ADMINISTRATION OF GULONOLACTONE DOES NOT EVOKE ASCORBIC-ACID SYNTHESIS IN TELEOST FISH

Evidence is presented that for common carp (Cyprinus carpio L.), intraperitoneal injection of L-gulonolactone, a precursor of ascorbic acid synthesis in the D-glucuronic acid pathway, does not result in an increased concentration of ascorbate in tissue. Control fish injected with an equimolar amount of ascorbic acid have shown a significant increase in ascorbic acid concentration in the kidney, hepatopancreas, plasma and spleen. The ascorbate status in the carp body, i.e., the ascorbate nutritional history, produced significant differences in ascorbate withdrawal from circulation and probably in the catabolic rate. Acute fasting decreased ascorbate uptake into tissues as compared to fish fed a diet lacking ascorbate. Intraperitoneally injected ascorbate affects common carp being fed a diet containing 295 mg of total ascorbic acid kg-1 by causing tissue to become saturated with vitamin C, similar to the tissues in the group undergoing acute fasting. There was no gulonolactone oxidase activity in the hepatopancreas of the common carp. These results suggest that the metabolic rate induced by feeding is the primary factor regulating ascorbate requirement.