DIETARY PSYLLIUM INCREASES FECAL BILE-ACID EXCRETION, TOTAL STEROID-EXCRETION AND BILE-ACID BIOSYNTHESIS IN RATS

Psyllium, a source of dietary fiber rich in soluble components results in lower serum cholesterol concentration in several species. Suggeste d mechanisms for the hypocholesterolemic effect include a greater excr etion of fecal bile acids and total steroids, and up-regulation of bil e acid biosynthesis. The activity of cholesterol 7 alpha-hydroxylase ( 7 alpha OHase), the rate limiting enzyme in bile acid biosynthesis, is higher in rats fed 5% psyllium. Whether this higher activity correspo nds to an increase in mRNA levels has not been determined. Four groups of 10 rats were fed a semipurified diet containing 5% cellulose (CEL; control), 5% cellulose plus 1% cholic acid (CCA), 5% cellulose plus 2 % cholestyramine (CHY) or 5% psyllium hydrocolloid (PSY) for 3 wk. Liv er cholesterol concentration, fecal bile acid and total steroid excret ion, 7 alpha OHase activity and 7 alpha OHase mRNA levels were measure d. Liver cholesterol content in rats fed CCA was significantly higher than in all other groups. Rats fed CHY and PSY had significantly lower liver cholesterol content than those fed GEL. Total fecal steroid and bile acid excretions were significantly greater in rats fed CCA, CHY and PSY than in those fed GEL. Activities and mRNA levels of 7 alpha O Hase in rats fed CHY and PSY were significantly higher than in rats fe d CEL or CCA. These data indicate that feeding psyllium to rats increa ses fecal bile acid and total steroid excretion as well as 7 alpha OHa se activity and 7 alpha OHase mRNA levels.