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In a previous communication (Kon, McGillivray & Thompson, 1955) we reported some of our findings on the metabolism of vitamin A and carotene administered intravenously to rats and calves partially deficient in vitamin A, and to rabbits with normal vitamin A reserves. These findings, in agreement with those of Bieri & Pollard (1954) and Bieri (1955), showed that carotene, when administered intravenously as an aqueous dispersion, could be converted into vitamin A by rats and rabbits at a site other than the intestine. The vitamin first appeared in the blood as the alcohol, whereas after oral administration the initial increase is mainly as ester (Thompson, Ganguly & Kon, 1949). With calves, however, no evidence of conversion of the intravenously administered carotene was found, which indicates a possible species difference (cf. Church, MacVicar, Bieri, Baker & Pope, 1954). One problem encountered in this work was the high toxicity for calves of the injected Tween dispersions and hence the relatively lower doses of carotene that could be used. It seemed important, therefore, to investigate further the conversion in rats given similar carotene levels. Studies were also made of the conversion in rats not deficient in vitamin A. In vitamin A-deficient rats the metabolism of other carotenoid pigments similarly administered was studied, together with the effects of hypo-and hyperthyroidism and of complete hepatectomy on the conversion of carotene. EXPERIMENTALThe methods and materials used were essentially as described in the earlier paper (Kon et al. 1955) with the additions or modifications listed below. Preparation of carotenoid pigmentsCarotene. Unless otherwise stated, crystalline carotene (L. Light and Co. Ltd) containing about 88% p-carotene was used. For comparing the activity of a-and /%carotene this material was separated by chromatography on magnesium oxide into c( and / 3 fractions.Lycopene. Lycopene was extracted from tomatoes by means of acetone in the cold and purified by chromatography on alumina.

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