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

Female sex steroids modify cytochrome-c oxidase (COX) activity in brown adi pose tissue. To check the possibility of extending this modulating effect u pon oxidative capacity to other tissues, COX activity was measured in diffe rent tissues from cold-acclimated female rats that were (1) intact in proes trus and diestrus I, (2) ovariectomized or(3)ovariectomized and treated wit h oestradiol and/or progesterone. Ln intact rats, COX activity varied withi n the oestrous cycle in brown adipose tissue and soleus muscle. Ovariectomy induced an increase in COX activity in most of the tissues studied, an inc rease reversed only after 10 days of treatment with oestradiol and/or proge sterone. These results indicate both a short-term (oestrous cycle) and a lo ng-term (ovariectomy) control of COX activity by female sex steroids, proba bly mediated by allosteric modulation and control of the enzyme synthesis r espectively. In thermogenic tissues, that is brown adipose tissue and skele tal muscles, the short-term control is interpreted as a cooperation between tissues to fulfil the requirements of temperature maintenance.