The Effect of Brimonidine on Intraocular Pressure via the Central Nervous System in the Conscious Pigmented Rabbit

Abstract

The central effects of brimonidine on intraocular pressure (IOP) in male pigmented rabbits were investigated. Twenty μL brimonidine was administered to the lateral eye, or intraorally. For intracerebroventricular (icy) treatment, the guide cannula was inserted two weeks before injection into the lateral ventriculus following Fifkova's brain map. Ten μL brimonidine was injected (5μL/min, icv) . After the treatments, IOP was measured by pneumatonometer and pupil diameter (PD) was measured using a ruler. Heart rate (HR) and mean arterial blood pressure (MABP) at metatarsus were also monitored after topical administration. IOPs were significantly decreased bilaterally by 0.05% brimonidine administered topically to the lateral eye (p<0.001, n=6), or 0.1% administered orally (p<0.001, n=11) compared to a saline treatment control group. After 0.0001 % brimonidine icy treatment, IOP was significantly decreased bilaterally (p<0.05, n=4) . PD, HR and MABP were not changed by 0.01% topical administration of brimonidine. The decrease in IOP which was induced by 0.01 % brimonidine icy treatment was inhibited by pretreatment with 0.1% yohimbin icy (p<0.05, n=4) . These results suggest that topical use of brimonidine might decrease IOP in the pigmented rabbit by a central α₂-receptor effect in addition to its local effect.