Sex-dependent thermogenesis, differences in mitochondrial morphology and function, and adrenergic response in brown adipose tissue

Gender-related differences in brown adipose tissue (BAT) thermogenesis of 110-day-old rats were studied by determining the morphological and functional features of BAT. The adrenergic control was assessed by studying the levels of beta(3)- and alpha(2A)-adrenergic receptors (AR) and by determining the lipolytic response to norepinephrine (beta(1)-,beta(2)-beta(3)-, and alpha(2)-AR agonist), isoprenaline (beta(1)-, beta(2)-, and beta(3)-AR agonist), and CGP12177A (selective partial beta(3)-AR agonist but beta(1)- and beta(2)-AR antagonist) together with post-receptor agents, forskolin and dibutyryl cyclic AMP. The female rats that had greater oxygen consumption showed higher UCP1 content, a higher multilocular arrangement, and both longer cristae and higher cristae dense mitochondria in BAT indicating heightened thermogenic capacity and activity; this picture is accompanied by a more sensitive beta(3)-AR to norepinephrine signal (EC50 10-fold lower for CGP12177A) and a lower expression of alpha(2A)-AR than male rats. Taken together, our results support the idea that the BAT hormonal environment could be involved in the control of different elements of lipolytic and thermogenic adrenergic pathways. Gender dimorphism is both at receptor (changing a2A-AR density and beta(3)-AR affinity) and post-receptor (modulating the links involved in the adrenergic signal transduction) levels. These changes in adrenergic control could be responsible, at least in part, both for the important mitochondrial recruitment differences and functional and morphological features of BAT in female rats under usual rodent housing temperatures.