Short-term calorie restriction and refeeding differently affect lipogenic enzymes in major white adipose tissue depots of young and old rats.

ABSTRACT

The metabolic effects of short-term calorie restriction (SCR) and subsequent refeeding were compared in different white adipose tissue (WAT) depots of young (5-month old) and old (24-month) male Wistar rats. The animals were subjected to a 40% calorie restricted diet (i.e. 40% lower food supply than of control rats) for 30 days, and then re-fed for 0, 2, or 4 days. WAT samples from perirenal (pWAT), epididymal (eWAT), and subcutaneous (sWAT) depots were analysed for the enzymatic activities of ATP-citrate lyase (ACL), fatty acid synthase (FAS), and glucose-6-phosphate dehydrogenase (G6PD). The total WAT mass almost doubled in old rats, however, aging did not alter the relative proportions of the major regional fat depots. Serum leptin concentration was prominently higher in old rats, in which SCR resulted in less suppression of leptin level than in young animals, whereas refeeding increased leptin concentration in young, but not old, rats. In young rats refeeding elevated leptin gene expression only in pWAT, while in old rats the expression was induced first in eWAT, and later in pWAT. A prominent age-related decrease of ACL and FAS activities, but not of G6PD activity, was found in all the studied WAT depots. In young control rats, ACL activity was highest in pWAT, FAS activity was similar in all WAT depots, and G6PD activity was lowest in eWAT. In old rats, the enzymatic activities were lower in eWAT than in the other depots. The patterns of response to SCR and refeeding varied by age and WAT location. SCR stimulated ACL activity in pWAT but not in other depots of young rats, while FAS activity in pWAT and sWAT did not change in young and decreased in the old animals. Among the studied depots, pWAT was most responsive to refeeding in both age groups. In conclusion, SCR in old rats, as compared to the young, may be accompanied by reduced 'rebound effect' upon returning to unrestricted diet.