Abstract
Comparative morphological studies on epididymal fat cells from young, old and obese rats were made by scanning and freeze-fracture electron microscopies. Scanning microscopy showed that adipocytes of young rats were spherical with a smooth surface, but with a few crater-like pits. As the rats became older, their fat cells increased in size and the surface of the cells became rough with an increase in the number of craters. In obese rats, there were more numerous craters in various sizes than in old rats. In ultra-thin sections, the accumulated lipid of adipocytes appeared uniform and amorphous. But in freeze-fractured adipocytes of young and old rats the central lipid was seen to have a multi-lamellar structure, like an onion. The fracture-face of lipid droplets in adipocytes from the obese rat was disfigured and complicated by the crossing of membranous lamellae. These findings suggest that the modes of lipid accumulation in the fat cells of old rats and obese rats differ. This difference may be related to the difference in the distributions and numbers of craters on the surface of adipocytes in these animals.
