Photoperiod and gender affect adipose tissue growth and cellularity in juvenile Syrian hamsters

Adult Syrian hamsters are reproductively active and at their annual body an d lipid mass nadirs in long 'summer-like' days (LDs), whereas they an repro ductively quiescent and at their annual body and lipid mass peaks in short 'winter-like' days (SDs). Because hamsters are born in the SDs of fall in t he wild, the development of the reproductive system of juvenile Syrian hams ters exposed to SDs has been studied in the laboratory, but not the develop ment of body and lipid mass. Therefore, we tested the effect of SDs on whit e adipose tissue (WAT) growth and cellularity (fat cell number, FCN; fat ce ll volume, FCV) in 3-15-week-old male and female Syrian hamsters. SDs incre ased body fat in both genders. This effect was partially independent of the decline in gonadal steroids because gonadal regression was only beginning in males (Week Il)and females (Week 15) when carcass lipid content was sign ificantly increased in males, and nearly so in females. This SD-induced inc reased adiposity was reflected in few regional differences in WAT growth, a nd then only in males (increased mesenteric and inguinal WAT masses). SDs i ncreased FCV for all non-gonadal WAT and increased FCN only in retroperiton eal WAT. SDs blunted the LD-induced increased FCV and FCN of parametrial an d epididymal WAT, respectively. For nearly all conditions and pads, FCV pea ked first, followed by increased FCN, the latter accounting for nearly all WAT growth. These data appear to support the view that adipocyte proliferat ion is stimulated once a 'critical' FCV is reached. (C) 2000 Elsevier Scien ce Inc. All rights reserved.