THE METABOLISM OF [C-14] BETA-CAROTENE AND THE PRESENCE OF OTHER CAROTENOIDS IN RATS AND MONKEYS

The metabolism of β-carotene has been studied in both rats and Rhesus monkeys, following the oral administration of [14C]β-carotene in olive oil supplemented with 1 mg/mL α-tocopherol. In the rats, peak serum accumulation of [14C]retinol occurred 4 h after a single oral dose, but we were not able to detect [14C]β-carotene in rat sera at any time up to 72 h after dosing. Small amounts of [14C]β-carotene were found in the livers, although 88-94% of the recovered radioactivity was localized in the retinol fraction after saponification. Although radioactivity was also found in fractions other than β-carotene and retinol, the amounts were too small to allow characterization. In the monkeys, peak accumulation of [14C]retinol in serum occurred between 8 and 24 h after suplementation. Some [14C]β-carotene was also present. Most of the absorbed radioactivity was stored in the liver as [14C]retinol, although 2-8% was present as [14C]β-carotene. Other organs also contained [14C]β-carotene, confirming the ability of the monkey to absorb intact β-carotene. In addition, monkey livers and other organs were found to contain lutein, zeaxanthin, α-cryptoxanthin, β-cryptoxanthin and β-carotene, presumably arising from dietary sources.