Ultrastructural alterations of rat brown adipocytes after short-term corticosterone treatment

The aim of the present study was to examine ultrastructural alterations of rat brown adipocytes and their mitochondria after shortterm corticosterone treatment. Animals were subcutaneously treated with three daily doses of corticosterone, 5 mg/kg each, dissolved in a small amount of ethanol and diluted with saline. Control animals received vehicle injection only (ethanol-saline). The results showed that short-term corticosterone treatment exerted a strong inhibitory effect on BAT thermogenic function, demonstrated by increased body mass gain. It also conspicuously affected the ultrastructural organization of brown adipocytes. Stereological analysis showed significant cell enlargement owing to lipid accumulation, together with decreased volume density of the nucleus and mitochondria. The mitochondrial machinery was not able to utilize imported free fatty acids complitely, which was demonstrated by sporadic occurrence of small lipid droplets in the mitochondrial matrix. Morphological signs of mitochondrial fusion, considered as indications of reduced function, were also noticed. In our opinion, besides its effect on brown adipocytes via glucocorticoid receptors, corticosterone also acts directly on the genome of their mitochondria.