Steroids in Germfree and Conventional Rats: 21‐Dehydroxylation by Intestinal Microorganisms

The metabolism of 3β,21‐dihydroxy‐5α‐pregnan‐20‐one in incubations with caecal microorganisms has been studied. Pregnane‐3,20‐diols and pregnane‐3,20,21‐triols were the major products. Relatively more pregnanediols were formed under aerobic than under anaerobic conditions. There was no formation of pregnanediols from 5α‐pregnane‐3β,20β(and 20α),21‐triol and no epimerization of the 20‐hydroxy group or loss of 20α(or 20β)‐²H in deuterium labelled pregnanetriols. The 3β‐hydroxy group underwent partial epimerization during the incubation. The results show the existence of a microbial 21‐dehydroxylation of 21‐hydroxy‐20‐oxo steroids and offer an explanation for the absence of 21‐hydroxylated steroids in faeces from conventional rats.