Reduction of 3-oxosteroids in human liver microsomes

The 3alpha- and 3beta-reduction of the following steroids was studied in human liver microsomes: 5alpha-androstane-3,17-dione, 17beta-hydroxy-5alpha-androstan-3-one, 5alpha-pregnane-3,20-dione, 5beta-pregnane-3,20-dione, 3-oxo-5beta-cholanoic acid and 7alpha-hydroxy-5alpha-cholestan-3-one. With NADH as cofactor there was a preferential 3alpha-reduction of the C19- and C21-3-oxo-steroids and a preferential 3beta-reduction of the C24- and C27-3-oxo-steroids. Substitution of NADH with NADPH influenced reduction of the substrates in different ways, indicating the presence of several 3alpha- and 3beta-hydroxysteroid dehydrogenases with different substrate specificity and specificity towards NADH and NADPH. Only small or insignificant sex differences could be observed in the reductions studied.