Comparative Biochemistry and Physiology Part B 137 (2004) 187–196 1096-4959/04/$ - see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.cbpc.2003.11.002 Swim exercise training and adaptations in the antioxidant defense system of myocardium of old rats: relationship to swim intensity and duration T. Ravi Kiran , M.V.V. Subramanyam , S. Asha Devi * a b a, Laboratory of Gerontology, Department of Zoology, Bangalore University, Bangalore 560 056, India a Department of Sericulture, Bangalore University, Bangalore 560 056, India b Received 3 July 2003; received in revised form 28 October 2003; accepted 6 November 2003 Abstract We examined a suitable swim program of different intensities and durations that could evoke changes in the myocardial antioxidant capacity in 22-month-old rats. Male rats (Rattus norvegicus) were assigned to either a sedentary control (SE-C) group or one of six trainee groups. Animals were swim-exercised for 4 weeks with either 20 min or 40 miny day, and three intensities, low, moderate and high. Low-intensity at 20 minyday elicited maximum swim velocity (S ) v and endurance capacity (P-0.05). While serum total cholesterol, triglyceride and low-density lipoprotein (LDL-C) levels were significantly reduced, high-density lipoprotein (HDL-C) showed an increase (P-0.05) in low-intensity trained rats (20 minyday) over SE-C. Notable reduction in blood lactate was also evident. Exercise training significantly increased superoxide dismutase (Mn-SOD), decreased lipid peroxidation products, malondialdehyde and lipofuscin in the left and right ventricles. Increased Mn-SOD with concomitant decrease in lipofuscin in left ventricle was significantly greater than in right ventricle. Moderate- to high-intensity exercise was not effective in either reducing lipid peroxidation products or elevating Mn-SOD activity. These data suggest that swim training at low-intensity of 20 minyday is beneficial as a major protective adaptation against oxidative stress in old myocardium.  2003 Elsevier Inc. All rights reserved. Keywords: Cholesterol; Endurance; Exercise; Lactate; Lipofuscin; Myocardium; Superoxide dismutase; Triglyceride 1. Introduction One of several mechanisms affected in old age is the impairment of self-defense system against reactive oxygen species (ROS) related to an imbal- ance between the prooxidants and antioxidants (Somani et al., 1995). However, ROS injury is felt largely in tissues with post-mitotic cells (Miquel, 1998). Interestingly, the generation of ROS in old age resembles that of ROS-induced ischaemia- *Corresponding author. Tel.: q91-080-321-4001y214; fax: q91-080-321-9295. E-mail address: asuba@blr.vsnl.net.in (S. Asha Devi). reperfused (I-R) heart (Matheis et al., 1992). Alterations in DNA, protein and lipid oxidations result in an impairment of cardiac performance (Downey, 1990; Park et al., 1992). There have been an increasing number of studies that have tried to evaluate the role of endogenous as well as exogenous antioxidants in detoxifying ROS, a move to ameliorate age-related cardiac injury (Reznick et al., 1992; Powers et al., 1993; Anitha and Asha, 1996; Prathima and Asha, 1999). Of several methods to do so, physical training has proved to be a promising approach to boost the enzymic antioxidant system (AOS) in the heart