Effects of dietary supplemented amino acids on endogenous hypercholesterolemia in rats.

Effects of additions of amino acids to a 20% casein diet on serum cholesterol (Ch) were studied in hypothyroid and hepatoma-bearing rats with endogenous hypercholesterolemia as well as in normal rats. In normal Wistar rats, methionine (Met) was hypercholesterolemic at the "nutritional" level (0.2-0.4%), but hypocholesterolemic at the "excess" level (1.2-2.4%). In Wistar rats with hypothyroidism induced by thiouracil, the addition of excess (1.2%) Met to the 20% casein diet reduced an endogenous hypercholesterolemia due to hypothyroidism by suppressing an elevation in (VLDL + LDL)-Ch with no significant influence on HDL-Ch. In Donryu rats received a subcutaneous implantation of AH109A cells (an ascites hepatoma line), either 1.2% Met, 1.2% cystine (Cys), or 1.2% Met and 2.5% glycine (Gly) in combination improved a hepatoma-induced hypercholesterolemia and abnormal serum lipoprotein profiles by suppressing a hepatoma-induced increase in (VLDL + LDL)-Ch. From Ch turnover studies in hepatoma-bearing rats, an impaired catabolism of Ch in the liver was suggested to be one cause for the hepatoma-induced elevation in (VLDL + LDL)-Ch. One of the dietary manipulations. met and Gly in combination (Met + Gly), was found to improve the impaired Ch catabolism, this leading to a reduction of the (VLDL + LDL)-Ch level by Met + Gly in hepatoma-bearing rats.