Preservation of various microsomal drug metabolizing components in tissue preparations from the livers, lungs, and small intestines of rodents.

The livers, lungs, and small intestines of untreated rabbits and the livers of control rats were stored intact, or as microsomal suspensions, under liquid nitrogen at -196 degrees C. Aniline hydroxylase, aminopyrine demethylase, benzpyrene hydroxylase, biphenyl hydroxylase, NADPH-cytochrome c reductase, UDP-glucuronyltransferase activities, the microsomal content of cytochrome P-450, and the aniline- and benzphetamine-induced spectral changes were compared in fresh and stored preparations. Few significant changes in any of the above parameters resulted from storage of rabbit tissue preparations in liquid nitrogen for periods of up to 28 days. Pretreatment of rabbits with phenobarbital did not affect the stability of their stored microsomal preparations. Enzyme activities in the livers of untreated or 3-methylcholanthrene-pretreated rats were less stable to storage than in tissue preparations from rabbits stored under identical conditions. However, when rat hepatic microsomes were resuspended in KCl-HEPES supplemented with 1 mM EDTA before storage, enzyme activities were largely unaffected by freezing in liquid nitrogen.