Factors affecting the concentration of ascorbic acid in the crystalline lens of cattle and rabbits.

It has been suggested that ascorbic acid is necessary for the transparency and metabolism of the crystalline lens (see Bellows, 1944). Primarily, this is based on well-authenticated observations of a loss of ascorbic acid from animal and human lenses undergoing spontaneous opacification. In experimentally induced cataract, however, loss of ascorbic acid does not always occur; thus, naphthalene and galactose given orally to rabbits produce cataracts which are accompanied by a decrease in ascorbic acid (Bellows & Rosner, 1937; Rosner, Farmer & Bellows, 1938), and rabbits given alloxan intravenously, or directly irradiated with X-rays, develop cataracts with no significant change in the ascorbic acid of the lens (Waters, 1950; Pirie, Van Heyningen & Boag, 1953). The cause of the variability of the ascorbic acid level in the cataractous lens is to be found in several factors likely to influence the distribution of ascorbic acid between this tissue and the aqueous humour. The principal factor extrinsic to the lens is the concentration of ascorbic acid in the aqueous humour; this is determined by the rate of secretion of ascorbic acid across the ciliary epithelium (Kinsey, 1947; Langham, 1950; Linn6r, 1952; BArany & Langham, 1953, 1955). There is now little, if any, evidence that synthesis of ascorbic acid occurs in the rabbit lens (Kinsey, 1950; Linn6r, 1952; Langham, 1955), but there are two intrinsic factors which could modify the ascorbic acid content, namely permeability and metabolism. That the metabolism of the lens itself might actively inhibit the disappearance ofascorbic acid is suggested by the recent isolation from cattle lenses of the enzyme glutathione reductase which catalyses the reduction of oxidized glutathione by reduced triphosphopyridine nucleotide (Van Heyningen & Pirie, 1953), and the well-known ability of glutathione to reduce dehydroascorbic acid at body pH (Borsook, Davenport, Jeffreys & Warner, 1937). In the present study the influence of these extrinsic and intrinsic factors on the concentration of ascorbic acid in the lens has been investigated. METHODS