Prolonged Effects of Elevated 17β-Estradiol on Physical Activity after Orchidectomy

The biological mechanisms regulating physical activity patterns appear to be linked to the sex hormones. Elucidation of these regulatory mechanisms may enhance individual physical activity patterns producing positive gains in health. PURPOSEThe purpose of this study was to evaluate the prolonged effects of estrogen on wheel running distance, duration, and speed in orchidectomized mice. METHODSThe physical activity patterns of 9-week old C57BL/6j male mice (n=28) were observed. Wheel running distance, duration, and speed were assessed under physiological conditions for seven days. Next, physical activity patterns were evaluated following bilateral orchidectomy (n=14) or sham orchidectomy (n=14) for an additional seven days. Orchidectomized mice were provided estrogen containing capsules for three additional weeks; control mice were provided estrogen-free capsules. Wheel running distance, duration, and speed were analyzed by three two-way (treatment group x phase of study) analysis of variance tests. RESULTSWheel running speed was unaffected by sex hormone status. Distance (mean±SD6.74±2.13 km at baseline) decreased significantly after orchidectomy (2.27±1.55 km) and remained low following initial estrogen treatment (3.04±1.05 km). Prolonged estrogen exposure sustained a significant elevation of daily distance (4.47±1.87 km). Prolonged estrogen exposure recovered and significantly sustained wheel running duration (baseline248±60 min; post-orchidectomy102±53 min; prolonged exposure170±63 min). CONCLUSIONSWheel running behavior was reduced significantly following orchidectomy and remained low following initial treatment with estrogens, but recovered to near control levels after two weeks of exposure to estrogens. The estrogenic mechanism regulating wheel running behavior in male mice appears to induce an extensive, but slow acting biological mechanism. Understanding the biological drive behind this mechanism may aid in developing useful therapeutic strategies to combat health issues related to physical inactivity.