SEX-ASSOCIATED DIFFERENCES IN COLD-INDUCED UCP1 SYNTHESIS IN RODENT BROWN ADIPOSE-TISSUE

The effects of acute and chronic acclimation to cold on uncoupling pro tein 1 (UCP1) levels, as well as on GDP-binding to mitochondria, cytoc hrome c oxidase activity and mitochondrial protein concentration in br own adipose tissue (BAT) of intact male and female rats have been anal yzed. Results reveal that females rats are more sensitive to cold beca use their threshold temperature for the thermogenic response is set at a higher value (around 22 degrees C) than that of males (around 18 de grees C), hence leading to differences in BAT UCP1 levels between the sexes at different environmental temperatures. In vitro experiments sh owed that steroid hormones, beta-estradiol, estrone and progesterone, can reduce norepinephrine-induced UCP1 synthesis in brown adipocytes d ifferentiated in primary culture. Thus the different sex associated re sponse of cold-induced thermogenesis in rats does not appear to be exp lained by a direct action of sex steroids upon the adipocyte, implying that other factors in the thermogenic regulatory system must be invol ved.