Potential ergogenic effects of l-arginine against oxidative and inflammatory stress induced by acute exercise in aging rats
Introduction
Exhaustive physical exercise has been shown to induce free radicals in vivo and lead to oxidative damage in multiple organs such as muscle, liver, lung, and heart in adult male or female albino rats (Kumar et al., 1992, Frankiewicz-Jozko et al., 1996, Ashton et al., 1998, Radak et al., 1998). In the recent years, there has been much interest in the role of improper activation or up-regulation of xanthine oxidase (XO) or myeloperoxidase (MPO) in the pathogenesis of inflammatory disorders, including strenuous exercise-induced damage of different tissues (Gomez-Cabrera et al., 2005, Morozov et al., 2006). XO, a metalloflavoprotein, plays a major role for oxygen-derived free radicals in post-ischemic tissue injury (McCord, 1985). It was found that XO increased significantly in the circulation and tissues during exhaustive exercise (Radak et al., 1995, Hellsten et al., 1997, Vina et al., 2000). Vina et al. (2000) further demonstrated that XO is responsible for free radical production and tissue damage during exhaustive exercise. In a previous study, Judge and his colleague proposed that XO-derived oxidants are chemotactic to neutrophils (Judge and Dodd, 2004), and that neutrophils infiltration into tissues is associated with strenuous exercise-induced tissue damage in human and animal studies (Fielding et al., 1993, Belcastro et al., 1996, Tiidus, 1998). MPO is released by activated neutrophils and its activity is used as a marker for neutrophils infiltration into tissues. These studies indicate that both of XO and MPO are the two main sources of extracellular free radicals released during strenuous exercise and are responsible for exhaustive exercise-induced oxidative stress in several tissues including heart, skeletal muscle, liver, lung, and kidney.
Recently, there has also been much interest in the role that reactive oxygen species (ROS) play in the pathogenesis of aging (Siomek et al., 2007, Barja, 2007). It has been found that the aged population is more susceptible to oxidative stress induced by many different physiologic situations, such as strenuous exercise (Ji, 2001, Reid and Durham, 2002, Jolitha et al., 2006). Our previous studies have shown that a diet supplemented with l-arginine (l-Arg) significantly attenuated pulmonary and cardiac oxidative stress during exhaustive exercise in young SD rats (Lin et al., 2005, Lin et al., 2006). Therefore, we hypothesized that l-Arg supplementation might also reduce the level of exhaustive exercise-induced tissue damage in aging rats. In this research, we examine whether l-Arg supplementation could reverse the combined inflammatory and oxidative damage that occur in cardiac, muscular, hepatic, pulmonary and renal tissues due to exhaustive exercise in aging rats.
Section snippets
Animals and treatment
Thirty 18-month-old male Sprague–Dawley rats weighing 550–600 g were purchased from the National Laboratory Animal Breeding and Research Center (Taipei, Taiwan). All rats were given free access to water and standard pelleted rat food (No. 5001; PMI Nutrition International, Brentwood, MO, USA) and were individually housed in a room maintained at 23 ± 2 °C and a 12 h light–dark cycle during the first week. This experiment was approved by the Fu-Jen Catholic University Animal Care and Usage Committee
Results
At the end of 30 days, the mean body weights of rats in each group were as follows: SC, 559 ± 36 g; SC + Arg, 592 ± 15 g; E, 596 ± 13 g; and E + Arg, 578 ± 16 g. There were no significant differences in body weight between the four groups. The mean endurance time of the l-arginine-treated group increased by 24% compared with that of the control group (63 ± 3 versus 51 ± 6 min; P < 0.05).
The elevations of cytosolic enzymes in plasma, such as AST, ALT, and LDH were characteristic responses to strenuous exercise and are
Discussion
Laboratory rats are commonly used to investigate the effects of aging and exhaustive exercise on biochemical changes in humans. Our study examined the effects of l-Arg on exhaustive exercise-induced multi-organ oxidative injury in an aging rat model.
Acknowledgement
This study was supported by the National Science Council of Taiwan (NSC 96-2413-H-029-003 to W.-T.L.), and a Grant (SKH-FJU-92-13) from the Shin Kong Wu Ho-Su Memorial Hospital, Taiwan, ROC.
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