Further Observations on the Metabolism of Carotene

It is now well established that carotene is a precursor of vitamin A, and its transformation into the vitamin is a function of the animal organism. During studies of the mechanism of this change, attention has been focused mainly on the liver, the storehouse of vitamin A in the animal body, and at least one investigator has claimed that the change takes place in the liver through the action of an hepatic enzyme (Olcott and McCann, 1931). But this claim has not been generally substantiated. On the other hand attempts to convert carotene into vitamin A with the help of liver tissue or liver extracts under different conditions have failed, and even the direct perfusion of the intact liver with suitable carotene solutions has not met with any degree of success (Ahmad, 1931; Rea and Drummond, 1932). The more recent observations, however, show that the change of carotene into vitamin A in the animal body may be a slow process, for the formation of vitamin A is not detected until 8 days after the introduction of carotene (Drummond and MaeWalter, 1933). In this study attempts have been made to follow the fate of carotene after its introduction into the venous circulation of an animal. Four different species of animals were used. They