Glucocorticoids in the CNS regulate BAT metabolism and plasma insulin in ob/ob mice

Adrenalectomy stimulates depressed brown adipose tissue (BAT) metabolism and decreases hyperinsulinemia in ob/ob mice, with minimal effects in lean mice. A single intracerebroventricular injection of dexamethasone (250 ng) into adrenalectomized ob/ob mice completely reversed the effects of adrenalectomy on BAT thermogenesis as assessed by mitochondrial GDP binding, approximately doubled plasma insulin, lowered whole body metabolic rates by 17%, and increased food intake by 19%. These responses were rapid in onset, with changes in BAT metabolism and plasma insulin occurring within 30 min of dexamethasone injection. Adrenalectomized lean mice were much less responsive to dexamethasone than their ob/ob counterparts. The dexamethasone-induced decrease in BAT thermogenesis in adrenalectomized ob/ob mice was associated with an organ-specific decrease in BAT sympathetic nerve activity as assessed by norepinephrine turnover, whereas the dexamethasone-induced increase in plasma insulin was blocked by atropine, suggesting involvement of the parasympathetic nervous system. Intracerebroventricular injection of corticotropin-releasing hormone did not affect BAT thermogenesis in dexamethasone-injected adrenalectomized ob/ob mice but markedly lowered plasma insulin concentrations, possibly by suppression of the parasympathetic nervous system. In conclusion, dexamethasone alters regulation of the autonomic nervous system in ob/ob mice.