Although the effect of aging on adipose tissue metabolism have been thoroughly studied for years, changes in the antilipolytic action of insulin in visceral white adipose tissue from aged rats are still not completely understood. By fact, some contradictory data on the inhibition of isoproterenol-induced lipolysis by insulin with aging have been reported. As aging is a significant risk factor for increasing adiposity and the development of obesity, we hypothesized that the inhibition of isoproterenol-induced lipolysis by insulin in rat visceral adipose tissue explants (vWAT) may be increased in aged rats.
Experiments were performed in ad libitum (AL) or caloric restricted for 3-months (CR) male Wistar rats of 3, 8 and 24 months. All rats were fasted for 36 h before euthanized under CO2 and sacrificed by decapitation. Adiposity index, adipose cell size, FA composition by GC from vWAT TAG and serum concentrations of glycerol, TAG, NEFA, lactate and KB were measured. Glycerol and NEFA release were measured in the medium of vWAT explants (100 mg) incubated for 3 h in the absence or presence of 1 μM isoproterenol without or with 1 μM insulin. The mRNA and total protein levels of ATGL, AQ7, HSL, as well as the phospohrylation of HSL, were studied by real-time PCR and immunoblotting.
Results: As expected, basal and isoproterenol-induced lipolysis were markedly decreased in the older and fatter rats. Surprisingly, the inhibition of isoproterenol-induced lipolysis by insulin in vWAT explants was higher in 24-month AL or CR compared to younger rats. Although vWAT TAG 18:1/18:0 ratio, which correlated negatively with insulin sensitivity, was significantly increased in old rats, our results were associated to lower ATGL, HSL protein and activation levels.
Conclusion: Higher antilipolytic action of insulin in rat vWAT with aging is associated to increased adiposity in older rats.