Liver Microsomal Hydroxylation of Steroid Hormones After Establishing an Indigenous Microflora in Germfree Rats

The liver microsomal metabolism of 4 [4 ¹⁴C]androstene 3,17 dione and 5α [4 ¹⁴C]androstane 3α,17β diol was studied in germfree, conventional and exgermfree rats with a normal indigenous microflora. Germfree rats were significantly more active than conventional rats in hydroxylating 4 androstene 3,17 dione in position 6β (P<0.02) and 5α androstane 3α,17β diol in positions 2β (P<0.05), 7α (P<0.02) and 18 (P<0.02). In addition 7α, 16α and 16β hydroxylation of 4 androstene 3,17 dione and 2α and 7β hydroxylation of 5α androstane 3α,17β diol tended to be greater in germfree rats than in conventional rats. In most cases the exgermfree rats, which had been reared outside the germfree isolators for 4 wk, showed similar activities of the microsomal hydroxylase systems as their conventional counterparts. Thus, exgermfree rats showed significantly less efficient 16β hydroxylation of 4 androstene 3,17 dione (P<0.02) and 2β (P<0.02) and 7α (P<0.05) hydroxylation of 5α androstane 3α,17β diol than germfree rats. The results show that the induced state of certain microsomal hydroxylase systems in germfree rats is reversible and dependent on the metabolic changes in the germfree rat consecutive to the absence of the normal indigenous microflora.