ASCORBATE POLYPHOSPHATE IS A BIOAVAILABLE VITAMIN-C SOURCE IN JUVENILE RAINBOW-TROUT - TISSUE SATURATION AND COMPARTMENTALIZATION MODEL

We studied the bioavailability of ascorbic acid ester, ascorbate polyp hosphate, to juvenile rainbow trout (Oncorhynchus mykiss). Fish were f ed molar equivalents of 0, 20, 40, 80, 160, 320 and 1280 mg ascorbic a cid/kg diet in the form of ascorbate polyphosphate. During the 18th wk of the experiment, when body weight increase averaged 3.5-fold, we di d not observe any deficiency symptoms in any group. Liver and kidney a scorbate concentrations differed significantly among groups after wk 9 . The ascorbic acid concentrations in liver were significantly differe nt in fish fed for 9 wk an equivalent of 0, 40 and 160 mg ascorbic aci d/kg as ascorbate polyphosphate, values were 22.7 +/- 3.4, 93.7 +/- 17 .0 and 368.0 +/- 60.8 nmol ascorbic acid/g. The ascorbic acid concentr ations in kidney were significantly different in fish fed for 18 wk an equivalent of 0, 20 and 40 mg ascorbic acid/kg as ascorbic polyphosph ate (23.9 +/- 4.0, 72.1 +/- 13.6 and 254.4 +/- 22.7 nmol ascorbic acid /g, respectively). After wk 18, fish from groups fed 0, 20, 320 and 12 80 mg ascorbic polyphosphate/kg were intraperitoneally injected with 2 5 mg ascorbic acid/kg body wt. We observed differences in the profiles of tissue ascorbate concentration during the 96 h following the injec tion between groups with high and low tissue ascorbate concentration, i.e., fish fed 320 and 0 mg ascorbic acid/kg, respectively. We conclud e that ascorbic acid metabolism in rainbow trout after intraperitoneal injection followed the three-compartmental model, with the intraperit oneal cavity as the first compartment, blood as the second, and tissue s as the third. On the basis of liver ascorbate concentrations (broken -line analysis) and results obtained following intraperitoneal injecti on of ascorbic acid, we estimated that minimal dietary supplementation equivalent to 360 mg ascorbic acid/kg diet in juvenile rainbow trout is leading to tissue ascorbate saturation.