Tissue homogenates microsome isolation from

In vitro models derived from material from farm animals have more or less been restricted to tissue homogenates or isolated cell fragments, like microsomes. Only recently the experiences with other animal species have resulted in the isolation and use of hepatocytes and liver slices. 

If metabolism in animal models is extensive or the generated metabolite(s) is shown to have toxic effects, in vitro metabolism studies using isolated P-450 isozymes, tissue homogenates containing the microsomal fraction, hepatocytes, and liver slices are commonly conducted to determine if the extent of metabolism and the metabolite profile is similar for animals and humans. The results from these in vitro metabolism comparison studies can be used to select the animal models for definitive development studies that have similar metabolism profiles to humans. 

Metabolism studies. GC-MS is a powerful technique for following and identifying the metabolic products from the in vitro incubation of tissue preparations with steroid substrates. Examples of such studies include the 16a-hydroxylation of 18-hydroxydeoxycorticosterone by human adrenal gland [254], the eiromatization of 3jS,15, 16 -trihydroxy-5-androsten-17-one by placental homogenates [255], and the demonstration of 1/3, 12/3, 6a and 6/3 hydroxylase enzyme activities in microsomal preparations of human foetal hepatic tissue [256]. In the latter study, testosterone was used as substrate and in addition to the hydroxylated metabolites isolated, several other testosterone derivatives indicated the presence of 3a, 3/3 and 17/3-hydroxysteroid oxidoreductase in the adrenal gland preparation. 

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