Ascorbic acid increases cardiovagal baroreflex sensitivity in healthy older men

Vitamin C deficiency can lead to pulmonary hypertension: a systematic review of case reports

BACKGROUND

In the early literature, unintentional vitamin C deficiency in humans was associated with heart failure. Experimental vitamin C deficiency in guinea pigs caused enlargement of the heart. The purpose of this study was to collect and analyze case reports on vitamin C and pulmonary hypertension.

METHODS

We searched Pubmed and Scopus for case studies in which vitamin C deficiency was considered to be the cause of pulmonary hypertension. We selected reports in which pulmonary hypertension was diagnosed by echocardiography or catheterization, for any age, sex, or dosage of vitamin C. We extracted quantitative data for our analysis. We used the mean pulmonary artery pressure (mPAP) as the outcome of primary interest.

RESULTS

We identified 32 case reports, 21 of which were published in the last 5 years. Dyspnea was reported in 69%, edema in 53% and fatigue in 28% of the patients. Vitamin C plasma levels, measured in 27 cases, were undetectable in 24 and very low in 3 cases. Diet was poor in 30 cases and 17 cases had neuropsychiatric disorders. Right ventricular enlargement was reported in 24 cases. During periods of vitamin C deficiency, the median mPAP was 48 mmHg (range 29-77 mmHg; N = 28). After the start of vitamin C administration, the median mPAP was 20 mmHg (range 12-33 mmHg; N = 18). For the latter 18 cases, mPAP was 2.4-fold (median) higher during vitamin C deficiency. Pulmonary vascular resistance (PVR) during vitamin C deficiency was reported for 9 cases, ranging from 4.1 to 41 Wood units. PVR was 9-fold (median; N = 5) higher during vitamin C deficiency than during vitamin C administration. In 8 cases, there was direct evidence that the cases were pulmonary artery hypertension (PAH). Probably the majority of the remaining cases were also PAH.

CONCLUSIONS

The cases analyzed in our study indicate that pulmonary hypertension can be one explanation for the reported heart failure of scurvy patients in the early literature. It would seem sensible to measure plasma vitamin C levels of patients with PH and examine the effects of vitamin C administration.

Bioavailability of Bioactive Compounds from Reconstituted Grapefruit Juice as Affected by the Obtention Process

Much attention has been paid to the health benefits of including fruits and vegetables in the diet. However, for the compounds responsible for this beneficial effect to be effective at the level of the human organism, they must be available for absorption after digestion. In this sense, in vivo studies are needed to demonstrate the bioavailability of these compounds and their physiological activity. In order to provide information in this regard, this study collects data on the levels of vitamin C (VC) and naringenin (NAG) in the blood serum of the 11 volunteer participants in this trial, before and after consuming two different grapefruit juices. The juices were prepared by rehydrating the grapefruit powder obtained by freeze-drying (FD) the fruit puree or by spray-drying (SD) the liquefied grapefruit. No significant differences (p > 0.05) neither by juice nor by participant were observed in any case. The mean relative increase of VC, NAG and the radical scavenging ability (RSA) in blood serum due to grapefruit juices intake was 12%, 28% and 26%, respectively. Just VC showed a positive and significant Pearson's correlation with RSA. The mean bioavailability of VC was quantified as 1.529 ± 0.002 mg VC/L serum per 100 mg of VC ingested.

Age-associated reductions in cardiovagal baroreflex sensitivity are exaggerated in middle-aged and older men with low testosterone

Aging is associated with reductions in cardiovagal baroreflex sensitivity (cBRS), which increases cardiovascular disease risk. Preclinical data indicate that low testosterone reduces cBRS. We determined whether low testosterone is associated with reduced cBRS in healthy men.

METHODS

Twenty-six men categorized as young (N=6; age=31±4 years; testosterone=535±60 ng/dL), middle-aged/older with normal (N=10; aged 56±3 years; testosterone=493±85 ng/dL), or low (N=10; age=57±6 years; testosterone=262±31 ng/dL) testosterone underwent recordings of beat-by-beat blood pressure and R-R interval during rest and two Valsalva maneuvers, and measures of carotid artery compliance. IL-6, CRP, oxidized LDL cholesterol and TAS were measured.

RESULTS

Middle-aged/older men had lower cBRS compared to young men (17.0±6.5 ms/mmHg; p=0.028); middle-age/older men with low testosterone had lower cBRS (5.5±3.2 ms/mmHg; p=0.039) compared to age-matched men with normal testosterone (10.7±4.0 ms/mmHg). No differences existed among groups during Phase II of the Valsalva maneuver; middle-aged/older men with low testosterone had reduced cBRS (4.7±2.6 ms/mmHg) compared to both young (12.8±2.8ms/mmHg; p<0.001) and middle-aged/older men with normal testosterone (8.6±4.4ms/mmHg; p=0.046) during Phase IV of the Valsalva maneuver. There were no differences in oxidized LDL, (p=0.882) or TAS across groups (p=0.633). IL-6 was significantly higher in middle-aged/older men with low testosterone compared to the other groups (p<0.05 for all) and inversely correlated with cBRS (r=-0.594, p=0.007). Middle-aged/older men had reduced carotid artery compliance compared to young, regardless of testosterone status (p<0.001).

CONCLUSIONS

These observations indicate that low testosterone in middle-aged/older men may contribute to a reduction in cBRS; increased inflammation may also contribute to a reduction in cBRS.

Vitamin C May Improve Left Ventricular Ejection Fraction: A Meta-Analysis

Background

Vitamin C deprivation can lead to fatigue, dyspnea, oedema and chest pain, which are also symptoms of heart failure (HF). In animal studies vitamin C has improved contractility and mechanical efficiency of the heart. Compared with healthy people, patients with HF have lower vitamin C levels, which are not explained by differences in dietary intake levels, and more severe HF seems to be associated with lower plasma vitamin C levels. This meta-analysis looks at the effect of vitamin C on left ventricular ejection fraction (LVEF).

Methods

We searched for trials reporting the effects of vitamin C on LVEF. We assessed the quality of the trials, and pooled selected trials using the inverse variance, fixed effect options. We used meta-regression to examine the association between the effect of vitamin C on LVEF level and the baseline LVEF level.

Results

We identified 15 trials, three of which were excluded from our meta-analysis. In six cardiac trials with 246 patients, vitamin C increased LVEF on average by 12.0% (95% CI 8.1–15.9%; P < 0.001). In six non-cardiac trials including 177 participants, vitamin C increased LVEF on average by 5.3% (95% CI 2.0–8.5%; P = 0.001). In meta-regression analysis we found that the effect of vitamin C was larger in trials with the lowest baseline LVEF levels with P = 0.001 for the test of slope. The meta-regression line crossed the null effect level at a baseline LVEF level close to 70%, with progressively greater benefit from vitamin C with lower LVEF levels. Some of the included trials had methodological limitations. In a sensitivity analysis including only the four most methodologically sound cardiac trials, the effect of vitamin C was not substantially changed.

Conclusions

In this meta-analysis, vitamin C increased LVEF in both cardiac and non-cardiac patients, with a strong negative association between the size of the vitamin C effect and the baseline LVEF. Further research on vitamin C and HF should be carried out, particularly in patients who have low LVEF together with low vitamin C intake or low plasma levels. Different dosages and different routes of administration should be compared.

Vascular Endothelial Function in Midlife/Older Adults Classified According to 2017 American College of Cardiology/American Heart Association Blood Pressure Guidelines

Background

Impaired endothelial function is thought to contribute to the increased cardiovascular risk associated with above‐normal blood pressure (BP). However, the association between endothelial function and BP classified by 2017 American College of Cardiology/American Heart Association guidelines is unknown. Our objective was to determine if endothelial function decreases in midlife/older adults across the 2017 American College of Cardiology/American Heart Association guidelines BP classifications and identify associated mechanisms of action.

Methods and Results

A retrospective analysis of endothelial function (brachial artery flow‐mediated dilation) from 988 midlife/older adults (aged 50+ years) stratified by BP status (normal BP; elevated BP; stage 1 hypertension; stage 2 hypertension) was performed. Endothelium‐independent dilation (sublingual nitroglycerin), reactive oxygen species–mediated suppression of endothelial function (∆brachial artery flow‐mediated dilation with vitamin C infusion), and endothelial cell and plasma markers of oxidative stress and inflammation were assessed in subgroups. Compared with normal BP (n=411), brachial artery flow‐mediated dilation was 12% (P=0.04), 15% (P<0.01) and 20% (P<0.01) lower with elevated BP (n=173), stage 1 hypertension (n=248) and stage 2 hypertension (n=156), respectively, whereas endothelium‐independent dilation did not differ (P=0.14). Vitamin C infusion increased brachial artery flow‐mediated dilation in those with above‐normal BP (P≤0.02) but not normal BP (P=0.11). Endothelial cell p47^phox (P<0.01), a marker of superoxide/reactive oxygen species–generating nicotinamide adenine dinucleotide phosphate oxidase, and circulating interleukin‐6 concentrations (P=0.01) were higher in individuals with above‐normal BP.

Conclusions

Vascular endothelial function is progressively impaired with increasing BP in otherwise healthy adults classified by 2017 American College of Cardiology/American Heart Association guidelines. Impaired endothelial function with above‐normal BP is mediated by excessive reactive oxygen species signaling associated with increased endothelial expression of nicotinamide adenine dinucleotide phosphate oxidase and circulating interleukin‐6.

Acute Effects of Passion Fruit Juice Supplementation on Cardiac Autonomic Function and Blood Glucose in Healthy Subjects

Ascorbic acid supplementation provides beneficial effects on enhancing cardiac autonomic function in patients with heart failure. Ascorbic acid also reduces blood sugar levels and enhances insulin activity, and encourages cardiac autonomic function. Passion fruit is rich in ascorbic acid and potential antioxidants. This study aimed to evaluate the acute effects of passion fruit juice (PFJ) supplementation primarily on cardiac autonomic function and secondary on blood glucose in healthy subjects. A randomized cross-over trial was conducted in 14 healthy subjects aged 21.29±0.73 years. Subjects were supplemented with either 50% PFJ, or glucose and fructose solution as a placebo (PLA) at 3.5 mL/kg body mass with a 1-week washout between treatments in a single-dose design. Short-term heart rate variability and blood glucose levels were evaluated prior to supplementation (T0) and following supplementation for 30, 60, 90, and 120 min (T30, T60, T90, and T120, respectively). Indexes of cardiac autonomic function at T30, including high frequency power (P=0.03) and total power (P=0.01), were significantly higher and the ratio of low frequency/high frequency power was significantly lower (P=0.01) in the PFJ group compared to the PLA group. Blood glucose levels significantly increased at T30 in both PLA (P=0.00) and PFJ (P=0.00) groups. However, there were no significant differences between groups. A single administration of PFJ enhanced cardiac autonomic function through augmentation of parasympathetic activity, although it did not attenuate postprandial hyperglycemia. PFJ may be potentially recognized as beverage able to prevent cardiovascular disease.

Effect of centrally acting angiotensin converting enzyme inhibitor on the exercise-induced increases in muscle sympathetic nerve activity

KEY POINTS

The arterial baroreflex's operating point pressure is reset upwards and rightwards from rest in direct relation to the increases in dynamic exercise intensity. The intraneural pathways and signalling mechanisms that lead to upwards and rightwards resetting of the operating point pressure, and hence the increases in central sympathetic outflow during exercise, remain to be identified. We tested the hypothesis that the central production of angiotensin II during dynamic exercise mediates the increases in sympathetic outflow and, therefore, the arterial baroreflex operating point pressure resetting during acute and prolonged dynamic exercise. The results identify that perindopril, a centrally acting angiotensin converting enzyme inhibitor, markedly attenuates the central sympathetic outflow during acute and prolonged dynamic exercise.

ABSTRACT

We tested the hypothesis that the signalling mechanisms associated with the dynamic exercise intensity related increases in muscle sympathetic nerve activity (MSNA) and arterial baroreflex resetting during exercise are located within the central nervous system. Participants performed three randomly ordered trials of 70° upright back-supported dynamic leg cycling after ingestion of placebo and two different lipid soluble angiotensin converting enzyme inhibitors (ACEi): perindopril (high lipid solubility), captopril (low lipid solubility). Repeated measurements of whole venous blood (n = 8), MSNA (n = 7) and arterial blood pressures (n = 14) were obtained at rest and during an acute (SS1) and prolonged (SS2) bout of steady state dynamic exercise. Arterial baroreflex function curves were modelled at rest and during exercise. Peripheral venous superoxide concentrations measured by electron spin resonance spectroscopy were elevated during exercise and were not altered by ACEi at rest (P ≥ 0.4) or during exercise (P ≥ 0.3). Baseline MSNA and mean arterial pressure were unchanged at rest (P ≥ 0.1; P ≥ 0.8, respectively). However, during both SS1 and SS2, the centrally acting ACEi perindopril attenuated MSNA compared to captopril and the placebo (P < 0.05). Arterial pressures at the operating point and threshold pressures were decreased with perindopril from baseline to SS1 with no further changes in the operating point pressure during SS2 under all three conditions. These data suggest that centrally acting ACEi is significantly more effective at attenuating the increase in the acute and prolonged exercise-induced increases in MSNA.

Adrenergic Agonists Bind to Adrenergic-Receptor-Like Regions of the Mu Opioid Receptor, Enhancing Morphine and Methionine-Enkephalin Binding: A New Approach to "Biased Opioids"?

Extensive evidence demonstrates functional interactions between the adrenergic and opioid systems in a diversity of tissues and organs. While some effects are due to receptor and second messenger cross-talk, recent research has revealed an extracellular, allosteric opioid binding site on adrenergic receptors that enhances adrenergic activity and its duration. The present research addresses whether opioid receptors may have an equivalent extracellular, allosteric adrenergic binding site that has similar enhancing effects on opioid binding. Comparison of adrenergic and opioid receptor sequences revealed that these receptors share very significant regions of similarity, particularly in some of the extracellular and transmembrane regions associated with adrenergic binding in the adrenergic receptors. Five of these shared regions from the mu opioid receptor (muOPR) were synthesized as peptides and tested for binding to adrenergic, opioid and control compounds using ultraviolet spectroscopy. Adrenergic compounds bound to several of these muOPR peptides with low micromolar affinity while acetylcholine, histamine and various adrenergic antagonists did not. Similar studies were then conducted with purified, intact muOPR with similar results. Combinations of epinephrine with methionine enkephalin or morphine increased the binding of both by about half a log unit. These results suggest that muOPR may be allosterically enhanced by adrenergic agonists.

Effect of Strength Training on Oxidative Stress and the Correlation of the Same with Forearm Vasodilatation and Blood Pressure of Hypertensive Elderly Women: A Randomized Clinical Trial

The aim of the study was to evaluate the effect of strength training on oxidative stress and the correlation of the same with forearm vasodilatation and mean blood pressure of hypertensive elderly women, at rest (basal) and during a static handgrip exercise. Insufficiently active hypertensive elderly women (N = 25; mean age = 66.1 years) were randomized into a 10 week strength training group (n = 13) or control (n = 12) group. Plasma malondialdehyde (MDA), total antioxidant capacity (TAC), plasma nitrite (NO2-), forearm blood flow (FBF), mean blood pressure (MBP) and vascular conductance ([FBF / MBP] x 100) were evaluated before and after the completion of the interventions. The strength training group increased the TAC (pre: Median = 39.0; Interquartile range = 34.0-41.5% vs post: Median = 44.0; Interquartile range = 38.0-51.5%; p = 0.006) and reduced the MDA (pre: 4.94 ± 1.10 μM vs post: 3.90 ± 1.35 μM; p = 0.025; CI-95%: -1.92 --0.16 μM). The strength training group increased basal vascular conductance (VC) (pre: 3.56 ±0.88 units vs post: 5.21 ±1.28 units; p = 0.001; CI-95%: 0.93-2.38 units) and decreased basal MBP (pre: 93.1 ±6.3 mmHg vs post: 88.9 ±5.4 mmHg; p = 0.035; CI-95%: -8.0 --0.4 mmHg). Such changes were also observed during static handgrip exercise. A moderate correlation was observed between changes in basal VC and MBP with changes in NO2- (ΔVC → r = -0.56, p = 0.047; ΔMBP → r = -0.41, p = 0.168) and MDA (ΔVC → r = 0.64, p = 0.019; ΔMBP → r = 0.31, p = 0.305). The strength training program reduced the oxidative stress of the hypertensive elderly women and this reduction was moderately correlated with their cardiovascular benefits.

TRIAL REGISTRATION

ensaiosclinicos.gov.br RBR-48c29w.

Liposomal-encapsulated Ascorbic Acid: Influence on Vitamin C Bioavailability and Capacity to Protect Against Ischemia-Reperfusion Injury

Intravenous administration of vitamin C has been shown to decrease oxidative stress and, in some instances, improve physiological function in adult humans. Oral vitamin C administration is typically less effective than intravenous, due in part to inferior vitamin C bioavailability. The purpose of this study was to determine the efficacy of oral delivery of vitamin C encapsulated in liposomes. On 4 separate randomly ordered occasions, 11 men and women were administered an oral placebo, or 4 g of vitamin C via oral, oral liposomal, or intravenous delivery. The data indicate that oral delivery of 4 g of vitamin C encapsulated in liposomes (1) produces circulating concentrations of vitamin C that are greater than unencapsulated oral but less than intravenous administration and (2) provides protection from ischemia–reperfusion-mediated oxidative stress that is similar to the protection provided by unencapsulated oral and intravenous administrations.

Estimated aortic stiffness is independently associated with cardiac baroreflex sensitivity in humans: role of ageing and habitual endurance exercise

We hypothesized that differences in cardiac baroreflex sensitivity (BRS) would be independently associated with aortic stiffness and augmentation index (AI), clinical biomarkers of cardiovascular disease (CVD) risk, among young sedentary and middle-aged/older sedentary and endurance-trained adults. A total of 36 healthy middle-aged/older (age 55-76 years, n=22 sedentary; n=14 endurance-trained) and 5 young sedentary (age 18-31 years) adults were included in a cross-sectional study. A subset of the middle-aged/older sedentary adults (n=12) completed an 8-week aerobic exercise intervention. Invasive brachial artery blood pressure waveforms were used to compute spontaneous cardiac BRS (via sequence technique) and estimated aortic pulse wave velocity (PWV) and AI (AI, via brachial-aortic transfer function and wave separation analysis). In the cross-sectional study, cardiac BRS was 71% lower in older compared with young sedentary adults (P<0.05), but only 40% lower in older adults who performed habitual endurance exercise (P=0.03). In a regression model that included age, sex, resting heart rate, mean arterial pressure (MAP), body mass index and maximal exercise oxygen uptake, estimated aortic PWV (β±SE = −5.76 ± 2.01, P=0.01) was the strongest predictor of BRS (Model R²=0.59, P<0.001). The 8 week exercise intervention improved BRS by 38% (P=0.04) and this change in BRS was associated with improved aortic PWV (r=−0.65, P=0.044, adjusted for changes in MAP). Age- and endurance exercise-related differences in cardiac BRS are independently associated with corresponding alterations in aortic PWV among healthy adults, consistent with a mechanistic link between variations in the sensitivity of the baroreflex and aortic stiffness with age and exercise.

Mechanisms mediating renal sympathetic nerve activation in obesity-related hypertension

Excessive renal sympathetic nerve activation may be one of the mechanisms underlying obesity-related hypertension. Impaired baroreflex sensitivity, adipokine disorders-such as leptin, adiponectin, and resistin-activation of the renin-angiotensin system, hyperinsulinemia, insulin resistance, and renal sodium retention present in obesity increase renal sympathetic nerve activity, thus contributing to the development of hypertension. Renal sympathetic denervation reduces both renal sympathetic activity and blood pressure in patients with obesity-related hypertension.

A common molecular motif characterizes extracellular allosteric enhancers of GPCR aminergic receptors and suggests enhancer mechanism of action

Several classes of compounds that have no intrinsic activity on aminergic systems nonetheless enhance the potency of aminergic receptor ligands three-fold or more while significantly increasing their duration of activity, preventing tachyphylaxis and reversing fade. Enhancer compounds include ascorbic acid, ethylenediaminetetraacetic acid, cortico-steroids, opioid peptides, opiates and opiate antagonists. This paper provides the first review of aminergic enhancement, demonstrating that all enhancers have a common, inobvious molecular motif and work through a common mechanism that is manifested by three common characteristics. First, aminergic enhancers bind directly to the amines they enhance, suggesting that the common structural motif is reflected in common binding targets. Second, one common target is the first extracellular loop of aminergic receptors. Third, at least some enhancers are antiphosphodiesterases. These observations suggest that aminergic enhancers act on the extracellular surface of aminergic receptors to keep the receptor in its high affinity state, trapping the ligand inside the receptor. Enhancer binding produces allosteric modifications of the receptor structure that interfere with phosphorylation of the receptor, thereby inhibiting down-regulation of the receptor. The mechanism explains how enhancers potentiate aminergic activity and increase duration of activity and makes testable predictions about additional compounds that should act as aminergic enhancers.

Ascorbic acid does not enhance hypoxia-induced vasodilation in healthy older men

In response to hypoxia, a net vasodilation occurs in the limb vasculature in young healthy humans and this is referred to as “hypoxia‐induced vasodilation”. We performed two separate experiments to determine (1) if hypoxia‐induced forearm vasodilation is impaired in older men (n = 8) compared to young men (n = 7) and (2) if acute systemic infusion of ascorbic acid would enhance hypoxia‐induced vasodilation in older men (n = 8). Heart rate, mean arterial pressure, oxygen saturation, minute ventilation, forearm vascular conductance (FVC, Doppler ultrasound), and cutaneous vascular conductance (CVC, laser Doppler flowmetry) were recorded continuously while subjects breathed 10% oxygen for 5 min. Changes from baseline were compared between groups and between treatments. The older adults had a significantly attenuated increase in FBF (13 ± 4 vs. 30 ± 7%) and FVC (16 ± 4 vs. 30 ± 7%) in response to 5 min of hypoxia. However, skin blood flow responses were comparable between groups (young: 35 ± 9, older: 30 ± 6%). In Experiment 2, FVC responses to 5 min of breathing 10% oxygen were not significantly different following saline (3 ± 10%) and ascorbic acid (8 ± 10%) in the older men. Ascorbic acid also had no physiological effects in the young men. These findings advance our basic understanding of how aging influences vascular responses to hypoxia and suggest that, in healthy humans, hypoxia‐induced vasodilation is not restrained by reactive oxygen species.

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In Experiment 1, heart rate (HR), mean arterial pressure (MAP), forearm vascular conductance (FVC), and forearm cutaneous vascular conductance (CVC) were measured in response to 5 min of continuous hypoxia (10% oxygen) in young men (black diamonds) and older men (white squares). In Experiment 2, older men breathed continuous hypoxia after receiving normal saline solution (NSS, white squares) and ascorbic acid (Vit C, black squares). These findings advance our basic understanding of how aging influences vascular responses to hypoxia and suggest that, in healthy humans, hypoxia‐induced vasodilation is not restrained by reactive oxygen species.

Blood pressure regulation XI: overview and future research directions

While the importance of regulating arterial blood pressure within a 'normal' range is widely appreciated, the definition of 'normal' and the means by which humans and other species regulate blood pressure under various conditions remain hotly debated. The effects of diverse physiological, pathological and environmental challenges on blood pressure and the mechanisms that attempt to maintain it at an optimal level are reviewed and critically analyzed in a series of articles published in this themed issue of the European Journal of Applied Physiology. We summarize here the major points made in these reviews, with emphasis on unifying concepts of regulatory mechanisms and future directions for research.

β-Adrenergic blockade enhances coronary vasoconstrictor response to forehead cooling

Forehead cooling activates the sympathetic nervous system and can trigger angina pectoris in susceptible individuals. However, the effect of forehead cooling on coronary blood flow velocity (CBV) is not well understood. In this human experiment, we tested the hypotheses that forehead cooling reduces CBV (i.e., coronary vasoconstriction) and that this vasoconstrictor effect would be enhanced under systemic β-adrenergic blockade. A total of 30 healthy subjects (age range, 23-79 years) underwent Doppler echocardiography evaluation of CBV in response to 60 s of forehead cooling (1°C ice bag on forehead). A subset of subjects (n = 10) also underwent the procedures after an intravenous infusion of propranolol. Rate pressure product (RPP) was used as an index of myocardial oxygen demand. Consistent with our first hypothesis, forehead cooling reduced CBV from 19.5 ± 0.7 to 17.5 ± 0.8 cm/s (P < 0.001), whereas mean arterial pressure increased by 11 ± 2 mmHg (P < 0.001). Consistent with our second hypothesis, forehead cooling reduced CBV under propranolol despite a significant rise in RPP. The current studies indicate that forehead cooling elicits a sympathetically mediated pressor response and a reduction in CBV, and this effect is augmented under β-blockade. The results are consistent with sympathetic activation of β-receptor coronary vasodilation in humans, as has been demonstrated in animals.

Renal vasoconstriction is augmented during exercise in patients with peripheral arterial disease

Peripheral arterial disease (PAD) patients have augmented blood pressure increases during exercise, heightening their cardiovascular risk. However, it is unknown whether patients have exaggerated renal vasoconstriction during exercise and if oxidative stress contributes to this response. Eleven PAD patients and 10 controls (CON) performed 4-min mild, rhythmic, plantar flexion exercise of increasing intensity (0.5-2 kg) with each leg (most and least affected in PAD). Eight patients also exercised with their most affected leg during ascorbic acid (AA) infusion. Renal blood flow velocity (RBFV; Doppler ultrasound), mean arterial blood pressure (MAP; Finometer), and heart rate (HR; electrocardiogram [ECG]) were measured. Renal vascular resistance (RVR), an index of renal vasoconstriction, was calculated as MAP/RBFV. Baseline RVR and MAP were similar while HR was higher in PAD than CON (2.08 ± 0.23 vs. 1.87 ± 0.20 au, 94 ± 3 vs. 93 ± 3 mmHg, and 72 ± 3 vs. 59 ± 3 bpm [P < 0.05] for PAD and CON, respectively). PAD had greater RVR increases during exercise than CON, specifically during the first minute (PAD most: 26 ± 5% and PAD least: 17 ± 5% vs. CON: 3 ± 3%; P < 0.05). AA did not alter baseline RVR, MAP, or HR. AA attenuated the augmented RVR increase in PAD during the first minute of exercise (PAD most: 33 ± 4% vs. PAD most with AA: 21 ± 4%; P < 0.05). In conclusion, these findings suggest that PAD patients have augmented renal vasoconstriction during exercise, with oxidative stress contributing to this response.

Effect of oxidative stress on sympathetic and renal vascular responses to ischemic exercise

Reactive oxygen species (ROS), produced acutely during skeletal muscle contraction, are known to stimulate group IV muscle afferents and accentuate the exercise pressor reflex (EPR) in rodents. The effect of ROS on the EPR in humans is unknown. We conducted a series of studies using ischemic fatiguing rhythmic handgrip to acutely increase ROS within skeletal muscle, ascorbic acid infusion to scavenge free radicals, and hyperoxia inhalation to further increase ROS production. We hypothesized that ascorbic acid would attenuate the EPR and that hyperoxia would accentuate the EPR. Ten young healthy subjects participated in two or three experimental trials on separate days. Beat-by-beat measurements of heart rate (HR), mean arterial pressure (MAP), muscle sympathetic nerve activity (MSNA), and renal vascular resistance index (RVRI) were measured and compared between treatments (saline and ascorbic acid; room air and hyperoxia). At fatigue, the reflex increases in MAP (31 ± 3 versus 29 ± 2 mmHg), HR (19 ± 3 versus 20 ± 3 bpm), MSNA burst rate (21 ± 4 versus 23 ± 4 burst/min), and RVRI (39 ± 12 versus 44 ± 13%) were not different between saline and ascorbic acid. Relative to room air, hyperoxia did not augment the reflex increases in MAP, HR, MSNA, or RVRI in response to exercise. Muscle metaboreflex activation and time/volume control experiments similarly showed no treatment effects. While contrary to our initial hypotheses, these findings suggest that ROS do not play a significant role in the normal reflex adjustments to ischemic exercise in young healthy humans.

Vitamin C prevents intrauterine programming of in vivo cardiovascular dysfunction in the rat

BACKGROUND

Fetal hypoxia is common and in vitro evidence supports its role in the programming of adult cardiovascular dysfunction through the generation of oxidative stress. Whether fetal chronic hypoxia programmes alterations in cardiovascular control in vivo, and if these alterations can be prevented by antioxidant treatment, is unknown. This study investigated the effects of prenatal fetal hypoxia, with and without maternal supplementation with vitamin C, on basal and stimulated cardiovascular function in vivo in the adult offspring at 4 months of age in the rat.

METHODS AND RESULTS

From days 6 to 20 of pregnancy, Wistar rats were subjected to Normoxia, Hypoxia (13% O2), Hypoxia+Vitamin C (5mg/ml in drinking water) or Normoxia+Vitamin C. At 4 months, male offspring were instrumented under urethane anaesthesia. Basal mean arterial blood pressure, heart rate and heart rate variability (HRV) were assessed, and stimulated baroreflex curves were generated with phenylephrine and sodium nitroprusside. Chronic fetal hypoxia increased the LF/HF HRV ratio and baroreflex gain, effects prevented by vitamin C administration during pregnancy.

CONCLUSIONS

Chronic intrauterine hypoxia programmes cardiovascular dysfunction in vivo in adult rat offspring; effects ameliorated by maternal treatment with vitamin C. The data support a role for fetal chronic hypoxia programming cardiovascular dysfunction in the adult rat offspring in vivo through the generation of oxidative stress in utero. 

Translational examination of changes in baroreflex function after renal denervation in hypertensive rats and humans

Renal denervation has shown promise in the treatment of resistant hypertension, although the mechanisms underlying the blood pressure (BP) reduction remain unclear. In a translational study of spontaneously hypertensive rats (n=7, surgical denervation) and resistant hypertensive human patients (n=8; 5 men, 33-71 years), we examined the relationship among changes in BP, sympathetic nerve activity, and cardiac and sympathetic baroreflex function after renal denervation. In humans, mean systolic BP (SBP; sphygmomanometry) and muscle sympathetic nerve activity (microneurography) were unchanged at 1 and 6 months after renal denervation (P<0.05). Interestingly, 4 of 8 patients showed a 10% decrease in SBP at 6 months, but sympathetic activity did not necessarily change in parallel with SBP. In contrast, all rats showed significant and immediate decreases in telemetric SBP and lumbar sympathetic activity (P<0.05), 7 days after denervation. Despite no change in SBP, human cardiac and sympathetic baroreflex function (sequence and threshold techniques) showed improvements at 1 and 6 months after denervation, particularly through increased sympathetic baroreflex sensitivity to falling BP. This was mirrored in spontaneously hypertensive rats; cardiac and sympathetic baroreflex sensitivity (spontaneous sequence and the Oxford technique) improved 7 days after denervation. The more consistent results in rats may be because of a more complete (>90% reduction in renal norepinephrine content) denervation. We conclude that (1) renal denervation improves BP in some patients, but sympathetic activity does not always change in parallel, and (2) baroreflex sensitivity is consistently improved in animals and humans, even when SBP has not decreased. Determining procedural success will be crucial in advancing this treatment modality.

Effects of the administration of a catalase inhibitor into the fourth cerebral ventricle on cardiovascular responses in spontaneously hypertensive rats exposed to sidestream cigarette smoke

OBJECTIVE

Previous studies have demonstrated a relationship between brain oxidative stress and cardiovascular regulation. We evaluated the effects of central catalase inhibition on cardiovascular responses in spontaneously hypertensive rats exposed to sidestream cigarette smoke.

METHODS

Male Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SH) (16 weeks old) were implanted with a stainless steel guide cannula leading into the fourth cerebral ventricle (4th V). The femoral artery and vein were cannulated for arterial pressure and heart rate measurement and drug infusion, respectively. The rats were exposed to sidestream cigarette smoke for 180 minutes/day, 5 days/week for 3 weeks (CO: 100-300 ppm). The baroreflex was tested using a pressor dose of phenylephrine (8 μg/kg, bolus) and a depressor dose of sodium nitroprusside (50 μg/kg, bolus). Cardiovascular responses were evaluated before and 5, 15, 30 and 60 minutes after injection of a catalase inhibitor (3-amino-1,2,4-triazole, 0.001 g/100 μL) into the 4th V.

RESULTS

Vehicle administration into the 4th V did not affect the cardiovascular response, whereas administration of the central catalase inhibitor increased the basal HR and attenuated the bradycardic peak (p<0.05) to a greater extent in WKY rats exposed to sidestream cigarette smoke than in WKY rats exposed to fresh air. However, in spontaneously hypertensive rats, the effect of the catalase inhibitor treatment was stronger in the fresh air condition (p<0.05).

CONCLUSION

Administration of a catalase inhibitor into the 4th V combined with exposure to sidestream cigarette smoke has a stronger effect in WKY rats than in SH rats.

Scavenging of NADPH oxidase-derived superoxide anions improves depressed baroreflex sensitivity in spontaneously hypertensive rats

In pathological conditions, such as hypertension, there is impairment in the autonomic control of blood pressure resulting in changes in baroreflex sensitivity. In the present study we tested the hypothesis that acute superoxide scavenging would restore the depressed baroreflex sensitivity (BRS) in spontaneously hypertensive rats (SHR). Male 10-week-old SHR (n = 14) and their controls (Wistar-Kyoto (WKY) rats; n = 14) underwent femoral artery and vein catheterization for conscious blood pressure recording and drug administration. The BRS was obtained by the drug-induced method using phenylephrine (8 μg/kg, i.v.) and sodium nitroprusside (25 μg/kg, i.v.) before and after the administration of tiron (30 mg/kg, i.v.), a superoxide dismutase mimetic, or apocynin (30 μg/kg), an NADPH oxidase inhibitor. Spontaneously hypertensive rats was significantly hypertensive compared with WKY rats (160 ± 7 vs 105 ± 2 mmHg, respectively). However, there was no significant difference in heart rate between the two groups (388 ± 10 vs 370 ± 20 b.p.m.). In addition, SHR exhibited a diminished BRS compared with WKY rats (-1.34 ± 0.11 vs -2.91 ± 0.20 b.p.m./mmHg, respectively). Administration of tiron improved BRS in SHR (from -1.34 ± 0.11 to 2.26 ± 0.21 b.p.m./mmHg), as did apocynin (to -2.14 ± 0.23 b.p.m./mmHg). Serum samples from SHR (n = 20) and WKY rats (n = 20) were collected for thiobarbituric acid-reactive substances assays before and after tiron or apocynin to confirm the reduction in oxidative stress. There was considerably greater oxidative stress in SHR compared with WKY rats (36.2 ± 3.0 vs 13.3 ± 2.6 nmol/L, respectively). Both apocynin and tiron treatment reduced the oxidative stress in SHR (from 36.2 ± 3.0 to 21.5 ± 3.0 nmol/L and from 37.2 ± 3.9 to 21.9 ± 1.6 nmol/L, respectively). The data suggest that acute scavenging of NADPH oxidase-derived superoxide improves baroreflex sensitivity in SHR.

α-lipoic acid reduces hypertension and increases baroreflex sensitivity in renovascular hypertensive rats

Renovascular hypertension has robust effects on control of blood pressure, including an impairment in baroreflex mechanisms, which involves oxidative stress. Although α-lipoic acid (LA) has been described as a potent antioxidant, its effect on renovascular hypertension and baroreflex sensitivity (BRS) has not been investigated. In the present study we analyzed the effects caused by chronic treatment with LA on blood pressure, heart rate and baroreflex sensitivity (sympathetic and parasympathetic components) in renovascular hypertensive rats. Male Wistar rats underwent 2-Kidney-1-Clip (2K1C) or sham surgery and were maintained untouched for four weeks to develop hypertension. Four weeks post-surgery, rats were treated with LA (60 mg/kg) or saline for 14 days orally. On the 15th day mean arterial pressure (MAP) and heart rate (HR) were recorded. In addition, baroreflex sensitivity test using phenylephrine (8 µg/kg, i.v.) and sodium nitroprusside (25 µg/kg, i.v.) was performed. Chronic treatment with LA decreased blood pressure in hypertensive animals; however, no significant changes in baseline HR were observed. Regarding baroreflex, LA treatment increased the sensitivity of both the sympathetic and parasympathetic components. All parameters studied were not affected by treatment with LA in normotensive animals. Our data suggest that chronic treatment with LA promotes antihypertensive effect and improves baroreflex sensitivity in rats with renovascular hypertension.

Oxidative stress contributes to the augmented exercise pressor reflex in peripheral arterial disease patients

Exaggerated blood pressure (BP) responses to dynamic exercise predict cardiovascular mortality in patients with peripheral arterial disease (PAD). However, the underlying mechanisms are unclear and no attempt has been made to attenuate this response using antioxidants. Three physiological studies were conducted in patients with PAD and controls. In Protocol 1, subjects underwent 4 min of low-intensity (0.5-2.0 kg), rhythmic plantar flexion in the supine posture. In Protocol 2, patients with PAD received high-dose ascorbic acid intravenously before exercise. In Protocol 3, involuntary exercise was conducted via electrical stimulation of the tibial nerve. The primary outcome measure was Δ mean arterial pressure (MAP) during the first 20 s of exercise (i.e. the onset of sympathoexcitation by muscle afferents). Compared to controls, patients with PAD had significantly greater ΔMAP during plantar flexion, particularly at 0.5 kg with the most affected leg (11 ± 2 vs. 2 ± 1 mmHg) as well as the least affected leg (7 ± 1 vs. 1 ± 1 mmHg). This augmented response occurred before the onset of claudication pain and was attenuated by ∼50% with ascorbic acid. Electrically evoked exercise also elicited larger haemodynamic changes in patients with PAD compared to controls. Further, the ΔMAP during 0.5 kg plantar flexion inversely correlated with the ankle-brachial index, indicating that patients with more severe resting limb ischaemia have a larger BP response to exercise. The BP response to low-intensity exercise was enhanced in PAD. Chronic limb ischaemia may sensitize muscle afferents and potentiate the BP response to muscle contraction in a dose-dependent manner.

Effect of acute administration of vitamin C on muscle sympathetic activity, cardiac sympathovagal balance, and baroreflex sensitivity in hypertensive patients

BACKGROUND

Essential hypertension is characterized by both increased oxidative stress and sympathetic traffic. Experimental studies have shown that reactive oxygen species can modulate autonomic activity.

OBJECTIVE

The aim of this study was to determine whether acute administration of the antioxidant vitamin C modifies sympathetic nerve activity in essential hypertension.

DESIGN

Thirty-two untreated patients with essential hypertension and 20 normotensive subjects received vitamin C (3 g intravenously in 5 min) or vehicle. Heart rate, noninvasive beat-to-beat blood pressure, and muscle sympathetic nerve activity (microneurography) were monitored at baseline and up to 20 min after the infusion. Spectral analysis of RR interval variability and spontaneous baroreflex sensitivity were also computed.

RESULTS

Vitamin C infusion significantly lowered blood pressure in hypertensive patients but not in normotensive subjects (maximal changes in systolic blood pressure: -4.9 ± 10.1 compared with -0.7 ± 4.0 mm Hg, respectively; P < 0.05). Moreover, muscle sympathetic nerve activity was significantly reduced after vitamin C infusion in hypertensive patients (from 53.3 ± 12.2 to 47.4 ± 11.5 bursts/100 heart beats; P < 0.01) but not in healthy subjects (from 42.0 ± 10.1 to 42.7 ± 11.8 bursts/100 heart beats; NS). On the contrary, in 16 hypertensive patients, sodium nitroprusside in equidepressor doses induced a significant increase in muscle sympathetic nerve activity compared with vitamin C (+10.0 ± 6.9 bursts/100 heart beats). Sympathovagal balance and spontaneous baroreflex sensitivity were restored during vitamin C infusion in hypertensive subjects.

CONCLUSIONS

These results indicate that acute administration of vitamin C is able to reduce cardiovascular adrenergic drive in hypertensive patients, which suggests that oxidative stress is involved in the regulation of sympathetic activity in essential hypertension.

Brain-derived neurotrophic factor ameliorates brain stem cardiovascular dysregulation during experimental temporal lobe status epilepticus

BACKGROUND

Status epilepticus (SE) is an acute, prolonged epileptic crisis with a mortality rate of 20-30%; the underlying mechanism is not completely understood. We assessed the hypothesis that brain stem cardiovascular dysregulation occurs during SE because of oxidative stress in rostral ventrolateral medulla (RVLM), a key nucleus of the baroreflex loop; to be ameliorated by brain-derived neurotrophic factor (BDNF) via an antioxidant action.

METHODOLOGY/PRINCIPAL FINDINGS

In a clinically relevant experimental model of temporal lobe SE (TLSE) using Sprague-Dawley rats, sustained hippocampal seizure activity was accompanied by progressive hypotension that was preceded by a reduction in baroreflex-mediated sympathetic vasomotor tone; heart rate and baroreflex-mediated cardiac responses remained unaltered. Biochemical experiments further showed concurrent augmentation of superoxide anion, phosphorylated p47(phox) subunit of NADPH oxidase and mRNA or protein levels of BDNF, tropomyosin receptor kinase B (TrkB), angiotensin AT1 receptor subtype (AT1R), nitric oxide synthase II (NOS II) or peroxynitrite in RVLM. Whereas pretreatment by microinjection bilaterally into RVLM of a superoxide dismutase mimetic (tempol), a specific antagonist of NADPH oxidase (apocynin) or an AT1R antagonist (losartan) blunted significantly the augmented superoxide anion or phosphorylated p47(phox) subunit in RVLM, hypotension and the reduced baroreflex-mediated sympathetic vasomotor tone during experimental TLSE, pretreatment with a recombinant human TrkB-Fc fusion protein or an antisense bdnf oligonucleotide significantly potentiated all those events, alongside peroxynitrite. However, none of the pretreatments affected the insignificant changes in heart rate and baroreflex-mediated cardiac responses.

CONCLUSIONS/SIGNIFICANCE

We conclude that formation of peroxynitrite by a reaction between superoxide anion generated by NADPH oxidase in RVLM on activation by AT1R and NOS II-derived NO leads to a reduction in baroreflex-mediated sympathetic vasomotor tone during experimental TLSE; to be ameliorated by the upregulated BDNF/TrkB signaling via inhibition of p47(phox) phosphorylation. This information offers a new vista in devising therapeutic strategy towards minimizing mortality associated with TLSE.

Obesity and adipokines: effects on sympathetic overactivity

Excess body weight is a major risk factor for cardiovascular disease, increasing the risk of hypertension, hyperglycaemia and dyslipidaemia, recognized as the metabolic syndrome. Adipose tissue acts as an endocrine organ by producing various signalling cytokines called adipokines (including leptin, free fatty acids, tumour necrosis factor-α, interleukin-6, C-reactive protein, angiotensinogen and adiponectin). A chronic dysregulation of certain adipokines can have deleterious effects on insulin signalling. Chronic sympathetic overactivity is also known to be present in central obesity, and recent findings demonstrate the consequence of an elevated sympathetic outflow to organs such as the heart, kidneys and blood vessels. Chronic sympathetic nervous system overactivity can also contribute to a further decline of insulin sensitivity, creating a vicious cycle that may contribute to the development of the metabolic syndrome and hypertension. The cause of this overactivity is not clear, but may be driven by certain adipokines. The purpose of this review is to summarize how obesity, notably central or visceral as observed in the metabolic syndrome, leads to adipokine expression contributing to changes in insulin sensitivity and overactivity of the sympathetic nervous system.

Catalase inhibition into the fourth cerebral ventricle affects bradycardic parasympathetic response to increase in arterial pressure without changing the baroreflex

Exogenous catalase influences neural control of cardiovascular system; however, we do not know yet if its inhibition into the fourth cerebral ventricle (4(th) V) influences baroreflex regulation. We evaluated the effects of central catalase inhibition on baroreflex in conscious Wistar rats. We used males Wistar rats (320-370 g), which were implanted with a stainless steel guide cannula into 4(th) V. The femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. After basal MAP and HR recordings, the baroreflex was tested with a pressor dose of phenylephrine (PHE, 8 μg/kg, bolus) and a depressor dose of sodium nitroprusside (SNP, 50 μg/kg, bolus). Baroreflex was evaluated before 5, 15, 30 and 60 minutes after 3-amino-1, 2, 4-triazole (ATZ, 0.001 g/100 μL) injection into the 4(th) V. Vehicle treatment did not change baroreflex responses. ATZ attenuated bradycardic peak and reduced HR range at 30 minutes. ATZ into the 4(th) V reduced bradycardic and tachycardic reflex responses to increase and decrease MAP, respectively (p<0.05) 30 minutes after its microinjection without significantly changing the basal MAP and HR. In conclusion, central catalase inhibition influenced the highest parasympathetic response to MAP increase in conscious Wistar rats without change baroreflex gain.

Receptor-mediated enhancement of beta adrenergic drug activity by ascorbate in vitro and in vivo

Rationale

Previous in vitro research demonstrated that ascorbate enhances potency and duration of activity of agonists binding to alpha 1 adrenergic and histamine receptors.

Objectives

Extending this work to beta 2 adrenergic systems in vitro and in vivo.

Methods

Ultraviolet spectroscopy was used to study ascorbate binding to adrenergic receptor preparations and peptides. Force transduction studies on acetylcholine-contracted trachealis preparations from pigs and guinea pigs measured the effect of ascorbate on relaxation due to submaximal doses of beta adrenergic agonists. The effect of inhaled albuterol with and without ascorbate was tested on horses with heaves and sheep with carbachol-induced bronchoconstriction.

Measurements

Binding constants for ascorbate binding to beta adrenergic receptor were derived from concentration-dependent spectral shifts. Dose- dependence curves were obtained for the relaxation of pre-contracted trachealis preparations due to beta agonists in the presence and absence of varied ascorbate. Tachyphylaxis and fade were also measured. Dose response curves were determined for the effect of albuterol plus-and-minus ascorbate on airway resistance in horses and sheep.

Main Results

Ascorbate binds to the beta 2 adrenergic receptor at physiological concentrations. The receptor recycles dehydroascorbate. Physiological and supra-physiological concentrations of ascorbate enhance submaximal epinephrine and isoproterenol relaxation of trachealis, producing a 3–10-fold increase in sensitivity, preventing tachyphylaxis, and reversing fade. In vivo, ascorbate improves albuterol's effect on heaves and produces a 10-fold enhancement of albuterol activity in “asthmatic” sheep.

Conclusions

Ascorbate enhances beta-adrenergic activity via a novel receptor-mediated mechanism; increases potency and duration of beta adrenergic agonists effective in asthma and COPD; prevents tachyphylaxis; and reverses fade. These novel effects are probably caused by a novel mechanism involving phosphorylation of aminergic receptors and have clinical and drug-development applications.

Acute superoxide scavenging restores depressed baroreflex sensitivity in renovascular hypertensive rats

In some pathological conditions such as hypertension, there is an impairment in the autonomic control of blood pressure resulting in changes in baroreflex sensitivity. In the present study we tested the hypothesis that acute superoxide scavenging would restore the reduced baroreflex sensitivity in renovascular hypertension. Male Wistar rats underwent 2-Kidney-1-Clip (2K1C) or sham surgery and were maintained untouched for six weeks to develop hypertension. After six weeks, animals from the 2K1C group were hypertensive when compared to the sham group (165±9 vs. 108±7mm Hg, P<0.05). As a proof of principle for the hypertension model adopted, animals from the 2K1C group presented increased non-clipped kidney and cardiac mass index and reduced clipped kidney mass index. Regarding baroreflex, 2K1C rats presented diminished baroreflex sensitivity when compared to the sham group (2K1C+saline: -1.61±0.15 vs. sham+saline: -2.79±0.24bpm mm Hg(-1), p<0.05). Moreover, acute administration of Vitamin C (150mg/Kg, i.v.) restored baroreflex sensitivity in 2K1C rats (2K1C+Vit C: -3.08±0.37 vs. 2K1C+saline: -1.61±0.15bpm mm Hg(-1), p<0.05). Furthermore, administration of apocynin (30μg/Kg, i.v.), a NADPH oxidase inhibitor, also improved baroreflex sensitivity in the 2K1C group (2K1C+apocynin: -2.81±0.24 vs. 2K1C+saline: -1.61±0.15bpm mm Hg(-1), p<0.05). In addition, autonomic blockade with either methylatropine or propranolol reduced the changes in heart rate to the same extent in all groups suggesting that improved baroreflex sensitivity by antioxidants were mediated by improvement in autonomic function. Taken together, these data suggest that NADPH oxidase-derived reactive oxygen species are involved in the blunted baroreflex sensitivity in renovascular hypertension and that acute scavenging of superoxide restores baroreflex sensitivity.

Chronic antioxidant treatment improves arterial renovascular hypertension and oxidative stress markers in the kidney in Wistar rats

BACKGROUND

Sympathetic vasomotor hyperactivity and baroreflex dysfunction are involved in the development and maintenance of renovascular arterial hypertension. We hypothesized that angiotensin (Ang) II-dependent oxidative stress contributes to the pathophysiology of the two-kidney, one-clip (2K-1C) model.

METHODS

The mean arterial pressure (MAP), baroreflex, and renal sympathetic nerve activity (rSNA) were evaluated after chronic administration of an antioxidant, vitamin C (vitC 150 mg/kg/day) in male Wistar 2K-1C rats. Additionally, the mRNA levels of Ang II subtype 1 receptor (AT(1)R), NAD(P)H oxidase subunits (p47phox and gp91phox), and major antioxidant enzymes were evaluated in the renal cortex.

RESULTS

After vitC treatment, the MAP (170 +/- 4 vs. 133 +/- 6 mm Hg; P < 0.05) and rSNA (161 +/- 5 vs. 118 +/- 12 spikes/s; P < 0.05) were significantly reduced only in the 2K-1C group. VitC improved the baroreflex control of heart rate (HR) and rSNA. The expression of AT(1)R, p47phox, and gp91phox was elevated (51, 184, and 132%, respectively) in the clipped kidney of 2K-1C group. VitC downregulated AT(1)R in the clipped kidney (31%). Catalase (CAT) expression was reduced in clipped (70%) and nonclipped (83%) kidneys of 2K-1C rats. VitC treatment augmented the expression of glutathione peroxidase (GPx) in both clipped (185%) and nonclipped (212%) kidneys of the 2K-1C group.

CONCLUSIONS

The present study suggests a role for oxidative stress in the cardiovascular and sympathetic alterations in renovascular hypertension, associated with changes in the expression of AT(1)R, NAD(P)H oxidase subunits, and antioxidant enzymes in the kidney.

Targeting cardiac sympatho-vagal imbalance using gene transfer of nitric oxide synthase

Heightened sympathetic excitation and diminished parasympathetic suppression of heart rate, cardiac contractility and vascular tone are all associated with cardiovascular diseases such as hypertension and ischemic heart disease. This phenotype often exists before these disease states have been established and is a strong correlate of mortality in the population. However, the causal role of the autonomic phenotype in the development and maintenance of hypertension and myocardial ischemia remains a subject of debate, as are the mechanisms responsible for regulating sympathovagal balance. Emerging evidence suggests oxidative stress and reactive oxygen species (such as nitric oxide (NO) and superoxide) play important roles in the modulation of autonomic balance, but so far the most important sites of action of these ubiquitous signaling molecules are unclear. In many cases, these mediators have opposing effects in separate tissues rendering conventional pharmacological approaches non-efficacious. Novel techniques have recently been used to augment these signaling pathways experimentally in a targeted fashion to central autonomic nuclei, cardiac neurons, and myocytes using gene transfer of NO synthase. This review article discusses these recent advances in the understanding of the roles of NO and its oxidative metabolites on autonomic imbalance in models of cardiovascular disease.

High-dose ascorbic acid infusion abolishes chronic vasoconstriction and restores resting leg blood flow in healthy older men

Resting whole leg blood flow and vascular conductance decrease linearly with advancing age in healthy adult men. The potential role of age-related increases in oxidative stress in these changes is unknown. Resting leg blood flow during saline and ascorbic acid infusion was studied in 10 young (25 +/- 1 yr) and 11 older (63 +/- 2 yr) healthy normotensive men. Plasma oxidized LDL, a marker of oxidative stress, was greater in the older men (P < 0.05). Absolute resting femoral artery blood flow at baseline (iv saline control infusion) was 25% lower in the older men (238 +/- 25 vs. 316 +/- 38 ml/min; P < 0.05), and it was inversely related to plasma oxidized LDL (r = -0.56, P < 0.01) in all subjects. Infusion of supraphysiological concentrations of ascorbic acid increased femoral artery blood flow by 37% in the older men (to 327 +/- 52 ml/min; P < 0.05), but not in the young men (352 +/- 41 ml/min; P = 0.28), thus abolishing group differences (P = 0.72). Mean arterial blood pressure was greater in the older men at baseline (86 +/- 4 vs. 78 +/- 2 mmHg; P < 0.05), but it was unaffected by ascorbic acid infusion (P >/= 0.70). As a result, the lower baseline femoral artery blood flow in the older men was mediated solely by a 32% lower femoral artery vascular conductance (P < 0.05). Baseline femoral vascular conductance also was inversely related to plasma oxidized LDL (r = -0.65, P < 0.01). Ascorbic acid increased femoral vascular conductance by 36% in the older men (P < 0.05) but not in the young men (P = 0.31). In conclusion, ascorbic acid infused at concentrations known to scavenge reactive oxygen species restores resting femoral artery blood flow in healthy older adult men by increasing vascular conductance. These results support the hypothesis that oxidative stress plays a major role in the reduced resting whole leg blood flow and increased leg vasoconstriction observed with aging in men.

Baroreflex control of muscle sympathetic nerve activity during skin surface cooling

Skin surface cooling improves orthostatic tolerance through a yet to be identified mechanism. One possibility is that skin surface cooling increases the gain of baroreflex control of efferent responses contributing to the maintenance of blood pressure. To test this hypothesis, muscle sympathetic nerve activity (MSNA), arterial blood pressure, and heart rate were recorded in nine healthy subjects during both normothermic and skin surface cooling conditions, while baroreflex control of MSNA and heart rate were assessed during rapid pharmacologically induced changes in arterial blood pressure. Skin surface cooling decreased mean skin temperature (34.9 ± 0.2 to 29.8 ± 0.6°C; P < 0.001) and increased mean arterial blood pressure (85 ± 2 to 93 ± 3 mmHg; P < 0.001) without changing MSNA ( P = 0.47) or heart rate ( P = 0.21). The slope of the relationship between MSNA and diastolic blood pressure during skin surface cooling (−3.54 ± 0.29 units·beat−1·mmHg−1) was not significantly different from normothermic conditions (−2.94 ± 0.21 units·beat−1·mmHg−1; P = 0.19). The slope depicting baroreflex control of heart rate was also not altered by skin surface cooling. However, skin surface cooling shifted the “operating point” of both baroreflex curves to high arterial blood pressures (i.e., rightward shift). Resetting baroreflex curves to higher pressure might contribute to the elevations in orthostatic tolerance associated with skin surface cooling.

Acute autonomic effects of vitamins and fats in male smokers

BACKGROUND/OBJECTIVES

Vitamins can help improve cardiovascular control. In contrast, smoking works in the opposite fashion, reducing the baroreflex control of heart rate (HR) possibly via oxidative stress. High-fat challenges also impair cardiovascular regulation. Whether vitamins have acute beneficial effects on the baroreflex control of HR in smokers is unclear.

SUBJECTS/METHODS

A randomized, placebo-controlled crossover study in 30 male smokers (34.2+/-6.9 years). Interventions were: (1) moderate (vitamin C (300 mg) and E (75 IU) and folic acid (1 mg)); (2) high doses of vitamins (vitamin C (2 g) and E (800 IU), and folic acid (5 mg)); or, (3) placebo. Vitamins were ingested with cream (a high-fat challenge) or milk (low-fat control). Four hours later, blood was withdrawn and radial pulse wave forms recorded via tonometry. Spontaneous beat-to-beat variations in HR and systolic blood pressure (SBP) were analysed by spectral analysis techniques and sympathovagal control of HR and baroreflex sensitivity (BRS) were assessed.

RESULTS

High doses of vitamins increased plasma vitamin C, E and folic acid levels (P<0.05) with no change in SBP, HR or BRS (P>0.05, analysis of variance). Plasma vitamin levels did not correlate with any cardiovascular parameters. Moderate vitamins increased the vagal control of HR (+23%; P<0.05) and cream led to small increases (P<0.05) in SBP (+2 mm Hg) and HR (+2 beats min(-1)) with no change in BRS.

CONCLUSIONS

In male smokers, circulating antioxidants had no effect on BRS and minor effects on the cardiovascular system were seen following acute fat and vitamin ingestion.

Effect of aging on baroreflex function in humans

Arterial blood pressure (BP) is regulated via the interaction of various local, humoral, and neural factors. In humans, the major neural pathway for acute BP regulation involves the baroreflexes. In response to baroreceptor activation/deactivation, as occurs during transient changes in BP, key determinants of BP, such as cardiac period/heart rate (via the sympathetic and parasympathetic nervous system) and vascular resistance (via the sympathetic nervous system), are modified to maintain BP homeostasis. In this review, the effects of aging on both the parasympathetic and sympathetic arms of the baroreflex are discussed. Aging is associated with decreased cardiovagal baroreflex sensitivity (i.e., blunted reflex changes in R-R interval in response to a change in BP). Mechanisms underlying this decrease may involve factors such as increased levels of oxidative stress, vascular stiffening, and decreased cardiac cholinergic responsiveness with age. Consequences of cardiovagal baroreflex impairment may include increased levels of BP variability, an impaired ability to respond to acute challenges to the maintenance of BP, and increased risk of sudden cardiac death. In contrast, baroreflex control of sympathetic outflow is not impaired with age. Collectively, changes in baroreflex function with age are associated with an impaired ability of the organism to buffer changes in BP. This is evidenced by the reduced potentiation of the pressor response to bolus infusion of a pressor drug after compared to before systemic ganglionic blockade in older compared with young adults.

Aldosterone impairs baroreflex sensitivity in healthy adults

Animal studies suggest that acute and chronic aldosterone administration impairs baroreceptor/baroreflex responses. We tested the hypothesis that aldosterone impairs baroreflex control of cardiac period [cardiovagal baroreflex sensitivity (BRS)] and muscle sympathetic nerve activity (MSNA, sympathetic BRS) in humans. Twenty-six young (25 +/- 1 yr old, mean +/- SE) adults were examined in this study. BRS was determined by using the modified Oxford technique (bolus infusion of nitroprusside, followed 60 s later by bolus infusion of phenylephrine) in triplicate before (Pre) and 30-min after (Post) beginning aldosterone (experimental, 12 pmol.kg(-1).min(-1); n = 10 subjects) or saline infusion (control; n = 10). BRS was quantified from the R-R interval-systolic blood pressure (BP) (cardiovagal BRS) and MSNA-diastolic BP (sympathetic BRS) relations. Aldosterone infusion increased serum aldosterone levels approximately fourfold (P < 0.05) and decreased (P < 0.05) cardiovagal (19.0 +/- 2.3 vs. 15.6 +/- 1.7 ms/mmHg Pre and Post, respectively) and sympathetic BRS [-4.4 +/- 0.4 vs. -3.0 +/- 0.4 arbitrary units (AU).beat(-1).mmHg(-1)]. In contrast, neither cardiovagal (19.3 +/- 3.3 vs. 20.2 +/- 3.3 ms/mmHg) nor sympathetic BRS (-3.8 +/- 0.5 vs. -3.6 +/- 0.5 AU.beat(-1).mmHg(-1)) were altered (Pre vs. Post) in the control group. BP, heart rate, and MSNA at rest were similar in experimental and control subjects before and after the intervention. Additionally, neural and cardiovascular responses to a cold pressor test and isometric handgrip to fatigue were unaffected by aldosterone infusion (n = 6 subjects). These data provide direct experimental support for the concept that aldosterone impairs baroreflex function (cardiovagal and sympathetic BRS) in humans. Therefore, aldosterone may be an important determinant/modulator of baroreflex function in humans.

Oxidative stress contributes to chronic leg vasoconstriction in estrogen-deficient postmenopausal women

Basal whole leg blood flow and vascular conductance are reduced in estrogen-deficient postmenopausal compared with premenopausal women. The underlying mechanisms are unknown, but oxidative stress could be involved. We studied 9 premenopausal [23 +/- 1 yr (mean +/- SE)] and 20 estrogen-deficient postmenopausal (55 +/- 1 yr) healthy women. During baseline control, oxidized low-density lipoprotein (LDL), a marker of oxidative stress, was 50% greater in the postmenopausal women (P < 0.001). Basal whole leg blood flow (duplex ultrasound of femoral artery) was 34% lower in the postmenopausal women because of a 38% lower leg vascular conductance (P < 0.0001); mean arterial pressure was not different. Intravenous administration of a supraphysiological dose of the antioxidant ascorbic acid increased leg blood flow by 15% in the postmenopausal women as a result of an increase in leg vascular conductance (both P < 0.001), but it did not affect leg blood flow in premenopausal controls or mean arterial pressure in either group. In the pooled subjects, the changes in leg blood flow and leg vascular conductance with ascorbic acid were related to baseline plasma oxidized LDL (r = 0.46 and 0.53, P < 0.01) and waist-to-hip ratio and total body fat (r = 0.41-0.44, all P < 0.05). Our results are consistent with the hypothesis that oxidative stress contributes to chronic leg vasoconstriction and reduced basal whole leg blood flow in estrogen-deficient postmenopausal women. This oxidative stress-related suppression of leg vascular conductance and blood flow may be linked in part to increased total and abdominal adiposity.

N-acetylcysteine attenuates TNF-alpha-induced human vascular endothelial cell apoptosis and restores eNOS expression

The circulatory inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) is increased in pathological conditions, such as diabetes, which initiate or exacerbate vascular endothelial injury. Both nitric oxide (NO) and reactive oxygen species may play a dual role (i.e., inhibiting or promoting) in TNF-alpha-induced endothelial cell apoptosis. We investigated the effects of the antioxidant N-acetylcysteine on TNF-alpha-induced apoptosis in human vascular endothelial cell (cell line ECV304) apoptosis, NO production and lipid peroxidation. Cultured vascular endothelial cell (ECV304) were either not treated (control), or treated with TNF-alpha (40 ng/ml) alone or TNF-alpha in the presence of N-acetylcysteine at 30 mmol/l or 1 mmol/l, respectively, for 24 h. Cell viability was measured by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. Cell apoptosis was assessed by flow cytometry. TNF-alpha-induced endothelial cell apoptosis was associated with increased inducible NO synthase but reduced endothelial NO synthase (eNOS) protein expression. NO production and the levels of the lipid peroxidation product malondialdehyde were concomitantly increased. Treatment with NAC at 30 mmol/l restored eNOS expression and further increased NO production as compared to TNF-alpha alone, resulting in improved cell viability and reduced apoptosis. This was accompanied by increased superoxide dismutase activity, increased glutathione peroxidase production and reduced malondialdehyde levels. N-acetylcysteine at 1 mmol/l, however, did not have significant effects on TNF-alpha-induced endothelial cell apoptosis and cell viability despite it slightly enhanced glutathione peroxidase production. N-acetylcysteine attenuation of TNF-alpha-induced human vascular endothelial cell apoptosis is associated with the restoration of eNOS expression.

Effect of repetitive hypoxic apnoeas on baroreflex function in humans

Baroreflex function is impaired in patients with obstructive sleep apnoea. We tested the hypothesis that short-term exposure to repetitive hypoxic apnoeas (RHA) produces prolonged impairment in baroreflex function. Baroreflex function was determined using the modified Oxford technique in 14 subjects (26 +/- 1 years). Baroreflex sensitivity (BRS) was quantified from the R-R interval-systolic blood pressure (BP; cardiovagal BRS), heart rate-systolic BP (HR BRS) and muscle sympathetic nerve activity (MSNA)-diastolic BP (sympathetic BRS) relations. RHA involved subjects performing repetitive end-expiratory apnoeas (20 s) every minute for 30 min during intermittent hypoxia to accentuate oxygen desaturation. After RHA, BP and MSNA at rest were elevated. BRS was measured approximately 7 (Post 1), approximately 30 (Post 2) and approximately 50 min (Post 3) after RHA to provide insight into the temporal pattern of responses. Cardiovagal BRS (16.8 +/- 1.3, 16.5 +/- 1.6, 17.6 +/- 2.0 and 17.4 +/- 1.5 ms mmHg(-1) for Pre, Post 1, Post 2 and Post 3, respectively), HR BRS (-1.1 +/- 0.1, -1.1 +/- 0.1, -1.3 +/- 0.1 and -1.4 +/- 0.1 beats min(-1) mmHg(-1)) and sympathetic BRS (-4.5 +/- 0.6, -4.4 +/- 0.7, -3.7 +/- 0.5 and -4.7 +/- 1.0 arbitrary units (au) beat(-1) mmHg(-1)) were unchanged by RHA. In contrast, the operating points of the baroreflexes were shifted rightward (to higher levels of BP) and upward (to higher levels of heart rate and MSNA) after RHA (P < 0.05). Time control studies performed in five additional subjects showed no change in any of the measured variables over time. Collectively, these data indicate that short-term exposure to RHA shifts ('resets') the baroreflex stimulus-response curve to higher levels of BP without influencing BRS for extended periods of time.

Metallothionein prolongs survival and antagonizes senescence‐associated cardiomyocyte diastolic dysfunction: role of oxidative stress

Senescence is accompanied by oxidative stress and cardiac dysfunction, although the link between the two remains unclear. This study examined the role of antioxidant metallothionein on cardiomyocyte function, superoxide generation, the oxidative stress biomarker aconitase activity, cytochrome c release, and expression of oxidative stress-related proteins, such as the GTPase RhoA and NADPH oxidase protein p47phox in young (5-6 mo) and aged (26-28 mo) FVB wild-type (WT) and cardiac-specific metallothionein transgenic mice. Metallothionein mice showed a longer life span (by approximately 4 mo) than FVB mice evaluated by the Kaplan-Meier survival curve. Compared with young cardiomyocytes, aged myocytes displayed prolonged TR(90), reduced tolerance to high stimulus frequency, and slowed intracellular Ca2+ decay, all of which were nullified by metallothionein. Aging increased superoxide generation, active RhoA abundance, cytochrome c release, and p47phox expression and suppressed aconitase activity without affecting protein nitrotyrosine formation in the hearts. These aging-induced changes in oxidative stress and related protein biomarkers were attenuated by metallothionein. Aged metallothionein mouse myocytes were more resistant to the superoxide donor pyrogallol-induced superoxide generation and apoptosis. In addition, aging-associated prolongation in TR90 was blunted by the Rho kinase inhibitor Y-27632. Collectively, our data demonstrated that metallothionein may alleviate aging-induced cardiac contractile defects and oxidative stress, which may contribute to prolonged life span in metallothionein transgenic mice.

Weight loss increases cardiovagal baroreflex function in obese young and older men

We tested the hypothesis that reductions in total body and abdominal visceral fat with energy restriction would be associated with increases in cardiovagal baroreflex sensitivity (BRS) in overweight/obese older men. To address this, overweight/obese (25 < or = body mass index < or = 35 kg/m(2)) young (OB-Y, n = 10, age = 32.9 +/- 2.3 yr) and older (OB-O, n = 6, age = 60 +/- 2.7 yr) men underwent 3 mo of energy restriction at a level designed to reduce body weight by 5-10%. Cardiovagal BRS (modified Oxford technique), body composition (dual-energy X-ray absorptiometry), and abdominal fat distribution (computed tomography) were measured in the overweight/obese men before weight loss and after 4 wk of weight stability at their reduced weight and compared with a group of nonobese young men (NO-Y, n = 13, age = 21.1 +/- 1.0 yr). Before weight loss, cardiovagal BRS was approximately 35% and approximately 60% lower (P < 0.05) in the OB-Y and OB-O compared with NO-Y. Body weight (-7.8 +/- 1.1 vs. -7.3 +/- 0.7 kg), total fat mass (-4.1 +/- 1.0 vs. -4.4 +/- 0.8 kg), and abdominal visceral fat (-27.6 +/- 6.9 vs. -43.5 +/- 10.1 cm(2)) were reduced (all P < 0.05) after weight loss, but the magnitude of reduction did not differ (all P > 0.05) between OB-Y and OB-O, respectively. Cardiovagal BRS increased (11.5 +/- 1.9 vs. 18.5 +/- 2.6 ms/mmHg and 6.7 +/- 1.2 vs. 12.8 +/- 4.2 ms/mmHg) after weight loss (both P < 0.05) in OB-Y and OB-O, respectively. After weight loss, cardiovagal BRS in the obese/overweight young and older men was approximately 105% and approximately 73% (P > 0.05) of NO-Y (17.5 +/- 2.2 ms/mmHg). Therefore, the results of this study indicate that weight loss increases the sensitivity of the cardiovagal baroreflex in overweight/obese young and older men.

Nocturnal hemodialysis increases arterial baroreflex sensitivity and compliance and normalizes blood pressure of hypertensive patients with end-stage renal disease

BACKGROUND

Impaired neural control of heart rate, elevated arterial stiffness, and hypertension place patients with end-stage renal disease (ESRD) at increased risk of cardiovascular mortality. Nocturnal hemodialysis (6 x 8 hours/week), a more intense program than conventional hemodialysis (3 x 4 hours/week), lowers blood pressure and restores brachial dilator responses to hyperemia and nitrates.

METHODS

We hypothesized that nocturnal hemodialysis would increase arterial baroreflex sensitivity for heart rate of hypertensive ESRD patients by an afferent vascular mechanism. Ten consecutive hypertensive ESRD patients (age 42 +/- 4) (mean +/- SEM) receiving conventional hemodialysis were studied before and 2 months after conversion to nocturnal hemodialysis. Regression slopes relating RR interval responses to rises or falls in systolic blood pressure were averaged to derive spontaneous baroreflex sensitivity for heart rate for each patient, and the stroke volume/pulse pressure ratio was used to estimate total arterial compliance.

RESULTS

Dialysis dose (Kt/V per session) increased from 1.2 +/- 0.05 to 2.1 +/- 0.1 (P < 0.05). Despite withdrawal of antihypertensive medications (from 2.9 to 0.1 drugs/patient), nocturnal hemodialysis lowered systolic blood pressure (from 143 +/- 4 to 120 +/- 6 mm Hg) (P= 0.001). Both baroreflex sensitivity (from 4.76 +/- 1.1 msec/mm Hg to 6.91 +/- 1.1 msec/mm Hg) (P= 0.04) and total arterial compliance (from 0.98 +/- 0.13 mL/mm Hg to 1.43 +/- 0.2 mL/mm Hg) (P= 0.02) were higher following conversion to nocturnal hemodialysis. Increases in baroreflex sensitivity correlated with increases in stroke volume/pulse pressure (r= 0.845, P= 0.002).

CONCLUSION

These findings are consistent with the concept that nocturnal hemodialysis increases baroreflex sensitivity via greater afferent baroreceptor responsiveness to pulsatile pressure. A more favorable risk profile, due to enhanced baroreflex regulation of the circulation and vascular compliance, may translate into lower cardiovascular event rates in ESRD patients receiving nocturnal hemodialysis.

Ascorbic acid selectively improves large elastic artery compliance in postmenopausal women

The compliance of large elastic arteries in the cardiothoracic region decreases with advancing age/menopause and plays an important role in the increased prevalence of cardiovascular diseases in postmenopausal women. We determined whether oxidative stress contributes to the reduced large elastic artery compliance of postmenopausal women. Carotid artery compliance was measured during acute intravenous infusions of saline (baseline control) and supraphysiological doses of the potent antioxidant ascorbic acid in premenopausal (n=10; 23+/-1; mean+/-SE) and estrogen-deficient postmenopausal (n=21; 55+/-1 years) healthy sedentary women. Carotid artery compliance was 56% lower in postmenopausal compared with premenopausal women during baseline control (P<0.0001). Ascorbic acid infusion increased carotid artery compliance by 26% in postmenopausal women (1.11+/-0.07 to 1.38+/-0.08 mm2/mm Hgx10(-1); P<0.001) but had no effect in premenopausal women (2.50+/-0.25 versus 2.43+/-0.20 mm2/mm Hgx10(-1)). Carotid artery diameter, blood pressure, and heart rate were unaffected by ascorbic acid. In the pooled population, the change in arterial compliance with ascorbic acid correlated with baseline waist-to-hip ratio (r=0.56; P=0.001), plasma norepinephrine (r=0.58; P=0.001), and LDL cholesterol (r=0.54; P=0.001). These results suggest that oxidative stress may be an important mechanism contributing to the reduced large elastic artery compliance of sedentary, estrogen-deficient postmenopausal women. Increased abdominal fat storage, sympathetic nervous system activity, and LDL cholesterol may be mechanistically involved in oxidative stress-associated suppression of arterial compliance in postmenopausal women.

Ascorbic acid does not affect the age-associated reduction in maximal cardiac output and oxygen consumption in healthy adults

Maximal aerobic capacity (V̇o2max) decreases progressively with age, primarily because of a reduction in maximal cardiac output (Q̇max). This age-associated decline in V̇o2max may be partially mediated by the development of oxidative stress that can suppress β-adrenergic-receptor responsiveness and, consequently, reduce Q̇max. To test this hypothesis, V̇o2max (indirect calorimetry) and Q̇max (open-circuit acetylene breathing) were determined in 12 young (23 ± 1 yr, mean ± SE) and 10 older (61 ± 1 yr) adults following systemic infusion of either saline (control) and/or the powerful antioxidant ascorbic acid (acute: bolus 0.06; drip 0.02 g/kg fat-free mass) and following chronic 30-day oral administration of ascorbic acid (500 mg/day). Plasma ascorbic acid concentration was not different between young and older adults and was increased similarly, independent of age [change (Δ) acute = 1,055 ± 117%; Δ chronic = 62 ± 19%]. Oxidized low-density lipoprotein concentration was greater ( P < 0.001) in older (57 ± 5 U/l) compared with young (34 ± 3 U/l) adults and was reduced in both groups ( P < 0.02) following acute (Δ = −6 ± 2%) but not chronic ( P = 0.18) ascorbic acid administration. Control (baseline) V̇o2max and Q̇max were positively related ( r = 0.76, P < 0.001) and were lower ( P < 0.05) in older (34 ± 2 ml·kg−1·min−1; 16.1 ± 1.1 l/min) compared with young (43 ± 3 ml·kg−1·min−1; 20.2 ± 0.9 l/min) adults. Following ascorbic acid administration, neither V̇o2max (young acute = 41 ± 2; young chronic = 42 ± 2; older acute = 34 ± 2; older chronic = 34 ± 2 ml·kg−1·min−1) nor Q̇max (young acute = 20.1 ± 0.9; young chronic = 19.1 ± 0.8; older acute = 16.2 ± 1.1; older chronic = 16.6 ± 1.4 l/min) was changed. These data suggest that ascorbic acid administration does not affect the age-associated reduction in Q̇max and V̇o2max.