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Ascorbate Polyphosphate Is a Bioavailable Vitamin C Source in Juvenile Rainbow Trout: Tissue Saturation and Compartmentalization Model^1,2,

School of Natural Resources, Ohio State University, Columbus, OH 43210 ^* F. Hoffmann La Roche, Basel, Switzerland

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 18th 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 mg 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. On the basis of liver ascorbate concentrations (broken-line analysis) and results obtained following intraperitoneal injection 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.

KEY WORDS: • ascorbic acid • fish • salmonids • vitamin C

¹ Supported by F. Hoffmann La Roche, Ltd., Basel, Switzerland, and project funded by the National Oceanic and Atmospheric Administration, Ohio Sea Grant College Program, NA 90 AA-D-SG 496. Salaries were partly provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, Piketon Research and Extension Station, The Ohio State University. Manuscript no. 35/95.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ Current address: Department of Biochemistry, Medical School, Wroclaw, Poland.

⁴ To whom correspondence should be addressed.

Manuscript received 9 March 1995. Revision accepted 26 July 1995.