Dietary fat-induced increase in blood pressure and insulin resistance in rats

Objectives To determine whether the dietary-fat-induced increase in blood pressure is caused by excess energy intake or the fat composition of the diet, what type of fat increases the blood pressure, and whether insulin resistance is involved in the dietary-fat-induced increase in blood pressure. Methods In a series of experiments, rats received: chow alone or chow supplemented with lard or sucrose to provide 33% of a total energy content increased by 50%; chow alone or chow in which 50% of the energy content was from substituted lard, safflower oil or medium-chain triglyceride oil; or chow alone or chow in which 50% of the energy content was from substituted lard, with or without troglitazone. Systolic blood pressure (SBP) was measured every week during each 8-week feeding period. A steady-state serum glucose method was used to determine the insulin sensitivity after the lard substitution with or without troglitazone. Results Both the lard and sucrose enrichment increased SEP and body weight compared with controls. Lard substitution significantly increased SEP and immunoreactive insulin, although body weight did not differ from control. Neither a diet substituted with safflower oil nor one substituted with medium-chain triglyceride oil influenced SEP. Troglitazone completely inhibited the increase in SEP and immunoreactive insulin induced by the lard. The steady-state serum glucose concentration was significantly greater after the lard substitution than after isoenergetic chow; this effect also was reversed by troglitazone, Conclusion Chronic feeding with lard increased SEP in rats, independently of excess energy intake. Of the fats tested, lard exerted an intrinsic presser effect, Troglitazone reversed the lard-induced increase in SEP. (C) 2000 Lippincott Williams & Wilkins.