Effects of phytosterol content in vegetable oil on life span of salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP)

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Recent studies using salt-loaded SHRSP reported that salt-loaded SHRSP exhibited different lifespan depending on the type of vegetable oil in their diet. In the present study, to evaluate whether the difference of phytosterol content in vegetable oil influences stroke onset and lifespan of salt-loaded SHRSP. Male SHRSP/Kpo were used at the age of 6 weeks. Test diets were prepared by using four kinds of vegetable oils which contain different amount of phytosterol. Three percent NaCl by weight was added to the test diets for acceleration of hypertension. Rats had free access to the diet and drinking water. Blood pressure was measured by the tail-pulse pickup method. The onset of stroke was judged by sudden losses of both bodyweight and food intake and characteristic symptoms.There were no significant differences in growth rate, food intake among the four experimental groups before the onset of stroke. Systolic blood pressure of the ricebran oil group tended to be higher compared with the … More other three groups. Phytosterol content in the vegetable oil shortens survival time of salt-loaded SHRSP in a dose-dependent manner, regardless of fatty acids composition of the vegetable oil.Next, to elucidate the mechanism of survival time-shortening effect of ricebran oil, we focused on the effect of ricebran oil on stroke onset and lipid metabolism in salt-loaded SHRSP. Rats were fed the test diets containing ricebran oil or soybean oil (control) as fat source and 3% NaCl for 38 days.In the serum, cholesterol and phospholipids levels were significantly higher compared with the control, which was due to the increase in the HDL fraction. It will be very important to elucidate why the HDL fraction increases and what relationship exists between stroke onset and the elevation of the HDL fraction.In the liver, cholesterol and triglyceride contents were significantly lower compared with the control. A comparative study on mRNA expression indicated that ricebran oil may inhibit HMG-CoA reductase, resulting in the reduction of hepatic cholesterol content. In addition, activation of PPAR (peroxisome proliferators-activeted receptor)α target genes may induce the reduction of hepatic triglyceride content. Conversely, reduction of LXR (liver X-receptor)α mRNA expression may induce the reduction of ABC (ATP-binding cassette transporter) G5 and ABCG8 mRNA expressions, which indicates accumulation of phytosterol in the liver. This hepatic accumulation of phytosterol might be closely related to the survival time-shortening effect of ricebran oil. Less