Studies on the Metabolism of Orange RN in the Pig

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Abstract
Orange RN (monosodium salt of 1-phenylazo-2-naphthol-6-sulfonic acid) was administered to female pigs either by i.v. injection or by stomach tube. After i.v. injection of Orange RN, 7.8 mg/kg, the following metabolites were identified in 24 h urines: Orange RN (31%), 1-(4-hydroxyphenylazo)-2-naphthol-6-sulfonic acid (3%), p-aminophenol and o-aminophenol (34% and 4% of the theoretical yield, respectively). 1-Amino-2-naphthol-6-sulfonic acid was present, but not determined. When the urine collection was extended to 72 h the excretion of p-aminophenol accounted for the remainder of the phenylazo moiety. The excretion pattern for p-aminophenol suggests 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 colored metabolites (Orange RN and 1-(4-hydroxyphenylazo)-2-naphthol-6-sulfonic 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-sulfonic acid was present, but not determined. [Orange RN has been used for the coloring of jam, pudding and meat products, especially sausages. Orange RN caused liver toxicity in pigs (results of other experimenters).].