Intraocular pressure and aqueous flow are decreased by cholera toxin

Delivery of 2.1 microgram of cholera toxin, a specific, irreversible activator of adenylate cyclase, via the blood lowers IOP from 17.4 to 11.2 mm Hg in 81/2 hr. decreases net aqueous flow by about 50% in 8 hr, and doubles blood flow to the anterior uvea at 8 to 13 hr. Intravitreal injection of 0.26 microgram of cholera toxin lowered IOP from 15.0 to 9.6 mm Hg, but heat-inactivated toxin had no effect on IOP. The toxin activates adenylate cyclase from ciliary processes 2.2-fold and stimulates cyclic AMP production by ciliary processes 7.4 times. Absence of aqueous flare, normal protein concentrations in the aqueous, and histologic examination all confirmed the functional and structural integrity of the blood-aqueous barrier after cholera toxin infusion. The data point to an important role for ciliary process adenylate cyclase in regulation of aqueous flow and maintenance of IOP.