I . The efficiency of absorption of and liver storage from a single oral dose of 10000 i.u, vitamin A palmitate decreased in chicks reared on a diet containing 10 % protein as compared to the efficiency in chicks reared on a diet in which the protein level was adequate. When the chicks were given orally an equivalent dose of vitamin A alcohol, the absorption was equally efficient at both dietary protein levels.
2.The vitamin A alcohol content of the intestine, plasma and liver of chicks dosed with vitamin A palmitate was decreased by protein restriction. The physiological change responsible for this decrease seems to be the lowering of the hydrolysing activity for vitamin A palmitate in pancreas and in the duodenal mucosa.3. The importance of this enzymic step in the absorption of an oral dose of vitamin A palmitate is shown by the finding that protein malnutrition reduced only slightly the final liver stores when vitamin A in its different forms (palmitate, acetate or alcohol) was injected directly into the blood stream.4. The uptake of injected vitamin A from the blood was much delayed when the vitamin was injected as palmitate, i.e. the ester of a long-chain fatty acid, instead of the acetate ester or the free alcohol.5. When vitamin A was injected, the liver content did not rise continuously with time, but showed a temporary decrease after a certain period. The phenomenon was apparently due to changes in the rate of the two inverse processes of uptake of the vitamin by the liver and liberation from it.The interrelationship between dietary protein level and vitamin A ester hydrolysis in vitro and in vivo was studied in rats by Deshmukh, Malathi & Ganguly (1964). They demonstrated that protein malnutrition reduced the hydrolysis of vitamin A acetate in rat intestine and that this reduction was related to reduced liver storage. In previous publications (Nir & Ascarelli, 1966; 1967a) we have shown that protein malnutrition and thiouracil reduced in the chick the percentage of liver vitamin A found in the alcohol form, and that hyperthyroidism increased it. In all instances liver depletion and storage level were related to the percentage of free vitamin A present in the liver. We have also shown that high ambient temperatures, which are believed to increase vitamin A requirements, also increased the percentage of free vitamin A in the liver (Nir & Ascarelli, 1967b). In the experiments of short duration reported here we have tested in vivo and in vitro the effect of dietary protein level on the activity of various tissues for the hydrolysis and synthesis of vitamin A esters. The examination of the different forms of the vitamin (ester and alcohol) in the organs at the different phases of absorption reveals that several steps may be involved in the malabsorption of the vitamin in protein-deficient chicks, the most important step being poor hydrolysis of vitamin A ester in the intestine.https://www.cambridge.org/core/terms. https://doi
