Aging accelerates dietary lard-induced increase in blood pressure in rats.

We investigated whether the dietary lard-induced increase in blood pressure (BP) is accelerated in aged rats compared to young ones. Three-month-old (young group), 10-month-old (middle-age group), and 18-month-old (older group) F344/N male rats were used. The rats were fed either chow alone or chow in which 50% of the energy content was from substituted lard. Systolic BP (SBP) and body weights (BW) were determined weekly during each 7-week feeding period. A Steady-state plasma glucose (SSPG) method was used to determine the insulin sensitivity. Bilateral testicular fat mass (epididymal fat; Epi-F) was removed in order to evaluate weight (Epi-FW). SBP began to increase at 2 weeks in the older lard-fed group, at 4 weeks in the middle-age lard-fed group, and at 5 weeks in the young lard-fed group after feeding was begun. There was no significant difference in the basal values of SBP among any ages-groups of the rats. After 4 weeks of lard feeding, increases in SBP, plasma insulin, leptin level, SSPG and Epi-FW/BW were observed in the older lard-fed group. In the younger rats, however, only hyperinsulinemia developed. At 7 weeks, increased BP in the younger rats was accompanied by increased plasma leptin level, SSPG and Epi-FW/BW. In summary, aging accelerates development of a dietary lard-induced increase in BP, which may be caused by the hyperleptinemia that may be the result of increased susceptibility to insulin resistance and/or visceral adiposity in older rats.