Some biochemical changes in naphthalene cataract.

LITTLE is known of the mechanism of the development of senile cataract in man, but it is generally assumed that it is due to a disturbance of the metabolism of the lens. The difficulties in attacking such a problem are great, but the experimental production ofcataract with specific agents offers a favourable approach. Naphthalene was chosen for the present study, the ability of which to produce lens opacities in rabbits has been known since the work of Bouchard and Charrin (1886). It may be noted that, in general, the histological changes associated with this type of cataract resemble closely those seen in senile cataract in man. It can be assumed that the cataractous change produced by feeding naphthalene to the experimental animal is due to some interference with the metabolism of the lens by this toxic agent. A pointer to this interference may be the presence of a high concentration of lactic acid in such lenses, a unique feature of naphthalene cataract, distinguishing it from all other types of experimentally-produced cataract. This was initially reported by Muller (1939), who found that the lactic acid content of the lens increased by 70 per cent. 12 to 48 hours after the administration of naphthalene to rabbits by stomach tube, a finding confirmed by Nordmann and Mandel (1952) in studies in vitro, using lenses from rabbits which had been fed naphthalene for 2 days. These authors found an increase of 86 per cent. above the normal in the production of lactic acid by these cataractous lenses after incubation at 37°C. for 1 hour. It was thought that an investigation of some of the enzymes concerned with the metabolism of lactic and pyruvic acid in normal and cataractous lenses might provide an explanation for this increase. The three enzymes chosen in this preliminary investigation are lactic dehydrogenase, glyoxalase, and malic enzyme. Lactic dehydrogenase catalyses the reversible reduction of pyruvic acid to lactic acid, glyoxalase the production of lactic acid from methyl glyoxal, and malic enzyme the oxidative decarboxylation of pyruvic acid to malic acid. Methods 4-month-old rabbits weighing approximately 2 kg. were used for all experiments. In order to produce cataracts, it was necessary to feed the rabbits with bran and carrots rather than the usual cabbage diet for at least one week before the experiments were started. It has been suggested that a high blood calcium level, obtained