Effects of rice proteins from two cultivars, Koshihikari and Shunyo, on hepatic cholesterol secretion by isolated perfused livers of rats fed cholesterol-enriched diets.

BACKGROUND/AIMS: The aim of the present study was to clarify the effect of rice proteins, with different contents of glutelin and prolamin, on the regulation of hepatic cholesterol output pathways and the development of hypocholesterolemia in rats.

METHODS

Seven-week-old male Wistar rats were fed 2 types of rice protein from either the cultivar Koshihikari (RRP) or the cultivar Shunyo (SRP), or casein as a control, for 2 weeks (n = 6 for each group). Each diet was supplemented with 1% cholesterol and 0.25% sodium cholate. Using an isolated perfused liver, hepatic secretion of cholesterol into bile and the circulation was measured during a 4-hour perfusion.

RESULTS

Total hepatic cholesterol secretions into the circulation were significantly reduced by both rice proteins (p < 0.05), and hepatic cholesterol secretions into very-low-density lipoproteins were also effectively decreased by RRP and SRP. In contrast, bile flow and biliary output of bile acids were significantly stimulated by RRP and SRP (p < 0.05).

CONCLUSIONS

These results demonstrate that the key metabolic pathways of hepatic cholesterol are modified by both rice proteins leading to similar hypocholesterolemic effects. The increased excretion of biliary bile acids associated with a decreased output of hepatic cholesterol into the circulation suggests a functional reciprocal interrelationship between both of the hepatic cholesterol secretory pathways in the rice-protein-fed rats, regardless of rice protein type.