Studies on the Biliary Excretion and Metabolites of the Antioxidant Ethoxyquin, 6-Ethoxy-2,2,4-Trimethyl-1,2-Dihydroquinoline in the Rat

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Abstract
Biliary excretion and metabolites of ethoxyquin [feed and apple and pear preservative], and gastro-intestinal absorption of ethoxyquin were studied in rat. An average of 28 36% of the dose of 14C following intragastric administration of [14C] ethoxyquin was recovered in the bile of bile-duct cannulated rats in 12 and 24 h, respectively. By GLC-mass spectrometry, 75-85% of the 14C excreted in the 12 h bile was identified as unchanged ethoxyquin, and the following metabolites were isolated and identified: 8-hydroxy-ethoxyquin, hydroxylated 8-hydroxy-ethoxyquin, 6-ethoxy-2,2,4-trimethyl-8-quinolone, hydroxylated 6-ethoxy-2,2,4-trimethyl-8-quinolone, 6-ethoxy-2,4-dimethylquinoline and 2,2,4-trimethyl-6-quinolone. Three groups of rats were used in the biliary excretion experiments, and the effect of standardization of experimental conditions was demonstrated. Infusion of sodium taurocholate following bile-duct cannulation did not affect the biliary excretion kinetics of ethoxyquin. Only .apprx. 3% of the radioactivity administered was absorbed from the gastrointestinal tract via the lymphatic pathway in thoracic-duct cannulated rats within 24 h. It was concluded that ethoxyquin was primarily absorbed by the portal route.