Stanley J. Cevario

The inhibitory actions of dopamine, hydroxyamphetamine and phenylephrine on aqueous humor formation

Abstract Dopamine, hydroxyamphetamine and phenylephrine have each been found to produce vasoconstriction and to decrease the rate of aqueous humor formation in enucleated, arterially perfused cat eyes. These data point out once again the role of the vasculature in the regulation of aqueous humor formation and support previous conclusions for the involvement of α-adrenergic receptors in these responses.

A possible vascular mechanism for the inhibition of aqueous humor formation by ouabain and acetazolamide

Abstract Ouabain and acetazolamide have been demonstrated to produce a decrease in the rate of aqueous humor formation in the enucleated, arterially perfused eye. Vasoconstriction was observed with each drug. This finding together with the additional observation that the actions of both ouabain and acetazolamide were completely inhibited by C-6 suggest that under the conditions in which the study was performed the decrease in aqueous production is not due to enzymatic actions on secretion. It is suggested that the mechanism of inhibition may be a vasoconstriction of afferent ciliary process blood vessels to decrease ultrafiltration. A specific receptor site of action for both ouabain and acetazolamide is postulated.

Timolol inhibition of aqueous humor production in the cat

Abstract 1. 1. The effects of timolol maleate, a beta-adrenergic blocking agent, have been studied on the aqueous humor dynamics in both the intact and the enucleated, arterially perfused cat eye. 2. 2. In the anesthetized cat, timolol (10.0 μg/kg, i.v.) produced within 30 min a transient elevation of aqueous humor production. Subsequently, the aqueous inflow decreased gradually to below control levels, with a maximal inhibition noted at approximately 90 min. The maximum mean elevation of inflow was 7.71 μ l min −1 while the subsequent maximum mean inhibition of inflow was 11.92 μ l min −1 . 3. 3. In an in vitro preparation, the administration of timolol after acetylcholine plus eserine (Ach + Es) did not alter the stimulatory effect of these drugs on the inflow rate and IOP. However, prior arterial perfusion of timolol (0.10 μg/ml) markedly depressed both the increased aqueous humor formation and IOP effects of Ach + Es. 4. 4. The delayed response of timolol to reduce inflow in the intact cat, and the ability of timolol to inhibit the responses of acetylcholine plus eserine (in the enucleated eye) raises some questions as to whether timolol action is mediated by specific blockage of beta-adrenergic receptors.

Blockade of the ocular effects of acetazolamide by phencyclidine

Abstract Phencyclidine, in low concentrations, has been found to block the vasoconstrictor action of acetazolamide in the isolated, arterially perfused iris-ciliary body of the cat. Similar concentrations of phencyclidine, in enucleated, arterially perfused whole cat eyes was found to prevent the action of acetazolamide to decrease the rate of aqueous humor formation. Experiments in living rhesus monkeys also demonstrate that the inhibitory effects of acetazolamide on aqueous humor formation can be effectively blocked by phencyclidinc.

Timolol inhibition of isoproterenol action—1. Effects on aqueous humor production and IOP

Abstract 1. 1. Experiments were performed with enucleated, arterially perfused cat eyes. 2. 2. Timolol was found to block the aqueous humor (AH) depressant action of d,l -isoproterenol but had no effect on the similar actions of l -epinephrine or of l -norepinephrine. 3. 3. The ocular hypotensive effect of the three adrenergic amines were unaltered by timolol. 4. 4. Although the AH actions of d,l -isoproterenol were blocked by timolol, the ability of isoproterenol to lower IOP remained intact.

Inhibition of aqueous humor flow by application of cold air to the cornea.

Abstract Cold air directed onto the cornea of the enucleated, arterially perfused cat eye produced a fall of intraocular pressure and a concomitant decrease in the rate of aqueous humor production. The response is readily reversible and is not inhibited by local anesthesia of the cornea nor by intra-arterially administered indomethacin or hexamethonium. In anesthetized cats, cold applied to the cornea produced effects on aqueous humor production similar to the actions observed in the enucleated eyes; however no significant alterations of IOP were noted.