Studies on fat digestion, absorption, and transport in the suckling rat. III. Composition of bile and evidence for enterohepatic circulation of bile salts.

Biliary secretions from suckling rats (10-15 days old) were characterized: bile flow rate was 197.3 microliters/hr per 100 g; bile salt pool size was 19.0 mumol/100 g; secretion rate was 14.5 mumol/hr per 100 g; synthesis rate was 12.0 mumol/day; and the daily turnover frequency was 18.3. Phospholipid and cholesterol secretion rates were 2.3 mumol/hr per 100 g and 0.17 mumol/hr per 100 g, respectively. The bile salt concentration in portal plasma was 0.17 mumol/ml. The fatty acid composition of biliary phosphatidylcholine and ethanolamine, as well as the stereospecific distribution of fatty acids in the former, were similar to that found in phospholipids from adult rat bile. Compositional analysis of bile acids showed greater than 98% taurine conjugates consisting of approximately 54% cholic acid, 40% beta-muricholic acid, 2% chenodeoxycholic acid, and 1% each of deoxycholic and hyodeoxycholic acids. Through the use of intestinal and liver perfusion experiments, we have obtained evidence for enterohepatic circulation of taurocholate in neonatal rats. The level of bile salts found in intestinal contents (49.5 mumol/g), and the biliary phospholipid concentration (11.8 mM) both exceed adult values (6-10 mumol/g and 6.3 mM, respectively) and may be important for the utilization of the large amount of milk triacylglycerols ingested during the suckling period.