Studies on the Structure, Biosynthesis and Bacterial Metabolism of 15‐Hydroxylated Steroids in the Female Rat

Gas‐liquid chromatography, gas chromatography‐mass spectrometry and radio‐gas chromatog‐raphy have been used to obtain a tentative identification of eight 15‐hydroxylated C₂₁O₄ steroids in faeces and urine from conventional female rats: 3α(and 3β),15α‐dihydroxy‐5α,14β‐pregnane‐11,20‐dione, 3α(and 3β),11β,15α‐trihydroxy‐5α,14β‐pregnan‐20‐one, 3α(and 3β),15α, 20β‐trihy‐droxy‐5α,14β‐pregnan‐11‐one and 5α,14β‐pregnan‐3α(and 3β),11β,15α,20β‐tetrol. The assign‐ment of stereochemistry is based on indirect evidence. The steroids were present in the free and monosulphate fractions and became labelled after administration of [4‐¹⁴C]pregnenolone and [4‐¹⁴C]corticosterone to the rats. Incubations in vitro with caecal contents from conventional rats showed that they were microbial metabolites of the 15α,21‐hydroxylated C₂₁O₅ steroids previously shown to be present in faeces and urine from germfree rats.