Temporal changes in fat pad mass and cellularity after lipectomy in Siberian hamsters.

Long-day-housed Siberian hamsters show increases in the mass of nonexcised white adipose tissue (WAT) 12 weeks after bilateral removal (x) of epididymal WAT (EWAT). Although EWAT shows no significant regeneration, surviving EWAT appears to increase in mass to a small degree. The purpose of the present study was to determine the time course for fat pad mass and cellularity changes after EWATx and to test whether surviving EWAT adipocytes undergo hypertrophy or hyperplasia. Male Siberian hamsters underwent EWATx or sham EWATx (SHAM). At Week 0 and at 2-week intervals up to 12 weeks postsurgery, a representative sample of animals from each group were killed. EWAT, retroperitoneal WAT (RWAT), and inguinal WAT (IWAT) were removed, weighed, and processed for cellularity measurement. IWAT and, to a nonsignificant degree, RWAT, increased in mass after EWATx due to fat cell hypertrophy. These changes began as early as Week 4 postlipectomy, but no mass or cellularity change was significant until Week 12. The surviving EWAT adipocytes of EWATx hamsters also were larger than those of SHAM hamsters and, unlike EWAT adipocyte number, increased with time within the EWATx group. SHAM hamsters showed slight increases in the mass of EWAT, but not IWAT or RWAT, due to a nonsignificant doubling of EWAT adipocyte number during the 3 months of the experiment.