Short-term daily exercise activity enhances endothelial NO synthesis in skeletal muscle arterioles of rats

Getting to the Heart of the Matter: Exploring the Intersection of Cardiovascular Disease, Sex and Race and How Exercise, and Gut Microbiota Influence these Relationships

Cardiovascular disease (CVD) is the leading cause of death worldwide, with physical inactivity being a known contributor to the global rates of CVD incidence. CVD incidence, however, is not uniform with recognized sex differences as well and racial and ethnic differences. Furthermore, gut microbiota have been associated with CVD, sex, and race/ethnicity. Researchers have begun to examine the interplay of these complicated yet interrelated topics. This review will present evidence that CVD (risk and development), and gut microbiota are distinct between the sexes and racial/ethnic groups, which appear to be influenced by acculturation, discrimination, stress, and lifestyle factors like exercise. Furthermore, this review will address the beneficial impacts of exercise on the cardiovascular system and will provide recommendations for future research in the field.

Effect of continuous aerobic exercise on endothelial function: A systematic review and meta-analysis of randomized controlled trials

Background: Current research suggests that continuous aerobic exercise can be effective in improving vascular endothelial function, while the effect between different intensities and durations of exercise is unclear. The aim of this study was to explore the effect of different durations and intensities of aerobic exercise on vascular endothelial function in different populations. Methods: Searches were performed in PubMed, Web of Science, and EBSCO databases. We included studies that satisfied the following criteria: 1) randomized controlled trials (RCTs); 2) including both an intervention and control group; 3) using flow-mediated dilation (FMD) as the outcome measure; and 4) testing FMD on the brachial artery. Results: From 3,368 search records initially identified, 41 studies were eligible for meta-analysis. There was a significant effect of continuous aerobic exercise on improving flow-mediated dilation (FMD) [weighted mean difference (WMD), 2.55, (95% CI, 1.93-3.16), p < 0.001]. Specifically, moderate-intensity [2.92 (2.02-3.825), p < 0.001] and vigorous-intensity exercise [2.58 (1.64-3.53), p < 0.001] significantly increased FMD. In addition, a longer duration [<12 weeks, 2.25 (1.54-2.95), p < 0.001; ≥12 weeks, 2.74 (1.95-3.54), p < 0.001], an older age [age <45, 2.09 (0.78-3.40), p = 0.002; 45 ≤ age <60, 2.25 (1.49-3.01), p < 0.001; age ≥60, 2.62 (1.31-3.94), p < 0.001], a larger basal body mass index (BMI) [20 < BMI < 25, 1.43 (0.98-1.88), p < 0.001; 25 ≤ BMI < 30, 2.49 (1.07-3.90), p < 0.001; BMI ≥ 30, 3.05 (1.69-4.42), p < 0.001], and a worse basal FMD [FMD < 4, 2.71 (0.92-4.49), p = 0.003; 4 ≤ FMD < 7, 2.63 (2.03-3.23), p < 0.001] were associated with larger improvements in FMD. Conclusion: Continuous aerobic exercise, especially moderate-intensity and vigorous-intensity aerobic exercise, contributed to improving FMD. The effect of continuous aerobic exercise on improving FMD was associated with duration and participant's characteristics. Specifically, a longer duration, an older age, a larger basal BMI, and a worse basal FMD contributed to more significant improvements in FMD. Systematic Review Registration: [https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=341442], identifier [CRD42022341442].

Functional and structural adaptations of the coronary macro- and microvasculature to regular aerobic exercise by activation of physiological, cellular, and molecular mechanisms: ESC Working Group on Coronary Pathophysiology and Microcirculation position paper

Regular aerobic exercise (RAEX) elicits several positive adaptations in all organs and tissues of the body, culminating in improved health and well-being. Indeed, in over half a century, many studies have shown the benefit of RAEX on cardiovascular outcome in terms of morbidity and mortality. RAEX elicits a wide range of functional and structural adaptations in the heart and its coronary circulation, all of which are to maintain optimal myocardial oxygen and nutritional supply during increased demand. Although there is no evidence suggesting that oxidative metabolism is limited by coronary blood flow (CBF) rate in the normal heart even during maximal exercise, increased CBF and capillary exchange capacities have been reported. Adaptations of coronary macro- and microvessels include outward remodelling of epicardial coronary arteries, increased coronary arteriolar size and density, and increased capillary surface area. In addition, there are adjustments in the neural and endothelial regulation of coronary macrovascular tone. Similarly, there are several adaptations at the level of microcirculation, including enhanced (such as nitric oxide mediated) smooth muscle-dependent pressure-induced myogenic constriction and upregulated endothelium-dependent/shear-stress-induced dilation, increasing the range of diameter change. Alterations in the signalling interaction between coronary vessels and cardiac metabolism have also been described. At the molecular and cellular level, ion channels are key players in the local coronary vascular adaptations to RAEX, with enhanced activation of influx of Ca2+ contributing to the increased myogenic tone (via voltage-gated Ca2+ channels) as well as the enhanced endothelium-dependent dilation (via TRPV4 channels). Finally, RAEX elicits a number of beneficial effects on several haemorheological variables that may further improve CBF and myocardial oxygen delivery and nutrient exchange in the microcirculation by stabilizing and extending the range and further optimizing the regulation of myocardial blood flow during exercise. These adaptations also act to prevent and/or delay the development of coronary and cardiac diseases.

Vascular Ageing and Aerobic Exercise

Impairment of vascular function, in particular endothelial dysfunction and large elastic artery stiffening, represents a major link between ageing and cardiovascular risk. Clinical and experimental studies identified numerous mechanisms responsible for age-related decline of endothelial function and arterial compliance. Since most of these mechanisms are related to oxidative stress or low-grade inflammation, strategies that suppress oxidative stress and inflammation could be effective for preventing age-related changes in arterial function. Indeed, aerobic physical activity, which has been shown to improve intracellular redox balance and mitochondrial health and reduce levels of systemic inflammatory markers, also improves endothelial function and arterial distensibility and reduces risk of cardiovascular diseases. The present paper provides a brief overview of processes underlying age-related changes in arterial function, as well as the mechanisms through which aerobic exercise might prevent or interrupt these processes, and thus attenuate vascular ageing.

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

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

Sex Differences in Exercise-Training-Related Functional and Morphological Adaptation of Rat Gracilis Muscle Arterioles

Background

The cardiovascular effects of training have been widely investigated; however, few studies have addressed sex differences in arteriolar adaptation. In the current study, we examined the adaptation of the gracilis arterioles of male and female rats in response to intensive training.

Methods

Wistar rats were divided into four groups: male exercise (ME) and female exercise (FE) animals that underwent a 12-week intensive swim-training program (5 days/week, 200 min/day); and male control (MC) and female control (FC) animals that were placed in water for 5 min daily. Exercise-induced cardiac hypertrophy was confirmed by echocardiography. Following the training, the gracilis muscle arterioles were prepared, and their biomechanical properties and functional reactivity were tested, using pressure arteriography. Collagen and smooth muscle remodeling were observed in the histological sections.

Results

Left ventricular mass was elevated in both sexes in response to chronic training. In the gracilis arterioles, the inner radius and wall tension increased in female animals, and the wall thickness and elastic modulus were reduced in males. Myogenic tone was reduced in the ME group, whereas norepinephrine-induced vasoconstriction was elevated in the FE group. More pronounced collagen staining was observed in the ME group than in the MC group. Relative hypertrophy and tangential stress of the gracilis arterioles were higher in females than in males. The direct vasoconstriction induced by testosterone was lower in females and was reduced as an effect of exercise in males.

Conclusion

The gracilis muscle arteriole was remodeled as a result of swim training, and this adaptation was sex dependent.

Effect of short-term endurance training on venous compliance in the calf and forearm differs between continuous and interval exercise in humans

We examined whether the effect of short-term endurance exercise training on venous compliance in the calf and forearm differed between continuous and interval workloads. Young healthy volunteers (10 women and 16 men) were randomly assigned to continuous (C-TRA; n = 8) and interval (I-TRA; n = 9) exercise training groups, and a control group (n = 9). Subjects in the C-TRA group performed a continuous cycling exercise at 60% of heart rate reserve (HRR), and subjects in the I-TRA group performed a cycling exercise consisting of alternating 2-min intervals at 40% HRR and 80% HRR. Training programs were performed for 40 min/day, 3 days/week for 8 weeks. Before and after training, limb volume in the calf and forearm was measured with subjects in the supine position by venous occlusion plethysmography using a venous collecting cuff placed around the thigh and upper arm. Cuff pressure was held at 60 mmHg for 8 min and then decreased to 0 mmHg at a rate of 1 mmHg/s. Venous compliance was calculated as the numerical derivative of the cuff pressure-limb volume curve. Calf venous compliance was increased after I-TRA, but not C-TRA. Forearm venous compliance was unchanged after C-TRA or I-TRA. These results suggest that the adaptation of venous compliance in response to endurance training for 8 week may occur in interval but not continuous exercise bouts and may be specific to the exercising limb.

Cardiovascular Effects and Benefits of Exercise

It is widely accepted that regular physical activity is beneficial for cardiovascular health. Frequent exercise is robustly associated with a decrease in cardiovascular mortality as well as the risk of developing cardiovascular disease. Physically active individuals have lower blood pressure, higher insulin sensitivity, and a more favorable plasma lipoprotein profile. Animal models of exercise show that repeated physical activity suppresses atherogenesis and increases the availability of vasodilatory mediators such as nitric oxide. Exercise has also been found to have beneficial effects on the heart. Acutely, exercise increases cardiac output and blood pressure, but individuals adapted to exercise show lower resting heart rate and cardiac hypertrophy. Both cardiac and vascular changes have been linked to a variety of changes in tissue metabolism and signaling, although our understanding of the contribution of the underlying mechanisms remains incomplete. Even though moderate levels of exercise have been found to be consistently associated with a reduction in cardiovascular disease risk, there is evidence to suggest that continuously high levels of exercise (e.g., marathon running) could have detrimental effects on cardiovascular health. Nevertheless, a specific dose response relationship between the extent and duration of exercise and the reduction in cardiovascular disease risk and mortality remains unclear. Further studies are needed to identify the mechanisms that impart cardiovascular benefits of exercise in order to develop more effective exercise regimens, test the interaction of exercise with diet, and develop pharmacological interventions for those unwilling or unable to exercise.

Remodeling of Wall Mechanics and the Myogenic Mechanism of Rat Intramural Coronary Arterioles in Response to a Short-Term Daily Exercise Program: Role of Endothelial Factors

PURPOSE

Exercise elicits early adaptation of coronary vessels enabling the coronary circulation to respond adequately to higher flow demands. We hypothesized that short-term daily exercise induces biomechanical and functional remodeling of the coronary resistance arteries related to pressure.

METHODS

Male rats were subjected to a progressively increasing 4-week treadmill exercise program (over 60 min/day, 1 mph in the final step). In vitro pressure-diameter measurements were performed on coronary segments (119 ± 5 μm in diameter at 50 mm Hg) with microarteriography. The magnitude of the myogenic response and contribution of endogenous nitric oxide and prostanoid production to the wall mechanics and pressure-diameter relationship were assessed.

RESULTS

Arterioles isolated from exercised ani mals - compared to the sedentary group - had thicker walls, increased distensibility, and a decreased elastic modulus as a result of reduced wall stress in the low pressure range. The arterioles of exercised rats exhibited a more powerful myogenic response and less endogenous vasoconstrictor prostanoid modulation at higher pressures, while vasodilator nitric oxide modulation of diameter was augmented at low pressures (< 60 mm Hg).

CONCLUSIONS

A short-term daily exercise program induces remodeling of rat intramural coronary arterioles, likely resulting in a greater range of coronary autoregulatory function (constrictor and dilator reserves) and more effective protection against great changes in intraluminal pressure, contributing thereby to the optimization of coronary blood flow during exercise.

The role of exercise in mitigating subcortical ischemic vascular cognitive impairment

Subcortical ischemic vascular cognitive impairment (SIVCI) is the most preventable form of cognitive dysfunction. There is converging evidence from animal and human studies that indicate vascular injury as the primary cause of SIVCI. Currently, there are no curative pharmaceutical treatments for vascular dementia; however, exercise may be a promising strategy to combat SIVCI. This review will focus on the role of exercise as a strategy to prevent or slow the progression of SIVCI, with particular emphasis on the mechanisms by which exercise may improve cerebrovascular function. We propose that exercise may be an effective strategy to combat SIVCI by improving cognitive function, increasing the bioavailability of neurotrophins, stimulating endothelial function, and controlling vascular risk factors. This article is part of the Special Issue "Vascular Dementia".

A Single Resistance Exercise Session Improves Aortic Endothelial Function in Hypertensive Rats

BACKGROUND

Physical exercise is an important tool for the improvement of endothelial function.

OBJECTIVE

To assess the effects of acute dynamic resistance exercise on the endothelial function of spontaneously hypertensive rats (SHR).

METHODS

Ten minutes after exercise, the aorta was removed to evaluate the expression of endothelial nitric oxide synthase (eNOS), phosphorylated endothelial nitric oxide synthase (p-eNOS1177) and inducible nitric oxide synthase (iNOS) and to generate concentration-response curves to acetylcholine (ACh) and to phenylephrine (PHE). The PHE protocol was also performed with damaged endothelium and before and after NG-nitro-L-arginine methyl ester (L-NAME) and indomethacin administration. The maximal response (Emax) and the sensitivity (EC50) to these drugs were evaluated.

RESULTS

ACh-induced relaxation increased in the aortic rings of exercised (Ex) rats (Emax= -80 ± 4.6%, p < 0.05) when compared to those of controls (Ct) (Emax = -50 ± 6.8%). The Emax to PHE was decreased following exercise conditions (95 ± 7.9%, p < 0.05) when compared to control conditions (120 ± 4.2%). This response was abolished after L-NAME administration or endothelial damage. In the presence of indomethacin, the aortic rings' reactivity to PHE was decreased in both groups (EC50= Ex -5.9 ± 0.14 vs. Ct -6.6 ± 0.33 log µM, p < 0.05 / Emax = Ex 9.5 ± 2.9 vs. Ct 17 ± 6.2%, p < 0.05). Exercise did not alter the expression of eNOS and iNOS, but increased the level of p-eNOS.

CONCLUSION

A single resistance exercise session improves endothelial function in hypertensive rats. This response seems to be mediated by increased NO production through eNOS activation.

Arginine and aerobic training prevent endothelial and metabolic alterations in rats at high risk for the development of the metabolic syndrome

Endothelial function is a key mechanism in the development of CVD. Arginine and exercise are important non-pharmacological strategies for mitigating the impact of metabolic changes in the metabolic syndrome, but the effect of their combined administration is unknown. Thus, the aim of this study was to investigate the isolated and combined effects of aerobic training and arginine supplementation on metabolic variables and vascular reactivity in rats at high risk for developing the metabolic syndrome. Wistar rats were divided into two groups: control and fructose (F – water with 10 % fructose). After 2 weeks, the F group was divided into four groups: F, fructose+arginine (FA, 880 mg/kg per d of l-arginine), fructose+training (FT) and fructose+arginine+training (FTA); treatments lasted for 8 weeks, and no difference was observed in body mass gain. Arginine did not improve the body protein content, and both the FA and FT groups show a reversal of the increase in adipose tissue. Insulin increase was prevented by training and arginine, without additive effect, and the increase in serum TAG was prevented only by training. The F group showed impaired endothelium-dependent vasodilation and hyperreactivity to phenylephrine, but arginine and training were capable of preventing these effects, even separately. Higher nitric oxide level was observed in the FA and FT groups, and no potentiating effect was detected. Thus, only training was able to prevent the increase in TAG and improve the protein mass, and training and arginine exert similar effects on fat content, insulin and endothelial function, but these effects are not additive.

Vascular Adaptation to Exercise in Humans: Role of Hemodynamic Stimuli

On the 400th anniversary of Harvey's Lumleian lectures, this review focuses on "hemodynamic" forces associated with the movement of blood through arteries in humans and the functional and structural adaptations that result from repeated episodic exposure to such stimuli. The late 20th century discovery that endothelial cells modify arterial tone via paracrine transduction provoked studies exploring the direct mechanical effects of blood flow and pressure on vascular function and adaptation in vivo. In this review, we address the impact of distinct hemodynamic signals that occur in response to exercise, the interrelationships between these signals, the nature of the adaptive responses that manifest under different physiological conditions, and the implications for human health. Exercise modifies blood flow, luminal shear stress, arterial pressure, and tangential wall stress, all of which can transduce changes in arterial function, diameter, and wall thickness. There are important clinical implications of the adaptation that occurs as a consequence of repeated hemodynamic stimulation associated with exercise training in humans, including impacts on atherosclerotic risk in conduit arteries, the control of blood pressure in resistance vessels, oxygen delivery and diffusion, and microvascular health. Exercise training studies have demonstrated that direct hemodynamic impacts on the health of the artery wall contribute to the well-established decrease in cardiovascular risk attributed to physical activity.

Intermittent parathyroid hormone administration attenuates endothelial dysfunction in old rats

Aging is an independent risk factor for cardiovascular disease and is characterized by a decline in endothelial function. Parathyroid hormone (PTH) administration has been shown to increase endothelial nitric oxide synthase (eNOS) expression. The purpose of this investigation was to determine the effect of intermittent PTH administration on aortic endothelial function in old rodents. We hypothesized that intermittent PTH administration would improve endothelial function in older rodents. Old (24-mo-old) and young (4-mo-old) Fischer-344 rats were given 10 injections of PTH 1-34 (43 μg·kg^-1·day^-1) or phosphate-buffered saline (100 μl/day) over 15 days. Endothelium-dependent relaxation of aortic rings in response to acetylcholine (10^-9 to 10^-5 M) was significantly impaired in old control (OC) compared with young control (YC) as indicated by a reduced area under the curve (AUC, 100 ± 6.28 vs. 54.08 ± 8.3%; P < 0.05) and impaired maximal relaxation (E_max, 70.1 ± 4.48 vs. 92.9 ± 4.38%; P < 0.05). E_max was improved in old animals treated with PTH (OPTH) (OC, 70.1 ± 4.48 vs. OPTH, 85 ± 7.48%; P < 0.05) as well as AUC (OC, 54.08 ± 8.3 vs. OPTH, 82.5 ± 5.7%; P < 0.05) while logEC₅₀ was not different. Endothelial-independent relaxation in response to sodium nitroprusside was not different among groups. Aortic eNOS protein expression was significantly decreased in OC compared with YC (P < 0.05). PTH treatment restored eNOS expression in OPTH animals (P < 0.05). These data suggest that PTH may play a role in attenuating age-related impairments in aortic endothelial function.

NEW & NOTEWORTHY

We have demonstrated that intermittent parathyroid hormone administration can rescue age-related vascular dysfunction by improving endothelial-dependent dilation in the aorta of older rodents. This demonstrates a novel potential benefit of parathyroid hormone administration in aging.

Shear stress-induced angiogenesis in mouse muscle is independent of the vasodilator mechanism and quickly reversible

AIM

Is modulation of skeletal muscle capillary supply by altering blood flow due to a presumptive shear stress response per se, or dependent on the vasodilator mechanism?

METHODS

The response to four different vasodilators, and cotreatment with blockers of NO and prostaglandin synthesis, was compared. Femoral artery blood flow was correlated with capillary-to-fibre ratio (C:F) and protein levels of putative angiogenic compounds.

RESULTS

All vasodilators induced a similar increase in blood flow after 14 days, with a similar effect on C:F (1.62 ± 0.05, 1.60 ± 0.01, 1.57 ± 0.06, 1.57 ± 0.07, respectively, all P < 0.05 vs. control 1.20 ± 0.01). Concomitant inhibitors revealed differential effects on blood flow and angiogenesis, demonstrating that a similar response may have different signalling origins. The time course of this response with the most commonly used vasodilator, prazosin, showed that blood flow increased from 0.40 mL min^-1 to 0.61 mL min^-1 by 28 days (P < 0.05), dropped within 1 week after the cessation of treatment (0.54 mL min^-1 ; P < 0.05) and returned to control levels by 6 weeks. In parallel with FBF, capillary rarefaction began within 1 week (P < 0.05), giving C:F values similar to control by 2 weeks. Of the dominant signalling pathways, prazosin decreased muscle VEGF, but increased its cognate receptor Flk-1 (both P < 0.01); levels of eNOS varied with blood flow (P < 0.05), and Ang-1 initially increased, while its receptor Tie-2 was unchanged, with only modest changes in the antiangiogenic factor TSP-1.

CONCLUSION

Hyperaemia-induced angiogenesis, likely in response to elevated shear stress, is independent of the vasodilator involved, with a rapid induction and quick regression following the stimulus withdrawal.

Effect of mild endurance exercise training and pravastatin on peripheral vasodilatation of forearm resistance vessels in patients with coronary artery disease

Background Improved endothelial function may contribute to the beneficial effects of cholesterol lowering therapy in patients with coronary artery disease (CAD), but results of the effect of statin therapy on endothelial function are disparate in these patients. Exercise training has been reported to improve endothelial function of patients at risk of or with established CAD. The goal of the study was to compare the effect of mild exercise training or statin therapy on forearm endothelial function in CAD patients with average cholesterol levels.

Design and methods Twenty-eight sedentary male patients with angiographically documented CAD and average pretreatment total plasma cholesterol levels (5.1±0.9 mmol/l) aged 42–75 years were included. They were randomly assigned in a 2:1 order to either statin therapy (pravastatin, 40 mg daily) or exercise training therapy (mild endurance exercise three or more times a week). The effects of 10 weeks of either treatment on endothelium-dependent and independent vasodilation of forearm resistance vessels was assessed by plethysmography. Cardiopulmonary exercise testing was performed at baseline and after 10 weeks.

Results Ten weeks of pravastatin therapy significantly reduced low-density lipoprotein cholesterol (from 3.8±0.6 to 3.1±0.6 mmol/l at study end, P=0.04) and the ratio of total to high-density lipoprotein cholesterol (from 4.9±0.8 to 3.7±0.7 mmol/l, P=0.002). Exercise training did not significantly modify the lipid profile. Peak oxygen consumption, maximal achieved workload and exercise duration tended to improve in the exercise training group but remained unchanged in the pravastatin-treated group. Neither 10 weeks of pravastatin nor mild endurance exercise training improved endothelium-dependent or independent vasomotor function in forearm resistance vessels.

Conclusions In patients with CAD and average cholesterol levels, 10 weeks of treatment with mild endurance exercise training or with pravastatin failed to improve endothelium-dependent or independent vasomotor function in forearm resistance vessels.

Effects of short-term training and detraining on VO2 kinetics: Faster VO2 kinetics response after one training session

This study examined the time course of short-term training and detraining-induced changes in oxygen uptake ( V ˙ O 2 ) kinetics. Twelve men (24 ± 3 years) were assigned to either a 50% or a 70% of V ˙ O 2 m a x training intensity (n = 6 per group). V ˙ O 2 was measured breath-by-breath. Changes in deoxygenated-hemoglobin concentration (Δ[HHb]) were measured by near-infrared spectroscopy. Moderate-intensity exercise on-transient V ˙ O 2 and Δ[HHb] were modeled with a mono-exponential and normalized (0-100% of response) and the [ H H b ] / V ˙ O 2 ratio was calculated. Similar changes in time constant of V ˙ O 2 ( t V ˙ O 2 ) were observed in both groups. The combined group mean for t V ˙ O 2 decreased ∼14% (32.3 to 27.9 s, P < 0.05) after one training session with a further ∼11% decrease (27.9 to 24.8 s, P < 0.05) following two training sessions. The t V ˙ O 2 p remained unchanged throughout the remaining of training and detraining. A significant "overshoot" in the [ H H b ] / V ˙ O 2 ratio was decreased (albeit not significant) after one training session, and abolished (P < 0.05) after the second one, with no overshoot observed thereafter. Speeding of V ˙ O 2 kinetics was remarkably quick with no further changes being observed with continuous training or during detraining. Improve matching of local O2 delivery to O2 utilization is a mechanism proposed to influence this response.

Vigorous exercise training improves reactivity of cerebral arterioles and reduces brain injury following transient focal ischemia

OBJECTIVE

Our objective was to examine whether vigorous exercise training (VExT) could influence nitric oxide synthase (NOS)-dependent vasodilation and transient focal ischemia-induced brain injury. Rats were divided into sedentary (SED) or VExT groups.

MATERIALS AND METHODS

Exercise was carried out 5 days/week for a period of 8-10 weeks. First, we measured responses of pial arterioles to an eNOS-dependent (ADP), an nNOS-dependent (NMDA) and a NOS-independent (nitroglycerin) agonist in SED and VExT rats. Second, we measured infarct volume in SED and VExT rats following middle cerebral artery occlusion (MCAO). Third, we measured superoxide levels in brain tissue of SED and VExT rats under basal and stimulated conditions.

RESULTS

We found that eNOS- and nNOS-dependent, but not NOS-independent vasodilation, was increased in VExT compared to SED rats, and this could be inhibited with L-NMMA in both groups. In addition, we found that VExT reduced infarct volume following MCAO when compared to SED rats. Further, superoxide levels were similar in brain tissue from SED and VExT rats under basal and stimulated conditions.

CONCLUSIONS

We suggest that VExT potentiates NOS-dependent vascular reactivity and reduces infarct volume following MCAO via a mechanism that appears to be independent of oxidative stress, but presumably related to an increase in the contribution of nitric oxide.

Time-course of vascular adaptations during 8 weeks of exercise training in subjects with type 2 diabetes and middle-aged controls

PURPOSE

Exercise training in healthy volunteers rapidly improves vascular function, preceding structural remodelling. No study examined the time-course of such adaptations in subjects with a priori endothelial dysfunction.

METHODS

We examined brachial artery endothelial and smooth muscle function using flow-mediated dilation (FMD) and glyceryl trinitrate (GTN) administration in 13 type 2 diabetes patients (59 ± 6 years) and 10 healthy subjects (58 ± 7 years) before, during (2-weekly) and after an 8-week training programme. Arterial structure was assessed via peak blood flow and artery diameter.

RESULTS

Training increased peak oxygen uptake (P = 0.03), comparable between groups (P = 0.276). We observed a similar impact of training on brachial artery vasomotor function across the training period in diabetes patients and controls (FMD/GTN-ratio), with a higher FMD/GTN-ratio at 2, 6 and 8 weeks (P = 0.036). Artery diameter, peak blood flow or peak diameter had not changed after training.

CONCLUSION

Training leads to rapid improvement in brachial artery vascular function in diabetes patients and controls. In contrast to previous observations in healthy young subjects, the increase in function was preserved after 8 weeks of training in middle-aged diabetes patients and controls, suggesting a different time-course in vascular adaptations in subjects with endothelial dysfunction.

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.

Doxorubicin-induced vascular dysfunction and its attenuation by exercise preconditioning

Doxorubicin (DOX) is a highly effective anthracycline antibiotic used to treat a wide array of cancers. Its use is limited because of dose-dependent cardiovascular toxicity. Although exercise training has been shown to protect against DOX-induced cardiotoxicity, it is unclear as to whether exercise can attenuate DOX-induced vascular dysfunction. The purpose of this study was to determine if exercise training provides protection against the deleterious vascular effects of DOX treatment and if any changes in vascular function are related to the accumulation of DOX in vascular tissue. Male Sprague-Dawley rats remained sedentary (SED) or engaged in 14 weeks of voluntary wheel running (WR). After the 14-week period, animals received 15 mg DOX per kilogram of body mass or an equivalent volume of saline. Twenty-four hours after DOX/saline exposure, the aorta was isolated and was used to examine vascular function and aortic DOX accumulation. Aortic rings from WR + DOX animals contracted with significantly greater force and showed improved endothelium-independent relaxation when compared with rings from SED + DOX animals. In contrast, no significant differences in endothelium-dependent aortic function were noted between WR + DOX and SED + DOX. Furthermore, no significant differences in aortic DOX accumulation were observed between the DOX groups. These results suggest that chronic exercise attenuates vascular smooth muscle dysfunction associated with DOX treatment and seems to be independent of DOX accumulation in vascular tissue.

Endothelial function increases after a 16-week diet and exercise intervention in overweight and obese young women

Weight loss improves endothelial function in overweight individuals. The effects of weight loss through combined aerobic and resistance training and caloric restriction on in vivo vascular measures and blood markers associated with the regulation of endothelial function have not been comprehensively examined. Therefore, we investigated brachial artery endothelial function and potential regulatory blood markers in twenty overweight women (30.3 ± 2.0 years) who participated in 16 weeks of aerobic (5 d/wk) and resistance training (2 d/wk) (combined: ≥250 kcal/d) and caloric restriction (−500 kcal/d versus requirement). Resting brachial artery flow mediated dilation (FMD) and circulating endothelin-1 (ET-1) and interleukin-6 (IL-6) were assessed at baseline and following the intervention. Relative and absolute FMD increased (before: 4.0 ± 0.5% versus after: 6.9 ± 0.6%, P < 0.05, and before: 0.14 ± 0.02 mm versus after: 0.23 ± 0.02 mm, P < 0.05, resp.), while body mass decreased (before: 86.9 ± 2.4 kg versus after: 81.1 ± 2.4 kg, P < 0.05) following the intervention. There were no changes in either blood marker (IL-6: before: 1.5 ± 0.2 pg/mL versus after: 1.5 ± 0.1 pg/mL, P > 0.05, and ET-1: before: 0.55 ± 0.05 pg/mL versus after: 0.59 ± 0.09 pg/mL, P > 0.05). 16 weeks of combined aerobic/resistance training and diet-induced weight loss improved endothelial function in overweight and obese young women, but this increase was not associated with changes in blood markers of vasoconstriction or inflammation.

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.

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.

Blood flow restricted exercise and vascular function

It is established that regular aerobic training improves vascular function, for example, endothelium-dependent vasodilatation and arterial stiffness or compliance and thereby constitutes a preventative measure against cardiovascular disease. In contrast, high-intensity resistance training impairs vascular function, while the influence of moderate-intensity resistance training on vascular function is still controversial. However, aerobic training is insufficient to inhibit loss in muscular strength with advancing age; thus, resistance training is recommended to prevent sarcopenia. Recently, several lines of study have provided compelling data showing that exercise and training with blood flow restriction (BFR) leads to muscle hypertrophy and strength increase. As such, BFR training might be a novel means of overcoming the contradiction between aerobic and high-intensity resistance training. Although it is not enough evidence to obtain consensus about impact of BFR training on vascular function, available evidences suggested that BFR training did not change coagulation factors and arterial compliance though with inconsistence results in endothelial function. This paper is a review of the literature on the impact of BFR exercise and training on vascular function, such as endothelial function, arterial compliance, or other potential factors in comparison with those of aerobic and resistance training.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

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

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

Short-term exercise training augments sympathetic vasoconstrictor responsiveness and endothelium-dependent vasodilation in resting skeletal muscle

We tested the hypotheses that 4 wk of exercise training would diminish the magnitude of vasoconstriction in response to sympathetic nerve stimulation and augment endothelium-dependent vasodilation (EDD) in resting skeletal muscle in a training intensity-dependent manner. Sprague-Dawley rats were randomly assigned to sedentary time-control (S), mild- (M; 20 m/min, 5% grade), or heavy-intensity (H; 40 m/min, 5% grade) treadmill exercise groups. Animals trained 5 days/wk for 4 wk with training volume matched between groups. Rats were anesthetized and instrumented for study 24 h after the last training session. Arterial pressure and femoral artery blood flow were measured, and femoral vascular conductance (FVC) was calculated. Lumbar sympathetic chain stimulation was delivered continuously at 2 Hz and in patterns at 20 and 40 Hz. EDD was assessed by the vascular response to intra-arterial bolus injections of ACh. The response (% change FVC) to sympathetic stimulation increased ( P < 0.05) in a training intensity-dependent manner at 2 Hz (S: −20.2 ± 9.8%, M: −34.0 ± 6.7%, and H: −44.9 ± 2.0%), 20 Hz (S: −22.0 ± 10.6%, M: −31.2 ± 8.4%, and H: −42.8 ± 5.9%), and 40 Hz (S: H −24.5 ± 8.5%, M: −35.1 ± 8.9%, H: −44.9 ± 6.5%). The magnitude of EDD also increased in a training intensity-dependent manner ( P < 0.05). These data demonstrate that short-term exercise training augments the magnitude of vasoconstriction in response to sympathetic stimulation and EDD in resting skeletal muscle in a training intensity-dependent manner.

Exercise training normalizes impaired NOS-dependent responses of cerebral arterioles in type 1 diabetic rats

Our goal was to examine whether exercise training (ExT) could normalize impaired nitric oxide synthase (NOS)-dependent dilation of cerebral (pial) arterioles during type 1 diabetes (T1D). We measured the in vivo diameter of pial arterioles in sedentary and exercised nondiabetic and diabetic rats in response to an endothelial NOS (eNOS)-dependent (ADP), an neuronal NOS (nNOS)-dependent [N-methyl-D-aspartate (NMDA)], and a NOS-independent (nitroglycerin) agonist. In addition, we measured superoxide anion levels in brain tissue under basal conditions in sedentary and exercised nondiabetic and diabetic rats. Furthermore, we used Western blot analysis to determine eNOS and nNOS protein levels in cerebral vessels/brain tissue in sedentary and exercised nondiabetic and diabetic rats. We found that ADP and NMDA produced a dilation of pial arterioles that was similar in sedentary and exercised nondiabetic rats. In contrast, ADP and NMDA produced only minimal vasodilation in sedentary diabetic rats. ExT restored impaired ADP- and NMDA-induced vasodilation observed in diabetic rats to that observed in nondiabetics. Nitroglycerin produced a dilation of pial arterioles that was similar in sedentary and exercised nondiabetic and diabetic rats. Superoxide levels in cortex tissue were similar in sedentary and exercised nondiabetic rats, were increased in sedentary diabetic rats, and were normalized by ExT in diabetic rats. Finally, we found that eNOS protein was increased in diabetic rats and further increased by ExT and that nNOS protein was not influenced by T1D but was increased by ExT. We conclude that ExT can alleviate impaired eNOS- and nNOS-dependent responses of pial arterioles during T1D.

Repeated increases in blood flow, independent of exercise, enhance conduit artery vasodilator function in humans

This study aimed to determine the importance of repeated increases in blood flow to conduit artery adaptation, using an exercise-independent repeated episodic stimulus. Recent studies suggest that exercise training improves vasodilator function of conduit arteries via shear stress-mediated mechanisms. However, exercise is a complex stimulus that may induce shear-independent adaptations. Nine healthy men immersed their forearms in water at 42°C for three 30-min sessions/wk across 8 wk. During each session, a pneumatic pressure cuff was inflated around one forearm to unilaterally modulate heating-induced increases in shear. Forearm heating was associated with an increase in brachial artery blood flow (P<0.001) and shear rate (P<0.001) in the uncuffed forearm; this response was attenuated in the cuffed limb (P<0.005). Repeated episodic exposure to bilateral heating induced an increase in endothelium-dependent vasodilation in response to 5-min ischemic (P<0.05) and ischemic handgrip exercise (P<0.005) stimuli in the uncuffed forearm, whereas the 8-wk heating intervention did not influence dilation to either stimulus in the cuffed limb. Endothelium-independent glyceryl trinitrate responses were not altered in either limb. Repeated heating increases blood flow to levels that enhance endothelium-mediated vasodilator function in humans. These findings reinforce the importance of the direct impacts of shear stress on the vascular endothelium in humans.

Exercise training restores impaired dilator responses of cerebral arterioles during chronic exposure to nicotine

Our goal was to determine whether exercise training (ExT) alleviates impaired nitric oxide synthase (NOS)-dependent dilation of pial arterioles during chronic exposure to nicotine. We measured dilation of cerebral (pial) arterioles in sedentary and exercised control and nicotine-treated (2 mg·kg(-1)·day(-1) for 4 wk via an osmotic minipump) rats to an endothelial NOS (eNOS)-dependent (ADP), a neuronal NOS (nNOS)-dependent [N-methyl-D-aspartic acid (NMDA)], and a NOS-independent (nitroglycerin) agonist. In addition, we harvested brain tissue from sedentary and exercised control and nicotine-treated rats to measure the production of superoxide anion and measured superoxide dismutase-1 (SOD-1) protein in cerebral microvessels using Western blot. We found that eNOS-and nNOS-dependent, but not NOS-independent, vasodilation was impaired in nicotine-treated compared with control rats. In addition, the production of superoxide anion (lucigenin chemiluminescence) was increased, and SOD-1 protein decreased, in rats treated with nicotine compared with control rats. Further, although ExT did not significantly affect eNOS- or nNOS-dependent vasodilation in control rats, ExT restored impaired eNOS- and nNOS-dependent responses in nicotine-treated rats. In addition, the increase in superoxide anion production observed in nicotine-treated rats was reduced by ExT, and SOD-1 protein was increased in nicotine-treated rats by ExT. We suggest that ExT restores impaired NOS-dependent dilation of pial arterioles during chronic exposure to nicotine by a mechanism related to the formation of superoxide anion.

Effects of exercise training on vasodilatory protein expression and activity in rats

Increased endothelium-dependent vasodilatation is associated with endurance exercise training. The purpose of this study was to test the hypothesis that increased endothelial nitric oxide synthase (eNOS) protein function, but not increased vascular smooth muscle sensitivity to NO, underlies augmented endothelium-dependent dilatation with training. To test these hypotheses, rats ran on a treadmill at 30 m/min (10% grade) for 60 min/day, 5 days/week, over 8-12 weeks (Trn). Training efficacy was demonstrated by greater (P < 0.05) hindlimb muscle citrate synthase activity and left ventricular mass-body mass ratio in Trn compared with sedentary control rats (Sed). Expression of eNOS protein in the aorta was increased with training (Sed, 1.00 ± 0.18 normalized units; Trn, 1.55 ± 0.23; P < 0.05). Aortic NOS activity was, however, unchanged by training (Sed, 1,505 ± 288 fmol/h/mg protein; Trn, 1,650 ± 247; n.s.). Expression of heat shock protein 90 and protein kinase B/Akt was not different between groups, nor was their association with eNOS. In follow-up series of rats, phosphorylated eNOS content (Serine 1177) was similar for Sed and Trn in both the aorta and gastrocnemius feed artery. Aortic NOS activity with eNOS phosphorylation status preserved was also similar between groups. Finally, cGMP concentration with a NO donor did not differ between groups (Sed, 73.0 ± 20.2 pmol/mg protein; Trn, 62.5 ± 12.9; n.s.). These findings indicate that training-induced increases in eNOS protein expression are not coupled to augmented function, illustrating the complexity of eNOS regulation. Further, they show that vascular sensitivity to NO is not altered by exercise training.

Vasoresponsiveness of collateral vessels in the rat hindlimb: influence of training

Exercise training is known to be an effective means of improving functional capacity and quality of life in patients with peripheral arterial insufficiency (PAI). However, the specific training-induced physiological adaptations occurring within collateral vessels remain to be clearly defined. The purpose of this study was to determine the effect of exercise training on vasomotor properties of isolated peripheral collateral arteries. We hypothesized that daily treadmill exercise would improve the poor vasodilatory capacity of collateral arteries isolated from rats exposed to surgical occlusion of the femoral artery. Following femoral artery ligation, animals were either kept sedentary or exercise trained daily for a period of 3 weeks. Hindlimb collateral arteries were then isolated, cannulated and pressurized via hydrostatic reservoirs to an intravascular pressure of either 45 or 120 cmH(2)O. Non-occluded contralateral vessels of the sedentary animals served as normal Control. Vasodilatory responses to acetylcholine (ACh; 1 x 10(9)-1 x 10(5)m) and sodium nitroprusside (SNP; 1 x 10(9)-1 x 10(4)m), constrictor responses to phenylephrine (PE; 1 x 10(9)-1 x 10(4)m), and flow-induced vasodilatation were determined. Endothelium-mediated vasodilatation responses were significantly greater to either ACh (P < 0.02) or intravascular flow (P < 0.001) in collateral arteries of trained rats. Neither blockade of cyclooxygenase with indomethacin (Indo; 5 microm) nor blockade of endothelial nitric oxide synthase with N(G)-nitro-L-arginine methyl ester (L-NAME; 300 microm) eliminated this ACh- or flow-induced vasodilatation. The depressed vasodilatory response to SNP caused by vascular occlusion was reversed with training. These data indicate that exercise training improves endothelium-mediated vasodilatory capacity of hindlimb collateral arteries, apparently by enhanced production of the putative endothelium-derived hyperpolarizing factor(s). If these findings were applicable to patients with PAI, they could contribute to an improved collateral vessel function and enhance exercise tolerance during routine physical activity.

Vasoresponsiveness of collateral vessels in the rat hindlimb: influence of training

Exercise training is known to be an effective means of improving functional capacity and quality of life in patients with peripheral arterial insufficiency (PAI). However, the specific training-induced physiological adaptations occurring within collateral vessels remain to be clearly defined. The purpose of this study was to determine the effect of exercise training on vasomotor properties of isolated peripheral collateral arteries. We hypothesized that daily treadmill exercise would improve the poor vasodilatory capacity of collateral arteries isolated from rats exposed to surgical occlusion of the femoral artery. Following femoral artery ligation, animals were either kept sedentary or exercise trained daily for a period of 3 weeks. Hindlimb collateral arteries were then isolated, cannulated and pressurized via hydrostatic reservoirs to an intravascular pressure of either 45 or 120 cmH(2)O. Non-occluded contralateral vessels of the sedentary animals served as normal Control. Vasodilatory responses to acetylcholine (ACh; 1 x 10(9)-1 x 10(5)m) and sodium nitroprusside (SNP; 1 x 10(9)-1 x 10(4)m), constrictor responses to phenylephrine (PE; 1 x 10(9)-1 x 10(4)m), and flow-induced vasodilatation were determined. Endothelium-mediated vasodilatation responses were significantly greater to either ACh (P < 0.02) or intravascular flow (P < 0.001) in collateral arteries of trained rats. Neither blockade of cyclooxygenase with indomethacin (Indo; 5 microm) nor blockade of endothelial nitric oxide synthase with N(G)-nitro-L-arginine methyl ester (L-NAME; 300 microm) eliminated this ACh- or flow-induced vasodilatation. The depressed vasodilatory response to SNP caused by vascular occlusion was reversed with training. These data indicate that exercise training improves endothelium-mediated vasodilatory capacity of hindlimb collateral arteries, apparently by enhanced production of the putative endothelium-derived hyperpolarizing factor(s). If these findings were applicable to patients with PAI, they could contribute to an improved collateral vessel function and enhance exercise tolerance during routine physical activity.

Impact of inactivity and exercise on the vasculature in humans

The effects of inactivity and exercise training on established and novel cardiovascular risk factors are relatively modest and do not account for the impact of inactivity and exercise on vascular risk. We examine evidence that inactivity and exercise have direct effects on both vasculature function and structure in humans. Physical deconditioning is associated with enhanced vasoconstrictor tone and has profound and rapid effects on arterial remodelling in both large and smaller arteries. Evidence for an effect of deconditioning on vasodilator function is less consistent. Studies of the impact of exercise training suggest that both functional and structural remodelling adaptations occur and that the magnitude and time-course of these changes depends upon training duration and intensity and the vessel beds involved. Inactivity and exercise have direct "vascular deconditioning and conditioning" effects which likely modify cardiovascular risk.

Exercise training reverses age-related decrements in endothelium-dependent dilation in skeletal muscle feed arteries

We tested two hypotheses, first that exercise training reverses age-related decrements in endothelium-dependent dilation in soleus muscle feed arteries and second that this improved endothelium-dependent dilation is the result of increased nitric oxide (NO) bioavailability due to increased content and phosphorylation of endothelial NO synthase (eNOS) and/or increased antioxidant enzyme content. Young (2 mo) and old (22 mo) male Fischer 344 rats were exercise trained (Ex) or remained sedentary (Sed) for 10-12 wk, yielding four groups of rats: 1) young Sed (4-5 mo), 2) young Ex (4-5 mo), 3) old Sed (24-25 mo), and 4) old Ex (24-25 mo). Soleus muscle feed arteries (SFA) were isolated and cannulated with two glass micropipettes for examination of endothelium-dependent (ACh) and endothelium-independent [sodium nitroprusside (SNP)] vasodilator function. To determine the mechanism(s) by which exercise affected dilator responses, ACh-induced dilation was assessed in the presence of N(omega)-nitro-l-arginine (l-NNA; to inhibit NO synthase), indomethacin (Indo; to inhibit cyclooxygenase), and l-NNA + Indo. Results indicated that ACh-induced dilation was blunted in old Sed SFA relative to young Sed SFA. Exercise training improved ACh-induced dilation in old SFA such that vasodilator responses in old Ex SFA were similar to young Sed and young Ex SFA. Addition of l-NNA, or l-NNA + Indo, abolished the exercise effect. Immunoblot analysis revealed that extracellular superoxide dismutase (SOD) protein content was increased by training in old SFA, whereas eNOS and SOD-1 protein content were not altered. Addition of exogenous SOD, or SOD + catalase, improved ACh-induced dilation in old Sed SFA such that vasodilator responses were similar to young Sed SFA. Addition of l-NNA abolished the effect of exogenous SOD in old Sed arteries. Collectively, these results indicate that exercise training reverses age-induced endothelial dysfunction in SFA by increasing NO bioavailability and that increases in vascular antioxidant capacity may play an integral role in the improvement in endothelial function.

Time course of change in vasodilator function and capacity in response to exercise training in humans

Studies of the impact of exercise training on arterial adaptation in healthy subjects have produced disparate results. It is possible that some studies failed to detect changes because functional and structural adaptations follow a different time course and may therefore not be detected at discrete time points. To gain insight into the time course of training-induced changes in artery function and structure, we examined conduit artery flow mediated dilatation (FMD), an index of nitric oxide (NO)-mediated artery function, and conduit dilator capacity (DC), a surrogate marker for arterial remodelling, in the brachial and popliteal arteries of 13 healthy male subjects (21.6 +/- 0.6 years) and seven non-active controls (22.8 +/- 0.2 years) studied at 2-week intervals across an 8-week cycle and treadmill exercise training programme. Brachial and popliteal artery FMD and DC did not change in control subjects at any time point. FMD increased from baseline (5.9 +/- 0.5%) at weeks 2 and 4 (9.1 +/- 0.6, 8.5 +/- 0.6%, respectively, P < 0.01), but returned towards baseline levels again by week 8 (6.9 +/- 0.7%). In contrast, brachial artery DC progressively increased from baseline (8.1 +/- 0.4%) at weeks 2, 4, 6 and 8 (9.2 +/- 0.6, 9.9 +/- 0.6, 10.0 +/- 0.5, 10.5 +/- 0.8%, P < 0.05). Similarly, popliteal artery FMD increased from baseline (6.2 +/- 0.7%) at weeks 2, 4 and 6 (9.1 +/- 0.6, 9.5 +/- 0.6, 7.8 +/- 0.5%, respectively, P < 0.05), but decreased again by week 8 (6.5 +/- 0.6%), whereas popliteal DC progressively increased from baseline (8.9 +/- 0.4%) at week 4 and 8 (10.5 +/- 0.7, 12.2 +/- 0.6%, respectively, P < 0.05). These data suggest that functional changes in conduit arteries occur rapidly and precede arterial remodelling in vivo. These data suggest that complimentary adaptations occur in arterial function and structure and future studies should adopt multiple time point assessments to comprehensively assess arterial adaptations to interventions such as exercise training in humans.

Exercise training enhances flow-induced vasodilation in skeletal muscle resistance arteries of aged rats: role of PGI2 and nitric oxide

Flow-induced vasodilation is attenuated with old age in rat skeletal muscle arterioles. The purpose of this study was to determine whether diminished cyclooxygenase (COX) signaling contributes to the age-induced attenuation of flow-induced vasodilation in gastrocnemius muscle arterioles and to determine whether, and through which mechanism(s), exercise training restores this deficit in old rats. Fischer 344 rats (3 and 22 mo old) were assigned to a sedentary or exercise-trained group. First-order arterioles were isolated from the gastrocnemius muscles, cannulated, and pressurized to 70 cm H(2)O. Diameter changes were determined in response to graded increases in intraluminal flow in the presence and absence of nitric oxide synthase (NOS) inhibition [10(-5) M N(G)-nitro-L-arginine methyl ester (L-NAME)], COX inhibition (10(-5) M indomethacin), or combination NOS (10(-5) M L-NAME) plus COX (10(-5) M indomethacin) inhibition. Aging reduced flow-induced vasodilation in gastrocnemius muscle arterioles. Exercise training restored responsiveness to flow in arterioles of aged rats and enhanced flow-induced vasodilation in arterioles from young rats. L-NAME inhibition of flow-induced vasodilation was greater in arterioles from old rats compared with those from young rats and was increased after exercise training in arterioles from both young and old rats. Although the indomethacin-sensitive portion of flow-induced dilation was not altered by age or training, both COX-1 mRNA expression and PGI(2) production increased with training in arterioles from old rats. These data demonstrate that exercise training restores flow-induced vasodilation in gastrocnemius muscle arterioles from old rats and enhances flow-induced vasodilation in gastrocnemius muscle arterioles from young rats. In arterioles from both old and young rats, the exercise training-induced enhancement of flow-induced dilation occurs primarily through a NOS mechanism.

Changes in capillary shear stress in skeletal muscles exposed to long-term activity: role of nitric oxide

OBJECTIVE

The purpose of this study was to establish whether suppression of angiogenesis by nitric oxide synthase (NOS) inhibition in skeletal muscles exposed to long-term activity can be explained by changes in capillary shear stress linked to the lack of nitric oxide production.

METHODS

Capillary shear stress was calculated from diameters (d) and red blood cell velocities (V(rbc)) measured at rest and after acute contractions in epi-illuminated extensor digitorum longus muscles of control rats and those in which ankle flexors had been stimulated via implanted electrodes (10 Hz, 8 h x day(-1)) for 2 or 7 days without and with inhibition of nitric oxide synthase activity by N(omega)-nitro-L-arginine (L-NNA, 3-4 mg x day(-1) in drinking water).

RESULTS

Neither chronic electrical stimulation nor L-NNA treatment altered capillary diameters. Capillary V(rbc) and shear stress (SS) were doubled in muscles after 2 days stimulation (298 +/- 22 microm x s(-1) and 11.4 +/- 1.0 dyne x cm(-2), respectively, p < .005) compared to controls (148 +/- 18 microm x s(-1) and 5.6 +/- 0.8 dyne x cm(-2)) but normalized after 7 days (153 +/- 27 microm x s(-1) and 6.2 +/- 1.0 dyne x cm(-2)), when the capillary bed is known to be enlarged. L-NNA, which increased blood pressure in all treated animals, abolished the increase in capillary SS after 2 days stimulation and decreased SS after 7 days.

CONCLUSIONS

These data support a role for NO in the early elevation of capillary shear stress that initiates angiogenesis in stimulated muscles, likely via modulation of upstream vascular resistance, and could explain the lack of capillary growth in stimulated muscles when nitric oxide generation is suppressed.

Endothelial function and exercise training: evidence from studies using animal models

This review summarizes and examines the evidence from experiments using animal models to determine the effect of endurance exercise training on endothelium-dependent dilation in the arterial circulation. The response of the endothelium to exercise training is complex and depends on a number of factors that include the duration of the training program, the size of the artery/arteriole, the anatomical location of the artery/arteriole, and the health of the individual. In healthy animals, short-term exercise training appears to cause enhanced endothelium-dependent dilation in some vascular beds, but it returns to normal levels as the duration of the training program increases. In general, evidence supports the notion that exercise training causes greater increases in endothelium-dependent dilation in various disease states than in healthy individuals. The evidence of a generalized effect of training on arterial endothelium in all regions of the body is inconsistent and appears to depend on the animal model used. Available results indicate that training duration, artery size, and anatomical location interact in ways not fully understood at this time to determine whether and to what extent endothelium-dependent dilation will be enhanced by exercise training.

Alterations of calf venous and arterial compliance following acclimation to heat administered at a fixed daily time in humans

We investigated the effects of heat acclimation on venous and arterial compliance in humans. Four male and four female volunteers were exposed to an ambient temperature of 40 degrees C and relative humidity of 40% for 4 h (1330-1730 hours) per day for 9-10 consecutive days. The calf venous compliance (CV) was estimated using venous occlusion plethysmography with a mercury-in-silastic strain gauge placed around the right calf at its maximum girth. The compliance of the small (CSA) and large (CLA) arteries were assessed by reflective and capacitance compliance by analyzing the radial artery blood pressure waveforms, basing on the use of a modified Windkessel model. The calf CV, CSA, CLA, systolic and diastolic blood pressures, heart rate and core temperature were determined twice a day, 0930-1100 hours (AM test) and 1500-1630 hours (PM test), in both heat-acclimated and non-heat-acclimated (control) conditions. Heat acclimation appeared to decrease blood pressures, heart rate and significantly lowered core temperature only in the PM test. In the control condition, the calf CV was not affected by the time of day and the CSA was significantly depressed in the PM test. After acclimation to heat, the calf CV significantly increased and the CSA did not decrease in the PM test. The results presented suggest that repeated heat exposure in humans, for 4 h at a fixed time daily, increases the calf CV and the CSA particularly during the period when the subjects were previously exposed to heat.