Long-term swimming exercise does not modulate the Akt-dependent endothelial nitric oxide synthase phosphorylation in healthy mice

Nitric oxide and its role in exercise physiology

INTRODUCTION

Nitric oxide (NO) is quite an essential molecule for human metabolism since it plays an active role in body functions. In the past 20 years, nitric oxide has become a milestone in terms of both athlete physiology and pharmacology studies. The most known and remarkable function of NO is its role in controlling vasodilatation, blood rate, and mitochondrial respiration and thus enhance performance. Therefore, it can be argued that exercise and NO have a positive relationship.

EVIDENCE ACQUISITION

In the scientific literature search related to this review, the US National Library of Medicine (PubMed) used MEDLINE and SportDiscus data and the terms "NO," "physical exercise," "vasodilatation," and "performance enhancement." The relevant literature took its source from the research of relevant articles from reference lists derived from data studies.

EVIDENCE SYNTHESIS

It was observed that there is a relationship between physical activity and nitric oxide, and it is demonstrated that physical activity enhances NO production. NO is supposed to improve sports performance, promote recovery, and benefit the athlete's health with its physiological support in vasodilatation, blood flow, and mitochondrial respiration.

CONCLUSIONS

Physical activity and nitric oxide resulted to be related. There is a concrete evidence that physical activity enhances NO production. Exercise should be recommended for increasing the level of NO for athletes and for patients with cardiovascular disorders for therapy.

Preclinical techniques to investigate exercise training in vascular pathophysiology

Atherosclerosis is a dynamic process starting with endothelial dysfunction and inflammation and eventually leading to life-threatening arterial plaques. Exercise generally improves endothelial function in a dose-dependent manner by altering hemodynamics, specifically by increased arterial pressure, pulsatility, and shear stress. However, athletes who regularly participate in high-intensity training can develop arterial plaques, suggesting alternative mechanisms through which excessive exercise promotes vascular disease. Understanding the mechanisms that drive atherosclerosis in sedentary versus exercise states may lead to novel rehabilitative methods aimed at improving exercise compliance and physical activity. Preclinical tools, including in vitro cell assays, in vivo animal models, and in silico computational methods, broaden our capabilities to study the mechanisms through which exercise impacts atherogenesis, from molecular maladaptation to vascular remodeling. Here, we describe how preclinical research tools have and can be used to study exercise effects on atherosclerosis. We then propose how advanced bioengineering techniques can be used to address gaps in our current understanding of vascular pathophysiology, including integrating in vitro, in vivo, and in silico studies across multiple tissue systems and size scales. Improving our understanding of the antiatherogenic exercise effects will enable engaging, targeted, and individualized exercise recommendations to promote cardiovascular health rather than treating cardiovascular disease that results from a sedentary lifestyle.

Molecular Mechanisms Mediating Adaptation to Exercise

Several experimental and human studies documented the preventive and therapeutic effects of exercise on the normal physiological function of different body systems during aging as well as various diseases. Recent studies using cellular and molecular (biochemical, proteomics, and genomics) techniques indicated that exercise modifies intracellular and extracellular signaling and pathways. In addition, in vivo or in vitro experiments, particularly, using knockout and transgenic animals, helped to mimic physiological conditions during and after exercise. According to the findings of these studies, some important signaling pathways modulated by exercise are Ca²⁺-dependent calcineurin/activated nuclear factor of activated T-cells, mammalian target of rapamycin, myostatin/Smad, and AMP-activated protein kinase regulation of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha. Such modulations contribute to cell adaptation and remodeling of muscle fiber type in response to exercise. Despite great improvement in this field, there are still several unanswered questions as well as unfixed issues concerning clinical trials' biases and limitations. Nevertheless, designing multicenter standard clinical trials while considering individual variability and the exercise modality and duration will improve the perspective we have on the mechanisms mediating adaptation to exercise and final outcomes.

Effects of aerobic exercise on the expressions and activities of nitric oxide synthases in the blood vessel endothelium in prediabetes mellitus

Previous studies by our group have indicated that exercise intervention can ameliorate endothelial dysfunction, which is an early pathophysiological change of prediabetes mellitus. The present study aimed to test the hypothesis that nitric oxide synthases (NOSs), which are expressed in blood vessel endothelium, contribute to the mitigation of vascular endothelium-dependent dysfunction by aerobic exercise in prediabetes mellitus. A prediabetic rat model was established by feeding the rats an additional high-energy diet, and was confirmed by testing blood glucose levels, the area-under-the-curve for the blood glucose tests (P<0.05) and the changes to the histological morphology of the thoracic aorta. Further examination identified that NOS expression changed significantly between the control and prediabetes groups, indicating endothelial dysfunction in the prediabetic rats. Following aerobic exercise, a significant increase in NOS, endothelial (eNOS) mRNA and protein expression (P<0.05), and a significant decrease in NOS, inducible (iNOS) mRNA and protein expression (P<0.05) was identified in the prediabetic rats compared with the control group. No significant change in nitric oxide synthase, brain expression was observed in the prediabetic rat group compared with the control group. Notably, there was also a significant increase and decrease in eNOS and iNOS activity, respectively, in the prediabetes group compared with the control group (P<0.05). Furthermore, nitric oxide (NO) concentration in the vascular endothelium was detected, which revealed a significant increase in NO concentration in the prediabetic rats following aerobic exercise compared with the control (P<0.05). The present study provided results that demonstrated that aerobic exercise ameliorated the vascular endothelium-dependent dysfunction through the NOS/NO signaling pathway, which is primarily regulated by NOS expression and activity, in prediabetes mellitus. The current study provided the theoretical basis for the use of exercise intervention to prevent diabetes mellitus during the early stage.

Effects of exercise training on nitric oxide, blood pressure and antioxidant enzymes

The relationship between exercise training and nitric oxide-related parameters was examined in a cross-sectional study and an intervention study. A cross-sectional study using 184 employees was conducted to observe the association of exercise habits with serum arginase (ELISA and activity), l-arginine, l-citrulline, l-ornithine, NOx, exhaled nitric oxide, blood pressure, FEV1%, hs-CRP, HDL-cholesterol, IgE, and life style factors. An intervention study was also conducted to evaluate the changes of serum arginase I, nitric oxide-related parameters, and mRNA levels of anti-oxidant enzymes in blood monocytes before and after 1 h of aerobic exercise training per day for a month. Exercise habits were associated with increased arginase activity and a moderate alcohol drinking habit, after adjustment with several covariates. Aerobic exercise training induced a decrease in l-arginine and diastolic blood pressure and induced an increase in NO2⁻ and urea. Moreover, mRNA expression of anti-oxidant enzymes, such as catalase and GPX1, and a life elongation enzyme, SIRT3, were significantly increased after aerobic exercise. The results that aerobic exercise training increased NO generation, reduced blood pressure, and induced anti-oxidant enzymes via SIRT3 suggest that exercise training may be an important factor for the prevention of disease by inducing intrinsic NO and anti-oxidant enzymes.

Exercise and NO production: relevance and implications in the cardiopulmonary system

This article reviews the existing knowledge about the effects of physical exercise on nitric oxide (NO) production in the cardiopulmonary system. The authors review the sources of NO in the cardiopulmonary system; involvement of three forms of NO synthases (eNOS, nNOS, and iNOS) in exercise physiology; exercise-induced modulation of NO and/or NOS in physiological and pathophysiological conditions in human subjects and animal models in the absence and presence of pharmacological modulators; and significance of exercise-induced NO production in health and disease. The authors suggest that physical activity significantly improves functioning of the cardiovascular system through an increase in NO bioavailability, potentiation of antioxidant defense, and decrease in the expression of reactive oxygen species-forming enzymes. Regular physical exercises are considered a useful approach to treat cardiovascular diseases. Future studies should focus on detailed identification of (i) the exercise-mediated mechanisms of NO exchange; (ii) optimal exercise approaches to improve cardiovascular function in health and disease; and (iii) physical effort thresholds.

The role of eNOS phosphorylation in causing drug-induced vascular injury

Previously we found that regulation of eNOS is an important part of the pathogenic process of Drug-induced vascular injury (DIVI) for PDE4i. The aims of the current study were to examine the phosphorylation of eNOS in mesentery versus aorta at known regulatory sites across DIVI-inducing drug classes and to compare changes across species. We found that phosphorylation at S615 in rats was elevated 35-fold 2 hr after the last dose of CI-1044 in mesentery versus 3-fold in aorta. Immunoprecipitation studies revealed that many of the upstream regulators of eNOS activation were associated with eNOS in 1 or more signalosome complexes. Next rats were treated with drugs from 4 other classes known to cause DIVI. Each drug was given alone and in combination with SIN-1 (NO donor) or L-NAME (eNOS inhibitor), and the level of eNOS phosphorylation in mesentery and aorta tissue was correlated with the extent of vascular injury and measured serum nitrite. Drugs or combinations produced altered serum nitrite levels as well as vascular injury score in the mesentery. The results suggested that phosphorylation of S615 may be associated with DIVI activity. Studies with the species-specific A2A adenosine agonist CI-947 in rats versus primates showed a similar pattern.