L. Bárdos: Vitamin A Absorption in Hens 3r Original communications T T T T T I I T I T T Absorption of Retinyl Acetate in Laying Hens László Bárdos Department of Animal Physiology and Health. University of Agricultural Sci.' Gödöllö, Hungary Internat. J. Vit. Nutr. Res. óó (1996)31-35 Received Íbr publication july 19, 1995 Summary: Absorption of retinyl acetate (RA) was studied in hens. Animals (n = 10-10) re- ceived I 2. 5 -, 2 5 -, 50-, I 00-, I 5 0-, 200-, 2 50- and 300x103 IU of RA in capsules (p.os). Before treatment (0) and 2nd, 4th, 6th and 8th hours later, as well as on the following day blood sam- ples were taken for retinoid analysis. Vitamin A peaks were detected in the blood in the 4th hour. The alterations in the plasma vitamin A levels were caused bcLsically by the elevations of the retinyl ester (RYL) fraction. The proportion of RYL w-cts 7-27Vo o.f the total plasma vitamin A value in all groups at the time of RA administra- rion (0 h). This RYL ratio was eLevated parallel to RA doses, and in case ofhtgher doses reached 80-907o (4th h). It hcts beenfound that the ffi- ciency oÍ RA clbsorption, in hens, is in inverse ratio to the dose that is used. The calculated rel- ative absorption cofficients of fficiency have a close negative correlation (r = -0.89; p < 0.01) to the doses. Relationship betweenthe maximum plasma retinoid concentrations and the dose/ metabolic body mass can be fitted to the saturo- rion function. It seems reasonable Ío conclude that in hens the absorption of retinol is an en- zyme dependent and/or caruier mediated pro- cess even in cases of pharmacological doses. Vitamin A Retinyl acetate Retinyl ester / retinol ratio Absorption Hen Introduction Vitamin A can exert its influence only after en- tering into the organism, that is, after its absotp- tion and metabolization from the fbod. Because of the lipoid character of the molecule, the ab- sorption of retinoids corresponds to the absorp- tion of lipids from the nourishment (or fodder). The absorption of vitamin A can be divided into three parls: 1. process which takes place in the intestinal lumen (intraluminar- );2. which ts car- ried out in the cytoplasm of the mucous cell (intracellular-); and 3. which can be detected in the circulation (intravasctl process) t1l In physiological concentration (up to 150 nM) re- tinol transport is a passive process and does not require energy l2l. At pharmacological concen- trations the process was found to be a simple passive diffusion in rats 13, 4l.A number of en- zymes have been described that might partrcr- pate in the metabolism of dietary carotenes and retinyl esters necessary for absorption. The pro- cess is mediated by a cellular retinoi-binding protein (CRBP-ID [5,6]. In chicken small intes- tine the CRBP(II) might play some role in the intestinal absorption of retinoids [7]. In some cases the diet contains undesirable factors which more or less destroy the vitamin A content of food and/or hinder the absorption of retinoids. Nitrate ingestion has been linked to impaired thyroid function, decreased feed con- I I T |. F I O 1996 Hogrefe & Huber Publishers ,[