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. Suggested mechanisms for the hypocholesterolemic effect include a greater excretion of fecal bile acids and total steroids, and up-regulation of bile 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 corresponds 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. Liver cholesterol concentration, fecal bile acid and total steroid excretion, 7 alpha OHase activity and 7 alpha OHase mRNA levels were measured. 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 OHase in rats fed CHY and PSY were significantly higher than in rats fed CEL or CCA. These data indicate that feeding psyllium to rats increases fecal bile acid and total steroid excretion as well as 7 alpha OHase activity and 7 alpha OHase mRNA levels.