OPPOSITE EFFECTS ON CHOLESTEROL-METABOLISM AND THEIR MECHANISMS INDUCED BY DIETARY OLEIC-ACID AND PALMITIC ACID IN HAMSTERS

The effects of dietary oleic acid on cholesterol metabolism were inves tigated and compared with those of palmitic acid in hamsters. Addition of 5% oleic acid to a 0.1% cholesterol-supplemented diet decreased pl asma total cholesterol, very low density lipoprotein (VLDL) cholestero l, and low density lipoprotein (LDL) cholesterol, increased hepatic LD L receptor activity, acid decreased plasma cholesteryl ester transfer protein (CETP) activity in comparison with 0.1% cholesterol alone. In contrast, addition of 5% palmitic acid to a 0.1% cholesterol-supplemen ted diet increased total cholesterol and LDL-cholesterol, increased pl asma CETP activity, and suppressed hepatic LDL receptor activity to a greater extent than 0.1% cholesterol alone. Neither oleic acid nor pal mitic acid altered hepatic microsomal 3-hydroxy-3-methylglutaryl-coenz yme A (HMG-CoA) reductase activity, but oleic acid increased hepatic m icrosomal cholesterol 7 alpha-hydroxylase activity. These results sugg est that dietary oleic acid inhibits the increases in total, VLDL-, an d LDL-cholesterol induced by dietary cholesterol by preventing both LD L receptor suppression and increased CETP activity, whereas dietary pa lmitic acid augments the cholesterol-induced increases in total and LD L-cholesterol by both further suppression of LDL receptor activity and further stimulation of CETP activity.