α-Retinol is distributed through serum retinol-binding protein-independent mechanisms in the lactating sow-nursing piglet dyad 1-3

Abstract

α-Retinol (aR) is a structural isomer of retinol [vitamin A (VA)] that does not bind to serum retinol-binding protein (RBP). In this study, α-retinyl acetate (aRA) was synthesized and given orally (35 μmol) to Vα-deficient lactating sows (n = 11) to assess its potential to trace RBP-independent retinol transport and tissue uptake. The aRA dose primarily appeared in sow serum as 4 α-retinyl esters (aRE) with peak serum total aR concentrations (the sum of the alcohol and ester forms) detected at 2 h (70±23 nmol/L, mean±SEM) postdose. From 0 to 40 h postdose, the percentage of serum total aR in the alcohol form did not increase. Rapid aR uptake into sow milk was observed with peak concentrations (371 ± 83 nmol/L) at 7.5 h postdose, consistent with the uptake of aRE from chylomicra. A high percentage of the aRA dose (626 15%, mean6 SD) was present in the livers of sows (n = 6) killed 22-28 d postdose. Approximately 15-26% of the sow aRA dose was transferred to the livers of the nursing piglets (n = 17) after 3 d. In piglets and sows, a similar percentage of hepatic total aR was detected in the ester form as that of hepatic total retinol. Taken together, these data suggest that an oral dose of aRA effectively traces the uptake, esterification, chylomicron transport, and hepatic storage of retinol and may be useful for deciphering the role of RBP-independent delivery of retinol to other tissues. © 2011 American Society for Nutrition.