title: Studies on rat liver microsomal steroid metabolism using 18O-labelled testosterone and progesterone.
abstract: In order to investigate the possible involvement of oxygen functions in the rat liver microsomal metabolism of progesterone and testosterone these steroids were specifically labelled with 18O in their oxo-functions and incubated with NADPH supplemented 105,000 g sediments. Gas chromatography-mass spectrometry was used to identify the metabolites formed as well as to quantitate the losses of 18O-label. With 18O-labelled testosterone as substrate two of the major monohydroxylated metabolites, i.e. 2 beta- and 6 beta-hydroxytestosterone were shown to have lost about 25 and 50% of their 18O respectively. A complete retention of label was found in 7 alpha- and 16 alpha-hydroxytestosterone. None of the monohydroxylated progesterone metabolites, i.e. the 2 alpha-, 6 beta- and 16 alpha-hydroxyprogesterone had lost any 18O following incubation with 3,20-18O-labelled progesterone. Control incubation (30', 37 degrees C) with buffer and 18O-labelled progesterone and testosterone revealed no exchange of 18O. Thus the partial loss of 3-18O-label during 2 beta- and 6 beta-hydroxylation of testosterone may indicate a covalent interaction between the steroid 3-oxo-group and one or more cytochrome P-450 species in the rat liver microsomes. In view of the potentiating effect of a 3-imine group in spontaneous 6 beta-hydroxylation the present in vitro data suggest that a steroid protein-interaction may occur via a 3-imine group during 6 beta-hydroxylation of testosterone in rat liver microsomes. Analysis of 5 alpha-reduced metabolites of both progesterone and testosterone showed significant losses of 3-18O, but due to the ease with which 3-oxo-5 alpha-steroids exchange their 3-18O with aqueous media an enzymatically induced loss of 3-18O could not be safely established. The 20-oxido-reductase which converted progesterone did not induce a loss of 20- or 3-18O thus indicating that the oxofunctions were not covalently engaged in the enzymatic binding of the steroid.
authors: Department of Obstetrics and Gynecology, Karolinska Hospital, Stockholm, Sweden.
authors: C G
authors: CG
authors: Eriksson
authors: P
authors: P
authors: Eneroth
mesh_terms: D000818:Animals; D001711:Biotransformation; D002855:Chromatography, Thin Layer; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism*; D010103:Oxygen Isotopes; D011374:Progesterone / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013739:Testosterone / Q000378:metabolism*
chemical_list: D010103:Oxygen Isotopes; D013739:Testosterone; D011374:Progesterone