Oestrogen attenuates post-exercise myeloperoxidase activity in skeletal muscle of male rats

The effects of 2 weeks of oestrogen (40 mu g kg BW-1 beta-estradiol 3-benzo ate) injection on 24 h postexercise myeloperoxidase (MPO) activities were d etermined in plantaris and soleus muscles and liver of sexually mature male and female rats. The treadmill running protocol (45-60 min, at 28 m min(-1 ). 15% grade) induced significant elevations in muscle MPO activities 24 h post-exercise in male rats, while prior oestrogen administration to male ra ts eliminated the post-exercise elevations in muscle MPO activities. Female rats experienced no significant post-exercise elevations in muscle MPO act ivities. Hence oestrogen administration to male rats attenuated post-exerci se muscle MPO activities to levels found in female animals. Liver MPO activ ities were not significantly affected by exercise, gender or oestrogen admi nistration. Oestrogen may be a factor in diminishing 24 h post-exercise ske letal muscle leukocyte infiltration and inflammatory response in both male and female muscle.