Comparison of rate of Hepatic Metabolism in vitro and Half-Life for Antipyrine in vivo in Three Species

Abstract

1. A radiometric assay for the total metabolism of antipyrine in vitro by hepatic microsomal preparations has been developed.

2. Apparent K_m and V values for the process were determined in rats, rabbits and in a marsupial (the quokka; Setonix brachyurus). K_m values were similar in rats and rabbits (3·5 and 5 mM respectively) but were somewhat lower in quokkas (1·4-1·5 mM). Estimates of V ranged from 49-64 nmol/mg microsomal protein/10 min and were similar in all three species. Pretreatment of rabbits with phenobarbitone significantly increased V without change in K_m.

3. Studies in individual rabbits and quokkas showed a good corrolation between rate of hepatic microsomal metabolism of antipyrine in vitro and its half-life in vivo.