ABSTRACT
        Background and Objectives: Previous studies have shown that morphine dependence leads to myocardial dysfunction. In addition, apelin plays a protective role in cardiac function. The purpose of this study was to evaluate effects of morphine dependence and three models of exercise training on serum apelin level of dependent and healthy rats.
       Methods: Ten healthy and 40 morphine-dependent rats were used in this study. The morphine-dependent rats were divided into four equal groups of control addicts, endurance training, strength training and concurrent training. The training exercises were carried out for eight weeks, five days a week. Serum apelin level was measured by ELISA, 72 hours after the last training session.
        Results: Statistical analysis demonstrated that apelin level increased significantly in morphine-dependent rats compared to healthy controls. On the other hand, endurance and concurrent training significantly increased serum apelin level in morphine-dependent rats compared to control addicts, but strength training had not effect on serum apelin level in morphine-dependent rats.
         Conclusion: Endurance and concurrent training may have cardioprotective effects on morphine-dependent rats by increasing serum apelin levels. Therefore, such training activities could be recommended to morphine-dependent patients to prevent cardiac disorders.
          Keywords: Apelin, Morphine, Exercise.