O₂ consumption, lipolysis, & cAMP in brown fat cells from aged F344 rats spontaneously losing body weight

Rapid deterioration of cold-induced thermoregulatory ability in aged male F344 rats is correlated with the spontaneous loss of body weight occurring near the end of the life span. This is accompanied by reduced brown fat thermogenic capacity [uncoupling protein (UCP) levels] and reduced NE (norepinephrine)-induced oxygen uptake (thermogenesis) of isolated brown fat cells (Fig. A). We tested if the latter reflects blunted cAMP production and/or fat mobilization. cAMP levels (Fig. B) and lipolysis (glycerol release; Fig. C) increased dose-dependently in response to NE, with no significant differences in weight stable (+) vs weight loss (O) 23-26 mo rats. Forskolin (50 μM)-stimulated cAMP and lipolysis were also comparable between groups. Thus, the reduced thermogenesis of brown fat cells from old F344 rats losing body weight likely reflects lower UCP levels per cell, rather than blunted ability to generate cAMP or mobilize fat (AG06665, AG05577).