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Article

Vegetable Oils High in Phytosterols Make Erythrocytes Less Deformable and Shorten the Life Span of Stroke-Prone Spontaneously Hypertensive Rats^{1 ,2}

Walisundera M. N. Ratnayake^*3, Mary R. L’Abbé^*, Rudi Mueller, Stephen Hayward^**, Louise Plouffe^*, Rudy Hollywood^* and Keith Trick^*

^* Nutrition Research Division, Toxicology Research Division, ^** Bureau of Biostatistics and Computer Applications, Food Directorate, Health Protection Branch, Health Canada, Banting Research Centre, Ottawa, ON, Canada K1A 0L2

³To whom correspondence should be addressed,

Previous studies have shown that canola oil (CA), compared with soybean oil (SO), shortens the life span of stroke-prone spontaneously hypertensive (SHRSP) rats, a widely used model for hemorrhagic stroke. SHRSP rats are highly sensitive to dietary cholesterol manipulations because a deficiency of membrane cholesterol makes their cell membranes weak and fragile. Phytosterols, abundant in CA but not in SO, can inhibit the absorption of cholesterol and also replace a part of cholesterol in cell membranes. This study was performed to determine whether the high concentration of phytosterols in CA might account for its life-shortening effect on SHRSP rats. Male, 35-d-old SHRSP rats (n = 28/group) were fed semipurified diets containing CA, SO, CA fortified with phytosterols (canola oil + phytosterols, CA + P), SO fortified with phytosterols (soybean oil + phytosterols, SO + P), corn oil (CO), olive oil (OO) or a fat blend that mimicked the fat composition of a representative Canadian diet (Canadian fat mimic, CFM; 10 g/100 g diet). These fats provided 97, 36, 207, 201, 114, 27 and 27 mg phytosterols/100 g diet, respectively. Ten rats from each group were killed after 30–32 d for blood and tissue analyses. The remaining rats (18/group) were used for determination of life span. The life span of SHRSP rats fed the high phytosterol oils (CA, CA + P, SO + P and CO) was significantly (P < 0.05) shorter than that of CFM- and SO-fed rats. At 30–32 d, the groups fed the high phytosterol oils had greater levels of phytosterols and significantly (P < 0.05) higher ratios of phytosterols/cholesterol in plasma, RBC, liver and kidney, and a significantly (P < 0.05) lower RBC membrane deformabilty index than the groups fed oils low in phytosterols (SO, OO and CFM). The mean survival times were correlated with RBC deformability index (r² = 0.91, P = 0.0033) and cholesterol concentration (r² = 0.94, P = 0.0016), and inversely correlated with RBC phytosterol concentration (r² = 0.58, P = 0.0798) and phytosterols/cholesterol (r² = 0.65, P = 0.0579), except in the OO group. This study suggests that the high concentration of phytosterols in CA and the addition of phytosterols to other fats make the cell membrane more rigid, which might be a factor contributing to the shortened life span of SHRSP rats.

KEY WORDS: • canola oil • cell membrane deformability • life span • phytosterols • stroke-prone spontaneously hypertensive rats

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