Effects of spontaneous and training induced physical activity on the body composition of OVX rats

Reduced estrogen levels occurring with menopausal transition are accompanied with significant changes in the energy homeostasis. For example, postmenopausal women have a higher risk of developing obesity, insulin resistance and dyslipidemia. Similarly, OVX rats are characterized by rapid increase of body weight and fat and exhibit dramatically reduced movement drive (compared to intact rats), however, an individual level of activity remains. In the present study, SHAM and OVX rats had free access to running wheels and we investigated the potential effects of additional treadmill training (for 6 weeks, 5 days a week) on body weight and body composition in a subset of OVX rats.

The spontaneous activities on the running wheel over the period averaged to 60483 m, 51486 m, and 322308 m in OVX, trained OVX, and SHAM rats, respectively. By contrast, total dietary intake appeared not to be significantly affected by any of the treatment levels. Growth curves were modelled by a non-linear asymptotic regression model. The three groups exhibited significantly different growth rates. Already during the hormonal decline (14 d), in OVX animals an average increase of the body weights of 22 g was observed compared to SHAM animals. Training reduced the body weight by 77 g as compared to untrained OVX animals. In untrained SHAM rats the corresponding reduction even amounted to 114 g. Relative visceral fat mass was highest in OVX rats and lowest in SHAM rats. Trained OVX rats exhibited intermediate values. By contrast, relative mass of M. soleus was highest in SHAM rats, whereas the OVX groups showed lower virtually identical data. The relative mass of M. gastrocnemius in SHAM and trained OVX rats tended to be higher than in untrained OVX rats.

In summary, ovariectomy changes spontaneous activity, growth curves and body composition significantly. Moderate training affects these parameters in a positive manner. Further analyses are needed to uncover the underlying molecular mechanisms.