Submitted on January 29, 2007
Accepted on December 13, 2007
Estrogen influences satellite cell activation and proliferation following downhill running in rats
Deborah L. Enns1 and Peter M. Tiidus2*
1 Kinesiology & PE, Wilfrid Laurier University, Waterloo, Canada
2 Department of Kinesiology & Physical Education, Wilfrid Laurier University, Waterloo, Canada
* To whom correspondence should be addressed. E-mail: ptiidus{at}wlu.ca.
To investigate the influence of estrogen on post-exercise muscle repair processes, we examined the effects of estrogen supplementation (0.25 mg pellet) on numbers of total, activated and proliferating satellite cells in rat skeletal muscles 72 h following downhill running. Ovariectomized female rats (n=44) were divided into 4 groups (n=11 per group): sham (no estrogen) controls (SC), sham, exercised (SE), estrogen-supplemented controls (EC) and estrogen-supplemented, exercised (EE). After 8 days of estrogen exposure, animals were exposed to 90 min of treadmill running at 17 m/min (-13.5°). Seventy-two hours later, soleus and white vastus muscles were removed and immunostained for total (Pax7), activated (MyoD) and proliferating (BrdU) satellite cells. 
-Glucuronidase activity was increased (P < 0.05) in both muscles following exercise; however, the post-exercise elevations in enzyme activity were attenuated in the EE group compared to the ES group in the soleus (P < 0.05). Immunohistochemical analysis revealed that exercised groups displayed increased numbers of myofibers containing total, activated and proliferating satellite cells compared to control groups (P < 0.05). Furthermore, greater numbers of fibers positive for markers of total, activated and proliferating satellite cells were observed post-exercise in EE animals compared to ES animals for both muscles (P < 0.05). The results demonstrate that estrogen may potentially influence post-damage repair of skeletal muscle through activation of satellite cells.
