Using biochemical indicators to determine the recommended dietary allowance (RDA) and body ascorbate compartmentalization for juvenile rainbow trout

Phosphorylated esters of ascorbic acid were studied in respect to their bioavailability to juvenile rainbow trout by measuring their nutritional effect and looking into biochemical basis for their utilization. Several biochemical indicators were tested and compared in their correlation to ascorbate status in fish.; The first objective was to determine the retention and depletion patterns for juvenile rainbow trout. Two strains were subject of these studies, Mt. Shasta, CA, and London, OH. The experiments consisted of two phases. In saturation phase fish were fed graded levels of ascorbic acid and equimolar amounts of ascorbate monophosphate. Fish with different ascorbate status, resulting from saturation phase, were than fed ascorbate-free diet-depletion phase. Significant differences in survivorship were observed in fish with different ascorbate status suggesting that the initial ascorbate level in depletion phase can influence the survival of the fish. Fish fed ascorbate monophosphate in the saturation phase performed significantly better in the depletion phase than fish fed equimolar amounts of ascorbic acid. Both strains of rainbow trout differed in their response to dietary ascorbate supplementation.; The studies on the bioavailability and requirements of ascorbate polyphosphate were conducted on St. Joaquin strain of rainbow trout fed graded levels of ascorbate polyphosphate for 18 weeks. Based on the correlation between dietary ascorbate supplementation and tissue ascorbate concentration the minimal ascorbic acid requirement for juvenile rainbow trout was established as 300 mg per kg of diet given that the vitamin is in the stable form.; Two salts (calcium and potassium/magnesium) of ascorbate monophosphate, were compared in their antiscorbutic action. No differences in bioavailability between two forms of ascorbate monophosphate were observed. Hematocrit, lysozyme activity and total plasma alkaline phosphatase activity were not correlated with ascorbate status in rainbow trout.; Rainbow trout intestinal alkaline phosphatase was studied as a possible enzyme involved in hydrolysis of phosphorylated esters of ascorbic acid. The enzyme readily hydrolyzed ascorbate mono-, tri-, and polyphosphate. K{dollar}sb{lcub}rm m{rcub}{dollar} values were established as 1.19, 4.1 and 3.7 mM, for ascorbate mono-, tri-and polyphosphates, respectively. The results indicate that this enzyme, capable of hydrolysing of the above substrates and releasing of ascorbic acid into circulation acts as ascorbate esters hydrolase.; Changes in bone alkaline phosphatase isoenzyme activity in blood plasma as indicator of ascorbate status in rainbow trout were studied. The distinction between liver and bone alkaline phosphatases in blood plasma was achieved by differential inhibition of these two forms by urea. The tendency of bone alkaline phosphatase to decline along with the decrease of liver ascorbate concentration was observed.; Finally, the overview of the role of ascorbic acid esters in fish nutrition was presented. The methods used in ascorbate determination were compared in their sensitivity and specificity. The comparison of ascorbate esters in their bioavailability, the modes of ascorbate hydrolysis and absorption and metabolism of ascorbic acid in teleost fish were discussed.