Genesis of oestrogenic inhibition of soleus muscle development in female mice

Abstract

The mechanism by which oestrogen inhibits development of muscle mass was investigated in the soleus muscle of 20 sexually immature female mice. Half of the population were injected weekly (from one to nine weeks old) with a physiological dose of 0.01 mg stilboestrol dipropionate (synthetic oestrogen). After each mouse was killed at 10 weeks old, the weight and muscle index was determined for each muscle. The number of muscle fibres was counted in each soleus muscle. The muscle fibre size for each muscle was determined by measuring the greatest diameter of at least 100 fibres. The number of muscle fibres was similar in both normal and oestrogen treated animals but the individual muscle fibre sizes were significantly smaller in oestrogen treated animals. These observations indicated, therefore, that oestrogen inhibits development of muscle mass in females by limiting the size of individual muscle fibres and not by inhibiting the multiplication of muscle fibres.