Increased fecal bile acid excretion and changes in the circulating bile acid pool are involved in the hypocholesterolemic and gallstone preventive actions of psyllium in hamsters

The lipid-lowering effect of psyllium (PSY) is well established. Enhanced f ecal bile acid excretion and a stimulation of hepatic bile acid synthesis a re discussed as primary mechanisms of this action. To further examine the e ffect of bile acid excretion and specifically of compositional alterations in the bile acid pool on the cholesterol-lowering and gallstone-preventing action of PSY, male golden Syrian hamsters were fed lithogenic diets contai ning 5 g/100 g fat, 0.4 g/100 g cholesterol and 0 (control), 4 or 6% PSY or 1% cholestyramine (CHY). PSY significantly lowered plasma total cholestero l and triacylglycerol at a magnitude comparable to that induced by CHY, Alt hough hepatic cholesteryl eater accumulation was completely inhibited by CH Y, PSY did not prevent the hepatic storage of esterified cholesterol, PSY a nd CHY caused distinct alterations in the bile acid profile. PSY caused a s elective reduction of taurine-conjugated bile acids, especially of tauroche nodeoxycholate. As a result, the glycine:taurine conjugation and the cholat e:chenodeoxycholate ratios were significantly higher in PSY-fed hamsters. P SY and CHY normalized the lithogenic index and prevented cholesterol gallst one formation compared with controls. Daily fecal bile acid excretion was s imilar to 400% greater in hamsters fed 6% PSY, whereas CHY caused an 11-fol d increase. Daily neutral sterol excretion did not differ in PSY-fed hamste rs but was >100% greater in those fed CHY than in controls. These data emph asize the potent lipid-lowering effect of PSY, Increased fecal bile acid ex cretion and alterations of the circulating bile acid pool by removal of dih ydroxy bile acids (e.g,, taurochenodeoxycholate) appear to be main modulato rs of the hypocholesterolemic action of PSY by leading to an up-regulation of hepatic bile acid synthesis.