AN IMPROVED MICROMETHOD FOR FRACTIONAL DETERMINATION OF VITAMIN A ALCOHOL AND ESTER AND THE CHANGES IN BOTH TYPES OF VITAMIN A IN BLOOD PLASMA, MILK AND LIVER AFTER LOADING WITH BOTH TYPES OF THE VITAMIN AND β-CAROTENE

Abstract

1. A micromethod for fractional determination of vitamin A alcohol and ester was devised and the free and ester forms of the vitamin in serum, milk and liver were determined. Using 1N KOH in 90 per cent ethanol in extraction, the fractional determination could be carried out with practically complete recoveries.2. With this method it was found that about 90 per cent of vitamin A in human serum was the free form and about 10 per cent the ester form, in agreement with the results obtained previously by the authors.3. The increase in vitamin A in the serum 3hours after oral administration of vitamin A alcohol or ester is chiefly in the ester form without significant change in the free form.4. Contrary to the findings of the serum, about 90 per cent of the vitamin in human milk was in the ester form and about 10 per cent in the free form. The ratio was fairly constant whether the milk is taken from the initial, middle or last portion of the congested breast or taken at different times of the day.5. The levels of vitamin A and ester in the milk after a single oral administration of 33.3mg of A alcohol or ester were highest after 4-6 hours, gradually decreasing thereafter. Whichever form was loaded, it was always the ester that increased significantly, as was the case with serum. There is a slight increase in the free but the rise is insignificant.6. Of the vitamin A in the liver, about 90 per cent was the ester form and about 10 per cent the free form. The ratio was about the same as in milk.7. The vitamin A level in the liver 15hours after a single oral administration of 1, 000μg of A alcohol or ester or of 2, 000μg of β-carotene in the mouse was found to be increased in the ester form, the rise being 26.7, 33.6 and 5.3 per cent, respectively. The increase in the free form was slight. The rise in vitamin A in the liver after administration of β-carotene was only about 40 per cent of that following the dose of vitamin A with the same I. U.