Cross-sectional and longitudinal analysis of age-associated changes in body composition of male brown Norway rats: Association of serum leptin levelswith peripheral adiposity

Aging-associated alterations in body composition are accompanied by changes in the endocrine system. We evaluated, in male Brown Norway rats, the effe cts of aging on body composition and the association with serum levels of l eptin, insulin, and testosterone. Body composition was assessed cross-secti onally in male rats (3, 8, 17, and 29 months) by a combination of dual ener gy x-ray absorptiometry (DEXA) and dissection of specific muscles and adipo se depots. Longitudinal changes in body composition were quantified by DEXA before and after 3 months of ad-libitum feeding. Body weight, lean mass, a bsolute and percentage fat increased with age, whereas percentage of lean m ass decreased. Leptin and insulin levels increased with age in proportion t o adiposity; the increase in leptin with age was related to increased total and peripheral, but not visceral,fat. Testosterone decreased with age, and was associated with decreased lean and skeletal muscle mass. These finding s suggest that alterations in body composition with age may be due to decre ased trophic and increased lipogenic hormones. Relative to other rodent mod els, Brown Norway rats undergo shifts in body composition and in the hormon al milieu that are consistent with changes seen in aging humans.