REDUCTION OF HYPERLIPIDEMIA AND PROTEINURIA WITHOUT GROWTH-RETARDATION IN NEPHRITIC RATS BY AMINO ACIDS-FORTIFIED LOW CASEIN DIETS

Effects of low casein diets supplemented with either cystine alone, cy stine plus glycine, or cystine plus threonine on hyperlipidemia and pr oteinuria were studied in rats with nephrotoxic serum nephritis. Rats were maintained on experimental diets for 14 days after an injection o f nephrotoxic serum. An 8.5% casein diet, as compared with a basal 20% casein diet, improved both the hyperlipidemia and proteinuria inciden t to nephrotoxic serum nephritis but retarded the growth of rats. The supplement of 0.3% cystine to the 8.5% casein diet alleviated the grow th retardation without loss of the reductive effect on hyperlipidemia and proteinuria but caused fatty liver. Glycine (2%) failed, but threo nine (0.36%) succeeded in diminishing the cystine-induced fatty liver when concomitantly added with cystine (0.3%) to the 8.5% casein diet. An 8% casein diet supplemented with cystine and threonine was also fou nd to reduce hyperlipidemia and proteinuria without growth retardation and fatty liver induction in nephritic rats. Fecal excretion of both neutral and acidic steroids in the 8% casein diet supplemented with cy stine and threonine diet-fed nephritic rats was significantly higher t han that in the 20% casein diet-fed nephritic rats. Hepatic cholestero l synthesis was unchanged between the two groups, whereas fatty acid s ynthesis of the 8% casein supplemented with cystine and threonine diet -fed rats was higher than that of 20% casein diet-fed animals. These r esults suggest that cystine-threonine-supplemented low casein diets ha ve beneficial effects on hyperlipidemia and proteinuria with neither g rowth retardation nor fatty liver induction in nephritis. They also su ggest that the hypocholesterolemic effect of the 8% casein supplemente d with cystine and threonine diet in nephritic rats may be, at least i n part, attributed to art increased excretion of steroids.