This experiment, a 3 x 3 factorial, was designed to determine whether the effects of type of dietary fat could be modified by hormonal status. Ovariectomized and shamoperated retired breeders were fed, for 56 days, diets containing 23% coconut oil, safflower oil or cocoa butter. All diets contained 0.5% cholesterol and 0.5% sodium glycotaurocholate. During the last 28 days of feeding, half the ovariectomized rats received, orally, 30 μg of Premarin per day while other rats received the vehicle only. Premarin, a conjugated equine estrogen, is commonly used to alleviate vasomotor discomforts associated with menopause. Over the period of oral dosing, food consumption and weight gain of ovariectomized rats that received the vehicle only did not differ from that of intact rats. However, both food consumption and body weight gain decreased as a result of Premarin administration. Weight gain and liver weights were greatest for rats fed safflower oil, intermediate for rats fed coconut oil and lowest for those fed cocoa butter. Normalizing for body weight did not alter this ranking of liver weights. Plasma total cholesterol levels of rats fed cocoa butter were higher than those of other rats, and the cocoa butter diet and intact hormonal status were synergistic with respect to plasma cholesterol levels. Plasma triglycerides were not influenced by hormonal status but were elevated by feeding coconut oil. Chemical composition of very low density lipoproteins (VLDL) isolated by gel filtration chromatography revealed high levels of cholesterol and protein when rats were fed cocoa butter, and the elevation of cholesterol and protein was especially prominent in VLDL of intact rats. A concomitant rise in VLDL triglyceride was not found with cocoa butter feeding. This suggests the presence of a modified lipoprotein within the VLDL fractions. It is speculated that intermediate density lipoproteins and p-migrating VLDL, which are cholesterol-rich with respect to VLDL, were induced by feeding cocoa butter. Rats fed coconut oil had the highest ratios of high density lipoproteins (HDL) to VLDL as determined from protein content of isolated lipoproteins. Similarly, as determined by electrophoresis of lipoproteins, ratios of HDL to VLDL plus low density lipoproteins (LDL) were greatest for rats fed coconut oil. In contrast to rats of other hormonal status, intact rats had the lowest ratios of HDL to VLDL plus LDL. This study emphasizes the difference in response of plasma lipoproteins to various dietary fats, including two saturated fats, and demonstrates that response of plasma total cholesterol and VLDL to type of dietary fat can be altered by hormonal status of rats. / Ph. D.