Studies on the metabolism of Orange Rn in the pig

Orange RN (monosodium salt of 1-phenylazo-2-naphthol-6-sulphonic acid) was administered to female pigs either by intraveneous injection or by stomach tube. After intravenous injection of Orange RN, 7.8 mg/kg, the following metabolites were indentified in 24-hour urines: Orange RN (31%), 1-(4-hydroxyphenlazo)-2-naphthol-6-sulphonic acid (3%), p-aminophenol and 0-aminophenol (34% and 4% of the theoretical yield, respectively). 1-Amino-2-naphthol-6-sulphonic acid was present, but not determined. When the urine collection was extended to 72 hours the excretion of p-aminophenol accounted for the remainder of the phenylazo moiety. The excretion pattern for p-aminophenol suggest that Orange RN is partly excreted in the bile and thereafter undergoes azo reduction in the gut. After administration of Orange RN, 78 mg/kg, by stomach tube the following metabolites were identified in the urine: Total coloured metabolites (Orange RN and 1-(4-hydroxyphenylazo)-2-naphtholphenol-6-sulphinic acid) (0.4% of the theoretical yield), p-aminophenol and o-aminophenol (52% and 6% of the theoretical yield, respectively) and aniline (0.3% of the theoretical yield). 1-Amino-2-naphthol-6-sulphonic acid was present, but not determined.