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The effect of exercise and dietary cholesterol on cholesterol synthesis in the hamster Ridgen, Julie Elizabeth


Physical inactivity and elevated plasma cholesterol are well characterized risk factors for the development of coronary heart disease (CHD). Consequently, manipulation of exercise intensity and dietary cholesterol may favourably alter lipid metabolism to reduce this risk. The present study examined both independent and interactive effects of exercise and dietary cholesterol on in vivo hepatic and intestinal cholesterol synthesis as well as plasma total and high density lipoprotein (HDL) cholesterol levels in hamsters. Male Syrian hamsters were randomized into one of i) low dietary cholesterol (0.03% w/w) sedentary (LC-S), ii) low cholesterol exercise (LC-E), iii) high cholesterol (0.12% w/w) sedentary (HC-S) or iv) high cholesterol exercise (HC-E) groups. Exercised hamsters were trained to run at increasing speeds on a motorized treadmill for 90 minutes daily over a two week period. Animals were subsequently run for 1 week at 70% of VO₂ max for 90 minutes each day. Cholesterol synthesis was determined by measuring the rate of incorporation of into digitonin precipitable sterols in liver and small intestine over 2 hours following IP injection of ³H₂O. Plasma total cholesterol was significantly increased by dietary cholesterol in HC versus LC groups independent of an exercise lowering effect in HC-E animals. HDL cholesterol was also elevated in response to dietary cholesterol in HC groups, however LC-E hamsters had lower plasma HDL cholesterol than any other group through an interaction between exercise and diet. Incorporation of ³H into liver cholesterol was increased in HC-S versus LC animals, whereas exercise lowered hepatic sterol synthesis in HC-E by an exercise and diet interaction. Although exercise did not affect intestinal cholesterol synthesis, dietary cholesterol significantly decreased intestinal cholesterol synthesis in HC when compared with LC groups. Thus both plasma total cholesterol and small intestine responded characteristically to changes in dietary cholesterol levels, in opposition to liver cholesterol synthesis, which showed a compensatory increase to the attenuation of intestinal sterol synthesis. The exercise induced decrease evident in plasma cholesterol levels and hepatic cholesterol synthesis was not, however, observed in the small intestine. Therefore the independent response of liver and small intestine to exercise and dietary cholesterol level in this study indicate important differences in the manner through which these organs regulate whole body cholesterol balance.

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