Effect of species differences and dietary vitamin C on the concentration of ascorbate- and acid-soluble thiol in fish eye

Abstract

Data presented confirm the essentiality of modification of the dinitrophenylhydrazine (DNPH) method to analyze the total ascorbic acid and dehydroascorbic acid in ocular tissues and stress the need of corrections for the interfering substances. Variations in ascorbate and thiol concentrations in the lens, retina and aqueous humour of freshwater fish belonging to the Cyprinidae family were examined. The interspecific variability of ascorbate concentration was highest in the aqueous humour and lowest in the retina. The high ascorbate concentration in the retina seems to reflect the importance of the sense of vision in fish life-style as compared to chemo- and acoustico lateralis senses. The regional distribution of the total ascorbate is in the order of decreasing concentrations: retina, lens and aqueous humour. However, the retinal ascorbate is almost exclusively in the oxidized form, and the lenticular ascorbate is almost exclusively in the reduced form. Thiol concentration in the lens is five- to tenfold that in the retina and aqueous humour. This explains the oxidation status of ascorbate in different eye compartments of the eye. After 30 days on diets containing various levels of ascorbic acid or ascorbic acid sulphate, the ascorbate concentration in the eye compartments of common carp ( Cyprinus carpio L.) was determined. Ocular tissue can be used to monitor the development of the ascorbate status in fish, and the retina is the most responsive tissue to the enhanced or depleted ascorbate levels.