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 polyphosphate, to juvenile rainbow trout (Oncorhynchus mykiss). Fish were fed molar equivalents of 0, 20, 40, 80, 160, 320 and 1280 mg ascorbic acid/kg diet in the form of ascorbate polyphosphate. During the 18 wk of the experiment, when body weight increase averaged 3.5-fold, we did not observe any deficiency symptoms in any group. Liver and kidney ascorbate concentrations differed significantly among groups after wk 9. The ascorbic acid concentrations in liver were significantly different in fish fed for 9 wk an equivalent of 0, 40 and 160 mg ascorbic acid/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 concentrations in kidney were significantly different in fish fed for 18 wk an equivalent of 0,20 and 40 mg ascorbic acid/kg as ascorbic polyphosphate (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 1280 mg ascorbic polyphosphate/kg were intraperitoneally injected with 25 mg/ascorbic acid/kg body wt. We observed differences in the profiles of tissue ascorbate concentration during the 96 h following the injection between groups with high and low tissue ascorbate concentration, i.e., fish fed 320 and 0 ascorbic acid/kg, respectively. We conclude that ascorbic acid metabolism in rainbow trout after intraperitoneal injection followed the three-compartmental model, with the intraperitoneal cavity as the first compartment, blood as the second, and tissues as the third.(ABSTRACT TRUNCATED AT 250 WORDS)