Absorption of retinyl acetate in laying hens.

Absorption of retinyl acetate (RA) was studied in hens. Animals (n = 10-10) received 12.5-,25-,50-,100-,150-,200-,250- and 300 x 10(3) 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 samples 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 basically by the elevations of the retinyl ester (RYL) fraction. The proportion of RYL was 7-27% of the total plasma vitamin A value in all groups at the time of RA administration (0 h). This RYL ratio was elevated parallel to RA doses, and in case of higher doses reached 80-90% (4th h). It has been found that the efficiency of RA absorption, in hens, is in inverse ratio to the dose that is used. The calculated relative absorption coefficients of efficiency have a close negative correlation (r = -0.89; p < 0.01) to the doses. Relationship between the maximum plasma retinoid concentrations and the dose/metabolic body mass can be fitted to the saturation function. It seems reasonable to conclude that in hens the absorption of retinol is an enzyme dependent and/or carrier mediated process even in cases of pharmacological doses.