The occurrence of brown adipose in man inhabiting the tropics.

Samples of cervical, mediastinal and perirenal fat tissue were obtained from eight subjects (ages: 17 days to 56 years) at necropsy. After formol fixation, the specimens were processed for sectioning and stained with hematoxylin and eosin, periodic acid--Schiff, or Holmes' silver techniques for light microscopy. All the tissue samples showed lobular organisation and a rich vascularity, with argentaffin (putative nerve) fibres at paravascular and parenchymal sites. Three histological forms of brown adipose tissue (BAT) were recognised: homogeneous lobules of multilocular adipocytes (Type I); mixed lobules consisting of islets of multilocular adipocytes surrounded by large unilocular cells (Type II); and lobules consisting mainly of small (less than 40 microns diameter) unilocular adipocytes (Type III). In two subjects (ages 17 days and 52 years), BAT (Types I and II respectively) was observed in tissue samples from all three sites. Perirenal samples from three other donors (ages 26-35 years) showed the presence of Type II or III BAT. Mediastinal BAT (Type II) was found in two subjects (26- and 35-years old). The significance of BAT in man inhabiting a warm environment is discussed.