COMPARTMENTAL ANALYSIS OF THE DYNAMICS OF BETA-CAROTENE METABOLISM INAN ADULT VOLUNTEER

Metabolism of a 73 mu mol oral dose of beta-carotene-d(8) in olive oil was determined from plasma beta-carotene-d(8) and retinol-d(4) concen tration-time curves in an adult male. beta-Carotene-d(8) and retinol-d (4) concentrations in serial plasma were measured using high performan ce liquid chromatography (HPLC) and gas chromatography-mass spectromet ry (GC-MS), respectively. Plasma beta-carotene-d(8) and retinol-d(4) c oncentration-time curves were described by a 5-term and a 3-term polye xponential equation, respectively, using an empirical description of b eta-carotene metabolism. A physiologic compartmental model of beta-car otene metabolism was also constructed and tested. This model suggests that 22% of the beta-carotene dose is absorbed: 17.8% as intact beta-c arotene and 4.2% as retinoid. Also, it suggests that both liver and en terocyte are important in converting beta-carotene to retinoid; 43% is converted in liver and 57% in enterocyte. Finally, it suggests that t he mean residence time for beta-carotene is 51 days and that the 73 mu mole dose does not alter the fractional transfer coefficients of the system after absorption takes place. The issue of central versus eccen tric cleavage of beta-carotene in humans can be studied with further m odeling combined with use of appropriately labeled beta-carotene.