REDUCTION OF SERUM RETINOL LEVELS FOLLOWING A SINGLE ORAL DOSE OF ALL-TRANS-RETINOIC ACID IN HUMANS

Following a single oral dose of all-trans retinoic acid (RA) (0.167 mm ole) in corn oil to 6 healthy human subjects, the mean serum retinol ( ROL) level fell by approximately 20% within 1 h and remained depressed for 24 h. After dosing, RA appeared in the blood within 30 min, peake d at 0. 3-0.5 mu mol/l, and then declined to very low concentrations a fter 7 h. All-trans retinoyl beta-glucuronide (RAG) appeared simultane ously with RA in the plasma, albeit more sporadically, whereas only tr aces of 4-oxoretinoic acid (4-oxoRA) were detected. Some possible phys iologic consequences of therapeutic uses of all-trans RA are discussed .