Serum leptin response to endogenous hyperinsulinemia in aging rats

To determine if aging is associated with altered serum leptin response to d iet-induced changes in endogenous hyperinsulinemia, male Fisher 344 (F334) rats at different age groups were studied while on regular rat chow and fol lowing 10 days of experimental diets consisting of 60% of the weight as fru ctose or glucose. The serum leptin concentration (ng/ml) gradually increase d from basal levers of 2.5 +/- 0.1 at age of 4 months to 3.7 +/- 0.1, 6.9 /- 0.9, 9.4 +/- 0.3 and 8.9 +/- 1.1 at 6, 12, 18 and 24 months of age, resp ectively (P < 0.001). Hyperinsulinemia associated with 60% fructose diet wa s associated with increased serum leptin levels in 4, 12, and 24 month old rats to 5.1 +/- 0.8, 6.7 +/- 1.2, and 8.6 +/- 1.1: respectively (P < 0.001) . Feeding 60% glucose diet also was associated with increased serum leptin levels in 4, 12 and 24 month old rats to 7.6 +/- 0.6, 7.2 +/- 0.7, and 9.1 +/- 1.1, respectively (P < 0.001). Restricting dietary intake to 60% of the calories consumed by control rats for 10 days resulted in a decrease in se rum leptin to 1.0 +/- 0.02 in 4 month old rats and 2.5 +/- 0.4 in 24 month old rats (P < 0.01). It is concluded that aging in F344 rats is associated with increased serum leptin concentrations. However. diet-related hyperinsu linemic effect on leptin is blunted in aging rats although leptin response to caloric restriction is maintained. The inability of aging rats to mount hyperleptinemic response to dietary changes may contribute to the age-relat ed increase in adiposity. (C) 2000 published by Elsevier Science Ireland Lt d. All rights reserved.