Retinoyl beta-glucuronide: an endogenous compound of human blood.

The occurrence of retinoyl beta-glucuronide and retinoic acid as normal endogenous components of vitamin A reserve in human blood has been demonstrated. Use of high-performance liquid chromatography, coupled with a sensitive detector and integrator, has enabled us to quantitate nanogram quantities of the two retinoids. Serum concentrations of retinoyl glucuronide and retinoic acid in all the volunteers studied ranged from 1.5 to 5.1 ng/ml (mean 2.42 ng/ml) and from 1.0 to 3.2 ng/ml (mean 1.80 ng/ml) serum, respectively. The identity of retinoyl beta-glucuronide was confirmed by its conversion to retinoic acid by the action of beta-glucuronidase and by study of the mass spectrum of the methylated derivative.