Measurement and alteration of the capacity of the distended biliary tree in the rat

A retrograde-push-back (RPB) technique was developed to estimate capacity of the biliary tree in the distended state. The technique involves establishing a relatively constant rate of [³H]mannitol excretion in bile, retrogradely infusing saline into the biliary tree to clear the biliary system of mannitol an estimating capacity as the volume of biliary fluid recollected to the point where excretion of mannitol was reestablished to one-half of the original rate. In male Sprague-Dawley rats, distended capacity was 37.3 ± 4.4 μl (mean ± SE) for animals with a mean liver weight of 10 g. Distended capacity should be measured by allowing free flow of bile to occur within 5 sec of completion of the retrograde saline infusion. Significant reentry of [³H]mannitol into the biliary tree takes place if the occlusion is maintained for longer periods. These facets of the method were investigated by measuring intrabiliary pressures in relation to distended capacities. Even though a linear relationship existed between the liver and rat body weights, a linear relationship could not be established between liver weights and distended capacities. Thus, it seems inappropriate at this time to express distended capacities on a microliters per gram of liver basis. In another group of rats, treatment with sodium taurolithocholate (12.5 μmol/kg, iv) reduced the distended capacity to 25.2 ± 2.8 μl from a control value of 32.9 ± 1.0 μl. In rats treated with phenobarbital sodium (75 mg/kg, ip, once daily) for 4 days, the increase in liver wet weight was not accompanied by an increase in distended biliary tree capacity. In the hamster (liver weight, 4.4 g) and rabbit (liver weight, 82.6 g), the distended capacities were 18.9 ± 1.8 and 849 ± 86 μl, respectively. In the guinea pig, RPB with [³H]mannitol produced an overshooting effect above the steady state excretion values. With [¹⁴C]erythritol this overshooting effect was not obtained and a distended capacity estimate of 111 ± 8 μl was obtained for livers weighing 22 g.