Mammalian steroid hormone reactions

Figure 1. Cytochrome P-450-mediated hydroxylatlon reactions in biosynthesis of major mammalian steroid hormones. (MIT)...

During the past 50 years, numerous experiments have been performed in attempts to unravel the complex pathways whereby steroid hormones, that is the corticosteroids, androgens and oestrogens, are formed in mammalian and other tissues. A very large number of books and reviews have already been written on the subject and this present chapter will seek to (a) summarize the pathways concerned and how the evidence for these was obtained and (b) provide an update of advances over the past decade, particularly with regard to the properties of the steroid transforming enzymes involved and the mechanism of the reactions catalysed by such enzymes. 

Among the diverse reactions carried out by mammalian CYPs are iV-dealkylation, O-deaUcylation, aromatic hydroxylation, A-oxidation, -oxidation, deamination, and dehalogenation (Table 3-2). CYPs are involved in the metabolism of dietary and xenobiotic agents, as well as the synthesis of endogenous compounds that are derived from cholesterol e.g., steroid hormones and bile adds). 

Some mammalian organs, particularly the liver and kidney, have the ability to convert numerous aliphatic or aromatic alcohols and carboxylic acids into their respective /3-D-glucosiduronic acids these can be transported in the blood or excreted through the urine or bile. This reaction pertains not only to such foreign substances as drugs, but also to such important endogenous compounds as steroid hormones, thyroxine, or bilirubin. 

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