[Metabolism of retro-progesterone and 17-hydroxy-retro-progesterone]

In comparative studes, the metabolism of retro-progesterone (9 beta,10alpha-pregn-4-ene-3, 20-dinoe) and 17-hydrozy-retro-progesterone (17-hydroxy-9 beta, 10 alpha-prgn-4-ene-3, 20-dione) as well as of progesterone and 17-hydroxy progesterone was investigated. The microsomal fraction from rat tests served as enzmye preparation. Whereas progesterone was metablised to 17-hydroxy-progesterone, testosterone and androstendion, retno-progesterone did not yield the corresponding reaction products. 16 alpha-Hydroxy-retro progresterone was found to be the main metabolite of retro-progesterone and identified by gas-liquid chromatopgray/mass spectrometry. In contrast to 17-hydroxy-progesterone, no transformation of 17-hudroxy-retro-progesterone to C19-steriods was observed. From these experiments, it can beconcluded that C21 -retro-steriods are not attacked by the 17alpha-hydrozylase and the C17-C20-desmolase of mammalian origin.