Dual control of cytochrome-c oxidase activity by female sex steroids.

Female sex steroids modify cytochrome-c oxidase (COX) activity in brown adipose tissue. To check the possibility of extending this modulating effect upon oxidative capacity to other tissues, COX activity was measured in different tissues from cold-acclimated female rats that were (1) intact in proestrus and diestrus I, (2) ovariectomized or (3) ovariectomized and treated with oestradiol and/or progesterone. In intact rats, COX activity varied within the oestrous cycle in brown adipose tissue and soleus muscle. Ovariectomy induced an increase in COX activity in most of the tissues studied, an increase reversed only after 10 days of treatment with oestradiol and/or progesterone. These results indicate both a short-term (oestrous cycle) and a long-term (ovariectomy) control of COX activity by female sex steroids, probably mediated by allosteric modulation and control of the enzyme synthesis respectively. In thermogenic tissues, that is brown adipose tissue and skeletal muscles, the short-term control is interpreted as a cooperation between tissues to fulfil the requirements of temperature maintenance.