Effects of long-term sucrose overfeeding on rat brown adipose tissue: a structural and immunohistochemical study

The aim of this study was to determine the effects of long-term sucrose overfeeding on functional capacity and ultrastructural characteristics of the rat brown adipose tissue (BAT). For the study, sixteen male Wistar rats, chow-fed and kept under standard laboratory conditions were divided into 2 equal groups. The rats from a control group drank tap water, while those from a sucrose overfed group were allowed to drink 10% sucrose solution for 21 days. Structural changes of BAT were analysed at the level of light and electron microscopy on routinely prepared tissue sections or using immunohistochemical staining, in combination with stereological methods. Obtained results have shown that significantly increased energy intake in sucrose overfed rats did not result in elevated body mass gain. The light microscopy analysis revealed that the BAT acquired the appearance of a thermogenically active tissue, with intensified vascularisation, reduced size of brown adipocytes and increased multilocularity. At the ultrastructural level, mitochondria of brown adipocytes became more abundant, enlarged, and contained more cristae in comparison to control animals. The immunoexpression of uncoupling protein 1 (UCP1) and noradrenaline, as markers of BAT thermogenic status was increased, while the pattern of PGC1α was slightly modified. Taken together, the results of this investigation indicated that BAT possesses the ability to increase thermogenic capacity/activity in response to high energy intake and to prevent body mass gain. These findings are particularly relevant in the view of recent reports on the existence of functional BAT in adult humans and its potential use to combat obesity.