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

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 micrograms) of retinyl acetate. Liver vitamin A values, expressed as retinol, and corresponding RDR values were 14 micrograms/g (28%), 30 micrograms/g (15%), and 58 to 434 micrograms/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 (greater than 5%) when reserves were less than or equal to 30 micrograms/g. Although the RDR cutoff point of greater than 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 micrograms/g, expressed as retinol, as a minimally adequate reserve.