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Interactive effects of dietary fat source and sterol intake on lipid metabolism in spontaneously hypertensive and normotensive rats

University of British Columbia

The effect of dietary fat source and cholesterol intake level on plasma, lipoprotein and tissue lipid composition, lipid balance, and red blood cell (RBC) antioxidant status in rats was studied. Spontaneously hypertensive rat (SHR) and Wistar Kyoto normotensive rat (WKY) were randomly assigned to one of the six semi-purified diets containing 16% lipid. The fat blends consisted of 13% from either butter, soybean oil or menhaden oil, plus 3% from canola oil. Cholesterol was added to dietary fat sources at final concentrations of either 0.05% or 0.5% (wt/wt). During the 6th week of the experiment, animals were placed in individual metabolic cages for a 5 day balance study, where feed intake was measured and excreta collected and measured daily. Animals were returned to individual aluminum cages and at the end of 10 weeks the experiment was concluded. Rats were anaesthetized and blood was drawn from the heart. Liver tissue was also removed. RBC, plasma, lipoprotein fractions and liver tissue were assayed for lipid composition. Malondialdehyde (MDA) production and glutathione depletion assays were +2 used to evaluate the oxidative status of RBC, while copper (Cu )-induced oxidation was performed on low density (LDL) lipoprotein fractions to evaluate LDL-oxidation potential. In SHR, blood pressure measurements at 12 weeks of age confirmed elevated pressures in all dietary groups. High cholesterol menhaden-fed animals of both strains produced lower plasma cholesterol concentrations compared to animals fed high cholesterol butter or soybean based diets (p <0.001). Dietary cholesterol feeding increased other physiologic parameters, including liver cholesterol (p <0.001), total crude lipid concentrations (p <0.001), RBC cholesterol concentration (p = 0.031), and RBC triacylglycerol (p <0.001), while it lowered MDA production at 5 mM H2O2 (p = 0.004). RBC-cholesterol was raised in high cholesterol fed SHR (p <0.05), while MDA production in the same treatment group was reduced (p <0.001). Cu+2 -induced LDL oxidation increased with time, but there were no significant differences between the individual dietary treatment groups. Reduced MDA production in high cholesterol fed SHR points to a protective effect of dietary cholesterol against oxidative stress induced in the RBC membranes collected from these particular animals. Of all high cholesterol fed groups, liver cholesterol was lowest (p < 0.05) in menhaden-fed SHR. Equivalent differences were not noticed in WKY. No differences were observed between liver cholesterol values from high cholesterol butter-fed and high cholesterol soybean-fed animals of either strain. Lower liver cholesterol concentrations combined with elevated VLDL-cholesterol levels produced in high cholesterol menhaden-fed SHR, indicated a differential effect of very long chain n-3 PUFAs on hepatic cholesterol metabolism in those animals. WKY rats, on the other hand, exhibited no differences in liver cholesterol among high cholesterol fed animals, but produced lower VLDL-cholesterol concentrations in menhaden-fed rats. All animals increased fecal cholesterol and fecal total crude lipid excretion when fed the high cholesterol diets, however SHR exhibited a relatively greater ability to excrete cholesterol than WKY. SHR appeared to adapt differently to high cholesterol intake than the WKY rats.

Thesis/Dissertation

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2009-03-12

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http://hdl.handle.net/2429/5947

Food Science

University of British Columbia

UBCV

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