In this study, the effect of long-term supplementation of coenzyme Q 10 (CoQ 10) on the responses of swim-trained rat aorta was investigated. Twenty-four adult male Wistar rats were divided into four groups: untrained, trained, untrained+CoQ 10, and trained+CoQ 10 group. In the trained groups rats swam for 60 min/day, five days/week for six weeks. The CoQ 10 supplements were administered by intraperitoneal injection at a daily dose of 10 mg·kg -1 of body weight five days/week for six weeks. Swimming of the rats was performed in a container containing tap water. Rats were sacrificed and thoracic aortas were removed for ex vivo analysis after the last swimming session. The aortas were cut into rings 2.5 mm in length. Concentration-response curves for phenylephrine (PHE, 10 -9-3×10 -4 M) and potassium chloride (KCl, 5-100 mM) were isometrically recorded. The sensitivity and maximal responses to PHE and KCl of aortic rings obtained from trained rats were lower than those of untrained rats. CoQ 10 supplementation decreased the responses to both vasoconstrictors in untrained and especially in trained groups. Although neither CoQ 10 nor training did affect malondialdehyde (MDA) and protein carbonyl (PC) levels, creatine kinase (CK) activity decreased and superoxide dismutase (SOD) activity increased only with exercise training. Glutathione (GSH) levels increased in CoQ 10 supplemented-untrained rats. In conclusion, our results suggest that CoQ 10 supplementation may have beneficial effects during exercise. © 2012 Akadémiai Kiadó, Budapest.