Effects of aging on vasoconstrictor and mechanical properties of rat skeletal muscle arterioles

Vascular limitations in blood pressure regulation with age in women: Insights from exercise and acute cardioselective β-blockade

Younger women rely on altering cardiac output (Q ̇ $\dot{Q}$ ) to regulate blood pressure (BP). In contrast, older women rely more on altering vascular tone. However, evidence suggests that the ability to alter systemic vascular conductance (SVC) is diminished in older women. In the present study, cardioselective β-blockade was utilized to diminish the relative contribution ofQ ̇ $\dot{Q}$ to BP regulation and thereby evaluate age-related vascular limitations in women at rest and during large muscle dynamic exercise. Younger (n = 13, mean age 26.0 years) and older (n = 14, mean age 61.8 years) healthy women performed submaximal bouts of semi-recumbent cycling exercise at varying intensities while receiving an intravenous infusion of esmolol, a β1-antagonist, or saline control in a repeated-measures crossover design.Q ̇ $\dot{Q}$ was attenuated during esmolol infusion, with greater reductions during exercise (moderate, -1.0 (95% CI, -1.6 to -0.5) L/min, P < 0.001; heavy, -2.0 (95% CI, -2.6 to -1.5) L/min, P < 0.001) than seated rest (-0.5 (95% CI, -1.1 to 0.0) L/min, P = 0.048), and this reduction was not significantly different between age groups (P = 0.122). Older women exhibited a greater attenuation in mean arterial pressure (MAP) during esmolol (-7 (95% CI, -9 to -4) mmHg, P < 0.001) relative to younger women (-2 (95% CI, -5 to 0) mmHg, P = 0.071). These changes coincided with a greater reduction of SVC in the younger women during esmolol (-15 (95% CI, -20 to -10) mL/min/mmHg, P < 0.001) compared to older women (-3 (95% CI, -9 to 2) mL/min/mmHg, P = 0.242). Together, these findings provide evidence that older, postmenopausal women have a diminished ability to adjust SVC in order to regulate MAP.

Effects of aging on diaphragm hyperemia and blood flow distribution in male and female Fischer 344 rats

Aging is associated with inspiratory muscle dysfunction; however, the impact of aging on diaphragm blood flow (BF) regulation, and whether sex differences exist, is unknown. We tested the hypotheses in young animals that diaphragm BF and vascular conductance (VC) would be greater in females and that aging would decrease the diaphragm's ability to increase BF with contractions. Young (4-6 mo) and old (22-24 mo) Fischer 344 rats were divided into four groups: young female (YF, n = 7), young male (YM, n = 8), old female (OF, n = 9), and old male (OM, n = 9). Diaphragm BF (mL/min/100 g) and VC (mL/mmHg/min/100 g) were determined, via fluorescent microspheres, at rest and during 1 Hz contractions. In YF versus OF, aging blunted the increase in medial costal diaphragm BF (44 ± 5% vs. 16 ± 12%; P < 0.05) and VC (43 ± 7% vs. 21 ± 12%; P < 0.05). Similarly, in YM versus OM, aging blunted the increase in medial costal diaphragm BF (43 ± 6% vs. 24 ± 12%; P < 0.05) and VC (50 ± 6% vs. 34 ± 10%; P < 0.05). In female rats, age increased dorsal costal diaphragm BF, whereas in male rats, age increased crural diaphragm BF (P < 0.05). Compared with age-matched females, dorsal costal diaphragm BF was lower in YM and OM (P < 0.05). In conclusion, aging results in an inability to augment medial costal diaphragm BF and alters regional diaphragm BF distribution in response to muscular contractions. Furthermore, sex differences in regional diaphragm BF are present in young and old animals.NEW & NOTEWORTHY This is the first study, to our knowledge, to demonstrate that old age impairs the hyperemic response and alters blood flow distribution in the diaphragm of both female and male rats. In addition, this investigation provides novel evidence of sex differences in regional diaphragm blood flow distribution with contractions. The data presented herein suggest that aging compromises diaphragm vascular function and provides a potential mechanism for the diaphragm contractile dysfunction associated with old age.

Adaptations of bone and bone vasculature to muscular stretch training

The magnitude of bone formation and remodeling is linked to both the magnitude of strain placed on the bone and the perfusion of bone. It was previously reported that an increase in bone perfusion and bone density occurs in the femur of old rats with moderate aerobic exercise training. This study determined the acute and chronic effects of static muscle stretching on bone blood flow and remodeling. Old male Fischer 344 rats were randomized to either a naive or stretch-trained group. Static stretching of ankle flexor muscles was achieved by placement of a dorsiflexion splint on the left ankle for 30 min/d, 5d/wk for 4wk. The opposite hindlimb served as a contralateral control (nonstretched) limb. Bone blood flow was assessed during and after acute stretching in naive rats, and at rest and during exercise in stretch-trained rats. Vascular reactivity of the nutrient artery of the proximal tibia was also assessed in stretch-trained rats. MicroCT analysis was used to assess bone volume and micro-architecture of the trabecular bone of both tibias near that growth plate. In naive rats, static stretching increased blood flow to the proximal tibial metaphasis. Blood flow to the proximal tibial metaphysis during treadmill exercise was higher in the stretched limb after 4 wk of daily stretching. Daily stretching also increased tibial bone weight and increased total volume in both the proximal and distal tibial metaphyses. In the trabecular bone immediately below the proximal tibial growth plate, total volume and bone volume increased, but bone volume/total volume was unchanged and trabecular connectivity decreased. In contrast, intravascular volume increased in this region of the bone. These data suggest that blood flow to the tibia increases during bouts of static stretching of the hindlimb muscles, and that 4 wk of daily muscle stretching leads to bone remodeling and an increase in intravascular volume of the tibial bone.

Functional, Structural and Proteomic Effects of Ageing in Resistance Arteries

The normal ageing process affects resistance arteries, leading to various functional and structural changes. Systolic hypertension is a common occurrence in human ageing, and it is associated with large artery stiffening, heightened pulsatility, small artery remodeling, and damage to critical microvascular structures. Starting from young adulthood, a progressive elevation in the mean arterial pressure is evidenced by clinical and epidemiological data as well as findings from animal models. The myogenic response, a protective mechanism for the microcirculation, may face disruptions during ageing. The dysregulation of calcium entry channels (L-type, T-type, and TRP channels), dysfunction in intracellular calcium storage and extrusion mechanisms, altered expression of potassium channels, and a change in smooth muscle calcium sensitization may contribute to the age-related dysregulation of myogenic tone. Flow-mediated vasodilation, a hallmark of endothelial function, is compromised in ageing. This endothelial dysfunction is related to increased oxidative stress, lower nitric oxide bioavailability, and a low-grade inflammatory response, further exacerbating vascular dysfunction. Resistance artery remodeling in ageing emerges as a hypertrophic response of the vessel wall that is typically observed in conjunction with outward remodeling (in normotension), or as inward hypertrophic remodeling (in hypertension). The remodeling process involves oxidative stress, inflammation, reorganization of actin cytoskeletal components, and extracellular matrix fiber proteins. Reactive oxygen species (ROS) signaling and chronic low-grade inflammation play substantial roles in age-related vascular dysfunction. Due to its role in the regulation of vascular tone and structural proteins, the RhoA/Rho-kinase pathway is an important target in age-related vascular dysfunction and diseases. Understanding the intricate interplay of these factors is crucial for developing targeted interventions to mitigate the consequences of ageing on resistance arteries and enhance the overall vascular health.

Impact of aging on vascular ion channels: perspectives and knowledge gaps across major organ systems

Individuals aged ≥65 yr will comprise ∼20% of the global population by 2030. Cardiovascular disease remains the leading cause of death in the world with age-related endothelial "dysfunction" as a key risk factor. As an organ in and of itself, vascular endothelium courses throughout the mammalian body to coordinate blood flow to all other organs and tissues (e.g., brain, heart, lung, skeletal muscle, gut, kidney, skin) in accord with metabolic demand. In turn, emerging evidence demonstrates that vascular aging and its comorbidities (e.g., neurodegeneration, diabetes, hypertension, kidney disease, heart failure, and cancer) are "channelopathies" in large part. With an emphasis on distinct functional traits and common arrangements across major organs systems, the present literature review encompasses regulation of vascular ion channels that underlie blood flow control throughout the body. The regulation of myoendothelial coupling and local versus conducted signaling are discussed with new perspectives for aging and the development of chronic diseases. Although equipped with an awareness of knowledge gaps in the vascular aging field, a section has been included to encompass general feasibility, role of biological sex, and additional conceptual and experimental considerations (e.g., cell regression and proliferation, gene profile analyses). The ultimate goal is for the reader to see and understand major points of deterioration in vascular function while gaining the ability to think of potential mechanistic and therapeutic strategies to sustain organ perfusion and whole body health with aging.

Arterial myogenic response and aging

The arterial myogenic response is an inherent property of resistance arteries. Myogenic tone is crucial for maintaining a relatively constant blood flow in response to changes in intraluminal pressure and protects delicate organs from excessive blood flow. Although this fundamental physiological phenomenon has been extensively studied, the underlying molecular mechanisms are largely unknown. Recent studies identified a crucial role of mechano-activated angiotensin II type 1 receptors (AT1R) in this process. The development of myogenic response is affected by aging. In this review, we summarize recent progress made to understand the role of AT1R and other mechanosensors in the control of arterial myogenic response. We discuss age-related alterations in myogenic response and possible underlying mechanisms and implications for healthy aging.

Prolonged mechanical ventilation increases diaphragm arteriole circumferential stretch without changes in stress/stretch: Implications for the pathogenesis of ventilator-induced diaphragm dysfunction

INTRODUCTION

Prolonged mechanical ventilation (MV; ≥6 h) results in large, time-dependent reductions in diaphragmatic blood flow and shear stress. We tested the hypothesis that MV would impair the structural and material properties (ie, increased stress/stretch relation and/or circumferential stretch) of first-order arterioles (1A) from the medial costal diaphragm.

METHODS

Shear stress was estimated from isolated arterioles and prior blood flow data from the diaphragm during spontaneous breathing (SB) and prolonged MV (6 h MV). Thereafter, female Sprague-Dawley rats (~5 months) were randomly divided into two groups, SB (n = 6) and 6 h MV (n = 6). Following SB and 6 h MV, 1A medial costal diaphragm arterioles were isolated, cannulated, and subjected to stepwise (0-140 cmH2 O) increases in intraluminal pressure in calcium-free Ringer's solution. Inner diameter and wall thickness were measured at each pressure step and used to calculate wall:lumen ratio, Cauchy-stress, and circumferential stretch.

RESULTS

Compared to SB, there was a ~90% reduction in arteriolar shear stress with prolonged MV (9 ± 2 vs 78 ± 20 dynes/cm2 ; p ≤ .05). In the unloaded condition (0 cmH2 O), the arteriolar intraluminal diameter was reduced (37 ± 8 vs 79 ± 13 μm) and wall:lumen ratio was increased (120 ± 18 vs 46 ± 10%) compared to SB (p ≤ .05). There were no differences in the passive diameter responses or the circumferential stress/stretch relationship between groups (p > .05), but at each pressure step, circumferential stretch was increased with 6 h MV vs SB (p ≤ .05).

CONCLUSION

During prolonged MV, medial costal diaphragm arteriolar shear stress is severely diminished. Despite no change in the material behavior (stress/stretch), prolonged MV resulted in altered structural and mechanical properties (ie, elevated circumferential stretch) of medial costal diaphragm arterioles. This provides important novel mechanistic insights into the impaired diaphragm blood flow capacity and vascular dysfunction following prolonged MV.

Vascular smooth muscle stiffness and its role in aging

Vascular smooth muscle cells (VSMC) are now considered important contributors to the pathophysiological and biophysical mechanisms underlying arterial stiffening in aging. Here, we review mechanisms whereby VSMC stiffening alters vascular function and contributes to the changes in vascular stiffening observed in aging and cardiovascular disease. Vascular stiffening in arterial aging was historically associated with changes in the extracellular matrix; however, new evidence suggests that endothelial and vascular smooth muscle cell stiffness also contribute to overall blood vessel stiffness. Furthermore, VSMC play an integral role in regulating matrix deposition and vessel wall contractility via interaction between the actomyosin contractile unit and adhesion structures that anchor the cell within the extracellular matrix. Aged-induce phenotypic modulation of VSMC from a contractile to a synthetic phenotype is associated with decreased cellular contractility and increased cell stiffness. Aged VSMC also display reduced mechanosensitivity and adaptation to mechanical signals from their microenvironment due to impaired intracellular signaling. Finally, evidence for decreased contractility in arteries from aged animals demonstrate that changes at the cellular level result in decreased functional properties at the tissue level.

Sympathetic vasoconstriction in skeletal muscle: Modulatory effects of aging, exercise training, and sex

The sympathetic nervous system (SNS) is a critically important regulator of the cardiovascular system. The SNS controls cardiac output and its distribution, as well as peripheral vascular resistance and blood pressure at rest and during exercise. Aging is associated with increased blood pressure and decreased skeletal muscle blood flow at rest and in response to exercise. The mechanisms responsible for the blunted skeletal muscle blood flow response to dynamic exercise with aging have not been fully elucidated; however, increased muscle sympathetic nerve activity (MSNA), elevated vascular resistance and a decline in endothelium-dependent vasodilation are commonly reported in older adults. In contrast to aging, exercise training has been shown to reduce blood pressure and enhance skeletal muscle vascular function. Exercise training has been shown to enhance nitric oxide-dependent vascular function and may improve the vasodilatory capacity of the skeletal muscle vasculature; however, surprisingly little is known about the effect of exercise training on the neural control of circulation. The control of blood pressure and skeletal muscle blood flow also differs between males and females. Blood pressure and MSNA appear to be lower in young females compared to males. However, females experience a larger increase in MSNA with aging compared to males. The mechanism(s) for the altered SNS control of vascular function in females remain to be determined. Novelty: • This review will summarize our current understanding of the effects of aging, exercise training and sex on sympathetic vasoconstriction at rest and during exercise. • Areas where additional research is needed are also identified.

Aerobic exercise training reduces cardiac function and coronary flow-induced vasodilation in mice lacking adiponectin

We tested the hypothesis that adiponectin deficiency attenuates cardiac and coronary microvascular function and prevents exercise training-induced adaptations of the myocardium and the coronary microvasculature in adult mice. Adult wild-type (WT) or adiponectin knockout (adiponectin KO) mice underwent treadmill exercise training or remained sedentary for 8-10 wk. Systolic and diastolic functions were assessed before and after exercise training or cage confinement. Vasoreactivity of coronary resistance arteries was assessed at the end of exercise training or cage confinement. Before exercise training, ejection fraction and fractional shortening were similar in adiponectin KO and WT mice, but isovolumic contraction time was significantly lengthened in adiponectin KO mice. Exercise training increased ejection fraction (12%) and fractional shortening (20%) with no change in isovolumic contraction time in WT mice. In adiponectin KO mice, both ejection fraction (-9%) and fractional shortening (-12%) were reduced after exercise training and these decreases were coupled to a further increase in isovolumic contraction time (20%). In sedentary mice, endothelium-dependent dilation to flow was higher in arterioles from adiponectin KO mice as compared with WT mice. Exercise training enhanced dilation to flow in WT mice but decreased flow-induced dilation in adiponectin KO mice. These data suggest that compensatory mechanisms contribute to the maintenance of cardiac and coronary microvascular function in sedentary mice lacking adiponectin; however, in the absence of adiponectin, cardiac and coronary microvascular adaptations to exercise training are compromised.NEW & NOTEWORTHY We report that compensatory mechanisms contribute to the maintenance of cardiac and coronary microvascular function in sedentary mice in which adiponectin has been deleted; however, when mice lacking adiponectin are subjected to the physiological stress of exercise training, beneficial coronary microvascular and cardiac adaptations are compromised or absent.

Endothelin B receptor dysfunction mediates elevated myogenic tone in cerebral arteries from aged male Fischer 344 rats

The human brain requires adequate cerebral blood flow to meet the high demand for nutrients and to clear waste products. With age, there is a chronic reduction in cerebral blood flow in small resistance arteries that can eventually limit proper brain function. The endothelin system is a key mediator in the regulation of cerebral blood flow, but the contributions of its constituent receptors in the endothelial and vascular smooth muscle layers of cerebral arteries have not been well defined in the context of aging. We isolated posterior cerebral arteries from young and aged Fischer 344 rats, as well as ET_B receptor knock-out rats and mounted the vessels in plexiglass pressure myograph chambers to measure myogenic tone in response to increasing pressure and targeted pharmacological treatments. We used an ET_A receptor antagonist (BQ-123), an ET_B receptor antagonist (BQ-788), endothelin-1, an endothelin-1 synthesis inhibitor (phosphoramidon), and vessel denudation to dissect the roles of each receptor in aging vasculature. Aged rats exhibited a higher myogenic tone than young rats, and the tone was sensitive to the ET_A antagonist, BQ-123, but insensitive to the ET_B antagonist, BQ-788. By contrast, the tone in the vessels from young rats was raised by BQ-788 but unaffected by BQ-123. When the endothelial layer that is normally enriched with ET_B1 receptors was removed from young vessels, myogenic tone increased. However, denudation of the endothelial layer did not influence vessels from aged animals. This indicated that endothelial ET_B1 receptors were not functional in the vessels from aged rats. There was also an increase in ET_A receptor expression with age, whereas ET_B receptor expression remained constant between young and aged animals. These results demonstrate that in young vessels, ET_B1 receptors maintain a lower myogenic tone, but in aged vessels, a loss of ET_B receptor activity allows ET_A receptors in vascular smooth muscle cells to raise myogenic tone. Our findings have potentially important clinical implications for treatments to improve cerebral perfusion in older adults with diseases characterized by reduced cerebral blood flow.

Whole-body vibration modulates leg muscle reflex and blood perfusion among people with chronic stroke: a randomized controlled crossover trial

This study aimed to investigate the acute effect of whole-body vibration (WBV) on the reflex and non-reflex components of spastic hypertonia and intramuscular blood perfusion among individuals with chronic stroke. Thirty-six people with chronic stroke (age: 61.4 ± 6.9 years) participated in this randomized controlled cross-over study. Each participant underwent two testing conditions: static standing for 5 minutes with WBV (30 Hz, 1.5 mm) or no-vibration. We assessed the soleus H-reflex, shear modulus (ultrasound elastography) and vascular index (color power Doppler ultrasound) of the medial gastrocnemius (MG) muscle on either paretic or non-paretic side at baseline and every 1-min post-intervention up to 5 minutes. The results revealed a significant inhibition of the H/M ratio bilaterally for the WBV condition (absolute change on paretic side: 0.61 ± 0.35, p = 0.001; non-paretic side: 0.34 ± 0.23, p = 0.001), but not the control condition. The inhibition of H-reflex was sustained up to 4 minutes and 3 minutes on the paretic and non-paretic side, respectively. The vascular index of MG muscle was significantly increased only for the WBV condition [paretic: from 0.55 ± 0.07 to 1.08 ± 0.18 (p = 0.001); non-paretic: from 0.82 ± 0.09 to 1.01 ± 0.13 (p < 0.001)], which lasted for 3 minutes and 5 minutes, respectively. No significant change of the shear modulus in the MG muscle was observed, regardless of the testing condition. Based on our results, WBV had an acute effect on modulating spastic hypertonia dominated by hyperreflexia in people with chronic stroke and facilitating greater intramuscular blood perfusion. No acute effect on passive muscle stiffness was observed.

Alteration of Pressure-Induced Vasodilation in Aging and Diabetes, a Neuro-Vascular Damage

Skin is constantly subjected to pressure at different levels. Pressure-induced vasodilation (PIV) is one of the response mechanisms to low pressure that maintains the homeostasis of the skin. PIV results from the interaction of primary afferent nerves and vascular endothelium of skin vessels. Thanks to this cutaneous neuro-vascular interaction, the cutaneous blood flow increase allows the maintenance of an optimal level of oxygenation and minimizes the lack of vascularization of the skin tissue under low pressure. It seems to be associated with the cutaneous protection mechanisms to prevent pressure ulcers. In some contexts, where microangiopathy and neuropathy can occur, such as aging and diabetes, PIV is impaired, leading to a dramatic early decrease in local skin blood flow when low pressure is applied. In aging, PIV alteration is due to endothelial dysfunction, essentially from an alteration of the nitric oxide pathway. In the inflamm-aging context, oxidative stress increases leading to endothelial cell and nerve damages. An age-related sensory neuropathy will exacerbate the alteration of PIV during the aging process. In diabetes, non-controlled hyperglycaemia leads to an increase in several pathological biochemical pathways that involve oxidative stress and can affect PIV. Sorbinil, alagebrium and alpha-lipoic acid are able individually to restore PIV through a possible oxidative stress reduction. Candesartan, an angiotensin II type 1 receptor blocker, is also able to restore PIV and prevent pressure ulcer formation. The possibility of preventing pressure ulcer associated to diabetes and/or aging with the restoration of PIV seems to be a promising research path.

Impaired diaphragm resistance vessel vasodilation with prolonged mechanical ventilation

Mechanical ventilation (MV) is a life-saving intervention, yet with prolonged MV (i.e., ≥6 h) there are time-dependent reductions in diaphragm blood flow and an impaired hyperemic response of unknown origin. Female Sprague-Dawley rats (4-8 mo, n = 118) were randomized into two groups; spontaneous breathing (SB) and 6-h (prolonged) MV. After MV or SB, vasodilation (flow-induced, endothelium-dependent and -independent agonists) and constriction (myogenic and α-adrenergic) responses were measured in first-order (1A) diaphragm resistance arterioles in vitro, and endothelial nitric oxide synthase (eNOS) mRNA expression was quantified. Following prolonged MV, there was a significant reduction in diaphragm arteriolar flow-induced (SB, 34.7 ± 3.8% vs. MV, 22.6 ± 2.0%; P ≤ 0.05), endothelium-dependent (via acetylcholine; SB, 64.3  ± 2.1% vs. MV, 36.4 ± 2.3%; P ≤ 0.05) and -independent (via sodium nitroprusside; SB, 65.0 ± 3.1% vs. MV, 46.0 ± 4.6%; P ≤ 0.05) vasodilation. Compared with SB, there was reduced eNOS mRNA expression (P ≤ 0.05). Prolonged MV diminished phenylephrine-induced vasoconstriction (SB, 37.3 ± 6.7% vs. MV, 19.0 ± 1.9%; P ≤ 0.05) but did not alter myogenic or passive pressure responses. The severe reductions in diaphragmatic blood flow at rest and during contractions, with prolonged MV, are associated with diaphragm vascular dysfunction which occurs through both endothelium-dependent and endothelium-independent mechanisms.NEW & NOTEWORTHY Following prolonged mechanical ventilation, vascular alterations occur through both endothelium-dependent and -independent pathways. This is the first study, to our knowledge, demonstrating that diaphragm arteriolar dysfunction occurs consequent to prolonged mechanical ventilation and likely contributes to the severe reductions in diaphragmatic blood flow and weaning difficulties.

Cerebral and skeletal muscle feed artery vasoconstrictor responses in a mouse model with greater large elastic artery stiffness

NEW FINDINGS

What is the central question of this study? Greater large artery stiffness is associated with dysfunctional resistance artery vasodilatory responses, impaired memory and greater risk of Alzheimer's disease. However, it is unknown whether stiffer large arteries affect cerebral and skeletal muscle feed artery responses to vasoconstrictors. What is the main finding and its importance? In a mouse model with greater large artery stiffness (Eln^+/- ), we find an exacerbated vasoconstrictor response to angiotensin II in cerebral arteries, but not skeletal muscle feed arteries, thus implicating altered cerebral artery angiotensin II responsiveness in the poor brain outcomes associated with greater large artery stiffness.

ABSTRACT

Greater stiffness of the large elastic arteries is associated with end-organ damage and dysfunction. At the same time, resistance artery vasoconstrictor responsiveness influences vascular tone and organ blood flow. However, it is unknown whether large elastic artery stiffness modulates the responsiveness to vasoconstrictors in resistance arteries of the cerebral or skeletal muscle circulations. We previously described the elastin haploinsufficient (Eln^+/- ) mouse as a model with greater aortic stiffness, but with similar cerebral and skeletal muscle feed artery stiffness to wild-type (Eln^+/+ ) mice. Here, we used this model to examine the relationship between large elastic artery stiffness and resistance artery vasoconstrictor responses. In middle cerebral arteries (MCAs), vasoconstriction in response to angiotensin II (Ang II) was ∼40% greater in Eln^+/- compared with Eln^+/+ mice (P = 0.02), and this group difference was ameliorated by losartan, indicating a role for Ang II type 1 receptors (AT1Rs). In gastrocnemius feed arteries, Eln^+/- and Eln^+/+ mice did not differ in the response to Ang II. In addition, the vasoconstrictor responses to noradrenaline, endothelin-1 and potassium chloride were not different between Eln^+/- and Eln^+/+ mice for either MCAs or gastrocnemius feed arteries. The MCA AT1R gene expression did not differ between groups, whereas Ang II type 2 receptor gene expression was ∼50% lower in MCAs from Eln^+/- versus Eln^+/+ mice (P = 0.01). In conclusion, greater large elastic artery stiffness is associated with an exacerbated vasoconstriction response to Ang II in cerebral arteries, but is not associated with the responses to other vasoconstrictors in either cerebral or skeletal muscle feed arteries.

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.

Importance of mechanical signals in promoting exercise-induced improvements in vasomotor function of aged skeletal muscle resistance arteries

Current research indicates that vasomotor responses are altered with aging in skeletal muscle resistance arteries. The changes in vasomotor function are characterized by impaired vasodilator and vasoconstrictor responses. The detrimental effects of aging on vasomotor function are attenuated in some vascular beds after a program of endurance exercise training. The signals associated with exercise responsible for inducing improvements in vasomotor function have been proposed to involve short-duration increases in intraluminal shear stress and/or pressure during individual bouts of exercise. Here, we review evidence that increases in shear stress and pressure, within a range believed to present in these arteries during exercise, promote healthy vasomotor function in aged resistance arteries. We conclude that available research is consistent with the interpretation that short-duration mechanical stimulation, through increases in shear stress and pressure, contributes to the beneficial effects of exercise on vasomotor function in aged skeletal muscle resistance arteries.

Vascular Smooth Muscle Contractile Function Declines With Age in Skeletal Muscle Feed Arteries

Aging induces a progressive decline in vasoconstrictor responses in central and peripheral arteries. This study investigated the hypothesis that vascular smooth muscle (VSM) contractile function declines with age in soleus muscle feed arteries (SFA). Contractile function of cannulated SFA isolated from young (4 months) and old (24 months) Fischer 344 rats was assessed by measuring constrictor responses of denuded (endothelium removed) SFA to norepinephrine (NE), phenylephrine (PE), and angiotensin II (Ang II). In addition, we investigated the role of RhoA signaling in modulation of VSM contractile function. Structural and functional characteristics of VSM cells were evaluated by fluorescence imaging and atomic force microscopy (AFM). Results indicated that constrictor responses to PE and Ang II were significantly impaired in old SFA, whereas constrictor responses to NE were preserved. In the presence of a Rho-kinase inhibitor (Y27632), constrictor responses to NE, Ang II, and PE were significantly reduced in young and old SFA. In addition, the age-group difference in constrictor responses to Ang II was eliminated. ROCK1 and ROCK2 content was similar in young and old VSM cells, whereas pROCK1 and pROCK2 were significantly elevated in old VSM cells. Aging was associated with a reduction in smooth muscle α-actin stress fibers and recruitment of proteins to cell-matrix adhesions. Old VSM cells presented an increase in integrin adhesion to the matrix and smooth muscle γ-actin fibers that was associated with increased cell stiffness. In conclusion, our results indicate that VSM contractile function declined with age in SFA. The decrement in contractile function was mediated in part by RhoA/ROCK signaling. Upregulation of pROCK in old VSM cells was not able to rescue contractility in old SFA. Collectively, these results indicate that changes at the VSM cell level play a central role in the reduced contractile function of aged SFA.

Activation of the β-common receptor by erythropoietin impairs acetylcholine-mediated vasodilation in mouse mesenteric arterioles

Clinically, erythropoietin (EPO) is known to increase systemic vascular resistance and arterial blood pressure. However, EPO stimulates the production of the potent vasodilator, nitric oxide (NO), in culture endothelial cells. The mechanism by which EPO causes vasoconstriction despite stimulating NO production may be dependent on its ability to activate two receptor complexes, the homodimeric EPO (EPOR2 ) and the heterodimeric EPOR/β-common receptor (βCR). The purpose of this study was to investigate the contribution of each receptor to the vasoactive properties of EPO. First-order, mesenteric arteries were isolated from 16-week-old male C57BL/6 mice, and arterial function was studied in pressure arteriographs. To determine the contribution of each receptor complex, EPO-stimulating peptide (ESP), which binds and activates the heterodimeric EPOR/βCR complex, and EPO, which activates both receptors, were added to the arteriograph chamber 20 min prior to evaluation of endothelium-dependent (acetylcholine, bradykinin, A23187) and endothelium-independent (sodium nitroprusside) vasodilator responses. Only ACh-induced vasodilation was impaired in arteries pretreated with EPO or ESP. EPO and ESP pretreatment abolished ACh-induced vasodilation by 100% and 60%, respectively. EPO and ESP did not affect endothelium-independent vasodilation by SNP. Additionally, a novel βCR inhibitory peptide (βIP), which was computationally developed, prevented the impairment of acetylcholine-induced vasodilation by EPO and ESP, further implicating the EPOR/βCR complex. Last, pretreatment with either EPO or ESP did not affect vasoconstriction by phenylephrine and KCl. Taken together, these findings suggest that acute activation of the heterodimeric EPOR/βCR in endothelial cells leads to a selective impairment of ACh-mediated vasodilator response in mouse mesenteric resistance arteries.

Age-related endothelial dysfunction in human skeletal muscle feed arteries: the role of free radicals derived from mitochondria in the vasculature

AIM

This study sought to determine the role of free radicals derived from mitochondria in the vasculature in the recognized age-related endothelial dysfunction of human skeletal muscle feed arteries (SMFAs).

METHODS

A total of 44 SMFAs were studied with and without acute exposure to the mitochondria-targeted antioxidant MitoQ and nitric oxide synthase (NOS) blockade. The relative abundance of proteins from the electron transport chain, phosphorylated (p-) to endothelial (e) NOS ratio, manganese superoxide dismutase (MnSOD) and the mitochondria-derived superoxide (O2-) levels were assessed in SMFA. Endothelium-dependent and endothelium-independent SMFA vasodilation was assessed in response to flow-induced shear stress, acetylcholine (ACh) and sodium nitroprusside (SNP).

RESULTS

MitoQ restored endothelium-dependent vasodilation in the old to that of the young when stimulated by both flow (young: 68 ± 5; old: 25 ± 7; old + MitoQ 65 ± 9%) and ACh (young: 97 ± 4; old: 59 ± 10; old + MitoQ: 98 ± 5%), but did not alter the initially uncompromised, endothelium-independent vasodilation (SNP). Compared to the young, MitoQ in the old diminished the initially elevated mitochondria-derived O2- levels and appeared to attenuate the breakdown of MnSOD. Furthermore, MitoQ increased the ratio of p-eNOS to NOS and the restoration of endothelium-dependent vasodilation in the old by MitoQ was ablated by NOS blockade.

CONCLUSION

This study demonstrated that MitoQ reverses age-related vascular dysfunction by what appears to be an NO-dependent mechanism in human SMFAs. These findings suggest that mitochondria-targeted antioxidants may have utility in terms of counteracting the attenuated blood flow and vascular dysfunction associated with advancing age.

Age-related Impairment of Vascular Structure and Functions

Among age-related diseases, cardiovascular and cerebrovascular diseases are major causes of death. Vascular dysfunction is a key characteristic of these diseases wherein age is an independent and essential risk factor. The present work will review morphological alterations of aging vessels in-depth, which includes the discussion of age-related microvessel loss and changes to vasculature involving the capillary basement membrane, intima, media, and adventitia as well as the accompanying vascular dysfunctions arising from these alterations.

Increased amplitude of inward rectifier K+ currents with advanced age in smooth muscle cells of murine superior epigastric arteries

Inward rectifier K+ channels (KIR) may contribute to skeletal muscle blood flow regulation and adapt to advanced age. Using mouse abdominal wall superior epigastric arteries (SEAs) from either young (3-6 mo) or old (24-26 mo) male C57BL/6 mice, we investigated whether SEA smooth muscle cells (SMCs) express functional KIR channels and how aging may affect KIR function. Freshly dissected SEAs were either enzymatically dissociated to isolate SMCs for electrophysiological recording (perforated patch) and mRNA expression or used intact for pressure myography. With 5 mM extracellular K+ concentration ([K+]o), exposure of SMCs to the KIR blocker Ba2+ (100 μM) had no significant effect (P > 0.05) on whole cell currents elicited by membrane potentials spanning -120 to -30 mV. Raising [K+]o to 15 mM activated Ba2+-sensitive KIR currents between -120 and -30 mV, which were greater in SMCs from old mice than in SMCs from young mice (P < 0.05). Pressure myography of SEAs revealed that while aging decreased maximum vessel diameter by ~8% (P < 0.05), it had no significant effect on resting diameter, myogenic tone, dilation to 15 mM [K+]o, Ba2+-induced constriction in 5 mM [K+]o, or constriction induced by 15 mM [K+]o in the presence of Ba2+ (P > 0.05). Quantitative RT-PCR revealed SMC expression of KIR2.1 and KIR2.2 mRNA that was not affected by age. Barium-induced constriction of SEAs from young and old mice suggests an integral role for KIR in regulating resting membrane potential and vasomotor tone. Increased functional expression of KIR channels during advanced age may compensate for other age-related changes in SEA function.NEW & NOTEWORTHY Ion channels are integral to blood flow regulation. We found greater functional expression of inward rectifying K+ channels in smooth muscle cells of resistance arteries of mouse skeletal muscle with advanced age. This adaptation to aging may contribute to the maintenance of vasomotor tone and blood flow regulation during exercise.

Effects of aging and exercise training on the dynamics of vasoconstriction in skeletal muscle resistance vessels

It is unknown whether aging or exercise training affect the dynamics of arteriolar vasoconstriction.

PURPOSE

We hypothesized that old age will slow, and exercise training will speed, the dynamics of skeletal muscle arteriolar vasoconstriction in resistance vessels of aged rats.

METHOD

Young (6 month old) and aged (24 month old) male Fischer-344 rats were assigned to sedentary (Sed: n = 6/age group) or exercise-trained (ET: n = 5 aged and 6 young; via treadmill running for 10-12 weeks) groups. After completion of training, arterioles from the red portion of the gastrocnemius muscle were removed, cannulated, and exposed to 10^-4 M norepinephrine (NE) or 20 mM caffeine. Changes in luminal diameter were recorded for analysis of constrictor dynamics.

RESULT

Old age blunted all kinetic parameters (i.e., time delay, time constant) resulting in vasoconstriction taking ~3 times as long to reach a steady state (SS) versus younger counterparts for NE (aged-sed: 15.6 ± 6.0 versus young-sed: 4.6 ± 0.5 s; P < 0.05) with a similar time course to caffeine. Exercise training resulted in a similar time to SS between age groups for NE (aged-ET: 6.8 ± 1.6 versus young-ET: 7.0 ± 0.6 s) and caffeine (aged-ET: 7.8 ± 0.6 versus young-ET: 8.6 ± 1.0 s).

CONCLUSION

The results of this study demonstrate that aging blunts the rate of vasoconstriction in skeletal muscle resistance vessels to the sympathetic neurotransmitter NE due, in part, to an attenuated rate of contraction from intracellular calcium release. Further, exercise training speeds the dynamics of constriction to both NE and caffeine with old age.

Long Lasting Microvascular Tone Alteration in Rat Offspring Exposed In Utero to Maternal Hyperglycaemia

Epidemiologic studies have demonstrated that cardiovascular risk is not only determined by conventional risk factors in adulthood, but also by early life events which may reprogram vascular function. To evaluate the effect of maternal diabetes on fetal programming of vascular tone in offspring and its evolution during adulthood, we investigated vascular reactivity of third order mesenteric arteries from diabetic mother offspring (DMO) and control mother offspring (CMO) aged 3 and 18 months. In arteries isolated from DMO the relaxation induced by prostacyclin analogues was reduced in both 3- and 18-month old animals although endothelium (acetylcholine)-mediated relaxation was reduced in 18-month old DMO only. Endothelium-independent (sodium nitroprusside) relaxation was not affected. Pressure-induced myogenic tone, which controls local blood flow, was reduced in 18-month old CMO compared to 3-month old CMO. Interestingly, myogenic tone was maintained at a high level in 18-month old DMO even though agonist-induced vasoconstriction was not altered. These perturbations, in 18-months old DMO rats, were associated with an increased pMLC/MLC, pPKA/PKA ratio and an activated RhoA protein. Thus, we highlighted perturbations in the reactivity of resistance mesenteric arteries in DMO, at as early as 3 months of age, followed by the maintenance of high myogenic tone in older rats. These modifications are in favour of excessive vasoconstrictor tone. These results evidenced a fetal programming of vascular functions of resistance arteries in adult rats exposed in utero to maternal diabetes, which could explain a re-setting of vascular functions and, at least in part, the occurrence of hypertension later in life.

Heterogeneous ageing of skeletal muscle microvascular function

The distribution of blood flow to skeletal muscle during exercise is altered with advancing age. Changes in arteriolar function that are muscle specific underlie age-induced changes in blood flow distribution. With advancing age, functional adaptations that occur in resistance arterioles from oxidative muscles differ from those that occur in glycolytic muscles. Age-related adaptations of morphology, as well as changes in both endothelial and vascular smooth muscle signalling, differ in muscle of diverse fibre type. Age-induced endothelial dysfunction has been reported in most skeletal muscle arterioles; however, unique alterations in signalling contribute to the dysfunction in arterioles from oxidative muscles as compared with those from glycolytic muscles. In resistance arterioles from oxidative muscle, loss of nitric oxide signalling contributes significantly to endothelial dysfunction, whereas in resistance arterioles from glycolytic muscle, alterations in both nitric oxide and prostanoid signalling underlie endothelial dysfunction. Similarly, adaptations of the vascular smooth muscle that occur with advancing age are heterogeneous between arterioles from oxidative and glycolytic muscles. In both oxidative and glycolytic muscle, late-life exercise training reverses age-related microvascular dysfunction, and exercise training appears to be particularly effective in reversing endothelial dysfunction. Patterns of microvascular ageing that develop among muscles of diverse fibre type and function may be attributable to changing patterns of physical activity with ageing. Importantly, aerobic exercise training, initiated even at an advanced age, restores muscle blood flow distribution patterns and vascular function in old animals to those seen in their young counterparts.

Impact of age on the vasodilatory function of human skeletal muscle feed arteries

Although advancing age is often associated with attenuated skeletal muscle blood flow and skeletal muscle feed arteries (SMFAs) have been recognized to play a regulatory role in the vasculature, little is known about the impact of age on the vasodilatory capacity of human SMFAs. Therefore, endothelium-dependent and -independent vasodilation were assessed in SMFAs (diameter: 544 ± 63 μm) obtained from 24 (equally represented) young (33 ± 2 yr) and old (71 ± 2 yr) subjects in response to three stimuli: 1) flow-induced shear stress, 2) ACh, and 3) sodium nitropusside (SNP). Both assessments of endothelium-dependent vasodilation, flow (young subjects: 68 ± 1% and old subjects: 32 ± 7%) and ACh (young subjects: 92 ± 3% and old subjects: 73 ± 4%), were significantly blunted (P < 0.05) in SMFAs of old compared with young subjects, with no such age-related differences in endothelium-independent vasodilation (SNP). In response to an increase in flow-induced shear stress, vasodilation kinetics (time constant to reach 63% of the amplitude of the response: 55 ± 1 s in young subjects and 92 ± 7 s in old subjects) and endothelial nitric oxide synthase (eNOS) activation (phospho-eNOS(s1177)/total eNOS: 1.0 ± 0.1 in young subjects and 0.2 ± 0.1 in old subjects) were also significantly attenuated in old compared with young subjects (P < 0.05). Furthermore, the vessel superoxide concentration was greater in old subjects (old subjects: 3.9 ± 1.0 area under curve/mg and young subjects: 1.7 ± 0.1 area under the curve/mg, P < 0.05). These findings reveal that the endothelium-dependent vasodilatory capacity, including vasodilation kinetics but not smooth muscle function, of human SMFAs is blunted with age and may be due to free radicals. Given the potential regulatory role of SMFAs in skeletal muscle blood flow, these findings may explain, at least in part, the often observed attenuated perfusion of skeletal muscle with advancing age that may contribute to exercise intolerance in the elderly.

Exercise training reverses aging-induced impairment of myogenic constriction in skeletal muscle arterioles

To investigate whether exercise training can reverse age-related impairment of myogenic vasoconstriction in skeletal muscle arterioles, young (4 mo) and old (22 mo) male Fischer 344 rats were randomly assigned to either sedentary or exercise-trained groups. The roles of the endothelium and Kv1 channels in age- and exercise training-induced adaptations of myogenic responses were assessed through evaluation of pressure-induced constriction in endothelium-intact and denuded soleus muscle arterioles in the presence and absence of the Kv1 channel blocker, correolide. Exercise training enhanced myogenic constriction in arterioles from both old and young rats. In arterioles from old rats, exercise training restored myogenic constriction to a level similar to that of arterioles from young sedentary rats. Removal of the endothelium did not alter myogenic constriction of arterioles from young sedentary rats, but reduced myogenic constriction in arterioles from young exercise-trained rats. In contrast, endothelial removal had no effect on myogenic constriction of arterioles from old exercise-trained rats, but increased myogenic vasoconstriction in old sedentary rats. The effect of Kv1 channel blockade was also dependent on age and training status. In arterioles from young sedentary rats, Kv1 blockade had little effect on myogenic constriction, whereas in old sedentary rats Kv1 blockade increased myogenic constriction. After exercise training, Kv1 channel blockade increased myogenic constriction in arterioles from both young and old rats. Thus exercise training restores myogenic constriction of arterioles from old rats and enhances myogenic constriction from young rats through adaptations of the endothelium and smooth muscle Kv1 channels.

Structural remodeling of coronary resistance arteries: effects of age and exercise training

Age is known to induce remodeling and stiffening of large-conduit arteries; however, little is known of the effects of age on remodeling and mechanical properties of coronary resistance arteries. We employed a rat model of aging to investigate whether 1) age increases wall thickness and stiffness of coronary resistance arteries, and 2) exercise training reverses putative age-induced increases in wall thickness and stiffness of coronary resistance arteries. Young (4 mo) and old (21 mo) Fischer 344 rats remained sedentary or underwent 10 wk of treadmill exercise training. Coronary resistance arteries were isolated for determination of wall-to-lumen ratio, effective elastic modulus, and active and passive responses to changes in intraluminal pressure. Elastin and collagen content of the vascular wall were assessed histologically. Wall-to-lumen ratio increased with age, but this increase was reversed by exercise training. In contrast, age reduced stiffness, and exercise training increased stiffness in coronary resistance arteries from old rats. Myogenic responsiveness was reduced with age and restored by exercise training. Collagen-to-elastin ratio (C/E) of the wall did not change with age and was reduced with exercise training in arteries from old rats. Thus age induces hypertrophic remodeling of the vessel wall and reduces the stiffness and myogenic function of coronary resistance arteries. Exercise training reduces wall-to-lumen ratio, increases wall stiffness, and restores myogenic function in aged coronary resistance arteries. The restorative effect of exercise training on myogenic function of coronary resistance arteries may be due to both changes in vascular smooth muscle phenotype and expression of extracellular matrix proteins.

Age-related remodeling of small arteries is accompanied by increased sphingomyelinase activity and accumulation of long-chain ceramides

The structure and function of large arteries alters with age leading to increased risk of cardiovascular disease. Age‐related large artery remodeling and arteriosclerosis is associated with increased collagen deposition, inflammation, and endothelial dysfunction. Bioactive sphingolipids are known to regulate these processes, and are also involved in aging and cellular senescence. However, less is known about age‐associated alterations in small artery morphology and function or whether changes in arterial sphingolipids occur in aging. We show that mesenteric small arteries from old sheep have increased lumen diameter and media thickness without a change in media to lumen ratio, indicative of outward hypertrophic remodeling. This remodeling occurred without overt changes in blood pressure or pulse pressure indicating it was a consequence of aging per se. There was no age‐associated change in mechanical properties of the arteries despite an increase in total collagen content and deposition of collagen in a thickened intima layer in arteries from old animals. Analysis of the sphingolipid profile showed an increase in long‐chain ceramide (C14–C20), but no change in the levels of sphingosine or sphingosine‐1‐phosphate in arteries from old compared to young animals. This was accompanied by a parallel increase in acid and neutral sphingomyelinase activity in old arteries compared to young. This study demonstrates remodeling of small arteries during aging that is accompanied by accumulation of long‐chain ceramides. This suggests that sphingolipids may be important mediators of vascular aging.

In this study, we have investigated remodeling of small arteries in a large animal model of aging, the sheep. We show that there is age‐related formation of neointima and increased collagen deposition that is accompanied by changes in sphingolipid metabolism resulting in ceramide accumulation in the tissues. These are the first data implicating sphingolipids as important mediators of vascular aging in small arteries. Given that aging is a major risk factor for cardiovascular disease, our study opens a new area for further research into the mechanisms that underlie vascular remodeling in aging.

Aging increases capacitance and spontaneous transient outward current amplitude of smooth muscle cells from murine superior epigastric arteries

Large conductance Ca(2+)-activated K(+) channels (BKCa) contribute to negative feedback regulation of smooth muscle cell (SMC) tone. However, the effects of aging on BKCa function are unclear. We tested the hypothesis that aging alters SMC BKCa function in superior epigastric arteries (SEAs) by using perforated patch recording of enzymatically isolated SMCs from 3- to 4-mo-old male C57BL/6 mice (Young) and 24- to 26-mo-old male C57BL/6 mice (Old). SMC capacitance from Young (15.7 ± 0.4 pF; n = 110) was less than Old (17.9 ± 0.5 pF; n = 104) (P < 0.05). SMCs displayed spontaneous transient outward currents (STOCs) at membrane potentials more positive than -30 mV; depolarization increased STOC amplitude and frequency (P < 0.05; n = 19-24). STOC frequency in Young (2.2 ± 0.6 Hz) was less than Old (4.2 ± 0.7 Hz) at -10 mV (P < 0.05, n = 27-30), with no difference in amplitude (1.0 ± 0.1 vs. 0.9 ± 0.1 pA/pF, respectively). At +30 mV, STOC amplitude in Young (3.2 ± 0.3 pA/pF) was less than Old (5.0 ± 0.5 pA/pF; P < 0.05, n = 61-67) with no difference in frequency (3.9 ± 0.4 vs. 3.2 ± 0.3 Hz, respectively). BKCa blockers (1 μM paxilline, 100 nM iberiotoxin, 1 mM tetraethylammonium) or a ryanodine receptor antagonist (100 μM tetracaine) inhibited STOCs (n ≥ 6; P < 0.05 each). Western blots revealed increased expression of BKCa α-subunit protein in Old. Pressure myography revealed no effect of age on SEA maximal diameter, myogenic tone, or paxilline-induced constriction (n = 10-12; P > 0.05). Enhanced functional expression of SMC BKCa-dependent STOCs in Old may represent an adaptation of resistance arteries to maintain functional integrity.

Smooth muscle specific disruption of the endothelin-A receptor in mice reduces arterial pressure, and vascular reactivity and affects vascular development

AIMS

The role of vascular smooth muscle endothelin A receptors (ETA) in development and normal physiology remains incompletely understood. To address this, mice were generated with smooth muscle-specific knockout (KO) of ETA.

MAIN METHODS

Mice were homozygous for loxP-flanked exons 6-8 of the EDNRA gene (floxed) or were also hemizygous for a transgene expressing Cre recombinase under control of the smooth muscle-specific SM22 promoter (KO mice).

KEY FINDINGS

Genotyping at 17 days postnatal yielded a 10:1 ratio of floxed:KO mice. Smooth muscle actin staining of embryos at day E10.5 revealed increased tortuosity in dorsal aortae while E12.5 embryos had mandibular, vascular and thymic abnormalities. Mice surviving to weaning developed and bred normally. ETA KO mice aged 2-3 months manifested EDNRA gene recombination in all organs tested. Aortas from KO mice had a >90% reduction in ETA mRNA content, but no differences in ET-1 or ETB mRNA levels. Addition of 0.01-100 nM ET-1 to isolated femoral arteries from floxed, but not KO, mice dose-dependently decreased vessel diameter (up to 80% reduction in the presence of ETB blockade). Intravenous infusion of ET-1 into floxed, but not KO, mice increased mean arterial pressure (MAP) (by ~10 mm Hg). Telemetric analysis revealed decreased MAP in KO mice (reduced by ~7-10 mm Hg) when fed a high salt diet.

SIGNIFICANCE

Smooth muscle ETA is important for normal vascular, mandibular and thymic development and is involved in the maintenance of arterial pressure under physiological conditions.

Effects of exercise training on tumor hypoxia and vascular function in the rodent preclinical orthotopic prostate cancer model

Regular physical exercise is considered to be an integral component of cancer care strategies. However, the effect of exercise training on tumor microvascular oxygenation, hypoxia, and vascular function, all of which can affect the tumor microenvironment, remains unknown. Using an orthotopic preclinical model of prostate cancer, we tested the hypotheses that, after exercise training, in the tumor, there would be an enhanced microvascular Po2, increased number of patent vessels, and reduced hypoxia. We also investigated tumor resistance artery contractile properties. Dunning R-3327 AT-1 tumor cells (10(4)) were injected into the ventral prostate of 4-5-mo-old male Copenhagen or Nude rats, which were randomly assigned to tumor-bearing exercise trained (TB-Ex trained; n = 15; treadmill exercise for 5-7 wk) or sedentary groups (TB-Sedentary; n = 12). Phosphorescence quenching was used to measure tumor microvascular Po2, and Hoechst-33342 and EF-5 were used to measure patent vessels and tumor hypoxia, respectively. Tumor resistance artery function was assessed in vitro using the isolated microvessel technique. Compared with sedentary counterparts, tumor microvascular Po2 increased ∼100% after exercise training (TB-Sedentary, 6.0 ± 0.3 vs. TB-Ex Trained, 12.2 ± 1.0 mmHg, P < 0.05). Exercise training did not affect the number of patent vessels but did significantly reduce tumor hypoxia in the conscious, resting condition from 39 ± 12% of the tumor area in TB-Sedentary to 4 ± 1% in TB-Ex Trained. Exercise training did not affect vessel contractile function. These results demonstrate that after exercise training, there is a large increase in the driving force of O2 from the tumor microcirculation, which likely contributes to the considerable reduction in tumor hypoxia. These results suggest that exercise training can modulate the microenvironment of the tumor, such that a sustained reduction in tumor hypoxia occurs, which may lead to a less aggressive phenotype and improve patient prognosis.

Aging compounds western diet-associated large artery endothelial dysfunction in mice: prevention by voluntary aerobic exercise

We tested the hypothesis that aging will exacerbate the negative vascular consequences of exposure to a common physiological stressor, i.e., consumption of a "western" (high fat/high sucrose) diet (WD), by inducing superoxide-associated reductions in nitric oxide (NO) bioavailability, and that this would be prevented by voluntary aerobic exercise. Incremental stiffness and endothelium-dependent dilation (EDD) were measured in the carotid arteries of young (5.4±0.3 mo, N=20) and old (30.4±0.2 mo, N=19) male B6D2F1 mice fed normal chow (NC: 17% fat, 0% sucrose) or a western diet (40% fat, 19% sucrose) and housed in either standard cages or cages equipped with running wheels for 10-14 weeks. Incremental stiffness was higher in old NC (P<0.05) and both young (P<0.01) and old (P<0.01) WD fed mice compared with young NC mice, but WD did not further increase stiffness in the old mice. In cage control mice, maximal EDD was 17% lower in both NC fed old mice and young WD fed mice (P<0.05). Consumption of WD by old mice led to a further 20% reduction in maximal EDD (P<0.05). Incremental stiffness was 28% lower and maximal EDD was 38% greater in old WD fed mice with access to running wheels vs. old WD fed control mice (P<0.05) and not different from young NC fed controls. Wheel running also tended to improve maximal EDD (+9%, P=0.11), but not incremental stiffness in young WD fed mice. Ex vivo treatment with the superoxide scavenger TEMPOL and NO inhibitor l-NAME abolished these respective effects of age, WD and voluntary running on EDD. Ingestion of a WD induces similar degrees of endothelial dysfunction in old and young adult B6D2F1 mice, and these effects are mediated by a superoxide-dependent impairment of NO bioavailability. However, the combination of old age and WD, a common occurrence in our aging society, results in a marked, additive reduction in endothelial function. Importantly, regular voluntary aerobic exercise reduces arterial stiffness and protects against the adverse influence of WD on endothelial function in old animals by preventing superoxide suppression of NO. These findings may have important implications for arterial aging and the prevention of age-associated cardiovascular diseases.

Mitochondrial dysfunction and sarcopenia of aging: from signaling pathways to clinical trials

Sarcopenia, the age-related loss of muscle mass and function, imposes a dramatic burden on individuals and society. The development of preventive and therapeutic strategies against sarcopenia is therefore perceived as an urgent need by health professionals and has instigated intensive research on the pathophysiology of this syndrome. The pathogenesis of sarcopenia is multifaceted and encompasses lifestyle habits, systemic factors (e.g., chronic inflammation and hormonal alterations), local environment perturbations (e.g., vascular dysfunction), and intramuscular specific processes. In this scenario, derangements in skeletal myocyte mitochondrial function are recognized as major factors contributing to the age-dependent muscle degeneration. In this review, we summarize prominent findings and controversial issues on the contribution of specific mitochondrial processes - including oxidative stress, quality control mechanisms and apoptotic signaling - on the development of sarcopenia. Extramuscular alterations accompanying the aging process with a potential impact on myocyte mitochondrial function are also discussed. We conclude with presenting methodological and safety considerations for the design of clinical trials targeting mitochondrial dysfunction to treat sarcopenia. Special emphasis is placed on the importance of monitoring the effects of an intervention on muscle mitochondrial function and identifying the optimal target population for the trial. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.

Enhanced spectral analysis of blood flow during post-occlusive reactive hyperaemia test in different tissue depths

The objective of this study was to investigate the impairment of microcirculation in schizophrenic patients by means of spectral analysis of blood flow signals and to determine if microcirculation is unequally altered in different tissue depths. Furthermore, the impact of gender and age on the spectral parameters of the Laser Doppler Flowmetry (LDF) signal in healthy and diseased microcirculation are to be analysed. The segmented spectral analysis (SSA) algorithm was applied to LDF signals of a provoked post-ischemic stage and compared to the traditional total spectral analysis, hypothesizing that SSA reveals more detailed information on the dynamic behaviour of the blood flow. 15 healthy subjects (CON, mean age 32.4 years) and 15 patients (PAT, mean age 33.0 years) were enrolled. Spectral analysis was performed on two LDF signals at a depth of 2mm and 6-8mm. Features in five frequency subintervals were determined. Our results indicate that microcirculation is strongly impaired in patients. SSA of blood flow revealed differences between CON and PAT in all three frequency intervals referring to local vasomotion (endothelial p=0.03; sympathetic p=0.02, myogenic p=0.03) as well as the respiratory (p=0.02) and cardiac (p=0.006) bands in the deeper tissue. In contrast, in the near-surface tissue only the endothelial (p=0.006) and cardiac (p=0.006) components were altered. Furthermore, SSA determined a gender- and age dependency regarding blood flow. In conclusion, we could demonstrate that microcirculation in schizophrenic patients is significantly impaired, depending on its location in the near-surface skin or in the superficial muscle tissue. These alterations of microcirculation are more pronounced in the deeper tissue depth of about 6-8mm and are influenced by gender and age.

Differential effects of aging and exercise on intra-abdominal adipose arteriolar function and blood flow regulation

Adipose tissue (AT), which typically comprises an increased percentage of body mass with advancing age, receives a large proportion of resting cardiac output. During exercise, an old age-associated inability to increase vascular resistance within the intra-abdominal AT may compromise the ability of the cardiovascular system to redistribute blood flow to the active musculature, contributing to the decline in exercise capacity observed in this population. We tested the hypotheses that 1) there would be an elevated perfusion of AT during exercise with old age that was associated with diminished vasoconstrictor responses of adipose-resistance arteries, and 2) chronic exercise training would mitigate the age-associated alterations in AT blood flow and vascular function. Young (6 mo; n = 40) and old (24 mo; n = 28) male Fischer 344 rats were divided into young sedentary (YSed), old sedentary (OSed), young exercise trained (YET), or old exercise trained (OET) groups, where training consisted of 10-12 wk of treadmill exercise. In vivo blood flow at rest and during exercise and in vitro α-adrenergic and myogenic vasoconstrictor responses in resistance arteries from AT were measured in all groups. In response to exercise, there was a directionally opposite change in AT blood flow in the OSed group (≈ 150% increase) and YSed (≈ 55% decrease) vs. resting values. Both α-adrenergic and myogenic vasoconstriction were diminished in OSed vs. YSed AT-resistance arteries. Exercise training resulted in a similar AT hyperemic response between age groups during exercise (YET, 9.9 ± 0.5 ml · min(-1) · 100(-1) g; OET, 8.1 ± 0.9 ml · min(-1) · 100(-1) g) and was associated with enhanced myogenic and α-adrenergic vasoconstriction of AT-resistance arteries from the OET group relative to OSed. These results indicate that there is an inability to increase vascular resistance in AT during exercise with old age, due, in part, to a diminished vasoconstriction of AT arteries. Furthermore, the results indicate that exercise training can augment vasoconstriction of AT arteries and mitigate age-related alterations in the regulation of AT blood flow during exercise.

Age and exercise training alter signaling through reactive oxygen species in the endothelium of skeletal muscle arterioles

Exercise training ameliorates age-related impairments in endothelium-dependent vasodilation in skeletal muscle arterioles. Additionally, exercise training is associated with increased superoxide production. The purpose of this study was to determine the role of superoxide and superoxide-derived reactive oxygen species (ROS) signaling in mediating endothelium-dependent vasodilation of soleus muscle resistance arterioles from young and old, sedentary and exercise-trained rats. Young (3 mo) and old (22 mo) male rats were either exercise trained or remained sedentary for 10 wk. To determine the impact of ROS signaling on endothelium-dependent vasodilation, responses to acetylcholine were studied under control conditions and during the scavenging of superoxide and/or hydrogen peroxide. To determine the impact of NADPH oxidase-derived ROS, endothelium-dependent vasodilation was determined following NADPH oxidase inhibition. Reactivity to superoxide and hydrogen peroxide was also determined. Tempol, a scavenger of superoxide, and inhibitors of NADPH oxidase reduced endothelium-dependent vasodilation in all groups. Similarly, treatment with catalase and simultaneous treatment with tempol and catalase reduced endothelium-dependent vasodilation in all groups. Decomposition of peroxynitrite also reduced endothelium-dependent vasodilation. Aging had no effect on arteriolar protein content of SOD-1, catalase, or glutathione peroxidase-1; however, exercise training increased protein content of SOD-1 in young and old rats, catalase in young rats, and glutathione peroxidase-1 in old rats. These data indicate that ROS signaling is necessary for endothelium-dependent vasodilation in soleus muscle arterioles, and that exercise training-induced enhancement of endothelial function occurs, in part, through an increase in ROS signaling.

Vascular dysfunction in young, mid-aged and aged mice with latent cytomegalovirus infections

Human cytomegalovirus (HCMV) is associated with vascular diseases in both immunosuppressed and immunocompetent individuals. CMV infections cycle between active and latent phases throughout life. We and others have shown vascular dysfunction during active mouse CMV (mCMV) infections. Few studies have examined changes in physiology during latent CMV infections, particularly vascular responses or whether the negative effects of aging on vascular function and fertility will be exacerbated under these conditions. We measured vascular responses in intact mesenteric and uterine arteries dissected from young, mid-aged, and aged latently mCMV-infected (mCMV genomes are present but infectious virus is undetectable) and age-matched uninfected mice using a pressure myograph. We tested responses to the α(1)-adrenergic agonist phenylephrine, the nitric oxide donor sodium nitroprusside, and the endothelium-dependent vasodilator methacholine. In young latently mCMV-infected mice, vasoconstriction was increased and vasodilation was decreased in mesenteric arteries, whereas both vasoconstriction and vasodilation were increased in uterine arteries compared with those in age-matched uninfected mice. In reproductively active mid-aged latently infected mice, mesenteric arteries showed little change, whereas uterine arteries showed greatly increased vasoconstriction. These vascular effects may have contributed to the decreased reproductive success observed in mid-aged latently mCMV-infected compared with age-matched uninfected mice (16.7 vs. 46.7%, respectively). In aged latently infected mice, vasodilation is increased in mesenteric and uterine arteries likely to compensate for increased vasoconstriction to mediators other than phenylephrine. The novel results of this study show that even when active mCMV infections become undetectable, vascular dysfunction continues and differs with age and artery origin.

Effects of aging and exercise training on skeletal muscle blood flow and resistance artery morphology

With old age, blood flow to the high-oxidative red skeletal muscle is reduced and blood flow to the low-oxidative white muscle is elevated during exercise. Changes in the number of feed arteries perforating the muscle are thought to contribute to this altered hyperemic response during exercise. We tested the hypothesis that exercise training would ameliorate age-related differences in blood flow during exercise and feed artery structure in skeletal muscle. Young (6-7 mo old, n = 36) and old (24 mo old, n = 25) male Fischer 344 rats were divided into young sedentary (Sed), old Sed, young exercise-trained (ET), and old ET groups, where training consisted of 10-12 wk of treadmill exercise. In Sed and ET rats, blood flow to the red and white portions of the gastrocnemius muscle (Gast(Red) and Gast(White)) and the number and luminal cross-sectional area (CSA) of all feed arteries perforating the muscle were measured at rest and during exercise. In the old ET group, blood flow was greater to Gast(Red) (264 ± 13 and 195 ± 9 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) and lower to Gast(White) (78 ± 5 and 120 ± 6 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) than in the old Sed group. There was no difference in the number of feed arteries between the old ET and old Sed group, although the CSA of feed arteries from old ET rats was larger. In young ET rats, there was an increase in the number of feed arteries perforating the muscle. Exercise training mitigated old age-associated differences in blood flow during exercise within gastrocnemius muscle. However, training-induced adaptations in resistance artery morphology differed between young (increase in feed artery number) and old (increase in artery CSA) animals. The altered blood flow pattern induced by exercise training with old age would improve the local matching of O(2) delivery to consumption within the skeletal muscle.

Effects of aging, TNF-α, and exercise training on angiotensin II-induced vasoconstriction of rat skeletal muscle arterioles

Skeletal muscle vascular resistance during physical exertion is higher with old age. The purpose of this study was to determine whether 1) aging enhances angiotensin II (ANG II)-induced vasoconstriction; 2) the proinflammatory cytokine tumor necrosis factor (TNF)-α contributes to alterations in ANG II-mediated vasoconstriction with aging; 3) exercise training attenuates putative age-associated increases in ANG II-mediated vasoconstriction; and 4) the mechanism(s) through which aging and exercise training alters ANG II-induced vasoconstriction in skeletal muscle arterioles. Male Fischer 344 rats were assigned to four groups: young sedentary (4 mo), old sedentary (24 mo), young trained, and old trained. In a separate group of young sedentary and old sedentary animals, a TNF type 1 receptor inhibitor was administered subcutaneously for 10 wk. First-order arterioles were isolated from soleus and gastrocnemius muscles for in vitro experimentation. Old age augmented ANG II-induced vasoconstriction in both soleus (young: 27 ± 3%; old: 38 ± 4%) and gastrocnemius (young: 42 ± 6%; old: 64 ± 9%) muscle arterioles; this augmented vasoconstriction was abolished with the removal of the endothelium, N(G)-nitro-l-arginine methyl ester, and chronic inhibition of TNF-α. In addition, exercise training ameliorated the age-induced increase in ANG II vasoconstriction. These findings demonstrate that old age enhances and exercise training diminishes ANG II-induced vasoconstrictor responses in skeletal muscle arterioles through an endothelium-dependent nitric oxide synthase signaling pathway. In addition, the enhancement of ANG II vasoconstriction with old age appears to be related to a proinflammatory state.

Effects of priming exercise on the speed of adjustment of muscle oxidative metabolism at the onset of moderate-intensity step transitions in older adults

Aging is associated with a functional decline of the oxidative metabolism due to progressive limitations of both O2 delivery and utilization. Priming exercise (PE) increases the speed of adjustment of oxidative metabolism during successive moderate-intensity transitions. We tested the hypothesis that such improvement is due to a better matching of O2 delivery to utilization within the working muscles. In 21 healthy older adults (65.7 ± 5 yr), we measured contemporaneously noninvasive indexes of the overall speed of adjustment of the oxidative metabolism (i.e., pulmonary V̇o2 kinetics), of the bulk O2 delivery (i.e., cardiac output), and of the rate of muscle deoxygenation (i.e., deoxygenated hemoglobin, HHb) during moderate-intensity step transitions, either with (ModB) or without (ModA) prior PE. The local matching of O2 delivery to utilization was evaluated by the ΔHHb/ΔV̇o2 ratio index. The overall speed of adjustment of the V̇o2 kinetics was significantly increased in ModB compared with ModA ( P < 0.05). On the contrary, the kinetics of cardiac output was unaffected by PE. At the muscle level, ModB was associated with a significant reduction of the “overshoot” in the ΔHHb/ΔV̇o2 ratio compared with ModA ( P < 0.05), suggesting an improved O2 delivery. Our data are compatible with the hypothesis that, in older adults, PE, prior to moderate-intensity exercise, beneficially affects the speed of adjustment of oxidative metabolism due to an acute improvement of the local matching of O2 delivery to utilization.

The effect of aging on adrenergic and nonadrenergic receptor expression and responsiveness in canine skeletal muscle

We tested the hypothesis that adrenergic and nonadrenergic receptor responsiveness and protein expression would be altered with advancing age. Young (n = 6; 22 ± 1 mo; mean ± SE) and old (n = 6; 118 ± 9 mo) beagles were instrumented with flow probes and an indwelling catheter for continuous measurement of external iliac blood flow and arterial blood pressure. Vascular conductance (VC) was calculated as hindlimb blood flow/mean arterial pressure. Selective agonists for α-1, α-2, neuropeptide-Y (NPY), and purinergic (P2X) receptors were infused at rest and during treadmill running at moderate (2.5 mph) and heavy (4 mph with 2.5% grade) exercise intensities. Feed arteries were dissected from gracilis muscles, and α-1D, α-1B, α-2A, P2X-4, P2X-1, and NPY-Y1 receptor protein expression was determined. Phenylephrine produced similar decreases (P > 0.05) in VC in young and old beagles at rest (young: -62 ± 5%; old: -59 ± 5%) and during moderate (young: -67 ± 5%; old: -62 ± 4%) and heavy (young: -54 ± 4%; old: -49 ± 3%) exercise. Clonidine caused similar (P > 0.05) decreases in VC in old compared with young dogs at rest (young: -59 ± 8%; old: -70 ± 6%) and during moderate (young: -52 ± 6%; old: -47 ± 5%)- and heavy (young: -42 ± 5%; old: -43 ± 5%)-intensity exercise. NPY infusion resulted in a similar decline in VC in young and old beagles at rest (young: -40 ± 7%; old: -39 ± 9%) and during moderate (young: -47 ± 6%; old: -40 ± 6%)- and heavy (young: -40 ± 3%; old: -38 ± 4%)-intensity exercise. α-β-Methylene-ATP also produced similar decreases in VC in young and old beagles at rest (young: -36 ± 6%; old: -40 ± 8%) and during exercise at moderate (young: -42 ± 5%; old: -40 ± 9%) and heavy (young: -47 ± 5%; old: -42 ± 8%) intensities. α-1B receptor protein expression was elevated (P < 0.05) in old compared with young dogs, whereas there were no age-related differences in α-1D or α-2A receptor expression and nonadrenergic P2X-4, P2X-1, and NPY-Y1 receptor expression. The present findings indicate that postsynaptic adrenergic and nonadrenergic receptor responsiveness was not altered by advancing age. Moreover, the expression of adrenergic and nonadrenergic receptors in skeletal-muscle feed arteries was largely unaffected by aging.

Aging alters the contribution of nitric oxide to regional muscle hemodynamic control at rest and during exercise in rats

Advanced age is associated with altered skeletal muscle hemodynamic control during the transition from rest to exercise. This study investigated the effects of aging on the functional role of nitric oxide (NO) in regulating total, inter-, and intramuscular hindlimb hemodynamic control at rest and during submaximal whole body exercise. We tested the hypothesis that NO synthase inhibition (N(G)-nitro-l-arginine methyl ester, l-NAME; 10 mg/kg) would result in attenuated reductions in vascular conductance (VC) primarily in oxidative muscles in old compared with young rats. Total and regional hindlimb muscle VCs were determined via radiolabeled microspheres at rest and during treadmill running (20 m/min, 5% grade) in nine young (6-8 mo) and seven old (27-29 mo) male Fisher 344 × Brown Norway rats. At rest, l-NAME increased mean arterial pressure (MAP) significantly by ∼17% and 21% in young and old rats, respectively. During exercise, l-NAME increased MAP significantly by ∼13% and 19% in young and old rats, respectively. Compared with young rats, l-NAME administration in old rats evoked attenuated reductions in 1) total hindlimb VC during exercise (i.e., down by ∼23% in old vs. 43% in young rats; P < 0.05), and 2) VC in predominantly oxidative muscles both at rest and during exercise (P < 0.05). Our results indicate that the dependency of highly oxidative muscles on NO-mediated vasodilation is markedly diminished, and therefore mechanisms other than NO-mediated vasodilation control the bulk of the increase in skeletal muscle VC during the transition from rest to exercise in old rats. Reduced NO contribution to vasomotor control with advanced age is associated with blood flow redistribution from highly oxidative to glycolytic muscles during exercise.

Gender differences affect blood flow recovery in a mouse model of hindlimb ischemia

Blood flow restoration to ischemic tissue is affected by various risk factors. The aim of this study was to examine gender effects on arteriogenesis and angiogenesis in a mouse ischemic hindlimb model. C57BL/6J mice were subjected to unilateral hindlimb ischemia. Flow recovery was less and hindlimb use impairment was greater in females. No gender difference in vessel number was found at baseline, although 7 days postsurgery females had fewer α-smooth muscle actin-positive vessels in the midpoint of the adductor region. Females had higher hindlimb vascular resistance, were less responsive to vasodilators, and were more sensitive to vasoconstrictors postligation. Western blotting showed that females had higher baseline levels of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) in the calf, while 7 days postligation males had higher levels of VEGF, eNOS, and phosphorylated vasodilator stimulated phosphoprotein. Females had less angiogenesis in a Matrigel plug assay and less endothelial cell proliferation in vitro. Females have impaired recovery of flow, a finding presumably caused by multiple factors including decreased collateral remodeling, less angiogenesis, impaired vasodilator response, and increased vasoconstrictor activity; our results also suggest the possibility that new collateral formation, from capillaries, is impaired in females.

Arterial stiffening with ageing is associated with transforming growth factor-β1-related changes in adventitial collagen: reversal by aerobic exercise

We tested the hypothesis that carotid artery stiffening with ageing is associated with transforming growth factor-β1 (TGF-β1)-related increases in adventitial collagen and reductions in medial elastin, which would be reversed by voluntary aerobic exercise. Ex vivo carotid artery incremental stiffness was greater in old (29–32 months, n = 11) vs. young (4–7 months, n = 8) cage control B6D2F1 mice (8.84 ± 1.80 vs. 4.54 ± 1.18 AU, P < 0.05), and was associated with selective increases in collagen I and III and TGF-β1 protein expression in the adventitia (P < 0.05), related to an increase in smooth muscle α-actin (SMαA) (myofibroblast phenotype) (P < 0.05). In cultured adventitial fibroblasts, TGF-β1 induced increases in superoxide and collagen I protein (P < 0.05), which were inhibited by Tempol, a superoxide dismutase. Medial elastin was reduced with ageing, accompanied by decreases in the pro-synthetic elastin enzyme, lysyl oxidase, and increases in the elastin-degrading enzyme, matrix metalloproteinase 2. Fibronectin was unchanged with ageing, but there was a small increase in calcification (P < 0.05). Increased incremental stiffness in old mice was completely reversed (3.98 ± 0.34 AU, n = 5) by 10–14 weeks of modest voluntary wheel running (1.13 ± 0.29 km day−1), whereas greater voluntary wheel running (10.62 ± 0.49 km day−1) had no effect on young mice. The amelioration of carotid artery stiffness by wheel running in old mice was associated with reductions in collagen I and III and TGF-β1, partial reversal of the myofibroblast phenotype (reduced SMαA) and reduced calcification (all P < 0.05 vs. old controls), whereas elastin and its modulating enzymes were unaffected. Adventitial TGF-β1-related oxidative stress may play a key role in collagen deposition and large elastic artery stiffening with ageing and the efficacious effects of voluntary aerobic exercise.

Aldose reductase and AGE-RAGE pathways: central roles in the pathogenesis of vascular dysfunction in aging rats

Aging is inevitably accompanied by gradual and irreversible innate endothelial dysfunction. In this study, we tested the hypothesis that accentuation of glucose metabolism via the aldose reductase (AR) pathway contributes to age-related vascular dysfunction. AR protein and activity levels were significantly increased in aged vs. young aortic homogenates from Fischer 344 rats. Immunostaining revealed that the principal site of increased AR protein was the aortic endothelium as well as smooth muscle cells. Studies revealed that endothelial-dependent relaxation (EDR) in response to acetylcholine was impaired in aged rats compared to young rats and that treatment with the AR inhibitor (ARI) zopolrestat significantly improved EDR in aged rats. Methylglyoxal (MG), a key precursor of advanced glycation endproducts (AGEs), was significantly increased in the aortas of aged rats vs. young rats. Consistent with central roles for AR in generation of MG in aging, ARI treatment significantly reduced MG levels in aged rat aorta to those in young rats. Treatment of aged rats with soluble(s) RAGE, a soluble form of the chief signal transduction receptor for AGEs, RAGE, significantly improved EDR in aged rats, thus establishing the contribution of age-related increases in AGEs to endothelial dysfunction. These findings reveal that significant increases in AR expression and activity in aged rat vasculature linked to endothelial dysfunction may be mitigated, at least in part, via ARI and that aging-linked increased flux via AR generates AGEs; species which transduce endothelial injury consequent to their interaction with RAGE. These data demonstrate for the first time that AR mediates aging-related vascular dysfunction, at least in part, via RAGE.