Brain ascorbate depletion as a response to stress.

Ascorbate-depleted rainbow trout were fed a single dose of L-1-14C-ascorbic acid, then held in metabolism chambers for four consecutive five-day periods. Tissue samples were analyzed for 14C, ascorbate, and ascorbate-2-sulfate. Brain ascorbate showed a long turnover time following a very slow uptake. The loss of brain ascorbate after five days in metabolism chambers was highly significant (p less than 0.001) when compared with similar dosed fish not chambered. A brain ascorbate pool which does not exchange with the body pool is proposed. Possible mechanisms are discussed and a kinetic model is suggested.

Utilization of ascorbate-2-sulfate in fish.

Although most vertebrate animals synthesize L-ascorbic acid (C1), some animal species lack the ability to produce L-gulonolactone oxidase and are thus dependent upon a dietary source of vitamin C. Fish are unique among this latter group in that they store a chemically stable form of vitamin C and appear to metabolize this compound differently from other vitamin C-requiring organisms. Ascorbate-2-sulfate (C2) contributes to total body stores of ascorbate, but the commonly used assays for ascorbate concentrations in tissues and body fluids do not generally measure C2. An HPLC assay distinguishes between and measures both C1 and C2. Modification of the less exact but commonly used DNPH method can provide adequate data to estimate total vitamers C, C1, and (by difference) C2. Since vitamin C is a required component of feed for salmonids, catfish, eels, shrimp and carp, use of C2 in feed formulation would provide a bioavailable form of ascorbate which is heat and water stable at pH 4-13.

Distribution of ascorbate-2-sulfate and distribution, half-life and turnover rates of [1-14C]ascorbic acid in rainbow trout.

Rainbow trout (250 g) were maintained at 15 degrees C for 3 months on a low ascorbic acid diet, given [1-14C]ascorbic acid by gavage, then fed the NAS/NRC requirement 12 times per week. Total urine, fecal water and branchial water were collected daily from five fish placed in metabolism chambers for four successive 5-day periods. Tissue samples were analyzed for 14C, ascorbic acid (C1) and ascorbate-2-sulfate sulfate (C2). Excretion analysis indicated t1/2 = 42 days. After 20 days, the feeding schedule was changed to 3 times per week. Fish fed 14C were sampled after 1, 2, 3 and 4 months. The half-life in each organ except brain was inversely proportional to the dietary level of ascorbate. Concentrations of C1 and C2 in the various tissues reflected dietary intake of vitamin C. Total C (CT = C1 + C2) levels were maintained in the liver even with the low vitamin C diet. Estimates of body pool for C1 are 27-29 mg/kg. At the higher ascorbate intake CT was 92-114 mg/kg, but decreased by 34% at the lower feeding rate to 51-62 mg/kg. Data indicate that there are two or more body pools that include a store of C2, which is readily interconverted in metabolizing tissues to and from C1. Since air and water stable C2 is antiscorbutic for fish, it is the preferred form of ascorbate for fish feeds.