Accumulation in Chick Livers of 9-cis Versus All-trans β-Carotene

Previous results indicated that β-carotene, as present within the unicellular alga Dunaliella, accumulated in the liver of chicks to a much higher degree than did synthetic all-trans β-carotene. Because the Dunaliella β-carotene is composed of an approximately equal mixture of two stereoisomers, 9-cis and all-trans, we tested whether a similar mixture of purified β-carotene isomers would yield comparable results. Indeed, analysis of liver following 2 wk of feeding show a 10-fold higher accumulation of β-carotene in the chicks fed a mixture of purified 9-cis and all-trans β-carotene as compared with those fed only all-trans β-carotene. The ratio of 9-cis to all-trans β-carotene in the liver was about three times higher than that present in the β-carotene fed to the chicks. Retinol and retinyl esters accumulated to a similar degree in the livers of chicks given all treatments.