A study on the conversion of carotene into vitamin A by fluorescence microphotometry

For the purpose to confirm whether carotene is converted into vitamin A mainly in the intestine, fluorescence microscope observations as well as the fluorescence microphotometry for the estimation of fading state of the fluorescence were carried out on the fresh sections of the intestine, lung and liver of rats after oral administration of 11-carotene dissolved in oil, and suspended in water, and vitamin A in sesame oil as control. Yellowsih-green fluorescence of carotene is similar to that of vitamin A in color but the fluorescence of vitamin A fades away very rapidly within one minute while that of carotene does not fade or fade more slowly than that of vitamin A. Observations have revealed that, contrary to expectation, the administered carotene is not so readily converted into vitamin A in the intestinal mucosa, but after passing through the intestine without conversion to vitamin A, it is transported to the mesenteric lymph vessels, portal vein, and reaches the liver. In the liver, carotene appears as fatty droplets or micronized particles in the parenchymal cell. The conversion of carotene into vitamin A could not be observed in the intestine, liver and lung in the observations made one hour after the oral adminstration of carotene. Hower, it seems that carotene dissolved in minute fat droplets may be converted into vitamin A at water phase in tissues, after dissolution of carotene in fat and micronization of the fat droplets.