Postnatal development of hepatic bile formation in the rabbit

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Abstract
To investigate postnatal maturation of hepatic bile formation, bile output was measured in four groups of rabbits: suckling infants at ages 10–14, 18–22, and 26–30 days, and adults. Bile output was collected directly from the common duct during three 1-hr periods: a basal period followed by intravenous infusion of 1 and then 2 μmol/min/kg of glycodeoxycholic acid. [14C]Erythritol and [3H]inulin clearances measured canalicular bile flow and biliary permeability. Under basal conditions and with the exogenous bile acid, bile flow and bile salt secretion were lowest in 10-to 14-day-old infants and showed a gradual increase with increasing age. Bile salt-dependent flow, the linear increase in flow relative to bile salt secretion, was higher in the 10-to 14-and 17-to 22-day-old compared to the adult and 25-to 30-day-old groups. The ratio of chloride to bile salt secreted was also higher in the two younger groups. Bile salt-independent flow at theoretical zero bile salt secretion was absent in the younger groups, but evident in the adult and 25-to 30-day-old rabbits. Canalicular flow estimated by erythritol clearance was linearly related to bile salt secretion. Inulin clearance relative to erythritol clearance was higher in the 10-to 14-day-old infants than the adults. Thus, bile flow and bile salt secretion are reduced in the young infant but rise to near adult levels at the time of weaning, 25–30 days in the rabbit. The increase in flow results from increased bile salt secretion and the appearance of bile salt-independent flow. Biliary permeability as measured by inulin clearance is increased in the young, allowing increased water and electrolyte movement per unit of bile salt to maintain bile flow despite a depressed bile salt secretion rate.