Pathways of retinol and retinoic acid metabolism in the rat

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Abstract
The metabolism of retinoic acid and retinyl acetate labelled with C14 in various positions was studied after intravenous injection of physiological amounts of these compounds into retinol-deficient rats. Analysis of the resultant radioactivity in the urine, carbon dioxide and feces to led to a postulation of the existence of 3 major pathways for the metabolism of these 2 compounds. Evidence is presented that retinoic acid and retinol are metabolized by either the same or at least similar pathways and that retinol becomes oxidized to the carboxyl state before any degradation of the isoprenoid side chain occurs. It is not possible to decide from these data whether retinoic acid is an intermediate in the retinol pathway. Possible sites for the regulation of retinol metabolism are discussed.