SHORT-DAY-LIKE BODY-WEIGHT CHANGES DO NOT PREVENT FAT PAD COMPENSATION AFTER LIPECTOMY IN SIBERIAN HAMSTERS

Long-day (LD)-housed Siberian hamsters show compensatory increases in white adipose tissue (WAT) weight after lipectomy, whereas hamsters ex posed to short days (SDs) for a long duration (22 wk) do not. We teste d whether SD-induced body weight changes prevent fat pad compensation after lipectomy. In experiment 1, hamsters with lesions of the paraven tricular nucleus of the hypothalamus (PVNx) rapidly increased body wei ght similarly to 22-wk SD-exposed hamsters. In experiment 2, LD-housed hamsters were food restricted for 22 wk. and then pair fed with SD-ho used hamsters for 12 wk to produce body weight changes mimicking those of ad libitum-fed SD-exposed animals. Epididymal WAT (EWAT) lipectomy (EWATx) of PVNx or food-restricted hamsters elicited compensatory inc reases in retroperitoneal and inguinal WAT (RWAT and IWAT) weights. Un like other fat pads, EWAT was less affected by food restriction or PVN x than by SD exposure. In general, food restriction decreased adipocyt e number, whereas SD exposure decreased adipocyte size. PVNx increased RWAT adipocyte size and IWAT adipocyte number. These results suggest that the lack of body fat compensation by EWATx hamsters exposed to SD s for a long duration is due to SD-associated responses other than bod y weight changes per se.