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ORIGINAL RESEARCH COMMUNICATION |
1 From the Interdepartmental Graduate Program in Nutritional Sciences, University of Wisconsin–Madison, Madison, WI.
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 µmol/L) and 2 h (7.70 ± 6.8 µmol/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 ß-glucuronide, and retinyl ß-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 ß-glucuronide metabolites and 4-oxoretinol suggest a preventive role against a rise in retinoic acid and retinol.
Key Words: Preformed vitamin A • retinyl ester • sows • time course • toxicity • vitamin A supplementation
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