FORMATION OF ALL-TRANS-RETINOIC ACID AND 13-CIS-RETINOIC ACID FROM ALL-TRANS-RETINYL PALMITATE IN HUMANS

Increments of levels of both 13-cis- and all-trans-retinoic acid in human plasma were observed after either a physiologic or a pharmacologic oral dose of all-trans-retinyl palmitate. Subjects receiving a physiologic dose showed mean +/- SEM plasma rises over baseline as follows: all-trans-retinoic acid = 1.1 +/- 0.3 nmol/L and 13-cis-retinoic acid = 4.7 +/- 1.1 nmol/L, which represented increases in 1.3 fold and 1.9 fold over fasting plasma levels. Those receiving a pharmacologic dose showed mean +/- SEM plasma rises over baseline as follows: all-trans-retinoic acid = 11.5 +/- 2.6 nmol/L and 13-cis-retinoic acid = 37.5 +/- 6.1 nmol/L, which represented increases of 3.9-fold and 8.4-fold over fasting plasma levels. Moreover, areas under the curve of the means of all-trans- and 13-cis-retinoic acid over 24 hours showed that larger amounts of 13-cis-retinoic acid appear in the circulation than all-trans-retinoic acid after feeding all-trans-retinyl palmitate. The increase in retinoic acid in the circulation may be an important source of retinoic acid for some organs.