Action of diamox and ammonium chloride on formation of aqueous humour.

THE investigation was undertaken to establish the cause of the decrease in intra-ocular pressure induced in normal rabbits by 2-acetylamino-1, 3, 4 thiadiazole 5-sulphonamidet, an inhibitor of the enzyme carbonic anhydrase. At the same time, it was hoped that a comparison of these results with the known ability ofDiamox to reduce the intra-ocular pressure in glaucomatous patients for extensive periods would help in assessing whether the intraocular dynamics of normal and pathological eyes are affected in a similar manner and to a comparable extent. The lowering of the intra-ocular pressure by Diamox has led to the suggestion that the enzyme carbonic anhydrase is essential to the formation of the aqueous humour, and this idea has found expression in the hypothesis that the reduction of the intra-ocular pressure by Diamox is due to an inhibition of secretion across the blood-aqueous barrier (Becker, 1955a; Friedenwald, 1955a, b). This view had its origin in the studies of Friedenwald and Stiehler (1938) on the transfer of acidic and basic dyes across the epithelial layers of the ciliary processes. Friedenwald (1949) suggested that hydroxyl ions were secreted into the aqueous humour, and that an excess of bicarbonate was produced from the reaction of the hydroxyl ions with carbonic acid. This view was supported by Kinsey (1950), who observed in rabbits that the concentrations of bydroxyl and bicarbonate ions in the aqueous humour exceeded those in the plasma. The participation of carbonic anhydrase in this secretory activity was supported by the reports of the presence of the enzyme in extracts of the iris and the ciliary processes (Wistrand, 1951; Kauth and Sommer, 1953; Green, Capper, Bocher, and Leopold, 1954; Gloster and Perkins, 1955a). Experiments designed to test either this hypothesis or alternative explanations of the action of Diamox in reducing the intra-ocular pressure have been reported by several investigators (Becker, 1955a, b, 1956; Becker and Constant, 1955; Green, Bocher, and Leopold, 1955; Langham and Lee, 1955a, b, c). There is general agreement that the reduction in the intraocular pressure is accompanied by a decreased rate of formation of aqueous humour, but the means by which this is brought about is still unresolved.