Relation of the relative dose response to liver concentrations of vitamin A in generally well-nourished surgical patients

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Abstract
In 12 adult, generally well-nourished, surgical patients, liver vitamin A concentrations obtained by the analysis of liver biopsies were compared with the relative dose response (RDR). RDR is defined as the percentage increase in plasma retinol level relative to the plasma retinol level 5 h after the oral administration of a standard oral dose (450 µg) of retinyl acetate. Liver vitamin A values, expressed as retinol, and corresponding RDR values were 14 µg/g (28%), 30 µg/g (15%), and 58 to 434 µg/g (0 to 12%). Other indicators of vitamin A nutriture, which did not correlate with liver vitamin A concentrations in this group, were serum retinol level, serum retinol-binding protein concentration, and the percentage saturation of serum retinol-binding protein. The relative distribution of fatty acyl esters in liver retinyl ester did not change with total liver reserves. The relative percentage of retinol to total liver vitamin A, however, was higher (>5%) when reserves were ≤30 µg/g. Although the RDR cutoff point of >14% suggested earlier by others is in reasonable accord with our results, a somewhat higher RDR cutoff value (possibly 20%) may agree better with the suggested criterion of a liver vitamin A concentration of 20 µg/g, expressed as retinol, as a minimally adequate reserve.