM; R max = 100 µM, applied for 30 s) revealed markedly reduced R 2 when compared with R 1 responses. MSMCs were transfected with dominant-negative GRKs or siRNAs targeting specific GRK/arrestins to probe their respective roles in P2Y-receptor desensitization. GRK2 inhibition, but not GRK3, GRK5, or GRK6, attenuated P2Y-receptor desensitization. siRNA-mediated knockdown of arrestin2 attenuated UTP-stimulated P2Y-receptor desensitization, whereas arrestin3 depletion did not. Specific siRNA knockdown of the P2Y2-receptor almost completely abolished UTP-stimulated IP3/Ca2+ signalling, strongly suggesting that our study is specifically characterizing this purinoceptor subtype. Conclusion These new data highlight roles of GRK2 and arrestin2 as important regulators of UTP-stimulated P2Y2-receptor responsiveness in resistance arteries, emphasizing their potential importance in regulating vasoconstrictor signalling pathways implicated in vascular disease.

The diameter of resistance arteries has a profound effect on the distribution of microvascular blood flow and the control of systemic blood pressure. Here, we review mechanisms that contribute to the regulation of resistance artery diameter, both acutely and chronically, their temporal characteristics, and their interdependence. Furthermore, we hypothesize the existence of a remodeling continuum that allows for the vascular wall to rapidly modify its structural characteristics, specifically through the re-positioning of vascular smooth muscle cells. Importantly, the concepts presented more closely link acute vasoregulatory responses with adaptive changes in vessel wall structure. These rapid structural adaptations provide resistance vessels the ability to maintain a desired diameter under presumed optimal energetic and mechanical conditions.

This is the first study to elucidate and quantify the microstructural bases of the mechanical properties of human resistance arteries. The geometrically accurate mechanical analysis provides new insights into strain fields existing in the walls of small arteries, and raises questions about the mechanobiology of vascular remodeling., Vascular diseases such as diabetes and hypertension cause changes to the vasculature that can lead to vessel stiffening and the loss of vasoactivity. The microstructural bases of these changes are not presently fully understood. We present a new methodology for stain-free visualization, at a microscopic scale, of the morphology of the main passive components of the walls of unfixed resistance arteries and their response to changes in transmural pressure. Human resistance arteries were dissected from subcutaneous fat biopsies, mounted on a perfusion myograph, and imaged at varying transmural pressures using a multimodal nonlinear microscope. High-resolution three-dimensional images of elastic fibers, collagen, and cell nuclei were constructed. The honeycomb structure of the elastic fibers comprising the internal elastic layer became visible at a transmural pressure of 30 mmHg. The adventitia, comprising wavy collagen fibers punctuated by straight elastic fibers, thinned under pressure as the collagen network straightened and pulled taut. Quantitative measurements of fiber orientation were made as a function of pressure. A multilayer analytical model was used to calculate the stiffness and stress in each layer. The adventitia was calculated to be up to 10 times as stiff as the media and experienced up to 8 times the stress, depending on lumen diameter. This work reveals that pressure-induced reorganization of fibrous proteins gives rise to very high local strain fields and highlights the unique mechanical roles of both fibrous networks. It thereby provides a basis for understanding the micromechanical significance of structural changes that occur with age and disease.

This work aimed to establish the lineage of cells similar to the interstitial cells of Cajal (ICC), the arterial ICC-like (AIL) cells, which have recently been described in resistance arteries, and to study their location in the artery wall. Segments of guinea-pig mesenteric arteries and single AIL cells freshly isolated from them were used. Confocal imaging of immunostained cells or segments and electron microscopy of artery segments were used to test for the presence and cellular localization of selected markers, and to localize AIL cells in intact artery segments. AIL cells were negative for PGP9.5, a neural marker, and for von Willebrand factor (vWF), an endothelial cell marker. They were positive for smooth muscle α-actin and smooth muscle myosin heavy chain (SM-MHC), but expressed only a small amount of smoothelin, a marker of contractile smooth muscle cells (SMC), and of myosin light chain kinase (MLCK), a critical enzyme in the regulation of smooth muscle contraction. Cell isolation in the presence of latrunculin B, an actin polymerization inhibitor, did not cause the disappearance of AIL cells from cell suspension. The fluorescence of basal lamina protein collagen IV was comparable between the AIL cells and the vascular SMCs and the fluorescence of laminin was higher in AIL cells compared to vascular SMCs. Moreover, cells with thin processes were found in the tunica media of small resistance arteries using transmis-sion electron microscopy. The results suggest that AIL cells are immature or phenotypically modulated vascular SMCs constitutively present in resistance arteries.

Objectives Our goal was to investigate whether the association between established cardiovascular risk factors and arterial reactivity differs between the lower and upper extremities. Background Resistance artery reactivity in the arm is associated with cardiovascular risk factors, coronary disease, and events. However, the relationship of lower versus upper extremity vasoreactivity to increasing cardiovascular risk factors has not been determined. Methods We studied 82 subjects in 3 groups: 33 young healthy (YH) (21 to 41 years), 30 older healthy (OH) (>50 years), and 19 older type 2 diabetic subjects (OD). We directly measured systolic shear rate, flow, and radius in brachial and femoral arteries at rest and during post-occlusion hyperemia using magnetic resonance imaging. Results Brachial and femoral systolic shear rate, flow, and radius were similar among the groups at rest. Brachial hyperemic shear rate and hyperemic flow normalized as a function of baseline radius were not statistically different when YH were compared with OH and OH with OD. In contrast, femoral hyperemic shear rate and hyperemic flow normalized to baseline radius were lower in OH than YH (680 ± 236 s−1 vs. 843 ± 157 s−1, p = 0.001, and 0.84 ± 0.25 mm1.27/s vs. 1.01 ± 0.16 mm1.27/s, p = 0.001) and lower in OD than OH (549 ± 183 s−1, p = 0.02, and 0.74 ± 0.19 mm1.27/s, p = 0.046). Conclusions Persons with increasing cardiovascular risk factor burden had progressively reduced arterial reactivity in lower but not upper extremities. This may help to explain why atherosclerosis usually develops more severely in legs than in arms, and suggests that legs may be more sensitive than arms for assessing early global atherosclerotic risk.

Resistance artery narrowing and stiffening are key elements in the pathogenesis of essential hypertension, but their origin is not completely understood. In mesenteric resistance arteries (MRA) from spontaneously hypertensive rats (SHR), we have shown that inward remodeling is associated with abnormal elastic fiber organization, leading to smaller fenestrae in the internal elastic lamina. Our current aim is to determine whether this alteration is an early event that precedes vessel narrowing, or if elastic fiber reorganization in SHR arteries occurs because of the remodeling process itself. Using MRA from 10-day-old, 30-day-old, and 6-mo-old SHR and normotensive Wistar Kyoto rats, we investigated the time course of the development of structural and mechanical alterations (pressure myography), elastic fiber organization (confocal microscopy), and amount of elastin (radioimmunoassay for desmosine) and collagen (picrosirius red). SHR MRA had an impairment of fenestrae enlargement during the first month of life. In 30-day-old SHR, smaller fenestrae and more packed elastic fibers in the internal elastic lamina were paralleled by increased wall stiffness. Collagen and elastin levels were unaltered at this age. MRA from 6-mo-old SHR also had smaller fenestrae and a denser network of adventitial elastic fibers, accompanied by increased collagen content and vessel narrowing. At this age, elastase digestion was less effective in SHR MRA, suggesting a lower susceptibility of elastic fibers to enzymatic degradation. These data suggest that abnormal elastic fiber deposition in SHR increases resistance artery stiffness at an early age, which might participate in vessel narrowing later in life.

Prolonged vasoconstrictor-stimulated phospholipase C activity can induce arterial constriction, hypertension, and smooth muscle hypertrophy/hyperplasia. Arrestin proteins are recruited by agonist-occupied G protein-coupled receptors to terminate signaling and counteract changes in vascular tone. Here we determine whether the development of hypertension affects arrestin expression in resistance arteries and how such changes alter arterial contractile signaling and function. Arrestin2/3 expression was increased in mesenteric arteries of 12-wk-old spontaneously hypertensive rats (SHR) compared with normotensive Wistar-Kyoto (WKY) controls, while no differences in arrestin expression were observed between 6-wk-old SHR and WKY animals. In mesenteric artery myography experiments, high extracellular K(+)-stimulated contractions were increased in both 6- and 12-wk-old SHR animals. Concentration-response experiments for uridine 5'-triphosphate (UTP) acting through P2Y receptors displayed a leftward shift in 12-wk, but not 6-wk-old animals. Desensitization of UTP-stimulated vessel contractions was increased in 12-wk-old (but not 6-wk-old) SHR animals. Dual IP3/Ca(2+) imaging in mesenteric arterial cells showed that desensitization of UTP and endothelin-1 (ET1) responses was enhanced in 12-wk-old (but not 6-wk-old) SHR compared with WKY rats. siRNA-mediated depletion of arrestin2 for UTP and arrestin3 for ET1, reversed the desensitization of PLC signaling. In conclusion, arrestin2 and 3 expression is elevated in resistance arteries during the emergence of the early hypertensive phenotype, which underlies an enhanced ability to desensitize vasoconstrictor signaling and vessel contraction. Such regulatory changes may act to compensate for increased vasoconstrictor-induced vessel contraction.

Although it is well established that exercise training conditions the vasculature (Joyner and Green, 2009), the status of arterial function in long-term trained subjects (i.e., athletes, ATH) has been recently disputed (Green, 2013; Montero et al., 2013). The controversy arose as to whether vasodilator function was enhanced in ATH compared with untrained healthy peers (Green et al., 2013). This contention was justified by the conflicting report of decreased (Green et al., 2011; Phillips et al., 2011) and normal (Franzoni et al., 2005b; Moe et al., 2005; Naylor et al., 2006; Ballard et al., 2008; Rognmo et al., 2008; Nualnim et al., 2011; Phillips et al., 2011; Rowley et al., 2012; Agrotou et al., 2013; Green et al., 2013) but also increased (Jensen-Urstad et al., 1999; Rywik et al., 1999; Rinder et al., 2000; Franzoni et al., 2005b; Kasikcioglu et al., 2005; Rickenlund et al., 2005; Tanriverdi et al., 2005; Galetta et al., 2006; Hagmar et al., 2006; Walther et al., 2008; Florescu et al., 2010; Nualnim et al., 2011; Welsch et al., 2013) flow-mediated dilation (FMD), a common index of conduit artery dilator function, in ATH vs. age-matched controls. Likewise, the evidence on resistance artery dilator function was apparently heterogeneous (Green et al., 2012). Presumably, differences in methodology, study population and the small sample size of previous reports, among others, may have contributed to cloud the status of arterial function in ATH, leading to wide speculation (Green, 2013; Montero et al., 2013). What follows is a brief viewpoint on the state-of-the-art including comprehensive meta-analytic data spanning through macro- and microvascular dilator function in primarily endurance-trained ATH, as well as an insight in to next challenges to the field.

The effect of maturation on collateral development of resistance arteries was investigated. Three to four sequential mesenteric arteries were ligated to create collateral pathways in anesthetized young (approximately 200 g) and mature (approximately 600 g) rats. Blood flow was similarly elevated in collaterals of young and mature animals. In vivo inner arterial diameter was increased only within young collaterals (33 +/- 7%, P0.001). Increases in number of intimal nuclei (57 +/- 10% vs. 52 +/- 14%) and cross-sectional medial area (33 +/- 13% vs. 38 +/- 5%) were similar between young and mature collaterals. Relative to the same animal controls, collateral endothelial nitric oxide synthase mRNA was increased as much in mature as in young rats. Proteomic analysis revealed significant differences in protein expression with maturation between control arteries as well as flow-loaded collateral vessels. The results indicate that, whereas intimal and medial remodeling events were similar in collaterals of young and mature rats, luminal expansion occurred only in young rats. Alteration in arterial protein expression with maturation and altered responses to stimuli for collateral development may contribute to this impairment.

Background: Chronic kidney disease (CKD) is associated with cardiovascular (CV) complications. However, interventional trials targeting classical CV risks factors have been often unsuccessful in advanced stage CKD, which emphasizes the need to better understand CKD-associated vascular disorders. Resistance arteries are a key determinant of blood pressure (BP) and their changes in different CV conditions contribute to target organ damage. The aim of the present study was to characterize resistance artery remodeling and function in CKD patients, compared to vessels from hypertensive (HTN) subjects. Method: Twenty-two stage 4 CKD patients (aged 63.6±3.1 years) and 16 HTN subjects (45.6±16.1 years) were included in the present study. They all underwent a subcutaneous biopsy under local anaesthesia. Small artery remodeling and function were studied on a pressurized myograph, and subcutaneous fat CD3 infiltration and media fibronectin expression by immunostaining. Vascular smooth muscle cells (VSMCs) were counted after hematoxilin-eosin staining. Results: CKD systolic BP was similar to HTN (133±18 vs. 143±10 mmHg, respectively). Vasodilatory responses to acetylcholine were lower in CKD compared to HTN (maximal relaxation (%), 74.3±3.4 vs. 87.5±2.7, P Conclusion: Despite higher levels of BP, resistance arteries isolated from CKD patients exhibited no vascular remodeling and lower arterial stiffness compared with HTN patients. These results are in line with the maladaptive hypotrophic remodeling observed in large vessels in CKD, suggesting a generalized vascular defect in mechanotransduction in CKD.

Fasted adipose tissue blood flow (ATBF) supplies energy via transport of stored free fatty acids, whereas after feeding ATBF increases to reduce circulating free fatty acids. Although high fat diet...

Background Recent studies have raised concern about the safety of erythropoiesis‐stimulating agents because of evidence of increased risk of hypertension and cardiovascular morbidity and mortality in chronic kidney disease (CKD) patients. In the present study, we investigated the effects of recombinant human erythropoietin (EPO) on endothelial function of gluteal subcutaneous resistance arteries isolated from 17 stage 4 patients (estimated glomerular filtration rate 21.9±7.4 mL/min per 1.73 m2) aged 63±13 years. Methods and Results Arteries were mounted on a pressurized myograph. EPO impaired endothelium‐dependent relaxation in a concentration‐dependent manner. The maximal response to acetylcholine with EPO at 1, 10, and 20 IU/mL was reduced by 12%, 34%, and 43%, respectively, compared with the absence of EPO (P

BACKGROUND: Endothelin-1 (ET1) is a potent vasoconstrictor peptide with pro-mitogenic and pro-inflammatory properties and is therefore of interest in the development of endothelial dysfunction, endothelium-dependent flow-related remodeling, and hypertension-related remodeling. ET1 can be formed through cleavage of big ET1 by endothelin-converting enzyme (ECE) and neutral endopeptidase (NEP).METHOD: We investigated whether the dual NEP/ECE inhibitor SOL1 improves resistance artery function and structure in 12 weeks old spontaneously hypertensive rats (SHRs) and whether arterial structural responses to decreased (-90%) or increased (+100%) blood flow are impaired in young SHRs. To this end two groups of SHRs received chronic 4-week treatment at two different time points (4-8 and 8-12 weeks) prior to the experiment. We compared in-vitro effects of cyclo-oxygenase inhibition (1 μmol/l indomethacine), nitric oxide synthase inhibition (100 μmol/l N(ω)-L-nitro arginine methyl ester), and stimulation of the endothelium by 0.001-10 μmol/l acetylcholine (ACh) in isolated third-order mesenteric arteries of SHRs and aged-matched Wistar-Kyoto (WKY) rats.RESULTS: SOL1 had no effect on blood pressure in SHRs or WKY rats. ACh caused biphasic effects in mesenteric arteries of SHRs. The contractile component (endothelium-derived contractile factor) was absent in WKY and abolished by acute indomethacin administration or chronic SOL1 treatment. Endothelium-derived nitric oxide-type responses did not differ in both strains and were not influenced by SOL1 treatment. Endothelium-derived hyperpolarizing factor-type responses were severely impaired in SHRs as compared to WKY rats and were normalized by chronic SOL1 treatment. In first-order mesenteric arteries, outward flow-induced remodeling was impaired in SHRs. Chronic SOL1 treatment did not restore this response.CONCLUSION: Thus chronic SOL1 treatment during the development of hypertension in SHRs has no effect on blood pressure but improves several aspects of endothelium-dependent vasomotor responses but not arterial remodeling.

The purpose of this study was to determine whether the increased sensitivity of uterine resistance arteries from late pregnant (LP) rats to alpha-adrenergic stimulation is due to an alteration in the fundamental relationship between cytosolic calcium (Ca2+) and arterial lumen diameter. Uterine arcuate arteries were permeabilized with Staphylococcus aureus alpha-toxin under optimal conditions and constricted to varying degrees with discrete Ca2+ concentrations at a distending pressure of 50 mmHg. Arterial segments from nonpregnant (NP) and LP rats exhibited similar Ca2+/lumen diameter characteristics. Ca2+ (0.1 microM) produced appreciable constriction, and lumen diameter decreased steeply between 0.175 and 0.25 microM Ca2+; maximal responses were attained with 0.5 microM Ca2+. Activation of guanine nucleotide binding proteins (G proteins) with guanosine 5'-triphosphate (GTP; 1-100 microM), as reportedly occurs during alpha-adrenergic stimulation, potentiated the Ca(2+)-induced constriction by 121 and 79% in arteries from LP and NP rats, respectively. No significant differences between the two animal groups were noted. Guanosine 5'-O-(gamma-thiotriphosphate) (GTP gamma S; 0.1-10 microM), a nonhydrolyzable analogue of GTP, effected a larger potentiating effect over that maximal response caused by GTP in arteries from NP rats. Ca(2+)- and Ca2+/GTP-induced constrictions were more potently reversed by guanosine 5'-O-(beta-thiodiphosphate) (GDP beta S)., a competitive inhibitor of GTP, in arteries from NP rats. These data suggest that pregnancy-induced increases in sensitivity to alpha-adrenergic stimulation may be related to altered G protein cycling rates, such that G proteins in smooth muscle cells in arcuate arteries from NP rats are more susceptible to deactivation. Alternatively, consistent with the model of G protein-mediated inhibition of myosin light chain phosphatase, myosin light chain phosphatase activity may be enhanced in uterine vascular smooth muscle from NP rats relative to that from LP rats.

We have investigated the effect of the novel hypotensive agent, flosequinan, on human small artery constrictor function. Concentration-dependent tension development to both noradrenaline and K+ was reduced in the presence of flosequinan. Arteries pre-contracted with noradrenaline demonstrated a greater concentration-dependent relaxation to flosequinan than did those pre-contracted with K+. Flosequinan depressed the sensitivity to extracellular Ca2+ of arteries pre-contracted with noradrenaline, but this effect was less marked in arteries pre-contracted with K+. These data support previous studies which suggest that flosequinan may affect receptor-mediated contraction by reducing Ca2+ sensitivity.

Aims The lipid and protein kinase phosphoinositide 3-kinase γ (PI3Kγ) is abundantly expressed in inflammatory cells and in the cardiovascular tissue. In recent years, its role in inflammation and in cardiac function and remodelling has been unravelled, highlighting the beneficial effects of its pharmacological inhibition. Furthermore, a role for PI3Kγ in the regulation of vascular tone has been emphasized. However, the impact of this signalling in the control of blood pressure is still poorly understood. Our study investigated the effect of a selective inhibition of PI3Kγ, obtained by using two independent small molecules, on blood pressure. Moreover, we dissected the molecular mechanisms involved in control of contraction of resistance arteries by PI3Kγ. Methods and results We showed that inhibition of PI3Kγ reduced blood pressure in normotensive and hypertensive mice in a concentration-dependent fashion. This effect was dependent on enhanced vasodilatation, documented in vivo by decreased peripheral vascular resistance, and ex vivo by vasorelaxing effects on isolated resistance vessels. The vasorelaxation induced by PI3Kγ inhibition relied on blunted pressure-induced Akt phosphorylation and a myogenic contractile response. Molecular insights revealed that PI3Kγ inhibition affected smooth muscle L-type calcium channel current density and calcium influx by impairing plasma membrane translocation of the α1C L-type calcium channel subunit responsible for channel open-state probability. Conclusion Overall our findings suggest that PI3Kγ inhibition could be a novel tool to modulate calcium influx in vascular smooth muscle cells, thus relaxing resistance arteries and lowering blood pressure.

Statins can have beneficial cholesterol-independent effects on vascular contractility, which may involve increases in the bioavailability of NO (nitric oxide) as a result of phosphorylation of eNOS (endothelial NO synthase). Although this has been attributed to phosphorylation of Akt (also known as protein kinase B), studies in cultured cells have shown that statins can phosphorylate AMPK (AMP-activated protein kinase); it is unknown whether this has functional effects in intact arteries. Thus we investigated the acute effects of simvastatin on resistance arterial contractile function, evaluating the involvement of NO, Akt and AMPK. Isolated rat mesenteric resistance arteries were mounted on a wire myograph. The effects of incubation (1 and 2 h) with simvastatin (0.1 or 1 μM) on contractile responses were examined in the presence and absence of L-NNA (N-nitro-L-arginine; 10 μM) or mevalonate (1 mM). Effects on eNOS, phospho-eNOS (Ser1177), and total and phospho-Akt and -AMPK protein expression were investigated using Western blotting. The effect of AMPK inhibition (compound C, 10 μM) on eNOS phosphorylation and contractile responses were also studied. Simvastatin (1 μM, 2 h) significantly reduced constriction to U46619 and phenylephrine and enhanced dilations to ACh (acetylcholine) in depolarized, but not in U46619-pre-constricted arteries. These effects were completely and partially prevented by L-NNA and mevalonate respectively. Simvastatin increased eNOS and AMPKα phosphorylation, but had no effect on Akt protein expression and phosphorylation after 2 h incubation. Compound C prevented the effects of simvastatin on eNOS phosphorylation and contractility. Thus simvastain can acutely modulate resistance arterial contractile function via mechanisms that involve the AMPK/phospho-eNOS (Ser1177)/NO-dependent pathway.

Background/Aims: To identify the relationship between systemic and local hemodynamics, as well as segmental biomechanical properties in a musculocutaneous resistance artery during angiotensin-II hypertension and its recovery. Methods: Rats were infused with angiotensin-II using implanted osmotic minipumps (ALZET 2ML4, 150 ng/kg/min) for 4 weeks. Measurements were made either immediately following infusion or after an additional 4-week recovery period. Parallel controls were created. Segmental geometry and blood flow were determined in vivo on microsurgically exposed segments of the saphenous arterial branch (350 µm). Pressure-radius plots of excised cylindrical segments were recorded by pressure arteriography. Results: Eutrophic hypertensive wall remodeling developed, with reduced passive radius, increased wall thickness, elevated low-stress elastic modulus, reduced norepinephrine contraction, and reduced endothelium-mediated dilation. Relaxed wall geometry fully healed in 4 weeks of recovery, but an increased contractility and a reduced in vivo lumen persisted. Regional hemodynamic resistance correlated positively with systemic arterial pressure and wall thickness in vivo, and negatively with in vivo lumen size throughout these studies. Conclusion: A partial recovery of the biomechanical parameters was found. Healing of eutrophic hypertensive remodeling of the resistance artery wall is a complex biomechanical process, not a simple reversal of the original pathological sequel.

The responses of rabbit resistance arteries to pressure and flow have been examined using two in vitro techniques – when mounted isometrically in a myograph and when perfused using a video system that automatically registers diameter. The latter approach allows pressure and flow to be independently controlled. Under such circumstances three responses were studied; myogenic contraction and flow-dependent constriction and dilation. All responses occurred after endothelium removal and were unaffected by indomethacin (10–6M). The pressure and flow effects can be elicited separately and have different ionic bases. The effective stimulus for the myogenic response is stretch and that for flow is presumably shear stress. The mechano-transducers for these effects are different and are located either in the vascular smooth muscle cells or their surrounding extracellular matrix.

It has been previously demonstrated that the morning rise (MoR) of blood pressure (BP) may predict major cardiovascular events in hypertensive patients. Structural alterations of small resistance arteries, as evaluated by the tunica media to internal lumen ratio (M/L) of subcutaneous small resistance arteries, may also predict cardiovascular events. Because an increased M/L may amplify the effect of hypertensive stimuli, the present study aimed to evaluate the possible relationships between MoR and M/L in a population of hypertensive patients.Sixty-four patients with essential hypertension were included in the present study. All patients were submitted to a biopsy of subcutaneous fat. Small resistance arteries were dissected and mounted on an isometric myograph, and the M/L was measured. In addition, MoR was calculated from ambulatory blood pressure monitoring (ABPM) according to four previously published different methods (MoR1 to MoR4).A statistically significant correlation was observed between M/L and MoR1 (r = 0.52, P0.001), MoR2 (r = 0.32, P0.01), MoR3 (r = 0.25, P0.05) and MoR4 (r = 0.27, P0.05), as well as between internal diameter of subcutaneous small arteries and MoR1 (r = -0.45, P0.001) and MoR2 (r = -0.28, P0.05).Our results indicate that subcutaneous small artery structure is related to MoR, possibly because an altered vascular structure may amplify BP changes or, vice versa, because a greater MoR may further damage peripheral vasculature.