9-CIS BETA-CAROTENE IN HUMAN PLASMA AND BLOOD-CELLS AFTER INGESTION OF BETA-CAROTENE

For 44 wk, thirty male volunteers were given daily either 60 mg of syn thesized all-trans beta-carotene, a naturally-occurring beta-carotene derived from Dunaliella bardawil, or a placebo. Basal levels of 9-cis beta-carotene in plasma, platelets, and mononuclear cells were 10, 20, and 25% of those of the all-trans form, respectively. The plasma leve ls reached a maximum after two weeks of administration and plateaued t hereafter in the subjects who took the beta-carotene preparations. The all-trans beta-carotene level in the subjects given the synthesized a ll-trans form was almost twice that for the Dunaliella preparation. Th e plasma 9-cis level was found to be higher in the all-trans beta-caro tene group than in the Dunaliella group, despite no intake of the 9-ci s form in the all-trans group and the higher intake of the 9-cis form in the Dunaliella group. This finding suggests that isomerization of t he all-trans form to the 9-cis form may occur in the body either durin g or after absorption.