effects of regular swimming exercise on the pain threshold following withdrawal syndrome in morphine-dependent rats

introduction: nowadays opioids are gaining acceptance for the management of moderate to severe and chronic pain. in addition, a number of studies have shown that plasma levels of β-endorphin (βep) in exercise trained are higher than sedentary rats. in our study we assume that exercise training can reduce pain after withdrawal syndrome in morphine-dependent rats. methods: male wistar rats (250±20 g, n=24) were addicted by morphine sulfate 0.4mg/ml (for 21 days) and animals were submitted to swimming training, five days a week for 8 weeks, in which first 60 minutes for 3 weeks and then 90 minutes in two weeks and at the end 120 min for 3weeks. at the end of each stage of exercise protocol naloxan hydrochloride (3mg/kg.ip) was injected. tail-flick was used to assess the effect of training on nociceptive threshold. results: data showed that swimming aerobic exercise significantly increased pain threshold in trained control and addicted rats (p<0.05) while pain responses did not significantly change in sedentary control and addicted rats. conclusion: our results indicate that swimming training has analgesic property in morphine withdrawal-induced hyperalgesia in rats. therefore, it can be used for the treatment and/or management of painful conditions.