CORTICOSTERONE DECREASES NONSHIVERING THERMOGENESIS AND INCREASES LIPID STORAGE IN BROWN ADIPOSE-TISSUE

Brown adipose tissue (BAT) contains glucocorticoid receptors; glucocor ticoids are required for maintaining differentiated BAT in culture. Th ese studies were performed to determine the effects of corticosterone on BAT thermogenic function and lipid storage. Rats were adrenalectomi zed and given subcutaneous corticosterone pellets in concentrations th at maintained plasma corticosterone constant across the range of 0-20 mu g/dl or were sham adrenalectomized. All variables were examined 5 d ays after surgery and corticosterone replacement. Measures of BAT func tion-thermogenic capacity [guanosine 5'-diphosphate (GDP) binding and uncoupling protein (UCP; a BAT-specific thermogenic protein)] and stor age (BAT wet wt, protein, and DNA levels) were made. Plasma hormones ( corticosterone, adrenocorticotropic hormone, insulin, 3,3',5-triiodoth yronine, and thyroxine were measured. Corticosterone significantly aff ected BAT thermogenic measures: UCP content and binding of GDP to BAT mitochondria decreased with increasing corticosterone; GDP binding cha racteristics in BAT from similarly prepared rats examined by Scatchard analysis showed that maximum bind ing (B-max) and dissociation consta nt (K-d) decreased with increasing corticosterone dose. BAT DNA was in creased by adrenalectomy and maintained at intact levels with all dose s of corticosterone; BAT lipid storage increased dramatically at corti costerone values higher than the daily mean level in intact rats. Hist ologically, the number and size of lipid droplets within BAT adipocyte s increased markedly with increased corticosterone. White adipose depo ts were more sensitive to circulating corticosterone concentrations th an were BAT depots and increased in weight at levels of corticosterone that were at or below the daily mean level of intact rats. We conclud e that, within its diurnal range of concentration, corticosterone acts to inhibit nonshivering thermogenesis and increase lipid storage. It is likely that the increase in storage function of BAT with increased corticosterone is a consequence of the steroid-induced hyperinsulinemi a.