Regular articleHigh polyunsaturated and monounsaturated fatty acid to saturated fatty acid ratio increases plasma very low density lipoprotein lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol in rats
Introduction
Beginning in the 1950s, systematic investigations have been conducted to determine how dietary fat affected plasma cholesterol concentrations. In human studies, monounsaturated fatty acid (MUFA, M)-rich diets led to a decrease [1], [2], [3] in the plasma LDL-C concentrations when compared with polyunsaturated fatty acid (PUFA, P)- or carbohydrate-rich diets. But there have been no studies substituting monounsaturated fatty acid (MUFA, M) for either saturated fatty acid (SFA, S) or PUFA on liver lipid metabolism in human subjects with high cholesterol supplement. However, most rodent animal models did not exhibit a hypocholesterolemic response of MUFA. In contrast, compared to dietary PUFA, intake of MUFA-rich diets by rats [4], [5], [6], [7], hamsters [8], guinea pigs [9], [10], and rabbits [11] elicited a hypercholesterolemic respnse.
It has been suggested that dietary cholesterol is an increase in LDL-C, but this effect may be modified by the type and amount of fatty acids in the diets, with saturated fatty acids increasing this effect and polyunsaturated fatty acids decreasing it [12], [13]. In rats fed with high-cholesterol diets, olive oil intake resulted in the highest concentration of cholesterol in serum and liver compared with coconut or corn oil [4]. Studies in the hamsters [14] indicated that when cholesterol was added to an olive oil-containing test diet, hepatic cholesteryl ester content was increased six to nine times as compared with a safflower oil- or coconut oil-containing diet. Moreover, cholesterol feeding resulted in increased hepatic secretion of VLDL particles and increased the rate of TAG biosynthesis in rats [15], [16], [17].
In our recent studies have focused on plasma and liver cholesterol lowering by dietary high P/M ratio, low M/S ratio, and (P+M)/S ratio below 3 [5], [6]. However, whether the effect of low dietary (P+M)/S ratio on plasma lipoprotein and liver lipids metabolism in rats will be remodified by dietary cholesterol remains unclear. Therefore, in this study, we asked whether high (P+M)/S ratio increases plasma lipoprotein lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol in rats. To answer this question, we assessed the effects of diets with the same P/S ratio of 1.0, but different (P+M)/S ratio of 1.5, 2, 4, or 5.7, and with or without 1% cholesterol supplement on plasma and liver lipids metabolism.
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Animals
In experiment 1, 32 male Wistar rats (Laboratory Animal Center, College of Medicine, National Taiwan University, Taipei, Taiwan), each weighing about 135g, were used for the study. All animal experimental procedures followed the Guide for the Care and Use of Laboratory Animal, National Science Council, Taiwan. Rats were divided into four groups of 8 rats in each on the basis of their weight. Rats were housed individually in a stainless steel, wire-bottomed cages and consumed a diet and water ad
Body weight gain and feed efficiency
In experiment 1 the food consumptions of rats from diet 1 to diet 4 group were Diet 1 19.4±2.6 g/day, Diet 2 18.6±3.3 g/day, Diet 3 18.5±3.2 g/day, and Diet 4 19.9±3.0 g/day. In experiment 2 the food consumptions of rats from diet 1 to diet 4 group were Diet 1 16.4±2.3 g/day, Diet 2 17.0±2.3 g/day, Diet 3 16.3±2.5 g/day, and Diet 4 17.0±2.1 g/day. However, there were no significant differences in body weight gain or feed efficiency (g weight gain/100g diet) among groups of rats in experiments 1
Discussion
The present study shows that high polyunsaturated- and monounsaturated fatty acid to saturated fatty acid [(P+M)/S] ratio increases plasma VLDL lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol. The evidence is that we found when the P/S ratio was held constant at 1.0 and rats fed with the ratio of (P+M)/S increased from 1.5, 2, 4, to 5.7, 1% C supplement resulted in a progressive increase in plasma total C, total TAG, total PL, VLDL-C, VLDL-TAG, VLDL-PL, LDL-C,
Acknowledgements
This work was supported by a grant (CMC90-M-17 and CMC91-M-15) from the China Medical College, Taiwan, Republic of China.
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