Oxidoreductive and hydroxylating metabolism of progesterone in rat liver epithelial cell lines

Mechanisms and sequences of reduction and hydroxylation of progesterone into 6-hydroxypregnanolones were studied in proliferating rat liver epithelial cell cultures. These cell lines had an intense metabolic activity and all the metabolites were unconjugated. The formation of 3 alpha,6 alpha- and 3 beta,6 alpha-dihydroxy-5 alpha-pregnan-20-one was observed when the cells were incubated with progesterone, 5 alpha-pregnane-3,20-dione, 3 alpha- or 3 beta-hydroxy-5 alpha-pregnan-20-one and 6 alpha-hydroxy-5 alpha-pregnane-3,20-dione but not with 6 alpha- or 6 beta-hydroxyprogesterone, 5 beta-pregnane-3,20-dione, 3 alpha- or 3 beta-hydroxy-5 beta-pregnan-20-one. These findings indicate that the potential precursors of the 6 alpha-hydroxypregnanolones have a 5 alpha-configuration. The reduction of 5 alpha-pregnane-3,20-dione at C-3 followed by a 6 alpha-hydroxylation can be postulated as the major, if not the only, metabolic pathway. However, the possibility that 6 alpha-hydroxylation may occur prior to reduction of the C-3 oxo group cannot be entirely ruled out. The stereospecificity of reduction at C-5 and hydroxylation at C-6 are discussed and compared with 6-hydroxylated progesterone metabolites found in man and some other mammals during pregnancy and the neonatal period.