[Hydrolytic splitting of vitamin A esters in the blood]

The retinol and retinylpalmitate content along with the retinylacetate and retinylpalmitate-hydrolase in the blood of the portal vein and in the peripheral blood from the superficial vein of the hind limb of dogs was determined in chronic experiments before and 1, 2, 3 and 4 hours after administration of the vitamin A preparations into the small intestine fistula. The introduction of an oily retinylacetate solution into the fistula was attended both by an increase of the retinylpalmitate content in the blood plasma and the appearance therein of the retinyl-palmitat-hydrolase activity. Introduction of an aquous-colloidal solution of retinyl-palmitate caused a rise in the latter's content in the blood but was not accompanied by the appearance of the retinyl-palmitate-hydrolase activity. In the blood taken on an empty stomach no capacity for retinyl-palmitate hydrolysis was in evidence. It is presumed that the emergence of the retinyl-palmitate activity in the blood following introduction of precisely the oily retinylacetate solution is due to an intensified supply of the pancreatic enzymes into the blood in response to the fat load. The retinylacetate-hydrolase activity was continually present in the blood and did not vary in its intensity in the dynamics of absorption.