Abstract
A study was conducted on the incorporation of [11- 3H]retinyl acetate into various retinyl esters in liver tissues of rats either vitamin A-sufficient. vitamin A-deficient or vitamin A-deficient and maintained on retinoic acid. Further, the metabolism of [11- 3H]retinyl acetate to polar metabolites in liver tissues of these three groups of animals was investigated. Retinol metabolites were analyzed by high-performance liquid chromatography. In vitamin A-sufficient rat liver, the incorporation of radioactivity into retinyl palmitate and stearate was observed at 0.25 h after the injection of the label. The label was further detected in retinyl laurate, myristate, palmitoleate, linoleate, pentadecanoate and heptadecanoate 3 h after the injection. The specific radioactivities (dpm/nmol) of all retinyl esters increased with time. However, the rate of increase in the specific radioactivity of retinyl laurate was found to be significantly higher (66-fold) than that of retinyl palmitate 24 h after the injection of the label. 7 days after the injection of the label, the specific radioactivity between different retinyl esters were found to be similar, indicating that newly dosed labelled vitamin A had now mixed uniformly with the endogenous pool of vitamin A in the liver. The esterification of labelled retinol was not detected in liver tissues of vitamin A-deficient or retinoic acid-supplemented rats at any of the time point studied. Among the polar metabolites analyzed, the formation of [ 3H]retinoic acid from [ 3H]retinyl acetate was found only in vitamin A-deficient rat liver 24 h after the injection of the label. A new polar metabolite of retinol (R M) was detected in liver of the three groups of animals. The formation of 3H-labelled metabolite R M from [ 3H]retinyl acetate was not detected until 7 days after the injection of the label in the vitamin A-sufficient rat liver, suggesting that metabolite R M could be derived from a more stable pool of vitamin A.
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