The biliary elimination of amaranth, indocyanine green and nitrazepam in germ-free rats

In anaesthetised bile duct-cannulated rats the overall rate of bile flow was 15-50% lower in both male and female germ-free (GF) rats. Except in the case of amaranth in female GF rats, this was reflected in a lower rate of biliary excretion of the three test xenobiotics, of which two (amaranth and indocyanine green) are excreted unchanged and one (nitrazepam) is excreted solely as metabolites. It was also noted that compared with conventional (CV) rats the relative liver weights (g/kg body weight) were about 20% lower in GF animals. After the intravenous injection of 14C-nitrazepam, thin-layer chromatographic separation of biliary nitrazepam-derived radioactivity revealed three loci (A, B and C in decreasing order of polarity). The relative proportions of A, B and C were similar in GF and CV rats, with C and B being the major and minor "metabolites" respectively. When 14C-nitrazepam was given intragastrically to non-anaesthetised rats, by 9 days about 20% and 70% of the dose had been recovered in the urine and faeces respectively of both GF and CV rats. The rate of elimination of urinary radioactivity was similar in GF and CV rats. However, faecal elimination was much slower in GF animals, for example after 24 hr the respective amounts of radioactivity excreted in GF and CV rats corresponded to 13% and 52% of the dose. These findings indicate that the indigenous bacterial population of an animal may indirectly affect the disposition of a xenobiotic whether or not it is metabolised by the bacteria.