Steroids in Germfree and Conventional Rats: Steroids in the Mono‐ and Disulphate Fractions of Faeces from Female Rats

Gas‐liquid chromatography, radio‐gas chromatography and gas chromatography‐mass spectrometry were used to identify steroid metabolites in the monosulphate and disulphate fractions of faeces from germfree female rats and in the monosulphate fraction of faeces from conventional female rats after intraperitoneal administration of [4‐¹⁴C]pregnenolone and [4‐¹⁴C]‐corticosterone. The germfree rats excreted the following steroids: monosulphate fraction: 3β, 17α‐dihydroxy‐5α‐pregnan‐20‐one, 5α‐pregnane‐3α,16α,20α‐triol, 2α,3β,16α‐trihydroxy‐5α‐pregnan‐20‐one and 3α,15β,16α‐trihydroxy‐5α‐pregnan‐20‐one; disulphate fraction: 3α‐ and 3β,11β,21‐trihydroxy‐5α‐pregnan‐20‐one. The following steroids were identified in faeces from conventional rats: oestriol, 3α,15α(and 15β)‐dihydroxy‐5α,17α(and 17β)‐pregnan‐20‐one,3α,19‐dihydroxy‐5α,17α‐pregnan‐20‐one, 5α‐pregnane‐3α,16α,20‐triol, 3β,11α‐dihydroxy‐5α‐pregnan‐20‐one. 2α, 3α‐dihydroxy‐5α,17α‐pregnan‐20‐one (tentatively identified), and 3α,17α‐dihydroxy‐5α‐pregnan‐20‐one. The different steroid patterns in faeces from germfree and conventional rats are explained by the metabolic reactions carried out by the intestinal flora. Radio‐gas chromatography showed that 3α‐ and 3β,11β,21‐trihydroxy‐5α‐pregnan‐20‐one and 3β,11α‐dihydroxy‐5α‐pregnan‐20‐one were metabolites of corticosterone. The formation of 3β,11α‐dihydroxy‐5α‐pregnan‐20‐one and of the 17α‐pregnane derivatives by intestinal microorganisms is discussed.