QUALITATIVE REGIONAL DIFFERENCES IN ADIPOSE-TISSUE GROWTH AND CELLULARITY IN MALE WISTAR RATS FED AD-LIBITUM

Adipose tissue grows primarily by a combination of increases in fat ce ll volume (hypertrophy) and in fat cell number (hyperplasia), but the regional growth pattern of white adipose tissue depots in animal speci es and in the human is still unclear. In this study we characterized f ully the age-related changes in adipose tissue growth, composition, an d cellularity of four fat depots of male Wistar rats that varied in ag e from 7 wk to 15 mo and in body weight from 178 to 808 g. Body weight and the weight of each of the four adipose depots studied (epididymal , mesenteric, subcutaneous inguinal, and retroperitoneal) increased pr ogressively with age and ad libitum feeding. Comparison of the cellula rity of the four adipose depots, however, showed remarkable and signif icant differences in the pattern of growth within the same animals. Th e cumulative growth of the two intraabdominal fat depots (mesenteric a nd epididymal) was due mostly to hypertrophy (increases in cell volume of 83 and 64%, respectively), whereas the growth of the other two dep ots (retroperitoneal and inguinal) was due predominantly to hyperplasi a (increases in cell number of 58 and 65%, respectively). These findin gs uncover major and unexpected regional differences in the modulation of adipose tissue growth within aging animals fed ad libitum and sugg est local, region-specific regulatory controls of this growth.