Evaluation of Autonomic Nervous System Dysfunction in Childhood Obesity and Prader-Willi Syndrome.

The autonomic nervous system (ANS) may play a role in the distribution of body fat and the development of obesity and its complications. Features of individuals with Prader-Willi syndrome (PWS) impacted by PWS molecular genetic classes suggest alterations in ANS function; however, these have been rarely studied and presented with conflicting results. The aim of this study was to investigate if the ANS function is altered in PWS. In this case-control study, we assessed ANS function in 20 subjects with PWS (6 males/14 females; median age 10.5 years) and 27 body mass index (BMI) z-score-matched controls (19 males/8 females; median age 12.8 years). Standardized non-invasive measures of cardiac baroreflex function, heart rate, blood pressure, heart rate variability, quantitative sudomotor axon reflex tests, and a symptom questionnaire were completed. The increase in heart rate in response to head-up tilt testing was blunted (p < 0.01) in PWS compared to controls. Besides a lower heart rate ratio with Valsalva in PWS (p < 0.01), no significant differences were observed in other measures of cardiac function or sweat production. Findings suggest possible altered sympathetic function in PWS.

Does sympathetic vasoconstriction contribute to metabolism: Perfusion matching in exercising skeletal muscle?

The process of matching skeletal muscle blood flow to metabolism is complex and multi-factorial. In response to exercise, increases in cardiac output, perfusion pressure and local vasodilation facilitate an intensity-dependent increase in muscle blood flow. Concomitantly, sympathetic nerve activity directed to both exercising and non-active muscles increases as a function of exercise intensity. Several studies have reported the presence of tonic sympathetic vasoconstriction in the vasculature of exercising muscle at the onset of exercise that persists through prolonged exercise bouts, though it is blunted in an exercise-intensity dependent manner (functional sympatholysis). The collective evidence has resulted in the current dogma that vasoactive molecules released from skeletal muscle, the vascular endothelium, and possibly red blood cells produce local vasodilation, while sympathetic vasoconstriction restrains vasodilation to direct blood flow to the most metabolically active muscles/fibers. Vascular smooth muscle is assumed to integrate a host of vasoactive signals resulting in a precise matching of muscle blood flow to metabolism. Unfortunately, a critical review of the available literature reveals that published studies have largely focused on bulk blood flow and existing experimental approaches with limited ability to reveal the matching of perfusion with metabolism, particularly between and within muscles. This paper will review our current understanding of the regulation of sympathetic vasoconstriction in contracting skeletal muscle and highlight areas where further investigation is necessary.

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 men and women. Blood pressure and MSNA appear to be lower in young women than in men. However, females experience a larger increase in MSNA with aging compared with males. The mechanism(s) underlying the altered SNS control of vascular function in females remains to be determined. Novelty: This review summarizes 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.

Effects of sex and exercise training on ß-adrenoreceptor-mediated opposition of evoked sympathetic vasoconstriction in resting and contracting muscle of rats.

This study investigated the hypothesis that ß-adrenoreceptor-mediated inhibition of sympathetic vasoconstriction would be enhanced in female compared with male rats, and that endurance exercise training would augment ß-adrenoreceptor-mediated inhibition of sympathetic vasoconstriction in male and female rats. Sprague-Dawley rats were randomized into sedentary (male: n = 7; female: n = 8) and exercise-trained (male: n = 9; female: n = 9) groups. Following 4 wk of exercise training or being sedentary, rats were anesthetized and surgically instrumented for stimulation of the lumbar sympathetic chain, muscle contraction and measurement of arterial blood pressure and femoral artery blood flow (FBF). Femoral vascular conductance (FVC) was calculated as FBF/mean arterial pressure. The percentage change of FVC in response to sympathetic stimulation delivered at 2 and 5 Hz was measured at rest and during contraction of the triceps surae muscles before and after ß-adrenoreceptor blockade (propranolol: 0.075 mg·kg-1 iv). We found that, at rest, ß-adrenoreceptor blockade decreased (main effect of drug, 2 Hz: P < 0.001; 5 Hz: P < 0.001) sympathetic vasoconstriction. During contraction, sympathetic vasoconstrictor responsiveness was lower (main effect of sex, 2 Hz: P = 0.001; 5 Hz: P = 0.023) in female compared with male rats, and sympatholysis was enhanced (main effect of sex, 2 Hz: P = 0.001; 5 Hz: P < 0.001) in female rats. ß-adrenoreceptor blockade decreased (main effect of drug, 2 Hz: P = 0.049; 5 Hz: P < 0.001) evoked sympathetic vasoconstriction in contracting muscle. The present study demonstrated that ß-adrenoreceptors do not blunt sympathetic vasoconstriction in resting or contracting skeletal muscle of male or female rats. Sympatholysis was enhanced in female rats; however, this was not attributable to ß-adrenoreceptor-mediated blunting of sympathetic vasoconstriction.NEW & NOTEWORTHY ß-adrenoreceptors do not inhibit sympathetic vasoconstriction in resting or contracting muscle of male or female rats, regardless of training status. Sympatholysis was enhanced in female, compared to male rats; however, ß-adrenoreceptors were not responsible for the enhanced sympatholysis. These findings indicate that ß-adrenoreceptors do not contribute to the regulation of sympathetic vasoconstriction in resting and contracting skeletal muscle and suggest that ß-adrenoreceptors do not underlie sex differences in the neural control of the circulation.

Effect of acute dietary nitrate supplementation on sympathetic vasoconstriction at rest and during exercise.

Dietary nitrate ( NO3- ) supplementation has been shown to reduce resting blood pressure. However, the mechanism responsible for the reduction in blood pressure has not been identified. Dietary NO3- supplementation may increase nitric oxide (NO) bioavailability, and NO has been shown to inhibit sympathetic vasoconstriction in resting and contracting skeletal muscle. Therefore, the purpose of this study was to investigate the hypothesis that acute dietary NO3- supplementation would attenuate sympathetic vasoconstrictor responsiveness at rest and during exercise. In a double-blind randomized crossover design, 12 men (23 ± 5 yr) performed a cold-pressor test (CPT) at rest and during moderate- and heavy-intensity alternate-leg knee-extension exercise after consumption of NO3- rich beetroot juice (~12.9 mmol NO3- ) or a NO3- -depleted placebo (~0.13 mmol NO3- ). Venous blood was sampled before and 2.5 h after the consumption of beetroot juice for the measurement of total plasma nitrite/ NO3- [NOx]. Beat-by-beat blood pressure was measured by Finometer. Leg blood flow was measured at the femoral artery via Doppler ultrasound, and leg vascular conductance (LVC) was calculated. Sympathetic vasoconstrictor responsiveness was calculated as the percentage decrease in LVC in response to the CPT. Total plasma [NOx] was greater (P < 0.001) in the NO3- (285 ± 120 µM) compared with the placebo (65 ± 30 µM) condition. However, mean arterial blood pressure and plasma catecholamines were not different (P > 0.05) between NO3- and placebo conditions at rest or during moderate- and heavy-intensity exercise. Sympathetic vasoconstrictor responsiveness (Δ% LVC) was not different (P > 0.05) between NO3- and placebo conditions at rest ( NO3- : -33 ± 10%; placebo: -35 ± 11%) or during moderate ( NO3- : -18 ± 8%; placebo: -20 ± 10%)- and heavy ( NO3- : -12 ± 8%; placebo: -11 ± 9%)-intensity exercise. These data demonstrate that acute dietary NO3- supplementation does not alter sympathetic vasoconstrictor responsiveness at rest or during exercise in young healthy males. NEW & NOTEWORTHY Dietary nitrate may increase nitric oxide bioavailability, and nitric oxide has been shown to attenuate sympathetic vasoconstriction in resting and contracting skeletal muscle and enhance functional sympatholysis. However, the effect of dietary nitrate on sympathetic vasoconstrictor responsiveness is unknown. Acute dietary nitrate supplementation did not alter blood pressure or sympathetic vasoconstrictor responsiveness at rest or during exercise in young healthy males.

ß-Adrenoreceptors do not oppose sympathetic vasoconstriction in resting and contracting skeletal muscle of male rats.

Sympathetic nervous system (SNS) vasoconstriction is primarily achieved through the binding of norepinephrine (NE) to α-adrenoreceptors. However, NE may also bind to ß-adrenoreceptors and cause vasodilation that may oppose/blunt SNS-mediated vasoconstriction. Therefore, this study investigated the hypothesis that ß-adrenoreceptor-mediated vasodilation opposes evoked vasoconstriction in resting and contracting skeletal muscle. Male (n = 9) Sprague-Dawley rats were anesthetized and surgically instrumented for stimulation of the lumbar sympathetic chain and measurement of arterial blood pressure and femoral artery blood flow. The percentage change of femoral vascular conductance in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae skeletal muscle contraction before (control) and after ß-adrenoreceptor blockade (propranolol; 0.075 mg·kg-1, intravenously). ß-Adrenoreceptor blockade did not alter (P > 0.05) baseline hemodynamics or the hyperemic response to exercise. At the 2 Hz stimulation frequency, sympathetic vasoconstriction was similar (P > 0.05) in control and ß-blockade conditions in resting (control, -34% ± 6%; ß-blockade, -33% ± 8%) and contracting (control, -16% ± 6%; ß-blockade, -14% ± 7%) muscle. At the 5 Hz stimulation frequency, sympathetic vasoconstrictor responsiveness was reduced (main effect of drug, P < 0.05) following ß-blockade (rest: control, -52% ± 7%; ß-blockade, -51% ± 9%; contraction: control, -32% ± 11%; ß-blockade, -29% ± 13%). Novelty These data indicate that ß-adrenoreceptor blockade did not augment sympathetic vasoconstriction at rest or during exercise. The study demonstrates that ß-adrenoreceptors do not oppose evoked sympathetic vasoconstriction in resting or contracting skeletal muscle or contribute to functional sympatholysis.

Effects of high-intensity interval training on fatigue and quality of life in testicular cancer survivors.

BACKGROUND: Testicular cancer survivors (TCS) are at increased risk of cancer-related fatigue (CRF), psychosocial impairment, and poor mental health-related quality of life (HRQoL). Here, we examine the effects of high-intensity interval training (HIIT) on patient-reported outcomes (PROs) in TCS. Secondarily, we explore cardiorespiratory fitness as a mediator of intervention effects and select baseline characteristics as moderators of intervention effects. METHODS: TCS (n = 63) were randomly assigned to 12 weeks of supervised HIIT or usual care (UC). PROs included CRF, depression, anxiety, stress, self-esteem, sleep quality, and HRQoL assessed at baseline, post-intervention, and 3-month follow-up. RESULTS: TCS (median 7 years postdiagnosis) completed 99% of training sessions and achieved 98% of target training intensity. ANCOVA revealed that, compared to UC, HIIT significantly improved post-intervention CRF (p = 0.003), self-esteem (p = 0.029), and multiple HRQoL domains (ps ≤ 0.05). Effects on CRF (p = 0.031) and vitality (p = 0.015) persisted at 3-month follow-up. Cardiorespiratory fitness changes mediated CRF and HRQoL improvements. CRF effects were larger for TCS with an inactive lifestyle, lower fitness, higher testosterone, and clinical fatigue at baseline. CONCLUSIONS: HIIT significantly improves CRF and HRQoL in TCS. Mediation by cardiorespiratory fitness and moderation by clinical characteristics suggests opportunities for targeted exercise interventions to optimise PROs in TCS.

Effects of high-intensity aerobic interval training on cardiovascular disease risk in testicular cancer survivors: A phase 2 randomized controlled trial.

BACKGROUND: Testicular cancer survivors (TCS) have an increased risk of treatment-related cardiovascular disease (CVD), which may limit their overall survival. We evaluated the effects of high-intensity aerobic interval training (HIIT) on traditional and novel CVD risk factors and surrogate markers of mortality in a population-based sample of TCS. METHODS: This phase 2 trial (ClinicalTrials.gov identifier NCT02459132) randomly assigned 63 TCS to usual care (UC) or 12 weeks of supervised HIIT (ie, alternating periods of vigorous-intensity and light-intensity aerobic exercise). The primary outcome was peak aerobic fitness (VO2peak ) assessed via a treadmill-based maximal cardiorespiratory exercise test. Secondary endpoints included CVD risk (eg, Framingham Risk Score), arterial health, parasympathetic nervous system function, and blood-based biomarkers. RESULTS: Postintervention VO2peak data were obtained for 61 participants (97%). HIIT participants attended 99% of the exercise sessions and achieved 98% of the target exercise intensity. Analysis of covariance demonstrated that HIIT was superior to UC for improving VO2peak (adjusted between-group mean difference, 3.7 mL O2 /kg/min; 95% confidence interval, 2.4-5.1 [P<.001]) and multiple secondary outcomes including CVD risk (P = .011), arterial thickness (P<.001), arterial stiffness (P<.001), postexercise parasympathetic reactivation (P = .001), inflammation (P = .045), and low-density lipoprotein (P = .014). Overall, HIIT reduced the prevalence of modifiable CVD risk factors by 20% compared with UC. CONCLUSIONS: This randomized trial provides the first evidence that HIIT improves cardiorespiratory fitness, multiple pathways of CVD risk, and surrogate markers of mortality in TCS. These findings have important implications for the management of TCS. Further research concerning the long-term effects of HIIT on CVD morbidity and mortality in TCS is warranted. Cancer 2017;123:4057-65. © 2017 American Cancer Society.

Sex differences in sympathetic vasoconstrictor responsiveness and sympatholysis.

Sex differences in the neurovascular control of blood pressure and vascular resistance have been reported. However, the mechanisms underlying the modulatory influence of sex have not been fully elucidated. Nitric oxide (NO) has been shown to inhibit sympathetic vasoconstriction in resting and contracting skeletal muscle, and estrogen modulates NO synthase (NOS) expression and NO bioavailability. Therefore NO-mediated inhibition of sympathetic vasoconstriction may be enhanced in females. Thus the purpose of the present study was to investigate the hypothesis that sympathetic vasoconstrictor responsiveness would be blunted and NO-mediated inhibition of sympathetic vasoconstriction would be enhanced in females compared with males. Male (M; n = 8) and female (F; n = 10) Sprague-Dawley rats were anesthetized and surgically instrumented for measurement of arterial blood pressure and femoral artery blood flow and stimulation of the lumbar sympathetic chain. The percentage change of femoral vascular conductance in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae muscle contraction before (control) and after NOS blockade [Nω-nitro-l-arginine methyl ester (l-NAME), 10 mg/kg iv]. At rest, sympathetic vasoconstrictor responsiveness was augmented (P < 0.05) in female compared with male rats at 2 Hz [F: -33 ± 8% (SD); M: -26 ± 6%] but was not different at 5 Hz (F: -55 ± 7%; M: -47 ± 7%). During muscle contraction, evoked vasoconstriction was similar (P > 0.05) in females and males at 2 Hz (F: -12 ± 5%; M: -13 ± 5%) but was blunted (P < 0.05) in females compared with males at 5 Hz (F: -24 ± 5%; M: -34 ± 8%). l-NAME increased (P < 0.05) sympathetic vasoconstrictor responsiveness in both groups at rest and during contraction. Contraction-mediated inhibition of vasoconstriction (sympatholysis) was enhanced (P < 0.05) in females compared with males; however, sympatholysis was not different (P > 0.05) between males and females in the presence of NOS blockade, indicating that NO-mediated sympatholysis was augmented in female rats. These data suggest that sex modulates sympathetic vascular control in resting and contracting skeletal muscle and that a portion of the enhanced sympatholysis in female rats was NO dependent.NEW & NOTEWORTHY Sex differences in the neurovascular regulation of blood pressure and vascular resistance have been documented. However, our understanding of the underlying mechanisms that mediate these differences is incomplete. The present study demonstrates that female rats have an enhanced capacity to inhibit sympathetic vasoconstriction during exercise (sympatholysis) and that NO mediates a portion of the enhanced sympatholysis.

Lack of correlation between cerebral vasomotor reactivity and dynamic cerebral autoregulation during stepwise increases in inspired CO2 concentration.

Cerebral vasomotor reactivity (CVMR) and dynamic cerebral autoregulation (CA) are measured extensively in clinical and research studies. However, the relationship between these measurements of cerebrovascular function is not well understood. In this study, we measured changes in cerebral blood flow velocity (CBFV) and arterial blood pressure (BP) in response to stepwise increases in inspired CO2 concentrations of 3 and 6% to assess CVMR and dynamic CA in 13 healthy young adults [2 women, 32 ± 9 (SD) yr]. CVMR was assessed as percentage changes in CBFV (CVMRCBFV) or cerebrovascular conductance index (CVCi, CVMRCVCi) in response to hypercapnia. Dynamic CA was estimated by performing transfer function analysis between spontaneous oscillations in BP and CBFV. Steady-state CBFV and CVCi both increased exponentially during hypercapnia; CVMRCBFV and CVMRCVCi were greater at 6% (3.85 ± 0.90 and 2.45 ± 0.79%/mmHg) than at 3% CO2 (2.09 ± 1.47 and 0.21 ± 1.56%/mmHg, P = 0.009 and 0.005, respectively). Furthermore, CVMRCBFV was greater than CVMRCVCi during either 3 or 6% CO2 (P = 0.017 and P < 0.001, respectively). Transfer function gain and coherence increased in the very low frequency range (0.02-0.07 Hz), and phase decreased in the low-frequency range (0.07-0.20 Hz) when breathing 6%, but not 3% CO2 There were no correlations between the measurements of CVMR and dynamic CA. These findings demonstrated influences of inspired CO2 concentrations on assessment of CVMR and dynamic CA. The lack of correlation between CVMR and dynamic CA suggests that cerebrovascular responses to changes in arterial CO2 and BP are mediated by distinct regulatory mechanisms.

Exercise training and α1-adrenoreceptor-mediated sympathetic vasoconstriction in resting and contracting skeletal muscle.

Exercise training (ET) increases sympathetic vasoconstrictor responsiveness and enhances contraction-mediated inhibition of sympathetic vasoconstriction (i.e., sympatholysis) through a nitric oxide (NO)-dependent mechanism. Changes in α2-adrenoreceptor vasoconstriction mediate a portion of these training adaptations, however the contribution of other postsynaptic receptors remains to be determined. Therefore, the purpose of this study was to investigate the effect of ET on α1-adrenoreceptor-mediated vasoconstriction in resting and contracting muscle. It was hypothesized that α1-adrenoreceptor-mediated sympatholysis would be enhanced following ET. Male Sprague Dawley rats were randomized to sedentary (S; n = 12) or heavy-intensity treadmill ET (n = 11) groups. Subsequently, rats were anesthetized and instrumented for lumbar sympathetic chain stimulation and measurement of femoral vascular conductance (FVC) at rest and during muscle contraction. The percentage change in FVC in response to sympathetic stimulation was measured in control, α1-adrenoreceptor blockade (Prazosin; 20 µg, IV), and combined α1 and NO synthase (NOS) blockade (l-NAME; 5 mg·kg(-1) IV) conditions. Sympathetic vasoconstrictor responsiveness was increased (P < 0.05) in ET compared to S rats at low, but not high (P > 0.05) stimulation frequencies at rest (S: 2 Hz: -25 ± 4%; 5 Hz: -45 ± 5 %; ET: 2 Hz: -35 ± 7%, 5 Hz: -52 ± 7%), whereas sympathetic vasoconstrictor responsiveness was not different (P > 0.05) between groups during contraction (S: 2 Hz: -11 ± 8%; 5 Hz: -26 ± 11%; ET: 2 Hz: -10 ± 7%, 5 Hz: -27 ± 12%). Prazosin blunted (P < 0.05) vasoconstrictor responsiveness in S and ET rats at rest and during contraction, and abolished group differences in vasoconstrictor responsiveness. Subsequent NOS blockade increased vasoconstrictor responses (P < 0.05) in S at rest and during contraction, whereas in ET vasoconstriction was increased (P < 0.05) in response to sympathetic stimulation at 2 Hz at rest and unchanged (P > 0.05) during contraction. ET enhanced (P < 0.05) sympatholysis, however the training-mediated improvements in sympatholysis were abolished by α1-adrenoreceptor blockade. Subsequent NOS inhibition did not alter (P > 0.05) sympatholysis in S or ET rats. In conclusion, ET augmented α1-adrenoreceptor-mediated vasoconstriction in resting skeletal muscle and enhanced α1-adrenoreceptor-mediated sympatholysis. Furthermore, these data suggest that NO is not required to inhibit α2-adrenoreceptor- and nonadrenoreceptor-mediated vasoconstriction during exercise.

Hindlimb unweighting does not alter vasoconstrictor responsiveness and nitric oxide-mediated inhibition of sympathetic vasoconstriction.

KEY POINTS: Physical inactivity increases the risk of cardiovascular disease and may alter sympathetic nervous system control of vascular resistance. Hindlimb unweighting (HU), a rodent model of physical inactivity, has been shown to diminish sympathetic vasoconstrictor responsiveness and reduce NO synthase expression in isolated skeletal muscle blood vessels. Our understanding of the effects of HU on sympathetic vascular regulation in vivo is very limited. The present findings demonstrate that HU did not alter sympathetic vasoconstrictor responsiveness and NO-mediated inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle. This study suggests that short-term physical inactivity does not alter in vivo sympathetic vascular control in the skeletal muscle vascular bed at rest and during contraction. ABSTRACT: We tested the hypothesis that physical inactivity would increase sympathetic vasoconstrictor responsiveness and diminish NO-mediated inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle. Sprague-Dawley rats (n = 33) were randomly assigned to sedentary time control (S) or hindlimb unweighted (HU) groups for 21 days. Following the intervention, rats were anaesthetized and instrumented for measurement of arterial blood pressure and femoral artery blood flow and stimulation of the lumbar sympathetic chain. The percentage change of femoral vascular conductance (%FVC) in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae muscle contraction before (control) and after NO synthase blockade with l-NAME (5 mg kg i.v.). Sympathetic vasoconstrictor responsiveness was not different (P > 0.05) in S and HU rats at rest (S, 2 Hz, -26 ± 8% and 5 Hz, -46 ± 12%; and HU, 2 Hz, -29 ± 9% and 5 Hz, -51 ± 10%) and during contraction (S, 2 Hz, -10 ± 7% and 5 Hz, -23 ± 11%; and HU, 2 Hz, -9 ± 5% and 5 Hz, -22 ± 7%). Nitric oxide synthase blockade caused a similar increase (P > 0.05) in sympathetic vasoconstrictor responsiveness in HU and S rats at rest (S, 2 Hz, -41 ± 7% and 5 Hz, -58 ± 8%; and HU, 2 Hz, -43 ± 6% and 5 Hz, -63 ± 8%) and during muscle contraction (S, 2 Hz, -15 ± 6% and 5 Hz, -31 ± 11%; and HU, 2 Hz, -12 ± 5% and 5 Hz, -29 ± 8%). Skeletal muscle NO synthase expression and ACh-mediated vasodilatation were also not different between HU and S rats. These data suggest that HU does not alter sympathetic vasoconstrictor responsiveness and NO-mediated inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle.

Vascular effects of aerobic exercise training in rat adult offspring exposed to hypoxia-induced intrauterine growth restriction.

KEY POINTS: Prenatal hypoxia, one of the most common consequences of complicated pregnancies, leads to intrauterine growth restriction (IUGR) and impairs later-life endothelium-dependent vascular function. Early interventions are needed to ultimately reduce later-life risk for cardiovascular disease. Aerobic exercise training has been shown to prevent cardiovascular diseases. Whether exercise can be used as an intervention to reverse the vascular phenotype of this susceptible population is unknown. Aerobic exercise training enhanced endothelium-derived hyperpolarization-mediated vasodilatation in gastrocnemius muscle arteries in male IUGR offspring, and did not improve nitric oxide-mediated vasodilatation in IUGR offspring. Understanding the mechanisms by which exercise impacts the cardiovascular system in a susceptible population and the consideration of sexual dimorphism is essential to define whether exercise could be used as a preventive strategy in this population. ABSTRACT: Hypoxia in utero is a critical insult causing intrauterine growth restriction (IUGR). Adult offspring born with hypoxia-induced IUGR have impaired endothelium-dependent vascular function. We tested whether aerobic exercise improves IUGR-induced endothelial dysfunction. Pregnant Sprague-Dawley rats were exposed to control (21% oxygen) or hypoxic (11% oxygen) conditions from gestational day 15 to 21. Male and female offspring from normoxic and hypoxic (IUGR) pregnancies were randomized at 10 weeks of age to either an exercise-trained or sedentary group. Exercise-trained rats ran on a treadmill for 30 min at 20 m min(-1) , 5 deg gradient, 5 days week(-1) , for 6 weeks. Concentration-response curves to phenylephrine and methylcholine were performed in second order mesenteric and gastrocnemius muscle arteries, in the presence or absence of l-NAME (100 µm), MnTBAP (peroxynitrite scavenger; 10 µm), apamin (0.1 µm) and TRAM-34 (an intermediate-conductance calcium-activated potassium channel blocker; 10 µm), or indomethacin (5 µm). In adult male IUGR offspring, prenatal hypoxia had no effect on total vasodilator responses in either vascular bed. Aerobic exercise training in IUGR males, however, improved endothelium-derived hyperpolarization (EDH)-mediated vasodilatation in gastrocnemius muscle arteries. Female IUGR offspring had reduced NO-mediated vasodilatation in both vascular beds, along with decreased total vasodilator responses and increased prostaglandin-mediated vasoconstriction in gastrocnemius muscle arteries. In contrast to males, aerobic exercise training in IUGR female offspring had no effect on either vascular bed. Exercise may not prove to be a beneficial therapy for specific vascular pathways affected by prenatal hypoxia, particularly in female offspring.

Acute tetrahydrobiopterin supplementation attenuates sympathetic vasoconstrictor responsiveness in resting and contracting skeletal muscle of healthy rats.

Tetrahydrobiopterin (BH4) is an essential cofactor for the production of nitric oxide (NO) and supplementation with BH4 improves NO-dependent vasodilation. NO also reduces sympathetic vasoconstrictor responsiveness in resting and contracting skeletal muscle. Thus, we hypothesized that supplementation with BH4 would blunt sympathetic vasoconstrictor responsiveness in resting and contracting skeletal muscle. Sprague-Dawley rats (n = 15, 399 ± 57 g) were anesthetized and instrumented with an indwelling brachial artery catheter, femoral artery flow probe, and a stimulating electrode on the lumbar sympathetic chain. Triceps surae muscles were stimulated to contract rhythmically at 30% and 60% of maximal contractile force (MCF). The percentage change of femoral vascular conductance (%FVC) in response to sympathetic stimulations delivered at 2 and 5 Hz was determined at rest and during muscle contraction in control and acute BH4 supplementation (20 mg·kg(-1) + 10 mg·kg(-1)·h(-1), IA) conditions. BH4 reduced (P < 0.05) the vasoconstrictor response to sympathetic stimulation (i.e., decrease in FVC) at rest (Control: 2 Hz: -28 ± 5%FVC; 5 Hz: -45 ± 5%; BH4: 2 Hz: -17 ± 4%FVC; 5 Hz: -34 ± 7%FVC) and during muscular contraction at 30% MCF (Control: 2 Hz: -14 ± 6%FVC; 5 Hz: -28 ± 11%; BH4: 2 Hz: -6 ± 6%FVC; 5 Hz: -16 ± 10%) and 60% MCF (Control: 2 Hz: -7 ± 3%FVC; 5 Hz: -16 ± 6%FVC; BH4: 2 Hz: -2 ± 3%FVC; 5 Hz: -11 ± 6%FVC). These data are consistent with our hypothesis that acute BH4 supplementation decreases sympathetic vasoconstrictor responsiveness in resting and contracting skeletal muscle.

Exercise training augments neuronal nitric oxide synthase-mediated inhibition of sympathetic vasoconstriction in contracting skeletal muscle of rats.

We tested the hypothesis that exercise training would increase neuronal nitric oxide synthase (nNOS)-mediated inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle. Sprague-Dawley rats (n = 18) were randomized to sedentary or exercise-trained (40 m min(-1), 5° grade; 5 days week(-1) for 4 weeks) groups. Following completion of sedentary behaviour or exercise training, rats were anaesthetized and instrumented with a brachial artery catheter, femoral artery flow probe and stimulating electrodes on the lumbar sympathetic chain. The percentage change of femoral vascular conductance (%FVC) in response to sympathetic chain stimulations delivered at 2 and 5 Hz was determined at rest and during triceps surae muscle contraction before (control) and after selective nNOS blockade with S-methyl-l-thiocitrulline (SMTC, 0.6 mg kg(-1), i.v.) and subsequent non-selective NOS blockade with l-NAME (5 mg kg(-1), i.v.; SMTC + l-NAME). At rest, sympathetic vasoconstrictor responsiveness was greater (P < 0.05) in exercise-trained compared to sedentary rats in control, SMTC and SMTC + l-NAME conditions. During contraction, the constrictor response was not different (P > 0.05) between exercise trained (2 Hz: -11 ± 4%FVC; 5 Hz: -21 ± 5%FVC) and sedentary rats (2 Hz: -7 ± 6%FVC; 5 Hz: -18 ± 10%FVC) in control conditions. SMTC augmented (P < 0.05) sympathetic vasoconstriction in sedentary and exercise-trained rats; however, sympathetic vasoconstrictor responsiveness was greater (P < 0.05) in exercise-trained (2 Hz: -27 ± 5%FVC; 5 Hz: -39 ± 5%FVC) compared to sedentary (2 Hz: -17 ± 6%FVC; 5 Hz: -27 ± 8%FVC) rats during selective nNOS inhibition. SMTC + l-NAME further augmented (P < 0.05) sympathetic vasoconstrictor responsiveness by a similar magnitude (P > 0.05) in exercise-trained and sedentary rats. These data demonstrate that exercise training augmented nNOS-mediated inhibition of sympathetic vasoconstriction in contracting muscle.

Short-term exercise training augments 2-adrenoreceptor-mediated sympathetic vasoconstriction in resting and contracting skeletal muscle.

We hypothesized that exercise training (ET) would alter α2-adrenoreceptor-mediated sympathetic vasoconstriction. Sprague-Dawley rats (n = 30) were randomized to sedentary (S), mild- (M) or heavy-intensity (H) treadmill ET groups (5 days per week for 4 weeks). Following the ET component of the study, rats were anaesthetized, and instrumented for lumbar sympathetic chain stimulation, triceps surae muscle contraction and measurement of femoral vascular conductance (FVC). The percentage change of FVC in response to sympathetic stimulation was determined at rest and during contraction in control, α2 blockade (yohimbine) and combined α2 + nitric oxide (NO) synthase (NOS) blockade (N-nitro-L-arginine methyl ester hydrochloride, L-NAME) conditions. ET augmented (P < 0.05) sympathetic vasoconstrictor responses at rest and during contraction. Yohimbine reduced (P < 0.05) the vasoconstrictor response in ET rats at rest (M: 2 Hz: 8 ± 2%, 5 Hz: 9 ± 4%; H: 2 Hz: 14 ± 5%, 5 Hz: 11 ± 6%) and during contraction (M: 2 Hz: 9 ± 2%, 5 Hz: 9 ± 5%; H: 2 Hz: 8 ± 3%, 5 Hz: 6 ± 6%) but did not change the response in S rats. The addition of L-NAME caused a larger increase (P < 0.05) in the vasoconstrictor response in ET than in S rats at rest (2 Hz: S: 8 ± 2%, M: 15 ± 3%, H: 23 ± 7%; 5 Hz: S: 8 ± 5%, M: 15 ± 3%, H: 17 ± 5%) and during contraction (2 Hz: S: 9 ± 3%, M: 18 ± 3%, H: 22 ± 6%; 5 Hz: S: 9 ± 5%, M: 22 ± 4%, H:26 ± 9%). Sympatholysis was greater (P < 0.05) in ET than in S rats. Blockade of α2-adrenoreceptors and NOS reduced (P < 0.05) sympatholysis in ET rats, but had no effect on sympatholysis in S rats. In conclusion, ET increased α2-mediated vasoconstriction at rest and during contraction.

Role of neuronal nitric oxide in the inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle of healthy rats.

Isoform-specific nitric oxide (NO) synthase (NOS) contributions to NO-mediated inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle are incompletely understood. The purpose of the present study was to investigate the role of neuronal NOS (nNOS) in the inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle of healthy rats. We hypothesized that acute pharmacological inhibition of nNOS would augment sympathetic vasoconstriction in resting and contracting skeletal muscle, demonstrating that nNOS is primarily responsible for NO-mediated inhibition of sympathetic vasoconstriction. Sprague-Dawley rats (n = 13) were anesthetized and instrumented with an indwelling brachial artery catheter, femoral artery flow probe, and lumbar sympathetic chain stimulating electrodes. Triceps surae muscles were stimulated to contract rhythmically at 60% of maximal contractile force. In series 1 (n = 9), the percent change in femoral vascular conductance (%FVC) in response to sympathetic stimulations delivered at 2 and 5 Hz was determined at rest and during muscle contraction before and after selective nNOS blockade with S-methyl-l-thiocitrulline (SMTC, 0.6 mg/kg iv) and subsequent nonselective NOS blockade with N(ω)-nitro-l-arginine methyl ester (l-NAME, 5 mg/kg iv). In series 2 (n = 4), l-NAME was injected first, and then SMTC was injected to determine if the effect of l-NAME on constrictor responses was influenced by selective nNOS inhibition. Sympathetic stimulation decreased FVC at rest (-25 ± 7 and -44 ± 8%FVC at 2 and 5 Hz, respectively) and during contraction (-7 ± 3 and -19 ± 5%FVC at 2 and 5 Hz, respectively). The decrease in FVC in response to sympathetic stimulation was greater in the presence of SMTC at rest (-32 ± 6 and -49 ± 8%FVC at 2 and 5 Hz, respectively) and during contraction (-21 ± 4 and -28 ± 4%FVC at 2 and 5 Hz, respectively). l-NAME further increased (P < 0.05) the sympathetic vasoconstrictor response at rest (-47 ± 4 and -60 ± 6%FVC at 2 and 5 Hz, respectively) and during muscle contraction (-33 ± 3 and -40 ± 6%FVC at 2 and 5 Hz, respectively). The effect of l-NAME was not altered by the order of nNOS inhibition. These data demonstrate that NO derived from nNOS and endothelial NOS contribute to the inhibition of sympathetic vasoconstriction in resting and contracting skeletal muscle.

Acute superoxide scavenging reduces sympathetic vasoconstrictor responsiveness in short-term exercise-trained rats.

We hypothesized that acute superoxide (O2(-)) scavenging would attenuate sympathetic vasoconstrictor responsiveness by augmenting nitric oxide (NO)-mediated inhibition of sympathetic vasoconstriction in exercise-trained rats. Sprague-Dawley rats were randomly assigned to sedentary time control (S; n = 7) or mild- (M: 20 m/min, 5° grade; n = 7) or heavy-intensity (H: 40 m/min, 5° grade; n = 7) exercise training (ET) groups and trained 5 days/wk for 4 wk with matched training volume. Following ET, rats were anesthetized and instrumented for lumbar sympathetic chain stimulation and measurement of femoral vascular conductance. In resting skeletal muscle, the percentage change of femoral vascular conductance in response to continuous (2 Hz) and patterned (20 and 40 Hz) sympathetic stimulation was determined during control conditions, O2(-) scavenging (TIRON, 1 g·kg(-1)·h(-1) iv) and combined O2(-) scavenging + nitric oxide synthase blockade (N(ω)-nitro-l-arginine methyl ester, 5 mg/kg iv). ET augmented the vasoconstrictor response to sympathetic stimulation in a training intensity-dependent manner (P < 0.05) (S: 2 Hz: -26 ± 7.1%; 20 Hz: -26.9 ± 7.3%; 40 Hz: -27.7 ± 7.0%; M: 2 Hz: -37.4 ± 8.3%; 20 Hz: -35.9 ± 7.4%; 40 Hz: -38.2 ± 9.4%; H: 2 Hz: -46.9 ± 7.8%; 20 Hz: -48.5 ± 7.2%; 40 Hz: -51.2 ± 7.3%). O2(-) scavenging did not alter (P > 0.05) the vasoconstrictor response in S rats (S: 2 Hz: -23.9 ± 7.6%; 20 Hz: -26.1 ± 9.1%; 40 Hz: -27.5 ± 7.2%), whereas the response in ET rats was diminished (M: 2 Hz: -26.3 ± 5.1%; 20 Hz: -28.7 ± 5.3%; 40 Hz: -28.5 ± 5.6%; H: 2 Hz: -35.5 ± 10.3%; 20 Hz: -38.6 ± 6.8%; 40 Hz: -43.9 ± 5.9%, P < 0.05). TIRON + N(ω)-nitro-l-arginine methyl ester increased vasoconstrictor responsiveness (P < 0.05) in ET rats (M: 2 Hz: -47.7 ± 9.8%; 20 Hz: -41.2 ± 7.2%; 40 Hz: -50.5 ± 7.9%; H: 2 Hz: -55.8 ± 7.6%; 20 Hz: -55.7 ± 7.8%; 40 Hz: -58.7 ± 6.2%), whereas, in S rats, the response was unchanged (2 Hz: -29.4 ± 8.7%; 20 Hz: -30.0 ± 7.4%; 40 Hz: -35.2 ± 10.3%; P > 0.05). These data indicate that the augmented sympathetic vasoconstrictor responsiveness in ET rats was related to increased oxidative stress and altered nitric oxide-mediated inhibition of vasoconstriction.

Short-term exercise training enhances functional sympatholysis through a nitric oxide-dependent mechanism.

We tested the hypothesis that short-term mild- (M) and heavy-intensity (H) exercise training would enhance sympatholysis through a nitric oxide (NO)-dependent mechanism. Sprague-Dawley rats (n = 36) were randomly assigned to sedentary (S) or to M (20 m min(-1) 5% gradient) or H exercise training groups (40 m min(-1) 5% gradient). Rats assigned to M and H groups trained on 5 days week(-1) for 4 weeks, with the volume of training being matched between groups. Rats were anaesthetized and instrumented for stimulation of the lumbar sympathetic chain and the measurement of arterial blood pressure and femoral artery blood flow. The triceps surae muscle group was stimulated to contract rhythmically at 30 and 60% of maximal contractile force (MCF). The percentage change of femoral vascular conductance (%FVC) in response to sympathetic stimulation delivered at 2 and 5 Hz was determined at rest and during contraction at 30 and 60% MCF. The vascular response to sympathetic stimulation was reduced as a function of MCF in all rats (P < 0.05). At 30% MCF, the magnitude of sympatholysis (%FVC rest - contraction; %FVC) was greater in H compared with M and S groups (%FVC at 2 Hz, S, 9 ± 5; M, 11 ± 8; and H, 18 ± 7; and %FVC at 5 Hz, S, 6 ± 6; M, 12 ± 9; and H, 18 ± 7; P < 0.05) and was greater in H and M compared with S at 60% MCF (%FVC at 2 Hz, S, 15 ± 5; M, 25 ± 3; and H, 36 ± 6; and %FVC at 5 Hz, S, 22 ± 6; M, 33 ± 9; and H, 39 ± 9; P < 0.05). Blockade of NO synthase did not alter the magnitude of sympatholysis in S during contraction at 30 or 60% MCF. In contrast, NO synthase inhibition diminished sympatholysis in H at 30% MCF and in M and H at 60% MCF (P < 0.05). The present findings indicate that short-term exercise training augments sympatholysis in a training-intensity-dependent manner and through an NO-dependent mechanism.