Hepatic microsomes as models for comparative metabolism in vivo

Abstract

Hepatic microsomal systems have been used to study the metabolism of lipophilic xenobiotics. Sometimes these systems give reasonable qualitative and quantitative predictions of metabolism in vivo. In vitro systems such as these can be used to study a much wider range of species than is possible in vivo.

Comparative studies have shown considerable species differences in hepatic microsomal mono-oxygenase activities, which show the general trend mammals>birds>fish. With mammals there is a negative correlation between average mono-oxy-genase activity and log body weight.

With lipophilic xenobiotics particular attention is given to cases where microsomal metabolism is so slow that it may influence rates of excretion and biological half-lives. Here, species differences in enzyme activity may result in corresponding differences in bioaccumulation.