Effect of ifenprodil on aqueous humor dynamics and optic nerve head circulation in rabbits

The purpose of this study was to study the effects of ifenprodil, a cerebral vasodilator with alpha and N-methyl-D-aspartate (NMDA) receptor antagonistic activities, on aqueous humor dynamics and optic nerve head (ONH) circulation in rabbits. Experiments were performed during the dark phase in rabbits conditioned to a schedule of alternating 12-hr periods of light and dark. Effects on blood-aqueous barrier permeability (K(d)), aqueous flow rate (F), outflow facility to general blood circulation (C(gen)), and uveoscleral outflow (F(u) were determined fluorophotometrically. Effects on ONH tissue circulation were estimated using the laser speckle method. Unilateral topical administration of 0.5% ifenprodil solution decreased intraocular pressure (IOP) with a maximum reduction of 3.4 mmHg and an effect duration of 3 hr without effects on the contralateral eye. A single instillation of 0.5% ifenprodil had no significant effect on K(d), F, or C(gen), whereas it substantially increased F(u). Twenty-day, twice-daily unilateral 0.5% ifenprodil instillation significantly increased tissue blood velocity in the ONH only in the treated eye.