Elsevier

Archives of Medical Research

Volume 35, Issue 4, July–August 2004, Pages 294-300
Archives of Medical Research

Original article
Variable effects of exercise intensity on reduced glutathione, thiobarbituric acid reactive substance levels, and glucose concentration

https://doi.org/10.1016/j.arcmed.2004.03.006Get rights and content

Abstract

Background

Physical exercise may be associated with a 10- to 20-fold increase in whole body oxygen uptake. Generation of free oxygen radicals (FORs) is elevated to a level that overwhelms tissue antioxidant defense systems in exercise. One of the most reliable indices of exercise-induced oxidant production is tissue glutathione oxidation.

Methods

In this study three different volunteer groups carried out various sports disciplines and worked at least as amateurs for 6–7 years before and after aerobic (Aer)-, anaerobic (Anae)-, or aerobic + anaerobic (Aer–Anae)-dominant exercises. Thiobarbituric acid reactive substances (TBARS) reduced glutathione (GSH) levels, glucose concentration was measured, and we investigated their relationships with different types of exercise. From all groups (n = 60, each group comprising 10 females and 10 males), we collected blood samples at the following five different times: before exercise; immediately after exercise, and 4, 24, and 48 h after completion of exercise. These samples were assayed for whole blood GSH, plasma TBARS levels, and glucose concentration.

Results

Significant increase in Aer–Anae was noted in levels of TBARS while decrease was observed in glutathione levels in exercise group as compared with prior levels in all groups. However, no statistical difference was observed in total group levels before and after exercise and in male and female groups compared before and after exercise. When gender differences were taken into account, females generally had higher levels of GSH, whereas TBARS levels were higher in males. When compared either before or after exercise, levels of glucose concentration—especially immediately after exercise period in all groups—were higher. In addition, in Anae groups glucose concentrations were higher at 4 and 24 h in females than in males. Aer exercise caused oxidative stress to a lesser degree, whereas Aer–Anae exercise caused oxidative stress of higher degree that was statistically significant.

Conclusions

According to our findings, exercise increased TBARS level significantly in all groups, especially more so in Aer–Anae groups. In addition, GSH was increased more in females than in males, while concentration of glucose did not change remarkably. Additionally, it can be stated that women are more resistant to oxidative stress.

Introduction

In recent years it has been suggested that free oxygen radicals (FORs) induced by acute exercise were involved in damage to muscles and other tissues. Despite little availability of direct evidence for FORs production during exercise, there is an abundance of literature providing indirect support that oxidative stress occurred during exercise 1., 2., 3., 4., 5.. Cells continuously produce FORs as part of the metabolic processes. Among the earliest biochemical reactions found were hydrolysis of fatty acids from membrane phospholipids, production of biologically active eicosanoids, and peroxidation of lipids with formation of FORs. These latter reactions were the main agents responsible for cellular damage (4). Superoxide, ferryl, and hydroxyl anions were common reactive compounds that caused lipid peroxidation 4., 5.. Under normal conditions, superoxide (O2) anions were generated during mitochondrial electron transport. There was a balance between antioxidants and oxidants produced by aerobic cellular systems. These free radicals were neutralized by an elaborate antioxidant defense system consisting of enzymes such as catalane, superoxide dismutase, and glutathione peroxidase, and numerous nonenzymatic antioxidants including vitamins A, E, and C, glutathione, ubiquinone, and flavonoids. Exercise can produce an imbalance between FORs and antioxidants, which was referred to as oxidative stress 2., 3..

Physical exercise could induce peroxidation of lipids in cellular membranes and increased level of thiobarbituric acid reactive substance (TBARS) in plasma observed in post-exercise sample is a consequence of leakage of peroxides from tissues, especially from muscle into plasma. Oxidative modification of plasma constituents was an expression of oxidative damage that occurred in tissues (6). Physical activity increased generation of FORs in several ways; for instance, oxidative phosphorylation increased in response to exercise and there was concomitant increase in FORs (3). Finally, regular physical exercise caused up to a 10-fold increase in oxygen consumption and 10- to 20-fold increase in metabolism of cells, in turn increasing formation of FORs (7). FORs promoted peroxidation of lipids and were able to attack polyunsaturated fatty acids in cell membrane, leading to a chain of chemical reactions called lipid peroxidation. Peroxidation products were observed in blood after extreme exercise (8). Most commonly measured were by-products of lipid peroxidation, but changes in status of antioxidant compounds such as glutathione, protein, DNA oxidation products, and antioxidant enzyme activities have also been used. Aldehydes, especially malonildialdehyde, which was an end-product of lipid peroxidation, were frequently used as markers of oxidative stress in response to exercise. They were all indirect measures of FORs activity 4., 5., 9., 10., 11.. The present study examined indices of lipid peroxidation and TBARS in plasma of subjects under different exercise conditions. Although TBA test was a very nonspecific technique, it was able to offer empirical insight into the complex process of lipid peroxidation, but it remained a simple and inexpensive technique 2., 12..

Training reduces production of lipid peroxide products and prevents oxidative damage in tissues by inducing the antioxidant system in athletes (13). One endogenous antioxidant, reduced glutathione (GSH), played a central role in coordinating synergism between different lipid- and aqueous-phase antioxidants. During normal function of antioxidant defense system, GSH was used by glutathione peroxidase (GSH-Px), a peroxidase used to detoxify hydrogen peroxide. It was a substrate for GSH-Px reducing hydrogen peroxide. Additionally, glutathione reductase was necessary to convert hydrogen peroxide into GSH, which would also contribute to detoxification of hydrogen peroxide. Primary scavenger for exercise generated by oxygen radicals was mitochondrial superoxide dismutase 13., 14., 15., 16., 17., 18., 19.. We documented 1) the manner in which endogenous GSH may affect exhaustive exercise-induced changes in tissue GSH status, lipid peroxides, and endurance and 2) the relative role of endogenous GSH in circumvention of exercise-induced oxidative stress (20). Physical exercise may cause oxidation of GSH in tissues such as blood, skeletal muscle, and liver 15., 18., 19., 20., 21..

Metabolism produced energy in the body. Immediate source of energy for biological work was adenosine triphosphate (ATP). Amount of ATP stored in muscles was limited. Therefore, muscle ATP needed to be replenished during exercise aerobically and anaerobically. This anaerobic energy process broke down muscle glycogen stores (or blood glucose) and produced only a limited amount of ATP. During longer-term aerobic exercise, it became necessary to consume oxygen, utilize additional muscle glycogen and blood glucose, and use lipids (fat) to sustain energy output 22., 23., 24., 25.. Fatty acids in circulation increased during exercise due to mobilization from lipid stores. At the same time, glycogen stores decreased. Because of continuous exercise, blood glucose concentrations could remain either normal or increase (24).

It is well known that there was a close relationship between oxidant stress and exercise, although it has not yet been investigated whether exercise-induced oxidant stress caused post-exercise alteration. The aim of this study was to determine the effect of different types of exercise on oxidative stress markers and the effect of gender on this exercise-mediated oxidative stress.

Section snippets

Subjects

Sixty students from the School of Physical Training and Higher Sport Education in Elazig, Turkey, between the ages of 19 and 22 years (mean 20.4 ± 1.2 years) and who were involved in sports as amateurs for at least 6 years were included in the study. All subjects (n = 60, 10 females and 10 males in each of three groups) initially signed voluntary and informed consent to participate in the experiment, which was approved in advance by the respective institutional Ethics Review Committees (July 23,

Results

Table 1 shows physical characteristics of subjects. Male and female subgroups were identified in all three groups. All participants in the three groups were found similar in terms of average age, height, BMI, and remaining characteristics (comparing for male/male, female/female, p >0.05).

Average levels of TBARS, GSH, and glucose measured in all three groups before and after exercise are shown in Table 2.

According to these findings, in Aer group average GSH levels were slightly higher (p <0.05)

Discussion

In the present study, plasma TBARS levels mildly increased after different types of exercise and subsequently returned to pre-exercise levels at 48 h post-exercise; however, they increased in TBARS levels, these findings not statistically meaningful in males and females. Several studies consistently showed that physical exercise may induce oxidative stress in both humans and experimental animals 28., 29., 30..

Several studies reported that single bouts of exercise increased TBARS blood levels 7.

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