Transport rates of hepatic uptake and biliary excretion of an organic cation, acetyl procainamide ethobromide

Abstract

Rates of hepatic uptake and biliary excretion, as well as the T max, of acetyl procainamide ethobromide (APAEB), an organic cation, were estimated in rats. The relationship between hepatic uptake and dose followed saturation kinetics. From the effect of isopropamide iodide on the uptake rate of APAEB and on the binding of APAEB to liver tissues, the saturated uptake was presumed to occur by membrane transport. The excretion rate versus the liver level, however, did not follow saturation kinetics clearly up to T max, whereas the excretory step is considered an active process. The calculated V max tor the excretory step was far greater than the maximal uptake rate and T max estimated by constant infusion of APAEB, indicating that the rate-determining step in the biliary excretion of APAEB is not the excretory but the uptake step which is in contrast with that observed with many organic anions.