Reduction in Aqueous Humour Formation as Caused by Iodate, Spirolactone, and Polyphloretin Phosphate.

SINCE the formation of the aqueous humour depends largely upon active transport across the blood-aqueous barrier (in particular the ciliary epithelium), the rate of formation will be influenced by substances which act upon the barrier by modifying its properties or behaviour. In the present paper results are presented which deal with the actions of three different types of substance, all ofwhich diminish the rate of formation of the aqueous. Evidence for a mechanism transporting sodium ions actively from the plasma to the aqueous has been discussed elsewhere (Cole, 1960b, 1961a), and it was thought that such a system might be subject to inhibition by an aldosterone antagonist, spirolactone, which has been shown to reduce sodium reabsorption in the renal tubules (Celia and Kagawa, 1957; Kagawa, Celia, and van Arman, 1957; Liddle, 1957, 1958; Vander, Wilde, and Malvin, 1960). Noell (1953, 1954) has shown that chronic administration of iodate, which has long been known to cause pathological changes of the pigment epithelium (Vito, 1935; Kalt, 1937; Sorsby, 1941), abolishes the steady retinal potential as a result of this selective damage. It appeared possible that this action on the pigmented cells might not be confined to the retina but might also extend anteriorly into the pigment-cell layer of the ciliary body and thereby interfere with the normal production of the aqueous humour. The third substance studied was polyphloretin phosphate, which has already been shown to prevent experimental ocular hypertension caused by increased permeability of the blood-aqueous barrier (Cole, 1961b). The possibility that ultrafiltration across the normal barrier contributes to the influx measured in experiments of the present type has already been raised (Cole, 1960b), and it was thought that, in contrast to the other two inhibiting agents, spirolactone and iodate, polyphloretin phosphate would tend to reduce this ultrafiltration component without inhibiting the active transport processes.l