Propranolol elimination as described by the venous equilibrium model using flow perturbations in the isolated perfused rat liver.

The kinetics of hepatic elimination of the high-clearance drug propranolol has been interpreted in a previous study from our laboratory, in which propranolol protein binding was varied, to conform to the venous equilibrium model. In another study by a different group, in which perfusate flow was varied, propranolol kinetics was interpreted to conform to the sinusoidal model. In the present study, we investigated the possibility that this discrepancy is due to the use of the two different discriminants, flow and protein binding, in the two studies. In eight livers, perfused in a recirculating design, steady-state elimination of propranolol (infused at a rate of 22.8 micrograms/min) was examined at perfusate flow rates of 16 and 32 mL/min. Hepatic outflow concentration was independent of perfusate flow rate, while the logarithmic average concentration was significantly lower at the higher flow. These data conform to the venous equilibrium model and are not consistent with the sinusoidal model. This shows that the outcome of these modeling experiments does not depend on the experimental approach used, and reaffirms that the venous equilibrium model is appropriate for propranolol under the conditions studied.