Oestradiol and progesterone control cytochrome c oxidase activity in thermogenic tissues

Natural Fluctuations of ft male sex steroids along the oestrus cycle are fo llowed by fluctuations of COX activity in thermogenic tissues. At proestrus , when plasma level of oestradiol and progesterone peal;, COX activity reac hes a maximum in skeletal muscles and a minimum in brown adipose tissue. Th ese opposite rhythms in both thermogenic tissues suggest they compensate ea ch other to maintain thermic homeostasis according to plasma level of sex s teroids. Nonetheless, a long-term inhibitory effect of sex hormones was evi denced by the marked increase in COX activity in both brown adipose tissue and muscles after ovariectomy, increase that was reversed by oestradiol and /or progesterone treatment.