[The influence of the sympathetic nervous system on brown adipose tissue: an experimental and histopathologic study...

Brown adipose tissue (BAT) is known to be a principal energy source of non-shivering thermogenesis and related diet-induced thermogenesis. These regulate body temperature and body weight and are controlled by the dissipation of excessive dietary caloric intake. We carried out histopathologic, immunohistochemical and biochemical studies of BAT in rats in relation to aging changes. Four groups of Donryu strain male rats (5 each of 1 month, 2 months, 4 months and 20 months of age) were used. They had been given commercial chow and tap water ad libitum and were kept in an air-conditioned room. Body weight (BW), interscapular BAT weight (IBATW) and g IBATW/g BW of rats were measured. Nor-adrenalin (NA), and dopamine-beta-hydroxylase (DBH) of IBAT were determined. To evaluate the catecholaminergic effects of BAT, morphometric quantitation of BAT was carried out based on the cytoplasmic locularity of fat globules in the BAT cells. Distribution of DBH in BAT was assessed immunohistochemically by the avidin biotin peroxidase complex method. With the use of statistical analysis of variance procedure, there were highly significant decreases in the ratio of g IBATW/g BW (p less than 0.0001) and in the concentrations of NA (p less than 0.0001) and DBH (p less than 0.01) between young (weaning at 1 month old) rats and adult (aged from 4 to 20 months) rats. In the morphometric measurement, by the statistical analysis system (SAS) Spearman correlation coefficient method, there was a significant increase of Type 5 cell (monocular brown adipose tissue cell) in 4 month and 20 month rats, compared to 1 month and 2 month rats (p less than 0.05). Immunohistochemical study of BAT showed localization of DBH in perivascular mesenchymal cells which corresponded with the morphologic distribution of catecholamine as reported by Lever. The results suggest that in the processes of aging in the rat there are reductions in the ratio of g IBATW/g BW, NA and the activity in DBH.