α1-Adrenergic responsiveness in human skeletal muscle feed arteries: the impact of reducing extracellular pH

The Effects of Acidosis on eNOS in the Systemic Vasculature: A Focus on Early Postnatal Ontogenesis

The activity of many vasomotor signaling pathways strongly depends on extracellular/intracellular pH. Nitric oxide (NO) is one of the most important vasodilators produced by the endothelium. In this review, we present evidence that in most vascular beds of mature mammalian organisms metabolic or respiratory acidosis increases functional endothelial NO-synthase (eNOS) activity, despite the observation that direct effects of low pH on eNOS enzymatic activity are inhibitory. This can be explained by the fact that acidosis increases the activity of signaling pathways that positively regulate eNOS activity. The role of NO in the regulation of vascular tone is greater in early postnatal ontogenesis compared to adulthood. Importantly, in early postnatal ontogenesis acidosis also augments functional eNOS activity and its contribution to the regulation of arterial contractility. Therefore, the effect of acidosis on total peripheral resistance in neonates may be stronger than in adults and can be one of the reasons for an undesirable decrease in blood pressure during neonatal asphyxia. The latter, however, should be proven in future studies.

Characterization of Systemic and Regional Hemodynamics and Vascular Dysfunction in Mice with Fecal Induced Peritonitis

Sepsis is associated with circulatory dysfunction contributing to disturbed blood flow and organ injury. Decreased organ perfusion in sepsis is attributed, in part, to the loss of vasoregulatory mechanisms. Identifying which vascular beds are most susceptible to dysfunction is important for monitoring the recovery of organ function and guiding interventions. This study aimed to investigate the development of vascular dysfunction as sepsis progressed to septic shock. Anesthetized C57Bl/6 mice were instrumented with a fiberoptic pressure sensor in the carotid artery for blood pressure measurements. In subgroups of mice, regional blood flow measurements were taken by positioning a perivascular flow probe around either the left carotid, left renal, or superior mesenteric arteries. Hemodynamic parameters and their responsiveness to bolus doses of vasoactive drugs were recorded prior to and continuously after injection of fecal slurry (1.3 mg/g body weight) for 4 h. Fecal slurry-induced peritonitis reduced mean arterial pressure (62.7 ± 2.4 mmHg vs. 37.5 ± 3.2 mmHg in vehicle and septic mice, respectively), impaired cardiac function, and eventually reduced organ blood flow (71.9%, 66.8%, and 65.1% in the superior mesenteric, renal, and carotid arteries, respectively). The mesenteric vasculature exhibited dysregulation before the renal and carotid arteries, and this underlying dysfunction preceded the blood pressure decline and impaired organ blood flow.

Extracorporeal cardiopulmonary resuscitation for cardiac arrest

PURPOSE OF REVIEW

Extracorporeal cardiopulmonary resuscitation (ECPR) is a contemporary resuscitation approach that employs veno-arterial extracorporeal membrane oxygenation (VA-ECMO). This approach is increasingly used worldwide to mitigate the widespread hemodynamic and multiorgan dysfunction that accompanies cardiac arrest.

RECENT FINDINGS

In this review, the physiology of VA-ECMO and ECPR, the role of ECPR in contemporary resuscitation care, the complications associated with ECPR and VA-ECMO usage, and intensive care considerations for this population are discussed.

SUMMARY

ECPR offers a promising mechanism to mitigate multiorgan injury and allow time for the institution of supportive interventions required to effectively treat cardiac arrest. More prospective data in the context of extensive prehospital and hospital collaboration is needed to promote its successful use.

Greater α1-adrenergic-mediated vasoconstriction in contracting skeletal muscle of patients with type 2 diabetes

Findings presented in this article are the first to show patients with type 2 diabetes mellitus have blunted hyperemic and vasodilatory responses to dynamic handgrip exercise. Moreover, we illustrate greater α1-adrenergic-mediated vasoconstriction may contribute to our initial observations. Collectively, these data suggest patients with type 2 diabetes may have impaired functional sympatholysis, which can contribute to their reduced exercise capacity.

Vasodilatory and vascular mitochondrial respiratory function with advancing age: evidence of a free radically mediated link in the human vasculature

Recognizing the age-related decline in skeletal muscle feed artery (SMFA) vasodilatory function, this study examined the link between vasodilatory and mitochondrial respiratory function in the human vasculature. Twenty-four SMFAs were harvested from young (35 ± 6 yr, n = 9) and old (71 ± 9 yr, n = 15) subjects. Vasodilation in SMFAs was assessed, by pressure myography, in response to flow-induced shear stress, acetylcholine (ACh), and sodium nitroprusside (SNP) while mitochondrial respiration was measured, by respirometry, in permeabilized SMFAs. Endothelium-dependent vasodilation was significantly attenuated in the old, induced by both flow (young: 92 ± 3, old: 45 ± 4%) and ACh (young: 92 ± 3, old: 54 ± 5%), with no significant difference in endothelium-independent vasodilation. Complex I and I + II state 3 respiration was significantly lower in the old (CI young: 10.1 ± 0.8, old: 7.0 ± 0.4 pmol·s^-1·mg^-1; CI + II young: 12.3 ± 0.6, old: 7.6 ± 0.4 pmol·s^-1·mg^-1). The respiratory control ratio (RCR) was also significantly attenuated in the old (young: 2.2 ± 0.1, old: 1.1 ± 0.1). Furthermore, state 3 (CI + II) and 4 respiration, as well as RCR, were significantly correlated (r = 0.49-0.86) with endothelium-dependent, but not endothelium-independent, function. Finally, the direct intervention with mitochondrial-targeted antioxidant (MitoQ) significantly improved endothelium-dependent vasodilation in the old but not in the young. Thus, the age-related decline in vasodilatory function is linked to attenuated vascular mitochondrial respiratory function, likely by augmented free radicals.NEW & NOTEWORTHY In human skeletal muscle feed arteries, the well-recognized age-related fall in endothelium-dependent vasodilatory function is strongly linked to a concomitant fall in vascular mitochondrial respiratory function. The direct intervention with the mitochondrial-targeted antioxidant restored vasodilatory function in the old but not in the young, supporting the concept that exacerbated mitochondrial-derived free radical production is linked to age-related vasodilatory dysfunction. Age-related vasodilatory dysfunction in humans is linked to attenuated vascular mitochondrial respiratory function, likely a consequence of augmented free radical production.

Improved Survival With Extracorporeal Cardiopulmonary Resuscitation Despite Progressive Metabolic Derangement Associated With Prolonged Resuscitation

The likelihood of neurologically favorable survival declines with prolonged resuscitation. However, the ability of extracorporeal cardiopulmonary resuscitation (ECPR) to modulate this decline is unknown. Our aim was to examine the effects of resuscitation duration on survival and metabolic profile in patients who undergo ECPR for refractory ventricular fibrillation/ventricular tachycardia out-of-hospital cardiac arrest.

Vasoreactivity of the Murine External Jugular Vein and Carotid Artery

INTRODUCTION

Impaired venous reactivity has potential to contribute to clinically significant pathologies such as arteriovenous fistula (AVF) maturation failure. Vascular segments commonly used in murine preclinical models of AVF include the carotid artery and external jugular vein. Detailed descriptions of isometric procedures to evaluate function of murine external jugular vein ex vivo have not been previously published.

OBJECTIVE

To establish isometric procedures to measure naive murine external jugular vein reactivity ex vivo.

METHODS

Vasomotor responses of external jugular veins and ipsilateral common carotid arteries from C57BL/6 mice were evaluated using isometric tension procedures.

RESULTS

External jugular veins developed tension (p < 0.05) to potassium chloride and U-46619, but not to phenylephrine, whereas common carotid arteries responded to all 3 agents (p < 0.05). While maximal responses to acetylcholine (ACh) were similar between the venous and arterial segments, the dose required to achieve this value was lower (p < 0.05) in the artery versus vein. Nitric oxide synthase inhibition attenuated (p < 0.05) but did not abolish ACh-evoked vasorelaxation in both vascular segments, whereas cyclooxygenase blockade had no effect. Endothelium-independent vasorelaxation to sodium nitroprusside was similar in the artery and vein.

CONCLUSION

Vasorelaxation and vasocontraction can be reliably assessed in the external jugular vein in C57BL/6 mice using isometric procedures.

Effect of Continuous-Flow Left Ventricular Assist Device Support on Coronary Artery Endothelial Function in Ischemic and Nonischemic Cardiomyopathy

Background:

The coronary vasculature encounters a reduction in pulsatility after implementing durable continuous-flow left ventricular assist device (CF-LVAD) circulatory support. Evidence exists that appropriate pulsatility is required to maintain endothelial cell homeostasis. We hypothesized that coronary artery endothelial function would be impaired after CF-LVAD intervention.

Methods and Results:

Coronary arteries from patients with end-stage heart failure caused by ischemic cardiomyopathy (ICM; n=16) or non-ICM (n=22) cardiomyopathy were isolated from the left ventricular apical core, which was removed for the CF-LVAD implantation. In 11 of these patients, paired coronary arteries were obtained from an adjacent region of myocardium after the CF-LVAD intervention (n=6 ICM, 5 non-ICM). Vascular function was assessed ex vivo using isometric tension procedures in these patients and in 7 nonfailing donor controls. Maximal endothelium-dependent vasorelaxation to BK (bradykinin; 10 − 6 –10 − 10 M) was blunted ( P <0.05) in arteries from patients with ICM compared with non-ICM and donor controls, whereas responses to sodium nitroprusside (10 −4 –10 −9 M) were similar among the groups. Contrary to our hypothesis, vasorelaxation responses to BK and sodium nitroprusside were similar before and 219±37 days after CF-LVAD support. Of these patients, an exploratory subgroup analysis revealed that BK-induced coronary artery vasorelaxation was greater ( P <0.05) after (87±6%) versus before (54±14%) CF-LVAD intervention in ICM patients, whereas sodium nitroprusside–evoked responses were similar.

Conclusions:

Coronary artery endothelial function is not impaired by durable CF-LVAD support and in ICM patients appears to be improved. Investigating coronary endothelial function using in vivo approaches in a larger patient population is warranted.

Vascular mitochondrial respiratory function: the impact of advancing age

Little is known about vascular mitochondrial respiratory function and the impact of age. Therefore, skeletal muscle feed arteries were harvested from young (33 ± 7 yr, n = 10), middle-aged (54 ± 5 yr, n = 10), and old (70 ± 7 yr, n = 10) subjects, and mitochondrial respiration as well as citrate synthase (CS) activity were assessed. Complex I (CI) and complex I + II (CI+II) state 3 respiration were greater in young (CI: 10.4 ± 0.8 pmol·s^-1·mg^-1 and CI+II: 12.4 ± 0.8 pmol·s^-1·mg^-1, P < 0.05) than middle-aged (CI: 7 ± 0.6 pmol·s^-1·mg^-1 and CI+II: 8.3 ± 0.5 pmol·s^-1·mg^-1) and old (CI: 7.2 ± 0.4 pmol·s^-1·mg^-1 and CI+II: 7.6 ± 0.5 pmol·s^-1·mg^-1) subjects and, as in the case of complex II (CII) state 3 respiration, were inversely correlated with age [ r = -0.56 (CI), r = -0.7 (CI+II), and r = 0.4 (CII), P < 0.05]. In contrast, state 4 respiration and mitochondria-specific superoxide levels were not different across groups. The respiratory control ratio was greater in young (2.2 ± 0.2, P < 0.05) than middle-aged and old (1.4 ± 0.1 and 1.1 ± 0.1, respectively) subjects and inversely correlated with age ( r = -0.71, P < 0.05). As CS activity was inversely correlated with age ( r = -0.54, P < 0.05), when normalized for mitochondrial content, the age-related differences and relationships with state 3 respiration were ablated. In contrast, mitochondrion-specific state 4 respiration was now lower in young (15 ± 1.4 pmol·s^-1·mg^-1·U CS^-1, P < 0.05) than middle-aged and old (23.4 ± 3.6 and 27.9 ± 3.4 pmol·s^-1·mg^-1·U CS^-1, respectively) subjects and correlated with age ( r = 0.46, P < 0.05). Similarly, superoxide/CS levels were lower in young (0.07 ± 0.01) than old (0.19 ± 0.41) subjects and correlated with age ( r = 0.44, P < 0.05). Therefore, with aging, vascular mitochondrial respiratory function declines, predominantly as a consequence of falling mitochondrial content. However, per mitochondrion, aging likely results in greater mitochondrion-derived oxidative stress, which may contribute to age-related vascular dysfunction. NEW & NOTEWORTHY This study determined, for the first time, that vascular mitochondrial oxidative respiratory capacity, oxidative coupling efficiency, and mitochondrial content fell progressively with advancing age. In terms of single mitochondrion-specific respiration, the age-related differences were completely ablated and the likelihood of free radical production increased progressively with advancing age. This study reveals that vascular mitochondrial respiratory capacity declines with advancing age, as a consequence of falling mitochondrial content, as does oxidative coupling efficiency.

Assessment of Human Adipose Tissue Microvascular Function Using Videomicroscopy

While obesity is closely linked to the development of metabolic and cardiovascular disease, little is known about mechanisms that govern these processes. It is hypothesized that pro-atherogenic mediators released from fat tissues particularly in association with central/visceral adiposity may promote pathogenic vascular changes locally and systemically, and the notion that cardiovascular disease may be the consequence of adipose tissue dysfunction continues to evolve. Here, we describe a unique method of videomicroscopy that involves analysis of vasodilator and vasoconstrictor responses of intact small human arterioles removed from the adipose depot of living human subjects. Videomicroscopy is used to examine functional properties of isolated microvessels in response to pharmacological or physiological stimuli using a pressured system that mimics in vivo conditions. The technique is a useful approach to gain understanding of the pathophysiology and molecular mechanisms that contribute to vascular dysfunction locally within the adipose tissue milieu. Moreover, abnormalities in the adipose tissue microvasculature have also been linked with systemic diseases. We applied this technique to examine depot-specific vascular responses in obese subjects. We assessed endothelium-dependent vasodilation to both increased flow and acetylcholine in adipose arterioles (50 - 350 µm internal diameter, 2 - 3 mm in length) isolated from two different adipose depots during bariatric surgery from the same individual. We demonstrated that arterioles from visceral fat exhibit impaired endothelium-dependent vasodilation compared to vessels isolated from the subcutaneous depot. The findings suggest that the visceral microenvironment is associated with vascular endothelial dysfunction which may be relevant to clinical observation linking increased visceral adiposity to systemic disease mechanisms. The videomicroscopy technique can be used to examine vascular phenotypes from different fat depots as well as compare findings across individuals with different degrees of obesity and metabolic dysfunction. The method can also be used to examine vascular responses longitudinally in response to clinical interventions.

TRPV1 channels in human skeletal muscle feed arteries: implications for vascular function

NEW FINDINGS

What is the central question of this study? We sought to determine whether human skeletal muscle feed arteries (SFMAs) express TRPV₁ channels and what role they play in modulating vascular function. What is the main finding and its importance? Human SMFAs do express functional TRPV₁ channels that modulate vascular function, specifically opposing α-adrenergic receptor-mediated vasocontraction and potentiating vasorelaxation, in an endothelium-dependent manner, as evidenced by the α₁ -receptor-mediated responses. Thus, the vasodilatory role of TRPV₁ channels, and their ligand capsaicin, could be a potential therapeutic target for improving vascular function. Additionally, given the 'sympatholytic' effect of TRPV₁ activation and known endogenous activators (anandamide, reactive oxygen species, H⁺ , etc.), TRPV₁ channels might contribute to functional sympatholysis during exercise. To examine the role of the transient receptor potential vanilloid type 1 (TRPV₁ ) ion channel in the vascular function of human skeletal muscle feed arteries (SMFAs) and whether activation of this heat-sensitive receptor could be involved in modulating vascular function, SMFAs from 16 humans (63 ± 5 years old, range 41-89 years) were studied using wire myography with capsaicin (TRPV₁ agonist) and without (control). Specifically, phenylephrine (α₁ -adrenergic receptor agonist), dexmedetomidine (α₂ -adrenergic receptor agonist), ACh and sodium nitroprusside concentration-response curves were established to assess the role of TRPV₁ channels in α-receptor-mediated vasocontraction as well as endothelium-dependent and -independent vasorelaxation, respectively. Compared with control conditions, capsaicin significantly attenuated maximal vasocontraction in response to phenylephrine [control, 52 ± 8% length-tension_max (LT_max ) and capsaicin, 21 ± 5%LT_max ] and dexmedetomidine (control, 29 ± 12%LT_max and capsaicin, 2 ± 3%LT_max ), while robustly enhancing maximal vasorelaxation with ACh (control, 78 ± 8% vasorelaxation and capsaicin, 108 ± 13% vasorelaxation) and less clearly enhancing the sodium nitroprusside response. Denudation of the endothelium greatly attenuated the maximal ACh-induced vasorelaxation equally in the control and capsaicin conditions (∼17% vasorelaxation) and abolished the attenuating effect of capsaicin on the maximal phenylephrine response (denuded + capsaicin, 61 ± 20%LT_max ). Immunohistochemistry identified a relatively high density of TRPV₁ channels in the endothelium compared with the smooth muscle of the SMFAs, but because of the far greater volume of smooth muscle, total TRPV₁ protein content was not significantly attenuated by denudation. Thus, SMFAs ubiquitously express functional TRPV₁ channels, which alter vascular function, in terms of α₁ -receptors, in a predominantly endothelium-dependent manner, conceivably contributing to the functional sympatholysis and unveiling a therapeutic target.

Acidosis reduces the function and expression of α1D-adrenoceptor in superior mesenteric artery of Capra hircus

Objective:

The objective of this study was to characterize the α₁-adrenoceptor (α₁-AR) subtypes and evaluate the effect of acidosis on α₁-AR function and expression in goat superior mesenteric artery (GSMA).

Materials and Methods:

GSMA rings were mounted in a thermostatically controlled (37.0°C ± 0.5°C) organ bath containing 20 ml of modified Krebs-Henseleit solution, maintained at pH_o of 7.4, 6.8, 6.0, 5.5, 5.0, and 4.5. Noradrenaline (NA)- and phenylephrine (PE)-induced contractile response was elicited in the absence or presence of endothelium and prazosin at pH_o of 7.4, 6.0, and 5.0. The responses were recorded isometrically by an automatic organ bath connected to PowerLab and analyzed using Labchart 7.1.3 software. Expression of α_1D-AR was compared at physiological and acidic pH_o using reverse transcription-polymerase chain reaction (RT-PCR).

Results:

NA- and PE-induced contractile responses were attenuated proportionately with a decrease in extracellular pH (pH_o), i.e. 7.4 → 6.8 → 6.0 → 5.5 → 5.0 → 4.5. Endothelium denudation increased the contractile response at both normal and acidic pH_o. Prazosin (1 nM, 10 nM, and 0.1 μM) inhibited the NA- and PE-induced contractile response at pH_o 7.4 and the blocking effect of prazosin was potentiated at pH_o of 6.0 and 5.0. RT-PCR analysis for α_1D-AR in GSMA showed that the mRNA expression of α_1D-AR was decreased under acidic pH_o as compared to physiological pH_o.

Conclusion:

(i) Adrenergic receptor mediates vasoconstriction in GSMA under normal physiological pH_o, and α_1D is the possible subtype involved in this event (ii) acidosis attenuates the vasocontractile response due to reduced function and expression of α_1D-AR and also increased the release of endothelial-relaxing factors.

Experimental reduction of miR-92a mimics arterial aging

MicroRNAs (miRs) are small non-coding RNAs that are important regulators of aging and cardiovascular diseases. MiR-92a is important in developmental vascular growth and tumorigenesis and two of its putative targets, tumor necrosis factor alpha receptor 1 (TNFR1) and collagen type 1, play a role in age-related arterial dysfunction. We hypothesized that reduced miR-92a expression contributes to age-related arterial dysfunction characterized by endothelial dysfunction and increased large artery stiffness. MiR-92a is reduced 39% (RT-PCR, p<0.05) in arteries of older adults compared to young adults. Similarly, there was a 40% reduction in miR-92a in aortas of old (29months, n=13) compared to young (6months, n=11) B6D2F1 mice, an established model of vascular aging. To determine if reduced miR-92a contributes to arterial dysfunction; miR-92a was inhibited in vivo in young mice using antagomirs (I.P., 4wks). Antagomir treatment was associated with a concomitant 48% increase in TNFR1 (Western blot, p<0.05), 19% increase in type 1 collagen (immunohistochemistry, p<0.01), and a reduction in endothelial dependent dilation (max dilation: 93±1 vs. 73±5%, p<0.01) in response to acetylcholine (ACh, 10(-9) to 10(-4)M). Treatment with the nitric oxide (NO) synthase inhibitor, L-NAME (10(-4)M), revealed that impaired ACh dilation after antagomir treatment resulted from reduced NO bioavailability. Inhibition of miR-92a also increased arterial stiffness (pulse wave velocity, 309±13 vs. 484±52cm/s, p<0.05). Together, these results suggest that experimental reductions in arterial miR-92a partially mimic the arterial aging phenotype and we speculate that modulating miR-92a may provide a therapeutic strategy to improve age-related arterial dysfunction.

Age-related arterial telomere uncapping and senescence is greater in women compared with men

Telomere uncapping increases with advancing age in human arteries and this telomere uncapping is associated with increased markers of senescence, independent of mean telomere length. However, whether there are sex specific differences in arterial telomere uncapping is unknown. We found that telomere uncapping (serine 139 phosphorylated histone γ-H2A.X in telomeres) in arteries was ~2.5 fold greater in post-menopausal women (n=17, 63±2 years) compared with pre-menopausal women (n=11, 30±2 years, p=0.02), while there was only a trend towards greater telomere uncapping in older men (n=26, 66±2 years) compared with young men (n=11, 31±2, p=0.11). Senescence markers, p53 bound to the p21 gene promoter and p21 gene expression, were 3-4 fold greater in post-menopausal compared with pre-menopausal women (p=0.01-0.02), but only 1.5-2 fold greater in older compared with young men (p=0.02-0.08). Blood glucose was related to telomere uncapping in women, while systolic blood pressure, pulse pressure and serum creatinine were related to telomere uncapping in men. Mean arterial telomere length decreased similarly in women and men with age (p<0.01). Thus, the age-related increase in arterial telomere uncapping and senescence is greater in women than men, despite similar age-related reductions in mean telomere length in both sexes.

Hemodynamic consequences of severe lactic acidosis in shock states: from bench to bedside

Lactic acidosis is a very common biological issue for shock patients. Experimental data clearly demonstrate that metabolic acidosis, including lactic acidosis, participates in the reduction of cardiac contractility and in the vascular hyporesponsiveness to vasopressors through various mechanisms. However, the contributions of each mechanism responsible for these deleterious effects have not been fully determined and their respective consequences on organ failure are still poorly defined, particularly in humans. Despite some convincing experimental data, no clinical trial has established the level at which pH becomes deleterious for hemodynamics. Consequently, the essential treatment for lactic acidosis in shock patients is to correct the cause. It is unknown, however, whether symptomatic pH correction is beneficial in shock patients. The latest Surviving Sepsis Campaign guidelines recommend against the use of buffer therapy with pH ≥7.15 and issue no recommendation for pH levels <7.15. Furthermore, based on strong experimental and clinical evidence, sodium bicarbonate infusion alone is not recommended for restoring pH. Indeed, bicarbonate induces carbon dioxide generation and hypocalcemia, both cardiovascular depressant factors. This review addresses the principal hemodynamic consequences of shock-associated lactic acidosis. Despite the lack of formal evidence, this review also highlights the various adapted supportive therapy options that could be putatively added to causal treatment in attempting to reverse the hemodynamic consequences of shock-associated lactic acidosis.

Role of arterial telomere dysfunction in hypertension: relative contributions of telomere shortening and telomere uncapping

OBJECTIVE

Telomere shortening in arteries could lead to telomere uncapping and cellular senescence, which in turn could promote the development of hypertension.

METHODS AND RESULTS

To assess the novel role of arterial telomere dysfunction in hypertension, we compared mean telomere length (qPCR), telomere uncapping (serine 139 phosphorylated histone γ-H2A.X (γ-H2) localized to telomeres: ChIP), and tumor suppressor protein p53 (P53)/cyclin-dependent kinase inhibitor 1A (P21)-induced senescence (P53 bound to P21 gene promoter: ChIP) in arteries from 55 age-matched hypertensive and nonhypertensive individuals. Arterial mean telomere length was not different in hypertensive patients compared with nonhypertensive individuals (P = 0.29). Arterial telomere uncapping and P53/P21-induced senescence were two-fold greater in hypertensive patients compared with nonhypertensive individuals (P = 0.04 and P = 0.02, respectively). Arterial mean telomere length was not associated with telomere uncapping or P53/P21-induced senescence (r = -0.02, P = 0.44 and r = 0.01, P = 0.50, respectively), but telomere uncapping was a highly influential covariate for the hypertension group difference in P53/P21-induced senescence (r = 0.62, P < 0.001, η(p)(2) = 0.35). Finally, telomere uncapping was a significant predictor of hypertension status (P = 0.03), whereas mean telomere length was not (P = 0.68).

CONCLUSION

Collectively, these findings demonstrate that arterial telomere uncapping and P53/P21-induced senescence are linked to hypertension independently of mean telomere length, and telomere uncapping influences hypertension status more than mean telomere length.

α1- and α2-adrenergic responsiveness in human skeletal muscle feed arteries: the role of TRPV ion channels in heat-induced sympatholysis

The purpose of this study was to determine if heat inhibits α2-adrenergic vasocontraction, similarly to α1-adrenergic contraction, in isolated human skeletal muscle feed arteries (SMFA) and elucidate the role of the temperature-sensitive vanilloid-type transient receptor potential (TRPV) ion channels in this response. Isolated SMFA from 37 subjects were studied using wire myography. α1 [Phenylephrine (PE)]- and α2 [dexmedetomidine (DEX)]-contractions were induced at 37 and 39°C with and without TRPV family and TRPV4-specific inhibition [ruthenium red (RR) and RN-1734, respectively]. Endothelial function [acetylcholine (ACh)] and smooth muscle function [sodium nitroprusside (SNP) and potassium chloride (KCl)] were also assessed under these conditions. Heat and TRPV inhibition was further examined in endothelium-denuded arteries. Contraction data are reported as a percentage of maximal contraction elicited by 100 mM KCl (LTmax). DEX elicited a small and variable contractile response, one-fifth the magnitude of PE, which was not as clearly attenuated when heated from 37 to 39°C (12 ± 4 to 6 ± 2% LTmax; P = 0.18) as were PE-induced contractions (59 ± 5 to 24 ± 4% LTmax; P < 0.05). Both forms of TRPV inhibition restored PE-induced contraction at 39°C (P < 0.05) implicating these channels, particularly the TRPV4 channels, in the heat-induced attenuation of α1-adrenergic vasocontraction. TRPV inhibition significantly blunted ACh relaxation while denudation prevented heat-induced sympatholysis without having an additive effect when combined with TRPV inhibition. In conclusion, physiological increases in temperature elicit a sympatholysis-like inhibition of α1-adrenergic vasocontraction in human SMFA that appears to be mediated by endothelial TRPV4 ion channels.

Interactive effect of acute sympathetic activation and exercise intensity on the dynamic response characteristics of vascular conductance in the human calf muscle

PURPOSE

The effect of acute activation of the sympathetic nervous system on the dynamic response of muscle hyperaemia during exercise at different intensities is not clear.

METHODS

To explore this, six men performed 16, 5-min bouts of intermittent calf contractions at two intensities (25 and 50 % MVC) and two levels of sympathetic activation (CPT cold pressor test, CON control). Mean arterial pressure (MAP) and leg vascular conductance (LVC leg blood flow/MAP) were measured during rest and contractions (3 s intervals), and dynamic response characteristics of LVC were estimated using curve-fitting and empirical modeling.

RESULTS

MAP was ~20 % greater (P ≤ 0.05) during CPT than CON before and during initial contractions at both intensities. At 25 % MVC, CPT reduced the exercise-induced change in LVC (0.109 vs 0.125 ml 100 ml(-1 )min(-1 )mmHg(-1); P < 0.05), an effect attributed to the reduction in the amplitude of the fast growth phase (0.091 vs 0.128 1 ml 100 ml(-1 )min(-1 )mmHg(-1); P < 0.05). At 50 % MVC, CPT also blunted the fast growth phase (0.147 vs 0.189 ml 100 ml(-1 )min(-1 )mmHg(-1); P < 0.05), but the total change in LVC during exercise was unaffected because of a significant reduction in the amplitude of the rapid decay phase and tendency (P = 0.1) for a lower amplitude of the slow decay phase.

CONCLUSION

Increased sympathetic constraint of vasodilation persists during initial contractions but is overcome at the high intensity by a mechanism apparently related to hyperaemic decay.

Persistence of functional sympatholysis post-exercise in human skeletal muscle

Blunting of sympathetic vasoconstriction in exercising muscle is well-established. Whether it persists during the early post-exercise period is unknown. This study tested the hypothesis that it persists in human skeletal muscle during the first 10 min of recovery from exercise. Eight healthy young males (21.4 ± 0.8 yrs, SE) performed 7 min of forearm rhythmic isometric handgrip exercise at 15% below forearm critical force (fCF). In separate trials, a cold pressor test (CPT) of 2 min duration was used to evoke forearm sympathetic vasoconstriction in each of Rest (R), Steady State Exercise (Ex), 2-4 min Post-Exercise (PEearly), and 8-10 min Post-Exercise (PElate). A 7 min control exercise trial with no CPT was also performed. Exercising forearm brachial artery blood flow, arterial blood pressure, cardiac output (CO), heart rate (HR), forearm deep venous catecholamine concentration, and arterialized venous catecholamine concentration were obtained immediately prior to and following the CPT in each trial. CPT resulted in a significant increase in forearm venous plasma norepinephrine concentration in all trials (P = 0.007), but no change in arterialized plasma norepinephrine (P = 0.32). CPT did not change forearm venous plasma epinephrine (P = 0.596) or arterialized plasma epinephrine concentration (P = 0.15). As assessed by the %reduction in forearm vascular conductance (FVC) the CPT evoked a robust vasoconstriction at rest that was severely blunted in exercise (R = -39.9 ± 4.6% vs. Ex = 5.5 ± 7.4%, P < 0.001). This blunting of vasoconstriction persisted at PEearly (-12.3 ± 10.1%, P = 0.02) and PElate (-18.1 ± 8.2%, P = 0.03) post-exercise. In conclusion, functional sympatholysis remains evident in human skeletal muscle as much as 10 min after the end of a bout of forearm exercise. Persistence of functional sympatholysis may have important implications for blood pressure regulation in the face of a challenge to blood pressure following exercise.

Age-related telomere uncapping is associated with cellular senescence and inflammation independent of telomere shortening in human arteries

Arterial telomere dysfunction may contribute to chronic arterial inflammation by inducing cellular senescence and subsequent senescence-associated inflammation. Although telomere shortening has been associated with arterial aging in humans, age-related telomere uncapping has not been described in non-cultured human tissues and may have substantial prognostic value. In skeletal muscle feed arteries from 104 younger, middle-aged, and older adults, we assessed the potential role of age-related telomere uncapping in arterial inflammation. Telomere uncapping, measured by p-histone γ-H2A.X (ser139) localized to telomeres (chromatin immunoprecipitation; ChIP), and telomeric repeat binding factor 2 bound to telomeres (ChIP) was greater in arteries from older adults compared with those from younger adults. There was greater tumor suppressor protein p53 (P53)/cyclin-dependent kinase inhibitor 1A (P21)-induced senescence, measured by P53 bound to P21 gene promoter (ChIP), and greater expression of P21, interleukin 8, and monocyte chemotactic protein 1 mRNA (RT-PCR) in arteries from older adults compared with younger adults. Telomere uncapping was a highly influential covariate for the age-group difference in P53/P21-induced senescence. Despite progressive age-related telomere shortening in human arteries, mean telomere length was not associated with telomere uncapping or P53/P21-induced senescence. Collectively, these findings demonstrate that advancing age is associated with greater telomere uncapping in arteries, which is linked to P53/P21-induced senescence independent of telomere shortening.

Protective role of acidic pH-activated chloride channel in severe acidosis-induced contraction from the aorta of spontaneously hypertensive rats

Severe acidic pH-activated chloride channel (I_Cl,acid) has been found in various mammalian cells. In the present study, we investigate whether this channel participates in reactions of the thoracic aorta to severe acidosis and whether it plays a role in hypertension. We measured isometric contraction in thoracic aorta rings from spontaneously hypertensive rats (SHRs) and normotensive Wistar rats. Severe acidosis induced contractions of both endothelium-intact and -denuded thoracic aorta rings. In Wistar rats, contractions did not differ at pH 6.4, 5.4 and 4.4. However, in SHRs, contractions were higher at pH 5.4 or 4.4 than pH 6.4, with no difference between contractions at pH 5.4 and 4.4. Nifedipine, I_Cl,acid blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and 4,4′-diisothiocyanatostilbene-2, 2′-disulfonic acid (DIDS) inhibited severe acidosis-induced contraction of aortas at different pH levels. When blocking I_Cl,acid, the remnant contraction was greater at pH 4.4 than pH 5.4 and 6.4 for both SHRs and Wistar rats. With nifedipine, the remnant contraction was greatly reduced at pH 4.4 as compared with at pH 6.4 and 5.4. With NPPB or DIDS, the ratio of remnant contractions at pH 4.4 and 5.4 (R_4.4/5.4) was lower for SHRs than Wistar rats (all <1). However, with nifedipine, the R_4.4/5.4 was higher for SHRs than Wistar rats (both >1). Furthermore, patch clamp recordings of I_Cl,acid and intracellular Ca²⁺ measurements in smooth muscle cells confirmed these findings. I_Cl,acid may protect arteries against excess vasoconstriction under extremely acidic extracellular conditions. This protective effect may be decreased in hypertension.

Heat and α1-adrenergic responsiveness in human skeletal muscle feed arteries: the role of nitric oxide

Increased local temperature exerts a sympatholytic effect on human skeletal muscle feed arteries. We hypothesized that this attenuated α(1)-adrenergic receptor responsiveness may be due to a temperature-induced increase in nitric oxide (NO) bioavailability, thereby reducing the impact of the α(1)-adrenergic receptor agonist phenylephrine (PE). Thirteen human skeletal muscle feed arteries were harvested, and wire myography was used to generate PE concentration-response curves at 37 °C and 39 °C, with and without the NO synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (L-NMMA). A subset of arteries (n = 4) were exposed to 37 °C or 39 °C, and the protein content of endothelial NOS (eNOS) and α(1)-adrenergic receptors was determined by Western blot analysis. Additionally, cultured bovine endothelial cells were exposed to static or shear stress conditions at 37 °C and 39 °C and assayed for eNOS activation (phosphorylation at Ser(1177)), eNOS expression, and NO metabolites [nitrate + nitrite (NOx)]. Maximal PE-induced vasocontraction (PE(max)) was lower at 39 °C than at 37 °C [39 ± 10 vs. 84 ± 30% maximal response to 100 mM KCl (KCl(max))]. NO blockade restored vasocontraction at 39 °C to that achieved at 37 °C (80 ± 26% KCl(max)). Western blot analysis of the feed arteries revealed that heating increased eNOS protein, but not α(1)-adrenergic receptors. Heating of bovine endothelial cells resulted in greater shear stress-induced eNOS activation and NOx production. Together, these data reveal for the first time that, in human skeletal muscle feed arteries, NO blockade can restore the heat-attenuated α(1)-adrenergic receptor-mediated vasocontraction and implicate endothelium-derived NO bioavailability as a major contributor to heat-induced sympatholysis. Consequently, these findings highlight the important role of vasodilators in modulating the vascular response to vasoconstrictors.

Human skeletal muscle feed arteries: evidence of regulatory potential

AIM

Recently, it has been recognized that human skeletal muscle feed arteries can be harvested during exploratory surgery for melanoma. This approach provides vessels for in vitro study from a wide spectrum of relatively healthy humans. Although, the regulatory role of skeletal muscle feed arteries in rodent models has been documented, whether such vessels in humans possess this functionality is unknown.

METHODS

Therefore, skeletal muscle feed arteries (~950 μm OD) from 10 humans (48 ± 4, 27-64 years) were studied using pressure myography. Vessel function was assessed using potassium chloride (KCl), phenylephrine (PE), acetylcholine (ACh) and sodium nitroprusside (SNP) concentration-response curves (CRCs) to characterize non-receptor and receptor-mediated vasoconstriction as well as endothelium-dependent and independent vasodilation respectively. To understand the physiological relevance of the diameter changes as a result of pharmacological stimulation, the estimated conductance ratio (CR) was calculated.

RESULTS

Vessel function protocols revealed significant vasoconstriction in response to PE and KCl (35 ± 6; 43 ± 9%vasoconstriction, respectively) and significant vasodilation with ACh and SNP (85 ± 7; 121 ± 17% vasodilation, respectively). Both PE and KCl significantly reduced the CR (0.26 ± 0.05 and 0.23 ± 0.07, respectively), whereas ACh and SNP increased the CR (2.56 ± 0.10 and 5.32 ± 1.3, respectively).

CONCLUSION

These novel findings provide evidence that human skeletal muscle feed arteries are capable of generating significant diameter changes that would translate into significant changes in vascular conductance. Thus, human skeletal muscle feed arteries likely play a significant role in regulating vascular conductance and subsequently blood flow in vivo.