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 (r(2) = 0.91, P = 0.0033) and
cholesterol concentration (r(2) = 0.94, P = 0.0016), and inversely correlated with RBC
phytosterol concentration (r(2) = 0.58, P = 0.0798) and
phytosterols/
cholesterol (r(2) = 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.