Carotene and Vitamin A

Studies in vitamin A. 7. Carotene metabolism in herbivores

“…Although the experimental basis for the hypothesis has been severely criticized (Rea & Drummond, 1932;Woolf & Moore, 1932), it was generally assumed until recently that the conversion takes place in the liver. Sexton, Mehl & Deuel (1946) first suggested that the liver was not the site of conversion, and demonstrated that injected carotene accumulated in the liver but did not appear to be converted into vitamin A.…”

“…It has been widely assumed that the site of the conversion of the active carotenoids into vitamin A is the liver itself, although the results of in vitro experiments designed to test this view are equivocal (see, e.g., Woolf & Moore, 1932). In the cow, carotenoids are present in the systemic blood plasma in amounts which reflect the dietary intake of carotenoids (Mitchell & Wise, 1944), and the plasma levels presumably represent a balance between absorption from the intestine and removal by the liver, the pigments being merely en route to the liver from the gut.…”