Effects of High Intensity Interval vs. Endurance Training on Cardiac Parameters in Ischemia/Reperfusion of Male Rats: Focus on Oxidative Stress

Abstract

Cardiovascular disease (CVD), such as heart ischemic or coronary artery disease, continues to be one of the major causes of death worldwide. Risk factors that have been considered to contribute to CVD development involve genetic features in combination with age and factors such as dyslipidemia, atherosclerosis, and hypertension. Additionally, the severity of these diseases is strongly affected by excess caloric intake and a lack of physical activity in a patient's lifestyle (Feng et al., 2019). Exercise as a category of physical activity is frequently regarded as an effective treatment to improve cardiovascular function, and it is also hypothesized that exercise training may be cardioprotective against ischemia–reperfusion (I/R) injury (Ghahremani et al., 2018). Although numerous data support the fact that regular physical activity improves heart function (Green and Smith, 2018; Pinckard et al., 2019), the optimal duration, frequency, and intensity of exercise (Serrano-Ostáriz et al., 2011) as well as the exact mechanism of this training-induced beneficial effect remains a matter of debate. It is well-established that exercise training is beneficial not only for cardiovascular but also for non-cardiovascular systems such as endocrine, immune system, and osteomuscular apparatus. Moreover, physical exercise possesses the capability of enhancing the antioxidant defense system, thus decreasing the level of lipid peroxidation both in adults and in aged individuals (Meijers and de Boer, 2017; Bouzid et al., 2018; Simioni et al., 2018). High-volume endurance training (ET), characterized by repeated sessions of continuous moderate intensity exercise, usually involves walking or cycling for 30–60 min to reach 40–80% peak oxygen uptake (VO₂max) (Fletcher et al., 2013). On the other hand, endurance training induces numerous physiological and biochemical adaptations that improve the oxidative capacity of skeletal muscles, modify the energy source used during effort episodes, and increase aerobic capacity (de Lade et al., 2018; Kelly et al., 2018). Furthermore, positive adaptations of this type of exercise on the cardiovascular system are also based on physiological remodeling with elevated O₂ consumption and improvement of cardiac contractile function (Rivas-Estany et al., 2013). Nevertheless, ET offers not only protection against regional ischemia; it also prevents decreasing of heart oxygen consumption subsequently after ischemia/reperfusion (I/R) injury (Li et al., 2014). While this type of exercise offers significant training adaptations, it requires a large time commitment. Therefore, researchers have been encouraged to begin studying new approaches to exercise such as high-intensity interval training (HIIT) with possibly the same positive effects on the cardiovascular system as ET. HIIT refers to repeated sessions of brief intermittent high-intensity exercise, between 80 and 100% of peak heart rate, interspersed with recovery periods or light exercise (Costa et al., 2018). It is often performed with maximal effort or intensity (i.e., to achieve ≥90% VO₂max) and proposed as an alternative regimen to traditional ET to improve cardiovascular health in individuals with CVD (Xie et al., 2017). During the past decades, great scientific attention has been focused on investigating the impact of HIIT due to its potential superior ability to improve cardiorespiratory fitness for a lesser weekly time commitment in comparison to ET. Literature data suggest that HIIT improves flow-mediated dilation in individuals with impaired vascular function related to obesity, hypertension, metabolic syndrome, type 2 diabetes, and coronary artery disease to a greater magnitude than ET (Costa et al., 2018; Hannan et al., 2018). Also, this type of training improves mitochondrial biogenesis, insulin sensitivity (Kessler et al., 2012) and glucose regulation (Gibala et al., 2012), HDL cholesterol, blood pressure (Kessler et al., 2012), and deep abdominal adiposity (Boutcher, 2011) more than ET, which is of great importance for patients with CVD. To have a more complete picture of the effects of HIIT in cardioprotection, we also created a pathological heart model. Animal studies have shown that physical exercise including both HIIT and ET confers cardioprotection against all levels of I/R-induced injury (Calvert, 2011; Frasier et al., 2011). Exercise-induced cardiovascular adaptations are considered to be intensity-dependent; however, there is still a knowledge gap regarding the exact and precise intensity of training leading to optimal cardiac effects, and the underlying mechanisms are still lacking. Taking into consideration that many people avoid regular exercise due to lack of time, the main question of our research was to investigate if high-intensity interval exercise could provide favorable effects on the cardiovascular system as well as usual moderate activity. Moreover, the purpose of this study was to reveal potential differences between two exercise regimens with emphasis on changes in redox status. The present study was carried out on 36 male Wistar albino rats (11 ± 1 week, bodyweight 180 ± 20 g). They were housed under controlled environmental conditions, at room temperature (22 ± 2°C) with an established photo-period of 12 h light/day in the Institute of Cardiovascular Physiology, Faculty of Medical Sciences, University of Kragujevac. For research purposes, all experimental animals were obtained from the Military Medical Academy, Belgrade, Serbia. The rats had free access to food and tap water—ad libitum. Animals in this study were healthy and had not been treated with any drugs or supplements. Rats were randomly divided into three groups (12 animals per group): a sedentary control group (CTRL), an endurance training group (ETr), and a high-intensity interval training group (HIITr). Animals from the second...