Elevated serum concentrations of beta-glucuronide metabolites and 4-oxoretinol in lactating sows after treatment with vitamin A: a model for evaluating supplementation in lactating women.

BACKGROUND The effects of large doses of preformed vitamin A, such as those provided in supplementation programs for the prevention of deficiency, on total serum vitamin A have been inadequately investigated. OBJECTIVE This study characterized the time course of serum vitamin A metabolites in lactating sows after single high doses of retinyl ester. DESIGN Lactating sows were fitted with jugular catheters and subsequently fed either 1.05 or 2.1 mmol retinyl ester (n = 6/group) or a corn oil vehicle (n = 3). Blood was collected at baseline and at intervals to 48 h and analyzed by gradient HPLC for retinol, retinyl esters, and metabolites. RESULTS The mean (+/-SD) total serum vitamin A concentration peaked at 1 h (3.69 +/- 4.0 mumol/L) and 2 h (7.70 +/- 6.8 mumol/L) in the low- and high-dose groups, respectively (P < 0.05). Retinyl esters accounted for most of the serum vitamin A in both groups at peak time points. Mean serum retinol concentrations changed little and accounted for most of the serum vitamin A at baseline (94% and 97% for the low- and high-dose groups, respectively) but for only 22% and 14% at peak times for the low- and high-dose groups, respectively. Postdosage increases were observed for total vitamin A and retinyl esters, 4-oxoretinol, retinoyl beta-glucuronide, and retinyl beta-glucuronide but not for retinoic acid. CONCLUSIONS Serum retinol concentration remains relatively static after a large dose of preformed vitamin A and therefore is not an appropriate measure of intervention efficacy. The increases in beta-glucuronide metabolites and 4-oxoretinol suggest a preventive role against a rise in retinoic acid and retinol.