Steroids in Germfree and Conventional Rats

Gas chromatography‐mass spectrometry and radio‐gas chromatography were used to identify metabolites of [ 14 C]corticosterone and [ 14 C]pregnenolone in faeces and urine from germfree and conventional male rats. The metabolites were generally more polar than those in female rats and the main part of those which could be identified were found in the free steroid fraction. In the conventional male rats a number of pregnane‐3,11,16,20,21‐pentol isomers constituted the major corticosterone metabolites identified both in urine and in faeces. In addition 3α(and 3β),20β‐dihydroxy‐5α‐pregnan‐11‐one and 5α‐pregnane‐3α(and 3β),11β,20β,21‐tetrol were excreted in faeces. In the germfree male rats, minor amounts of some C 19 O 3 and C 21 O 3 steroids were excreted as monosulphates in faeces. However, 5α‐pregnane‐3α(and 3β),11β,21‐tetrols were the predominant steroids in this fraction. These compounds also constituted the major part of steroids identified in the disulphate fraction, which also contained 3α(and 3β),11β,21‐trihydroxy‐5α‐pregnan‐20‐one. All radioactive steroids excreted in the urine of germfree male rats were unconjugated. Although none of these compounds could be fully identified evidence was obtained for the presence of several C 19 O 5 , C 21 O 4 , C 21 O 5 , C 21 O 6 and C 21 O 7 steroids. The findings are discussed in relation to previous information on the steroid metabolizing activities of the intestinal flora and sex differences in the metabolism of steroids in rats.