Background: Developmental changes in passive bile salt absorption may alter the enterohepatic circulation.
Methods: 14-, 21-, and 40-day-old anesthetized male Sprague-Dawley rats were studied. Jejunum and ileum were isolated, cannulated, and injected or perfused with a taurocholate, [3H]taurocholate, and nonabsorbable marker solution. Bile was collected.
Results: Using bolus injection, jejunal taurocholate absorption rates and total taurocholate absorption were nonsaturable, linearly related to taurocholate dose, and decreased from 14 days (1.62 nmol.cm-1.min-1) to 21 days (1.05 nmol.cm-1.min-1) and 40 days (0.54 nmol.cm-1.min-1). While total taurocholate absorption decreased (14 days, 52.4%; 21 days, 43.7%; 40 days, 30.5%), hepatic taurocholate clearance increased (14 days, 18.2%; 21 days, 23.7%; 40 days, 37.3%). Hepatic taurocholate clearance was saturated only at 14 days. Using jejunal perfusion, total taurocholate absorption (14 days, 62.0%; 21 days, 43.1%; 40 days, 45.3%) and taurocholate absorption rate decreased with age (14 days, 941.13 nmol.cm-2.min-1 per micromole of taurocholate; 21 days, 411.28 nmol.cm-2.min-1 per micromole of taurocholate; 40 days, 334.50 nmol.cm-2.min-1 per micromole of taurocholate).
Conclusions: Passive jejunal bile salt absorption and decreased hepatic bile salt clearance could account for the low intraluminal and high serum bile salt levels observed in immature animals and in human neonates.