Is 3 Weeks of Exercise Enough to Change Blood Pressure and Cardiac Redox State in Hypertensive Rats?
Article Category: Original Scientific Article
Published Online: Dec 31, 2019
Page range: 319 - 326
Received: Sep 20, 2017
Accepted: Sep 26, 2017
DOI: https://doi.org/10.1515/sjecr-2017-0049
Keywords
© 2019 Biljana Jakovljevic et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.
Environmental factors, such as psychological stress, exercise, and dietary sodium intake, have long been considered relevant to both the etiology and control of human essential hypertension. Reduction in the stresses of everyday life, increased levels of exercise, and reduced dietary sodium intake have been recommend as having a beneficial effect in controlling arterial blood pressure. Similarly, high levels of life stress, sedentary lifestyle, and high dietary sodium intake have frequently been linked to cardiovascular diseases (1, 2). Hypertension is considered to be major risk factor for coronary heart diseases contributing to morbidity and mortality worldwide. Importantly, experimental animal studies clearly demonstrate a well-documented promotion of endothelial dysfunction in hypertension by production of oxidative stress markers (3, 4). This occurs due to imbalance between reactive oxygen species (ROS) and antioxidant capacity in favour of oxidants (5). Therefore, treatment of hypertension can be focused on oxidative stress as a possible target.
Regular physical exercise has been considered an effective method which can perform a multitude of beneficial effects for health, such as promotion of health and lifespan, betterment of quality of life and reduce the incidence of disease (6). In addition it has been published in some papers that physical exercise lowers blood pressure (BP) patients with essential hypertension (7) and in male spontaneously hypertensive rats (SHR) (8, 9). Interestingly, controversial effects were determined in female SHR (10). Although the antihypertensive mechanisms of exercise are not completely understood yet, numerous mechanisms are supposed to be involved in reduction of BP while exercising such as decrease in levels of angiotensin II and melioration of nitric oxide (NO) production (11), higher concentration of the plasmatic atrial natriuretic peptide (8), lower production of oxidative stress markers (12). Changes in redox status caused by swimming represent modification in an antioxidant enzyme, alters muscle gene expression thus contributing to exercise-induced adaptations to skeletal muscle. However, it should be taken into consideration that various factors influence the oxidative stress response to swimming training, such as type of exercise, intensity, duration, gender and age of athletes etc (13). Physical exercise may be of potential importance for prevention or treatment of hypertension or hypertension-associated pat.
In recent years there are increased interest on effects of short time physical load on cardiovascular system. Therefore, the objective of this investigation was to explore effects of short-term exercise training on BP and oxidative stress parameters in a rat model of high-salt-induced hypertension.
The study was performed in the laboratory for the cardiovascular physiology of the Faculty of Medical Sciences, University of Kragujevac, Serbia. It was approved by Ethical committee of the Faculty, and performed according to the Faculty’s rules for the welfare of laboratory animals, which are in consent with Good laboratory practice and European Council Directive (86/609/EEC).
Forty male Wistar albino rats, body weight between 180 and 200 g (at the beginning of the experiment), six weeks old (obtained from the Military Medical Academy, Belgrade, Serbia) were housed under controlled environmental conditions, with a temperature of 22±2 °C and a 12-h light/dark cycle. The rats had
At 6 weeks old rats were randomly divided into the following groups (10 animals per group):
hypertensive rats that swam for 3 weeks (S-HTA-3); sedentery hypertensive control rats (HTA-3); normotensive rats that swam for 3 weeks (S-NTA-3); sedentery normotensive control rats (NTA-3).
Hypertensive animals were on high sodium (8% NaCl solution) diet for 4 weeks (period of induction hypertension), and this animals did not drink tap water during the experimental protocol.
BP was monitored before (initial values), after period of induction hypertension (confirmation of hypertension) and after the training period (assessment of the impact of swimming on hypertension).
Rats swam in a specially constructed swimming pool made of glass (80×60×100 cm) in which water temperature (37 ± 1 °C) was maintained by an electric heater, and a pump continuously made waves in order to prevent rats from floating. The training protocol was conducted during the same period of the day (8:00–10:00 am) for all the training sessions. The first week consisted of an adaptation period, initiated with 10 min of continuous swimming training on the first day. Swimming time was increased daily until reaching 60 min at the end of the fifth day. From the second week, the exercise duration was kept constant (60 min/day, 5 days/week) with 2 days of rest. Rats from the control group were put in water for 1 min a day, 5 days a week, in order to achieve the water-induced stress effect. This was maintained until the end of the training period, which lasted 3 weeks. To avoid effects related to acute exercise, animals rested for 48 h before being sacrificed for all additional procedures. The swimming was continuously supervised. Body weight was monitored weekly.
Systolic BP (SBP), diastolic BP (DBP), mean arterial pressure (MAP) and heart rate (HR) were evaluated in conscious rats before and after period of induction of hypertension and after the training or sedentary period and was determined by an indirect tail-cuff method (IITC Life Science, Inc., USA). Animals were restrained for 5–10 min and conditioned to the procedure with cuff inflation-deflation cycles. The results of three stable measurements of BP were averaged.
The hearts of male
The composition of the non-recirculating Krebs-Henseleit perfusate was as follows (mM): NaCl 118, KCI 4.7, CaCI2x2H2O 2.5, MgSO4x7H2O 1.7, NaHCO3 25, KH-2PO4 1.2, glucose 11, pyruvate 2, equilibrated with 95 % O2 plus 5% CO2 and warmed to 37 oC (pH 7.4).
Samples of coronary venous effluent were collected on each value of perfusion pressure (40–120 cmH2O). The following parameters of oxidative stress were determined spectrophotometrically (UV-1800 Shimadzu UV spectrophotometer, Japan): the levels of index of lipid peroxidation, measured as thiobarbituric acid-reactive substances (TBARS), nitrites (NO2−), superoxide anion radical (O2−) and hydrogen peroxide (H2O2).
The degree of lipid peroxidation in the coronary venous effluent was estimated by measuring TBARS, using 1 % thiobarbituric acid in 0.05 NaOH, which was incubated with the coronary effluent at 100 °C for 15 min and measured at 530 nm. Krebs–Henseleit solution was used as a blank probe (14).
Nitric oxide decomposes rapidly to form stable nitrite/nitrate products. The nitrite level (NO2−) was measured and used as an index of nitric oxide (NO) production, using Griess’s reagent. A total of 0.5 ml of perfusate was precipitated with 200 μl of 30 % sulpho-salicylic acid, vortexed for 30 min, and centrifuged at 3000 x g. Equal volumes of the supernatant and Griess’s reagent, containing 1 % sulphanilamide in 5 % phosphoric acid/0.1 % naphthalene ethylenediaminedihydrochloride were added and incubated for 10 min in the dark and measured at 543 nm. The nitrite levels were calculated using sodium nitrite as the standard (15).
The measurement of the level of hydrogen peroxide (H2O2) was based on the oxidation of phenol red by hydrogen peroxide in a reaction catalyzed by horseradish peroxidase (HRPO). Two hundred microliters of perfusate was precipitated using 800 ml of freshly prepared phenol red solution; 10 μl of (1:20) HRPO (made ex tempore) was subsequently added. For the blank probe, an adequate volume of Krebs–Henseleit solution was used instead of coronary venous effluent. The level of H2O2 was measured at 610 nm (16).
The level of the superoxide anion radical (O2−) was measured via a nitro blue tetrazolium (NBT) reaction in TRIS buffer with coronary venous effluent, at 530 nm. Krebs–Henseleit solution was used as a blank probe (17).
Complete statistical evaluation was performed with SPSS Statistics 18. Normality of parameter distribution was checked with the Kolmogorov–Smirnov test. Mann–Whitney U test was used for comparison of groups. Statistic p values less than 0.05 were considered to be statistically significant.
The mean values of body weight of S-HTA-3 and SNTA-3 rats and their controls did not significantly differ throughout the first week of research, while the values of body weight of S-HTA-3 compared to S-NTA-3 rats were significantly higher from the second week to the end of the study (II week - p = 0.043; III week - p = 0.033; IV week - p = 0.028; week - p = 0.028; VI week - p = 0.028; VII week - p = 0.011). The mean values of body weight of hypertensive controls compared to normotensive controls were significantly higher from the second week to the end of the study (II week - p = 0.033; III week - p = 0.023; IV week - p = 0.018; V week - p = 0.018; VI week - p = 0.008; VII week - p = 0.008) (
Fig. 1
Mean body weight of hypertensive and normotensive rats. The values are represented as mean ± SD. S-HTA-3-hypertensive rats that swam for 3 weeks; HTA-3-sedentery hypertensive control rats; S-NTA-3-normotensive rats that swam for 3 weeks; NTA-3-sedentery normotensive control rats. * statistical significance between S-HTA-3 vs S-NTA-3; # statistical significance between HTA-3 vs NTA-3.
Initial levels of BP (period of induction of hypertension) were not different between the groups (average value 115.58/82.340 ± 8.14/5.18). After 4 weeks of treatment with high salt water, hypertension was confirmed in hypertensive groups (198.85/114 ± 9.31/6.23). There was significant differences between HTA-3 and S-HTA-3 group in values of SBP, DBP, MAP. The value of pressures (SBP, DBP, MAP) in S-HTA-3 rats were significantly higher compared with S-NTA rats, while there were no difference in values of HR between groups (
The average values of hemodynamic parameters of hypertensive and normotensive rats that swam for three weeks and their controls in last week
| Groups | Hemodynamic parameters | |||
|---|---|---|---|---|
| SBP (mmHg) | DBP (mmHg) | MAP (mmHg) | HR (bpm) | |
| S-HTA-3 | 196,37 ± 6,87 a,b | 104,31 ± 7,12 a,b | 137,68 ± 6,64 a,b | 330,19 ± 19,27 |
| HTA-3 | 205,69 ± 7,19 | 115,81 ± 8,73 | 142,23 ± 7,12 | 325,17 ± 14,37 |
| S-NTA-3 | 120,01 ± 4,27 | 80,18 ± 6,45 | 92,03 ± 6,75 | 339,28 ± 17,21 |
| NTA-3 | 123,98 ± 6,15 | 83,23 ± 7,65 | 96,13 ± 4,27 | 327,48 ± 16,57 |
Data are means ± SD. SBP, systolic pressure; DBP, diastolic pressure; MAP, mean arterial pressure; HR, heart rate. Statistical significance was considered for a
Parameters of oxidative stress in coronary effluent at different coronary perfusion pressures in swimming and sedentary hypertensive and normotensive rats are shown in
Fig. 2
Effects of 3 weeks of swimming on TBARS levels of hypertensive and normotensive rats. The values are represented as mean ± SD. S-HTA-3-hypertensive rats that swam for 3 weeks; HTA-3-sedentery hypertensive control rats; S-NTA-3-normotensive rats that swam for 3 weeks; NTA-3-sedentery normotensive control rats. *statistical significance at the level of p < 0.05 is shown in
Fig. 3
Effects of 3 weeks of swimming on NO2− levels of hypertensive and normotensive rats. The values are represented as mean ± SD. S-HTA-3-hypertensive rats that swam for 3 weeks; HTA-3-sedentery hypertensive control rats; S-NTA-3-normotensive rats that swam for 3 weeks; NTA-3-sedentery normotensive control rats. *statistical significance at the level of p < 0.05 is shown in
Fig. 4
Effects of 3 weeks of swimming on O2− levels of hypertensive and normotensive rats. The values are represented as mean ± SD. S-HTA-3-hypertensive rats that swam for 3 weeks; HTA-3-sedentery hypertensive control rats; S-NTA-3-normotensive rats that swam for 3 weeks; NTA-3-sedentery normotensive control rats. *statistical significance at the level of p < 0.05 is shown in
Fig. 5
Effects of 3 week of swimming on H2O2 levels of hypertensive and normotensive rats. The values are represented as mean ± SD. S-HTA-3-hypertensive rats that swam for 3 weeks; HTA-3-sedentery hypertensive control rats; S-NTA-3-normotensive rats that swam for 3 weeks; NTA-3-sedentery normotensive control rats. *statistical significance at the level of p < 0.05 is shown in
Significance in level of oxidative stress parameters between hypertensive and normotensive rats who swam for three weeks at different values of coronary perfusion pressures
| S-HTA-3 vs. HTA-3 | S-NTA-3 vs. NTA-3 | S-HTA-3 vs. S-NTA-3 | HTA-3 vs. NTA-3 | S-HTA-3 vs. HTA-3 | S-NTA-3 vs. NTA-3 | S-HTA-3 vs. S-NTA-3 | HTA-3 vs. NTA-3 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | |
| S-HTA-3 vs. HTA-3 | S-NTA-3 vs. NTA-3 | S-HTA-3 vs. S-NTA-3 | HTA-3 vs. NTA-3 | S-HTA-3 vs. HTA-3 | S-NTA-3 vs. NTA-3 | S-HTA-3 vs. S-NTA-3 | HTA-3 vs. NTA-3 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | |
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | ||
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | ||
| p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | p>0,050 | ||
S-HTA-3-hypertensive rats that swam for 3 weeks; HTA-3-sedentery hypertensive control rats; S-NTA-3-normotensive rats that swam for 3 weeks; NTA-3-sedentery normotensive control rats.
There were no significant differences in values of TBARS, NO2− and O2− between the groups (swimming vs sedentary and normotensive vs hypertensive) (
Comparing S-HTA-3 and S-NTA-3 with sedentary groups significant changes was not observed in values of H2O2
First research that was conducted in 1978, gave information about the association between exercise and oxidative stress (18). After many investigations in this field, it was described that increased aerobic meabolism is prospective sourse of oxidative stress during anaerobic exercise (19). Futrhermore, aerobic exercise has been shown to be effective in a significant reduction of ROS and in decrease of the occurrence of ROS associated diseases, including hyper-tension (20). Although many studies aimed to determine the influence of tredmill or cycle ergometer exercise on oxidative stress markers (21), our aim was to examine the effects of short-term swimming exercise considering that swimming has been proposed as a convenient model for identifying the physiological, biochemical and molecular responses to acute exercise training and the adaptations to chronic exercise training (22, 23).
Due to the fact that numerous patients choose a non-weight-bearing physical activity such as swimming, it is important to determine if this kind of practice has potential antihypertensive effects (24). Regular physical activity contributed in reduction of elevated BP in hypertensive patients and hypertensive animals in which hypertension was induced by N(ω)-nitro-L-arginine methyl ester (L-NAME) (25, 26), deoxycorticosterone acetate (DOCA) (27) as well as in spontaneously hypertensive (28), Dahl saltsensitive and salt-resistant rats (29).
Taken together, these studies suggest the beneficial effects of aerobic training upon arterial blood pressure which seems to be intensity-dependent (28, 30). Our findings are in accordance with previous work that showed decrease in arterial pressure and MAP after four and eight weeks of a swimming program in spontaneously hyper-tensive rats (31,32,33). Nevertheless, it is important to recognize that even a 5–6 mmHg decrease in arterial blood pressure which is similar to that observed in our study can be associated with a approximately 42% reduction in stroke incidence and a approximately 14% reduction in coronary heart disease as noted in several epidemiologic studies (34). Significant reduction of SBP, DBP and MAP in our study proved that swimming training can be prescribed to patients with hypertension as a non-pharmacological treatment. Reason for reduction of BP may be due to lower sympathetic activity induced by physical activity which can be a consequence of progression of arterial baroreflex and chemosensitive cardiopulmonary baroreflex sensitivity in SHR. In present study swimming also led to maintenance of body weight in hypertensive rats which certainly contributed to reduction of BP (35).
A link between hypertension and oxidative stress is well established. Redox imbalance, increased bioavailability of ROS or/and decreased antioxidant capacity has been demonstrated both in humans and animals (36). However the presence of oxidative stress within the myocardium have been very poorly investigated. Therefore we sought to assess the changes in cardiac oxidative stress parameters of hyper-tensive rats after short-term swimming or sedentary period.
Analysis of parameters that we determined in the coronary venous effluent during coronary autoregulation refers to the oxidative stress in the endocardium of the left ventricle. Our data have shown that values of pro-oxidant markers such as TBARS, NO2−, O2− were not affected by 3 weeks swimming protocol. According to Claudio et al excercise training prevented the increase of ROS production in ovariectomized hypertensive rats demonstrating increased expresion of antioxidative enzymes. Potential explanation for non excessive production of ROS besides above mentioned mechanism, may also be lower electron leakage from mitochondria or chronic exposure of tissue to ROS, induced by training, which makes the organ more resistant to the effects that derive from the mechanisms of oxidative stress (37).
On the other hand, investigation conducted on hypertensive rats trained 6 weeks showed that exercise lead to significant reduction of TBARS values in serum when compared to sedentary group. Also significant decrease of NO was noticed in sedentary hypertensive group but level of NO increased in trained hypertensive group (38). Furthermore, Bertagnolli and co-workers noticed similar changes in favor of lipid peroxidation in 10 weeks trained SHR group. These significant changes in ROS release may be due to longer duration of physical load (39).
Surprisingly, none of the researchers has not dealed with determination of H2O2 levels in hypertensive physicaly active subjects. We noticed that levels of H2O2 were significantly higher in S-HTA-3 group comparing to SNTA at CPP of 80–120 cmH2O. Other researchers measured tissue total oxidant status (TOS) in heart tissue and expressed their results in terms of micromolar hydrogen peroxide equivalent per liter (lmol H2O2 equiv/L/mg protein). Their observation was that hypertensive animals had higher tissue oxidative stress levels than normotensives (40). Assumption for high concentration of hydrogen peroxide in hypertensive swimming rats may be activation of angiotensin II probably through angiotensin AT1 receptor-dependent stimulation of NADPH oxidase (Nox) enzymes (41).
On the basis of all mentioned above it can be assumed that the most important determinating factors of exrcise induced modification of cardiac oxidative stress can be duration and/or intensity.
Our results clearly indicate that reduction of BP may start after 3rd week of training. In addition it seems that duration of three weeks of swimming does not promote cardiac oxidative stress damages. These findings could be one step closer for better understanding of short-time exercise on blood preassure and oxidative stress of the heart.