Acute sympathetic activation blunts the hyperemic and vasodilatory response to passive leg movement

Heightened muscle sympathetic nerve activity (MSNA) contributes to impaired vasodilatory capacity and vascular dysfunction associated with aging and cardiovascular disease. The contribution of elevated MSNA to the vasodilatory response during passive leg movement (PLM) has not been adequately addressed. This study sought to test the hypothesis that elevated MSNA diminishes the vasodilatory response to PLM in healthy young males (n = 11, 25 ± 2 year). Post exercise circulatory occlusion (PECO) following 2 min of isometric handgrip (HG) exercise performed at 25% (ExPECO 25%) and 40% (ExPECO 40%) of maximum voluntary contraction was used to incrementally engage the metaboreceptors and augment MSNA. Control trials were performed without PECO (ExCON 25% and ExCON 40%) to account for changes due to HG exercise. PLM was performed 2 min after the cessation of exercise and central and peripheral hemodynamics were assessed. MSNA was directly recorded by microneurography in the peroneal nerve (n = 8). Measures of MSNA (i.e., burst incidences) increased during ExPECO 25% (+ 15 ± 5 burst/100 bpm) and ExPECO 40% (+ 22 ± 4 burst/100 bpm) and returned to pre-HG levels during ExCON trials. Vasodilation, assessed by the change in leg vascular conductance during PLM, was reduced by 16% and 44% during ExPECO 25% and ExPECO 40%, respectively. These findings indicate that elevated MSNA attenuates the vasodilatory response to PLM and that the magnitude of reduction in vasodilation during PLM is graded in relation to the degree of sympathoexcitation.

Obesity does not alter vascular function and handgrip exercise hemodynamics in middle-aged patients with hypertension

Lifestyle modification including exercise training is often the first line of defense in the treatment of obesity and hypertension (HTN), however, little is known regarding how these potentially compounding disease states impact vasodilatory and hemodynamic responses at baseline and exercise. Therefore, this study sought to compare the impact of obesity on vascular function and hemodynamics at baseline and during handgrip (HG) exercise among individuals with HTN. Non-obese (13M/7F, 56 ± 16 yr, 25 ± 4 kg/m2) and obese (17M/4F, 50 ± 7 yr, 35 ± 4 kg/m2) middle-aged individuals with HTN forwent antihypertensive medication use for ≥2 wk before assessment of vascular function by brachial artery flow-mediated dilation (FMD) and exercise hemodynamics during progressive HG exercise at 15-30-45% maximal voluntary contraction (MVC). FMD was not different between Non-Obese (4.1 ± 1.7%) and Obese (5.2 ± 1.9%, P = 0.11). Systolic blood pressure (SBP) was elevated by ∼15% during the supine baseline and during HG exercise in the obese group. The blood flow response to HG exercise at 30% and 45% MVC was ∼20% greater (P < 0.05) in the obese group but not different after normalizing for the higher, albeit, nonsignificant differences in workloads (MVC: obese: 24 ± 5 kg, non-obese: 21 ± 5 kg, P = 0.11). Vascular conductance and the brachial artery shear-induced vasodilatory response during HG were not different between groups (P > 0.05). Taken together, despite elevated SBP during HG exercise, obesity does not lead to additional impairments in vascular function and peripheral exercising hemodynamics in patients with HTN. Obesity may not be a contraindication when prescribing exercise for the treatment of HTN among middle-aged adults, however, the elevated SBP should be appropriately monitored.NEW & NOTEWORTHY This study examined vascular function and handgrip exercise hemodynamics in obese and nonobese individuals with hypertension. Obesity, when combined with hypertension, was neither associated with additional vascular function impairments at baseline nor peripheral hemodynamics and vasodilation during exercise compared with nonobese hypertension. Interestingly, systolic blood pressure and pulse pressure were greater in the obese group during supine baseline and exercise. These findings should not be ignored and may be particularly important for rehabilitation strategies.

Patient-reported outcomes measurement information system physical function and knee injury and osteoarthritis outcome score relationship on performance measures in people undergoing total knee arthroplasty

PURPOSE

Primary purpose was to identify relationships between performance-based measures onto both computerized adaptive testing [Physical Function-Computer Adaptive Testing (PF-CAT)] and joint-specific legacy [Knee injury and Osteoarthritis Outcome Score-Activities of Daily Living (KOOS-ADL)] instruments pre- and 12-month post-TKA.

METHODS

The PF-CAT and KOOS-ADL were identified as outcomes and performance on the 40-m fast-paced walking test, stair climb test and chair stand test were identified as predictors. Linear regression was used for all comparisons after adjusting for confounders.

RESULTS

Sixty-eight people with TKA (56.7% male) were tested. Better scores on the 40-m fast-paced walking (KOOS-ADL, p = 0.02), stair climb (KOOS-ADL, p = 0.05) and chair stand (KOOS-ADL, p < 0.01) associated with better self-reported scores pre-TKA. Better scores on the 40-m fast-paced walking (PF-CAT, p = 0.05; KOOS-ADL, p = 0.01), stair climb (KOOS-ADL, p < 0.01), chair stand (PF-CAT, p < 0.01) and range of motion (KOOS-ADL, p = 0.02) were associated with better self-reported scores 12-month post-TKA. Decrease knee range of motion related to poorer 40-m fast-paced walking (p = 0.01) and stair climb (p = 0.03) scores pre-TKA. Quadriceps weakness related to poorer 40-m fast-paced walking (p = 0.04) score pre-TKA.

CONCLUSION

Self-reported instruments are a moderate, but inconsistent surrogate to performance-based measures pre- and post-TKA. Our findings indicate that both self-reported and performance-based measures are necessary to fully characterize physical function and should be used jointly to aid in the recovery analysis of people undergoing TKA.Implications for RehabilitationMonitoring the trajectory of pre- to post-total knee arthroplasty (TKA) physical function is important as it directly relates to mortality, morbidity and poorer quality of life in older adults.Both self-reported and performance-based measures of physical function are used to determine progress in recovery for patients pre- and post- TKA.This study provides evidence that perceived physical function measures are a moderate, but an inconsistent, surrogate to objective physical function measures pre- and post-TKA.Joint specific deficits in knee range of motion and quadriceps strength were weakly associated with deficits in function measures pre-TKA, but no association was observed 12-month post-TKA.Our findings indicate that both self-reported and performance-based measures are necessary to fully characterize physical function and should be used jointly to aid in the complete recovery analysis of people undergoing TKA.

Cardiovascular responses to static handgrip exercise and postexercise ischemia in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is characterized by reduced ability to sustain physical activity that may be due partly to disease-related changes in autonomic function that contribute to dysregulated cardiovascular control during muscular contraction. Thus, we used a combination of static handgrip exercise (HG) and postexercise ischemia (PEI) to examine the pressor response to exercise and isolate the skeletal muscle metaboreflex, respectively. Mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), and total peripheral resistance (TPR) were assessed during 2-min of static HG at 30 and 40% of maximum voluntary contraction (MVC) and subsequent PEI in 16 patients with HFpEF and 17 healthy, similarly aged controls. Changes in MAP were lower in patients with HFpEF compared with controls during both 30%MVC (Δ11 ± 7 vs. Δ15 ± 8 mmHg) and 40%MVC (Δ19 ± 14 vs. Δ30 ± 8 mmHg), and a similar pattern of response was evident during PEI (30%MVC: Δ8 ± 5 vs. Δ12 ± 8 mmHg; 40%MVC: Δ13 ± 10 vs. Δ18 ± 9 mmHg) (group effect: P = 0.078 and P = 0.017 at 30% and 40% MVC, respectively). Changes in HR, CO, and TPR did not differ between groups during HG or PEI (P > 0.05). Taken together, these data suggest a reduced pressor response to static muscle contractions in patients with HFpEF compared with similarly aged controls that may be mediated partly by a blunted muscle metaboreflex. These findings support a disease-related dysregulation in neural cardiovascular control that may reduce an ability to sustain physical activity in HFpEF.NEW & NOTEWORTHY The current investigation has identified a diminution in the exercise-induced rise in arterial blood pressure (BP) that persisted during postexercise ischemia (PEI) in an intensity-dependent manner in patients with heart failure with preserved ejection fraction (HFpEF) compared with older, healthy controls. These findings suggest that the pressor response to exercise is reduced in patients with HFpEF, and this deficit may be mediated, in part, by a blunted muscle metaboreflex, highlighting the consequences of impaired neural cardiovascular control during exercise in this patient group.

Pharmacological modulation of adrenergic tone alters the vasodilatory response to passive leg movement in young but not in old adults

The age-related increase in α-adrenergic tone may contribute to decreased leg vascular conductance (LVC) both at rest and during exercise in the old. However, the effect on passive leg movement (PLM)-induced LVC, a measure of vascular function, which is markedly attenuated in this population, is unknown. Thus, in eight young (25 ± 5 yr) and seven old (65 ± 7 yr) subjects, this investigation examined the impact of systemic β-adrenergic blockade (propanalol, PROP) alone, and PROP combined with either α1-adrenergic stimulation (phenylephrine, PE) or α-adrenergic inhibition (phentolamine, PHEN), on PLM-induced vasodilation. LVC, calculated from femoral artery blood flow and pressure, was determined and PLM-induced Δ peak (LVCΔpeak) and total vasodilation (LVCAUC, area under curve) were documented. PROP decreased LVCΔpeak (PROP: 4.8 ± 1.8, Saline: 7.7 ± 2.7 mL·mmHg-1, P < 0.001) and LVCAUC (PROP: 1.1 ± 0.7, Saline: 2.4 ± 1.6 mL·mmHg-1, P = 0.002) in the young, but not in the old (LVCΔpeak, P = 0.931; LVCAUC, P = 0.999). PE reduced baseline LVC (PE: 1.6 ± 0.4, PROP: 2.3 ± 0.4 mL·min-1·mmHg-1, P < 0.01), LVCΔpeak (PE: 3.2 ± 1.3, PROP: 4.8 ± 1.8 mL·min-1·mmHg-1, P = 0.004), and LVCAUC (PE: 0.5 ± 0.4, PROP: 1.1 ± 0.7 mL·mmHg-1, P = 0.011) in the young, but not in the old (baseline LVC, P = 0.199; LVCΔpeak, P = 0.904; LVCAUC, P = 0.823). PHEN increased LVC at rest and throughout PLM in both groups (drug effect: P < 0.05), however LVCΔpeak was only improved in the young (PHEN: 6.4 ± 3.1, PROP: 4.4 ± 1.5 mL·min-1·mmHg-1, P = 0.004), and not in the old (P = 0.904). Furthermore, the magnitude of α-adrenergic modulation (PHEN - PE) of LVCΔpeak was greater in the young compared with the old (Young: 3.35 ± 2.32, Old: 0.40 ± 1.59 mL·min-1·mmHg-1, P = 0.019). Therefore, elevated α-adrenergic tone does not appear to contribute to the attenuated vascular function with age identified by PLM.NEW & NOTEWORTHY Stimulation of α1-adrenergic receptors eliminated age-related differences in passive leg movement (PLM) by decreasing PLM-induced vasodilation in the young. Systemic β-blockade attenuated the central hemodynamic component of the PLM response in young individuals. Inhibition of α-adrenergic receptors did not improve the PLM response in older individuals, though withdrawal of α-adrenergic modulation augmented baseline and maximal vasodilation in both groups. Accordingly, α-adrenergic signaling plays a role in modulating the PLM vasodilatory response in young but not in old adults, and elevated α-adrenergic tone does not appear to contribute to the attenuated vascular function with age identified by PLM.

Activating P2Y1 receptors improves function in arteries with repressed autophagy

AIM

The importance of endothelial cell (EC) autophagy to vascular homeostasis in the context of health and disease is evolving. Earlier, we reported that intact EC autophagy is requisite to maintain shear-stress-induced nitric oxide (NO) generation via glycolysis-dependent purinergic signalling to endothelial NO synthase (eNOS). Here, we illustrate the translational and functional significance of these findings.

METHODS AND RESULTS

First, we assessed translational relevance using older male humans and mice that exhibit blunted EC autophagy and impaired arterial function vs. adult controls. Active hyperaemia evoked by rhythmic handgrip exercise-elevated radial artery shear-rate similarly from baseline in adult and older subjects for 60 min. Compared with baseline, indexes of autophagy initiation, p-eNOSS1177 activation, and NO generation, occurred in radial artery ECs obtained from adult but not older volunteers. Regarding mice, indexes of autophagy and p-eNOSS1177 activation were robust in ECs from adult but not older animals that completed 60-min treadmill-running. Furthermore, 20 dyne • cm2 laminar shear stress × 45-min increased autophagic flux, glycolysis, ATP production, and p-eNOSS1177 in primary arterial ECs obtained from adult but not older mice. Concerning functional relevance, we next questioned whether the inability to initiate EC autophagy, glycolysis, and p-eNOSS1177in vitro precipitates arterial dysfunction ex vivo. Compromised intraluminal flow-mediated vasodilation displayed by arteries from older vs. adult mice was recapitulated in vessels from adult mice by (i) NO synthase inhibition; (ii) acute autophagy impairment using 3-methyladenine (3-MA); (iii) EC Atg3 depletion (iecAtg3KO mice); (iv) purinergic 2Y1-receptor (P2Y1-R) blockade; and (v) germline depletion of P2Y1-Rs. Importantly, P2Y1-R activation using 2-methylthio-ADP (2-Me-ADP) improved vasodilatory capacity in arteries from (i) adult mice treated with 3-MA; (ii) adult iecAtg3KO mice; and (iii) older animals with repressed EC autophagy.

CONCLUSIONS

Arterial dysfunction concurrent with pharmacological, genetic, and age-associated EC autophagy compromise is improved by activating P2Y1-Rs.

Impaired hemodynamic response to exercise in patients with peripheral artery disease: evidence of a link to inflammation and oxidative stress

An exaggerated mean arterial blood pressure (MAP) response to exercise in patients with peripheral artery disease (PAD), likely driven by inflammation and oxidative stress and, perhaps, required to achieve an adequate blood flow response, is well described. However, the blood flow response to exercise in patients with PAD actually remains equivocal. Therefore, eight patients with PAD and eight healthy controls completed 3 min of plantar flexion exercise at both an absolute work rate (WR) (2.7 W, to evaluate blood flow) and a relative intensity (40%WRmax, to evaluate MAP). The exercise-induced change in popliteal artery blood flow (BF, Ultrasound Doppler), MAP (Finapress), and vascular conductance (VC) were quantified. In addition, resting markers of inflammation and oxidative stress were measured in plasma and muscle biopsies. Exercise-induced ΔBF, assessed at 2.7 W, was lower in PAD compared with controls (PAD: 251 ± 150 vs. Controls: 545 ± 187 mL/min, P < 0.001), whereas ΔMAP, assessed at 40%WRmax, was greater for PAD (PAD: 23 ± 14 vs. Controls: 11 ± 6 mmHg, P = 0.028). The exercise-induced ΔVC was lower for PAD during both the absolute WR (PAD: 1.9 ± 1.6 vs. Controls: 4.7 ± 1.9 mL/min/mmHg) and relative intensity exercise (PAD: 1.9 ± 1.8 vs. Controls: 5.0 ± 2.2 mL/min/mmHg) trials (both, P < 0.01). Inflammatory and oxidative stress markers, including plasma interleukin-6 and muscle protein carbonyls, were elevated in PAD (both, P < 0.05), and significantly correlated with the hemodynamic changes during exercise (r = -0.57 to -0.78, P < 0.05). Thus, despite an exaggerated ΔMAP response, patients with PAD exhibit an impaired exercise-induced ΔBF and ΔVC, and both inflammation and oxidative stress likely play a role in this attenuated hemodynamic response.

Patient-reported outcomes measurement information system physical function and knee injury and osteoarthritis outcome score relationship on performance measures in people undergoing total knee arthroplasty

PURPOSE

Primary purpose was to identify relationships between performance-based measures onto both computerized adaptive testing [Physical Function-Computer Adaptive Testing (PF-CAT)] and joint-specific legacy [Knee injury and Osteoarthritis Outcome Score-Activities of Daily Living (KOOS-ADL)] instruments pre- and 12-month post-TKA.

METHODS

The PF-CAT and KOOS-ADL were identified as outcomes and performance on the 40-m fast-paced walking test, stair climb test and chair stand test were identified as predictors. Linear regression was used for all comparisons after adjusting for confounders.

RESULTS

Sixty-eight people with TKA (56.7% male) were tested. Better scores on the 40-m fast-paced walking (KOOS-ADL, p = 0.02), stair climb (KOOS-ADL, p = 0.05) and chair stand (KOOS-ADL, p < 0.01) associated with better self-reported scores pre-TKA. Better scores on the 40-m fast-paced walking (PF-CAT, p = 0.05; KOOS-ADL, p = 0.01), stair climb (KOOS-ADL, p < 0.01), chair stand (PF-CAT, p < 0.01) and range of motion (KOOS-ADL, p = 0.02) were associated with better self-reported scores 12-month post-TKA. Decrease knee range of motion related to poorer 40-m fast-paced walking (p = 0.01) and stair climb (p = 0.03) scores pre-TKA. Quadriceps weakness related to poorer 40-m fast-paced walking (p = 0.04) score pre-TKA.

CONCLUSION

Self-reported instruments are a moderate, but inconsistent surrogate to performance-based measures pre- and post-TKA. Our findings indicate that both self-reported and performance-based measures are necessary to fully characterize physical function and should be used jointly to aid in the recovery analysis of people undergoing TKA.Implications for RehabilitationMonitoring the trajectory of pre- to post-total knee arthroplasty (TKA) physical function is important as it directly relates to mortality, morbidity and poorer quality of life in older adults.Both self-reported and performance-based measures of physical function are used to determine progress in recovery for patients pre- and post- TKA.This study provides evidence that perceived physical function measures are a moderate, but an inconsistent, surrogate to objective physical function measures pre- and post-TKA.Joint specific deficits in knee range of motion and quadriceps strength were weakly associated with deficits in function measures pre-TKA, but no association was observed 12-month post-TKA.Our findings indicate that both self-reported and performance-based measures are necessary to fully characterize physical function and should be used jointly to aid in the complete recovery analysis of people undergoing TKA.

Dietary Nitrate Supplementation and Small Muscle Mass Exercise Hemodynamics in Patients with Essential Hypertension

Exaggerated blood pressure and diminished limb hemodynamics during exercise in patients with hypertension often are not resolved by antihypertensive medications. We hypothesized that, independent of antihypertensive medication status, dietary nitrate supplementation would increase limb blood flow, decrease mean arterial pressure (MAP), and increase limb vascular conductance during exercise in patients with hypertension. Patients with hypertension either abstained from (n=14, Off-Meds) or continued (n=12, On-Meds) antihypertensive medications. Within each group, patients consumed (cross-over design) nitrate-rich or nitrate-depleted (placebo) beetroot juice for 3-days before performing handgrip (HG) and knee-extensor exercise (KE). Blood flow and MAP were measured using Doppler ultrasound and an automated monitor, respectively. Dietary nitrate increased plasma-[nitrite] Off-Meds and On-Meds. There were no significant effects of dietary nitrate on blood flow, MAP, or vascular conductance during HG in Off-Meds or On-Meds. For KE, dietary nitrate decreased MAP (mean±SD across all three exercise intensities, 118±14 vs. 122±14 mmHg, p=0.024) and increased vascular conductance (26.2±6.1 vs. 24.7±7.0 ml/min/mmHg, p=0.024), but did not affect blood flow for Off-Meds, with no effects On-Meds. Dietary nitrate-induced changes in blood flow (r=-0.67, p<0.001), MAP (r=-0.43, p=0.009), and vascular conductance (r=-0.64, p<0.001) during KE, but only vascular conductance (r=-0.35, p=0.039) during HG, were significantly related to the magnitude of placebo values, with no differentiation between groups. Thus, the effects of dietary nitrate on limb hemodynamics and MAP during exercise in patients with hypertension are dependent on the values at baseline, independent of antihypertensive medication status, and dependent on whether exercise was performed by the forearm or quadriceps.

Short-term exposure to a clinical dose of metformin increases skeletal muscle mitochondrial H2O2 emission and production in healthy, older adults: A randomized controlled trial

BACKGROUND AND AIMS

Metformin is the most commonly prescribed medication to treat diabetes. Emerging evidence suggests that metformin could have off target effects that might help promote healthy muscle aging, but these effects have not been thoroughly studied in glucose tolerant older individuals. The purpose of this study was to investigate the short-term effects of metformin consumption on skeletal muscle mitochondrial bioenergetics in healthy older adults.

METHODS

We obtained muscle biopsy samples from 16 healthy older adults previously naïve to metformin and treated with metformin (METF; 3F, 5M), or placebo (CON; 3F, 5M), for two weeks using a randomized and blinded study design. Samples were analyzed using high-resolution respirometry, immunofluorescence, and immunoblotting to assess muscle mitochondrial bioenergetics, satellite cell (SC) content, and associated protein markers.

RESULTS

We found that metformin treatment did not alter maximal mitochondrial respiration rates in muscle compared to CON. In contrast, mitochondrial H2O2 emission and production were elevated in muscle samples from METF versus CON (METF emission: 2.59 ± 0.72 SE Fold, P = 0.04; METF production: 2.29 ± 0.53 SE Fold, P = 0.02). Furthermore, the change in H2O2 emission was positively correlated with the change in type 1 myofiber SC content and this was biased in METF participants (Pooled: R2 = 0.5816, P = 0.0006; METF: R2 = 0.674, P = 0.0125).

CONCLUSIONS

These findings suggest that acute exposure to metformin does not impact mitochondrial respiration in aged, glucose-tolerant muscle, but rather, influences mitochondrial-free radical and SC dynamics.

CLINICAL TRIAL REGISTRATION

NCT03107884, clinicaltrials.gov.

Persistent vascular dysfunction following an acute nonpharmacological reduction in blood pressure in hypertensive patients

BACKGROUND

Vascular dysfunction, an independent risk factor for cardiovascular disease, often persists in patients with hypertension, despite improvements in blood pressure control induced by antihypertensive medications.

METHODS

As some of these medications may directly affect vascular function, this study sought to comprehensively examine the impact of reducing blood pressure, by a nonpharmacological approach (5 days of sodium restriction), on vascular function in 22 hypertensive individuals (14 men/8 women, 50 ± 10 years). Following a 2-week withdrawal of antihypertensive medications, two 5-day dietary phases, liberal sodium (liberal sodium, 200 mmol/day) followed by restricted sodium (restricted sodium, 10 mmol/day), were completed. Resting blood pressure was assessed and vascular function, at both the conduit and microvascular levels, was evaluated by brachial artery flow-mediated dilation (FMD), reactive hyperemia, progressive handgrip exercise, and passive leg movement (PLM).

RESULTS

Despite a sodium restriction-induced fall in blood pressure (liberal sodium: 141 ± 14/85 ± 9; restricted sodium 124 ± 12/79 ± 9 mmHg, P < 0.01 for both SBP and DBP), FMD (liberal sodium: 4.6 ± 1.8%; restricted sodium: 5.1 ± 2.1%, P = 0.27), and reactive hyperemia (liberal sodium: 548 ± 201; restricted sodium: 615 ± 206 ml, P = 0.08) were not altered. Similarly, brachial artery vasodilation during handgrip exercise was not different between conditions (liberal sodium: Δ0.36 ± 0.19 mm; restricted sodium: Δ0.42 ± 0.18 mm, P = 0.16). Lastly, PLM-induced changes in peak blood flow (liberal sodium: 5.3 ± 2.5; restricted sodium: 5.8 ± 3.6 ml/min per mmHg, P = 0.30) and the total vasodilatory response [liberal sodium: 2 (0.9-2.5) vs. restricted sodium: 1.7 (1.1-2.6) ml/min per mmHg; P = 0.5] were also not different between conditions.

CONCLUSION

Thus vascular dysfunction, at both the conduit and microvascular levels, persists in patients with hypertension even when blood pressure is acutely reduced by a nonpharmacological approach.

Cardiovasomobility: an integrative understanding of how disuse impacts cardiovascular and skeletal muscle health

Cardiovasomobility is a novel concept that encompasses the integration of cardiovascular and skeletal muscle function in health and disease with critical modification by physical activity, or lack thereof. Compelling evidence indicates that physical activity improves health while a sedentary, or inactive, lifestyle accelerates cardiovascular and skeletal muscle dysfunction and hastens disease progression. Identifying causative factors for vascular and skeletal muscle dysfunction, especially in humans, has proven difficult due to the limitations associated with cross-sectional investigations. Therefore, experimental models of physical inactivity and disuse, which mimic hospitalization, injury, and illness, provide important insight into the mechanisms and consequences of vascular and skeletal muscle dysfunction. This review provides an overview of the experimental models of disuse and inactivity and focuses on the integrated responses of the vasculature and skeletal muscle in response to disuse/inactivity. The time course and magnitude of dysfunction evoked by various models of disuse/inactivity are discussed in detail, and evidence in support of the critical roles of mitochondrial function and oxidative stress are presented. Lastly, strategies aimed at preserving vascular and skeletal muscle dysfunction during disuse/inactivity are reviewed. Within the context of cardiovasomobility, experimental manipulation of physical activity provides valuable insight into the mechanisms responsible for vascular and skeletal muscle dysfunction that limit mobility, degrade quality of life, and hasten the onset of disease.

Acute high-intensity exercise and skeletal muscle mitochondrial respiratory function: role of metabolic perturbation

Recently it was documented that fatiguing, high-intensity exercise resulted in a significant attenuation in maximal skeletal muscle mitochondrial respiratory capacity, potentially due to the intramuscular metabolic perturbation elicited by such intense exercise. With the utilization of intrathecal fentanyl to attenuate afferent feedback from group III/IV muscle afferents, permitting increased muscle activation and greater intramuscular metabolic disturbance, this study aimed to better elucidate the role of metabolic perturbation on mitochondrial respiratory function. Eight young, healthy males performed high-intensity cycle exercise in control (CTRL) and fentanyl-treated (FENT) conditions. Liquid chromatography-mass spectrometry and high-resolution respirometry were used to assess metabolites and mitochondrial respiratory function, respectively, pre- and postexercise in muscle biopsies from the vastus lateralis. Compared with CTRL, FENT yielded a significantly greater exercise-induced metabolic perturbation (PCr: -67% vs. -82%, Pi: 353% vs. 534%, pH: -0.22 vs. -0.31, lactate: 820% vs. 1,160%). Somewhat surprisingly, despite this greater metabolic perturbation in FENT compared with CTRL, with the only exception of respiratory control ratio (RCR) (-3% and -36%) for which the impact of FENT was significantly greater, the degree of attenuated mitochondrial respiratory capacity postexercise was not different between CTRL and FENT, respectively, as assessed by maximal respiratory flux through complex I (-15% and -33%), complex II (-36% and -23%), complex I + II (-31% and -20%), and state 3_CI+CII control ratio (-24% and -39%). Although a basement effect cannot be ruled out, this failure of an augmented metabolic perturbation to extensively further attenuate mitochondrial function questions the direct role of high-intensity exercise-induced metabolite accumulation in this postexercise response.

Abstract MP26: Activating P2Y 1 Receptors Improves Function In Arteries With Repressed Autophagy

Objective: The importance of endothelial cell (EC) autophagy to vascular homeostasis is evolving. Earlier we reported that purinergic 2Y 1 receptor (P2Y 1 -R) activation rejuvenates shear-stress induced nitric oxide (NO) generation in bovine aortic endothelial cells that is otherwise compromised after pharmacological and genetic autophagy repression. Here we determined the translational and functional relevance of these findings.

Approach and Results: First we assessed translational relevance using older humans and mice that exhibit blunted EC autophagy at rest together with impaired arterial function vs. appropriate controls. Rhythmic handgrip exercise elevated radial artery shear rate similarly in adult and older males for 60-min. Compared to baseline, autophagy initiation, p-eNOS S1177 activation, and NO generation, occurred in radial artery ECs from adult but not older subjects.Regarding mice, indexes of autophagy and p-eNOS S1177 activation were robust in ECs from adult but not older mice in response to 60-min treadmill-running. Next we questioned whether an inability to initiate EC autophagy precipitates arterial dysfunction. Age-associated reductions in intraluminal flow-mediated vasodilation observed in older vs. adult mice were recapitulated in arteries from adult mice by : (i) NO synthase inhibition; (ii) autophagy impairment using 3-methyladenine (3-MA); (iii) EC Atg3 depletion (iecAtg3KO mice); (iv) P2Y 1 -R blockade; and (v) germline depletion of P2Y 1 -Rs. Importantly, P2Y 1 -R activation using 2-methylthio-ADP (2-Me-ADP) improved vasodilatory capacity in arteries from : (i) adult mice treated with 3-MA; (ii) adult iecAtg3KO mice; and (iii) older animals with repressed EC autophagy.

Conclusions: Arterial dysfunction concurrent with pharmacological, genetic, and age-associated EC autophagy compromise is improved by activating P2Y 1 -Rs.

Impact of presymptomatic COVID-19 on vascular and skeletal muscle function: a case study

The impact of COVID-19 has been largely described after symptom development. Although the SARS-CoV-2 virus elevates heart rate (HR) prior to symptom onset, whether this virus evokes other presymptomatic alterations is unknown. This case study details the presymptomatic impact of COVID-19 on vascular and skeletal muscle function in a young woman [24 yr, 173.5 cm, 89 kg, body mass index (BMI): 29.6 kg·m^-2]. Vascular and skeletal muscle function were assessed as part of a separate study with the first and second visits separated by 2 wk. On the evening following the second visit, the participant developed a fever and a rapid antigen test confirmed a positive COVID-19 diagnosis. Compared with the first visit, the participant presented with a markedly elevated HR (∼30 beats/min) and a lower mean blood pressure (∼8 mmHg) at the second visit. Vascular function measured by brachial artery flow-mediated dilation, reactive hyperemia, and passive leg movement were all noticeably attenuated (25%-65%) as was leg blood flow during knee extension exercise. Muscle strength was diminished as was ADP-stimulated respiration (30%), assessed in vitro, whereas there was a 25% increase in the apparent Km. Lastly, an elevation in IL-10 was observed prior to symptom onset. Notably, 2.5 mo after diagnosis symptoms of fatigue and cough were still present. Together, these findings provide unique insight into the physiological responses immediately prior to onset of COVID-19 symptoms; they suggest that SARS-CoV-2 negatively impacts vascular and skeletal muscle function prior to the onset of common symptoms and may set the stage for the widespread sequelae observed following COVID-19 diagnosis.NEW & NOTEWORTHY This unique case study details the impact of SARS-CoV-2 infection on vascular and skeletal muscle function in a young predominantly presymptomatic woman. Prior to COVID-19 diagnosis, substantial reductions in vascular, skeletal muscle, and mitochondrial function were observed along with an elevation in IL-10. This integrative case study indicates that the presymptomatic impact of COVID-19 is widespread and may help elucidate the acute and long-term sequelae of this disease.

The dynamic adjustment of mean arterial pressure during exercise: a potential tool for discerning cardiovascular health status

The regulation of mean arterial pressure (MAP) during exercise has important physiological and clinical implications. Kinetics analysis on numerous physiological variables following the transition from unloaded-to-loaded exercise has revealed important information regarding their control. Surprisingly, the dynamic response of MAP during this transition remains to be quantified. Therefore, ten healthy participants (5/5 M/F, 24 ± 3 yr) completed repeated transitions from unloaded to moderate- and heavy-intensity dynamic single-leg knee-extensor exercise to investigate the on-kinetics of MAP. Following the transition to loaded exercise, MAP increased in a first-order dynamic manner, subsequent to a time delay (moderate: 23 ± 10; heavy: 19 ± 9 s, P > 0.05) at a speed (τ, moderate: 59 ± 30; heavy: 66 ± 19 s, P > 0.05), which did not differ between intensities, but the MAP amplitude was doubled during heavy-intensity exercise (moderate: 12 ± 5; heavy: 24 ± 8 mmHg, P < 0.001). The reproducibility [coefficient of variation (CV)] during heavy intensity for unloaded baseline, amplitude, and mean response time, when assessed as individual transitions, was 7 ± 1%, 18 ± 2%, and 25 ± 4%, respectively. Averaging two transitions improved the CVs to 4 ± 1%, 8 ± 2%, and 13 ± 3%, respectively. Preliminary findings supporting the clinical relevance of evaluating MAP kinetics in middle-aged hypertensive (n = 5) and, age-matched, normotensive (n = 5) participants revealed an exaggerated MAP response in both older groups (P < 0.05), but the MAP response was slowed only for the patients with hypertension (P < 0.05). It is concluded that kinetics modeling of MAP is practical for heavy-intensity knee-extensor exercise and may provide insight into cardiovascular health and the effect of aging.NEW & NOTEWORTHY Kinetics analysis of physiological variables following workload transitions provides important information, but this has not been performed on mean arterial pressure (MAP), despite the clear clinical importance of this variable. This investigation reveals that kinetic modeling of MAP following unloaded-to-loaded knee-extensor exercise is practical and repeatable. Additional preliminary findings in hypertensive and, age-matched, normotensive subjects suggest that MAP kinetics may provide insight into cardiovascular health and the effect of aging.

Spinal cord injury and vascular function: evidence from diameter-matched vessels

The effect of a spinal cord injury (SCI) on vascular function has been clouded by both the physiological and mathematical bias of assessing vasodilation in arteries with differing diameters both above and below the lesion and when comparing with healthy, nondisabled controls (CTRL). Thus, we measured vascular function, with flow-mediated vasodilation (FMD), in 10 SCI and 10 CTRL with all arteries matched for diameter (≈0.5 cm): brachial artery (BA, arm, functional limb in both groups) and popliteal artery (PA, leg, disused limb in SCI, functional limb in CTRL). PA %FMD was significantly attenuated in SCI (5.6 ± 0.6%) compared with CTRL (8.4 ± 1.3%), with no difference in the BA (SCI: 8.6 ± 0.9%; CTRL: 8.7 ± 0.7%). However, unlike the arm, where muscle mass was preserved, the legs of the SCI were significantly smaller than CTRL (∼70%). Thus, reactive hyperemia (RH), which is heavily dependent on the volume of muscle occluded, in the PA was attenuated in the SCI (144 ± 22 mL) compared with CTRL (258 ± 16 mL) but not different in the BA. Consequently, shear rate was significantly diminished in the PA of the SCI, such that %FMD/shear rate (vascular responsiveness) was actually greater in the SCI (1.5 ± 0.1% · s^-1) than CTRL (1.2 ± 0.1% · s^-1). Of note, this was significantly greater than both their own BA (0.9 ± 0.1% · s^-1) and that of the CTRL (0.9 ± 0.1% · s^-1). Therefore, examining vessels of similar size, this study reveals normal vascular function above the lesion and vascular dysfunction below the lesion. However, below the lesion there was, actually, evidence of increased vascular responsiveness in this population.NEW & NOTEWORTHY This study examined the effect of a spinal cord injury (SCI) and subsequent limb disuse on vascular function, assessed by %FMD, in diameter-matched vessels above and below the lesion in subjects with SCI and controls. The results reveal normal vascular function above the lesion and vascular dysfunction below the lesion (%FMD). However, below the lesion there was, actually, evidence of increased vascular responsiveness (%FMD/shear rate) in this population.

Skeletal Muscle Mitochondrial Adaptations to Maximal Strength Training in Older Adults

Maximal strength training (MST) results in robust improvements in skeletal muscle force production, efficiency, and mass. However, the effects of MST on muscle mitochondria are still unknown. Accordingly, the purpose of this study was to examine, from the molecular level to whole-muscle, mitochondrial adaptations induced by 8 weeks of knee-extension MST in the quadriceps of 10 older adults using immunoblotting, spectrophotometry, high-resolution respirometry in permeabilized muscle fibers, in vivo 31P magnetic resonance spectroscopy (31P-MRS), and gas exchange. As anticipated, MST resulted in an increased isometric knee-extensor force from 133 ± 36 to 147 ± 49 Nm (p < .05) and quadriceps muscle volume from 1,410 ± 103 to 1,555 ± 455 cm3 (p < .05). Mitochondrial complex (I-V) protein abundance and citrate synthase activity were not significantly altered by MST. Assessed ex vivo, maximal ADP-stimulated respiration (state 3CI+CII, PRE: 23 ± 6 and POST: 14 ± 5 ρM·mg-1·s-1, p < .05), was decreased by MST, predominantly, as a result of a decline in complex I-linked respiration (p < .05). Additionally, state 3 free-fatty acid linked respiration was decreased following MST (PRE: 19 ± 5 and POST: 14 ± 3 ρM·mg-1·s-1, p < .05). Assessed in vivo, MST slowed the PCr recovery time constant (PRE: 49 ± 13 and POST: 57 ± 16 seconds, p < .05) and lowered, by ~20% (p = .055), the quadriceps peak rate of oxidative ATP synthesis, but did not significantly alter the oxidation of lipid. Although these, likely qualitative, mitochondrial adaptations are potentially negative in terms of skeletal muscle energetic capacity, they need to be considered in light of the many improvements in muscle function that MST affords older adults.

The role of the endothelium in the hyperemic response to passive leg movement: looking beyond nitric oxide

Passive leg movement (PLM) evokes a robust and predominantly nitric oxide (NO)-mediated increase in blood flow that declines with age and disease. Consequently, PLM is becoming increasingly accepted as a sensitive assessment of endothelium-mediated vascular function. However, a substantial PLM-induced hyperemic response is still evoked despite nitric oxide synthase (NOS) inhibition. Therefore, in nine young healthy men (25 ± 4 yr), this investigation aimed to determine whether the combination of two potent endothelium-dependent vasodilators, specifically prostaglandin (PG) and endothelium-derived hyperpolarizing factor (EDHF), account for the remaining hyperemic response to the two variants of PLM, PLM (60 movements) and single PLM (sPLM, 1 movement), when NOS is inhibited. The leg blood flow (LBF, Doppler ultrasound) response to PLM and sPLM following the intra-arterial infusion of N^G-monomethyl-l-arginine (l-NMMA), to inhibit NOS, was compared to the combined inhibition of NOS, cyclooxygenase (COX), and cytochrome P-450 (CYP450) by l-NMMA, ketorolac tromethamine (KET), and fluconazole (FLUC), respectively. NOS inhibition attenuated the overall LBF [area under the curve (LBF_AUC)] response to both PLM (control: 456 ± 194, l-NMMA: 168 ± 127 mL, P < 0.01) and sPLM (control: 185 ± 171, l-NMMA: 62 ± 31 mL, P = 0.03). The combined inhibition of NOS, COX, and CYP450 (i.e., l-NMMA+KET+FLUC) did not further attenuate the hyperemic responses to PLM (LBF_AUC: 271 ± 97 mL, P > 0.05) or sPLM (LBF_AUC: 72 ± 45 mL, P > 0.05). Therefore, PG and EDHF do not collectively contribute to the non-NOS-derived NO-mediated, endothelium-dependent hyperemic response to either PLM or sPLM in healthy young men. These findings add to the mounting evidence and understanding of the vasodilatory pathways assessed by the PLM and sPLM vascular function tests.NEW & NOTEWORTHY Passive leg movement (PLM) evokes a highly nitric oxide (NO)-mediated hyperemic response and may provide a novel evaluation of vascular function. The contributions of endothelium-dependent vasodilatory pathways, beyond NO and including prostaglandins and endothelium-derived hyperpolarizing factor, to the PLM-induced hyperemic response to PLM have not been evaluated. With intra-arterial drug infusion, the combined inhibition of nitric oxide synthase (NOS), cyclooxygenase, and cytochrome P-450 (CYP450) pathways did not further diminish the hyperemic response to PLM compared with NOS inhibition alone.

Nitric oxide synthase inhibition with N(G)-monomethyl-l-arginine: Determining the window of effect in the human vasculature

Nitric oxide synthase (NOS) inhibition with N(G)-monomethyl-l-arginine (L-NMMA) is often used to assess the role of NO in human cardiovascular function. However, the window of effect for L-NMMA on human vascular function is unknown, which is critical for designing and interpreting human-based studies. This study utilized the passive leg movement (PLM) assessment of vascular function, which is predominantly NO-mediated, in 7 young male subjects under control conditions, immediately following intra-arterial L-NMMA infusion (0.24 mg⋅dl^-1⋅min^-1), and at 45-60 and 90-105 min post L-NMMA infusion. The leg blood flow (LBF) and leg vascular conductance (LVC) responses to PLM, measured with Doppler ultrasound and expressed as the change from baseline to peak (ΔLBF_peak and ΔLVC_peak) and area under the curve (LBF_AUC and LVC_ACU), were assessed. PLM-induced robust control ΔLBF_peak (1135 ± 324 ml⋅min^-1) and ΔLVC_peak (10.7 ± 3.6 ml⋅min^-1⋅mmHg^-1) responses that were significantly attenuated (704 ± 196 ml⋅min^-1 and 6.7 ± 2 ml⋅min^-1⋅mmHg^-1) immediately following L-NMMA infusion. Likewise, control condition PLM ΔLBF_AUC (455 ± 202 ml) and ΔLVC_AUC (4.0 ± 1.4 ml⋅mmHg^-1) were significantly attenuated (141 ± 130 ml and 1.3 ± 1.2 ml⋅mmHg^-1) immediately following L-NMMA infusion. However, by 45-60 min post L-NMMA infusion all PLM variables were not significantly different from control, and this was still the case at 90-105 min post L-NMMA infusion. These findings reveal that the potent reduction in NO bioavailability afforded by NOS inhibition with L-NMMA has a window of effect of less than 45-60 min in the human vasculature. These data are particularly important for the commonly employed approach of pharmacologically inhibiting NOS with L-NMMA in the human vasculature.

Cardiovascular responses to rhythmic handgrip exercise in heart failure with preserved ejection fraction

Although the contribution of noncardiac complications to the pathophysiology of heart failure with preserved ejection fraction (HFpEF) have been increasingly recognized, disease-related changes in peripheral vascular control remain poorly understood. We utilized small muscle mass handgrip exercise to concomitantly evaluate exercising muscle blood flow and conduit vessel endothelium-dependent vasodilation in individuals with HFpEF (n = 25) compared with hypertensive controls (HTN) (n = 25). Heart rate (HR), stroke volume (SV), cardiac output (CO), mean arterial pressure (MAP), brachial artery blood velocity, and brachial artery diameter were assessed during progressive intermittent handgrip (HG) exercise [15-30-45% maximal voluntary contraction (MVC)]. Forearm blood flow (FBF) and vascular conductance (FVC) were determined to quantify the peripheral hemodynamic response to HG exercise, and changes in brachial artery diameter were evaluated to assess endothelium-dependent vasodilation. HR, SV, and CO were not different between groups across exercise intensities. However, although FBF was not different between groups at the lowest exercise intensity, FBF was significantly lower (20-40%) in individuals with HFpEF at the two higher exercise intensities (30% MVC: 229 ± 8 versus 274 ± 23 ml/min; 45% MVC: 283 ± 17 versus 399 ± 34 ml/min, HFpEF versus HTN). FVC was not different between groups at 15 and 30% MVC but was ∼20% lower in HFpEF at the highest exercise intensity. Brachial artery diameter increased across exercise intensities in both HFpEF and HTN, with no difference between groups. These findings demonstrate an attenuation in muscle blood flow during exercise in HFpEF in the absence of disease-related changes in central hemodynamics or endothelial function.NEW & NOTEWORTHY The current study identified, for the first time, an attenuation in exercising muscle blood flow during handgrip exercise in individuals with heart failure with preserved ejection fraction (HFpEF) compared with overweight individuals with hypertension, two of the most common comorbidities associated with HFpEF. These decrements in exercise hyperemia cannot be attributed to disease-related changes in central hemodynamics or endothelial function, providing additional evidence for disease-related vascular dysregulation, which may be a predominant contributor to exercise intolerance in individuals with HFpEF.

Effect of histamine-receptor antagonism on leg blood flow during exercise

Histamine mediates vasodilation during inflammatory and immune responses, as well as following endurance exercise. During exercise, intramuscular histamine concentration increases, and its production, appears related to exercise intensity and duration. However, whether histamine contributes to exercise hyperemia and promotes exercise blood flow in an intensity- or duration-dependent pattern is unknown. The purpose of this study was to compare leg blood flow across a range of exercise intensities, before and after prolonged exercise, with and without histamine-receptor antagonism. It was hypothesized that combined oral histamine H₁/H₂-receptor antagonism would decrease leg blood flow, and the effect would be greater at higher intensities and following prolonged exercise. Sixteen (7F, 9M) volunteers performed single-leg knee-extension exercise after consuming either placebo or combined histamine H₁/H₂-receptor antagonists (Blockade). Exercise consisted of two graded protocols at 20, 40, 60, and 80% of peak power, separated by 60 min of knee-extension exercise at 60% of peak power. Femoral artery blood flow was measured by ultrasonography. Femoral artery blood flow increased with exercise intensity up to 2,660 ± 97 mL/min at 80% of peak power during Placebo (P < 0.05). Blood flow was further elevated with Blockade to 2,836 ± 124 mL/min (P < 0.05) at 80% peak power (9.1 ± 4.8% higher than placebo). These patterns were not affected by prolonged exercise (P = 0.13). On average, femoral blood flow during prolonged exercise was 12.7 ± 2.8% higher with Blockade vs. Placebo (P < 0.05). Contrary to the hypothesis, these results suggest that histamine receptor antagonism during exercise, regardless of intensity or duration, increases leg blood flow measured by ultrasonography.NEW & NOTEWORTHY Leg blood flow during exercise was increased by taking antihistamines, which block the receptors for histamine, a molecule often associated with inflammatory and immune responses. The elevated blood flow occurred over exercise intensities ranging from 20 to 80% of peak capacity and during exercise of 60 min duration. These results suggest that exercise-induced elevations in histamine concentrations are involved in novel, poorly understood, and perhaps complex ways in the exercise response.

Passive leg movement in chronic obstructive pulmonary disease: evidence of locomotor muscle vascular dysfunction

Chronic obstructive pulmonary disease (COPD), characterized by pulmonary dysfunction, is now also recognized to be associated with free radical-mediated vascular dysfunction. However, as previous investigations have utilized the brachial artery flow-mediated dilation technique, whether such vascular dysfunction exists in the locomotor muscle of patients with COPD remains unclear. Therefore, in patients with COPD (n = 13, 66 ± 6 yr) and healthy age- and sex-matched control subjects (n = 12, 68 ± 6 yr), second-by-second measurements of leg blood flow (LBF) (ultrasound Doppler), mean arterial pressure (MAP) (Finapres), and leg vascular conductance (LVC) were recorded before and during both 2 min of continuous upright seated continuous-movement passive leg movement (PLM) and a single-movement PLM (sPLM). In response to PLM, both peak change in LBF (COPD 321 ± 54, Control 470 ± 55 ∆mL/min) and LVC (COPD 3.0 ± 0.5, Control 5.4 ± 0.5 ∆mL·min^-1·mmHg^-1) were significantly attenuated in patients with COPD compared with control subjects (P < 0.05). This attenuation in the patients with COPD was also evident in response to sPLM, with peak change in LBF tending to be lower (COPD 142 ± 26, Control 169 ± 14 ∆mL/min) and LVC being significantly lower (P < 0.05) in the patients than the control subjects (COPD 1.6 ± 0.4, Control 2.5 ± 0.3 ∆mL·min^-1·mmHg^-1). Therefore, utilizing both PLM and sPLM, this study provides evidence of locomotor muscle vascular dysfunction in patients with COPD, perhaps due to redox imbalance and reduced nitric oxide bioavailability, which is in agreement with an increased cardiovascular disease risk in this population. This locomotor muscle vascular dysfunction, in combination with the clearly dysfunctional lungs, may contribute to the exercise intolerance associated with COPD.NEW & NOTEWORTHY Utilizing both the single and continuous passive leg movement (PLM) models, which induce nitric oxide (NO)-dependent hyperemia, this study provides evidence of vascular dysfunction in the locomotor muscle of patients with chronic obstructive pulmonary disease (COPD), independent of central hemodynamics. This impaired hyperemia may be the result of an oxidant-mediated attenuation in NO bioavailability. In addition to clearly dysfunctional lungs, vascular dysfunction in locomotor muscle may contribute to the exercise intolerance associated with COPD and increased cardiovascular disease risk.

Assessment of resistance vessel function in human skeletal muscle: guidelines for experimental design, Doppler ultrasound, and pharmacology

The introduction of duplex Doppler ultrasound almost half a century ago signified a revolutionary advance in the ability to assess limb blood flow in humans. It is now widely used to assess blood flow under a variety of experimental conditions to study skeletal muscle resistance vessel function. Despite its pervasive adoption, there is substantial variability between studies in relation to experimental protocols, procedures for data analysis, and interpretation of findings. This guideline results from a collegial discussion among physiologists and pharmacologists, with the goal of providing general as well as specific recommendations regarding the conduct of human studies involving Doppler ultrasound-based measures of resistance vessel function in skeletal muscle. Indeed, the focus is on methods used to assess resistance vessel function and not upstream conduit artery function (i.e., macrovasculature), which has been expertly reviewed elsewhere. In particular, we address topics related to experimental design, data collection, and signal processing as well as review common procedures used to assess resistance vessel function, including postocclusive reactive hyperemia, passive limb movement, acute single limb exercise, and pharmacological interventions.

Salt restriction lowers blood pressure at rest and during exercise without altering peripheral hemodynamics in hypertensive individuals

Dietary salt restriction is a well-established approach to lower blood pressure and reduce cardiovascular disease risk in hypertensive individuals. However, little is currently known regarding the effects of salt restriction on central and peripheral hemodynamic responses to exercise in those with hypertension. Therefore, this study sought to determine the impact of salt restriction on the central and peripheral hemodynamic responses to static-intermittent handgrip (HG) and dynamic single-leg knee extension (KE) exercise in individuals with hypertension. Twenty-two subjects (14 men and 8 women, 51 ± 10 yr, 173 ± 11 cm, 99 ± 23 kg) forewent their antihypertensive medication use for at least 2 wk before embarking on a 5-day liberal salt (LS: 200 mmol/day) diet followed by a 5-day restricted salt (RS: 10 mmol/day) diet. Subjects were studied at rest and during static intermittent HG exercise at 15, 30, and 45% of maximal voluntary contraction and KE exercise at 40, 60, and 80% of maximum KE work rate. Salt restriction lowered resting systolic blood pressure (supine: -12 ± 12 mmHg, seated: -17 ± 12 mmHg) and diastolic blood pressure (supine: -3 ± 9 mmHg, seated: -5 ± 7 mmHg, P < 0.05). Despite an ~8 mmHg lower mean arterial blood pressure during both HG and KE exercise following salt restriction, neither central nor peripheral hemodynamics were altered. Therefore, salt restriction can lower blood pressure during exercise in subjects with hypertension, reducing the risk of cardiovascular events, without impacting central and peripheral hemodynamics during either arm or leg exercise.NEW & NOTEWORTHY This is the first study to examine the potential blood pressure-lowering benefit of a salt-restrictive diet in individuals with hypertension without any deleterious effects of exercising blood flow. While mean arterial pressure decreased by ~8 mmHg following salt restriction, these findings provide evidence for salt restriction to provide protective effects of reducing blood pressure without inhibiting central or peripheral hemodynamics required to sustain arm or leg exercise in subjects with hypertension.

The role of endothelin A receptors in peripheral vascular control at rest and during exercise in patients with hypertension

KEY POINTS

Exercise in patients with hypertension can be accompanied by an abnormal cardiovascular response that includes attenuated blood flow and an augmented pressor response. Endothelin-1, a very potent vasoconstrictor, is a key modulator of blood flow and pressure during in health and has been implicated as a potential cause of the dysfunction in hypertension. We assessed the role of endothelin-1, acting through endothelin A (ET_A ) receptors, in modulating the central and peripheral cardiovascular responses to exercise in patients with hypertension via local antagonism of these receptors during exercise. ET_A receptor antagonism markedly increased leg blood flow, vascular conductance, oxygen delivery, and oxygen consumption during exercise; interestingly, these changes occurred in the presence of reduced leg perfusion pressure, indicating that these augmentations were driven by changes in vascular resistance. These data indicate that ET_A receptor antagonism could be a viable therapeutic approach to improve blood flow during exercise in hypertension.

ABSTRACT

Patients with hypertension can exhibit impaired muscle blood flow and exaggerated increases in blood pressure during exercise. While endothelin (ET)-1 plays a role in regulating blood flow and pressure during exercise in health, little is known about the role of ET-1 in the cardiovascular response to exercise in hypertension. Therefore, eight volunteers diagnosed with hypertension were studied during exercise with either saline or BQ-123 (ET_A receptor antagonist) infusion following a 2-week withdrawal of anti-hypertensive medications. The common femoral artery and vein were catheterized for drug infusion, blood collection and blood pressure measurements, and leg blood flow was measured by Doppler ultrasound. Patients exercised at both absolute (0, 5, 10, 15 W) and relative (40, 60, 80% peak power) intensities. BQ-123 increased blood flow at rest (79 ± 87 ml/min; P = 0.03) and augmented the exercise-induced hyperaemia at most intensities (80% saline: Δ3818±1222 vs. BQ-123: Δ4812±1469 ml/min; P = 0.001). BQ-123 reduced leg MAP at rest (-8 ± 4 mmHg; P < 0.001) and lower intensities (0-10 W; P < 0.05). Systemic diastolic blood pressure was reduced (0 W, 40%; P < 0.05), but systemic MAP was defended by an increased cardiac output. The exercise pressor response (ΔMAP) did not differ between conditions (80% saline: 25 ± 10, BQ-123: 30 ± 7 mmHg; P = 0.17). Thus, ET-1, acting through the ET_A receptors, contributes to the control of blood pressure at rest and lower intensity exercise in these patients. Furthermore, the finding that ET-1 constrains the blood flow response to exercise suggests that ET_A receptor antagonism could be a therapeutic approach to improve blood flow during exercise in hypertension.

Physiological Impact and Clinical Relevance of Passive Exercise/Movement

Passive exercise/movement has a long history in both medicine and physiology. Early clinical applications of passive exercise/movement utilized pneumatic and direct limb compression to stimulate the vasculature and evoke changes in blood flow to avoid complications brought about by stasis and vascular disease. Over the last 50 years, passive exercise/movement has continued to progress and has provided physiologists with a reductionist approach to mechanistically examine the cardiorespiratory, hyperemic, and afferent responses to movement without the confounding influence of metabolism that accompanies active exercise. This review, in addition to providing an historical perspective, focuses on the recent advancements utilizing passive leg movement, and how the hyperemic response at the onset of this passive movement has evolved from a method to evaluate the central and peripheral regulation of blood flow during exercise to an innovative and promising tool to assess vascular function. As an assessment of vascular function, passive leg movement is relatively simple to perform and provides a nitric oxide-dependent evaluation of endothelial function across the lifespan that is sensitive to changes in activity/fitness and disease state (heart failure, peripheral artery disease, sepsis). The continual refinement and characterization of passive leg movement are aimed at improving our understanding of blood flow regulation and the development of a clinically ready approach to predict and monitor the progression of cardiovascular disease.

Influence of dietary inorganic nitrate on blood pressure and vascular function in hypertension: prospective implications for adjunctive treatment

Dietary inorganic nitrate (nitrate) is a promising adjunctive treatment to reduce blood pressure and improve vascular function in hypertension. However, it remains unknown if the efficacy of nitrate is dependent upon an elevated blood pressure or altered by medication in patients with hypertension. Therefore, blood pressure and vascular function, measured by passive leg movement (PLM) and flow-mediated dilation (FMD), were assessed following 3 days of placebo (nitrate-free beetroot juice) and nitrate (nitrate-rich beetroot juice) administration in 13 patients (age: 53 ± 12 yr) with hypertension taking antihypertensive medications (study 1) and in 14 patients (49 ± 13 yr) with hypertension not taking antihypertensive medications (study 2). In study 1, plasma nitrite concentration was greater for nitrate than placebo (341 ± 118 vs. 308 ± 123 nmol/L, P < 0.05), yet blood pressure and vascular function were unaltered. In study 2, plasma nitrite concentration was greater for nitrate than placebo (340 ± 102 vs. 295 ± 93 nmol/L, P < 0.01). Systolic (136 ± 16 vs. 141 ± 19 mmHg), diastolic (84 ± 13 vs. 88 ± 12 mmHg), and mean (101 ± 12 vs. 106 ± 13 mmHg) blood pressures were lower (P < 0.05), whereas the PLM change in leg vascular conductance (6.0 ± 3.0 vs. 5.1 ± 2.6 mL·min^-1·mmHg^-1) and FMD (6.1 ± 2.4% vs. 4.1 ± 2.7%) were greater (P < 0.05) for nitrate than placebo. The changes in systolic blood pressure (r = -0.60) and FMD (r = -0.48) induced by nitrate were inversely correlated (P < 0.05) to the respective baseline values obtained in the placebo condition. Thus, the efficacy of nitrate to improve blood pressure and vascular function in hypertension appears to be dependent on the degree of blood pressure elevation and vascular dysfunction and not antihypertensive medication status, per se.NEW & NOTEWORTHY Dietary nitrate (nitrate) is a promising intervention to improve blood pressure and vascular function in hypertension. We demonstrate that these beneficial effects of nitrate are inversely related to the baseline value in a continuous manner with no distinction between antihypertensive medication status. Thus, the efficacy of nitrate to improve blood pressure and vascular function in hypertension appears to be dependent on the degree of blood pressure elevation and vascular dysfunction and not antihypertensive mediation status.

Acute High-Intensity Exercise Impairs Skeletal Muscle Respiratory Capacity

PURPOSE

The effect of an acute bout of exercise, especially high-intensity exercise, on the function of mitochondrial respiratory complexes is not well understood, with potential implications for both the healthy population and patients undergoing exercise-based rehabilitation. Therefore, this study sought to comprehensively examine respiratory flux through the different complexes of the electron transport chain in skeletal muscle mitochondria before and immediately after high-intensity aerobic exercise.

METHODS

Muscle biopsies of the vastus lateralis were obtained at baseline and immediately after a 5-km time trial performed on a cycle ergometer. Mitochondrial respiratory flux through the complexes of the electron transport chain was measured in permeabilized skeletal muscle fibers by high-resolution respirometry.

RESULTS

Complex I + II state 3 (state 3CI + CII) respiration, a measure of oxidative phosphorylation capacity, was diminished immediately after the exercise (pre, 27 ± 3 ρm·mg·s; post, 17 ± 2 ρm·mg·s; P < 0.05). This decreased oxidative phosphorylation capacity was predominantly the consequence of attenuated complex II-driven state 3 (state 3CII) respiration (pre, 17 ± 1 ρm·mg·s; post, 9 ± 2 ρm·mg·s; P < 0.05). Although complex I-driven state 3 (3CI) respiration was also lower (pre, 20 ± 2 ρm·mg·s; post, 14 ± 4 ρm·mg·s), this did not reach statistical significance (P = 0.27). In contrast, citrate synthase activity, proton leak (state 2 respiration), and complex IV capacity were not significantly altered immediately after the exercise.

CONCLUSIONS

These findings reveal that acute high-intensity aerobic exercise significantly inhibits skeletal muscle state 3CII and oxidative phosphorylation capacity. This, likely transient, mitochondrial defect might amplify the exercise-induced development of fatigue and play an important role in initiating exercise-induced mitochondrial adaptations.

Strong Relationship Between Vascular Function in the Coronary and Brachial Arteries

Early detection of coronary artery dysfunction is of paramount cardiovascular clinical importance, but a noninvasive assessment is lacking. Indeed, the brachial artery flow-mediated dilation test only weakly correlated with acetylcholine-induced coronary artery function ( r=0.36). However, brachial artery flow-mediated dilation methodologies have, over time, substantially improved. This study sought to determine if updates to this technique have improved the relationship with coronary artery function and the noninvasive indication of coronary artery dysfunction. Coronary artery and brachial artery function were assessed in 28 patients referred for cardiac catheterization (61±11 years). Coronary artery function was determined by the change in artery diameter with a 1.82 μg/min intracoronary acetylcholine infusion. Based on the change in vessel diameter, patients were characterized as having dysfunctional coronary arteries (>5% vasoconstriction) or relatively functional coronary arteries (<5% vasoconstriction). Brachial artery function was determined by flow-mediated dilation, adhering to current guidelines. The acetylcholine-induced change in vessel diameter was smaller in patients with dysfunctional compared with relatively functional coronary arteries (-11.8±4.6% versus 5.8±9.8%, P<0.001). Consistent with this, brachial artery flow-mediated dilation was attenuated in patients with dysfunctional compared with relatively functional coronaries (2.9±1.9% versus 6.2±4.2%, P=0.007). Brachial artery flow-mediated dilation was strongly correlated with the acetylcholine-induced change in coronary artery diameter ( r=0.77, P<0.0001) and was a strong indicator of coronary artery dysfunction (receiver operator characteristic=78%). The current data support that updates to the brachial artery flow-mediated dilation technique have strengthened the relationship with coronary artery function, which may now provide a clinically meaningful indication of coronary artery dysfunction.

Delineating the age-related attenuation of vascular function: Evidence supporting the efficacy of the single passive leg movement as a screening tool

Continuous passive leg movement (PLM) is a promising clinical assessment of the age-related decline in peripheral vascular function. To further refine PLM, this study evaluated the efficacy of a single PLM (sPLM), a simplified variant of the more established continuous movement approach, to delineate between healthy young and old men based on vascular function. Twelve young (26 ± 5 yr) and 12 old (70 ± 7 yr) subjects underwent sPLM (a single passive flexion and extension of the knee joint through 90°), with leg blood flow (LBF, common femoral artery with Doppler ultrasound), blood pressure (finger photoplethysmography), and leg vascular conductance (LVC) assessed. A receiver operator characteristic curve analysis was used to determine an age-specific cut score, and a factor analysis was performed to assess covariance. Baseline LBF and LVC were not different between groups (P = 0.6). The high level of covariance and similar predictive value for all PLM-induced LBF and LVC responses indicates LBF, alone, can act as a surrogate variable in this paradigm. The peak sPLM-induced increase in LBF from baseline was attenuated in the old (Young: 717 ± 227, Old: 260 ± 97 ml/min, P < 0.001; cut score: 372 ml/min), as was the total LBF response (Young: 155 ± 67, Old: 26 ± 17 ml, P < 0.001; cut score: 58 ml). sPLM, a simplified version of PLM, exhibits the prerequisite qualities of a valid screening test for peripheral vascular dysfunction, as evidenced by an age-related attenuation in the peripheral hyperemic response and a clearly delineated age-specific cut score. NEW & NOTEWORTHY Single passive leg movement (sPLM) exhibits the prerequisite qualities of a valid screening test for peripheral vascular dysfunction. sPLM displayed an age-related reduction in the peripheral hemodynamic response for amplitude, duration, initial rate of change, and total change with clearly delineated age-specific cut scores. sPLM has a strong candidate variable that is a simple single numeric value, for which to appraise peripheral vascular function, the 45-s hyperemic response (leg blood flow area under the curve: 45 s).

α-Adrenergic receptor regulation of skeletal muscle blood flow during exercise in heart failure patients with reduced ejection fraction

Patients suffering from heart failure with reduced ejection fraction (HFrEF) experience impaired limb blood flow during exercise, which may be due to a disease-related increase in α-adrenergic receptor vasoconstriction. Thus, in eight patients with HFrEF (63 ± 4 yr) and eight well-matched controls (63 ± 2 yr), we examined changes in leg blood flow (Doppler ultrasound) during intra-arterial infusion of phenylephrine (PE; an α₁-adrenergic receptor agonist) and phentolamine (Phen; a nonspecific α-adrenergic receptor antagonist) at rest and during dynamic single-leg knee-extensor exercise (0, 5, and 10 W). At rest, the PE-induced reduction in blood flow was significantly attenuated in patients with HFrEF (-15 ± 7%) compared with controls (-36 ± 5%). During exercise, the controls exhibited a blunted reduction in blood flow induced by PE (-12 ± 4, -10 ± 4, and -9 ± 2% at 0, 5, and 10 W, respectively) compared with rest, while the PE-induced change in blood flow was unchanged compared with rest in the HFrEF group (-8 ± 5, -10 ± 3, and -14 ± 3%, respectively). Phen administration increased leg blood flow to a greater extent in the HFrEF group at rest (+178 ± 34% vs. +114 ± 28%, HFrEF vs. control) and during exercise (36 ± 6, 37 ± 7, and 39 ± 6% vs. 13 ± 3, 14 ± 1, and 8 ± 3% at 0, 5, and 10 W, respectively, in HFrEF vs. control). Together, these findings imply that a HFrEF-related increase in α-adrenergic vasoconstriction restrains exercising skeletal muscle blood flow, potentially contributing to diminished exercise capacity in this population.

Elevated arterial shear rate increases indexes of endothelial cell autophagy and nitric oxide synthase activation in humans

Continuous laminar shear stress increases the process of autophagy, activates endothelial nitric oxide (NO) synthase phosphorylation at serine 1177 (p-eNOSS1177), and generates NO in bovine and human arterial endothelial cells (ECs) compared with static controls. However, the translational relevance of these findings has not been explored. In the current study, primary ECs were collected from the radial artery of 7 men using sterile J-wires before (Pre) and after (Post) 60 min of rhythmic handgrip exercise (HG) performed with the same arm. After ECs were identified by positive costaining for vascular endothelial cadherin and 4',6'-diamidino-2-phenylindole, immunofluorescent antibodies were used to assess indices of autophagy, NO generation, and superoxide anion (O2·-) production. Commercially available primary human arterial ECs were stained and processed in parallel to serve as controls. All end points were evaluated using 75 ECs from each subject. Relative to Pre-HG, HG elevated arterial shear rate ( P < 0.05) ~3-fold, whereas heart rate, arterial pressure, and cardiac output were not altered. Compared with values obtained from ECs Pre-HG, Post-HG ECs displayed increased ( P < 0.05) expression of p-eNOSS1177, NO generation, O2·- production, BECLIN1, microtubule-associated proteins 1A/1B light chain 3B, autophagy-related gene 3, and lysosomal-associated membrane protein 2A and decreased ( P < 0.05) expression (i.e., enhanced degradation) of the adaptor protein p62/sequestosome-1. These novel findings provide evidence that elevated arterial shear rate associated with functional hyperemia initiates autophagy, activates p-eNOSS1177, and increases NO and O2·- generation in primary human ECs. NEW & NOTEWORTHY Previously, our group reported in bovine arterial and human arterial endothelial cells (ECs) that shear stress initiates trafficking of the autophagosome to the lysosome and increases endothelial nitric oxide (NO) synthase phosphorylation at serine 1177, NO generation, and O2·- production. Here, the translational relevance of these findings is documented. Specifically, functional hyperemia induced by rhythmic handgrip exercise elevates arterial shear rate to an extent that increases indices of autophagy, NO generation, and O2·- production in primary arterial ECs collected from healthy men.

Impaired Muscle Efficiency but Preserved Peripheral Hemodynamics and Mitochondrial Function With Advancing Age: Evidence From Exercise in the Young, Old, and Oldest-Old

Muscle weakness in the elderly has been linked to recurrent falls and morbidity; therefore, elucidating the mechanisms contributing to the loss of muscle function and mobility with advancing age is critical. To this aim, we comprehensively examined skeletal muscle metabolic function and hemodynamics in 11 young (23 ± 2 years), 11 old (68 ± 2 years), and 10 oldest-old (84 ± 2 years) physical activity-matched participants. Specifically, oxidative stress markers, mitochondrial function, and the ATP cost of contraction as well as peripheral hemodynamics were assessed during dynamic plantar flexion exercise at 40 per cent of maximal work rate (WRmax). Both the PCr recovery time constant and the peak rate of mitochondrial ATP synthesis were not significantly different between groups. In contrast, the ATP cost of dynamic contractions (young: 1.5 ± 1.0, old: 3.4 ± 2.1, oldest-old: 6.1 ± 3.6 mM min-1 W-1) and systemic markers of oxidative stress were signficantly increased with age, with the ATP cost of contraction being negatively correlated with WRmax (r = .59, p < .05). End-of-exercise blood flow per Watt rose significantly with increasing age (young: 37 ± 20, old: 82 ± 68, oldest-old: 154 ± 93 mL min-1 W-1). These findings suggest that the progressive deterioration of muscle contractile efficiency with advancing age may play an important role in the decline in skeletal muscle functional capacity in the elderly.

Maximal strength training increases muscle force generating capacity and the anaerobic ATP synthesis flux without altering the cost of contraction in elderly

Aging is associated with a progressive decline in skeletal muscle function, then leading to impaired exercise tolerance. Maximal strength training (MST) appears to be a practical and effective intervention to increase both exercise capacity and efficiency. However, the underlying physiological mechanisms responsible for these functional improvements are still unclear. Accordingly, the purpose of this study was to examine the intramuscular and metabolic adaptations induced by 8 weeks of knee-extension MST in the quadriceps of 10 older individuals (75 ± 9 yrs) by employing a combination of molecular, magnetic resonance ¹H-imaging and ³¹P-spectroscopy, muscle biopsies, motor nerve stimulation, and indirect calorimetry techniques. Dynamic and isometric muscle strength were both significantly increased by MST. The greater torque-time integral during sustained isometric maximal contraction post-MST (P = 0.002) was associated with increased rates of ATP synthesis from anaerobic glycolysis (PRE: 10 ± 7 mM·min^-1; POST: 14 ± 7 mM·min^-1, P = 0.02) and creatine kinase reaction (PRE: 31 ± 10 mM·min^-1; POST: 41 ± 10 mM·min^-1, P = 0.006) such that the ATP cost of contraction was not significantly altered. Expression of fast myosin heavy chain, quadriceps muscle volume, and submaximal cycling net efficiency were also increased with MST (P = 0.005; P = 0.03 and P = 0.03, respectively). Overall, MST induced a shift toward a more glycolytic muscle phenotype allowing for greater muscle force production during sustained maximal contraction. Consequently, some of the MST-induced improvements in exercise tolerance might stem from a greater anaerobic capacity to generate ATP, while the improvement in exercise efficiency appears to be independent from an alteration in the ATP cost of contraction.

Oxygen availability and skeletal muscle oxidative capacity in patients with peripheral artery disease: implications from in vivo and in vitro assessments

Evidence suggests that the peak skeletal muscle mitochondrial ATP synthesis rate ( V_max) in patients with peripheral artery disease (PAD) may be attenuated due to disease-related impairments in O₂ supply. However, in vitro assessments suggest intrinsic deficits in mitochondrial respiration despite ample O₂ availability. To address this conundrum, Doppler ultrasound, near-infrared spectroscopy, phosphorus magnetic resonance spectroscopy, and high-resolution respirometry were combined to assess convective O₂ delivery, tissue oxygenation, V_max, and skeletal muscle mitochondrial capacity (complex I + II, state 3 respiration), respectively, in the gastrocnemius muscle of 10 patients with early stage PAD and 11 physical activity-matched healthy control (HC) subjects. All participants were studied in free-flow control conditions (FF) and with reactive hyperemia (RH) induced by a period of brief ischemia during the last 30 s of submaximal plantar flexion exercise. Patients with PAD repeated the FF and RH trials under hyperoxic conditions (FF + 100% O₂ and RH + 100% O₂). Compared with HC subjects, patients with PAD exhibited attenuated O₂ delivery at the same absolute work rate and attenuated tissue reoxygenation and V_max after relative intensity-matched exercise. Compared with the FF condition, only RH + 100% O₂ significantly increased convective O₂ delivery (~44%), tissue reoxygenation (~54%), and V_max (~60%) in patients with PAD ( P < 0.05), such that V_max was now not different from HC subjects. Furthermore, there was no evidence of an intrinsic mitochondrial deficit in PAD, as assessed in vitro with adequate O₂. Thus, in combination, this comprehensive in vivo and in vitro investigation implicates O₂ supply as the predominant factor limiting mitochondrial oxidative capacity in early stage PAD. NEW & NOTEWORTHY Currently, there is little accord as to the role of O₂ availability and mitochondrial function in the skeletal muscle dysfunction associated with peripheral artery disease. This is the first study to comprehensively use both in vivo and in vitro approaches to document that the skeletal muscle dysfunction associated with early stage peripheral artery disease is predominantly a consequence of limited O₂ supply and not the impact of an intrinsic mitochondrial defect in this pathology.

Increased skeletal muscle mitochondrial free radical production in peripheral arterial disease despite preserved mitochondrial respiratory capacity

NEW FINDINGS

What is the central question of this study? What is the degree to which skeletal muscle mitochondria-derived reactive oxygen species (ROS) production is linked to impaired skeletal muscle function in patients with early-stage peripheral arterial disease (PAD) and what is the impact on mitochondrial respiratory capacity? What is the main finding and its importance? This is the first study to document increased mitochondria-derived reactive oxygen species production associated with elevated intramuscular oxidative stress, despite preserved mitochondrial respiratory function, in patients with PAD. Furthermore, systemic inflammation, mitochondria-derived ROS production and skeletal muscle oxidative stress were strongly correlated to disease severity, as indicated by ankle-brachial index, in patients with PAD.

ABSTRACT

Skeletal muscle mitochondrial dysfunction, which is not fully explained by disease-related arterial occlusion, has been implicated in the pathophysiology of peripheral arterial disease (PAD). Therefore, this study comprehensively assessed mitochondrial respiratory function in biopsies from the gastrocnemius of 10 patients with PAD (Fontaine Stage II) and 12 healthy controls (HC). Intramuscular and systemic inflammation, mitochondria-derived reactive oxygen species (ROS) production, and oxidative stress were also assessed to better understand the mechanisms responsible for the proposed PAD-induced mitochondrial dysfunction. Interestingly, mitochondrial respiratory capacity, assessed as complex I (CI) and complex II (CII)-driven State 3 respiration, measured separately and in combination (State 3 CI+II), revealed no difference between the patients with PAD and the HC. However, mitochondria-derived ROS production was significantly elevated in PAD (HC: 1.0 ± 0.9; PAD: 4.3 ± 1.0 AU (mg tissue)^-1 ). Furthermore, patients with PAD exhibited significantly greater concentrations of the pro-inflammatory markers tumour necrosis factor α in plasma (HC: 0.9 ± 0.4; PAD: 2.0 ± 0.3 pg ml^-1 ) and interleukin 6 in both plasma (HC: 2.3 ± 0.4; PAD: 4.3 ± 0.5 pg ml^-1 ) and muscle (∼75% greater). Intramuscular oxidative stress, assessed by protein carbonyls and 4-hydroxynonenal, was significantly greater in PAD compared to HC. Ankle brachial index was significantly correlated with intramuscular inflammation, oxidative stress and mitochondria-derived ROS production. Thus, elevated intramuscular inflammation, oxidative stress and mitochondria-derived ROS production are likely to contribute to the pathophysiology of the skeletal muscle dysfunction associated with PAD, even in the presence of preserved mitochondrial respiratory function in this population.

Abstract 010: Similar Increases in Arterial Shear-rate Evoked by Handgrip Exercise Activate Autophagy and Enos to a Lesser Extent in Primary Endothelial Cells From Older vs. Adult Subjects

We reported that genetic or pharmacological suppression of autophagy in bovine and human arterial endothelial cells (ECs) prevents shear-stress induced p-eNOS S1177 and NO generation (Bharath et al., Arterioscler Thromb Vasc Biol , 2017). To date, one human study indicates an aging-associated repression of EC autophagy is concurrent with arterial dysfunction (LaRocca et al., J Physiol , 2012). We tested the hypothesis that a physiological elevation of arterial shear-rate activates autophagy and p-eNOS S1177 to a lesser extent in primary ECs from older vs. adult participants. After familiarization with laboratory procedures, flow-mediated vasodilation (%FMD) was observed to be lower (p<0.05) in 4 older (68±5 yr; 3.9±1.3 %) vs. 5 adult (23±3 yr; 7.9±1.1 %) male subjects. Within 1-week, a catheter was placed into the radial artery (RA). ECs were collected 30-min later via j-wire from the RA. Next, subjects performed rhythmic handgrip exercise (RHE) for 60-min that elevated (p<0.05) arterial shear-rate similarly (2.6 ± 0.2-fold) between groups from pre-exercise values. Shear-rate [8V mean /brachial artery (BA) diameter] was obtained by assessing BA diameter, BA blood flow velocity (V mean ), and BA blood flow [(V mean π (vessel diameter / 2) 2 x 60)] at 5-10 min intervals using Doppler ultrasound. Compared to pre-exercise values, RHE did not alter heart rate, stroke volume, cardiac output, or arterial pressure (plethysmography) in either group. Immediately following RHE ECs were collected from the RA. Using quantitative immunofluorescence, primary ECs (75 ECs per endpoint per subject) were identified by positive co-staining for VE-cadherin and DAPI via confocal microscopy. Immortalized human arterial ECs processed and stained in parallel served as fluorescence intensity controls. Relative to pre-exercise, ECs from adult but not old subjects at 60-min displayed increased expression of microtubule associated protein light chain 3 (p<0.04), lysosomal associated membrane protein 2a (p<0.01), autophagy-related gene 3 (p=0.06), and p-eNOS S1177 (p<0.02), and decreased expression of the adaptor protein p62 (p<0.02). These data indicate aging limits shear-induced EC autophagy and eNOS activation in response to functional hyperemia.