Effect of a low protein diet on bile flow and composition in rats.

The effect of feeding a low protein (LP) diet on bile flow and biliary lipid and protein secretion was studied with young female rats. Animals fed a 8% protein diet (LP) for 4, 8 and 12 wk had a significantly lower bile flow and a lower biliary bile acid and protein secretion rate compared with rats fed a 26% protein (normal) diet (NP). The bile acid-independent fraction of bile flow was significantly increased. The slope of the regression line to zero bile acid was markedly smaller in the LP than in the NP group, indicating lower bile acid-dependent bile flow. Biliary phospholipid and cholesterol secretion rates were significantly higher in the LP than in the NP group, demonstrating an uncoupling between bile acid and lipid secretion at the low rates of bile acid secretion. The percentage increase for these parameters was of similar magnitude (30%). Absolute concentrations of bile acid, phospholipid and cholesterol were significantly higher in LP-fed rats than in NP rats, while relative concentration of bile acid was lower and those of cholesterol and phospholipid were higher. Analysis of biliary bile acids showed that the percent contribution of chenodeoxycholic acid and of deoxycholic acid increased significantly in the LP-fed rats, while that of cholic acid decreased. These data indicate that the lower bile flow in the rats fed LP can be attributed to lower bile salt-dependent flow associated with significantly lower choleretic potency of bile acids secreted.