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Effects of Various Dietary Arginine and Lysine Concentrations on Plasma and Liver Cholesterol Concentrations in Rats

Background: It has been hypothesized that the arginine:lysine ratio of dietary proteins influences cholesterol concentrations in plasma and liver of men and animals. This study was performed to test this hypothesis in rats by using diets with various concentrations of arginine and lysine, differing in their arginine:lysine ratios. Methods: Two experiments with growing rats were performed, some of which received diets containing 4.5, 9 or 18 g arginine/kg and 9 or 18 g lysine/kg, respectively, for a period of 21 days. In the first experiment, a cholesterol-free diet was used; in the second experiment, a diet supplemented with cholesterol and sodium cholate as hypercholesterolaemic compounds was used. Results: In experiment 1, increasing the arginine concentration lowered HDL and plasma cholesterol concentration; however, cholesterol concentrations in liver, LDL and VLDL remained unchanged. In experiment 2, increasing the arginine concentration lowered HDL cholesterol and increased liver cholesterol (p < 0.05); cholesterol concentrations in plasma, LDL and VLDL remained unchanged. The only effect of the dietary lysine concentration concerned the effect on VLDL and liver cholesterol concentration, which were both lower in rats fed the diets with 18 g lysine/kg than in those fed the diets with 9 g lysine/kg (p < 0.05). Varying the dietary arginine:lysine ratio between 0.25 and 2.0 had no influence on cholesterol concentration in LDL and VLDL in both experiments; HDL cholesterol concentration was lowered by increasing this ratio (p < 0.05). Conclusion: The present study does not support the hypothesis that an increase in the dietary arginine:lysine ratio causes hypocholesterolaemic effects in rats.