Tetrahydrobiopterin ameliorates the exaggerated exercise pressor response in patients with chronic kidney disease: a randomized controlled trial

The exercise pressor reflex: An update

The exercise pressor reflex is a feedback mechanism engaged upon stimulation of mechano- and metabosensitive skeletal muscle afferents. Activation of these afferents elicits a reflex increase in heart rate, blood pressure, and ventilation in an intensity-dependent manner. Consequently, the exercise pressor reflex has been postulated to be one of the principal mediators of the cardiorespiratory responses to exercise. In this updated review, we will discuss classical and recent advancements in our understating of the exercise pressor reflex function in both human and animal models. Particular attention will be paid to the afferent mechanisms and pathways involved during its activation, its effects on different target organs, its potential role in the abnormal cardiovascular response to exercise in diseased states, and the impact of age and biological sex on these responses. Finally, we will highlight some unanswered questions in the literature that may inspire future investigations in the field.

Influence of Angiotensin Converting Enzyme I/D Polymorphism on Hemodynamic and Antioxidant Response to Long-Term Intradialytic Resistance Training in Patients With Chronic Kidney Disease: A Randomized Controlled Trial

ABSTRACT

Corrêa, HdL, Deus, LA, Neves, RVP, Reis, AL, de Freitas, GS, de Araújo, TB, da Silva Barbosa, JM, Prestes, J, Simões, HG, Amorim, CE, dos Santos, MAP, Haro, A, de Melo, GF, Gadelha, AB, Neto, LS, and Rosa, TdS. Influence of angiotensin converting enzyme I/D polymorphism on hemodynamic and antioxidant response to long-term intradialytic resistance training in patients with chronic kidney disease: a randomized controlled trial. J Strength Cond Res 35(10): 2902-2909, 2021-The aim of the study was to verify the influence of Angiotensin-converting enzyme (ACE) I/D genotype on blood pressure, muscle mass, and redox balance response to long-term resistance training (RT) in end-stage renal disease patients. Three hundred and twenty subjects were randomized into 4 groups: II + ID control (II + ID CTL, n = 80), II + ID RT (II + ID RT, n = 79), DD control (DD CTL n = 83), and DD RT (DD RT, n = 78). The RT lasted 24 weeks with a frequency of 3 times per week, on alternative days. Each section consisted of 3 sets of 8-12 repetitions in 11 exercises, with training loads at 6 point (somewhat hard) to 8 point (hard) based on OMNI-RES scale and was prescribed during dialysis (intradialytic). Statistical significance was accepted with p < 0.05. The most relevant benefits in blood pressure were found for DD homozygotes (p < 0.0001), whereas allele I carriers displayed a higher increase in muscle mass (p < 0.0001). Hemodialysis clinics that already use RT for their patients could include the genotyping of ACE to identify the predisposal of the patients to respond to RT and to counteract kidney disease-related comorbidities.

Low-load resistance training with blood flow restriction prevent renal function decline: The role of the redox balance, angiotensin 1-7 and vasopressin✰,✰✰

AIMS

We sought to investigate the effect of resistance training (RT) and low-load RT with moderate blood flow restriction (RT+BFR) on blood pressure, exercise pressor response, redox balance and vasoactive peptides, body composition and muscle strength in patients with stage two of chronic kidney disease (CKD).

METHODS

We conducted a 6-month randomized controlled exercise intervention in 90 male and female hypertensive CKD patients (58±9 years with estimated glomerular filtration rate (eGFR; of 66.1 ± 1.2 mL/kg/1.73m²). Participants were randomized to one of three groups (n = 30/group); control group (CTL), RT, and RT+BFR. RT and RT+BFR performed three weekly training sessions using similar periodization for six months (two-month mesocycles), but of different intensities.

RESULTS

There was similarly effects between RT and RT+BFR in reducing systolic and diastolic blood pressure during daytime and 24hour period (RT: 10.4%; RT+BFR: 10.3% of decrease), fat mass, F₂-isoprostanes, asymmetric dimethylarginine (ADMA) and vasopressin (p<0.05 pre-vs post). Also promoted the increase of angiotensin 1-7, nitric oxide (NO), catalase, Trolox equivalent and muscle strength (p<0.05). Both training models attenuated the decline of estimated glomerular filtration rate (p<0.0001 vs CTL). However, only RT+BFR was associated with lower discomfort during exercise (p<0.0001 pre-vs post). Statistical significance was considered with p < 0.05.

CONCLUSION

These findings suggest low-load RT+BFR as a promising non-pharmacological strategy to control blood pressure, oxidative stress, vasoactive peptides, and consequently, attenuate the decrease of the eGFR.

Exercise intolerance in kidney diseases: physiological contributors and therapeutic strategies

Exertional fatigue, defined as the overwhelming and debilitating sense of sustained exhaustion that impacts the ability to perform activities of daily living, is highly prevalent in chronic kidney disease (CKD) and end-stage renal disease (ESRD). Subjective reports of exertional fatigue are paralleled by objective measurements of exercise intolerance throughout the spectrum of the disease. The prevalence of exercise intolerance is clinically noteworthy, as it leads to increased frailty, worsened quality of life, and an increased risk of mortality. The physiological underpinnings of exercise intolerance are multifaceted and still not fully understood. This review aims to provide a comprehensive outline of the potential physiological contributors, both central and peripheral, to kidney disease-related exercise intolerance and highlight current and prospective interventions to target this symptom. In this review, the CKD-related metabolic derangements, cardiac and pulmonary dysfunction, altered physiological responses to oxygen consumption, vascular derangements, and sarcopenia are discussed in the context of exercise intolerance. Lifestyle interventions to improve exertional fatigue, such as aerobic and resistance exercise training, are discussed, and the lack of dietary interventions to improve exercise tolerance is highlighted. Current and prospective pharmaceutical and nutraceutical strategies to improve exertional fatigue are also broached. An extensive understanding of the pathophysiological mechanisms of exercise intolerance will allow for the development of more targeted therapeutic approached to improve exertional fatigue and health-related quality of life in CKD and ESRD.

Sympathetic nerve traffic overactivity in chronic kidney disease: a systematic review and meta-analysis

BACKGROUND

Studies based on microneurographic sympathetic nerve activity (MSNA) recordings have shown that the sympathetic system is overactivated in chronic kidney disease (CKD) patients but the relationship between MSNA and renal function and other risk factors has not been systematically reviewed in this population.

DESIGN AND MEASUREMENTS

This meta-analysis compares MSNA in cardiovascular complications-free CKD patients (n = 638) and healthy individuals (n = 372) and assesses the relationship of MSNA with the eGFR, age, BMI and hemodynamic variables.

RESULTS

In a global analysis, MSNA was higher in CKD patients than in healthy control individuals (P < 0.001). The difference in MSNA between patients and healthy individuals was more marked in end-stage kidney diseases patients than in stage 3A 3B CKD patients (P < 0.001). In an analysis combining patients and healthy individuals, MSNA rose gradually across progressively lower eGFR categories (P < 0.01). In separate meta-regression analyses in CKD patients and in healthy individuals, MSNA associated directly with age (CKD: r = 0.57, P = 0.022; healthy individuals: r = 0.71, P = 0.031) and with the BMI (r = 0.75, P = 0.001 and r = 0.93, P = 0.003). In both groups, MSNA correlated with heart rate (r = 0.77, P = 0.02 and r = 0.66, P = 0.01) but was unrelated to plasma norepinephrine.

CONCLUSION

Independently of comorbidities, MSNA is markedly increased in CKD patients as compared with healthy individuals and it is related to renal function, age, the BMI and heart rate. Sympathetic activation intensifies as CKD progresses toward kidney failure and such an intensification is paralleled by a progressive rise in heart rate but it is not reflected by plasma norepinephrine.

Reproducibility of the neurocardiovascular responses to common laboratory-based sympathoexcitatory stimuli in young adults

The magnitude of blood pressure (BP) and muscle sympathetic nerve activity (MSNA) responses to laboratory stressors is commonly used to compare neurocardiovascular responsiveness between groups and conditions. However, no studies have rigorously examined the reproducibility of BP and MSNA responsiveness. Here, we assess the within-visit reproducibility of BP (finger photoplethysmography) and MSNA (microneurography) responses to isometric handgrip (HG) and postexercise ischemia (PEI) in young healthy adults (n = 30). In a subset (n = 21), we also examined the between-visit reproducibility of responsiveness to HG, PEI, and the cold pressor test (CPT). Intraclass correlation coefficients (ICCs) were used as a primary reproducibility measure (e.g., ICC >0.75 is considered very good). Within a visit, the increase in mean arterial pressure during HG [ICC = 0.85 (0.69-0.93); P < 0.001] and PEI [ICC = 0.85 (0.69-0.93); P < 0.001] demonstrated very good reproducibility. Furthermore, the between-visit reproducibility of the pressor response to HG [ICC = 0.85 (0.62-0.94); P < 0.001], PEI [ICC = 0.84 (CI = 0.58-0.94); P < 0.001], and the CPT [ICC = 0.89 (0.72-0.95) P < 0.001]) were also very good. However, there was greater variability in both the within- [HG: ICC = 0.58 (-0.22-0.85), P = 0.001; PEI: ICC = 0.33 (-0.24-0.69), P = 0.042] and between-visit reproducibility of MSNA responsiveness [HG: ICC = 0.87 (0.53-0.96), P = 0.001; PEI: ICC = 0.24 (-0.62-0.78), P = 0.27; CPT: ICC = 0.77 (0.29-0.93), P = 0.007]. The magnitude of the BP response to several standard laboratory stimuli was very good, whereas the variability of the MSNA response to these perturbations was generally less consistent, particularly during PEI. These data provide novel insight for both study design and data interpretation when comparing neurocardiovascular responsiveness between different conditions, groups, or studies, as well as before and after interventions/treatments.NEW & NOTEWORTHY The magnitude of the increases in blood pressure and muscle sympathetic nerve activity in response to sympathoexcitatory stimuli such as static handgrip, postexercise ischemia, and the cold pressor test are commonly used to assess neurocardiovascular responsiveness. However, limited studies have comprehensively examined the reproducibility of these responses. We demonstrate that the reproducibility of the pressor response to these perturbations was very good within an individual, whereas the reproducibility of the MSNA response was less consistent.

Neural control of cardiovascular function in black adults: implications for racial differences in autonomic regulation

Black adults are at increased risk for developing hypertension and cardiovascular and chronic kidney disease and have greater associated morbidity/mortality than white adults who are otherwise demographically similar. Despite the key role of the autonomic nervous system in the regulation of cardiovascular function, the mechanistic contributions of sympathetic nerves to racial differences in cardiovascular dysfunction and disease remain poorly understood. In this review, we present an update and synthesis of current understanding regarding the roles of autonomic neural mechanisms in normal and pathophysiological cardiovascular control in black and white adults. At rest, many hemodynamic and autonomic variables, including blood pressure, cardiac output, and sympathetic nerve activity, are similar in healthy black and white adults. However, resting sympathetic vascular transduction and carotid baroreflex responses are altered in ways that tend to promote increased vasoconstriction and higher blood pressure, even in healthy, normotensive black adults. Acute sympathoexcitatory maneuvers, including exercise and cold pressor test, often result in augmented sympathetic and hemodynamic responses in healthy black adults. Clinically, although mechanistic evidence is scarce in this area, existing data support the idea that excessive sympathetic activation and/or transduction into peripheral vasoconstriction contribute importantly to the pathophysiology of hypertension and chronic kidney disease in black compared with white adults. Important areas for future work include more detailed study of sympathetic and hemodynamic reactivity to exercise and other stressors in male and female black adults and, particularly, sympathetic control of renal function, an important area of clinical concern in black patients.

Nutraceuticals as a potential adjunct therapy toward improving vascular health in CKD

Chronic kidney disease (CKD) is a major public health epidemic and increases risk for developing cardiovascular disease (CVD). Vascular dysfunction is a major independent risk factor toward increased risk for CVD in CKD. Several mechanisms have been postulated to result in vascular dysfunction in CKD, including oxidative stress-mediated inflammation by redox imbalance and reduced nitric oxide (NO) bioavailability and synthesis. Therefore, strategies that decrease oxidative stress and/or increase NO bioactivity may have major clinical implications toward improving vascular health and reducing the burden of CVD in CKD. Nutraceutical therapy in the form of polyphenols, dietary nitrates, or selective mitochondria-targeting therapies has recently been shown to improve vascular function by reducing oxidative stress and/or increasing NO bioavailability and synthesis. This review, therefore, highlights these three emerging nutraceuticals recently implicated in pathophysiological improvement of vascular function in CKD. This review also describes those pathophysiological mechanisms thought to be responsible for the beneficial effects on the vasculature and possible experimental considerations that may exist within human CKD populations. It is clear throughout this review that human-based mechanistic preclinical and health-related clinical studies are lacking regarding whether nutraceuticals do indeed improve vascular function in patients with CKD. As such, a comprehensive, detailed, and fully integrated understanding of nutraceuticals and vasculature function is necessary in patients with CKD. Many opportunities exist for original mechanistic and therapeutic discoveries and investigations on select nutraceuticals and their impact on vascular outcomes in patients with CKD, and these will remain exciting avenues of research in the future.

The effect of exercise on blood pressure in chronic kidney disease: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND AND OBJECTIVES

Management of hypertension in chronic kidney disease (CKD) remains a major challenge. We conducted a systematic review to assess whether exercise is an effective strategy for lowering blood pressure in this population.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

We searched MEDLINE, EMBASE, the Cochrane Library, CINAHL and Web of Science for randomized controlled trials (RCTs) that examined the effect of exercise on blood pressure in adults with non-dialysis CKD, stages 3-5. Outcomes were non-ambulatory systolic blood pressure (primary), other blood pressure parameters, 24-hour ambulatory blood pressure, pulse-wave velocity, and flow-mediated dilatation. Results were summarized using random effects models.

RESULTS

Twelve studies with 505 participants were included. Ten trials (335 participants) reporting non-ambulatory systolic blood pressure were meta-analysed. All included studies were a high risk of bias. Using the last available time point, exercise was not associated with an effect on systolic blood pressure (mean difference, MD -4.33 mmHg, 95% confidence interval, CI -9.04, 0.38). The MD after 12-16 and 24-26 weeks of exercise was significant (-4.93 mmHg, 95% CI -8.83, -1.03 and -10.94 mmHg, 95% CI -15.83, -6.05, respectively) but not at 48-52 weeks (1.07 mmHg, 95% CI -6.62, 8.77). Overall, exercise did not have an effect on 24-hour ambulatory blood pressure (-5.40 mmHg, 95% CI -12.67, 1.87) or after 48-52 weeks (-7.50 mmHg 95% CI -20.21, 5.21) while an effect was seen at 24 weeks (-18.00 mmHg, 95% CI -29.92, -6.08). Exercise did not have a significant effect on measures of arterial stiffness or endothelial function.

CONCLUSION

Limited evidence from shorter term studies suggests that exercise is a potential strategy to lower blood pressure in CKD. However, to recommend exercise for blood pressure control in this population, high quality, longer term studies specifically designed to evaluate hypertension are needed.

Endothelial dysfunction correlates with exaggerated exercise pressor response during whole body maximal exercise in chronic kidney disease

Chronic kidney disease (CKD) patients have exercise intolerance associated with increased cardiovascular mortality. Previous studies demonstrate that blood pressure (BP) and sympathetic nerve responses to handgrip exercise are exaggerated in CKD. These patients also have decreased nitric oxide (NO) bioavailability and endothelial dysfunction, which could potentially lead to an impaired ability to vasodilate during exercise. We hypothesized that CKD patients have exaggerated BP responses during maximal whole body exercise and that endothelial dysfunction correlates with greater exercise pressor responses in these patients. Brachial artery flow-mediated dilation (FMD) was assessed before maximal treadmill exercise in 56 participants: 38 CKD (56.7 ± 1.2 yr old, 38 men) and 21 controls (52.8 ± 1.8 yr old, 20 men). During maximal treadmill exercise, the slope-of-rise in systolic BP (+10.32 vs. +7.75 mmHg/stage, P < 0.001), mean arterial pressure (+3.50 vs. +2.63 mmHg/stage, P = 0.004), and heart rate (+11.87 vs. +10.69 beats·min^-1·stage^-1, P = 0.031) was significantly greater in CKD compared with controls. Baseline FMD was significantly lower in CKD (2.76 ± 0.42% vs. 5.84 ± 0.97%, P = 0.008). Lower FMD values were significantly associated with a higher slope-of-rise in systolic BP (+11.05 vs. 8.71 mmHg/stage, P = 0.003) during exercise in CKD, as well as poorer exercise capacity measured as peak oxygen uptake (V̇o_2peak; 19.47 ± 1.47 vs. 24.57 ± 1.51 ml·min^-1·kg^-1, P < 0.001). These findings demonstrate that low FMD in CKD correlates with augmented BP responses during exercise and lower V̇o_2peak, suggesting that endothelial dysfunction may contribute to exaggerated exercise pressor responses and poor exercise capacity in CKD patients.

Folic acid supplementation increases cutaneous vasodilator sensitivity to sympathetic nerve activity in older adults

During heat stress, blunted increases in skin sympathetic nervous system activity (SSNA) and reductions in end-organ vascular responsiveness contribute to the age-related reduction in reflex cutaneous vasodilation. In older adults, folic acid supplementation improves the cutaneous vascular conductance (CVC) response to passive heating; however, the influence of folic acid supplementation on SSNA:CVC transduction is unknown. Fourteen older adults (66 ± 1 yr, 8 male/6 female) ingested folic acid (5 mg/day) or placebo for 6 wk in a randomized, double-blind, crossover design. In protocol 1, esophageal temperature (T_es) was increased by 1.0°C (water-perfused suit) while SSNA (peroneal microneurography) and red cell flux in the innervated dermatome (laser Doppler flowmetry; dorsum of the foot) were continuously measured. In protocol 2, two intradermal microdialysis fibers were placed in the skin of the lateral calf for graded infusions of acetylcholine (ACh; 10^-10 to 10^-1 M) with and without nitric oxide synthase (NOS) blockade (20 mM nitro-l-arginine methyl ester). Folic acid improved reflex vasodilation (46 ± 4% vs. 31 ± 3% CVC_max for placebo; P < 0.001) without affecting the increase in SSNA (Δ506 ± 104% vs. Δ415 ± 73% for placebo; NS). Folic acid increased the slope of the SSNA-to-CVC relation (0.08 ± 0.02 vs. 0.05 ± 0.01 for placebo; P < 0.05) and extended the response range. Folic acid augmented ACh-induced vasodilation (83 ± 3% vs. 66 ± 4% CVC_max for placebo; P = 0.002); however, there was no difference between treatments at the NOS-inhibited site (53 ± 4% vs. 52 ± 4% CVC_max for placebo; NS). These data demonstrate that folic acid supplementation enhances reflex vasodilation by increasing the sensitivity of skin arterioles to central sympathetic nerve outflow during hyperthermia in aged human subjects.

Oxidative Stress and Hypertensive Diseases

It has become clear that reactive oxygen species (ROS) contribute to the development of hypertension via myriad effects. ROS are essential for normal cell function; however, they mediate pathologic changes in the brain, the kidney, and blood vessels that contribute to the genesis of chronic hypertension. There is also emerging evidence that ROS contribute to immune activation in hypertension. This article discusses these events and how they coordinate to contribute to hypertension and its consequent end-organ damage.