Previous investigations in our laboratory have shown a significant decrease in interscapular brown adipose tissue (IBAT) mass and thermogenic capacity, as measured by the amount of uncoupling protein (UCP), in older versus younger male F344 rats. These changes have been directly correlated to the decreased ability of older rats to thermoregulate during acute cold exposure. It is unclear, however, as to the mechanisms accounting for the age-related "atrophy" of brown adipose tissue. As a first step in defining a possible mechanism, we exposed 6-, 12-, and 26-month-old F344 male rats to mild chronic cold exposure, a method known to stimulate brown fat growth, as well as UCP production, in young rats. IBAT mass, protein, UCP, cell size, and cellular proliferation (as indicated by in-vivo 5-bromo2'-deoxy-uridine uptake) were measured in response to the cold challenge. Serum growth hormone, insulin-like growth factor I, and norepinephrine were also measured. In the young rats, cold exposure significantly increased IBAT mass (92%), and UCP levels (296%) relative to non-cold values. However, in the 26month-old rats, although IBAT mass increased significantly (33%) after cold exposure, UCP levels did not. Cold exposure produced dramatic elevations in IBAT cellular proliferation in the 6-month-old rats (26-fold increase); but did not affect cellular proliferation in the 26-month-old rats. There was no correlation between the concentrations of serum growth factors and the attenuated cellular proliferation or UCP levels in IBAT of the 26-month-old rats. These data suggest that the attenuated IBAT thermogenic capacity of older rats reflects, at lease in part, decreased cell proliferative capacity as well as decreased net UCP generation.
|Original language||English (US)|
|State||Published - 1996|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology