Effect of dietary protein level on in vivo and in vitro vitamin A esterase activity in the chick

Abstract

1. 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 this 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 the 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 of 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.