In vitro hydroxylation of testosterone in rabbits: influence of age and sex*

Introduction Hydroxylated metabolites of testosterone (T) have been proposed as useful markers of specific isoform P450 activity in rats (1). Only few studies have been devoted to characterisation of P450 biotransformation activity in food producing species thus the aim of this study was to define the influence of sex and age in rabbits on the metabolic profile of hydroxylated testosterone (OHT) metabolites using an HPLC method able to separate nine metabolites. The role played by CYP3A was also studied in Rifampicin (RIF) induced rabbits. Material and methods Liver microsomes were obtained (2) from rabbits. five male (3±0.4 kg), five female (3±0.2 kg), five young male (1,5±0,3 kg), and two male induced with RIF (50 mg/kg, 4 days, ip). Microsomes (0.2 mg/ml) were incubated for 10 min, at 37°C with 250 µM T. Hydroxylated metabolites were extracted with methylene chloride and separated according to Purdon (3) with HPLC using a C18column and ternary phase gradient elution. Elution times were compared with those of pure standards (Steraloids). Discussion Main differences are: the absence in males of 16alfa-OHT; the greater production (*P<0,001) of 6beta-OHT, 11alfa-OHT, 16beta-OHT and 2beta-OHT compared to females; the decreased production (#P<0.001) of 6beta-OHT and 16alfa-OHT in young rabbits versus adult ones. Based on data reported for other species (1, 4) apparently, the isoforms involved in rabbits are CYP3A for 6beta-OHT, and 2beta-OHT; and CYP2B for 16alfa-OHT, and 16beta-OHT. RIF induced microsomes gave a significantly (°P<0,001) greater quantities of 6beta-OHT, 2beta-OHT supporting, also in rabbits, the CYP3A role played in the production of these hydroxyl-derivatives.