Oral doses of α-retinyl ester track chylomicron uptake and distribution of vitamin A in a male piglet model for newborn infants

Abstract

α-Retinol has utility in determining chylomicron trafficking of vitamin A to tissues given that it will not be recirculated in blood on retinol binding protein (RBP). In this study, α-retinol was used as a chylomicron tag to investigate short-term uptake from high-dose supplements given to piglets as a model for neonates. The distribution of orally administered α-retinol doses in liver and extrahepatic tissues was assessed at varying times after dosing. Male piglets (n = 24 per group) from vitamin A-depleted sows were orally given 26.2 or 52.4 μmol of α-retinyl acetate, the molar equivalent of 25,000 and 50,000 IU of vitamin A, respectively. Tissues were collected and analyzed by HPLC. Lung (6.46 ± 2.94 nmol/g), spleen (22.1 ± 11.3 nmol/g), and adrenal gland (17.0 ± 11.2 nmol/g) α-retinol concentrations peaked at 7 h after dosing, and, by 7 d, α-retinol was essentially cleared from these tissues (≤0.25 ± 0.12 nmol/g). This demonstrates that the lung, spleen, and adrenal gland receive substantial vitamin A from chylomicra to maintain concentrations. Conversely, storage of α-retinol in the liver reached a plateau at 24 h (1.72 ± 0.58 μmol/liver) and was retained through 7 d (2.10 ± 0.38 μmol/liver) (P > 0.05). This indicates that α-retinol was not substantially utilized locally in the liver nor transported out from the liver via RBP. In serum, the majority of α-retinol was in the ester form, which confirms that α-retinol does not bind to RBP but does circulate. α-Retinyl esters were detectable at 7 d in the serum but were not different from baseline. Collectively, these data suggest that crucial immune organs need constant dietary intake to maintain vitamin A concentrations because α-retinol was quickly taken up by tissues and decreased to baseline in all tissues except long-term storage in the liver.